In-situ reinforcement of transition metal boride ceramicsCopyright: © GHI
The borides of the transition metals Ti, Cr, Zr, Hf, Ta, and W have extremely high melting points with over 3000 degree celsius and are therefore difficult to sinter, but exhibit exceptionally high hardness and stiffness. Their low fracture toughness can be increased by sintering mixed crystals of special compositions at temperatures above 2100 degree celsius and annealing them at lower temperatures. The mixed crystals precipitate less soluble borides in the form of small platelets or foils, which impede crack propagation or lead to crack branching. For titanium diboride , the fracture toughness was increased from 5.6 to over 11 megapascal per square meter and the flexural strength from 500 to over 1100 megapascal. For this purpose, comprehensive investigations are carried out in the multi-component systems.