Study On Casting Defect Repair And Fatigue Performance Of K4169 Superalloy Thin-wall Casting

With the rapid development of the aviation industry,the demand for complex thin-walled structural parts of high-temperature alloys in aeroengines is increasing,and the structural parts of aeroengines are developing in the direction of larger thrust-to-weight ratio,thinner and lighter.As the engine structural parts are subjected to complex fatigue loads during the flight,in addition to meeting the requirements of high strength,superalloys also need to meet the requirements of high fatigue life at the same time.At present,high-temperature alloy castings are mainly poured by vacuum smelting.Due to the influence of the pouring process,the castings are often prone to structural defects such as shrinkage,looseness,and cold partition,resulting in a serious decline in the quality of the castings and seriously affecting the mechanical properties of the components.Repairing defective superalloy castings and conducting fatigue performance research are of great significance.Argon tungsten arc welding is widely used in component connection and pore filling because of its good weld quality and beautiful shape.This article intends to use tungsten arc welding technology to repair the defects of K4169 high-temperature alloy thin-walled castings in different times.The finite element simulation method simulates the temperature field and stress field of the welded joint,studies the microstructure and fatigue properties of the superalloy before and after repair,and uses the method of numerical simulation to study the fatigue resistance of the K4169 superalloy after welding repair.In order to provide a new technical path to further improve the fatigue performance of superalloys,the main research contents and conclusions of this paper are as follows:(1)The finite element simulation of the welding process was carried out.By designing four groove forms of no chamfer,0.2mm chamfer,0.5mm chamfer and1 mm chamfer,1-5 passes of welding repair were carried out for each groove respectively,and the temperature field and stress field under each groove form were analyzed and compared,the results found that the residual stress of the stress field around the center of the weld is the smallest when the welding repair is performed under the 1mm chamfer groove form.At the same time,an optimal welding groove form is proposed: such as welding repair When the hole diameter is 5mm,a double-sided groove with a 1mm chamfer is taken.(2)According to the results of the finite element analysis,the 1mm grooves of the holes were repaired by 1-5 passes by using the tungsten argon arc welding technology,and the microstructure before and after the repair was analyzed.The results show that the structure of the as-cast superalloy is mainly austenite matrix and Laves phase and δ phase segregated at the grain boundary.After repair by welding,the welded joint structure has been significantly refined,but the geometric diameter of the Laves phase in the weld is larger than the geometric diameter of the Laves phase in the base metal,and it becomes larger with the increase of the number of welding.The geometric δ phase in the weld The length is less than the geometric length of theδ phase in the base metal,and the Laves and δ phases are uniformly distributed in the weld.(3)The fatigue properties of superalloy samples before and after welding repair were studied.The results show that casting defects and welding times have a greater impact on the fatigue performance of welded joints.The average fatigue life of alloy samples with casting defects is only 27,683 cycles,the average fatigue life of samples without casting defects is 71,755 cycles,and the fatigue life of once repair welding is91,479 cycles.As the number of welding passes increases,the fatigue life of castings decreases.When the repair welding is performed 5 times,the fatigue life is 64005 cycles,which is consistent with the change trend of the fatigue performance simulation results of the specimen after the repair welding.In the fatigue life simulation,the fatigue life of the joint repaired by once welding is 49590 cycles,and as the number of welding increases,the fatigue life gradually decreases.The fatigue fracture analysis results show that the fatigue crack propagation direction in the base metal is perpendicular to the load stress direction,and the fracture is relatively flat.When the fatigue crack propagates in the weld,the fatigue section is rugged and the propagation path is longer than the propagation path of the fatigue crack in the base metal.This is the main reason for the high fatigue life of repair welded specimens.