Effect of high energy argon implantation into NiTi shape memory alloy

The super-elastic properties of NiTi alloy are used for several medical applications in dentistry, such as orthodontic wires (useful to correct the dental position), palatal expanders and endodontic instruments. Implantation process may be one solution to enhance the surface properties, corrosion, wear and fatigue resistance, of such instruments. A previous work, for which implantations were performed with N+ and B+ ions at 150 keV, has shown that the hardening mechanism is due to the formation of an amorphous layer whose thickness increased with dose in the near surface region. In this paper, in order to increase the treated thickness, especially the amorphous layer, argon implantations at high energy (1.5 MeV) have been performed. The structural modifications have been observed with Grazing Incidence X-ray Diffraction (GIXRD), as a function of Ar+ dose. The processes involved in the crystalline to amorphous phase transformation of NiTi under ion beam irradiation have been particularly investigated. Characterisation of the near surface composition was made by Rutherford Backscattering Spectroscopy (RBS). Nanoindentation tests have been used to study the evolutions of hardness and elastic modulus through the treated thickness after implantation.