Laser-Induced Superelasticity in NiTinol Stent Strut

Shape setting is a fundamental step of NiTi components manufacturing. It is undertaken for fixing programmed shapes and for optimizing both the shape memory and the superelastic properties of SMA. Conventional NiTinol shape setting is performed by constraining the material in furnace where it is heat treated completely, and thus local component functionalization is not allowed. Recently, it has been demonstrated the feasibility of fast laser shape setting of straight thin NiTinol wires to induce a superelastic behavior comparable to the commercial wires. This work reports the use of a laser beam for promoting a local superelasticity in a NiTi diamond-like strut. In details, the struts were cut from a cold worked NiTi thin tape, and then a focused laser heating was implemented just on the parts of the element in which the superelasticity is strictly required. Thermo-mechanical testing of the struts, after local laser process conditions, indicates that a laser beam scanning is suitable for provoking local microstructure modifications, which enables the superelastic functioning of the strut-like element. Scanning electron microscopy has shown that residual martensite variants, present in the cold worked material, disappear in the portion of the diamond elements where the laser beam passed.