Research On Tlp Welding Process And Post-weld Heat Treatment Of Inconel 718 Superalloy

High temperature alloys not only have excellent corrosion resistance and oxidation resistance,but also exhibit higher tensile strength,creep strength and excellent fatigue resistance at higher temperatures,so they are widely used in aerospace,petrochemical,and Gas turbines,battleship combat readiness and other fields.The welded joints of high-temperature alloy parts commonly used in these fields require high quality.Transient liquid phase diffusion welding(TLP),as one of the precision welding methods,combines the advantages of solid phase diffusion welding and brazing,overcomes the shortcomings of traditional fusion welding,and satisfies Inconel 718 high temperature alloy structural parts without processing after welding and serving at high temperatures.When the joint quality is stable,the welding seam composition is uniform,and the welding residual stress is small,it is of great practical significance to study the TLP welding of Inconel 718 superalloy.This paper designs the TLP connection scheme(welding temperature,holding time and thickness of the interlayer)of Inconel718 superalloy and BNi₂ intermediate layer and four post-weld heat treatment processes.OM,SEM and EDS were used to analyze the microstructure,element distribution,fracture precipitation morphology and element composition of the Inconel 718/BNi₂ joint interface area.The microhardness and shear strength performance of the TLP joint were tested.The relationship between the microstructure and mechanical properties of the joint interface and the process parameters was analyzed,and the relationship between the distribution of interface elements,the formation of precipitated phases and the process was clarified.The paper studied the influence of process parameters on the interface structure and properties of TLP joints.The connection can be achieved under the conditions of welding temperature of 1050?and 1100?,welding pressure of 1MPa,and holding time of 30?120min,but the segregation phenomenon at the interface between the isothermal solidification zone and the diffusion zone is more serious when the holding time is 30min at1050?.The precipitates accumulated in the diffusion zone at 1050°C welding are more coarse.In joints kept at 1100°C for 30?120 minutes,with the extension of the holding time,the elements in the middle layer diffuse more fully,which helps to homogenize the joint composition,and at the same time,the joint shear strength increases,reaching a maximum of 511 MPa.Increasing the thickness of the intermediate layer will cause component segregation in the isothermal solidification zone and serious accumulation of precipitates,resulting in a decrease in the shear strength of the joint,but the aggregation phenomenon will be significantly improved with the extension of the holding time.The paper also studied the influence of four groups of heat treatment processes on the interface structure of TLP joints.Compared with the welded joints,the grain size of the heat-treated joints all grow up,and the grains of the sample grow most obviously under the2#(homogenization treatment+aging treatment)heat treatment process,followed by 3#(solution treatment+aging treatment),1#(homogenization treatment+solution treatment+aging treatment),4#(aging treatment).In terms of the uniformity of the joint composition,compared with the welded joint,the most significant change in the heat-treated joint is the disappearance of the B element and the increase in the content of the C element.Among them,the 1#heat treatment process has the highest degree of homogenization,and the mass ratio at the joint(wt.%))Is almost the same as the base metal,followed by 2#,3#and 4#respectively.In terms of joint hardness,compared with welded joints,the hardness of sample joints increased to different degrees after heat treatment.Among them,the hardness of the base material and isothermal solidification zone of 1#heat-treated joint is the largest,and the hardness of the diffusion zone of 4#heat-treated joint is the largest.