Characterization of high-temperature deformation behavior of as-cast Ti60 titanium alloy using processing map

摘要

Isothermal compression testing of as-cast Ti60 titanium alloy is carried out at the deformation temperature range of 970-1120 ℃ with 50 ℃ intervals, strain rate range of 0.01-10 s~(-1) and height reduction of 75%. The hot deformation behavior of as-cast Ti60 titanium alloy is characterized based on the analysis of the stress-strain behavior, kinetics and the processing map. The constitutive equation of as-cast Ti60 titanium alloy is established, which describes the flow stress as a function of the strain rate and deformation temperature. The apparent activation energies are calculated to be 574.8 kJ/mol in the α+β two-phase field and 194.0 kJ/mol in the β single-phase field, respectively. Based on the dynamic material model and the Prasad's instability criterion, the processing maps for the alloy are constructed at strains of 0.4 and 0.7. The maps exhibit a stable domain in the temperature range of 970-1120 ℃ and strain rate range of 0.01-0.1 s~(-1) with two peaks in power dissipation of 70% and 70％, occurring at 970℃/0.01 s~(-1) and 1120℃/0.01 s~(-1), respectively. The high efficiency values of power dissipation indicate dynamic recrystallization in these fields, and dynamic recrystallization fraction increases with increasing deformation temperature. Therefore, the optimal processing condition for cogging procedure of as-cast Ti60 titanium alloy is 1120℃/0.01 s~(-1). Moreover, the material also undergoes flow instabilities domain occurring at strain rates higher than 1 s~(-1). This instability domain exhibits flow localization and cracking which should be avoided during hot processing in order to obtain the satisfactory properties.