The Study Of Hot Deformation Behavior And Numerical Simulation Of Heat Treatment Of TC18Titanium Alloy

Titanium alloy is one kind of widely used material in the aviation industry, which has the property of high strength, good plasticity and good performance under high temperature. At the same time, as the Young’s module of titanium alloy is relatively low compared to other metals, while the yield stress approaches the break stress, the welding procedure and machining can easily cause remained stress, so heat treatment is always used as the lasting working procedure. TC18titanium alloy is one kind of titanium which has more beta phase than a phase, and it has been used as the structure part of the planes for a long time. The shank part this article studies is the key part of one model of plane, and it is made up of four parts which are assembled by welding. After the heat treatment following the welding procedure, some place on the shank part occur a significant deformation, so that the whole shank part cannot be used. The purpose of this article is to get the flow stress equation at high temperature and the stress relaxation equation at high temperature by experiments. This article includes four main experiments, the structure observing and mechanical properties testing of four classical heat treatment of TC18titanium alloy, high temperature yield stress and Young’s module testing, hot compressing experiment at650-1000℃with strain rate0.001-1s-1, stress relaxation experiment under500℃、600℃、650℃、700℃. The numerical simulation part includes the simulation of welding, annealing.The flow stress equation obtained from the result of hot compressing in two phase area is: while in beta single phase area the equation will be: The hot processing map is eatablished and the results show that the instable area of hot deformation is650℃-800℃with strain rate of0.02s-1-ls-1, and the rescrystallization area is possibly distributed in the area of750℃-850℃with the strain rate of0.001s-1-0.01s-1, and the proper deforming area is750℃-850℃with the strain rate of0.001s-1-0.01s-1and850℃-950℃with the strain rate of0.01s-1-0.1s-1.The stress relaxation equation under650℃of TC18titanium alloy after annealing treatment is σ=4.05+(σ0-4.05)Aeτ,while A=1.0334,τ=4.9057. And experiments show that the primary stress has no influence on the stress relaxation limit, and after double annealing the TC18titanium has a higher ability of anti stress relaxation.The simulation results show that after annealing at810℃the remained stresshas changed from700MPa to86.4MPa, while the ultimate deforma tion is1.21mm.Both the shank part and the solid part has occurred a cymb iform shape ofdeformation.The result of this study can supply some guidance for the producing of theshank part, and the flow stress equation obtained by hot compressing experimentcan be used to predict true stress at high temperature, while the stress relaxationequation can be applied to the simulation of deformation control for TC18titaniumalloy parts at high temperature.