Effect of HfC and SiC on microstructure and mechanical properties of HfB2-based ceramics

Abstract

SiC and HfC were used to tailor microstructures and improve properties of hot pressed HfB2-based ceramics. SiC and HfC particle, as the second phase, could hinder grain growth of HfB2. Compared with HfC, SiC grains grew slower, which was more effective to hinder grain growth of HfB2. The ternary ceramics HfB2–20vol%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 HfB2–20vol%SiC was transgranular, however, in HfB2–10vol%HfC–10vol%SiC and HfB2–20vol%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 4.34MPam1/2 and 5.05MPam1/2, which were 17.3% and 26.7% higher than HS20 (3.72MPam1/2), respectively. The flexural strengths of HfB2–HfC–SiC ceramics were improved to ~750MPa, which were about 1.3 times higher than that of HfB2–20SiC.