Microstructure evolution and mechanical properties of a high Nb–TiAl alloy via HIP and heat treatment

Abstract

Hot isostatic pressing (HIP) and heat treatment (HT) are useful methods for adjustment and control of microstructure and mechanical properties of TiAl alloys, especially for casting components. Due to the vast varieties in chemical composition, phase constitution and microstructure of TiAl alloys, the evolution of microstructure and precise control of mechanical properties are vague and uncertain. In this study, the microstructure, phase content and mechanical properties of Ti–46Al–6Nb-0.1C (at%) alloy are systematically investigated during the whole processing state. HIP and HT can change the microstructure, phase content, and lamellae thickness within the lamellar colonies through phase transformation, which in turn significantly affect the tensile properties. Small lamellar spacing and high α2 phase content can improve the strength of the alloy, while equiaxed γ grains and thick γ lamellae can improve its plasticity at room temperature. HIP at 1270 °C can improve its plasticity but reduce the ultimate tensile strength. Subsequent with HT at 1350 °C, microstructure can be modulated with thin lamellae, resulting in higher uniformity and well-balanced mechanical properties.