Diffusion Bonding Of Titanium Alloy To Tin Bronze

In this paper,titanium alloy and tin bronze was bonded in the vaccum hot pressing furnace with or without Cu interlayer and Ni interlayer through diffusion bonding.After bonding,microhardness and shear strength test have been used to evaluate mechanical property of joint.Through scanning electron microscope,energy disperse spectroscopy and X-ray diffraction to observe and analyze microstructure of joint,reacted generation at interface and type of fracture,and expound upon diffusion mechanism.In directly diffusion bonding,main intermetallic compounds consist of CuTi₂,CuTi,Cu₆Sn₅ and CuSn₃Ti₅.Due to Sn of tin bronze diffuse to the joint which generate several IMCs,the Sn content of near weld zone in copper alloy side decrease,and form a 16?m thick tin deficiency area.The large difference of linear coefficient expansion between two base metals could lead to the generation of crack during the cooling process.Enhance pressure could reduce but not completely eliminate crack.At 850?,30min and 5MPa,thickness of diffusion area is 20?m,hardness is over400HV,and maximum shear strength is 52MPa.The type of fracture is brittle fracture,and plenty of IMCs is source of crack,CuSn₃Ti₅ is the weak area in the joint.Cu foil has high malleability which is advantageous to interface closely and improve the microstructure of diffusion bonding joint;meanwhile,Cu foil can prevent the Sn of tin bronze diffuse to the titanium alloy which reduces the kind and quantity of IMCs.Add Cu interlayer can improve the shear strength of joint.Main intermetallic compounds consist of CuTi₂,CuTi and Cu₄Ti₃ at Cu foil/titanium alloy side.The homogeneous atoms diffusion generates at Cu foil/tin bronze side,and no IMCs generate.When the parameter is 850?,30min and 5MPa,thickness of total diffusion zone at Cu foil/titanium alloy side is 13?m,including 1?m thick CuTi₂,8?m thick CuTi and 4?m thick Cu₄Ti₃,hardness of diffusion zone is over 400HV and maximum shear strength is 59MPa.When pressure is 1MPa,brittle fracture occur at Cu foil/tin bronze side because a lot of void occur in the interface between Cu foil and tin bronze.When pressure is 5Mpa,original interface at Cu foil/tin bronze side disappear to realize metallurgical bonding,and plenty IMCs of diffusion zone at Cu foil/titanium alloy side is the weak area.Ni interlayer can improve mechanical property.Liner coefficient expansion of pure nickel is between titanium alloy and tin bronze.It not only can prevent the Sn diffuse to the titanium alloy,but also reduce the residual stress during cooling process which can avoid the generation of cracks in diffusion zone.Main intermetallic compounds at Ni foil/titanium alloy side consist of Ni₃Ti,NiTi and NiTi₂.Original interface of Ni foil/tin bronze vanish and be replace by Cu-Ni solid solution and a little kirkendall void.Pressure is a important factor in diffusion bonding.At 850?and 30min,when pressure is 1MPa,joint cannot bond;when pressure is 2MPa,shear strength is 54MPa;when pressure is 5MPa,maximum shear strength is 107MPa.Under 5MPa pressure,mix fracture occurs at interface between Ni foil and Ni₃Ti IMC.Holding time has significant influence to microstructure and shear strength of diffusion bonding joint with Ni interlayer.At 850?and 5MPa,when holding time is15min,shear strength is 82MPa,only two IMCs?Ni₃Ti and NiTi₂?generate and total thickness is 4.5?m;when holding time is 30min,shear strength access peak,third IMCs?NiTi?generate and total thickness is 10?m.Then,as increase of holding time,thickness of Ni-Ti IMCs increase and shear strength decrease gradually.Product on interface of joint depends on the thermodynamics and dynamics in diffuse process.In Cu-Ti solid diffusion system,Cu atoms break the lattice binding earlier to solid solute into Ti atom.After Cu atom supersaturated solid solute in Ti atom,three Cu-Ti IMCs?CuTi₂,Cu₄Ti₃ and CuTi?generate successively.In Ni-Ti solid diffusion system,Ni atoms break the lattice binding earlier to solid solute into Ti atom.After Ni atom supersaturated solid solute in Ti atom,three Ni-Ti IMCs?Ni₃Ti,NiTi₂ and NiTi?generate successively.