Ultrahigh-pressure consolidation and deformation of tantalum carbide at ambient and high temperatures

The deformation mechanism of the ultrahigh-temperature ceramic, tantalum carbide (TaC), consolidated at room temperature at a very high hydrostatic pressure of 7.7 GPa is investigated using high-resolution transmission electron microscopy. The deformation behavior of TaC at room temperature is also compared with that consolidated at high temperature (1830 degrees C) at a similar pressure. TaC could be consolidated to a bulk structure (90% theoretical density) at room temperature. The deformation mechanisms operating at room temperature and 1830 degrees C are found to be significantly different. The room-temperature deformation is dominated by the short-range movement of dislocations in multiple orientations, along with nanotwinning, grain rotation, crystallite misorientation with low-angle grain boundary formation and lattice structure destruction at interfaces. In contrast, at high temperature, the strain is accommodated mostly by a single slip system, forming a parallel array of dislocations. The consolidation at room temperature occurs by heavy deformation with the support from short range diffusion, whereas the consolidation at high temperature is mostly diffusion dominated, indicating a classic sintering mechanism. The improved degree of consolidation with fewer defects results in significantly improved elastic modulus and hardness in the case of high-temperature consolidate. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.