Patent Application
20160303649
The present disclosure relates generally to light weight, high stiffness metal and thermally stable matrix composites. The composites are in the form of a metal matrix reinforced with micron-scale ceramic particles. Also disclosed are methods for making and using the composites, and articles made from the composites.
Fe-36Ni alloys, known commercially as Invar®, have been used in applications where materials with low coefficients of thermal expansion (CTE) are essential. However, conventional wrought Fe-36Ni alloys (36 wt. % nickel, 64 wt. % iron) have a high density, low specific stiffness, and low yield strength, which is a major drawback for applications in which weight is critical, such as satellites, electronics, and other aerospace applications.
It would be desirable to develop materials that have a low coefficient of thermal expansion, low density, and high yield strength. Such materials would be particularly useful in light weight, high stiffness structures, such as in various aerospace, defense, or space applications.
The present disclosure relates to a lightweight, high-stiffness metal matrix reinforced with ceramic particles dispersed therein and a method for making the same. The metal matrix is made from a metal alloy that has a low coefficient of thermal expansion (CTE), which is further reduced by the addition of the ceramic particles, which are submicron-scale or micron-scale ceramic particles.
Disclosed in various embodiments are metal matrix composites that comprise: a matrix formed from a metal alloy that has a low coefficient of thermal expansion (CTE); and ceramic particles dispersed in the matrix.
The metal alloy may be selected from the group consisting of iron-nickel alloys and iron-nickel-cobalt alloys. In embodiments, the metal alloy is an iron-nickel alloy containing from about 75 weight percent (wt %) to about 55 weight percent iron and from about 25 wt % to about 45 wt % nickel. In particular embodiments, the metal alloy is an iron-nickel alloy containing about 64 weight percent iron and about 36 weight percent nickel. In other embodiments, the metal alloy is an iron-nickel-cobalt alloy containing from about 75 wt % to about 45 wt % iron; from about 25 wt % to about 45 wt % nickel; and from about 2 wt % to about 18 wt % cobalt. In particular embodiments, the metal alloy is an iron-nickel-cobalt alloy containing about 63 weight percent iron and about 32 weight percent nickel and about 5 weight percent cobalt.
The metal alloy may have a coefficient of thermal expansion of about 1.4 ppm/° K over a range of −60° C. to +60° C.
The ceramic particles can be made from a material selected from the group consisting of nitrides, carbides, oxides, silicides, borides, and mixtures thereof. In more specific embodiments, the ceramic particles are nitrides selected from the group consisting of Si3N4, AlN, CrN, HfN, NbN, TaN, TiN, VN, and ZrN. In other embodiments, the ceramic particles are carbides selected from the group consisting of Cr3C2, HfC, Mo2C, NbC, SiC, TaC, TiC, VC, WC, and ZrC. In yet other embodiments, the ceramic particles are oxides selected from the group consisting of Al2O3, HfO2, SiO2, Ta2O5, TiO2, Y2O3, ZrO2, and ZrSiO4.
The ceramic particles can comprise from about 10 vol % to about 45 vol % of the metal matrix composite. In specific embodiments, the ceramic particles comprise about 20 vol %, or about 25 vol %, or about 30 vol %, of the metal matrix composite.
The ceramic particles may have an average particle size of about 100 nanometers to about 30 microns, or they may be micron-scale particles with an average particle size of 1 micron to about 30 microns. The micron-scale ceramic particles may have an average particle size of about 3 microns to about 15 microns.
The metal matrix composite may have a density of less than 7.5 g/cc. The metal matrix composite may alternatively have a coefficient of thermal expansion of from about 0.5 ppm/° K to about 1.0 ppm/° K over a range of −60° C. to +60° C. In specific embodiments, the metal matrix composite has a density of less than 7.5 g/cc and has a coefficient of thermal expansion of less than 1.0 ppm/° K over a range of −60° C. to +60° C.
The metal matrix composite may have a specific modulus of 20 GPa/g/cc to 32 GPa/g/cc.
The metal matrix composite may have a 0.2% offset yield strength of 250 MPa to 600 MPa according to tensile test EN6892/1: 2009 or ASTM E8M.
The metal matrix composite may have a ductility of at least 2% when measured according to tensile test EN6892/1: 2009 or ASTM E8M.
Also disclosed are methods for producing a metal matrix composite, comprising the steps of: mixing (i) a metal alloy powder that has a low coefficient of thermal expansion (CTE) with (ii) ceramic particles to form a mixture; mechanically alloying the mixture; hot isostatic pressing the mixture to obtain a billet; and forging the billet to obtain the metal matrix composite.
The metal and ceramic powders should be mixed with a high energy technique to distribute the ceramic reinforcement particles into the metal matrix. Suitable techniques for this mixing include ball milling, mechanical attritors, teamer mills, rotary mills and other methods to provide high energy mixing to the powder constituents. Mechanical alloying should be completed in an atmosphere to avoid excessive oxidation of powders preferable in an inert atmosphere using nitrogen or argon gas. The processing parameters should be selected to achieve an even distribution of the ceramic particles in the metallic matrix.
