Patent Application
20200277686
The invention relates to a copper-nickel-tin alloy having excellent castability, hot formability and cold formability, high resistance to abrasive wear, adhesive wear and fretting wear, and improved corrosion resistance and stress relaxation resistance according to the preamble of any of claims 1 to 3, to a process for production thereof according to the preamble of claims 9 to 10 and to the use thereof according to the preamble of claims 16 to 18.
Owing to their good strength properties and their good corrosion resistance and conductivity for heat and electrical current, the binary copper/tin alloys have great significance in mechanical engineering and motor vehicle construction, and in large parts of electronics and electrical engineering.
This group of materials has high resistance to abrasive wear. Moreover, the copper/tin alloys assure good sliding properties and high fatigue endurance, which results in their excellent suitability for sliding elements in engine construction and motor vehicle construction, and in mechanical engineering in general.
By comparison with the binary copper/tin materials, the copper-nickel-tin alloys have improved mechanical properties such as hardness, tensile strength and yield point. The increase in the mechanical indices is achieved here via the hardenability of the Cu—Ni—Sn alloys.
As well as the importance of the ratio of the elements nickel and tin for the temperature at which there is spontaneous spinodal segregation in the Cu—Ni—Sn alloys, the precipitation processes are essential for the establishment of the properties of this group of materials.
In the literature, the presence of discontinuous precipitates particularly at the particle boundaries of the microstructure of the Cu—Ni—Sn alloys is associated with a deterioration in toughness properties under dynamic stress.
For instance, publication DE 0 833 954 T1 proposes producing a spinodal Cu—Ni—Sn strand-casting alloy with 8% to 16% by weight of Ni, 5% to 8% by weight of Sn and optionally with up to 0.3% by weight of Mn, up to 0.3% by weight of B, up to 0.3% by weight of Zr, up to 0.3% by weight of Fe, up to 0.3% by weight of Nb and up to 0.3% by weight of Mg without any processing by kneading. After the performance of a solution annealing treatment of the cast state and after spinodal aging, the alloy has to be cooled rapidly in each case by means of water quenching in order to obtain a spinodally segregated microstructure without discontinuous precipitates.
By contrast, publication DE 23 50 389 C, with regard to a Cu—Ni—Sn alloy having 2% to 98% by weight of Ni and 2% to 20% by weight of Sn, states that cold forming with at least one degree of forming of s=75% has to be conducted in order to be able to prevent the occurrence of embrittling discontinuous precipitates during age annealing.
Document DE 691 05 805 T2 mentions the difficulties that occur in the industrial large-scale production of semifinished products and components from the copper-nickel-tin alloys. For instance, the occurrence of Sn-rich segregations, particularly at the grain boundaries of the cast microstructure, greatly restricts the opportunity for economic further processing. The Sn-rich segregations, which cannot be easily eliminated even by means of a thermomechanical processing operation on the cast state of the Cu—Ni—Sn alloys, prevent homogeneous distribution of the alloy elements in the matrix. However, this is a fundamental prerequisite for the hardenability of this group of materials. What is therefore proposed is to finely atomize the melt of a copper alloy with 4% to 18% by weight of Ni and 3% to 13% by weight of Sn, and to collect the spray particles on a collection surface. Subsequent rapid cooling is intended to counteract the formation of the Sn-rich grain boundary segregations.
Document DE 41 26 079 C2 discloses that a number of copper alloys can be produced by the conventional method of block casting with subsequent hot forming and cold forming with intermediate annealing operations only with poor economic viability, if at all, because hot forming is difficult owing to grain boundary precipitates, segregations or other inhomogeneities.
These copper alloys also include the copper-nickel-tin materials. To assure cold forming of the cast state of such alloys, therefore, a thin strip casting method with exact control of the solidification rate of the melt is recommended.
As a result of rising operating temperatures and pressures in modern engines, machines, installations and aggregates, a wide variety of different mechanisms of damage to the individual system elements occurs. Thus, there is an ever greater necessity, especially in the case of the design of sliding elements and plug connectors from the point of view of materials and construction, to take account not only of the types of sliding wear but also of the mechanism of damage by oscillating friction wear.
Oscillating friction wear, also called fretting in the jargon, is a kind of friction wear that occurs between oscillating contact faces. In addition to the geometry wear or volume wear of the components, the reaction with the surrounding medium results in friction corrosion. The damage to the material can distinctly lower local strength in the wear zone, especially fatigue strength. Fatigue cracks can proceed from the damaged component surface, and these lead to fatigue fracture/fatigue failure. Under friction corrosion, the fatigue strength of a component can drop well below the fatigue index of the material.
Oscillating friction wear differs considerably in its mechanism from the types of sliding wear with movement in one sense. More particularly, the effects of corrosion are particularly marked in the case of oscillating friction wear.
Document DE 10 2012 105 089 A1 describes the consequences of damage caused by oscillating friction wear of slide bearings. To assure a stable position of the slide bearings, they are indented into the bearing seat. The indenting operation builds up high stress on the slide bearing, which is even further increased by the increasing stresses, by the thermal expansions and by the dynamic shaft loads in modern engines. As a result of the excess stress, changes in geometry of the slide bearing can occur, which reduces the original bearing overlap. This enables micro-movements of the slide bearing relative to the bearing seat. These cyclical relative movements with low oscillation width at the contact faces between bearing and bearing seat lead to oscillating friction wear/friction corrosion/fretting of the backing of the slide bearing. The consequence is the initiation of cracks and ultimately the friction fatigue failure of the slide bearing. The results of fretting tests with various slide bearing materials suggest that particularly Cu—Ni—Sn alloys with an Ni content above 2% by weight, as is the case in the spinodally hardening copper-nickel-tin alloys, have inadequate resistance to fretting wear.
In engines and machines, electrical plug connectors are frequently disposed in an environment in which they are subjected to mechanical oscillating vibrations. If the elements of a connection arrangement are present in different assemblies that perform relative movements to one another as a result of mechanical stresses, the result can be corresponding relative movement of the connection elements. These relative movements lead to oscillating friction wear and to friction corrosion of the contact zone of the plug connectors. Microcracks form in this contact zone, which greatly reduces the fatigue resistance of the plug connector material. Failure of the plug connector through fatigue failure can be the consequence. Moreover, owing to friction corrosion, there is a rise in the contact resistance.
A crucial factor for sufficient resistance to oscillating friction wear/friction corrosion/fretting is accordingly a combination of the material properties of wear resistance, ductility and corrosion resistance.
In order to increase the wear resistance of the copper-nickel-tin alloys, it is necessary to add suitable wear substrates to these materials. These wear substrates in the form of hard particles are intended to assume the function of protection from the consequences of abrasive and adhesive wear. Useful hard particles in the Cu—Ni—Sn alloys include various forms of precipitation.
Document U.S. Pat. No. 6,379,478 B1 discloses the teaching of a copper alloy for plug connectors with 0.4% to 3.0% by weight of Ni, 1% to 11% by weight of Sn, 0.1% to 1% by weight of Si and 0.01% to 0.06% by weight of P. The fine precipitates of the nickel silicides and nickel phosphides are said to assure high strength and good stress relaxation resistance of the alloy.
For production of a sliding layer on a steel base substrate, document U.S. Pat. No. 2,129,197 A names a copper alloy which is applied by application welding to the base substrate and contains 77% to 92% by weight of Cu, 8% to 18% by weight of Sn, 1% to 5% by weight of Ni, 0.5% to 3% by weight of Si and 0.25% to 1% by weight of Fe. Wear substrates used here are said to be the silicides and phosphides of the alloy elements nickel and iron.
Document U.S. Pat. No. 3,392,017 A discloses a low-melting copper alloy having up to 0.4% by weight of Si, 1% to 10% by weight of Ni, 0.02% to 0.5% by weight of B, 0.1% to 1% by weight of P and 4% to 25% by weight of Sn. This alloy can be applied to suitable metallic substrate surfaces in the form of casting rods as filler material. By comparison with the prior art, the alloy has improved ductility and is machine-processible. Other than for deposit welding, this Cu—Sn—Ni—Si—P—B alloy is usable for deposition by means of spraying methods. The addition of phosphorus, silicon and boron is said here to improve the spontaneous flow properties of the molten alloy and the wetting of the substrate surface, and to make it unnecessary to use any additional flux.
The teaching disclosed in this document stipulates a particularly high P content of 0.2% to 0.6% by weight with an obligatory Si content in the alloy of 0.05% to 0.15% by weight. This underlines the primary demand for the spontaneous flow properties of the material. With this high P content, the hot formability of the alloy will be poor, and the spinodal segregatability of the microstructure will be inadequate.
