Study On Process And Mechanism Of Low Temperature Joining Of ZrO₂/TC4 With Bi-B-Zn Glass

Due to its natural brittleness,ZrO₂ ceramic is hard to be manufactured to large and complex components and integrated to complex systems.Joining ZrO₂ to metals is an effective way to solve the problem.TC4 alloy?Ti-6Al-4V?,the most widely employed titanium alloy,is well suitable for bonding with ZrO₂,due to their approximate thermal expansion coefficient.The joining of ZrO₂ ceramic and TC4 alloy shows the great application potential in the aerospace industry and dental implants.Now,active metal brazing has been widely used for joining ZrO₂ ceramic and TC4 alloy with Ag-Cu-Ti solder.However,there are some problems which restrict it's use,such as high temperature,high residual stress and high production cost.In view of the shortcomings of active metal brazing,joining Bi-B-Zn glass was used to connect ZrO₂ ceramics with TC4 alloy at low temperature in air atmosphere.The influence of joining parameters on the shear strength of the joints was studied.The effects of joining temperature and holding time on the microstructure of the joints were clarified.The interface between glass solder and zirconia ceramics and TC4 alloy was analyzed.The relationship among joining parameters,microstructure and mechanical properties of the joints was determined.Finally,the shear strength of ZrO₂ / TC4 joints under the optimal joining parameters was comparable the properties of the joints using commercial Ag-Cu-Ti solder,but the joining temperature was decreased from 870 ? to 500 ?.Firstly,the low-melting glass with Bi2O3: B2O3: Zn O = 35: 50: 15 was prepared by melt-quenching method.The glass transition temperature?Tg?of the glass was 355 ?,and the thermal stability??T?was 84 ?.The Bi-B-Zn glass showed amorphous state.Before joining ZrO₂ and TC4,the surface of TC4 alloy was pre-oxided for proving the wettability of Bi-B-Zn glass solder and the interface adhesion between glass solder and TC4 alloy.The joining of ZrO₂/TC4 was carried out from 420 to 520 ?.The shear strength of ZrO₂/TC4 joints increased firstly and then decreased with the increasing of the joining temperature.When the joining temperature was 500 ?,the shear strength of the joints had a maximum value of 48.75 MPa.When the joining temperature was higher than 440 ?,Bi4B2O9,Bi2O3 and Bi24B2O39 were crystallized in the joints.The constant of crystallization phase which resulted in the joint strengthening increased with the increasing of the joining temperature.When the joining temperature was lower than 440 ?,the joint with little crystallization phase exhibited low shear strength.During the joining processing,Ti element in the oxide layer of TC4 alloy diffused into the glass solder in the interface of TC4/Bi-B-Zn glass solder formed Bi4Ti3O12,which enhanced the interface bonding.There was no element diffusion between ZrO₂ and Bi-B-Zn glass solder,so ZrO₂ and glass were bonded by van der Waals force,and ZrO₂/glass interface became the weak position of the joints.Therefore,the shear strength of joints increased with the increasing of the temperature from 440 ? to 500 ?,which was ascribed to the increase of the actual contact area between glass solder and ZrO₂ ceramic.However,the joint strength obviously deteriorated due to the increased of the joint porosity.The relationship between joints strength and holding time was similar to that of joint temperature,but the influence was no significant.