Cast-alumina metal matrix composites

Details Cast-alumina metal matrix composites Cast-alumina metal matrix composites

1997-08-20

2001-02-06

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

All metal or with adjacent metals

Component of composite having metal continuous phase...

C428S293100, C148S549000, C148S439000

Reexamination Certificate

active

06183877

ABSTRACT:

FIELD OF INVENTION
This invention relates to aluminum-base metals containing alumina and carbon or graphite particles. In particular, this invention relates to the casting of alumina-containing metal matrix composites (MMCs).
BACKGROUND OF THE INVENTION
Rohatgi et al, in U.S. Pat. No. 5,626,692, disclose that nickel-coated graphite particles and silicon carbide particles can combine to produce a neutral buoyancy mixture. This neutral buoyancy mixture hinders low-density graphite from floating and high-density silicon carbide particles from sinking in molten aluminum-base matrices. The stability of this molten mixture allows casting of metal matrix composites without special rapid-solidification equipment. This neutral buoyancy method provided the first commercially viable method for casting aluminum-base composites with silicon carbide and graphite particles.
These hybrid silicon carbide-graphite composites provide excellent wear resistance at low cost. Although manufacturers readily machine these hybrid composites, the “hard” silicon carbide particles accelerate tool wear rates of tungsten carbide tools Diamond (PCD and CVD-diamond-coated carbides) have sufficient hardness to machine silicon carbide reinforced metal matrix composites. These diamonds tools however are very expensive, do not resist shocks that occur with interrupted cutting and are only available in limited shapes and sizes. The accelerated wear rates of machining silicon carbide-containing composites can increase machining costs of some applications beyond acceptable limits for certain applications.
It is an object of the invention to form a wear resistant composite.
It is a further object of the invention to provide a composite that facilitates casting without excessive segregation.
It is a further object of this invention to provide a composite that machines with decreased tool wear rates.
SUMMARY OF THE INVENTION
This composite consists of an aluminum-alloy matrix containing by volume percent, 0.4 to 8.8 alumina, 1 to 4.4 carbon or graphite and 0.5 to 20 nickel-bearing aluminide. The alumina particles have an average size between 3 and 250 &mgr;m and the carbon and graphite particles have an average size between 10 and 250 &mgr;m. The composite is cast by stirring alumina and carbon or graphite contained in a molten aluminum or aluminum-base alloy to form a molten mixture. The molten mixture is cast directly from a temperature above the liquidus of the matrix alloy. While solidifying, carbon or graphite particles delay or hinder the settling of alumina to create a more uniform composite structure. The resulting composite structure contains an aluminum-base alloy, alumina, carbon or graphite and nickel-bearing aluminide dispersoids.


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