According to document U.S. Pat. No. 4,818,307 A, the size of the hard particles precipitated in a copper-based alloy has a great influence on the wear resistance thereof. For instance, complex silicide formations/boride formations of the elements nickel and iron that reach a size of 5 to 100 μm considerably increase the wear resistance of a copper alloy with 5% to 30% by weight of Ni, 1% to 5% by weight of Si, 0.5% to 3% by weight of B and 4% to 30% by weight of Fe. The element tin is not present in this material. This material is applied as antiwear layer to a suitable substrate by means of deposit welding.
Document U.S. Pat. No. 5,004,581 A describes the same copper alloy as the aforementioned U.S. Pat. No. 4,818,307 A with an additional content of tin within the content range from 5% to 15% by weight and/or of zinc within the content range from 3% to 30% by weight. The addition of Sn and/or zinc particularly improves the resistance of the material to adhesive wear. This material is likewise applied as antiwear layer to a suitable substrate by means of deposit welding.
However, the copper alloy, according to documents U.S. Pat. Nos. 4,818,307 A and 5,004,581 A, owing to the required size of the silicide formations/boride formations of the elements nickel and iron of 5 to 100 μm, will have only very limited cold formability.
The disclosure of a precipitation-hardenable copper-nickel-tin alloy comes from document U.S. Pat. No. 5,041,176 A. This copper base alloy contains 0.1% to 10% by weight of Ni, 0.1% to 10% by weight of Sn, 0.05% to 5% by weight of Si, 0.01% to 5% by weight of Fe and 0.0001% to 1% by weight of boron. This material has a content of dispersed intermetallic phases of the Ni—Si system. The properties of the alloy are also elucidated by working examples that do not have any Fe content.
Document KR 10 2002 0 008 710 A (Abstract) states that spinodal Cu—Ni—Sn alloys having an Sn content greater than 6% by weight are not hot-formable. The reason given is Sn-rich segregations at the grain boundaries of the cast microstructure of the Cu—Ni—Sn alloys. Therefore, for the Cu—Ni—Sn multisubstance alloy disclosed, for high-strength wires and sheets, the composition of 1% to 8% by weight of Ni, 2% to 6% by weight of Sn and 0.1% to 5% by weight of two or more elements from the group of Al, Si, Sr, Ti and B is specified.
Document U.S. Pat. No. 5,028,282 A discloses a copper alloy having 6% to 25% by weight of Ni, 4% to 9% by weight of Sn and further additions with a content of 0.04% to 5% by weight (individually or together). These further additions are (in % by weight):
It is stated that the alloy elements Zn, Mn, Mg, P and B are added for deoxidation of the melt of the alloy. The elements Ti, Cr, Zr, Fe and Co have a grain-refining and strength-enhancing function.
By alloying with metalloids, for example boron, silicon and phosphorus, it is possible to achieve lowering of the relatively high base melt temperature, which is important for processing purposes. Therefore, these alloy additions are used particularly in the field of wear-resistant coating materials and high-temperature materials, which include, for example, the alloys of the Ni—Si—B and Ni—Cr—Si—B systems. In these materials, particularly the alloy elements boron and silicon are considered to be responsible for the significant lowering of the melting temperature of nickel-base hard alloys, which makes it possible to use them as spontaneously flowing nickel-base hard alloys.
Published specification DE 20 33 744 B includes important remarks relating to a further function of the alloy element boron in Si-containing metallic melts. According to this, addition of boron brings about digestion of the oxides that form in the melt and the formation of boron silicates which ascend to the surface of the coating layers and hence prevent the further ingress of oxygen. In this way, it is possible to achieve a smooth surface of the coating layer.
Document DE 102 08 635 B4 describes the processes in a diffusion solder site at which intermetallic phases are present. By means of diffusion soldering, parts having a different coefficient of thermal expansion are to be bonded to one another. In the case of thermomechanical stress on this solder site or in the soldering operation itself, great stresses occur at the interfaces, which can lead to cracks particularly in the environment of the intermetallic phases. A remedy proposed is mixing of the solder components with particles that bring about balancing of the different coefficients of expansion of the joining partners. For instance, particles of boron silicates or phosphorus silicates, owing to their advantageous coefficients of thermal expansion, can minimize thermomechanical stress in the solder bond. Moreover, spread of the cracks that have already been induced is hindered by these particles.
Published specification DE 24 40 010 B emphasizes the effect of the element boron particularly on the electrical conductivity of a cast silicon alloy with 0.1% to 2.0% by weight of boron and 4% to 14% by weight of iron. In this Si-based alloy, a high-melting Si—B phase precipitates out, which is referred to as silicon boride.
The silicon borides that are usually present in the SiB3, SiB4, SiB6 and/or SiBn polymorphs, determined by the boron content, differ significantly from silicon in terms of their properties. These silicon borides have metallic character, and they are therefore electrically conductive. They have exceptionally high thermal stability and oxidation stability. The SiB6 polymorph used with preference for sintered products, owing to its very high hardness and its high abrasive wear resistance, is used in ceramics production and ceramics processing for example.
The conventional wear-resistant hard alloys for surface coating consist of a comparatively ductile matrix composed of the metals iron, cobalt and nickel with intercalated silicides and borides as hard particles (Knotek, O.; Lugscheider, E.; Reimann, H.: Ein Beitrag zur Beurteilung verschleißfester Nickel-Bor-Silicium-Hartlegierungen [A Contribution to the Assessment of Wear-Resistant Hard Nickel-Boron-Silicon Alloys]. Zeitschrift für Werkstofftechnik 8 (1977) 10, p. 331-335). The broad use of the hard alloys of the Ni—Cr—Si, Ni—Cr—B, Ni—B—Si and Ni—Cr—B—Si systems is based on the increase in wear resistance by these hard particles. The Ni—B—Si alloys contain, as well as the silicides Ni3Si and Ni5Si2, also the borides Ni3B and the Ni—Si borides/Ni silicoborides Ni6Si2B. Also reported is a certain slowness to form silicide in the presence of the element boron. Further studies of the Ni—B—Si alloy system led to the detection of the high-melting Ni—Si borides Ni6Si2B and Ni4.29Si2B1.43 (Lugscheider, E.; Reimann, H.; Knotek, O.: Das Dreistoffsystem Nickel-Bor-Silicium [The Triphasic Nickel-Boron-Silicon System]. Monatshefte für Chemie 106 (1975) 5, p. 1155-1165). These high-melting Ni—Si borides exist in a relatively wide range of homogeneity in the direction of boron and silicon.
In many applications, the element zinc is added to the copper-nickel-tin alloys in order to reduce the metal cost. In functional terms, the effect of the alloy element zinc is more significant formation of Sn-rich or Ni—Sn-rich phases from the melt. Moreover, zinc enhances the formation of precipitates in the spinodal Cu—Ni—Sn alloys.
In addition, in numerous applications, a certain Pb content is also added to the copper-nickel-tin alloys to improve the dry-running properties and for better material-removing workability.
It is an object of the invention to provide a high-strength copper-nickel-tin alloy which has excellent hot formability over the entire nickel content and tin content range of 2% to 10% by weight in each case. A precursor material that has been produced by means of conventional casting methods without the necessity of performing spray compaction or thin strip casting should be usable for hot forming.
After casting, the copper-nickel-tin alloy should be free of gas pores and shrinkage pores and stress cracks, and be characterized by a microstructure with homogeneous distribution of the tin-enriched phase constituents. Moreover, intermetallic phases should already be present in the microstructure of the copper-nickel-tin alloy after casting. This is important in order that the alloy, even in the cast state, has high strength, high hardness and adequate wear resistance. In addition, even the cast state should feature high corrosion resistance.
The cast state of the copper-nickel-tin alloy should not first have to be homogenized by means of a suitable annealing treatment in order to be able to establish adequate hot formability.
With regard to the processing properties of the copper-nickel-tin alloy, the aim is firstly that the cold formability thereof is not significantly worsened in spite of the content of intermetallic phases with respect to the conventional Cu—Ni—Sn alloys. On the other hand, in respect of the alloy, the requirement for a minimum degree of forming in the cold forming operation conducted should be eliminated. This is considered to be a prerequisite according to the prior art in order to be able to assure spinodal segregation of the microstructure of the Cu—Ni—Sn materials without the formation of discontinuous precipitates.
