Research On Superplasticity Of Ti-10V-2Fe-3Al Alloy

Near B -titanium Ti-1023 alloy of high-strength, good fatigue strength and excellent hardenability has both a relatively low 3 -transus temperature(798C) and a low forging temperature range, which make it suitable for superplastic isothermal forging to manufacture complex forge pieces.In this paper, 130mm diameter hot-rolled bars ( 3 transus temperature is 798 C) were used in experiments. The superplastic property of Ti-1023 alloy was studied systematically by the experiments of tensile and compression. The preparation method of fine-crystalline structure and the processing parameters of superplastic forging are optimized. It provided the experimental foundation to determine the superplastic isothermal forging process of complex structural piece with thin web and high ribs of Ti-1023 alloy.High and low temperature thermomechanical treatment process(860C,>60% deformation, water cooling+780 C ,>60% deformation, water cooling+780 C,>60% deformation, air cooling+750C,l hour annealing, air cooling) is used for the rolled bars. Homogeneous and fine equiaxed crystal microstructure is obtained and the size of globular primary a phases is smaller than 2.5 n m. Therefore the alloy appears excellent superplasticity. The average elongation is 845% and the maximum value in individual specimen: 1087%. This process is an effective way to refine the microstructure of Ti-1023.The specimens appears superplasticity (elongation!97%~845%) in the range of temperature from 700C to 820C and strain rate from 1.1 X 10-2s-1 to 1.1 X 10-4s-1. The optimal superplastic deformation condition is 750C and 3.3 X 10-4 s-1 , in which the average elongation is 845% and the flow stress is 27.9MPa. Therefore, Ti-1023 alloy can be used for isothermal superplastic deformation pieces with thin web and high rib.The experimental result of superplastic compression indicates that strain rate has intensive effect on flow stress of Ti-1023 alloy and the effect of temperature is related with strain rate. The variation rule of superplasticity, flow stress andmicrostructure is consistent. When the specimens are deformed in a long time at the optimal superplastic deformation condition, the microstructure is coarsened sharply. If the deformation time is shortened properly or the deformation temperature is decreased appropriately or strain rate is increased, homogeneous and fine equiaxed crystal microstructure can be obtained.