Deformation of Poly crystalline Transition Metal Carbides

Plastic deformation was studied in hot-pressed poly crystalline specimens of titanium carbide, vanadium carbide, niobium carbide, tantalum carbide, and tungsten carbide tested in four-point bending and under compression to 2100°C. Transition from brittle to ductile behavior occurred at approximately half the absolute melting temperature for each material. Above this temperature the yield strengths decreased exponentially with increasing temperature. Between the ductile-brittle transition temperature and about 1900°C the apparent activation energy for flow in the carbides with the rock-salt structure was near O.S ev/atom. Above 1900°C the value was approximately 2 ev/atom; the value for tungsten carbide was apparently 0.3 ev/atom to 2070°C. Vanadium carbide and titanium carbide recovered extensively on annealing for short times near 2000°C. No such recovery occurred in tungsten carbide under these conditions. The results for polycrystalline carbides were compared with available data for single crystals of titanium carbide.