Hardening and Strengthening Effects Induced by Incorporation of Titanium in Hexagonal Boron Nitride Ceramics

In this research, the effects of different amounts of titanium on the sinterability, microstructure, hardness, and flexural strength of spark plasma sintered hBN-based materials were studied. The addition of 20 wt.% Ti improved the relative density of hBN by almost 6% because of progressing a chemical reaction between Ti and the hBN matrix. Although the x-ray diffraction spectrums suggested the in-situ formation of TiN_0.9, together with the TiB₂ phase, further investigation revealed the diffusion of boron atoms from the TiB₂ compound into the non-stoichiometric TiN_0.9, creating Ti(N,B) solid solution. This phenomenon was also found to be responsible for improvements in the mechanical properties of the SPSed samples. The flexural strength of hBN was noticeably improved by incorporating titanium additive, benefiting from the in-situ formation of titanium diboride and Ti(N,B) compounds. The composite reinforced with 20 wt.% Ti secured the highest Vickers hardness (~ 95 VH_0.1 kg) and flexural strength (~ 150 MPa).