A further demand with regard to the further processing of Cu—Ni—Sn materials corresponding to the prior art is based on the cooling rate after the age hardening of the materials. Thus, it is considered necessary, after the spinodal age hardening, to rapidly cool the materials by means of water quenching in order to obtain a spinodally segregated microstructure without discontinuous precipitates. Since, however, as a result of this cooling method, hazardous intrinsic stresses can form after age hardening, it is a further object of the invention to prevent, even with regard to the alloy, the formation of discontinuous precipitates over the entire manufacturing process including age hardening.
By means of a further processing operation comprising at least one annealing operation or at least one hot forming and/or cold forming operation as well as at least one annealing operation, a fine-grain, hard particle-containing microstructure having high strength, high heat resistance, high hardness, high stress relaxation resistance and corrosion resistance, adequate electrical conductivity and a high degree of resistance to the mechanisms of friction wear and of oscillating friction wear can be established.
With regard to a copper-nickel-tin alloy the invention is reflected by the features according to any of claims 1 to 3, with regard to a production process by the features of claims 9 to 10 and with regard to a use by the features of claims 16 to 18. The further dependent claims relate to advantageous forms and developments of the invention.
The invention includes a high-strength copper-nickel-tin alloy having excellent castability, hot formability and cold formability, high resistance to abrasive wear, adhesive wear and fretting wear, and improved corrosion resistance and stress relaxation resistance, consisting of (in % by weight):
optionally up to a maximum of 2.0% Co,
optionally up to a maximum of 2.0% Zn,
optionally up to a maximum of 0.25% Pb,
balance: copper and unavoidable impurities,
characterized in that
the Si/B ratio of the element contents in % by weight of the elements silicon and boron is a minimum of 0.4 and a maximum of 8;
the copper-nickel-tin alloy includes Si-containing phases and B-containing phases and phases of the systems Ni—Si—B, Ni—B, Ni—P and Ni—Si that significantly improve the processing properties and use properties of the alloy.
The invention also includes a high-strength copper-nickel-tin alloy having excellent castability, hot formability and cold formability, high resistance to abrasive wear, adhesive wear and fretting wear, and improved corrosion resistance and stress relaxation resistance, consisting of (in % by weight):
optionally up to a maximum of 2.0% Co,
optionally up to a maximum of 2.0% Zn,
optionally up to a maximum of 0.25% Pb,
balance: copper and unavoidable impurities,
characterized in that
the Si/B ratio of the element contents in % by weight of the elements silicon and boron is a minimum of 0.4 and a maximum of 8;
the following microstructure constituents are present in the alloy after casting:
a) an Si-containing and P-containing metallic base composition having, based on the overall microstructure,
a1) up to 35% by volume of first phase constituents that can be reported by the empirical formula CuhNikSnm and have an (h+k)/m ratio of the element contents in atom % of 2 to 6,
a2) up to 15% by volume of second phase constituents that can be reported by the empirical formula CupNirSns and have a (p+r)/s ratio of the element contents in atom % of 10 to 15 and
a3) a balance of solid copper solution;
b) phases which, based on the overall microstructure, are present
b1) at 0.01% to 10% by volume as Si-containing and B-containing phases,
b2) at 1% to 15% by volume as Ni—Si borides having the empirical formula NixSi2B with x=4 to 6,
b3) at 1% to 15% by volume as Ni borides,
b4) at 1% to 5% by volume as Ni phosphides,
b5) at 1% to 5% by volume as Ni silicides
in the microstructure, which are present individually and/or as addition compounds and/or mixed compounds and are ensheathed by tin and/or the first phase constituents and/or the second phase constituents;
in the course of casting the Si-containing and B-containing phases in the form of silicon borides, the Ni—Si borides and the Ni borides, Ni phosphides and Ni silicides that are present individually and/or as addition compounds and/or mixed compounds constitute seeds for uniform crystallization during the solidification/cooling of the melt, such that the first phase constituents and/or the second phase constituents are distributed uniformly in the microstructure like islands and/or like a mesh;
the Si-containing and B-containing phases that are in the form of boron silicates and/or boron phosphorus silicates, together with the phosphorus silicates, assume the role of a wear-protecting and corrosion-protecting coating on the semifinished materials and components of the alloy.
Advantageously, the first phase constituents and/or the second phase constituents are present in the cast microstructure of the alloy at least 1% by volume.
The uniform distribution of the first phase constituents and/or the second phase constituents in island form and/or in mesh form means that the microstructure is free of segregations. Segregations of this kind are understood to mean accumulations of the first phase constituents and/or the second phase constituents in the cast microstructure, which take the form of grain boundary segregations which, under thermal and/or mechanical stress on the casting, can cause damage to the microstructure in the form of cracks that can lead to fracture. The microstructure after the casting is still free of gas pores, shrinkage pores, stress cracks and discontinuous precipitates of the (Cu, Ni)—Sn system.
In this variant, the alloy is in the cast state.
The invention further includes a high-strength copper-nickel-tin alloy having excellent castability, hot formability and cold formability, high resistance to abrasive wear, adhesive wear and fretting wear, and improved corrosion resistance and stress relaxation resistance, consisting of (in % by weight):
optionally up to a maximum of 2.0% Co,
optionally up to a maximum of 2.0% Zn,
optionally up to a maximum of 0.25% Pb,
balance: copper and unavoidable impurities,
characterized in that
the Si/B ratio of the element contents in % by weight of the elements silicon and boron is a minimum of 0.4 and a maximum of 8;
after the further processing of the alloy by at least one annealing operation or by at least one hot forming operation and/or cold forming operation, as well as at least one annealing operation, the following microstructure constituents are present:
A) a metallic base composition having, based on the overall microstructure,
A1) up to 15% by volume of first phase constituents that can be reported by the empirical formula CuhNikSnm and have an (h+k)/m ratio of the element contents in atom % of 2 to 6,
A2) up to 5% by volume of second phase constituents that can be reported by the empirical formula CupNirSnm and have a (p+r)/s ratio of the element contents in atom % of 10 to 15 and
A3) a balance of solid copper solution;
B) phases which, based on the overall microstructure, are present
B1) at 2% to 30% by volume as Si-containing and B-containing phases, Ni—Si borides having the empirical formula NixSi2B with x=4 to 6, as Ni borides, Ni phosphides and as Ni silicides in the microstructure, which are present individually and/or as addition compounds and/or mixed compounds and are ensheathed by precipitates of the (Cu, Ni)—Sn system,
B2) at up to 80% by volume as continuous precipitates of the (Cu, Ni)—Sn system in the microstructure,
B3) at 2% to 30% by volume as Ni phosphides and Ni silicides in the microstructure that are present individually and/or as addition compounds and/or mixed compounds, are ensheathed by precipitates of the (Cu, Ni)—Sn system and have a size of less than 3 μm;
the Si-containing and B-containing phases that are in the form of silicon borides, the Ni—Si borides and the Ni borides, Ni phosphides and Ni silicides that are present individually and/or as addition compounds and/or mixed compounds constitute seeds for static and dynamic recrystallization of the microstructure during the further processing of the alloy, which enables the establishment of a uniform and fine-grain microstructure;
the Si-containing and B-containing phases that are in the form of boron silicates and/or boron phosphorus silicates, together with the phosphorus silicates, assume the role of a wear-protecting and corrosion-protecting coating on the semifinished materials and components of the alloy.
Advantageously, the continuous precipitates of the (Cu, Ni)—Sn system are present in the microstructure of the further-processed state of the alloy at at least 0.1% by volume.
Even after the further processing of the alloy, the microstructure is free of segregations. Segregations of this kind are understood to mean accumulations of the first phase constituents and/or the second phase constituents in the microstructure that take the form of grain boundary segregations which, particularly under dynamic stress on the components, can cause damage to the microstructure in the form of cracks that can lead to fracture.
The microstructure of the alloy after further processing is free of gas pores, shrinkage pores and stress cracks. It should be emphasized as an essential feature of the invention that the microstructure of the further-processed state is free of discontinuous precipitates of the (Cu, Ni)—Sn system.
In this second variant, the alloy is in the further-processed state.
This invention proceeds from the consideration that a copper-nickel-tin alloy with Si-containing and B-containing phases and with phases of the Ni—Si—B, Ni—B, Ni—P and Ni—Si systems is provided. These phases significantly improve the processing properties of castability, hot formability and cold formability. In addition, these phases improve the use properties of the alloy by an increase in strength and resistance to abrasive wear, adhesive wear and fretting wear. These phases additionally improve corrosion resistance and stress relaxation resistance as further use properties of the invention.
