| TZM（Titanium-Zirconium-Molybdenum）alloy has been used to manufacture rocket engine nozzle due to its high temperature strength,but the toughness of TZM is weak.Nb-Zr alloy has been used in aerospace field due to its low density,high temperature strength and excellent toughness.Therefore,the successful connection between TZM and Nb-Zr alloy will be of great significance to the manufacture of components with high strength and good toughness.Until now,the study on connection of TZM and Nb-Zr is limited.Besides,Mo-Nb is an immiscible system and it is difficult to connect them successfully using directly diffusion bonding.Thus,Ni interlayer was used in this paper to diffusion bond and contact-reactive braze TZM and Nb-Zr alloy.Besides,a new bonding technique was developed（called liquid metallic film bonding）to promote the diffusion between base material elements,eliminate intermetallic compounds and improve the joint mechanical properties.In this paper,SEM,TEM,and shear tests were used to analyze the interfacial microstructure and mechanical properties of the joints and the effects of bonding parameters on microstructure and properties was studied.Moreover,simulation and calculation were used to analyze the joint residual stress,interfacial energy and the energy barrier of elements diffusion.It was found that when Ni interlayer was used to diffusion bond TZM and Nb-Zr alloy,compared to directly diffusion bonding,the bonding temperature was decresed from 1100°C to 1000°C and the maximum value of joint residual stress was decreased from 708MPa to 408MPa.NiMo,Ni3Mo+Ni4Mo,Ni8Nb,Ni3Nb,Ni6Nb7 diffusion layers were formed in the TZM/Ni/Nb-Zr diffusion bonded joint and the maximum shear strength,264MPa,was obtained when bonded at 1100°C holding for 30min under pressure of 10MPa with 45μmNi interlayer.Moreover,the fracture was mainly occurred on NiMo and Ni6Nb7 layer.To improve the joint microstructure,brazing was used to bond TZM and Nb-Zr alloy according to the contact-reaction between Ni and Zr.It was found that Ni10Zr7、NiZr and NiZr2 were formed in the joint,which was related to the 60%reduction of interface energy after reaction.With the change of parameters,the distribution of Ni10Zr7,the amount of Nb and the thickness of Ni-Zr compounds changed thereupon.The maximum shear strength,345MPa,was obtained when brazed at 1200°C holding for 30min and with 120μm Ni interlayer.The fracture occurred along brittle Ni10Zr7 compounds.To eliminate intermetallic compounds in the joint,liquid metallic film bonding was used to bond TZM and Nb-Zr alloy with Ni interlayer.A transient pressure was applied to force the liquid out of the joint when liquid phase was completely formed.As a result,there were almost no intermetallic compounds in the joint.Due to the dissolution of Ni into TZM and Nb-Zr alloy,diffusion energy barrier of Nb in Mo and that of Mo in Nb was reduced by 0.2eV and 0.1eV,and the diffusion distance between Mo and Nb reached 10μm.The joint shear strength obtained at 1200°C for 30min was508MPa and after 600°C,800°C high temperature shear tests,545MPa and 523MPa was obtained.Besides,the applicability of this bonding technique was proved on Mo/Cu and Nb/Cu immiscible systems. |
