Patent Application
20170151609
The invention relates to a process for producing a component of a metal alloy that is at least partly amorphous.
The invention further relates to a component made of a metal alloy with an amorphous phase and the use of such a component.
Amorphous metals and their alloys have been known for several decades. For example, thin bands and their production are described in published patent application DE 35 24 018 A1, which involves producing a thin metallic glass by melt quenching on a support. Also patent specification EP 2 430 205 B1 describes a composite made of an amorphous alloy, requiring a quenching rate of 102 K/s for producing this composite. The disadvantage of such known methods is that they can only produce thin layers or very compact components having a cross section of a few millimeters.
Thus, it is a problem to produce large, complex-shaped components that have an amorphous structure. The necessary cooling rates are not technically feasible for complex components or semi-finished products with large volumes. WO 2008/039134 A1 discloses a process in which a larger component is produced from an amorphous metal powder. This is done by building the component in layers using a type of 3D printing in which parts of the layers are melted with an electron beam.
The disadvantage of this process is that it requires a lot of effort and expense to implement. In addition, such a process cannot produce components with sufficiently homogeneous physical properties. The local melting of the powder causes the alloy's crystallization temperature to be exceeded punctually, and if the melt's cooling rate is too low the alloy crystallizes. To be more precise, the input of heat produced by local melting and recooling of the powder close to the surface can cause the alloy's crystallization temperature to be exceeded punctually in deeper layers that are already an amorphous solid, causing the alloy to crystallize. This produces an unwanted amount of the crystalline phase in the component and irregular distribution of it.
Thus, the goal of the invention is to overcome the disadvantages of the prior art. In particular, the goal of the invention is to develop a process that is simple and economical to implement for producing a partly amorphous metal alloy component that can have a volume of 0.1 cm3 or more, preferably 1 cm3 or more, and that can be produced in different shapes and even complex shapes. The physical properties of the component produced and the distribution of the amorphous phase in it should also be as homogeneous as possible. It is also the goal of this invention to provide such a component. The process should be simple to implement and its results should have good reproducibility. The proportion of the amorphous metallic phase in the component produced should be as high as possible. It is also desirable for the component produced to be as compact as possible and to have only a few pores. Another goal can considered to be that the process can be implemented with as many different alloys as possible that have an amorphous phase. It is also advantageous if the process can be implemented with apparatus and tools that are as simple as possible and usually available in laboratories.
The goals of the invention are achieved by a process for producing a component of an at least partly amorphous metal alloy comprising the following steps:
A) Providing a powder of an at least partly amorphous metal alloy, the powder consisting of spherical particles having a diameter of less than 125 μm;
B) Pressing the powder into the desired shape of the component to be produced;
C) Compressing and sintering the powder by a heat treatment, during or after the pressing, at a temperature between the transformation temperature and the crystallization temperature of the amorphous phase of the metal alloy, the duration of the heat treatment being selected so that after the heat treatment the component is sintered and has an amorphous proportion of at least 85 percent.
It is preferable for the duration of the heat treatment to be selected to be at least long enough that after the heat treatment the powder is sintered, and short enough that after heat treatment the component still has an amorphous proportion of at least 85 percent.
It is preferable for the powder to consist of particles 100% of which have a diameter less than 125 μm. Such particle sizes or particle distributions are frequently also designated as D100=125 μm.
In physics and chemistry, the term “amorphous material” designates a substance in which the atoms do not form ordered structures, but rather an irregular pattern, and only have short-range order, but not long-range order. In contrast to amorphous materials, regularly structured materials are designated as crystalline.
In the context of this invention, spherical particles need not be geometrically perfect spheres, but rather can also deviate from the spherical shape. Preferred spherical powder particles have a rounded, at least approximately spherical shape, and the ratio of their longest cross section to their shortest cross section is no more than 2 to 1. Thus, in the context of this invention, the term “spherical geometry” does not mean a strictly geometric or mathematical sphere. These cross sections refer to extreme dimensions running within the powder particles. Especially preferred spherical powder particles can have a ratio of the longest cross section to the shortest cross section of no more than 1.5 to 1; very especially preferred ones can be spherical. In the context of this invention, the diameter is taken to be the largest cross section of the powder particles.
