Effect of WSi2 and Si3N4 contents on the thermal expansion behaviors of (Mo,W)Si2-Si3N4 composites

Abstract (Mo,W)Si 2 -Si 3 N 4 composites with different contents of WSi 2 and Si 3 N 4 as an oxidization resistance coating material of molybdenum substrate were fabricated by spark plasma sintering (SPS) and their thermal expansion behaviors were studied within a temperature range of 200–1400 °C in argon atmosphere. The phases and microstructures of the composites were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS). The coefficients of thermal expansion (CTEs) of (Mo,W)Si 2 -Si 3 N 4 composites decreased with increase of WSi 2 content until 6 vol%, which was attributed to the effect of (Mo,W) 5 Si 3 phase content and grain size. However, the CTEs of the composites decreased with the increase of volume fraction of Si 3 N 4 . The relation between the volume fraction of Si 3 N 4 and the CTE of the composite was accordance with the Turner's model. The (Mo,W)Si 2 -Si 3 N 4 composite with 6 vol% WSi 2 and 30 vol% Si 3 N 4 showed a closer CTE to Mo substrate and a better thermal shock resistance.