GH4169/GH738 Alloy Laser Additive Repair Process Research

GH738 alloy has excellent high-temperature properties,and is widely applied in the manufacture of the key components of the aircraft engine such as the sealing ring,the turbine disk,the fastener,etc.Under high-temperature,high-speed and high-pressure operating conditions,the surface of the part is prone to wear and oxidative ablation.In view of the repair needs of GH738 alloy damaged parts,GH4169 alloy powder was used to study the microstructure and properties of GH738 alloy laser additive repair.The influence of process parameters on the characteristic size and macroscopic shape of the molten pool was revealed.The variation of microstructure and properties of GH4169/GH738 alloy by laser additive repair under substrate preheating conditions were studied.The effect of aging heat treatment on the microstructure and properties of GH4169/GH738 alloy by laser additive repair were explored.The main research work is as follows:Aiming at the problem that cracks,pores and other fusion defects are prone to occur during the laser additive repair of GH4169/GH738 alloy,the influence of process parameters on the characteristic size of the molten pool was studied,and the microstructure and properties analysis of deposition samples were carried out.The results show that the bottom microstructure of the repair zone is columnar dendrite,the center of the repair zone and the top microstructure of the repair zone are composed of columnar dendrite and equiaxed dendrite,and the fragmented Laves phase is distributed between the dendrites in the repair zone.Compared with the substrate,the number ofγ’phases in the heat affected zone decreases,and the MC carbides are decomposed to produce M₂₃C₆carbides.The hardness is about 291HV_0.3in the repair zone,and the hardness is about 321HV_0.3in the heat-affected zone.Furthermore,both of which are lower than the hardness of the substrate(361HV_0.3).The substrate has a friction coefficient of about 0.537,the repair zone has a friction coefficient of about 0.695.Compared with the repair zone,the wear rate of substrate is reduced by 52.1%.The substrate has better wear resistance.Aiming at the problem of large residual stress in the process of laser additive repair,the influence of preheating temperature on temperature field distribution was revealed by numerical simulation method,and the microstructure and properties test analysis of laser additive repair under substrate preheating conditions were carried out.The results show that the cooling rate of the molten pool is reduced with the preheating temperature increasing,and the temperature gradient of the sedimentary layer is also decreasing.Compared with the unwarmed specimen,the stress of the specimen in theσ_xdirection decreased by 30.9%and 37.1%in theσ_ydirection after preheating at 300°C.After the substrate is preheated,the Laves phase precipitated between the dendrites in the repair zone becomes thicker.The hardness of the repair zone after preheating is about 355HV_0.3,which is 18%higher than that of unwarmed.And after preheating,the wear rate and friction coefficient of the repair zone have been significantly reduced,and the wear resistance has been significantly improved.Aiming at the problem of insufficient enhanced phase precipitation in sedimentary microstructure,resulting in poor mechanical properties,the effects of different aging heat treatment temperatures on the microstructure and properties of laser additive repair were studied.It is found that after heat treatment,the Laves phase between the dendrites in the repair zone is gradually melted,and theγ′andγ′′phases begin to precipitate.When the aging temperature is 740°C,theγ′andγ′′phases are significantly coarsified,and the distribution is relatively uniform.The hardness of the repair zone is obviously increased after heat treatment.At the same time,with the increase of aging temperature,the hardness is increasing,and the wear rate and friction coefficient of the repair zone have been significantly reduced.When the aging temperature is 740°C,the wear rate is reduced by72.9%compared with the deposition state.The repair zone has good wear resistance.