The spherical shape of the powder particles has the following advantages:
The spherical particles form a free-flowing powder, which is helpful, especially when processing by layers using a powder tank and squeegee;
It is possible to achieve a high bulk density of the powder;
The powder particles have similarly curved surfaces that soften when heat treated under the same conditions (temperature and time, or with the same input of thermal energy)—or under conditions that are at least a close approximation to those conditions. This causes them to connect especially well with adjacent powder particles, or sinter, and to do so within a short time span or at a previously known point in time or at a previously known time interval. Another advantage of high bulk density is that the component shrinks less when it is sintered. This allows near net shape manufacturing.
In a preferred embodiment of this invention, the component can be considered sintered especially when it has a density of at least 97% of the theoretical density of the completely amorphous metal alloy.
In the context of this invention, sintering is understood to mean a process in which the powder particles soften on the surface and connect with one another, and remain connected after cooling. This produces a cohesive body or component from the powder.
The transformation temperature of an amorphous phase is frequently also referred to as the glass-transition temperature or the transformation point or the glass-transition point, and it should be made clear here that these terms are equivalent to the transformation temperature.
It is preferable for the powder to be shaped by putting it into a mold or tool, and then pressing the powder in the mold or tool, or with the tool.
The inventive process involves heating to the transformation temperature and cooling as quickly as possible, since even at these temperatures below the transformation temperature crystallization on the seed crystals that are inevitably present occurs before the softening of the powder particles that could lead to sintering of the powder. The inventive process should cause the powder particles to undergo plastic deformation, which compacts the powder and thus accelerates the sintering of the powder. Temperature overshoot above the desired or final temperature should be kept as small as possible.
The powder particle size or distribution can be achieved by the manufacturing process and by screening a starting powder. Thus, the powder prepared according to the inventive process is produced by screening a starting powder, before it is provided or used for the inventive process. That is, unless the starting powder already has the desired properties after the manufacturing process. In addition, screening can also reduce or minimize the number of powder particles whose shape strongly deviates from spherical as a result of the sintering of several powder particles (so-called satellite formation) contained in the starting powder.
The invention also proposes, as a preferred embodiment of the process, that the heat treatment be done under vacuum, it being preferred for the powder to be compressed by heat treatment under a vacuum of at least 10−3 mbar.
This achieves the powder surface reacting less strongly with surrounding gases. The reason why this is important is that metal oxides and other reaction products act as nucleating agents for crystalline phases, so they have a negative effect on the purity of the amorphous phase in the component that is produced.
For the same reason, the inventive process can additionally or alternatively provide that the heat treatment be done under a shielding gas, in particular a noble gas, such as, for example, argon, preferably having a purity of at least 99.99%, especially preferably having a purity of at least 99.999%. Such embodiments can preferably provide that the atmosphere under which the pressing and heat treatment, or only the heat treatment, takes place be largely freed of residual gases by repeated evacuation and purging with a noble gas, especially argon.
Alternatively, the inventive process can also provide that the heat treatment be done under a reducing gas, in particular a forming gas, to keep the amount of interfering metal oxides as small as possible.
Another measure that can reduce the metal oxides in the component is the use of an oxygen getter during the heat treatment and/or manufacturing of the powder.
The inventive process can also provide that the powder be compressed by hot isostatic pressing or hot pressing.
The combination of pressure and heat treatment makes the component more compact. In addition, it improves the connection of the powder particles among one another by plastic deformation and accelerates the sintering behavior, allowing shorter heat treatment and reducing the proportion of the crystalline phase in the component.
A further development of the invention can also provide that the duration of heat treatment be selected so that the component's amorphous proportion is at least 90 percent, preferably more than 95 percent, especially preferably more than 98 percent.
The higher the proportion of the amorphous phase in the component, the closer it approaches the desired physical properties of consisting completely of the amorphous phase.
Preferred embodiments of this invention can also provide that the powder used be made of an amorphous metal alloy or an at least partly amorphous metal alloy comprising at least 50 weight percent zirconium.
