Corrosion and tribocorrosion resistance of superhydrophobic LPBF-NiTi alloys surface fabricated by nanosecond laser and ultrasonic fluorination

NiTi alloys have been extensively studied for their excellent super-elasticity (SE) and shape memory effects (SME). With the development of laser powder bed fusion (LPBF), it is possible to process the complex structure of NiTi alloy, which results in the mechanical properties of LPBF-NiTi alloys receiving great attention. However, the processing method is different from the traditional one, which not only has an impact on the mechanical properties but also seriously affects the anti-corrosion resistance and causes a substantial deterioration. In the research work of this paper, nanosecond laser processing was used to fabricate the bionic mastoid-shaped micro-nano structure on the LPBF-NiTi alloys. An efficient and convenient ultrasonic fluorination treatment was used to achieve the full surface coverage of FAS-17 in 10 min, and the superhydrophobic LPBF-NiTi alloy surface (CA similar to 157 degrees) was successfully achieved. The constructed superhydrophobic LPBF-NiTi alloy surface exhibits excellent anti-corrosion resistance compared with the original surface, and the i(corr) from (4.42 +/- 0.5) x 10(-7) A center dot cm(-2) reduced to (3.21 +/- 0.5) x 10(-9) A center dot cm(-2). Meanwhile, the superhydrophobic surface showed outstanding stability in the 15-day immersion test n 3.5 wt% NaCl solution. And it is also stable after the tribocorrosion tests in 3.5 wt% NaCl solution at 1 N and 5 N pressures. The remarkable anti-corrosion resistance and stability of the superhydrophobic surface can be attributed to the micro-nano structure rich in the TiO2 oxide layer, the air layer formed by the superhydrophobic surface insulates the corrosive liquid and the stable hydrophobic agent film.