Modifications of subsurface microstructure of NiTi shape memory alloys for improvement of fatigue performance (NITISURF)

The project aims at improving thermomechanical fatigue performance of NiTi components via purposeful modification of their surface. Basic strategy will be to employ several different approaches including selective thermomechanical treatment of subsurface layers using background knowledge developed in the past, Ion Implantation into surface, laser surface processing and stretchable surface coatings. In order to suppress nucleation of fatigue cracks in the excessively deforming surface exposed to the combination of mechanical and chemical attacks in service, we will modify the subsurface microstructure and introduce oriented residual stresses into the surface layer without destroying its ability to transform martensitically in cyclic thermomechanical loads and sustain large cyclic deformations without cracking. Main impact of the project results is anticipated in the area of superelastic medical devices (NiTi stents, catheters, orthodontic wires), and NiTi actuators in transport, space, robotics sectors or elastocaloric cooling applications. The project aims at improving fatigue performance of superelastic NiTi components by modifying microstructure of its subsurface layer and introducing internal residual stress without destroying its ability to sustain large reversible strains in cyclic thermomechanical loads in service.