High Temperature Tensile Deformation Response of γ + α₂ Titanium Aluminide Processed through Ingot Metallurgy Route

Abstract

High temperature service capability and deformation behavior of γ + α₂ TiAl alloy made through ingot melting route has been studied under tensile load at temperature (T = 750–900 °C) and strain rate ($\dot{\varepsilon }$ = 10⁻¹–10⁻³ s⁻¹). Reduction in strength is not seen till 800 °C at all the three strain rates, indicating safe use of alloy up to this temperature. Further, it has been observed that % elongation to failure (e_f) increases with increase in T or decreasing $\dot{\varepsilon }$. Significant increase in e_f is observed with decrease in $\dot{\varepsilon }$ from 10⁻² to 10⁻³ s⁻¹ at test temperature of 850 °C or above. At 900 °C and 10⁻³ s⁻¹, e_f is observed to be 47%. Microstructure consisting of γ and α₂ phases with lamellar morphology and β phase are distributed uniformly along grain boundaries. Refinement of lamellae and dynamic recrystallization (DRX) assisted by twinning is found to be the primary reason for flow softening, which lead to improvement in e_f of alloy at T ≥ 850 °C. It is observed that temperature plays a major role in initiation of DRX as observed with increasing T whereas $\dot{\varepsilon }$ plays major role in twinning as observed with decreasing $\dot{\varepsilon }$ even at lower temperatures.