(07)STRENGTHENING BORON CARBIDE AND PREVENTION OF HIGH PRESSURE AMORPHIZATION BY INDUCING METALS OR METAL BORIDES ACROSS THE GRAIN BOUNDARY DURING HOT PRESSING OR SINTERING

摘要

Boron carbides are industrially well recognized for their low-density high-hardness properties and they are widely used for fabricating abrasives and shielding materials. However, the major weakness experienced in boron carbide is that it loses its mechanical strength after being impacted with a shock beyond its Hugoniot Elastic Limit (~17GPa). There are many controversies and hypotheses based on crystallographic analysis attributing to the point defects due to the generation of boron vacancies in C-B-C chains after being impacted with shock. However, it is still not clear if the strength weakening or amorphization is really due to the collapse of single crystal structure, or due to the failure of the compressed structural network of the boron carbide grains as a whole, or both. It is possible that boron carbide's failure beyond HEL stems simply from the lack of continuity in the compressed body and insufficient exchanges across the grain boundaries of boron carbide upon compression. In this paper a few hot pressed as well as sintered boron carbide systems are reviewed that showed super-high strength, which are able to withstand pressures well above HEL. Regardless how small it might be, boron carbides are known to have carbon impurities. Probably the presence of a small amount of a suitable third element that can combine with the free carbon and simultaneously influence the crystal structure through migration across the grain boundary, is the key to improve strength.