Study On Technique And Microstructure Of Ultrasonic-assisted Brazed Joint Between Zirconia And Titanium Alloy

Zirconia has been widely applied in many fields as its high hardness,high wear resistance,and good biocompatibility.Meanwhile,the good properties of Ti-6Al-4V,such as high specific strength,high toughness,and high corrosion resistance,have attracted many people’s attention.However,it is still diffficult to weld zirconia and titanium to utilize the advantages of them since the huge difference of coefficient of linear expansion between zirconia and titanium.In this paper,a new method based on ultrasonic was proposed to solve this problem with pure Al or Al-5Si filler.Results of the experiments showed that with the increase of ultrasonic time,ultrasonic power,and temperature,the average value of bonding ratio of joint and the shear strength of joint increased,then fall slightly.When ultrasonic time was 20 s,ultrasonic power was 180 W,and temperature was 700℃,the average value of bonding ratio of pure Al joint reached 93.24% and the average value of shear strength of pure Al joint was 92.83 MPa.For Al-5Si filler,the average values of bonding ratio of joint and the shear strength of joint were 92.49% and 90.68 MPa,respectively.When ultrasonic time was 20 s,ultrasonic power was 180 W,and temperature was 700℃,a new phase Ti Al3 was found at the boundary of Ti-6Al-4V and pure Al and some ZrO₂ flocs were also found at the boundary of ZrO₂ and pure Al.Unlike pure Al,at the boundary of Ti-6Al-4V and Al-5Si,needle-like Ti7Al5Si12 and bulk Ti（Al,Si）3 were found.It should be noted that Ti7Al5Si12 grew to the Ti-6Al-4V with the increase of ultrasonic time.Through the analysis of the morphology of brazing seam and the test of the joints,the formation mechanism of Ti Al3 in pure Al brazing seam,including four steps,was established.Step one to four were formation of Ti Al,Ti2Al5,Ti Al3 and Al-rich,and Kirkendall voids,respectively.In Al-5Si brazing seam,needle-like Ti7Al5Si12 formed at first,and then with the diffusion of Si atom furtherly,bulk Ti（Al,Si）3 formed at the surface of Ti-6Al-4V.The formation mechanism of ZrO₂ floc included two steps: wetting and spreading of Al-based filler and the formation of ZrO₂ floc.To analyze the properties of joint more furtherly,some fracture tests were conducted.The results indicated that both fracture types of pure Al joint and Al-5Si joint were ductility fracture.