Process,Microstructure And Properties Of As-cast K452 Nickel Base Superalloy By Laser Repairing

Superalloys are widely used in hot end components of aero engine and gas turbine due to their advantages of excellent high-temperature strength,good thermal corrosion resistance,and fatigue resistance.However,superalloy parts are prone to defects during manufacturing and service,and it has important economic value for the high-quality repair of defective parts.However,superalloys with high Al?Ti content have poor weldability and are prone to crack during repairing.Laser additive repair technology has the advantages of high energy density,local heating and small heat affected zone,which is widely used in the field of parts repair.To solve above problems,In this paper,the laser repair process of K452 superalloy is studied,as well as the mechanism,influencing factors and inhibition measures of liquation crack,and the crack-free repair sample is obtained.On this basis,the microstructure of the repaired specimens are analyzed and its mechanical properties are tested.The influence of laser power,scanning rate and powder feeding rate on the tendency of forming and cracking were analyzed through the continuous laser repair process experiment of the system.The optimal process window was obtained.On this basis,the appropriate duty cycle and frequency are obtained by pulse laser forming and remelting experiments,which are 70%-80%and 20-40 Hz,respectively.The liquation cracks tend to be generated during the laser additive repair of K452superalloy.The crack originates from the heat affected zone and extends along the grain boundary to the substrate and repair area.The low heat-input pulse laser process effectively suppresses the generation of cracks.Large area casting defect repair was simulated by slotting repair.when the pulsed laser energy density was lower than 30 J/mm~2,the liquation crack was completely suppressed.However,the lack-of-fusion occurs in the repaired area and the substrate interface and the overlapping area.The groove interface was first repaired by pulsed laser with energy density of 35 J/mm~2.After fully cooling,the middle region was repaired by increasing the energy density of pulsed laser.The defect-free large-area repaired samples were obtained.The segregation of elements such as Nb and Mo during the solidification process of the repaired area leads to the precipitation of irregular Laves phase.The?'phase of HAZ is undergoes different degrees of solid solution due to laser thermal cycling.After standard heat treatment,the?'phase of HAZ transforms into a spherical shape and is evenly distributed with an average size of 240 nm.The average hardness of the repair area of the pulsed laser repair sample is 267.9 HV,and the tensile strength and yield strength at room temperature are 823 MPa and 650 MPa,respectively,which reached the strength of the as-cast substrate.After standard heat treatment,the fracture of the repaired specimens occurs in the substrate area at room temperature,which indicates that the repaired area is stronger than that of the substrate.The fracture of the repaired specimens occurs in the repaired area at high temperature,which indicate that the strength of the substrate is greater than that of the repaired area,and the tensile strength of the repaired specimen reaches 97.5%of that of the substrate.