The copper-nickel-tin alloy of the invention can be produced by means of the sandcasting process, the shell mold casting process, precision casting process, full mold casting process, pressure diecasting process, lost foam process and permanent mold casting process or with the aid of the continuous or semicontinous strand casting process.
The use of primary forming techniques that are complex in terms of process technology and costly is possible but is not an absolute necessity for the production of the copper-nickel-tin alloy of the invention. For example, it is possible to dispense with the use of spray compaction or thin strip casting. The cast formats of the copper-nickel-tin alloy of the invention can especially be hot-formed directly over the entire range of Sn content and Ni content without the absolute necessity of performing homogenization annealing, for example by hot rolling, strand pressing or forging. It is also remarkable that, after shell mold casting or strand casting of the formats made from the alloy of the invention, it is also unnecessary to conduct any complex forging processes or compression processes at elevated temperature in order to weld, i.e. to close, pores and cracks in the material. Thus, the processing-related restrictions that existed to date in the production of semifinished products and components from copper-nickel-tin alloys are further eliminated.
The metallic base material of the microstructure of the copper-nickel-tin alloy of the invention in the cast state, with rising Sn content of the alloy, depending on the casting process, consists of increasing proportions of tin-enriched phases distributed uniformly in the solid copper solution (a phase).
These tin-enriched phases of the metallic base material can be divided into first phase constituents and second phase constituents. The first phase constituents can be reported by the empirical formula CunNikSnm and have an (h+k)/m ratio of the element contents in atom % of 2 to 6. The second phase constituents can be reported by the empirical formula CupNirSns and have a (p+r)/s ratio of the element contents in atom % of 10 to 15.
The alloy of the invention is characterized by Si-containing and B-containing phases that can be divided into two groups.
The first group relates to the Si-containing and B-containing phases that take the form of silicon borides and may be in the SiB3, SiB4, SiB6 and SiBn polymorphs. The “n” in the compound SiBn indicates the high solubility of the element boron in the silicon lattice.
The second group of the Si-containing and B-containing phases relates to the silicatic compounds of the boron silicates and/or boron phosphorus silicates.
In the copper-nickel-tin alloy of the invention, the microstructure component of the Si-containing and B-containing phases in the form of silicon borides and in the form of boron silicates and/or boron phosphorus silicates is not less than 0.01% by volume and not more than 10% by volume.
The uniform arrangement of the first phase constituents and/or second phase constituents in the microstructure of the alloy of the invention results particularly from the effect of the Si-containing and B-containing phases that are in the form of silicon borides, and the Ni—Si borides with the empirical formula NixSi2B with x=4 to 6 that mainly already precipitate out in the melt. Subsequently, during the solidification/cooling of the melt, there is precipitation of the Ni borides preferably on the silicon borides and Ni—Si borides that are already present. The entirety of the boridic compounds that are present individually and/or as addition compounds and/or mixed compounds serves as primary seeds during the first solidification/cooling of the melt.
Later on in the solidification/cooling of the melt, the Ni phosphides and Ni silicides precipitate out preferentially as secondary seeds on the primary seeds of the silicon borides, Ni—Si borides and the Ni borides that are already present, individually and/or as addition compounds and/or mixed compounds.
The Ni—Si borides and the Ni borides are each present in the microstructure at 1% to 15% by volume, and the Ni phosphides and Ni silicides each at 1% to 5% by volume.
Thus, in the microstructure, the Si-containing and B-containing phases that are in the form of silicon borides, the Ni—Si borides with the empirical formula NixSi2B with x=4 to 6 and the Ni borides, Ni phosphides and Ni silicides are present individually and/or as addition compounds and/or mixed compounds.
These phases are referred to hereinafter as crystallization seeds.
Finally, the element tin and/or the first phase constituents and/or the second phase constituents of the metallic base material preferably crystallize in the regions of the crystallization seeds, as a result of which the crystallization seeds of tin and/or the first phase constituents and/or the second phase constituents are ensheathed.
These crystallization seeds ensheathed by tin and/or the first phase constituents and/or the second phase constituents are referred to hereinafter as hard particles of the first class.
The hard particles of the first class, in the cast state of the alloy of the invention, have a size of less than 80 μm. Advantageously, the size of the hard particles of the first class is less than 50 μm.
With rising Sn content of the alloy, the arrangement of the first phase constituents and/or the second phase constituents in island form is transformed to a meshlike arrangement in the microstructure.
In the cast microstructure of the copper-nickel-tin alloy of the invention, the first phase constituents may assume a proportion of up to 35% by volume. The second phase constituents assume a microstructure fraction of up to 15% by volume. Advantageously, the first phase constituents and/or the second phase constituents are present in the microstructure of the cast state of the alloy at at least 1% by volume.
As a result of the addition of the alloy element boron, during the casting of the alloy of the invention, there is inhibited and hence only incomplete formation of the phosphides and silicides. For this reason, a content of phosphorus and silicon remains dissolved in the metallic base material of the cast state.
The conventional copper-nickel-tin alloys have a comparatively broad solidification interval. This broad solidification interval in casting increases the risk of gas absorption and, as a result, of incomplete, coarse, usually dendritic crystallization of the melt. The consequence is often gas pores and coarse Sn-rich segregations, at the phase boundary of which there is frequent occurrence of shrinkage pores and stress cracks. In this group of materials, the Sn-rich segregations additionally occur preferentially at the grain boundaries.
By means of the combined content of boron, silicon and phosphorus, various processes in the melt of the alloy of the invention are activated, which crucially alter the solidification characteristics thereof by comparison with the conventional copper-nickel-tin alloys.
In the melt of the invention, the elements boron, silicon and phosphorus assume a deoxidizing function. The addition of boron and silicon makes it possible to lower the phosphorus content without reducing the intensity of the deoxidation of the melt. Using this measure, it is possible to suppress the adverse effects of adequate deoxidation of the melt by means of an addition of phosphorus. Thus, a high P content would additionally extend the solidification interval of the copper-nickel-tin alloy which is already very large in any case, which would result in an increase in the propensity to pores and propensity to segregation in this material type. The adverse effects of the addition of phosphorus are reduced by the restriction of the P content in the alloy of the invention to the range from 0.001% to 0.09% by weight.
The lowering of the base melting temperature particularly by the element boron and the crystallization seeds lead to a reduction of the solidification interval of the alloy of the invention. As a result, the cast state of the invention has a very uniform microstructure with a fine distribution of the individual phase constituents. Thus, no tin-enriched segregations occur in the alloy of the invention, particularly at the grain boundaries.
In the melt of the alloy of the invention, the effect of the elements boron, silicon and phosphorus is a reduction of the metal oxides. The elements themselves are oxidized at the same time and usually ascend to the surface of the castings, where they form, in the form of boron silicates and/or boron phosphorus silicates and of phosphorus silicates, a protective layer that protects the castings from absorption of gas. Exceptionally smooth surfaces of the castings of the alloy of the invention were found, which indicate the formation of such a protective layer. The microstructure of the cast state of the invention was also free of gas pores over the entire cross section of the castings.
In the context of the remarks relating to the documents cited, the advantages of the introduction of boron silicates and phosphorus silicates for the avoidance of stress cracks between phases having different coefficients of thermal expansion during diffusion soldering were mentioned.
A basic concept of the invention is that applying the effect of boron silicates, boron phosphorus silicates and phosphorus silicates with regard to the matching of the different coefficients of thermal expansion of the joining partners in diffusion soldering to the processes in the casting, hot forming and thermal treatment of the copper-nickel-tin materials. Owing to the broad solidification interval of these alloys, high mechanical stresses occur between the low-Sn and Sn-rich structure regions that crystallize in an offset manner and can lead to cracks and pores. In addition, these damage features can also occur in the hot forming and high-temperature annealing operations on the copper-nickel-tin alloys owing to the different hot forming characteristics and the different coefficients of thermal expansion of the low-Sn and Sn-rich microstructure constituents.
The effect of the combined addition of boron, silicon and phosphorus to the copper-nickel-tin alloy of the invention is firstly, during the solidification of the melt, by means of the effect of the crystallization seeds, a microstructure having a uniform distribution of the first phase constituents and/or the second phase constituents of the metallic base material in the form of islands and/or in the form of a mesh. In addition to the crystallization seeds, the Si-containing and B-containing phases that form during the solidification of the melt and in the form of boron silicates and/or boron phosphorus silicates, together with the phosphorus silicates, assure the necessary matching of the coefficients of the thermal expansion of the first phase constituents and/or the second phase constituents and of the solid copper solution of the metallic base material. In this way, the formation of pores and stress cracks between the phases with different Sn content is prevented.
