Hot deformation behavior of TC11/Ti–22Al–25Nb dual-alloy in isothermal compression

Abstract

The high-temperature flow behavior of TC11/Ti–22Al–25Nb electron beam (EB) weldments was investigated by the isothermal compression tests at the temperature of 900–1060 °C and the strain rate of 0.001–10 s−1. Based on the experimental data, the constitutive equation that describes the flow stress as a function of strain rate and deformation temperature is obtained. The apparent activation energy of deformation is calculated, which decreases with increasing the strain and the value is 334 kJ/mol at strain of 0.90. The efficiency of power dissipation η changes obviously with the variation of deformation conditions. Under the strain rates of 0.01, 0.1 and 1 s−1, the value of η increases with increasing the true strain for different deformation temperatures. While the value of η decreases with increasing the strain under the strain rates of 0.001 and 10 s−1. The optimum processing condition is (topi=1060 °C, opi=0.1 s−1) with the peak efficiency of 0.51. Under this deformation, dynamic recrystallization (DRX) is observed obviously in the microstructure of welding zone. Under the condition of 1060 °C and 0.001 s−1, the deformation mechanism is dominated by dynamic recovery (DRV) and the value of η decreases sharply (η=0.02). The flow instability is predicted to occur since the instability parameter ξ() becomes negative. The hot working process can be carried out safely in the domain with the strain rate of 0.001–0.6 s−1 and the temperature of 900–1060 °C.