Amorphous metal alloys containing zirconium are especially well suited for implementing the inventive process, since many of these alloys have a large difference between their transformation temperatures and crystallization temperatures, which makes the process easier to implement.
Very especially preferred embodiments of this invention can also provide that the powder used be made of an amorphous metal alloy or an at least partly amorphous metal alloy comprising
In these alloys, the remaining proportion up to 100 weight percent is zirconium. The alloy can contain the usual impurities. These amorphous metal alloys containing zirconium are very especially well-suited to implement the inventive process.
Furthermore, the inventive process can provide that the spherical amorphous metal alloy powder be produced by atomization, preferably in an inert gas, in particular argon, especially preferably in an inert gas whose purity is 99.99%, 99.999% or higher. In the context of this invention, the term “amorphous metal alloy” also refers to a metal alloy whose proportion of the amorphous phase is at least 85 volume percent.
Of course the powder is produced before it is made provided. Atomization can produce powder particles with a spherical shape in a simple and economical way. The use of a noble gas, especially argon or highly purified argon during the atomization has the effect that the powder contains as few interfering impurities such as metal oxides as possible.
A further development of this invention can also provide that the powder have less than 1 weight percent of particles with a diameter smaller than 5 μm, or that the powder be screened or treated by air classification, so that it has less than 1 weight percent of particles with a diameter smaller than 5 μm.
In the inventive process it is preferable for powder particles with a diameter of less than 5 μm to be removed by air classification, or more precisely for the proportion of powder particles with a diameter of less than 5 μm to be reduced by air classification.
The small proportion of powder particles with a diameter smaller than 5 μm limits the surface of the powder (the total of the surfaces of all powder particles) that is sensitive to oxidation or another interfering chemical reaction of the powder particles with the surrounding gas. Furthermore, limiting the particle size of the powder ensures that the powder particles soften under similar conditions (with respect to temperature and time or energy input), since the curvatures of the surfaces and volumes of the powder particles are then similar, which allows compact filling of the powder by pressing. A small proportion of fine powder particles (smaller than 5 μm) does not have a detrimental effect, since such powder particles can fit into the interstitial spaces between larger particles, and thus increase the density of the unsintered powder. However, too large a quantity of fine powder particles can have a detrimental effect on the powder's fluidity, so that it is preferable to remove them. The fine (small) powder particles namely tend to agglomerate with larger particles.
A preferred further development of the inventive process proposes that the heat treatment of the powder take place at a temperature (T) between the transformation temperature and a maximum temperature that exceeds the transformation temperature (TT) by 30% of the temperature difference between the transformation temperature (TT) and the crystallization temperature (TC) of the amorphous phase of the metal alloy, preferably exceeding it by 20% or 10% of this temperature difference.
If the heat treatment takes place at or just above the transformation temperature, the formation and growth of the crystalline phase will be relatively small, and thus the purity of the amorphous phase (the proportion of the amorphous phase) in the component in the component will be high. Expressed as a formula, the temperature T at which the heat treatment of the powder takes place should meet the following conditions with respect to the transformation temperature TT and the crystallization temperature TC of the amorphous phase of the metal alloy:
T
T
<T<T
T+(30/100)*(TC−TT) or
preferably TT<T<TT+(20/100)*(TC−TT) or
especially preferably TT<T<TT+(10/100)*(TC−TT).
The temperature ranges indicated in the preceding mathematical formulas within which the heat treatment should take place will achieve sintering with little formation of crystalline phases in the component.
An especially advantageous embodiment of the inventive process provides that the duration of the heat treatment be selected as a function of the geometric shape, especially the thickness, of the component to be produced, preferably as a function of the largest relevant diameter of the component to be produced.
The geometric shape, or the thickness, of the component to be produced is taken into consideration to ensure that the heat conduction in the shaped powder or the component that is being shaped is sufficient that the powder inside the component or the inside of the component is also heated to or above the transformation temperature, so that the powder inside the component is also sintered.
