Effect of nickel powder particle size on the microstructure and thermophysical properties of spark plasma sintered NiCrCoAlTiW-Ta superalloy

The spark plasma sintering technique (SPS) was used to consolidate admixed elemental powder in order to fabricate NiCrCoAlTiW-Ta superalloy. Nickel which is the key element that formed the matrix powder particle size was varied in the range of 3-44, 45-106 and 106-150 μm. The effect of varying the starting powder particle size, on the formation of intermetallic phases was investigated. Also, important thermophysical properties in the development of superalloys for high temperature applications were investigated by using laser flash machine, in the range of 100-800 °C. The constituents of the microstructure for the sintered alloy includes, the gamma (γ) matrix phase (Ni), precipitated intermetallic gamma prime (γ') phase Ni3(Al, Ti) and the precipitated solid solution strengthening elements (Cr and W). There was an increase in the density with decreasing powder particle size. Also, the averave grain size increased with increasing powder particle size. The thermophysical properties obtained, which include thermal conductivity and diffusivity increase with increasing temperature. Non-linear behaviour and inflection points were observed as the temperature increases due to short range order and disorder phenomenon which is associated with superalloys. The powder particle size has little or no significant effect of the thermophysical behaviour as the pattern observed were almost the same.