Equipartition of Nano Particles in a Metallic Matrix to Form a Metal Matrix Composite (MMC)

Abstract

A metal matrix composite with a uniformly distributed ceramic component is made by mixing nano size ceramic particles with a surfactant and/or dispersing agent in a polar liquid to produce a colloidal solution, blending the ceramic particles with micron or sub-micron size metallic particles, and then compacting the blended ceramic and metallic particles into a solid mass.

Claims

1. A method of making a metal matrix composite comprising: mixing ceramic particles with a surfactant in a polar liquid solvent to produce a colloidal solution; blending metallic particles with the ceramic particles in the colloidal solution; removing the solvent; compacting the blended ceramic and metallic particles into a solid mass.

2. The method of claim 1 wherein the ceramic particles are in the range of approximately 5 to 1000 nanometers in diameter.

3. The method of claim 1 wherein the metallic particles are less than approximately 2 microns in size.

4. The method of claim 1 wherein the polar liquid is an alcohol.

5. The method of claim 4 wherein the polar liquid is isopropyl alcohol.

6. The method of claim 1 wherein the surfactant is a phosphonic acid.

7. The method of claim 6 wherein the surfactant is hexylphosphonic acid.

8. The method of claim 1 further comprising adding a soluble polymer dispersing agent to the polar liquid solvent.

9. The method of claim 8 wherein the soluble polymer dispersing agent is poly vinyl pirrolidone.

10. The method of claim 1 wherein the ceramic and metallic particles are blended ultrasonically.

11. The method of claim 1 wherein the ceramic and metallic particles are blended in a dry state.

12. The method of claim 1 wherein the ceramic and metallic particles are blended in a polar liquid.

13. The method of claim 12 wherein the ceramic and metallic particles are blended with a high shear blender.

14. The method of claim 1 wherein the blended ceramic and metallic particles are compacted by cold isostatic pressing and sintering.

15. The method of claim 1 wherein the blended ceramic and metallic particles are compacted by vacuum hot pressing.

16. The method of claim 1 wherein the blended ceramic and metallic particles are compacted by hot powder forging.

17. The method of claim 1 further comprising extruding the solid mass.

18. The method of claim 1 further comprising rolling the solid mass.

19. The method of claim 1 wherein the metallic particles are aluminum.

20. The method of claim 19 wherein the ceramic is alumina.

21. The method of claim 20 wherein the alumina particles are one of alpha-phase, gamma-phase, or a combination of alpha-phase and gamma-phase.

Description

DETAILED DESCRIPTION

[0010] In the following description, for purposes of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods and devices are omitted so as to not obscure the description of the present invention with unnecessary detail.

[0011] In one embodiment of the invention, a metal matrix composite with a uniformly distributed ceramic component is made using a process comprising several steps as described below. In this particular example, the composite is an aluminum-alumina (Al.sub.2O.sub.3) matrix; however, it is to be understood that the invention is not limited in this regard and may be applied to any other composite comprising a metal-ceramic matrix. Suitable ceramic powders include, but are not necessarily limited to, oxides, borides, carbides and nitrides.

[0012] First, mix a population of alpha-phase, nano-sized alumina particles (approximately 5 nanometers to approximately 1000 nano meters in diameter) in a polar liquid, such as isopropyl alcohol (IPA, which is also referred to as 2-propanol or isopropanol), with a surfactant and/or dispersing agent that is soluble in the polar liquid, such as certain phosphonic acids, e.g., hexyl phosphonic acid. Alternatively, the alumina particles may be gamma-phase or a combination of alpha-phase and gamma-phase. The role of the surfactant/dispersant is to facilitate wetting of the alumina nano powder in the solvent of choice. For instance, hexyl phosphonic acid rapidly and covalently binds to the surface of de-hydrated alumina nanoparticles using its phosphonic acid group. The hexyl group facilitates nanoparticle dispersion by providing an interface that interacts with the solvent as well as with other dispersing agents or stabilizers. Another advantage of creating a hexyl-capped surface is to mitigate the strong pH-dependent suspendability of charged alumina nanoparticles in organic solvents. This is particularly useful for alumina nanoparticles, which are known to have an isoelectric point close to pH 9.0. A hexyl-capped surface is expected to have an isoelectric point close to pH 7.0, facilitating dispersion in organic solvents, such as IPA. Thus, de-hydrated alumina nanoparticles are added to a stirring solution of hexyl phosphonic acid in IPA. A probe sonicator (60 Hz) is also placed in the same solution to facilitate full dispersion of the nanoparticles by ultrasonic agitation. As large agglomerates are dispersed, phosphonic acid molecules rapidly cap the surface of these nanoparticles preventing de-agglomerations.

[0013] Second, during the dispersion process, the pH is adjusted to the optimal value of isoelectric point, determined previously by measurements of zeta potential. Addition of a dispersing polymer, such as poly vinyl pirrolidone (PVP) and continuous ultrasonic agitation helps keep the individual nanoparticles separated and suspended in the organic solvent. The end result is the creation of a stable colloidal alumina solution. Large agglomerates or certain impurities (such as fused nanoparticles or alien material) may be removed by centrifugation. Colloids can be formed at any temperature that reasonably permits solubility of the surfactant and dispersing polymer in the solvent. When IPA is used as a solvent, the most convenient temperature range is between 15-75 degrees Celsius.

[0014] Third, once a stable colloidal solution is formed (for example, by allowing the solution to stand for 6 hours or exposing it to 20 g for 5 minutes such that no further sediments form and all the nano alumina particles are in suspension), micron or submicron size aluminum metallic particles are added while under vigorous stirring and ultrasonic agitation. The solvent is then removed by evaporation, forming a matrix of alumina nanoparticles uniformly distributed among grains of micron or submicron size aluminum particles.

[0015] Note that if the centrifuge step is not required, this method may be used to create nano-alumina and micron-aluminum matrix composites in a single step, in any desired concentration, typically ranging from 1% to 40%. This is a significant advantage over the traditional prior art methods for creating these MMCs discussed above.

[0016] Fourth, in case other components are required in the final MMC, such as boron carbide microparticles or other ceramic microparticles, these components can be added after the addition of the aluminum powder. These other components can be added in a variety of concentrations, typically ranging from 0.1% to 20%.

[0017] Fifth, the blended powders from the foregoing step are consolidated into a solid mass. This may be accomplished by cold isostatic pressing, (CIP) and sintering, by vacuum hot pressing or by hot powder forging.

[0018] In the case of CIP or hot vacuum pressing, the compacted solids from the preceding step may then be either extruded or rolled to the final shapes and sizes required by the end user. In the case of extrusion, an extrusion ratio of at least 49:1 is desirable to force the alumina nanoparticles inside the aluminum grains.

[0019] It will be recognized that the above-described invention may be embodied in other specific forms without departing from the spirit or essential characteristics of the disclosure. Thus, it is understood that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims.