Effects of silver based filler metals on microstructure and properties of laser brazed joints between TiNi shape memory alloy and stainless steel

Abstract

The effects of silver based filler metals on the microstructure and properties of laser brazed joints between TiNi shape memory alloy (SMA) and stainless steel (SS) have been investigated and potentially desirable filler metal has been demonstrated. All of the filler metals, Ag–20Cu–12Zn, Ag–20Cu–16Zn–5Sn and Ag–22Cu–18Zn–8Sn filler metals, have good wettability on SS but Ag–20Cu–12Zn and Ag–20Cu–16Zn–5Sn filler metals exhibit worse wettability on TiNi SMA. The laser brazed joints using three different filler metals primarily consists of a α-Ag solid solution, a 9 αα-Cu solid solution and eutectic structures but the phase composition of the joint using Ag–20Cu–12Zn filler metal is a little different from that using other two filler metals. Part of the two base metals melts and enters the brazing seams during laser brazing when the joints were brazed with Ag–20Cu–12Zn and Ag–20Cu–16Zn–5Sn filler metals but only part of SS melts when the joint was brazed with Ag–22Cu–18Zn–8Sn filler metal. The tensile strength of the laser brazed joint using Ag–22Cu–18Zn–8Sn filler metal, superelasticity and shape memory effect of TiNi SMA in the heat affected zone are obviously higher than those using other two filler metals. From the standpoint of wettability on TiNi SMA and SS, as well as the microstructure and properties of the laser brazed joint, Ag–22Cu–18Zn–8Sn filler metal shows potential for application in comparison with the other two filler metals.