A further effect of the inventive alloy content of the copper-nickel-tin alloy is a significant change in the grain structure in the cast state. Thus, it was found that, in the primary cast microstructure, a substructure with a grain size of the subgrains of less than 30 μm is formed.
Alternatively, the alloy of the invention can be subjected to further processing by annealing or by a hot forming and/or cold forming operation as well as at least one annealing operation.
One means of further processing the copper-nickel-tin alloy of the invention is to convert the castings to the final form with the properties as required by means of at least one cold forming operation as well as at least one annealing operation.
As a result of the uniform cast microstructure and the hard particles of the first class that have precipitated out therein, the alloy of the invention, even in the cast state, has high strength. As a result, the castings have relatively low cold formability that makes it difficult to process them further economically. For this reason, the performance of a homogenization annealing operation on the castings prior to a cold forming operation has been found to be advantageous.
For assurance of the age hardenability of the invention, accelerated cooling after the homogenization annealing processes has been found to be advantageous. It has been here found that, owing to the slowness of the precipitation mechanisms and separation mechanisms, aside from water quenching, cooling methods with a relatively low cooling rate can also be used. For instance, the use of accelerated air cooling has been found likewise to be practicable in order to reduce the hardness-enhancing and strength-increasing effect of the precipitation processes and separation processes in the microstructure during the homogenization annealing operation of the invention to a sufficient degree.
The outstanding effect of the crystallization seeds for the recrystallization of the microstructure of the invention is manifested in the microstructure which can be established after cold forming by means of annealing within the temperature range from 170 to 880° C. and annealing time between 10 minutes and 6 hours. The exceptionally fine structure of the recrystallized alloy enables further cold forming steps with a degree of forming s of usually more than 70%. In this way, ultrahigh-strength states of the alloy can be established.
These high degrees of cold forming that have become possible in the further processing of the invention can establish particularly high values for tensile strength Rm, yield point Rp0.2 and hardness. Particularly the level of the Rp0.2 parameter is important for the sliding elements and guide elements. In addition, a high value of Rp0.2 is a prerequisite for the necessary spring characteristics of plug connectors in electronics and electrical engineering.
In the remarks in numerous documents that describe the prior art relating to the processing and the properties of the copper-nickel-tin materials, reference is made to the need to observe a minimum degree of cold forming of 75%, for example, in order to prevent the precipitation of discontinuous precipitates of the (Cu, Ni)—Sn system in the microstructure.
By contrast, the microstructure of the alloy of the invention, irrespective of the degree of cold forming, remains free of discontinuous precipitates of the (Cu, Ni)—Sn system. For instance, for particularly advantageous embodiments of the invention, it was found that, even in the case of extremely small degrees of cold forming of less than 20%, the microstructure of the invention remains free of discontinuous precipitates of the (Cu, Ni)—Sn system.
The conventional, spinodally segregatable Cu—Ni—Sn materials, according to the prior art, are considered to be hot formable with great difficulty, if at all.
The effect of the crystallization seeds was likewise observed during the process of hot forming of the copper-nickel-tin alloy of the invention. The crystallization seeds are considered to be primarily responsible for the fact that the dynamic recrystallization in the hot forming of the alloy of the invention takes place preferentially within the temperature range from 600 to 880° C. This results in a further increase in the uniformity and fine granularity of the microstructure.
Advantageously, the cooling of the semifinished products and components after the hot forming can be effected with calmed or accelerated air or with water.
As is the case after casting, it was also possible to establish an exceptionally smooth surface of the parts after the hot forming of the castings. This observation suggests the formation of Si-containing and B-containing phases that take the form of boron silicates and/or boron phosphorus silicates, and of phosphorus silicates, which takes place in the material during the hot forming. The silicates together with the crystallization seeds, even during the hot forming, result in matching of the different coefficients of thermal expansion of the phases of the metallic base material of the invention. Thus, the surface of the hot-formed parts and the microstructure, as is the case after casting, were free of cracks and pores after the hot forming as well.
Advantageously, at least one annealing treatment of the cast state and/or the hot-formed state of the invention can be conducted within the temperature range from 170 to 880° C. with the duration of 10 minutes to 6 hours, and alternatively with cooling under calmed or accelerated air or with water.
One aspect of the invention relates to an advantageous process for further processing of the cast state or the hot-formed state or the annealed cast state or the annealed hot-formed state that includes the performance of at least one cold forming operation.
Preferably, at least one annealing treatment of the cold-formed state of the invention can be conducted within the temperature range from 170 to 880° C. with the duration of 10 minutes to 6 hours, and alternatively with cooling under calmed or accelerated air or with water.
Advantageously, a stress relief annealing/age hardening annealing operation can be conducted within the temperature range from 170 to 550° C. with the duration of 0.5 to 8 hours.
After further processing of the alloy by at least one annealing operation or by at least one hot forming and/or cold forming operation as well as at least one annealing operation, precipitates of the (Cu, Ni)—Sn system are preferably formed in the regions of the crystallization seeds, as a result of which the crystallization seeds are ensheathed by these precipitates.
These crystallization seeds ensheathed by precipitates of the (Cu, Ni)—Sn system are referred to hereinafter as hard particles of the second class.
As a result of the further processing of the alloy of the invention, the size of the hard particles of the second class decreases compared to the size of the hard particles of \the first class. Particularly with an increasing degree of cold forming, there is an advancing reduction in size of the hard particles of the second class since these, being the hardest constituents of the alloy, cannot contribute to the change in shape of the metallic base material that surrounds them. Depending on the degree of cold forming, the resulting hard particles of the second class and/or the resulting segments of the hard particles of the second class have a size of less than 40 μm to even less than 5 μm.
The Ni content and the Sn content of the invention each vary within the limits between 2.0% and 10.0% by weight. An Ni content and/or an Sn content of below 2.0% by weight would result in excessively low strength values and hardness values. Moreover, the running properties of the alloy under sliding stress would be inadequate. The resistance of the alloy to abrasive and adhesive wear would not meet the demands. At an Ni content and/or an Sn content of more than 10.0% by weight, the toughness properties of the alloy of the invention would worsen rapidly, as a result of which the dynamic durability of the components made of the material is lowered.
With regard to the assurance of optimal dynamic durability of the components made of the alloy of the invention, the content of nickel and tin within the range from 3.0% to 9.0% by weight in each case is found to be advantageous. In this regard, for the invention, the range from 4.0% to 8.0% by weight in each case is particularly preferred for the content of the elements nickel and tin.
With regard to the Ni-containing and Sn-containing copper materials, it is known from the prior art that the degree of spinodal segregation of the microstructure rises with increasing Ni/Sn ratio of the element contents in % by weight of the elements nickel and tin. This is true of an Ni content and an Sn content over and above about 2% by weight. With decreasing Ni/Sn ratio, the mechanism of the precipitation formation of the (Cu, Ni)—Sn system gains greater weight, which leads to a reduction in the spinodally segregated microstructure fraction. One particular consequence is a greater degree of formation of discontinuous precipitates of the (Cu, Ni)—Sn system with decreasing Ni/Sn ratio.
The essential features of the copper-nickel-tin alloy of the invention include the crucial suppression of the effect of the Ni/Sn ratio on the formation of discontinuous precipitates in the microstructure. Thus, it has been found that, in the microstructure of the invention, largely irrespective of the Ni/Sn ratio and irrespective of the age hardening conditions, there is no precipitation of discontinuous precipitates of the (Cu, Ni)—Sn system.
During further processing of the alloy of the invention, by contrast, continuous precipitates of the (Cu, Ni)—Sn system form at up to 80% by volume. Advantageously, the continuous precipitates of the (Cu, Ni)—Sn system are present in the microstructure of the further-processed state of the alloy at at least 0.1% by volume.
The effect of the crystallization seeds during the solidification/cooling of the melt, the effect of the crystallization seeds as recrystallization seeds and the effect of the silicate-based phases for the purpose of wear protection and corrosion protection can only achieve a degree of technical significance in the alloy of the invention when the silicon content is at least 0.01% by weight and the boron content at least 0.002% by weight. If, by contrast, the Si content exceeds 1.5% by weight and/or the B content 0.45% by weight, this leads to a deterioration in casting characteristics. The excessively high content of crystallization seeds would make the melt crucially thicker. Moreover, the result would be reduced toughness properties of the alloy of the invention.