The hot isostatic pressing may be performed at a temperature of 1000° C. to 1200° C. and a pressure of 30 to 150 MPa for a period of sufficient to allow the metal section to reach the required temperature, typically between 1 and 8 hours. The hot isostatic pressing may be performed on commercially available steel or nickel HIP systems.
Forging or extrusion processes may be performed at a temperature of 1000 to 1200° C., a range of forge or extrusion processes can be applied using hydraulic, mechanical or gravity presses.
These and other non-limiting characteristics of the disclosure are more particularly disclosed below.
The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.
A more complete understanding of the components, processes and apparatuses disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely schematic representations based on convenience and the ease of demonstrating the present disclosure, and are, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments.
Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.
The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of and “consisting essentially of.” The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients/steps and permit the presence of other ingredients/steps. However, such description should be construed as also describing compositions or processes as “consisting of and “consisting essentially of the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any impurities that might result therefrom, and excludes other ingredients/steps.
Numerical values in the specification and claims of this application should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.
All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of from 2 grams to 10 grams” is inclusive of the endpoints, 2 grams and 10 grams, and all the intermediate values).
The term “about” can be used to include any numerical value that can vary without changing the basic function of that value. When used with a range, “about” also discloses the range defined by the absolute values of the two endpoints, e.g. “about 2 to about 4” also discloses the range from 2 to 4.” The term “about” may refer to plus or minus 10% of the indicated number.
The present disclosure relates to materials having an average particle size. The average particle size is defined as the particle diameter at which a cumulative percentage of 50% (by volume) of the total number of particles are attained. In other words, 50% of the particles have a diameter above the average particle size, and 50% of the particles have a diameter below the average particle size. The size distribution of the particles will be Gaussian, with upper and lower quartiles at 25% and 75% of the stated average particle size, and all particles being less than 150% of the stated average particle size.
The present disclosure may refer to temperatures for certain process steps. It is noted that these generally refer to the temperature at which the heat source (e.g. furnace, oven) is set, and do not necessarily refer to the temperature which must be attained by the material being exposed to the heat. The term “room temperature” refers to a range of from 20° C. to 25° C.
The term “specific stiffness” refers to the ratio of the elastic modulus to the density of a material. Where minimal structural weight is desired, the specific stiffness is desirably a higher value.
The present disclosure relates to metal matrix composite materials formed from a metal alloy that has a low CTE, and which is strengthened by the presence of submicron-scale or micron-scale ceramic particles homogeneously dispersed therein. The metal matrix composite material has improved specific stiffness and yield strength compared to conventional wrought Fe-36Ni alloy (36 wt % nickel, 64 wt % iron). Previous metal matrix composites of this type did not have sufficient ductility, which is essential to manufacturing components from such composites and important to allow a reliable material for components design and operation.
The metal matrix composite includes a metal matrix that is formed from a metal alloy having a low coefficient of thermal expansion (CTE). The term “low” means the metal alloy has a C.TE of less than 7 ppm/° K over a temperature range of −60° C. to +60° C. In more specific embodiments, the metal alloy has a C.TE of less than 2 ppm/° K over a temperature range of −60° C. to +60° C., or has a C.TE of about 1.4 ppm/° K over a temperature range of −60° C. to +60° C.
While the low CTE alloy can be selected from any suitable low CTE alloy, in particular embodiments, the low CTE alloy is an iron-nickel alloy (i.e. binary alloy) or an iron-nickel-cobalt alloy (i.e. a ternary alloy). In particular embodiments, the metal alloy is an iron-nickel alloy containing from about 75 weight percent (wt %) to about 55 weight percent iron and from about 25 wt % to about 45 wt % nickel. In other embodiments, the metal alloy is an iron-nickel-cobalt alloy containing from about 75 wt % to about 45 wt % iron; from about 25 wt % to about 45 wt % nickel; and from about 2 wt % to about 18 wt % cobalt, or from about 2 wt % to about 8 wt % cobalt. In particular embodiments, the low CTE alloy used is an Invar® 36 alloy, which contains about 64 wt % iron and about 36 wt % nickel. Other alloys contemplated herein may contain up to about 42 wt % nickel (remainder iron and/or cobalt). Conventional Invar® alloys have a density of 8.1 g/cm3 or greater. They also have a C.TE of about 1.4 ppm/° K. Another exemplary low CTE alloy is known by the commercial name Kovar®, which contains about 54 wt % iron, about 29 wt % nickel, and about 15 wt % cobalt and has a C.TE of about 5-6 ppm/° K.
The metal matrix composite also includes submicron-scale or micron-scale ceramic particles. The term “submicron-scale” means the particles have an average particle size below 1 micrometer, and in embodiments the average particle size is about 100 nanometers at minimum. The term “micron-scale” means the particles have an average particle size of 1 micrometer (i.e. micron or pm) to 1000 microns. In particular embodiments, the ceramic particles have an average particle size of 100 nanometers to about 30 microns, including from 1 micron to about 30 microns, including from about 3 microns to about 15 microns.
