Repetitive Nanosecond Laser-Induced Oxidation and Phase Transformation in NiTi Alloy

NiTi shape memory alloys, known as Nitinol, are highly valuable in medical fields for their unique attributes, including superelasticity, wear resistance, and biocompatibility. Laser treatment provides precise control over surface characteristics, enhancing biocompatibility. This study focuses on the effects of laser irradiation on NiTi alloy surfaces, particularly considering the number of laser scans and their impact on surface features. Even at low laser power, multiple high-frequency scans significantly alter surface roughness and induce phase transformation. After 16 repeated laser irradiations, amorphous Ti oxide transforms into crystalline anatase. Remarkably, anatase can further transform into rutile due to the influence of Ni nearby and TiO, due to insufficient oxygen content. The most notable outcome is the formation of a thick Ti oxide layer, causing unbound Ni to emerge on the surface, resulting in a Ni oxide layer. These findings highlight the importance of precisely adjusting laser parameters to achieve tailored surface properties for medical applications, addressing challenges and enhancing biocompatibility. Graphical abstract