Effect of synthesis temperature and aging on the microstructure and hardness of Ti-Zr-C

The mixed carbide Ti-Zr-C has been synthesized through carbothermal reduction of TiZrO4 at 2200 °C, 2300 °C, and 2400 °C. As-synthesized carbide was subsequently aged at 1400 °C to study phase separation. Microstructural investigations and nano-indentation measurements were performed. It was found that the synthesis temperature was important for the homogeneity and porosity of the as-synthesized powder, which strongly influenced the subsequent phase separation upon aging. The phase separation occurred via discontinuous precipitation, and high-angle boundaries were preferred. Furthermore, the characteristics of discontinuous precipitation in the present Ti-Zr-C system with a miscibility gap were compared to those of classical discontinuous precipitation. Finally, fully decomposed particles were found to be slightly harder than the unaged carbide particles. •Synthesis temperature affects the homogeneity of Ti-Zr-C powder carbothermally reduced from TiZrO4 powder.•The decomposition of Ti-Zr-C particles upon aging was more pronounced for the samples synthesized at lower temperatures.•Fully decomposed particles were slightly harder than unaged particles.•Discontinuous precipitation (DP) mainly occurred at grain boundaries with misorientations of 25-50 °.•The DP reaction within a miscibility gap is compared to classical DP reaction.