EFFECT OF SINTERING ATMOSPHERE ON SURFACE AND

Paper in proceeding, 2012

The effect of sintering atmosphere on high-temperature isothermal oxidation was investigated for molybdenum disilicide composites of MoSi2+15 vol% ZrO2 pressure-less sintered in Ar and H2. XRD and SEM analysis revealed that the outermost surface of as-sintered composite consists of a (Mo, Zr)5Si3 layer, and the surface microstructure depended on the sintering gases. Isothermal and thermal cycling oxidation tests were performed at 1400°C for 1000 hours and at 1200°C for 1000 cycles in air, respectively. The as-sintered composites experienced a severe weight loss at initial oxidation, and protective scales were formed after 24 h and 300 h for H2 and Ar sintered composites, respectively. In contrast, if the as-sintered surface was removed by grinding the material exhibited parabolic response with a low parabolic oxidation rate constant and excellent thermal shock property comparable to monolithic molybdenum disilicide. This work evidenced that the inherent oxidation resistance and self-curing property of MoSi2+15 vol% ZrO2 composite, and a strong influence of as-sintered surface microstructure of the composite on high temperature oxidation behaviour.