The largest relevant diameter of the component can be geometrically determined as the [diameter of the] largest inscribed sphere. In determining the largest relevant diameter, it is possible to disregard channels or gaps in the body that do not contribute to the input of heat through a surrounding gas and/or another heat source, or do so only to a small extent (for example, totaling less than 5%).
Preferably, it can be provided that the duration of heat treatment be in the time range from 3 to 900 seconds per millimeter of the component's thickness or wall thickness or greatest relevant diameter of the component to be produced, preferably in the time range from 5 to 600 seconds.
Taking into consideration the component's shape, thickness, and wall thickness, and/or its largest relevant diameter allows the duration of the heat treatment to be selected so that the powder is sufficiently sintered, but simultaneously keeps the formation of the crystalline phase in the component as small as possible, ideally minimal. For certain components and for some applications, it can already be sufficient if only the edges of the component are completely sintered, and if powder that has not yet been sintered is present inside the component. However, it is preferable for the component to be completely sintered (even inside).
The goals of this invention are also solved by a component made of a pressed, sintered, spherical, amorphous metal alloy powder, the component having an amorphous proportion of at least 85 percent.
This component can be produced using one of the inventive processes. Such inventive processes have been previously described.
The goals of the invention are also achieved by the use of a component such as a gear, frictional wheel, wear-resistant component, housing, watch case, part of a transmission, or semi-finished product.
The invention is based on the surprising finding that the use of spherical powder particles of an appropriate size and heat treatment at the appropriate temperature for an appropriate short period of time is able to produce, from a powder of an amorphous metal alloy, also larger and/or complex components that have a high proportion (at least 85 volume percent) of the amorphous phase, and thus possess the advantageous physical properties of the amorphous metal alloy. Thus, this invention describes for the first time a process that can produce a component made from an amorphous metal alloy or from a metal alloy having an amorphous phase of at least 85% by sintering a powder, while retaining a high proportion of the amorphous phase. It is preferable for the duration of heat treatment to be adapted to the dimensions of the component to be produced, to obtain as high a proportion of the amorphous phase as possible when the powder is sintered, or to keep the proportion of the crystalline phase in the metal alloy as small as possible. For the same reason, it is advantageous to carry out the heat treatment under a shielding gas or under vacuum, to keep the proportion of metal oxides or other air reaction products in the powder and thus in the component as small as possible. Such metal oxides and other reaction products act especially as crystal nuclei and reduce the proportion of the amorphous phase in the component.
In the context of this invention, it was found that inventive processes have especially good results if the amorphous metal powders used to produce the component are produced through atomization and the powders are X-ray amorphous, their particles preferably being smaller than 125 μm. In atomization, the resulting molten alloy droplets are very quickly cooled by the flow of process gas (argon), which promotes the presence of an amorphous powder fraction. A further development of the invention proposes that the fines (particles smaller than 5 μm) and coarse grain larger than 125 μm be largely separated from this powder, for example removed by screening and/or by air classification of the powder. Such powder fractions are then an optimal starting material (the powder provided) for producing complex amorphous components by pressing and heat treatment; here the pressure and temperature steps have very good results with respect to the amorphous behavior of the component, whether performed one after the other or in combination. Using powders produced in this way gives a component with an especially high proportion of the amorphous metallic phase. Simultaneously, the component produced in this way and from such a powder has a high proportion of sintered powder particles and low porosity, preferably a porosity of less than 5%. The upper particle size limit prevents such particles having a larger cross section than the layers that are produced; such particles could then be removed with a squeegee, leaving the layer incomplete.
It is important that the amorphous powder is not heated up to the crystallization temperature or beyond by the method, because otherwise crystallization occurs and the amorphous nature of the alloy is lost. On the other hand, it is necessary to heat the material at least to the transformation temperature, i.e. the temperature at which the amorphous phase of the metal alloy is transiting during the cooling from the plastic range in the rigid state. In this temperature range, the powder particles can connect, but without crystallizing. The transformation temperature can also be referred to as glass transition temperature and is also often referred to as.
