Study On Forging Process Optimization In Ti₃Al Based Alloy Using Processing Maps

Ti3Al base alloy is a kind of intermetallic compounds with low density and good high temperature properties. The material is widely used in the manufacture of various parts in the engine. But this material has strong resistance to deformation and narrow range of forging deformation paramete, it prone to defect and difficult to forming. Processing map based on dynamic material modeling can with which not only flow instability regions can be avoided but also optimized ranges of temperature and strain rate can be identified. It have extensive application in hot forming process. The hot compression tests of Ti3Al based alloy were carried out in the temperature range of950-1350℃and strain rate range of0.001-10.0s-1. Through the investigated of flow stress-strain curves, the the flow stress model of Ti3Al based alloy was constructed.The processing maps of Ti3Al base alloy at various strains are drawn by using Prasad criterion and Murty criterion. Get the parameter regions of flow instability, the better thermomechanical parameters, the optimum of deformation thermomechanical parameters and the deformation mechanism by investigated of the processing map and microstructure observation. The conclusions can be drawn as follows.The Ti3Al base alloy flow stresses on deformation temperature and strain rate are sensitive. The flow stresses of Ti3Al based alloy increase with increasing strain rates and decreasing temperatures. The flow stress-strain curves is flow steadily at low strain rate, but the flow stress will appear softening phenomenon gradually in the high strain rate. Error analysis shows that flow stress model can exactly predict flow stresses of Ti3Al based alloy in different deformation conditions. Error analysis indicated that the difference between the calculated and experimental flow stress approximately within15%has the96.4%of the strongholds, and the accuracy of10%of the data point total is89.7%.The analysis of processing maps show that the processing maps drawn by using Prasad criterion and Murty criterion are approximately the same. Choose Prasad criterion based on the processing graph optimization results for reference because of the found the processing map based on Prasad criterion is some more accurate by observed combined with metallographic microstructure.According to the criterion based on Prasad processing map that the regions of flow instability corresponding manifestations of flow instability including adiabatic shear bands local flow, cracks, flow localization, mixed microstructures like "necklace" and large grained. The better thermomechanical parameters for forging are in the temperature ranges and the strain rate ranges of975℃-1050℃and0.001s-1-0.05s-1,1150℃-1200℃and0.001s-1-0.05s-1,1300℃-1350℃and0.056s-1-1.778s-1.There is one more zone of1220℃-1275℃and0.001s-1-0.003s-1besides the above mentioned three better thermomechanical parameters range at strains below1.0. The optimum thermomechanical parameters for forging lies in the temperature range of985℃-1020℃and0.001s-1,1140℃-1175℃and0.001s-1-0.031s-1,1350℃and0.1s-1-0.178s-1. There is one more zone of1245℃-1260℃and0.001s-1besides the above mentioned three optimum thermomechanical parameters range at strains below1.0. The corresponding main deformation mechanism for globularization of slices organization, superplasicity, dynamic recrystallization and appear sub-grain.