Primary hot working characteristics and microstructural evolution of as-cast and homogenized Ti-4Al-2.5V-1.5Fe alloy

Abstract

Hot deformation characteristics of Ti-4Al-2.5V-1.5Fe-0.25O alloy in as-cast and homogenized condition was studied using isothermal hot compression tests in both β and α + β fields at strain rates ranging from 3 × 10−4 s−1 to 1 s−1. To understand the hot deformation behaviour and to identify the optimum regime for the primary breakdown of titanium alloy ingot, processing map based on strain rate sensitivity (m), kinetic analysis, and microstructural characterization were used. Micro-mechanisms of deformation in the β-field were analyzed with the help of reconstruction of parent β grain orientations using electron backscatter diffraction data. Kinetic analysis and microstructural characterization of samples deformed at low strain rates (ε̇<10−2 s−1) in β-field confirmed dynamic recovery assisted by dislocation glide/climb. In comparison, the samples deformed at higher strain rates (ε̇>10‐2s−1) in β-field exhibited deformation bands and recrystallized grains formed through static recrystallization. In the α + β field, kinetic parameters at low strain rates (ε̇<10−2 s−1) indicated dynamic globurization, which were corroborated by microstructural analysis. Samples deformed at high strain rates (ε̇>10−2 s−1) in the α + β field exhibited adiabatic shear bands, strain-induced porosity and lamellar α-kinking. The optimum regime for thermomechanical processing (900°C to 1150°C and 3ⅹ10−4 s−1 to 3ⅹ10−2 s−1) is arrived at by combining the strain rate sensitivity map and microstructural analysis. Further, constitutive equations have been developed to predict the steady-state flow stress values in β and α + β fields.