Inelastic deformation of (Ti, V)C alloys - Part 2 Lad relaxation studies

The high temperature plastic deformation of (Ti, V)C alloys was studied by load relaxation experiments. The deformation experiments were performed at 1200 to 1600° C on fully dense, single phase, polycrystalline TiC, TiC-25% VC, TiC-50% VC and TiC-75% VC, prepared by hot-pressing. The analysis of log σ-log {Mathematical expression} data along with the evaluation of strain rate sensitivity ∼ 0.9 to 1.5 and the grain size dependence ∼ 2.6 indicates that the high temperature plastic deformation of these carbides occurs by grain-boundary diffusion, which is in accordance with hot-pressing results. Also, transmission electron microscopy of deformed samples, revealing little evidence for dislocation activity, supported this conclusion. The diffusion coefficients obtained in this study are in good agreement with those obtained for boundary diffusion, with the activation energy ∼ 390 kJ mol^-1 for TiC and ∼ 307±13 kJ mol^-1 for other compositions. A sharp decrease in the strength of (Ti, V)C alloys with the addition of VC is associated with the softening and/or melting of second phase material accumulated along the grain boundaries.