Fabrication and properties of ZrB 2–SiC–BN machinable ceramics

Abstract

ZrB 2–SiC–BN ceramics were fabricated by hot-pressing under argon at 1800 °C and 23 MPa pressure. The microstructure, mechanical and oxidation resistance properties of the composite were investigated. The flexural strength and fracture toughness of ZrB 2–SiC–BN (40 vol%ZrB 2–25 vol%SiC–35 vol%BN) composite were 378 MPa and 4.1 MPa m 1/2, respectively. The former increased by 34% and the latter decreased by 15% compared to those of the conventional ZrB 2–SiC (80 vol%ZrB 2–20 vol%SiC). Noticeably, the hardness decreased tremendously by about 67% and the machinability improved noticeably compared to the relative property of the ZrB 2–SiC ceramic. The anisothermal and isothermal oxidation behaviors of ZrB 2–SiC–BN composites from 1100 to 1500 °C in air atmosphere showed that the weight gain of the 80 vol%ZrB 2–20 vol%SiC and 43.1 vol%ZrB 2–26.9 vol%SiC–30 vol%BN composites after oxidation at 1500 °C for 5 h were 0.0714 and 0.0268 g/cm 2, respectively, which indicates that the addition of the BN enhances oxidation resistance of ZrB 2–SiC composite. The improved oxidation resistance is attributed to the formation of ample liquid borosilicate film below 1300 °C and a compact film of zirconium silicate above 1300 °C. The formed borosilicate and zirconium silicate on the surface of ZrB 2–SiC–BN ceramics act as an effective barriers for further diffusion of oxygen into the fresh interface of ZrB 2–SiC–BN.