Corrosion behavior of the laser-brazed joint of TiNi shape memory alloy and stainless steel in artificial saliva

A laser brazing has been employed to join TiNi shape memory alloy (SMA) and stainless steel (SS) using the silver-based filler metal with composition of 52%Ag, 22%Cu, 18%Zn and 8%Sn (wt%). The corrosion behavior of the laser-brazed joint in artificial saliva was investigated using immersion and electrochemical tests. TiNi SMA, SS, and the filler metal were used for comparison. Experimental results showed that the corrosion resistance of the laser-brazed joint is better than that of the filler metal and is nearly close to that of TiNi SMA base metal though it is markedly lower than that of SS base metal. The corrosion resistance of all the specimens in artificial saliva depends on the pH values of the solutions. The lower the pH values of the solutions, the higher the corrosion mass loss rate, the lower the corrosion potential and the higher the current density of the specimens. Both SS and TiNi SMA emerge the characteristics of localized or pitting corrosion while the filler metal shows the characteristics of uniform corrosion. The brazing seam and the interfaces between the base metals and the filler metal of the joint might be the preferred locations for corrosion. The tensile strength and shape memory effect of the joint have been slightly influenced by corrosion, which is favorable to the application of the laser-brazed joint of TiNi SMA and SS in orthodontics clinics.