Elastic Deformation, Plastic Flow, and Dislocations in Single Crystals of Titanium Carbide

Abstract

Single crystals of the brittle refractory-hard-metal TiC have been plastically deformed at temperatures from 800° to 2200°C. Dislocation etch-pit studies on {100} cleavage surfaces after bending showed that the slip plane is {111} in the rocksalt structure. The slip direction is taken to be that of the shortest Burgers vector, 〈110〉. The slip system is then the same as that of fcc metals and diamond cubic semiconductors. The resolved shear stress for slip in TiC at 1100°C was found to be large: ∼10 kg/mm2. TiC crystals loaded at room temperature did not deform plastically, but did accommodate elastic strain up to 1.2% if the surfaces were electropolished. A shear stress of 0.4 of the theoretical strength was obtained. These results are consistent with the long-held hypothesis that the binding in hard metal carbides is partially covalent and not exclusively metallic. The Peierls stress resisting dislocation motion should then be large, as in the covalent crystals Ge and Si, and thermal activation would be required for plastic flow. The observed formation of debris by jogs in moving dislocations might alternatively be responsible for the large flow stress. The effects of impurities, precipitates, and composition differences are being investigated.