Self-propagating high-temperature synthesis of single-phase binary tantalum-hafnium carbide (Ta,Hf)C and its consolidation by hot pressing and spark plasma sintering

Manufacturing of the single-phase binary carbide (Ta,Hf)C by self-propagating high-temperature synthesis (SHS) from a mechanically activated (MA) reaction mixture is discussed. The effect of mechanical activation conditions on the microstructure and phase composition of the reaction mixtures and the SHS products was studied. The measured combustion temperature (2127 degrees C) was significantly lower than the calculated adiabatic temperature (3001 degrees C), which is related to the intensive gas release during combustion and the possible loss of thermal contact between a thermocouple and a briquette. After MA in the air, the SHS product was a virtually single-phase carbide with the lattice parameter a = 0.4487 nm, which corresponds to 18.0 at% of dissolved HfC; HfO2 content was less than 1%. The SHS product was a high-porosity sinter cake with a carbide grain size of less than 10 mu m. The resulting product was refined in a planetary ball mill. Dense samples with relative density up to 90.0 +/- 5.0%, the hardness of 24.0-27.4 GPa, Young's modulus of 423.6-484.4 GPa, and elastic recovery values of 44.3-46.1 were fabricated by hot-pressing and spark plasma sintering methods using the SHS micron-sized (Ta,Hf)C powders.