Laserwelding of microwires made of nickel-titanium shape memory alloys and austenitic steel

The special properties of nickel-titanium shape memory alloys are currently used in micro engineering and medical technology. In order to integrate nickel-titanium components into existing parts and modules, they often need to be joined to other materials. For this reason, the present contribution deals with the laser welding of thin pseudoelastic nickel-titanium wires (100 mu m) with a neodymium-doped Yttrium Aluminium Garnet laser. Based on extensive parameter studies, joints without defects were produced. This study deals with the microstructure in the fusion and heat-affected zones, the performance of the joints in static tensile tests and their functional fatigue. It can be shown that nickel-titanium/nickel-titanium joints reach about 75% of the ultimate tensile strength of pure nickel-titanium wires. In case of welding nickel-titanium to steel no interlayer was used. The dissimilar nickel-titanium/steel joints provide a bonding strength in the fusion and heat-affected zones higher than the plateau stress level. Nickel-titanium/steel joints of thin wires, as a new aspect, enable the possibility to benefit from the pseudoelastic properties of the nickel-titanium component.