Study of Hot Deformation Characteristics of an As-Cast Ti-22Al-25Nb Alloy

Abstract

The hot deformation characteristics of an as-cast Ti-22Al-25Nb alloy has been studied in the temperature range of 1323-1523K and the strain rate range of 0.001-10s-1, using hot compression tests. The experimental results indicated that discontinuous yielding occurs during the hot deformation performed at the strain rate of 10s-1, while the flow curves are of a steady-state type at lower strain rate range. Activation energy was obtained by analyzing the steady-state flow stress with a standard constitutive equation. They are 260-282kJ/mol in the temperature range of 1473-1523K, and 145-155kJ/mol in 1323-1423K. The processing map developed using the principles of dynamic material modeling exhibits three domains for the present alloy: 1) a domain of dynamic recrystallization of B2 phase in the temperature range of 1373-1423K at the strain rate range of 0.01-0.001s-1, with the power dissipation efficiency of about 35-50%, 2) a domain of dynamic recovery of B2 phase in the temperature range of 1473-1523K at the strain rate less than 0.01s-1, with the power dissipation efficiency of about 20-30%, 3) a domain of flow instability in the form of adiabatic shear band in the temperature range of 1323-1373K at the strain rate larger than 1s-1.