Microstructural evolution, mechanical and thermal properties of TiC-ZrC-Cr ₃ C ₂ composites

Dense TiC-ZrC-Cr ₃ C ₂ composites with various TiC content from 19.6 mol% to 78.4 mol% have been fabricated by hot-pressing sintering at 1950 °C using 2.0 mol% Cr ₃ C ₂ as sintering aid. The effect of TiC content on the microstructure, mechanical and thermal properties of TiC-ZrC-Cr ₃ C ₂ composites are investigated systematically. The single (Zr, Ti, Cr)C solid solution is obtained when TiC content is 19.6 mol%, while with increasing TiC content, the composites begin to consist of Zr-rich (Zr, Ti)C solid solution and Ti-rich (Ti, Zr, Cr)C solid solution phase. SEM and EDS analysis confirm that Cr element is not favorable to diffuse into ZrC lattice to form (Zr, Cr)C solid solution. Flexural strength and Vickers hardness increase gradually with increasing TiC content, but fracture toughness does not improve significantly. Fracture toughness are in the range of 3.34–4.01 MPa∙m ^1/2 for all composites, and the optimum value reaches 4.01 MPa·m ^1/2 with 49.0 mol% TiC. Experimental results of the thermal expansion coefficient reveal that the addition of TiC raises the thermal expansivity of TiC-ZrC-Cr ₃ C ₂ composites. Noticeably, the thermal conductivities of TiC-ZrC-Cr ₃ C ₂ composites show a decrement trend with increasing TiC content, not as theoretical predicting by the rule of mixtures. For instance, the thermal conductivity at 25 °C ranges from 18.0 W/m∙K for 8Z2T2C composite down to 10.6 W/m∙K for 2Z8T2C composite.