Microstructure and mechanical and thermal properties of ternary carbides in Hf–Al–C system

A Hf-Al-C composite composed of Hf(3)Al(3)C(5), Hf(2)Al(4)C(5) and Hf(3)Al(4)C(6) has been successfully synthesized by a hot pressing method; its microstructure and mechanical and thermal properties were systematically characterized. Hf-Al-C composite conserves the high hardness and stiffness similar to HfC. Interestingly, the composite exhibits Much higher strength and fracture toughness than HfC due to its fine and anisotropic grains. Diffusion-accommodated grain-boundary sliding of Hf-Al-C ceramics at high temperature is inhibited by glass-free grain boundaries and tight interlocking of grains at grain-edge triple junctions, resulting in high remaining stiffness up to 1600 degrees C. Dislocations on the basal planes of Hf-Al-C ceramics with a Burgers vector of 1/3 can be activated at high temperature. Hf-Al-C composite shows higher coefficient of thermal expansion and specific heat capacity as well as lower thermal conductivity than HfC. The superior mechanical and thermal properties make Hf-Al-C compounds good high-temperature structural materials. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.