Research On Laser Deposition Repair And Properties Of GH738/K417G Alloy

K417G is a low-density,high-strength nickel-based cast superalloy,which is widely used in the manufacture of turbine blades and guide vanes of aero-engines and gas turbines,etc.K417G alloy parts are used under severe conditions for a long time,and the blade edges are prone to cracking,corrosion and wear damage due to the erosion of high-temperature airflow.In this regard,GH738 superalloy powder was used to study the organization and properties of laser deposition repair of K417G superalloy,focusing on the microstructure characteristics,microhardness and frictional wear properties of the repaired specimens in the deposited state,matrix preheating repair and aging heat treatment state at different temperatures of laser deposition repair of GH738/K417G alloy.Aiming at the problems of cracks that are prone to occur during the laser deposition repair of GH738/K417G superalloy,the optimization test of laser deposition repair process parameters was carried out,and the defect-free tissue was obtained.The microstructure,hardness and friction wear properties of sedimentary repair specimens were studied.The results show that the sedimentary repair zone was composed of columnar dendrite and equiaxed crystals growing epitaxically,and the carbide content in the repair zone was less,and there was noγ′phase.Compared with the matrix,the carbide content in the heat-affected zone is significantly increased,and the content of eutectic phase is reduced.The hardness of the restoration zone in the deposited state gradually decreases in the direction of the deposition height,with the highest hardness in the heat affected zone at 420HV_0.3.The wear mechanism of the matrix was abrasive wear,adhesive wear and oxidation wear,with an average friction coefficient of 0.685 and a wear amount of 1.33mg,and the wear mechanism of the sedimentary repair zone was abrasive wear and oxidation wear,with an average friction coefficient of 0.829 and a wear amount of 1.56mg.GH738/K417G superalloy has the problem of weakening performance after laser deposition repair,and the laser deposition repair test under matrix preheating is carried out,and the temperature field under different preheating temperature conditions is simulated and analyzed by finite element method,and the effective preheating temperature is obtained,and the microstructure,microhardness and friction and wear properties of the repair specimen under preheating conditions are analyzed.The results show that with the increase of preheating temperature,the cooling rate and temperature gradient gradually decrease.And the effective temperature of substrate preheating is 300℃and above.When the preheating temperature was 300℃,the precipitation of carbides in the repair zone increased.The average hardness of the repair zone increased by 33HV_0.3,which was 10.2%higher than that of unwarmed;The coefficient of friction in the repair zone was 0.77,which was 7.2%lower than that of unpreheated,and the wear amount was 1.45mg,indicating that the matrix preheating could effectively improve the performance of the repair zone.After laser deposition repair of GH738/K417G superalloy,its microstructure was metastable and there were residual stresses inside the sample,and a double-stage aging heat treatment test with different temperatures was carried out,and the microstructure,microhardness and friction and wear properties of the heat-treated specimen were explored.The results show that with the increase of time-sensitive temperature,the average size of theγ′phase gradually increases,and the degree of carbide continuity precipitated between grain boundaries also gradually increases.When the aging temperature is 840℃,the average size of theγ′phase is 70nm,and the carbides are precipitated in chains along the grain boundaries.At this time,the average hardness of the repair zone is the highest,which is 501HV_0.3,which is 141HV_0.3higher than the average hardness of the matrix;the friction coefficient is 0.38,which is 45%lower than the matrix,and the wear amount is 0.71mg,which is 0.62mg lower than the matrix,and excellent wear resistance is obtained.The wear mechanism of the heat-treated repair zone is mild abrasive wear and oxidative wear.