However, since it is technically hardly possible and uneconomical to be absolutely free of impurities, and also free especially of oxygen, microcrystalline inclusions cannot be avoided. Small proportions of oxygen lying in the two-digit ppm range cause corresponding oxidation of the components of the alloy that have an affinity for oxygen. These are then present as small crystal nuclei, and thus can lead to small oxide inclusions with grains that are recognizable in a micrograph at 1,000× magnification or as peaks in X-ray diffractometry. Similar effects can also be caused by further or other impurities of the starting materials and by other elements, such as nitrogen, for example.
The duration of the heat treatment depends mainly on the volume of the component, and should not, as a rule, be too long, since every crystal nucleus, however small, acts as a seed crystal, and thus crystallites can grow, that is the undesired crystalline phase in the component spreads. Experiments with zircon-based alloys were able to show that heat treatment in the inventive temperature range with a maximum duration of 400 seconds per 1 mm of component cross section provides especially good results. The heating phase should also be as rapid as possible, since the undesired crystal growth sometimes already occurs 50 Kelvin below the transformation temperature.
Other sample embodiments of the invention are explained below using a schematically illustrated flowchart, which, however, does not limit the invention.
In the flowchart, T designates the working temperature, TT the transformation temperature of the amorphous metal alloy, and TC the crystallization temperature of the amorphous phase of the metal alloy.
An amorphous metal powder is produced from a metal alloy whose composition is suitable to form an amorphous phase, or which already consists of the amorphous phase. Then, the powder undergoes fractionation, in which the powder particles that are too small or too large are removed, in particular by screening and air classification. The powder can then be pressed into a desired shape, either with or without the input of heat. If the powder is pressed into shape without the input of heat, it then undergoes a heat treatment that, in the context of this invention, is called sintering or that causes sintering. The maximum duration of the heat treatment during or after pressing is 900 seconds per 1 mm of component cross section, and the temperature of this heat treatment is above the transformation temperature TT and below the crystallization temperature TC of the amorphous phase of the metal alloy used.
Specific sample embodiments follow, in which inventive processes are described and for which the results obtained are evaluated.
An alloy made of 70.5 weight percent zirconium (Haines & Maassen Metallhandelsgesellschaft mbH Bonn, Zr-201-Zirkon Crystalbar), 0.2 weight percent hafnium (Alpha Aesar GmbH & Co KG Karlsruhe, Hafnium Crystal Bar milled chips 99.7% article number 10204), 23.9 weight percent copper (Alpha Aesar GmbH & Co KG Karlsruhe, Copper plate, Oxygen free, High Conductivity (OFCH) article number 45210), 3.6 weight percent aluminum (Alpha Aesar GmbH & Co KG Karlsruhe, Aluminium Ingot 99.999% article number 10571), and 1.8 weight percent niobium (Alpha Aesar GmbH & Co KG Karlsruhe, niobium foil 99.97% article number 00238) was melted in an induction melting system (VSG, inductively heated vacuum, melting, and casting system, Nürmont, Freiberg) under 800 mbar of argon (Argon 6.0, Linde AG, Pullach) and poured into a water-cooled copper mold. A fine powder was produced from the alloy produced in this way by spraying the melt with argon in a Nanoval atomization apparatus (Nanoval GmbH & Co. KG, Berlin) using a process such as is disclosed in WO 99/30858 A1, for example.
Separation by means of air classification with a Condux fine classifier CFS (Netzsch-Feinmahltechnik GmbH Selb Deutschland) removes the fines, so that less than 0.1% of the particles are smaller than 5 μm in size, i.e., at least 99.9% of the particles have a diameter or dimensions of 5 μm or greater, and screening through a test sieve with a mesh size of 125 μm (Retsch GmbH, Haan-Deutschland, article number 60.131.000125) removes all powder particles that are larger than 125 μm. The powder produced in this way is investigated by means of X-ray diffractometry, and the proportion that is amorphous is greater than 95%.
