Boron carbide-copper infiltrated cermets

Porous boron carbide preforms, prepared with and without excess carbon, were infiltrated with a Cu-Si alloy. Contrary to unalloyed copper, the Cu-Si alloy wets and infiltrates the porous preforms. A thermodynamic analysis of the B-C-Cu-Si system indicated that a Si content of the alloy above 15 at% leads to the formation of SiC. At higher Si content, the composition of boron carbide in contact with the melt also changes towards higher boron content. Metallographic examination validated these conclusions. The SiC compound forms preferentially around the free carbon particles in preforms containing excess carbon, and also in the vicinity of carbide that did not contain any excess carbon. Eventually, SiC, a product of the reaction between the carbide and the melt, forms a continuous barrier that impedes completion of the reaction and accounts for the limited increase of hardness as a result of lengthy heat treatments.