Interfacial Microstructure And Mechanical Properties Of TZM/Ti₂AlNb Diffusion Bonded Joint

Titanium-Zirconium-Molybdenum(TZM)alloy,one of the most typical molybdenum alloys,has excellent high temperature properties and has been successfully used in aerospace,nuclear,electronics and military industries.However,TZM alloy has the disadvantages of high density,high temperature oxidation resistance and poor toughness.Ti₂AlNb alloy is a high-temperature alloy with low relative density,good fracture toughness and strong oxidation resistance.Therefore,the successful connection of the two to obtain TZM and Ti₂AlNb composite components to fully use the high temperature resistance of TZM and the low density and oxidation resistance of Ti₂AlNb,further promote the application of molybdenum alloy and titanium alloy in the aerospace field.In this paper,diffusion bonding was applied to join TZM and Ti₂AlNb alloys.The effects of different process parameters on microstructure and mechanical properties were studied.Controlling the structure and mechanical properties of the joint by with and without Ni and Ni/Nb foil.The effects of different process parameters on the microstructure and mechanical properties were analyzed.The interfacial reaction mechanism of diffusion bonding was studied.The effects of different diffusion bonding temperatures on the joint were investigated by direct diffusion bonding of TZM and Ti₂AlNb alloys.The highest shear strength(240MPa)was obtained at 950°C-60min-20MPa.The residual stress of the joint was 347MPa.The diffusion layer thickness of TZM/Ti₂AlNb joints was studied by Fick's Law.The kinetic equation of diffusion layer growth was established.The Ni interlayer diffusion bonding TZM and Ti₂AlNb alloy were used.The typical structure of the joint was:TZM/Ni Mo+Ni₃Mo/Ni₄Mo/Ni/Ti Ni₃/Al Ni₂Ti+Ti₃Ni₄+(Ti,Ni,Nb)phase/Ti₂Ni+B2(Ni)/Ti₂AlNb.The diffusion bonding process can be divided into a physical contact phase,a solid-liquid diffusion phase,a diffusion layer thickening phase,and a cooling solidification phase.The highest shear strength of the joint obtained at 950°C-60min-20MPa-60?m Ni was 340MPa.The thickness of the Ni interlayer was increased,and the residual stress of the joint was lowered from 316MPa to 78MPa.The fracture mainly occurred at the hard and brittle Ti₂Ni compound in the joint.In order to eliminate the continuous Ti–Ni reaction layer in the joint,the Ni/Nb composite interlayer was used to diffuse the TZM and Ti₂AlNb alloy.the Nb foil acted as a barrier layer,which blocked the diffusion of Ni and Ti₂AlNb.The typical structure of the joint at this time was:TZM/Ni Mo+Ni₃Mo/Ni₄Mo/Ni/Ni₃Nb/Ni₆Nb₇/Nb/B2/Ti₂AlNb.With the increase of diffusion temperature,the thickness of each reaction layer increased continuously.The room temperature shear strength of the joint increased with the increase of diffusion temperature,and increased first and then decreased with the increase of holding time.The maximum room temperature shear strength was 422MPa at 950°C for 90min under 20MPa.The joint fracture occurred in the Mo-Ni reaction layer close to the base material.The shear strengths measured at500°C and 650°C were 298MPa and 212MPa,respectively,and joint fracture occurred in the Mo-Ni reaction layer and the remained Ni foil and Nb foil,respectively.