An advantageous range for the Si content has been considered to be within the limits from 0.05% to 0.9% by weight. A particularly advantageous content for silicon has been found to be from 0.1% to 0.6% by weight.
For the element boron, the content of 0.01% to 0.4% by weight is considered to be advantageous. The content for boron of 0.02% to 0.3% by weight has been found to be particularly advantageous.
For the assurance of an adequate content of Ni—Si borides and of Si-containing and B-containing phases that are in the form of boron silicates and/or boron phosphorus silicates, a lower limit for the element ratio of the elements silicon and boron has been found to be important. For this reason, the minimum Si/B ratio of the element contents of the elements silicon and boron in % by weight in the alloy of the invention is 0.4. An advantageous minimum Si/B ratio of the element contents of the elements silicon and boron for the alloy of the invention in % by weight is 0.8. Preferably, the minimum Si/B ratio of the element contents of the elements silicon and boron in % by weight is 1.
For a further important feature of the invention, the fixing of an upper limit for the Si/B ratio of the element contents of the elements silicon and boron in % by weight of 8 is important. After the casting, fractions of the silicon are present dissolved in the metallic base material and bound in the hard particles of the first class.
During a thermal or thermomechanical further processing operation of the cast state, there is at least partial dissolution of the silicide component of the hard particles of the first class. This increases the Si content of the metallic base material: If this exceeds an upper limit, there is precipitation of an excess proportion of Ni silicides with increasing size. These would crucially lower the cold formability of the invention.
For this reason, the maximum Si/B ratio of the element contents of the elements silicon and boron in % by weight of the alloy of the invention is 8. By virtue of this measure, it is possible to lower the size of the Ni silicides that form during a thermal or thermomechanical further is processing operation of the cast state of the alloy to below 3 μm. In addition, this limits the content of Ni silicides. In this regard, the limitation of the Si/B ratio of the element contents of the elements silicon and boron in % by weight to the maximum value of 6 has been found to be particularly advantageous.
The precipitation of the crystallization seeds affects the viscosity of the melt of the alloy of the invention. This fact emphasizes why an addition of phosphorus is indispensable. The effect of phosphorus is that the melt is sufficiently mobile in spite of the crystallization seeds, which is of great significance for castability of the invention. The phosphorus content of the alloy of the invention is 0.001% to 0.09% by weight.
Below 0.001% by weight, the P content no longer contributes to assurance of sufficient castability of the invention. If the phosphorus content of the alloy assumes values above 0.09% by weight, on the one hand, an excessively large Ni component is bound in the form of phosphides, which lowers the spinodal separability of the microstructure. On the other hand, in the case of a P content above 0.09% by weight, there would be a crucial deterioration in the hot formability of the invention. For this reason, a P content of 0.01% to 0.09% by weight has been found to be particularly advantageous. Preference is given to a P content in the range from 0.02% to 0.08% by weight.
The alloy element phosphorus is of very great significance for another reason. Together with the required maximum Si/B ratio of the element contents of the elements silicon and boron in % by weight of 8, it can be attributed to the phosphorus content of the alloy that, after further processing of the invention, Ni phosphides and Ni silicides, which are present individually and/or as addition compounds and/or mixed compounds and are ensheathed by precipitates of the (Cu, Ni)—Sn system, with a size of not more than 3 μm and with a content of 2% up to 30% by volume can form in the microstructure.
These Ni phosphides and Ni silicides, which are present individually and/or as addition compounds and/or mixed compounds and are ensheathed by precipitates of the (Cu, Ni)—Sn system and have a size of not more than 3 μm, are referred to hereinafter as hard particles of the third class.
In the microstructure of the further-processed state of the particularly preferred configuration of the invention, the hard particles of the third class even have a size of less than 1 μm.
These hard particles of the third class firstly supplement the hard particles of the second class in their function as wear substrates. Thus, they increase the strength and hardness of the metallic base material and hence improve the resistance of the alloy to abrasive wear stress. Secondly, the hard particles of the third class increase the resistance of the alloy to adhesive wear. Finally, the effect of these hard particles of the third class is a crucial increase in the hot strength and the stress relaxation resistance of the alloy of the invention. This is an important prerequisite for the use of the alloy of the invention particularly for sliding elements and components and connecting elements in electronics/electrical engineering.
Owing to the content of hard particles of the first class in the microstructure of the cast state and of hard particles of the second and third classes in the microstructure of the further-processed state, the alloy of the invention has the character of a precipitation-hardenable material. Advantageously, the invention corresponds to a precipitation-hardenable and spinodally segregatable copper-nickel-tin alloy.
The sum total of the element contents of the elements silicon, boron and phosphorus is advantageously at least 0.2% by weight.
The cast variant and the further-processed variant of the alloy of the invention may include the following optional elements:
The element cobalt may be added to the copper-nickel-tin alloy of the invention at a content of up to 2.0% by weight. Owing to the similarity relationship between the elements nickel and cobalt and owing to the likewise Si boride-forming, boride-forming, silicide-forming and phosphide-forming properties of cobalt in relation to nickel, the alloy element cobalt may be added in order to take part in the formation of the crystallization seeds and of the hard particles of the first, second and third classes in the alloy. As a result, it is possible to reduce the Ni content bound within the hard particles. This can achieve the effect that the Ni content effectively available in the metallic base material for the spinodal segregation of the microstructure rises. With the addition of advantageously 0.1% to 2.0% by weight of Co, it is thus possible to considerably increase the strength and hardness of the invention.
The element zinc can be added to the copper-nickel-tin alloy of the invention with a content of 0.1% to 2.0% by weight. It was found that the alloy element zinc, depending on the Ni content and Sn content of the alloy, increases the proportion of the first phase constituents and/or second phase constituents in the metallic base material of the invention, which results in an increase in strength and hardness. The interactions between the Ni component and the Zn component are considered to be responsible for this. As a result of these interactions between the Ni component and the Zn component, a decrease in the size of the hard particles of the first and second classes was likewise found, which thus formed in finer distribution in the microstructure.
Below 0.1% by weight of Zn, it was not possible to observe these effects on the microstructure and the mechanical properties of the invention. At Zn contents above 2.0% by weight, the toughness properties of the alloy were lowered to a lower level. There was also a deterioration in the corrosion resistance of the copper-nickel-tin alloy of the invention. Advantageously, a zinc content in the range from 0.1% to 1.5% by weight can be added to the invention.
Optionally, small proportions of lead above the contamination limit up to a maximum of 0.25% by weight may be added to the copper-nickel-tin alloy of the invention. In a particularly preferred advantageous embodiment of the invention, the copper-nickel-tin alloy is free of lead apart from any unavoidable contaminations, which meets current environmental standards. In this connection, lead contents up to a maximum of 0.1% by weight of Pb are contemplated.
The formation of Si-containing and B-containing phases that are in the form of boron silicates and/or boron phosphorus silicates and of phosphorus silicates does not just lead to a significant reduction in the content of pores and cracks in the microstructure of the alloy of the invention. These silicate-based phases also assume the role of a wear-protecting and corrosion-protecting coating on the components.
During the adhesive wear stress on a component made of the copper-nickel-tin alloy of the invention, the alloy element tin makes a particular contribution to the formation of what is called a tribological layer between the friction partners. Particularly under mixed friction conditions, this mechanism is important when the dry-running properties of a material become increasingly important. The tribological layer leads to a reduction in size of the purely metallic contact area between the friction partners, which prevents welding or fretting of the elements.
Owing to the rise in efficiency of modern engines, machines and aggregates, ever higher operating pressures and operating temperatures are occurring. This is being observed particularly in the newly developed internal combustion engines where the aim is ever more complete combustion of the fuel. In addition to the elevated temperatures in the space around the internal combustion engines, there is the evolution of heat that occurs during the operation of the slide bearing systems. Owing to the high temperatures in bearing operation, in the parts made of the alloy of the invention, similarly to during casting and hot forming, there is formation of Si-containing and B-containing phases in the form of boron silicates and/or boron phosphorus silicates, and of phosphorus silicates. These compounds also reinforce the tribological layer which forms primarily because of the alloy element tin, which results in increased adhesive wear resistance of the sliding elements made of the alloy of the invention.
Thus, the alloy of the invention assures a combination of the properties of wear resistance and corrosion resistance. This combination of properties leads to a high resistance, as required, against the mechanisms of friction wear and to a high material resistance against frictional corrosion. In this way, the invention is of excellent suitability for use as sliding element and plug connector, since it has a high degree of resistance to sliding wear and to oscillating friction wear, called fretting.
