Effect of CO2 laser welding on the shape-memory and corrosion characteristics of TiNi alloys

A CO2 laser has been employed to join binary Ti50Ni50 and Ti49.5Ni50.5 shape-memory alloys (SMAs), with an emphasis on the shape-memory and corrosion characteristics. Experimental results showed that a slightly lowered martensite start (M-S) temperature and no deterioration in shape-memory character of both alloys were found after laser welding. The welded Ti50Ni50, With an increased amount of B2 phase in the weld metal (WM), had higher strength and considerably lower elongation than the base metal (BM). Potentiodynamic tests revealed the satisfactory performance of laser-welded Ti50Ni50 in 1.5 M H2SO4 and 1.5 M HNO3 solutions. However, the WM exhibited a significantly higher corrosion rate and a less stable passivity than the BM in artificial saliva. On the other hand, the pseudoelastic behavior of the laser weld was investigated only for the Ti49.5Ni50.5 alloy, to facilitate tension cycling at room temperature. The cyclic deformation of Ti49.5Ni50.5 indicated that the stress required to form stress-induced martensite (sigma (m)) and the permanent residual strain (epsilon (p)) were higher after welding at a given number of cycles (N), which were certainly related to the more inhomogeneous nature of the WM.