Fabrication and properties of ZrB2-SiC-BN machinable ceramics

Abstract

ZrB2-SiC-BN ceramics were fabricated by hot-pressing under argon at 1800 degrees C and 23MPa pressure. The microstructure, mechanical and oxidation resistance properties of the composite were investigated. The flexural strength and fracture toughness of ZrB2-SiC-BN (40 vol%ZrB2-25 vol%SiC-35 vol%BN) composite were 378 MPa and 4.1 MPa M 112, respectively. The former increased by 34% and the latter decreased by 15% compared to those of the conventional ZrB2-SiC (80vol%ZrB2-20vol%SiC). Noticeably, the hardness decreased tremendously by about 67% and the machinability improved noticeably compared to the relative property of the ZrB2-SiC ceramic. The anisothermal and isothermal oxidation behaviors of ZrB2-SiC-BN composites from 1100 to 1500 degrees C in air atmosphere showed that the weight gain of the 80 vol%ZrB2-20 vol%SiC and 43.1 vol%ZrB2-26.9 vol%SiC-30 vol%BN composites after oxidation at 1500 degrees 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 ZrB2-SiC composite. The improved oxidation resistance is attributed to the formation of ample liquid borosilicate film below 1300 degrees C and a compact film of zirconium silicate above 1300 degrees C. The formed borosilicate and zirconium silicate on the surface of ZrB2-SiC-BN ceramics act as an effective barriers for further diffusion of oxygen into the fresh interface of ZrB2-SiC-BN. (C) 2009 Elsevier Ltd. All rights reserved