Effect of sintering temperature and TiB2 content on the grain size of B4C-TiB2 composites

Abstract

Boron carbide (B4C) is a ceramic with great properties such as low density, the third hardness after diamond and cubic BN. However, it is a limited use cause of its poor sinterability and low fracture toughness. Titanium diboride (TiB2) has been used as an ideal additive to get B4C ceramics with good properties. B4C-TiB2 composites were prepared by spark plasma sintering (SPS) at 1950℃ under a pressure of 50 MPa, using TiB2 and B4C powder mixture as starting materials. The effect of TiB2 content on the mechanical performance and grain size of B4C-TiB2 composites was investigated. The B4C-TiB2 composites with 20 mol% TiB2 addition show great comprehensive properties, the relative density of 97.91 %, a Vickers hardness of 29.82 ± 0.14 GPa, and fracture toughness of 3.70 ± 0.08 MPa·m1/2 respectively. The results indicated that as the TiB2 content increase, the hardness of the composite decreases and the fracture toughness increases. The main mechanism of the TiB2 phase toughening B4C ceramic is crack deflection as a result of the differences in their thermal expansion coefficients. The analysis of grain size distribution by electron backscattered diffraction (EBSD) shows that the pinning effect of TiB2 can refine B4C grain. The pinning effect is another reason for the high hardness and high toughness of the B4C-TiB2 composites. Dislocations are observed in the TEM image of the composite, which also improves the hardness and toughness of the material.