Effect of HfC and SiC on microstructure and mechanical properties of HfB 2 -based ceramics

SiC and HfC were used to tailor microstructures and improve properties of hot pressed HfB 2 -based ceramics. SiC and HfC particle, as the second phase, could hinder grain growth of HfB 2 . Compared with HfC, SiC grains grew slower, which was more effective to hinder grain growth of HfB 2 . The ternary ceramics HfB 2 –20vol%HfC–20vol%SiC had the finest microstructure, indicating the effect of SiC and HfC on grain growth. Several SiC clusters were found on related fracture surfaces. Large SiC clusters can cause high levels of residual stress and stress concentration, which are harmful to mechanical properties of boride-SiC ceramics. The predominant fracture mode of HfB 2 –20vol%SiC was transgranular, however, in HfB 2 –10vol%HfC–10vol%SiC and HfB 2 –20vol%HfC–20vol%SiC ceramics, the dominating fracture mode shift from transgranular to intergranular. With the incorporation of HfC, the fracture toughness of HH10S10 and HH20S20 increased to 4.34 MPa m 1/2 and 5.05 MPa m 1/2 , which were 17.3% and 26.7% higher than HS20 (3.72 MPa m 1/2 ), respectively. The flexural strengths of HfB 2 –HfC–SiC ceramics were improved to ~750 MPa, which were about 1.3 times higher than that of HfB 2 –20SiC.