Investigation On Properties And Brazing Connection Mechanism Of ZrO₂ Ceramic/Ti-6Al-4V Joints

The Yttria-stabilized Zirconia（YSZ）bioceramics have high hardness,high-temperature resistance,corrosion resistance,abrasion resistance,and good biocompatibility.However,its fracture toughness,impact resistance and thermal shock resistance are poor.While Ti-6Al-4V alloy has the characteristics of light weight,high strength,good tensile strength and toughness,and superior corrosion resistance.In addition,the coefficient of thermal expansion of Ti-6Al-4V alloy is close to that of YSZ ceramics.Therefore,brazed YSZ ceramics and titanium alloy components can be applied in the packaging of implantable neural micro-stimulator devices,which has a broad application prospects in the biomedical field.The research on high temperature active filler and interfacial reaction mechanism is the most important trend in the field of metal-ceramic brazing.This paper designed and prepared a new type active Ti-28Ni brazing filler foil and the wettability of Ti-28Ni filler metal on YSZ ceramics was investigated.The influence of vacuum brazing process parameters on the microstructure and properties of ceramic/Ti-6Al-4V alloy joint was researched.The interface reaction and joint formation mechanism were also analyzed.At the same time,in order to reduce the interfacial residual stress,YSZ ceramics and titanium alloys were brazed with Ti-28Ni/Cu/Ti-28Ni laminated brazing filler foil.The effect of Cu foil thickness on joint microstructure and properties were studied.The results are as follows:（1）The final contact angle of Ti-28Ni filler metal on YSZ ceramics is 73°when held at 1100℃ for 30min.Active Ti reacts with oxygen atoms in ZrO₂ to form a reaction TiO layer,which promotes the wettability under high temperature and high vacuum.（2）YSZ ceramic and Ti-6Al-4V alloy are successfully brazed by using Ti-28Ni and Ti-28Ni/Cu/Ti-28Ni filler metals.The interface microstructure of two joints are ZrO₂ ceramic/Ti₂O/Ni₂Ti₄O/Ti-rich phase/Ti₂Ni+α-Ti and ZrO₂ ceramic/Ti₂O/Ti₃O/Ti₆O/Cu₃TiO₄/Ti₂（Cu,Ni）/Ti-richlayer/Ti₂（Cu,Ni）/Ti₂Cu+α-Ti/Cu/Ti₂Cu+α-Ti/Ti-6Al-4V alloy respectively.The formation of Tix O（x=2,3,6）,Ni2Ti4O and Cu3TiO4 phases on the ceramic surface changes the state of the ceramic surface,which plays an important role in the joining of YSZ ceramics and Ti-6Al-4V alloys.（3）Brazing process parameters has a strong effect on joint properties.The maximum shear strength of the joint with Ti-28Ni filler metal is 112.7 MPa when held at 1060℃ for 10min.The joint exhibits brittle fracture.With the increase of holding time and brazing temperature,the diffusion of atoms in the brazing seam are accelerated.The Ti-rich layer gradual decreases and finally disappears,while the Ni2Ti4O layer tends to grow.（4）When using Ti-28Ni/Cu/Ti-28Ni laminated filler metal,the thickness of the copper foil has a significant effect on the joint properties.When the brazing temperature is 1060℃,the holding time is 15min and the Cu foil thickness is 80μm,the highest room-temperature shear strength of the joint is 130.5MPa.The joint strength shows an improvement of 51.9 MPa compared with that without Cu foil.When the thickness of Cu foil increases from 80μm to 120μm,due to the strong affinity of Cu and Ti atoms,a large amount of Ti₂Cu is produced in the interface of joint,which deteriorates the properties of the joints.And Ti₂Cu phase consumes a large amount of Ti atoms in the joint.The width of the Ti-rich layer gradually decreases.The fracture occurs in the Ti-rich and Ti₂（Cu,Ni）layers,and the joints show brittle cleavage fracture characteristic.