The Processing Map And The Forging Process Optimization Of Casting TB6 Titanium Alloy

TB6 titanium alloy is a kind of titanium alloy in order to meet the damage tolerance design principles and production of high structural efficiency , which obtain a wide range of applications in the civil and military aircraft for its good overall performance. Because the deformed microstructure of TB6 titanium alloy is sensitive to the deformation of thermal parameters such as the deformation temperatures and the strain rates and this alloy has a small tolerance of forging thermomechanical parameters, it is essential to optimize the thermomechanical parameters of TB6 titanium alloy. In this paper, the hot deformation behavior of casting TB6 titanium alloy was analyzed by using the test data obtained from the isothermal and constant strain rate compression tests, and the forging thermomechanical parameters were optimized by using the processing map technology based on dynamic material model. The obtained results are of great value for making reasonable forging process to manufacture casting TB6 titanium alloy forgings with excellent and uniform microstructures as well as properties that can be repeated under the same processing conditions.The isothermal and constant strain rate compression tests were carried out in the temperature range of 800～1150℃and strain rate range of 0.001～10\s-1 by Thermecmaster-Z simulator. The true stress-true strain curves at different temperatures and strain rates were plotted with the data obtained from the test, and the influence of the temperature and strain rate on the flow stress of casting TB6 titanium alloy was analyzed. The results indicated that the flow stress decreases with the increasing temperatures and decreasing strain rates. In view of the value of flow stress, the strain rate range of 0.001～0.1 s-1 is suitable for working in the low-temperature(800～950℃)and the strain rate range of 0.001～1s-1 is suitable for working in the high-temperatur(e1000～1150℃). The average deformation activation energy of TB6 titanium alloy at a stain of 0.8 was calculated as 225.32kJ/mol.The hot compression test data of casting TB6 titanium alloy were treated reasonably, and the processing maps for this alloy were developed at various stains with data based on Prasad criterion and Murty criterion, respectively. The comparison and analysis of the processing maps based on Prasad criterion and Murty criterion showed that the processing maps based on Murty criterion can predict and optimize the forging thermomechanical parameters more accurately. By analyzing the stability and instability regions of the processing maps and observing microstructure of the samples deformed in different regions in the processing maps based on Murty criterion, the deformation mechanisms in different regions were identified and the thermomechanical parameters of this alloy were optimized. The results showed that the flow localization tended to occur in the temperature range of 800～890℃and strain rate range of 0.01～1s-1, and the crack tended to occur in the temperature range of 800～890℃and strain rate range of 1～10 s-1. There are four regimes corresponding to preferable deformation thermomechanical parameters described as following: 800～950℃,0.001～0.008s-1,1025～1075℃,0.001～0.032s-1,920～975℃,1.8～10s-1 and 1030～1065℃,3.2～10s-1, respectively. The optimum of deformation thermomechanical parameters were in the order of the temperature between 850～875℃, the strain rate at 0.001s-1 and the temperature between 1050～1075℃, the strain rate at 0.001s-1 with the deformation mechanisms of large-grained superplasticity and dynamic recrystallization, respectively.