As well as the important contribution of the hard particles of the third class to increasing the resistance of the invention to the abrasive and adhesive mechanism of friction wear, the hard particles of the third class make a crucial contribution to increasing oscillation resistance. Together with the hard particles of the second class, the hard particles of the third class constitute hindrances to the spread of fatigue cracks that can be introduced into the stressed component particularly under oscillating friction wear, called fretting. Thus, the hard particles of the second and third classes particularly supplement the wear-protecting and corrosion-protecting effect of the Si-containing and B-containing phases that are in the form of boron silicates and/or boron phosphorus silicates, and of the phosphorus silicates with regard to the increase in resistance of the alloy of the invention to oscillating friction wear, called fretting.
Heat resistance and stress relaxation resistance are among the further essential properties of an alloy which is used for end uses where higher temperatures occur. For assurance of sufficiently high heat resistance and stress relaxation resistance, a high density of fine precipitates is considered to be advantageous. Precipitates of this kind in the alloy of the invention are the hard particles of the third class and the continuous precipitates of the (Cu, Ni)—Sn system.
Owing to the uniform and fine-grain microstructure with substantial freedom from pores, freedom from cracks and freedom from segregations and the content of hard particles of the first class, the alloy of the invention, even in the cast state, has a high degree of strength, hardness, ductility, complex wear resistance and corrosion resistance. This combination of properties means that sliding elements and guide elements can be produced even from the cast formats. The cast state of the invention can additionally also be used for the production of housings for fittings and of housings for water pumps, oil pumps and fuel pumps. The alloy of the invention is also usable for propellers, wings, screws and hubs for shipbuilding.
The further-processed variant of the invention may find use for the fields of use having particularly high complex and/or dynamic component stress.
The excellent strength properties and wear resistance and corrosion resistance of the copper-nickel-tin alloy of the invention mean that a further use is possible. Thus, the invention is suitable for metallic articles in constructions for the breeding of seawater-dwelling organisms (aquaculture). In addition, the invention can be used to produce pipes, seals and connecting bolts that are required in the maritime and chemical industries.
For the use of the alloy of the invention for production of percussion instruments, the material is of great significance. Especially cymbals of high quality have to date been manufactured from usually tin-containing copper alloys by means of hot forming and at least one annealing operation before they are converted to the final shape, usually by means of a bell or shell. Subsequently, the cymbals are annealed once again before the material-removing final processing thereof. The production of the various variants of the cymbals (for example ride cymbals, hi-hats, crash cymbals, china cymbals, splash cymbals and effect cymbals) accordingly requires particularly advantageous hot formability of the material, which is assured by the alloy of the invention. Within the range limits of the chemical composition of the invention, different microstructure components of the phases of the metallic base material and the different hard particles can be set within a very wide range. In this way, it is possible even from an alloy point of view to affect the sound characteristics of the cymbals.
Especially for the production of composite slide bearings, the invention may be used to be applied to a composite partner by means of a joining method. Thus, composite production between sheets, plates or strips of the invention and steel cylinders or steel strips, preferably made of a quenched and tempered steel, is possible by means of forging, soldering or welding with the optional performance of at least one annealing operation within the temperature range from 170 to 880° C. It is likewise possible, for example, to produce composite bearing cups or composite bearing bushes by roll cladding, inductive or conductive roll cladding or by laser roll cladding, likewise with the optional performance of at least one annealing operation within the temperature range from 170 to 880° C.
The formation of the microstructure in the alloy of the invention gives rise to further options for the production of composite sliding elements such as composite bearing cups or composite bearing bushes. For instance, it is possible to apply a coating of tin or of an Sn-rich material which serves as running layer in bearing operation to a base body from the invention by means of hot-dip tinning or electrolytic tinning, sputtering or by the PVD method or CVD method.
In this way, high-performance composite sliding elements such as composite bearing cups or composite bearing bushes can also be produced as a three-layer system, with a bearing backing made of steel, the actual bearing made of the alloy of the invention and the running layer made of tin or of the Sn-rich coating. This multilayer system has a particularly advantageous effect on the adaptability and the ease of running-in of the slide bearing and improves the embeddability of extraneous particles and abrasive particles, with no damage resulting from overriding of the layer composite system as a result of pore formation and crack formation in the boundary region of the individual layers even under thermal or thermomechanical stress on the slide bearing.
The great potential of the copper-nickel-tin materials particularly with regard to strength, spring properties and stress relaxation resistance can be utilized, via the use of the alloy of the invention, for the field of use of tinned components, wire elements, guiding elements and connecting elements in electronics and electrical engineering as well. Thus, the microstructure of the invention reduces the mechanism of damage of pore formation and crack formation in the boundary region between the alloy of the invention and the tinning even at elevated temperatures, which counteracts any increase in the electrical passage resistance of the components or even detachment of the tinning.
Machine processing of the semifinished products and components made from the conventional copper-nickel-tin kneading alloys with an Ni content and Sn content of up to about 10% by weight in each case is possible only with great difficulty owing to inadequate material removability. Thus, particularly the occurrence of long turnings causes long machine shutdown times since the turnings first have to be removed by hand from the processing area of the machine.
In the alloy of the invention, by contrast, the different hard particles act as turning breakers. The short friable turnings and/or entangled turnings that thus arise facilitate material removability, and for that reason the semifinished products and components made from the cast state and the further-processed state of the alloy of the invention have better machine processibility.
An important working example of the invention is elucidated by tables 1 to 10. Cast plaques of the copper-nickel-tin alloy of the invention and of the reference material were produced by strand casting. The chemical composition of the casts is apparent from tab. 1.
Tab. 1 shows the chemical composition of working example A and of the reference material R. Working example A is characterized by an Ni content of 6.0% by weight, an Sn content of 5.75% by weight, an Si content of 0.3% by weight, a B content of 0.15% by weight, a P content of 0.070% by weight and by a balance of copper. The reference material R, a conventional copper-nickel-tin-phosphorus alloy, has an Ni content of 5.78% by weight, an Sn content of 5.75% by weight, a P content of 0.032% by weight and a balance of copper.
The microstructure of the strand-cast plaques of the reference material R has gas pores and shrinkage pores, and Sn-rich segregations particularly at the grain boundaries.
By contrast with the reference material R, the strand casting of working example A, owing to the effect of the crystallization seeds, has a uniformly solidified, pore-free and segregation-free microstructure.
The metallic base material of the cast state of working example A consists of a solid copper solution with, based on the overall microstructure, about 10% to 15% by volume of intercalated first phase constituents in the form of islands, which can be reported by the empirical formula CuhNikSnm and have a ratio (h+k)/m of the element contents in atom % of 2 to 6. It was possible to detect the compounds CuNikSn23 and CuNi9Sn20 with a ratio (h+k)/m of 3.4 and 4. Also intercalated in the form of islands in the metallic base material at, based on the overall microstructure, about 5% to 10% by volume are second phase constituents that can be reported by the empirical formula CupNirSns and have a ratio (p+r)/s of the element contents in atom % of 10 to 15. The compounds CuNi3Sn8 and CuNi4Sn7 were detected with a ratio (p+r)/s of 11.5 and 13.3. The first and second phase constituents of the metallic base material are predominantly crystallized in the region of the crystallization seeds and ensheath them.
The analysis of the hard particles of the first class in the cast state of working example A gave pointers to the compound SiB6 as a representative of the Si-containing and B-containing phases, to Ni6Si2B as a representative of the Ni—Si borides, to Ni3B as a representative of the Ni borides, to Ni3P as a representative of the Ni phosphides and to Ni2Si as a representative of the Ni silicides, which are present in the microstructure individually and/or as addition compounds and/or mixed compounds. In addition, these hard particles are ensheathed by tin and/or the first phase constituents and/or second phase constituents of the metallic base material.
During the process of casting working example A, a substructure formed in the primary cast grains. These subgrains in the cast microstructure of working example A of the invention have a grain size of less than 10 μm. As a result of the subgrain structure and the hard particles precipitated in the microstructure of working example A of the invention, the hardness HB of the cast state, at 156, is well above the hardness of 94 HB of the strand casting of R (tab. 2).
Likewise shown in tab. 2 are the hardness values that have been ascertained on the strand casting of alloys A and R that has been age-hardened at 400° C. with a duration of 3 hours. The rise in hardness from 94 to 145 HB is at its greatest for the reference material R. The hardening is attributable particularly to thermally activated formation of segregation of the Sn-rich phase in the microstructure. The tin-enriched phase constituents precipitate out in much finer form in the region of the hard particles in the microstructure of working example A. For this reason, the rise in hardness from 156 to 176 HB is not as marked.
