Physical and mechanical properties of hexagonal boron nitride ceramic fabricated by pressureless sintering without additive

Hexagonal boron nitride hBN ceramic was successfully fabricated by pressureless sintering at 2100C using submicrometre hBN powders without any sintering additive. The as-prepared hBN ceramic showed a room temperature flexural strength of 30.7MPa. Its flexural strength increased with the increment of temperature in N2 atmosphere, and it retained a strength of 57.2MPa nearly two times of the room temperature strength at 1600C due to clean grain boundaries with no glassy phase. Additionally, the as-prepared hBN ceramic showed a high thermal conductivity of 31.76Wm1k1 and a good thermal shock resistance, which retained a relatively high residual flexural strength of 22.6MPa 73.5 of the original flexural strength at T800C. The as-prepared hBN ceramic presents a good application prospect at high temperature.