The addition of SiC particles into a MoSi2-doped ZrB2 matrix: Effects on densification, microstructure and thermo-physical properties

The densification, microstructure and properties were studied for MoSi2-doped ZrB2-containing SiC particles. MoSi2 is added to ZrB2 as sintering aid. The enhanced densification was driven by a pseudo-binary reaction involving ZrB2 and transient Mo borides, which were formed as products of the reaction between MoSi2 and the surface oxides on the ZrB2 particles. The ZrB2 grains had a core-rim microstructure. Room temperature strengths up to 800 MPa were measured. At 1500 degrees C (in air), strengths decreased to 240 MPa. The addition of SiC increased the fracture toughness (4.1 MPa root mat RT), compared to ZrB2 (3.4 MPa root m at RT). The resistance to thermal shock of ZrB2 also increased with the addition of SiC. The measured critical thermal shock temperature difference increased from 330 degrees C for ZrB2 to 385 degrees C when SiC was added. The addition of Sic also decreased the oxidation rate of ZrB2. The investigations gave evidence of the beneficial influence of MoSi2 as sintering aid on densification and properties of ZrB2-based materials. (C) 2008 Elsevier B.V. All rights reserved.