Today, Ni-Ti alloys are used as functional materials in numerous industrial sectors such as aerospace, automotive engineering, medical technology and consumer goods. Their special properties in terms of shape memory effect and superelasticity offer a great potential for the development of innovative smart products. However, the traditional forming and machining of these alloys into concrete products poses a decisive challenge. Assembling plain structures by laser welding to obtain a desired complex product shape offers an economical alternative in many cases, but is associated with negative effects of the welding heat on the material’s microstructure.

Against this background, experimental investigations on laser welding of Ni55/Ti45 foil with a thickness of 125 µm by means of a fibre laser were carried out, supported by methods of Design of Experiments. Such foils are important, for example, for reconfigurable systems such as mobile phone antennas or temperature-sensitive actuators. The influences of laser power, welding speed, focus position and beam oscillation on the microstructure in the weld seam and heat-affected zone were analysed, together with the mechanical characteristics of the welded joints. In particular, the effect of an oscillation on the laser beam was investigated for the first time for the welding of a Ni55/Ti45 alloy, in which an oscillating transverse movement is additionally superimposed on the laser beam feed movement. Due to the very low thickness the preparation of the foils for the microstructure characterization is quite challenging. Best results were obtained by ion milling. The fracture surfaces as well the influence of the welding on the transformation temperature were also investigated.