One intention of the invention is that of maintaining the good cold formability of the conventional copper-nickel-tin alloys in spite of the introduction of hard particles. To verify the degree to which this aim is achieved, the manufacturing program 1 according to tab. 3 was conducted. This manufacturing program consisted of one cycle of cold forming and annealing operations, wherein the cold rolling steps were each effected with the maximum possible degree of cold forming.
Owing to the high hardness of the cast state of working example A, it was calcined at the temperature of 740° C. with the duration of 2 hours and subsequently cooled down in an accelerated manner in water. This brought about the assimilation of the properties of the cast state of A and R with regard to strength and hardness.
The degrees of cold forming ε of 60% and 91% that are achievable for working example A underline the fact that the alloy of the invention, in spite of the content of hard particles, can achieve and even surpass the shape-changing properties of the conventional copper-nickel-tin alloy R.
The thermal sensitivity of the reference material R with regard to the formation of the Sn-rich segregations was also found in the annealing between the two cold forming steps (No. 4 in tab. 3). For this reason, the annealing temperature of 740° C. that was used for the intermediate annealing of the cold-rolled plaque of alloy A had to be lowered to 690° C. for R.
After the performance of manufacturing program 1, the indices of the strips of materials A and R were ascertained after the last cold rolling operation and on completion of the age hardening that are listed in tab. 4.
It becomes clear that the strengths and hardness of the strips of working example A that have been cold-rolled and age-hardened at 300° C. are higher than the respective properties of the strips of reference material R.
Favored by the high content of hard particles, over and above the temperature of about 400° C., recrystallization of the microstructure of alloy A takes place. This recrystallization leads to a drop in strengths and in hardness, and so the effect of the precipitation hardening and spinodal segregation cannot be manifested.
The microstructure of the further-processed working example A, after age hardening at 450° C., includes the hard particles of the second class (labeled 3 in
In addition, further phases have precipitated out in the microstructure of the further-processed alloy A. These include the continuous precipitates of the (Cu, Ni)—Sn system that are labeled 4 in
The size of the hard particles of the third class of less than 3 μm is characteristic of the further-processed alloy of the invention. For the further-processed working example A of the invention, after age hardening at 450° C., it is actually less than 1 μm (labeled 5 in
In order to reduce the effect of the cold formability and the recrystallization temperature on the properties of the individual alloys, a further manufacturing program was conducted. This manufacturing program 2 pursued the aim of processing the strand-cast plaques of materials A and R by means of cold-forming and annealing operations to give strips, using identical parameters in each case for the degrees of cold forming and the annealing temperatures (tab. 5).
Owing to the high hardness of the cast state of working example A, it was again calcined before the first cold rolling step at the temperature of 740° C. with the duration of 2 hours and subsequently cooled in an accelerated manner in water.
After the last cold-rolling step to the final thickness of 3.0 mm, the strips of working example A have the highest strength values and hardness values (tab. 6).
The age hardening operation at 400° C. for three hours, owing to the spinodal segregation of the microstructure, the rise in the strengths R. (from 498 to 717 MPa) and Rp0.2 (from 439 to 649 MPa) and in the hardness HB (from 166 to 230 MPa) was at its clearest for alloy R. However, the microstructure of the age-hardened states of alloy R is very inhomogeneous with a grain size between 5 and 30 μm. Moreover, the microstructure of the age-hardened states of the reference material R is marked by discontinuous precipitates of the (Cu, Ni)—Sn system (labeled 1 in
By contrast, the microstructure of the age-hardened strips of working example A of the invention is very uniform with a grain size of 2 to 8 μm. Moreover, the structure of working example A lacks the discontinuous precipitates even after age hardening at 450° C. for three hours followed by air cooling. By contrast, the hard particles of the second class are detectable in the microstructure. These phases are labeled 3 in
In addition, further phases have precipitated out in the microstructure of the further-processed alloy A. These include the continuous precipitates of the (Cu, Ni)—Sn system labeled 4 in
The strengths Rm and Rp0.2 of the strips of alloy A after age hardening at 400° C./3 h/air, owing to the spinodal segregation of the microstructure, assume the values of 675 and 600 MPa. Thus, Rm and Rp0.2 are lower than the indices of the correspondingly age-hardened state of alloy R. Should the strength level of R be a particular requirement, it is possible to add a higher proportion of the alloy element nickel to the alloy of the invention.
The next step included the testing of the hot formability of the strand casting of alloys A and R. For this purpose, the cast plaques were hot-rolled at the temperature of 720° C. (tab. 7). For the further processing steps of cold forming and intermediate annealing, the parameters of manufacturing program 2 were adopted.
During the hot rolling of the cast plaques of reference alloy R, deep heat cracks formed even after a few passes, which led to failure of the plaques through fracture.
By contrast, the cast plaques of working example A of the invention were hot-rollable without damage and could be manufactured to the final thickness of 3.0 mm after multiple cold rolling processes and calcination processes. The properties of the age-hardened strips (tab. 8) correspond largely to those of the strips that have been produced without hot forming by manufacturing program 2 (tab. 6).
Likewise comparable is also the microstructure of the strips made from working example A of the alloy of the invention that were manufactured without and with a hot forming step. Thus,
In addition,
The analysis of the hard particles of the second and third class in this further-processed state of working example A again gave pointers to the compound SiB6 as a representative of the Si-containing and B-containing phases, to Ni6Si2B as a representative of the Ni—Si borides, to Ni3B as a representative of the Ni borides, to Ni3P as a representative of the Ni phosphides and to Ni2Si as a representative of the Ni silicides, which are present individually and/or as addition compounds and/or mixed compounds in the microstructure. In addition, these hard particles are ensheathed by precipitates of the (Cu, Ni)—Sn system.
In the construction of installations, devices, engines and machinery, components having relatively high dimensions are required for numerous applications. For example, this is often the case in the field of slide bearings. The production of the corresponding components requires a precursor material of appropriately large dimensions. Owing to the limited producibility of infinitely large castings, therefore, it is necessary to establish the required material properties if at all possible by means of small degrees of cold forming as well.
Tab. 9 lists the process steps that are used in the course of manufacturing program 4. The manufacturing operation was effected with one cycle of cold forming and annealing operations. Owing to the temperature sensitivity ascertained in the conventional strand casting of reference material R and of comparatively high strength and hardness of the cast state of working example A, only the cast plaques of alloy A were calcined prior to the first cold rolling operation at 740° C.
The first cold rolling operation on the cast plaque of alloy R and on the annealed cast plaque of alloy A was implemented with a degree of forming of 16%. An annealing operation at 690° C. was followed by a cold rolling operation with of 12%. Finally, age hardening of the strips took place at the temperatures of 350, 400 and 450° C.
The low degree of cold forming in the first cold rolling step of =16%, together with the subsequent annealing operation at 690° C., was insufficient to eliminate the dendritic and coarse-grain microstructure of the reference material R. Moreover, this thermomechanical treatment enhanced the coverage of the grain boundaries of the alloy R with Sn-rich segregations.
Across the dendritic structure and across the grain boundaries of R covered by Sn-rich segregations, cracks running from the surface deep into the interior of the strip formed during the second cold rolling step.
The crack-free and homogeneous microstructure of the strips of working example A is characterized by the arrangement of the hard particles of the second and third class. As was already the case after the preceding manufacturing programs, the hard particles of the third class, even after this manufacturing program 4, have a size of less than 1 μm.
The resulting properties of the strips after the last cold rolling operation and after the age hardening operation are shown in tab. 10. Owing to the high density of cracks, it was not possible to take undamaged tensile samples from the strips of material R. Thus, it was possible to undertake only metallographic analysis and the measurement of hardness on these strips.
Working example A has a high degree of age hardenability which is manifested by interaction of the mechanisms of precipitation hardening and spinodal segregation of the microstructure. Thus, there is a rise in the indices R. and Rp0.2 as a result of age hardening at 400° C. from 517 to 639 and from 481 to 568 MPa.
As a result, it can be stated that, by means of variation of the chemical composition, the degrees of forming for the cold forming operation(s) and by means of variation in the age hardening conditions, it is possible to adjust the degree of precipitation hardening and the degree of spinodal segregation of the microstructure of the invention to the required material properties. In this way, it is possible to bring particularly the strength, hardness, ductility and electrical conductivity of the alloy of the invention into line with the field of use envisaged.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 008 754.4 | Jul 2016 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/000756 | 6/27/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 20190300985 A1 | Oct 2019 | US |