5.0 grams of the powder fraction obtained in this way are compressed in a laboratory press 54MP250D (mssiencetific Chromatographie-Handel GmbH, Berlin) with a compression mold (32 mm, P0764, mssiencetific Chromatographie-Handel GmbH, Berlin) and a 15 ton force of pressure. The pressed parts are then compressed in vacuum sintering (Gero high-temperature vacuum tempering furnace LHTW 100-200/22, Neuhausen) at 410° C. and a pressure of about 10−5 mbar for 120 seconds. The pressed parts are then finally compressed by hot isostatic pressing under a pressure of 200 megapascal (200 MPa) in highly purified argon (Argon 6.0, Linde AG, Pullach) at a temperature of 400° C. for 90 seconds.
Fifteen components produced in this way are investigated by means of metallographic micrographs to determine the amorphous proportion of the surface in the texture. This investigation showed that an average of 92% of the surfaces are amorphous.
An alloy made of 70.5 weight percent zirconium (Haines & Maassen Metallhandelsgesellschaft mbH Bonn, Zr-201-Zirkon Crystalbar), 0.2 weight percent hafnium (Alpha Aesar GmbH & Co KG Karlsruhe, Hafnium Crystal Bar milled chips 99.7% article number 10204), 23.9 weight percent copper (Alpha Aesar GmbH & Co KG Karlsruhe, Copper plate, Oxygen free, High Conductivity (OFCH) article number 45210), 3.6 weight percent aluminum (Alpha Aesar GmbH & Co KG Karlsruhe, Aluminium Ingot 99.999% article number 10571) and 1.8 weight percent niobium (Alpha Aesar GmbH & Co KG Karlsruhe, niobium foil 99.97% article number 00238) was melted in an induction melting system (VSG, inductively heated vacuum, melting, and casting system, Nürmont, Freiberg) under 800 mbar of argon (Argon 6.0, Linde AG, Pullach) and poured into a water-cooled copper mold. A fine powder was produced from the alloy produced in this way by spraying the melt with argon in a Nanoval atomization apparatus (Nanoval GmbH & Co. KG, Berlin) using a process such as is disclosed in WO 99/30858 A1, for example. Separation by means of air classification with a Condux fine classifier CFS (Netzsch-Feinmahltechnik GmbH Selb Deutschland) removed the fines, so that less than 0.1% of the particles are smaller than 5 μm in size, and screening through a test sieve with a mesh size of 125 μm (Retsch GmbH, Haan-Deutschland, article number 60.131.000125) removed all powder particles that are larger than 125 μm. The powder produced in this way was investigated by means of X-ray diffractometry, and the proportion that is amorphous is greater than 95%.
In every case, 15.0 grams of this powder fraction obtained in this way were sintered by hot pressing with a pressure of 200 megapascal (200 MPa) at a temperature of 400° C. for 3 minutes.
Fifteen components produced in this way were investigated by means of metallographic micrographs to determine the amorphous proportion of the surface in the texture. This investigation showed that an average of 85% of the surfaces are amorphous.
An alloy made of 70.6 weight percent zirconium (Haines & Maassen Metallhandelsgesellschaft mbH Bonn, Zr-201-Zirkon Crystalbar), 23.9 weight percent copper (Alpha Aesar GmbH & Co KG Karlsruhe, Copper plate, Oxygen free, High Conductivity (OFCH) article number 45210), 3.7 weight percent aluminum (Alpha Aesar GmbH & Co KG Karlsruhe, Aluminium Ingot 99.999% article number 10571) and 1.8 weight percent niobium (Alpha Aesar GmbH & Co KG Karlsruhe, niobium foil 99.97% article number 00238) was melted in an induction melting system (VSG, inductively heated vacuum, melting, and casting system, Nürmont, Freiberg) under 800 mbar of argon (Argon 6.0, Linde AG, Pullach) and poured into a water-cooled copper mold. A fine powder was produced from the alloy produced in this way by spraying the melt with argon in a Nanoval atomization apparatus (Nanoval GmbH & Co. KG, Berlin) using a process such as is disclosed in WO 99/30858 A1, for example.
Separation by means of air classification with a Condux fine classifier CFS (Netzsch-Feinmahltechnik GmbH Selb Deutschland) removed the fines, so that less than 0.1% of the particles are smaller than 5 μm in size, and screening through a test sieve with a mesh size of 125 μm (Retsch GmbH, Haan-Deutschland, article number 60.131.000125) removed all powder particles that are larger than 125 μm. The powder produced in this way was investigated by means of X-ray diffractometry, and its amorphous proportion is greater than 95%.
