Microstructural evolution of hot-forged high Nb containing TiAl alloy during high temperature tension

Abstract

Microstructural evolution of the as-forged Ti-44Al-8Nb-0.2W-0.2B-Y alloy during high temperature tensile tests between 650 and 950°C, at strain rates of 1×10−4s−1, 2×10−4s−1 and 5×10−4s−1, is investigated in this study. Tensile properties of the alloy are extremely sensitive to the test temperature and strain rate. At a strain rate of 5×10−4s−1, ductile-brittle transition temperature (DBTT) of this alloy is between 750 and 800°C. At lower temperatures, the principal deformation mechanism involves breaking down of remnant lamellar structure and deformation of twins. Above 900°C, dynamic recrystallization (DRX) occurs and the extent of DRX improves with an increase in temperature and strain as well as a decrease in strain rate. Under specific test conditions, the ω phase forms by the solid-state phase transformation: α2→γ+ω. The inhomogeneous microstructure remarkably influences the mechanical properties of the hot-forged pancake.