The ceramic particles are made from nitrides, carbides, oxides, silicides, or borides, or mixtures thereof. Suitable nitrides include, for example, Si3N4, AlN, CrN, HfN, NbN, TaN, TiN, VN, and ZrN. Suitable carbides include, for example, Cr3C2, HfC, Mo2C, NbC, SiC, TaC, TiC, VC, WC, and ZrC. Suitable oxides include, for example, Al2O3, HfO2, SiO2, Ta2O5, TiO2, Y2O3, ZrO2, and ZrSiO4. The ceramic particles themselves also have a low coefficient of thermal expansion. Again, this means the ceramic particles have a C.TE of less than 2 ppm/° K over a temperature range of −60° C. to +60° C.
In this regard, the use of micron-scale ceramic particles appears to improve the distribution of the ceramic particles within the metal matrix, so that they are homogeneously distributed within the metal matrix. This also maintains improved mechanical and physical properties, particularly compared to metal matrices that use nano-scale particles.
The metal matrix composite is formed by mechanical alloying, then hot isostatic pressing, then forging or extruding. Powders of the metals use to make the metal matrix are mixed with the ceramic particles. It is desirable to use preferably high purity metal powders to minimize impurities and ensure optimum CTE properties and minimization of thermal stresses in the resulting matrix over a wide range of temperature changes. The ceramics particles are generally present in an amount of about 10 volume percent (vol %) to about 45 vol % of the metal matrix composite, and in specific embodiments are about 20 vol % or about 25 vol % or about 30 vol % of the composite. The relative amounts of the powders and particles are measured to achieve these ratios. The mixture is milled, with the powders and particles being repeatedly cold welded, fractured, and re-welded in an inert atmosphere due to the milling.
Next, the mixture is consolidated by hot isostatic pressing (HIP). This is a process in which the powder is consolidated into a billet. In the HIP process, the powder is exposed to both elevated temperature and high gas pressure in a high pressure containment vessel, to turn the powder into a compact solid, i.e. a billet. The HIP process eliminates voids and pores. The hot isostatic pressing may be performed at a temperature of 1000° C. to 1200° C. and a pressure of about 90 MPa to about 120 MPa for a period of about 2 hours to 10 hours.
Finally, the billet is forged to obtain the metal matrix composite. This is a process in which the billet is shaped by applying compressive force. The forging may be performed at a temperature of 1000° C. to 1200° C. using a forging press with a capacity to allow deformation of the material at the forge temperature. The HIP and forging deformation together give high ductility to the resulting composite.
The resulting metal matrix composite generally has a lower density and a lower CTE compared to the metal alloy itself. The specific stiffness is usually also improved, as is the 0.2% offset yield strength. The ceramic particles are homogeneously distributed throughout the metal matrix as well, thus avoiding agglomerates of the ceramic particles and preferably with few areas devoid of reinforcement. This can be shown through microstructure analysis using optical microscope at ×500 to ×1000 magnification.
In embodiments, the metal matrix composite has a density of less than 7.5 g/cm3. Again, this compares well against the 8.1 g/cm3 of conventional Invar® 36. The metal matrix composite may have a coefficient of thermal expansion of from about 0.5 ppm/° K to about 1.0 ppm/° K over a range of −60° C. to +60° C., including about 0.8 ppm/° K. In particular embodiments, the metal matrix composite has a density of less than 7.5 g/cc and has a coefficient of thermal expansion of less than 1.0 ppm/° K over a range of −60° C. to +60° C. The metal matrix composite has a specific modulus of of 20 GPa/g/cc to 32 GPa/g/cc. The metal matrix composite may have a 0.2% offset yield strength of 250 to 550MPa. The metal matrix composite may have a ductility of at least 2% when measured according to any one of tensile tests EN6892/1: 2009 or ASTM E8M.
Combinations of these properties are also contemplated.
The metal matrix composites can be useful as high performance materials for use in lightweight high stability articles or structures. These are useful in aerospace, space, electronics and defense applications, and in electronics packaging.
The following examples are provided to illustrate the metal matrix composites, processes, articles, and properties of the present disclosure. The examples are merely illustrative and are not intended to limit the disclosure to the materials, conditions, or process parameters set forth therein.
As shown in the microstructure view of the metal matrix composite material in
A metal matrix composite of the present disclosure, formed from Fe-36Ni and containing 20 vol % of silicon nitride particles, can be compared to Invar® 36 in the following table.
As seen in the Table below and the graphs of
A major problem with using Invar® as a material for optics applications is that it suffers from a time-dependent dimensional change in an isothermal environment.
As seen here, the curve for LoVAR® is very flat, showing exceptional dimensional stability compared to commercially available low CTE heat treatments for Invar®. After 160 hours, the samples had the following dimensional change:
Finally,
It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
This application claims priority to U.S. Provisional Patent Application Ser. No. 62/127,451, filed on Mar. 3, 2015. That application is hereby fully incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 62127451 | Mar 2015 | US |
