Research On Process And Mechanism Of Transiet Liquid Phase Bonding Of Gh4169Alloy And Post-weld Heat Treatment

In order to meet the demand of actual project subject of bonding hollow turbindisks, transient liquid phase bonding of GH4169superalloys was carried out in thispaper. Respectively using BNi2interlayer and self-made interlayer, the interfacialmicrostructure of joints was analyzed by means of scanning electron microscope(SEM), energy dispersive x-ray detector (EDS) and X-ray diffractometer (XRD). Theeffect of parameters on microstructure and mechanical properties was investigated,and the mechanism of transient liquid phase bonding of GH4169superalloy wasdiscussed. Post-weld heat treatment was carried out on the joints, and the effect oninterfacial microstructure and mechanical properties was investigated. The affectingmechanism of post-weld heat treatment was also analyzed.Transient liquid phase bonding was carried out with BNi2interlayer. Interfacalmicrostructure was mainly analyzed. Common joints consisted of isothermalsolidification zone and precipitates diffusion zone. Small Ni-Si-Nb ternaryprecipitates were observed at the grain boundaries near the center line. Cr-rich andCr-Mo-Nb borides with different morphologies were observed in the diffusion zone.With increasing the bonding temperature or diffusion time, the size of Ni-Si-Nbternary precipitates increased. The ternary precipitates became continuous and theborides became more disperse. Improved processes were tried to control the reactionproducts in the joints. Many precipitates could be seen in the high temperaturebonding/low temperature diffusion joints. With increasing the diffusion time,precipitates could be reduced but not be eliminated. There was no obviouslyimproving impact in the initial period. The amount of precipitates in the Lowtemperature bonding/high temperature diffusion joints was significantly reduced. Theprecipitates disappeared when increasing the diffusion temperature to1180℃. Jointswith homogeneous structure were obtained. Good results were received bycontrolling in the later period.The effect of parameters on mechanical properties of joints with BNi2interlayerwas investigated. A tendency of firstly increased and finally reduced was observedduiring the changing of tensile strength of common process bonding joints. Biggesttensile strength of1074MPa was obtained at1050℃and120min, which was93.4%of the welded base metal. The fracture mainly occurred at diffusion zone, and theplastic property of the joints was poor. The low temperature diffusion time had littleeffect on the tensile strength of the joints. The highest tensile strength was603MPawhen the low temperature diffusion time was240min. Brittle fracture occurred at welded seam. The diffusion temperature significantly affected the low temperaturebonding/high temperature diffusion joints. The elongation percentage of the jointswas35%when the diffusion temperature was1180℃. Synchronism deformation oftransient liquid phase bonding joints and base metal was observed.Ni-Cr-Fe-Si-B interlayer with a same mass ratio of Ni, Cr and Fe to GH4169superalloy was self-made. The melting point reducing elements and strengtheningelements were determined as B(2%), Si(4%), Nb(5.1), Mo(2.9), Ti(0.9)(wt.%). Theeffect of parameters on microstructure and properties of GH4169superalloy jointsbonded with self-made interlayer was analyzed. Microstructure of common processbonding joints consisted of small Ni-Si-Nb ternary precipitates and borides. Bondingtemperature had a more significantly effect on the microstructure. Due to manyprecipitates existing in the joints, the tensile strength was low and the plasticproperty was poor. Excellent uniformity of the structure was achieved when bondingwith low temperature bonding/high temperature diffusion process. The property wasbetter than that of the joints bonded with BNi2interlayer, and the elongationpercentage was more than50%.Effect of post-weld heat treatment on interfacial microstructure and mechanicalproperties was investigated in order to improve the joining quality. Ni-Si-Nb ternaryprecipitates appeared in the isothermal solidification zone of the joints bonded withBNi2interlayer. A few Cr-Mo-Nb borides precipitated in the joints bonded with Ni-Cr-Fe-Si-B interlayer. The latter joints were purer. The tensile strength of lowtemperature bonding/high temperature diffusion joints was obviously increased bypost-weld heat treatment. The tensile strength of1050℃/60min+1180℃/60min(BNi2)joints was1130MPa,92.6%of that of the base metal, and the elongation percentagewas5%~7%. Elevated temperature strength of that joint was850MPa with anelongation percentage of5%. The strength of1150℃/60min+1185℃/60min(Ni-Cr-Fe-Si-B) joints was1075MPa,93.8%of the strength of base metal, and theelongation percentage was10%. Elevated temperature strength of this joint was alittle lower than the former, but the fracture occurred from weld line to base metal.The elevated temperature strength reached to more than95%of base metal, with theelongation percentage maintaining at10%.The above two kind of joints after post-weld heat treatment could both satisfiedthe request of this subject. A more puer interfacial microstructure with excellentmechanical properties could be obtained using Ni-Cr-Fe-Si-B interlayer. It is moreappropriate to achieve this subject by the self-made Ni-Cr-Fe-Si-B interlayer.