In every case, 15.0 grams of this powder fraction obtained in this way were sintered by pressing with a pressure of 200 megapascal (200 MPa) at a temperature of 400° C. for 3 minutes.
Fifteen components produced in this way are investigated by means of metallographic micrographs to determine the amorphous proportion of the surface in the texture. This investigation showed that an average of 87% of the surfaces are amorphous.
An alloy made of 70.6 weight percent zirconium (Haines & Maassen Metallhandelsgesellschaft mbH Bonn, Zr-201-Zirkon Crystalbar), 23.9 weight percent copper (Alpha Aesar GmbH & Co KG Karlsruhe, Copper plate, Oxygen free, High Conductivity (OFCH) article number 45210), 3.7 weight percent aluminum (Alpha Aesar GmbH & Co KG Karlsruhe, Aluminium Ingot 99.999% article number 10571) and 1.8 weight percent niobium (Alpha Aesar GmbH & Co KG Karlsruhe, niobium foil 99.97% article number 00238) was melted in an induction melting system (VSG, inductively heated vacuum, melting, and casting system, Nürmont, Freiberg) under 800 mbar of argon (Argon 6.0, Linde AG, Pullach) and poured into a water-cooled copper mold. A fine powder was produced from the alloy produced in this way by spraying the melt with argon in a Nanoval atomization apparatus (Nanoval GmbH & Co. KG, Berlin) using a process such as is disclosed in WO 99/30858 A1, for example.
Separation by means of air classification with a Condux fine classifier CFS (Netzsch-Feinmahltechnik GmbH Selb Deutschland) removed the fines, so that less than 0.1% of the particles are smaller than 5 μm in size, and screening through a test sieve with a mesh size of 125 μm (Retsch GmbH, Haan-Deutschland, article number 60.131.000125) removed all powder particles that are larger than 125 μm. The powder produced in this way was investigated by means of X-ray diffractometry, and the proportion that is amorphous is greater than 95%.
50 grams of the powder fraction obtained in this way were compressed in a laboratory press 54MP250D (mssiencetific Chromatographie-Handel GmbH, Berlin) with a compression mold (32 mm, P0764, mssiencetific Chromatographie-Handel GmbH, Berlin) and a maximum force of pressure of 25 tons, and were sintered under highly purified argon (Argon 6.0, Linde AG, Pullach) at a temperature of 410° C. for 5 minutes.
The component produced in this way was investigated by means of several metallographic micrographs [to determine] the amorphous proportion of the surface in the texture. This investigation showed that an average of 90% of the surfaces are amorphous.
The following table presents the measured results for examples 1 through 4 in connection with a reference measurement:
Testing and Checking Methods
1) Method for Determining Particle Size of Metal Alloy Powders:
The particle size of inorganic powders was determined by laser light scattering using a Sympatec Helos BR/R3 (Sympatec GmbH), equipped with a RODOS/M dry disperser with a VIBRI vibratory feeder (Sympatec GmbH). Sample quantities of at least 10 g were fed in dry, dispersed at a primary pressure of 1 bar, and the measurement was started. The starting criterion was an optical concentration of 1.9% to 2.1%. The measurement time was 10 seconds. The results were evaluated by MIE theory, and d50 was used as the measure of particle size.
2) Test Method for Determining Density:
For determining density, a geometrically exact rectangular parallelepiped can be produced by grinding the surfaces, so that they can be exactly measured with a digital micrometer (PR1367, Mitutoyo Messgeräte Leonberg GmbH, Leonberg). The volume is now determined mathematically. Then, the exact weight is determined on an analytical balance (XPE analytical balances of Mettler-Toledo GmbH). Dividing the measured weight by the calculated volume gives the density.
The theoretical density of an amorphous alloy corresponds to the density at the melting point.
