Densification of γ-TiAl Powders by Spark Plasma Sintering

Abstract

The superior thermo-physical properties of γ–TiAl alloys like low density, good oxidation resistance and high strength retention at elevated temperature makes it a suitable material for high temperature structural applications. However they have poor low temperature ductility and poor creep resistance at service temperatures. It is expected that nanocrystalline γ–TiAl alloys can overcome this difficulty with improved mechanical properties. Spark plasma sintering (SPS), one of the novel powder metallurgy techniques offers the advantage of manufacturing nanostructured materials. The present paper reports on the basic investigation of densification behaviour of nanostructured γ–TiAl alloy consolidated by spark plasma sintering. As received prealloyed γ–TiAl powder was milled in a high energy ball mill with optimized parameters for 20 and 40 hours. The structural transformations of these powders were studied by X-ray diffraction (XRD) and electron microscopy (SEM). These milled powders as well as unmilled powders were consolidated by spark plasma sintering with varying temperature. The density of these sintered samples was measured by Archimedes principle. The density of spark plasma sintered samples were 92%, 96% and 98% for unmilled, 20hrs and 40hrs, respectively. The densification behavior of these powders with respect to temperature has been studied by measuring the instantaneous linear shrinkage of the specimen that was indicated by the z-axis displacement. It was observed that 60% of densification occurred at temperature range of 700-1000°C .