Studies On High Temperature Adhesion Behavior And Microstructure Of TIG Welding Joint Of GH3625 Alloy

Environmental pollution is becoming more and more serious,and fossil energy is becoming increasingly scarce.It has become a global consensus to find alternative energy sources.Nuclear power has attracted more and more attention because of its minimal environmental pollution and low power generation cost.The fourth-generation high-temperature gas-cooled reactor(HTGR)is a reactor type recognized by the nuclear industry as having good safety.The control rod system of HTGR is used to control the nuclear reaction speed and stop the reactor.The main structure of the control rod system is GH3625 alloy(hereinafter referred to as 625 alloy).It is based on the research background of the fourth-generation HTGR in this paper,the following two aspects research work of spherical joint and links in nickel-base alloy components are carried out respectively.On the one hand,the adhesion behavior of spherical joints at 560?-920? high temperature service environment were studied.The vacuum hot pressing furnace was used to simulate the actual service condition of vacuum hot pressed adhesion test.The critical temperature of the adhesion as 625 alloy and the coated samples,and the change of the bonding strength at different test temperatures and holding time were studied.On the other hand,to study the organizational characteristics of chain link after TIG welding.The microstructure of welding joint of 625 alloy after different welding current and long-term aging of different temperature was studied.With the help of advanced analytical means such as OM,SEM,EDS and XRD,the mechanism of high temperature adhesion of 625 alloy and the change law of microstructure of TIG welding are studied.Thus,it has important guiding significance for the behavior of high temperature adhesion of 625 alloy and TIG welding.The 625 alloy adhesion test show that the bonding strength of adhesive specimens is significantly correlated with the test temperature and the holding time.Under the condition of stress 10 MPa and test heat preservation time 24 h,the critical temperature of adhesion phenomenon of 625 alloy is 650?,and the 625 alloy with coating two increases the critical adhesion temperature by 80? compared with that of the alloy.The coating one and coating two can reduce adhesion and adhesion strength to a large extent.The microstructure of TIG welding joint shows that The welding joints of the 625 alloy are mainly divided into two zones,one is weld and the other is fusion zone.Heat affected zone is not obvious.The weld microstructure of the welding joint is dendritic solidification structure,which contains two precipitates,namely MC phase and Laves phase respectively.The dendrite spacing of welding joints increases gradually and the content of MC phase and Laves phase change with the increase of welding current.The microstructure of welding joint at 560? after aging 300 h has no obvious change,and the needle-like ? phase has certain distribution characteristics after 760?300h.