Mechanical behavior of a fine-grained duplex γ-TiAl alloy

Abstract

The mechanical behavior of a fine-grained duplex γ-TiAl alloy was studied in compression at strain rates ranging from 0.001 to 2000 s−1 and temperatures from −196°C to 1200°C. The temperature dependence of the yield and flow stresses is found to depend on the strain rate. At strain rates of 0.001 and 0.1 s−1, the yield stress decreases as the temperature increases, with a plateau between 600°C and 800°C. At strain rates of 35 and 2000 s−1, the yield stress exhibits a positive temperature dependence at temperatures above 600°C; however, postyield flow stresses exhibit a reduced temperature dependency. The work-hardening rate decreases dramatically with temperature at low and high temperatures, with a plateau occurring at intermediate temperatures for all strain rates. The work-hardening-rate plateau is seen to extend to higher temperatures as the strain rate increases. The strain-rate sensitivity at strain rates of 0.1 s−1 and greater is lower than 0.1, although it increases slightly with temperature. At 0.001 s−1, the strain-rate sensitivity increases dramatically at high temperatures (equal to 4.5 at 1200°C). The anomalous (positive) temperature dependence of the yield stress at high strain rates (>1 s−1) and high temperatures (>600°C) is explained via a dislocation-jog pinning mechanism. The negative temperature dependence of the yield stress at low strain rates ( 900°C) is though to be due to a thermally activated dislocation-jog climb process in the grain interiors and/or deformation and recovery processes at/near grain boundaries. The decreased anomalous temperature dependence of the flow stress at high strain rates and high temperatures is ascribed to dynamic recovery promoted by adiabatic heating.