Abstract: A metal matrix composite of aluminum, magnesium or titanium, and their alloys, containing particles of a silicon boride composition. A preferred form of the boride is silicon hexaboride. A small amount of carbon can be present in the silicon boride composition as Si--B--C. The particles can be pre-blended with particles of the metal prior to melting, or can be added after the melting of the metal. Because of the similar specific gravity of silicon boron compounds and aluminum, very little stirring is required to achieve a homogeneous mixture in the melt. This substantially reduces formation of oxide and hydrogen inclusions. Improved machinability is achieved through utilization of rounded particles. The composite has improved strength, stiffness and reduced thermal coefficient of expansion, thus making the composite composition more useful in industry.

Abstract: Strengthened and toughened ceramic composite bodies are achieved through the use of a silicon boride composition of silicon borides and borides of the form Si-B-C. This strengthening and hardening is achieved when the silicon boride composition is present over a wide range, although a preferred amount is about 20 wt. %. This strengthening and toughening occurs for oxides, carbides, nitrides, and mixtures thereof, for example. One silicon boride composition for this application is silicon hexaboride. Further enhancement is achieved by the addition of up to about 25 wt. % carbon in the silicon hexaboride. Accordingly, the preferred silicon boride composition is a Si-B-C composition, with carbon being added to SiB.sub.6, for example.