Hot deformation behavior and processing parameter optimization of BT25y alloy with an initial equiaxed microstructure using processing map

The high-temperature plastic deformation behavior of BT25y alloy with an initial equiaxed microstructure was investigated by hot compression tests. Processing maps were established to evaluate the power dissipation efficiency (η) and identify the flow instability regions. When the strain reaches steady state, the optimum processing window is distributed in the area covering most of the studied deformation temperatures and strain rates of 1 × 10⁻² to 1 × 10⁻¹ s⁻¹. True strain has great effects on the power dissipation efficiency under the condition of 880 °C/1 × 10⁻³ s⁻¹, but the efficiency values remain approximately constant (η = 0.40) at conditions of 900–940 °C/1 × 10⁻² to 1 × 10⁻¹ s⁻¹ and 980–1000 °C/1 × 10⁻¹ s⁻¹. Besides, the instability regions are distributed in high strain rate areas no matter how many of the strains. Based on the processing map and microstructural observation, it can be concluded that the deformation mechanisms related to Region I with small strain rate and lower temperature in α + β phase field, Region II with medium strain rate and higher temperature in α + β phase field, Region III with medium strain rate and high temperature in β phase field are superplasticity and strain-induced transformation, dynamic recrystallization (DRX) and phase transformation, β phase dynamic recovery and local DRX, respectively.