The Effect Of Transient Liquid Phase Bonding On Microstructure And Mechanical Properties Of Mar-M247 Nickel-based Superalloys Joints

Mar-M247 alloy belongs to as cast nickel based superalloy which owns high thermostability,oxidation resistance and corrosion resistance.It is the key materials to produce the high temperature components in gas turbine in aviation and energy fields.Welding is often applied to Mar-M247 due to the demand of manufacturing and repairing.The welding joints by present used fusion welding often show welding crack and other welding defects.The welding cycle is also very long and the welding efficiency is also very low.In order to solve these problems,transient liquid phase(TLP)bonding is introduced to join Mar-M247 nickel based superalloy.The home-made Ni-Cr-Co-W-Ta-B amorphous foils and commercial Ni-Cr-B amorphous foils were chosen as the interlayer when TLP bonding of Mar-M247 nickel based superalloy in this paper.The microstructure of joints was analysized by means of optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction(XRD),and the mechanical properties of the specimens were tested in Vickers hardness tester and tensile test machine.The effect of TLP bonding parameters on the microstructure and mechanical properties of Mar-M247 nickel based superalloy joints were investigated.When TLP bonding Mar-M247 with the Ni-Cr-Co-W-Ta-B interlayer,the bonding temperatures were chosen as 1090?,1120?,1150? and 1180?.The holding times were chosen as 1min,60 min,120min and 240 min.When bonding at 1150? for 240 min,the joints had completed isothermal solidification.The joint was consisted of isothermally solidified zone,diffusion zone and base metal.The athermally solidified zone were removed.The mechanical properties of joints showed that the minimum hardness value of 297.0 HV was achieved on the ? phase solid solution in the bond centerline area.The maxium tensile strength of joint was 443.0 MPa.The fracture occurred around the bond centerline area,and it showed ductile failure on the fracture surface.When TLP bonding Mar-M247 with the Ni-Cr-B interlayer,the bonding temperatures were chosen as 1090?,1120?,1150? and 1180?.The holding times were chosen as 1min,10 min,30min and 60 min.When bonding at 1150? for 60 min,the joints had completed isothermal solidification.The mechanical properties of joints on this condition showed that the minimum hardness value of 259.6 HV was achieved on the ? phase solid solution in the bond centerline area.The ultimate tensile strength of joint was 845.0 MPa,the yield strength was 713.0MPa and the elongation was 11.5%.The fracture occurred around the base metal,and it showed ductile failure on the fracture surface.When bonding temperature and holding time were defined,the complicated elements interdiffusion resulted from introducing more base metal alloying elements in the Ni-Cr-Co-W-Ta-B interlayer made the isothermal solidification rate slower compared with TLP bonding by using Ni-Cr-B interlayer.It also took a longer time to complete isothermal solidification.When the interlayer and holding time were defined,the mechanical properties of joints increased at first,and then decreased with the increase in bonding temperature.The joints had best performance whrn bonding at 1150 ?.When interlayer and bonding temperature were defined,the athermally solidified zone transformed to isothermal solidified zone with increase in holding time.The melting point depressant element B diffused from the interlayer to base metal,and formed boride precipitates in the diffusion affected zone.It had a difference in required time for complete isothermal solidification by using the transient liquid phase bonding kenetics model and by conducting experiments.In the theorectical model,the required time for complete isothermal solidification mainly depended on the diffusivity of B element,while the diffusivity of B element mainly depended on bonding temperature.By experimental analysis,bonding temperature not only influenced the diffusivity,but also influenced concerntration gradient and solid solubility simultaneously.The interdiffusion between base metal alloying elements and B and the precipitates in grain boundaries also influenced the diffusion coefficient of B.