At present, the design concept of aviation structural materials is gradually changing from simple static strength design to modern damage tolerance design, which requires
titanium elbow to have high fracture toughness and low fatigue crack growth rate under the condition of certain strength. Tc4-dt titanium alloy is a new type of damage tolerance titanium alloy developed by Our country under this concept. At present, the research on TC4-DT titanium alloy is mainly focused on the damage tolerance, but the research on its hot forming behavior is less. Since the microstructure has a great influence on the damage tolerance, it is significant to study the deformation mechanism of TC4-DT titanium alloy at high temperature. In this paper, the effects of deformation temperature, strain rate and deformation degree on flow stress and microstructure of TC4-DT titanium alloy during hot compression deformation were studied. Arrhenius thermal deformation constitutive equation of titanium alloy was established and dynamic recrystallization behavior was analyzed to provide theoretical reference for practical production.
According to the true stress-strain curves of TC4-DT titanium elbow alloy under different thermal deformation conditions, it can be seen that at the initial stage of deformation, work hardening effect occurs in titanium alloy, and the flow stress increases with the increase of strain, and the flow stress reaches the peak at a small strain. The softening mechanism takes the main position. The rheological softening of the flow stress is more obvious than that of the low strain rate, and the deformation resistance of titanium alloy decreases with the increase of temperature. At lower temperatures (e.g. 850℃ and 900℃), stress softening gradually decreases with increasing strain, and softening phenomenon occurs. In addition, the phenomenon is quite obvious at high strain rate. After the stress peak, the flow stress decreases with the increase of strain, and the decrease of flow stress tends to moderate when the strain reaches a certain degree. When the strain rate is lower than 10S-1 at a higher temperature (950~1000℃), the flow stress shows steady serrated fluctuation and shows a continuous softening process. When the deformation temperature is 950% and the strain rate is 10S1 at 1000°, the stress always increases with the strain, indicating that the work hardening is always dominant.
The thermal excitation force of TC4-DT titanium elbow alloy is 971.67kJ? Mol - is much larger than the self-diffusing excitation force of pure A and B titanium alloys, which may be related to the simultaneous phase transformation behavior during thermal deformation. At low temperature, there are few slippage systems that can be activated in titanium alloy, and dislocations produce plug deposits at defects such as grain boundaries, which cannot be effectively released by the recovery mechanism controlled by diffusion. It indicates that the thermal deformation of titanium alloy under this condition is controlled by processes other than high temperature diffusion. At the same time, the flow stress curve of titanium alloy was observed, and the dynamic recrystallization curve was found at low temperature, which indicated that the dynamic recrystallization softening mechanism played a dominant role in the hot deformation process of titanium alloy. Therefore, dynamic recrystallization occurred during the hot deformation process of titanium alloy.
Conclusion:
1. The flow stress of hot compression deformation of TC4-DT titanium alloy increases significantly with the increase of strain rate, and the rheological softening of high strain rate at lower temperature is more obvious than that at low strain rate. At higher temperature, even no softening phenomenon occurs, work hardening is still the dominant position.
2. The thermal deformation excitation energy of TC4-DT titanium elbow alloy is 971.67kJ? The mol-L self-diffusing excitation energy of pure A and B titanium alloys is much higher than that of pure A and B titanium alloys.
