Plastic flow and dislocation structures in tantalum carbide: Deformation at low and intermediate homologous temperatures

Dislocation structures and plastic flow in TaC 0.99 have been studied in material deformed by microindentation at 20°C, and in specimens crept at temperatures between 0.37 and 0.43 T m (1300–1500°C). Extensive local plastic deformation occurred during indentation, accomplished mainly by the motion of a 2 edge dislocations gliding on {111}. The resulting defect structure consisted primarily of long screw dislocations, suggesting a relatively high mobility for edge segments and a large Peierls stress for screw dislocation motion. This {111} slip system also operated in specimens crept at 0.37–0.43 T m. Thermal activation apparently increased the mobility of screw segments, resulting in substructures containing mixed dislocations with no preferred orientation. Microstructural observations, and analysis of kinetic data for power-law creep, suggest that intermediate temperature creep deformation of TaC 0.99 occurs mainly by climb-controlled grain boundary sliding with severely limited intergranular accommodation.