Research On The Plastic Deformation Behavior And Stress Simulation Of TC4 Titanium Alloy Diffusion Joint

TC4 titanium alloy has outstanding advantages such as high specific strength and specific rigidity,heat resistance,toughness,weldability,corrosion resistance and fatigue resistance.It has become the most widely used titanium alloy in the world and is widely used in aerospace,ship and automobile engineering fields.In view of the fact that there is little research on the plastic deformation behavior of diffusion-bonding joints,this topic will focus on the plastic deformation behavior of TC4 titanium alloys during the diffusion bonding process,design joint runner structures with different characteristics,and study the influence of welding process parameters on macro plastic deformation of joints in different runners;analyze the microstructure and texture of the joint,simulate the stress distribution of the joint of different runner structures under different welding process parameters through the method of finite element modelling,and clarify the relationship between joint runner structure,process parameters,joint microstructure and plastic deformation behavior.This research is of great significance to fill the deficiencies in the research of plastic deformation of diffusion welding joints and to guide the welding process of titanium alloys.Different diffusion bonding temperature and pressure were used to conduct the TC4/TC4 diffusion bonding test,and the plastic deformation of the joint was studied.As the temperature or pressure increases,the runner space is squeezed and filled by the metal below,the degree of deformation increases,and the rate of change in the cross-sectional area of the slot increases.In addition,when the temperature increases,the rate of change in the cross-sectional area of the slot increases linearly,and as the pressure increases,the rate of change in the cross-sectional area increases first and then increases gently.The deformation behavior of TC4/TC4 diffusion welding joints is analyzed according to the different runner structures of the joint.When the bonding temperature and pressure are constant,the change rate of the cross-sectional area of the rectangular slot is always the lowest value,indicating that the diffusion bonding joint of the rectangular flow channel structure has the least deformation after welding compared with other flow channel structures.When the bonding temperature(900?)or pressure(1.5MPa)is low,the area change rate of the right-angle slot hole is the largest;when the bonding temperature(900?)or pressure(3MPa)increases,the rate of change of the cross-sectional area of the circular arch slot becomes the largest,indicating that the structure of the round arch runner is more sensitive to changes in temperature and pressure,and its diffusion joints are more easily deformed after welding.In addition,the deformation behavior of isosceles slots is similar to that of right-angle slots,but the degree of deformation is always lower than the latter.Metallographic structure observation and EBSD analysis methods were used to analyze the grain morphology and texture of the TC4/TC4 diffusion welding joint microstructure in different areas.In terms of grain morphology,the grain structure at the weld is relatively fine and uniform.In the area above the weld and around the hole,some?titanium grains grow significantly.In terms of grain orientation,with the weld as the boundary,the crystal plane orientation above the interface tends to(0001),while the crystal grain below the interface tends to the most slippery surface of?titanium(101~—0).Using the thermal-mechanical sequential coupling method,the finite element numerical simulation of the TC4/TC4 diffusion connection process is performed.The results show that the channel structure and bonding temperature have a significant effect on the stress and strain distribution of the TC4/TC4 diffusion joint.The equivalent stress shows a different distribution in different areas of the joint and the channel.The sequence of the stress value distribution in the vicinity of the channel is the same as the sequence of the change rate of the cross-sectional area of the channel.It explains the different deformation degree of different channels under the same process parameter.The change of bonding temperature has little effect on the stress-strain distribution trend of the channel,and has a greater influence on the value of stress and strain.As the temperature increases,the degree of channel deformation is different,and the degree of residual stress released by the deformation is also different,resulting in the equivalent stress of the joint.The maximum value changes differently.