Study On Diffusion Bonding Of Mo-base Refractory Alloy And Ni-base Superalloy

With the development of the aviation industry,the demand for high-temperature structural components is increasing.It is of practical significance to connect a high melting point,high strength molybdenum alloy and a nickel-based superalloy GH4099with a high temperature and corrosion resistant,It is not only can decrease the brittleness of molybdenum alloy,and make the joint have good comprehensive mechanical properties,but also can improve the high temperature strength of the welded joint and increase the usage range.Diffusion welding has the characteristics of small welding deformation and wide welding range.Due to the large difference in physical properties between the two materials,it is difficult to achieve effective connection by traditional fusion welding methods.Therefore,Therefore,the weldability of small-sized samples was studied by the Gleeble thermal simulated method.The suitable intermediate layer materials were chosen.Then the weldability of large components was studied by using Hot Isostatic Pressing(HIP)equipment.The addition of Cu middle layer is used to join molybdenum alloy Mo10Cu and nickel-based superalloy GH4099 by HIP diffusion welding method.The molybdenum alloy MHC and nickel-based superalloy GH4099were joined by HIP or thermal simulated diffusion welding method by the choice of middle layers Cu,Ag Cu Ti,Ti Zr Cu Ni,Ni Cr Si B,B-Ni2 solder and Nb+Ni.The influence of the type of intermediate layer and the change of temperature on the mechanical properties of the welded joint were investigated by characterization of the joint microstructure and element diffusion.Based on the characterized results,the optimal intermediate layer type and welding process parameters were obtained.By PVD(physical vapor deposition)electroplating of Cu film on the surface of Mo10Cu,Mo10Cu and GH4099 can be joined by the HIP diffusion joining.The weld is mainly composed of copper-nickel solid solution and pure copper,and the joint has good mechanical properties.It is found that the copper content of 10%in Mo10Cu has a large effect on weldability.The effective diffusion of Cu in base metaland Cu in intermediate layer is the main reason for the connection.The thickness of the intermediate layer controls the formation of copper-nickel solid solution.The experimental results show that the electroplated Cu film cannot achieve the connection between MHC and GH4099 as an interlayer,so the other intermediate layer will be chosen.When the Ag Cu Ti intermediate layer is used to join MHC and GH4099 by HIP diffusion welding method,the welding temperature of the Ag Cu Ti intermediate layer is relatively low,but the diffusion of elements to the base materials on both sides is very little.At the same time,the brittle phase Ti₂Ni at the joints aggregates,which results in extremely low joint strength.When Ti Zr Cu Ni intermediate layer is used to join MHC and GH4099 by HIP diffusion welding method,the welding temperature has a great effect on the mechanical properties of the joint.At a peaking temperature of 950?and a holding time of 10 minutes,the shear strength of 71 MPa can be obtained.But the cracks in the weld are the main reason for joint failure.When Ni Cr Si B foil intermediate layer is used to join MHC and GH4099 by thermal simulated diffusion welding method,,the shear strength of the joint can reach 116MPa.The microstructure of the weld is a?-Ni-based solid solution.The joint is mainly fractured at the MHC base material,and a small part occurs at the intermediate layer.The Mo Ni brittle phase in the weld weakens the joint strength.The main cause of joint failure is the stress concentration of the MHC base metal.B-Ni2 solder with similar component and Ni Cr Si B foil is used to join MHC and GH4099 by vacuum brazed diffusion method at 1050?The weld is composed of an isothermal solidification zone and a non-isothermal solidification zone.The isothermal solidification zone is composed of Ni-based solid solution.The non-isothermal solidification zone is mainly composed of Ni3B,precipitated phase Ni3Si And the Mo Ni brittle phase also appears near the interface of the MHC side.In view of the high service temperature of welded joints,the introduction of an Nb+Ni intermediate layer aims to improve the high temperature strength of the joints.The diffusion welding method is used to firstly connect Nb and MHC at 1300?,and then to achieve(MHC-Nb)/Ni/GH4099 HIP diffusion connection at 1000?by adding a pure Ni intermediate layer.Since Nb and Mo are infinitely solid solution,the required activation energy for diffusion of elements is large.The shear strength of MHC/Nb joints is only 41 MPa when welding at 1300?.The Nb/Ni/GH4099 joint has good weldability.The tensile strength of welded joints joinedat 1000?for 1 hour can reach 260MPa.Therefore,it is crucial to improve the strength of the MHC-Nb diffusion connection for improving the strength of the joint.