Sintering Mechanism of Pure B4C Ceramic Prepared by Hot Oscillating Pressing and with Excellent Mechanical Properties

Pure boron carbide (B 4 C) ceramics are sintered by hot oscillating pressing at temperatures of 1700–1900 °C for different soaking times. The densification mechanism, grain growth kinetics, and mechanical properties obtained under these sintering conditions are systematically investigated. It is found that the fully densified B 4 C ceramic is obtained at 1900 °C within 120 min, possessing an excellent combination of hardness (≈38.5 GPa) and fracture toughness (4.8 MPa m 1/2 ). The densification mechanisms during sintering are as follows: viscous flow at the initial stage (relative density D ranged from 55% to 65%) under 1700 °C; lattice diffusion/grain boundary diffusion at the sintering stage (62% < < 75%) of 1800 and 1850 °C; grain boundary sliding by dislocation motion at the late stage (65% < < 82%) of 1700 °C and the sintering stage (75% < D < 90%) at 1800–1900 °C; and dislocation gliding and stacking faults at the final stage (90% < D < 95%) occurring at 1850–1900 °C. The dislocation motion exhibits a critical impact on the densification process of the hot oscillating–pressed B 4 C ceramic. The grain growth kinetics at 1900 °C is controlled by grain boundary diffusion.