Effects of Si and Al on twin boundary energy of TiC

Effects of aluminum and silicon on the twin boundary energy (TBE) of titanium carbide (TiC) have been investigated using transmission electron microscopy and first-principles calculations. The results demonstrate that Al is more effective relative to Si to reduce the twin boundary energy of TiC. By electronic structure analysis, the high TBE of pure TiC can be attributed to the energy penalty accompanying the formation of trigonal prismatic coordination of Ti atoms at twin boundaries. For the SUM doped TiC, the lower TBE's are partly due to the absence of the energy penalty accompanying the formation of trigonal prismatic coordination of Si/Al atoms, and are partly due to the stabilizing effect via the formation of pi bonding between carbon neighbors of Si/Al atoms. The pi bonding between carbon neighbors of Al is stronger than that of Si, providing an explanation for the larger twin-stabilizing effect of Al. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.