| TC4 titanium alloy has become the main material for manufacturing thin-walled parts such as fan,compressor disk and blade of aeroengine due to its good physical and chemical properties.Titanium alloy parts are easy to crack and wear due to long-term service in high temperature and high pressure environment.In order to reduce the maintenance cost and cycle of titanium alloy parts,it is necessary to repair the damaged titanium alloy parts with high quality.Welding is a common method to repair titanium alloy parts,which can improve the reliability of material connection.Argon arc welding is usually used in the manufacture of titanium alloy parts,but the heat of argon arc welding is concentrated,and the damaged titanium alloy parts can be repaired by argon arc welding,which will cause serious deformation.Electron beam welding(EBW)has the advantage of small welding deformation.The serious deformation of damaged titanium alloy parts can be effectively reduced by EBW.In the welding process,due to the accumulation of high-density energy,residual stress and other problems will appear in the welded joints of titanium alloy parts,which seriously affect the service performance of titanium alloy parts after repair,and bring serious security risks.Heat treatment can regulate the microstructure,reduce the residual stress and improve the mechanical properties,and the heating temperature of stress relief annealing heat treatment is low,which is not easy to cause serious deformation and other problems.Therefore,in this thesis,the microstructure and properties of heat treatment of TC4 titanium alloy repaired by argon arc-electron beam composite welding were studied.The main research contents and results are as follows:(1)In view of the difference between the microstructure of argon arc-electron beam composite welding and that of casting and forging,it is necessary to explore a set of stress relief annealing heat treatment process which can improve the properties of argon arc-electron beam composite welding samples effectively.The effect of stress relief annealing heat treatment with different heating temperature and holding time on the microstructure and hardness of argon arc welding samples was studied.With the increase of annealing temperature and holding time,the hardness increases slightly and the microstructure has no obvious change.The effect of local heat treatment with different heating width on the microstructure and properties of welded joints of titanium alloy parts is different.With the increase of heating width,the hardness increases slightly,and the microstructure has no obvious change.(2)The effect of local heat treatment on the microstructure and properties of electron beam welded samples was studied.After local heat treatment,the hardness increased slightly,but the microstructure has no obvious change.Compared with TC4 titanium alloy forgings,the tensile strength and yield strength of the local heat treatment samples are 22.67 MPa and 16.67 MPa higher,and the elongation after fracture is 1.43% lower,The tensile fracture mode is ductile fracture.(3)In order to solve the problem that the structure of argon arc-electron beam composite welding parts is complex and it is inconvenient to use vacuum furnace heat treatment,the effect of local heat treatment on the microstructure and properties of composite welding samples was studied.Compared with the vacuum furnace heat treatment,the effect of local heat treatment on the residual stress reduction of the weld center is 5.25% higher than that of the vacuum furnace heat treatment,and the effect of heat affected zone is 6.86% lower.The hardness of the heat treatment sample in vacuum furnace is the largest,and that of the local heat treatment sample is slightly smaller,but it is bigger than that of the welded sample.Compared with the vacuum furnace heat treatment sample,the tensile strength and yield strength of the local heat treatment sample are 96.4mpa and 38.3mpa lower,and the microstructure has no obvious change. |
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