Fabrication of TiC-ZrC-Co composites with refined microstructure using ultrafine TiC-ZrC mixture powders

Abstract

Ultrafine TiC-ZrC mixture powders with various Ti/Zr molar ratios (9:1, 8:2, 7:3, and 6:4) were synthesized by carbothermal reduction of high-energy milled TiO2-ZrO2-C. ZrC was found to be insoluble in the TiC lattice at 1400-1500 degrees C; as a result, carbothermal reduction of TiO2-ZrO2-C mixtures led to the formation of the TiC-ZrC mixture powders rather than the (Ti,Zr)C solid solution. TiC-ZrC-Co composites prepared using the TiC-ZrC mixture powders exhibited a refined microstructure, due to the inhibition of the coalescence of TiC grains by ZrC grains distributed in the TiC-ZrC mixture powders. In other words, the ZrC particles distributed in the mixture powders inhibited the coalescence of TiC grains during liquid-phase sintering, resulting in the formation of TiC-ZrC-Co composites with refined microstructure. The refined microstructure of these composites favorably influenced their properties: in particular, the experimental measurements highlighted a significant improvement in the mechanical properties (H-v = 14.8-16.0 GPa, K-IC = 7.2-7.6 MPa m(1/2)) of the composites prepared from the ultrafine TiC-ZrC mixture powders, compared with those (H-v = 11.1-13.3 GPa, K-IC = 5.7-6.3 MPa m(1/2)) of conventional TiC-ZrC-Co composites. (C) 2018 Elsevier B.V. All rights reserved.