Mechanism of improving cyclic tensile behavior and corrosion resistance of laser-treated NiTi shape memory alloys

This study employed a 250 W laser surface treatment to improve the cyclic tensile behavior and corrosion resistance of NiTi shape memory alloy used in high-temperature and high-pressure boilers. The treatment resulted in the decomposition of Ti-C-O particles in melt pool, subsequently forming a metastable solid solution structure which inhibited sources of microgalvanic corrosion. The elastic modulus of the material was enhanced to 44.19 GPa, and the pinning of dislocations by solid solution interstitial atoms (C/O) led to a reduction in residual deformation by 21.2%. The improved corrosion resistance can be attributed to the formation of a dense bipolar passivation film. This film resulted in a 96% decrease in hole concentration in the p-type region, a sixfold increase in charge transfer resistance, and a 97% decrease in the corrosion rate. Comparative experiments revealed that the use of a 500 W laser, due to thermal accumulation, produced porosity defects, compromising the integrity of the material and leading to inferior performance.