Study On The Effects And Mechanism Of Deep Cryogenic Treatment Time On Organization And Properties Of Electron-beam-welded TC4 Joints

In view of TC4 titanium alloy has a very broad application in the aerospace,marine vessels,machinery,metallurgy,chemical energy,building materials,medical equipment and articles for daily use and so on,the performance requirements of the welding structure is becoming more and more strict,especially fatigue performance.As a method to improve material performance process,cryogenic treatment will be introduced into the research on the influence of TC4 titanium alloy welded joint fatigue performance in this article.Based on cryogenic time as a variable,this paper examines the effect of the different cryogenic time on mechanical properties of TC4 titanium alloy electron beam welding joint and by the change of residual stress tensile and impact strength after cryogenic,it is concluded that an optimal time of cryogenic.At the same time by using the optimal time of cryogenic and not cryogenic compares the two sets of sample fatigue test.Groups are divided to study the different cryogenic time effect on the properties of TC4 titanium alloy electron beam welding joint,through the measurement of residual stress,the residual stress of TC4 titanium alloy electron beam welding joint are found decreased obviously after cryogenic treatment.In cryogenic 24 h after weld,the longitudinal residual stress was reduced by 34.13%,the transverse residual stress was reduced by 47.43%.At the same time,the joint tensile strength increases with the cryogenic time,cryogenic time reached after 24 h,tensile strength increased by 4.1%,and elongation of 31.9%.Cryogenic treatment after 24 h hours,the hardness of parent metal is increased by about 6.87%,hardness of the center welding is increased by about 1.61%.Effectiveness and economy are combined consideration,the cryogenic 24 h was selected as the best time of cryogenic.Based on cryogenic 0 h and 24 h of TC4 titanium alloy electron beam welding joint fatigue experiment,which reveals the life of welding joints increasing 4-6 times after cryogenic..By comparing metallographic organization,SEM,TEM and XRD analysis before and after cryogenic,shows why the reducement of residual stress,enhancement of mechanical properties and the extension of fatigue life after the cryogenic treatment.Mainly on the one hand,the weld microstructure of cryogenic treatment after the beta phase into acicular martensite alph a ? phase,at the same time of fine grains,also increased the top structure of dense,and the strength of the joint and the plastic has a certain degree of improvement.On the other hand,the movement and redistribution of dislocations reduced the residual stress and the stress concentration,extending the fatigue life of joint.