Effect of multi-pass deformation on hot flow behavior and microstructure evolution mechanism of Ti–6Al–4V alloy fabricated by hot isostatic pressing

Abstract

The hot flow behavior, spheroidization, dynamic recrystallization (DRX) and fusing of lamellar ɑ phase for hot isostatic pressed Ti–6Al–4V titanium alloy was investigated at 950°C-900°C–850 °C with the total deformation amount of 70% during multi-pass deformation. The results show that all the flow stress value presented a peak value, followed by different flow softening extent. The flow stress is very susceptible to deformation parameters such as strain, strain rate and deformation temperature, and also the peak value decreased as the increase of temperature and the decrease of strain rate. The main softening mechanisms for different deformation pass are the DRX of β phase for one-pass deformation, spheroidization of lamellar α phase for two-pass deformation and DRX of α phase for three-pass deformation, respectively. The lamellar α spheroidization deformed in two-pass at 900 °C increased with decreased strain rate or the increased strain, and the maximum spheroidization fraction of lamellar α phase was 43% at 0.01s−1. The spheroidized mechanism of lamellar α phase is major give rise to the combined action of kinking deformation and element diffusion. Nevertheless, in the three-pass deformation process, the spheroidization degree did not significantly increase as increased strain, which principal give rise to the fusion of the same orientation of lamellar α phase. The fusion mechanism is the result of the joint action of the orientation of lamellar α phase and dislocation slip. And, the fraction of DRX of α phase is obviously higher than that of spheroidization in three-pass deformation, which is the main softening mechanisms.

Keywords

• Hot isostatic pressing(HIP)
• Ti–6Al–4V alloy
• Multi-pass deformation
• Spheroidization