At present, the design concept of aerospace structural materials is gradually changing from pure static strength design to modern damage tolerance design. Titanium elbows are required to have a high fracture toughness and a low fatigue crack growth rate under certain strength conditions. . GR5-DT titanium alloy is a new type of damage-tolerant titanium alloy independently developed by my country under this concept. At present, the research on GR5-DT titanium alloy mainly focuses on damage tolerance performance, and there is little research on its hot forming behavior. Since the microstructure has a great influence on the damage tolerance performance, it is of great significance to study the deformation mechanism of GR5-DT titanium alloy under high-temperature conditions. This paper mainly studies the effects of deformation temperature, strain rate, and deformation degree on flow stress and microstructure of GR5-DT titanium alloy during hot compression deformation establishes the Arrhenius type hot deformation constitutive equation of titanium alloy and analyzes the dynamic recrystallization behavior. , Provide a theoretical reference for actual production.
After related experiments, from the true stress-true strain curve of GR5-DT titanium elbow alloy under different thermal deformation conditions, it can be seen that in the initial stage of deformation, the titanium alloy has a work-hardening effect, and the flow stress increases with strain. As the temperature increases, the flow stress reaches its peak under a small strain; then the softening mechanism occupies the main position. The flow softening of flow stress is more obvious than when the strain rate is low. The deformation resistance of titanium alloy decreases with the increase of temperature. At lower temperatures (such as 850°C and 900°C), the stress softening gradually decreases as the strain increases and softening occurs. In addition, the phenomenon is quite obvious when the strain rate is high. After the peak of the stress, the flow stress decreases with the increase of the strain. The decrease of the flow stress tends to relax when the strain reaches a certain level; when the temperature is higher (such as 950~1000℃) ), and when the strain rate is lower than 10s-1, the flow stress fluctuates in a steady-state zigzag shape, showing a continuous softening process; when the deformation temperature is 950% and the strain rate of 1000° is 10s1, the stress increases with the strain. It shows that work hardening has always been the dominant position.
The experimentally measured thermal excitation force of TC4-DT titanium elbow alloy is 971.67kJ?mol-, which is much greater than the self-diffusion excitation force of pure a and B titanium alloys. The reason may be related to the simultaneous phase transformation behavior during thermal deformation. There are fewer slip systems that can be activated in titanium alloys at low temperatures, and dislocations produce plugging in defects such as grain boundaries, which cannot be effectively released through the recovery mechanism controlled by diffusion. This shows that the thermal deformation of titanium alloys under this condition is caused by Process control other than high-temperature diffusion. Observing the flow stress curve of the titanium alloy at the same time, it is found that the change process is characterized by a dynamic recrystallization curve at low temperature, indicating that the dynamic recrystallization softening mechanism is dominant in the hot deformation process of the alloy. Therefore, it is considered that the hot deformation process of the titanium alloy Dynamic recrystallization occurs.
in conclusion:
1. The flow stress of GR5-DT titanium alloy thermal compression deformation increases significantly with the increase of strain rate, and the rheological softening at high strain rate at a lower temperature is more obvious than that at low strain rate, and at higher temperature When the softening phenomenon does not occur, work hardening is still the dominant position.
2. The thermal deformation excitation energy of GR5-DT titanium elbow alloy measured by the experiment is 971.67kJ?mol-l, which is much larger than the self-diffusion excitation energy of pure a, B titanium alloy. It is believed that dynamic recrystallization occurs.