3) Test Method for Determining the Proportion of Amorphous Surface in the Component:
To do this, in every case fifteen metallographic sections are prepared as described in DIN EN ISO 1463, each of which is polished with SiC paper 1200 (Struers GmbH, Willich), and then in the following polishing steps with 6 μm, 3 μm, and 1 μm diamond products (Struers GmbH, Willich), and finally with OP-S chemical-mechanical oxide polishing suspensions (Struers GmbH, Willich). The ground surfaces produced in this way are examined under an optical microscope (Leica DM 4000 M, Leica DM 6000 M) with a magnification of 1,000 to determine the crystalline proportion of the surface in the micrograph. This involves using the software Leica Phase Expert to evaluate the proportion of the surface that is crystalline as a percentage of the total area of the section, the dark areas being evaluated as crystalline and the light areas being evaluated as amorphous. To do this, the amorphous matrix is defined as a reference phase and expressed as a percentage of the total measured area. In every case, 10 different sample surfaces were measured and averaged.
4) Test Method for Determining Transformation Temperatures:
This was done using a Netzsch 404 F1 Pegasus® differential scanning calorimeter (Erich NETZSCH GmbH & Co. Holding KG) equipped with a high temperature tube furnace with a resistance meander heater, an integrated control thermocouple type S, DSC404F1A72 sample carrier system, Al2O3 crucible with cover, an OTS™ system to remove residual oxygen during measurement, including three getter rings, and an evacuation system for automatic operation with a two-stage rotary pump. All measurements were carried out under a shielding gas (Argon 6.0, Linde AG) with a flow rate of 50 mL/min. The results were evaluated using the software Proteus® 6.1. The transformation temperature was determined using the tangent method (glass transition) in the range between 380° C. and 420° C. (onset, mid, inflection, end). The crystallization temperature was determined using complex peak evaluation in the temperature range 450-500° C. (area, peak, onset, end, width, height), and the Tm was determined using complex peak evaluation in the temperature range 875-930° C. (area, peak, onset, end, width, height). To carry out the measurement, a 25 mg±0.5 mg sample was weighed in the crucible, and the measurement was carried out at the following heating rates and temperature ranges.
20-375° C.: heating rate 20 K/min
375-500° C.: heating rate 1 K/min
500-850° C.: heating rate 20 K/min
above 850° C.: heating rate 10 K/min
The amorphous proportion of the component was determined by determining the crystallization enthalpy by the complex peak method using a 100% amorphous sample (obtained by melt spinning) with a crystallization enthalpy of −47.0 J/g as a reference.
The quotient of the crystallization enthalpy of the component to that of the reference gives the proportion of the amorphous phase.
5) Determining Elemental Composition by Means of Emission Spectrometry Analysis (Inductively Coupled Plasma):
This was done using a Varian Vista-MPX emission spectrometer (Varian Inc.). For each metal, two calibration samples were prepared from standard solutions with known metal content (e.g., 1,000 mg/L) in an aqua regia matrix (concentrated hydrochloric acid and concentrated nitric acid, in the ratio 3:1), and the measurements were carried out.
The parameters of the ICP instrument were:
Power: 1.25 kW
Plasma gas: 15.0 L/min (argon)
Carrier gas: 1.50 L/min (argon)
Atomization gas pressure: 220 kPa (argon)
Repetition: 20 s
Stabilization time: 45 s
Observation height: 10 mm
Draw in sample: 45 s
Rinsing time: 10 s
Pump speed: 20 rpm
Repetitions: 3
To measure a sample: 0.10 g±0.02 g of the sample is put in a container, to which 3 mL of nitric acid and 9 mL of hydrochloric acid are added, as indicated above, and allowed to dissolve for 60 minutes in a microwave oven (company: Anton Paar, device: Multiwave 3000) at 800-1,200 W. The dissolved sample is transferred into a 100 mL flask with 50 volume percent hydrochloric acid and measured.
The inventive features disclosed in the preceding description, as well as in the claims, the flowchart, and the sample embodiments can be essential for implementing the invention in its various embodiments; this is true both for each individual feature and also for any combination of features.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14168461.3 | May 2014 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/060410 | 5/12/2015 | WO | 00 |
