Influence of TiC and Ni addition on densification and mechanical properties of microwave sintered ZrB2 based composites

The effects of TiC (10-30 vol%) and Ni (1-2 vol%) incorporation on densification, microstructural evolution and mechanical properties of microwave sintered ZrB2 matrix-based composites were investigated in the present study. The findings reveal that TiC addition significantly improves the densification of ZrB2 based composites, while the inclusion of Ni further improves densification of ZrB2-20 vol% TiC composite by reducing porosity and restricting the grain growth of both ZrB2 and TiC phases. Additionally, the highest Vickers hardness of 22.25 f 1.33 GPa and compressive strength of 1556.2 f 40.17 MPa were obtained for the ZrB2-20 vol% TiC composite due to lower porosity, lower grain size and higher TiC diffusion in the ZrB2 matrix. The fracture toughness enhanced with TiC and Ni addition and the maximum fracture toughness was observed as 6.66 f 0.47 MPa.m0.5 along with the highest critical energy release rate of 95.16 f 11.68 J/m2 for the ZrB2-20 vol% TiC-2 vol% Ni composite owing to the activation of toughening mechanisms like crack bridging, crack deflection and open pores as crack deflectors. Nanoindentation studies revealed significant improvements in elastic modulus and stiffness with the addition of TiC. The maximum elastic modulus and stiffness were observed as 482.91 f 36.36 GPa and 237.24 f 20.28 mu N/nm for ZrB2-20 vol% TiC composite. The study highlights the potential of incorporating metallic additives with secondary reinforcements to enhance the mechanical properties and microstructures of ZrB2 matrix, making them potential materials for high-temperature applications such as control surfaces, nose caps and leading edges of supersonic aircrafts.