Microstructure and Properties of Laser Deposition Repair of GH738/K417G Superalloy
The laser deposition repair test of K417G high-temperature alloy was conducted by using GH738 high-temperature alloy powder,and the laser deposition repair test of K417G high-temperature alloy was conducted by using LDM4030 laser coaxial powder feeding additive manufacturing equipment,and the causes of cracks in the deposited layer were analyzed and the laser process parame-ters were optimized.Heat treatment of the repaired specimens of high-temperature alloys was necessary to meet the performance re-quirements,so the mechanical properties of the repaired specimens could be tested only after the standard aging heat treatment,which was carried out by GSL-1400X tube vacuum furnace.The microstructure and hardness of the repaired specimens before and after the aging heat treatment,as well as the frictional wear properties of the heat treated specimens,were studied.The microstructure of the specimens was observed using an OLYMPUS-BX53M optical microscope and an energy dispersive spectrometer equipped S310 scan-ning electron microscope,and the hardness was tested in the cross-section of the specimens along the deposition height direction using an HVS-1000A microhardness tester;the frictional wear properties were tested using a BMMW-1A Universal friction and wear tester was used for friction and wear performance testing.Based on the principle of similar thermal property parameters of laser deposited re-pair materials,and in order to improve the wear resistance of the repair area,a material with higher hardness than K417G alloy should be selected for repair;the hardness of GH738 alloy is not only higher than that of K417G alloy,but also has similar melting point and thermal expansion coefficient with K417G alloy,so GH738 alloy was selected as the repair material for K417G alloy.Therefore,GH738 alloy was chosen as the repair material for K417G alloy.The laser process parameters were optimized by orthogonal experimen-tal method and the principle of heat input and aspect ratio,and the optimal single-pass process parameters were obtained:laser power was 700 W,scanning speed was 8 mm·s-1,powder feeding speed was 4.4 g·min-1,and the optimal lap rate of 40％and optimal layer height of 0.24 mm were obtained through lap rate and layer height optimization test;it was found that the cracks in the deposited layer belonged to liquefied cracks,and the formation of liquefied cracks was related to the heat input amount,so the heat input amount as one of the bases for parameter optimization.After the aging heat treatment,the specimens were analyzed for organization,hardness and friction wear properties,and the results showed that the organization of the repair zone in the deposited state consisted of epitaxial-ly grown columnar dendrites and equiaxed crystals,with the dendrite size of about 2 μm,and the columnar dendrite organization at the bottom of the repair zone was perpendicular to the horizontal direction of the substrate and grew continuously through different de-posited layers toward the deposition height,and the columnar crystals in the middle appeared deflected in the restoration area,the top part of the columnar dendritic tissue was perpendicular to the horizontal direction of the matrix,and the central columnar crystal was deflected.The size of γ'phase in the matrix was about 750 nm,while γ'phase in the heat-affected zone is refined,the size was re-duced,about 500 nm,and the number of γ'phases increased;the content of carbide was also increased and the size was relatively re-duced,and the content of eutectic phase was also reduced.After aging heat treatment,the average size of dendrites reached 13 μm by growth consolidation,and the contact of dendrites with different orientations in the organization of the restoration zone occurred during the growth process to form new grain boundaries and grains,and the grain boundaries of the newly formed equiaxed crystals were ex-tremely obvious;the precipitation of γ'phase and carbide in the restoration zone increased significantly,and the size was uniform and distributed diffusely in the restoration zone,and carbide precipitated continuously on the newly formed grain boundaries The carbides were distributed in a chain-like manner.The average hardness of the deposited state matrix was HV0.3 360.84,the average hardness of the heat-affected zone was HV0.3 409.57,and the average hardness of the repaired zone was HV0.3 330.92;the hardness of the repaired zone in the deposited state gradually decreases along the deposition height direction.The average hardness of the matrix in the aging heat treatment state was HV0.3 386.58,the average hardness of the heat-affected zone was HV0.3 425.37,and the average hardness of the repair zone was HV0.3 446.58;the average hardness of the repair zone after the aging heat treatment was increased by HV03 115.66,which was 15.5％higher than that of the matrix,indicating that the aging heat treatment could effectively improve the hardness of the repair zone.The main wear mechanism of the base body was abrasive wear,adhesive wear and oxidation wear,and the average friction coefficient was 0.69;the wear mechanism of the repaired zone in the age heat treatment state was mainly light abrasive wear and oxida-tion wear,and the average friction coefficient was 0.38;the friction coefficient of the repaired zone in the age heat treatment state was only 55％of that of the base body,which indicated that the repaired zone in the age heat treatment state had better wear resistance than the base body.The innovation of this paper was to use GH738 high-temperature alloy powder to repair K417G high-temperature alloy by laser deposition,which provided a new idea and a reasonable reference for repairing damaged parts of K417G high-temperature alloy.
NETL
NSTL
万方数据
