Preparation of porous microstructures on NiTi alloy surface with femtosecond laser pulses

Porous microstructures on Nickel-Titanium (NiTi) alloy surfaces were prepared by linearly polarized femtosecond lasers with moving focal point at a certain speed. It was found that various novel microstructures from feather-like ripples to cluster-like porous textures could be formed with increasing laser energy. Particularly, when the laser energy was 400 mu J, a periodic porous metal surface was generated. Measurement of X-ray diffraction showed that the grains on the sample surface were refined through femtosecond laser ablation processes, but the crystal structures still kept their original states. Analysis by X-ray photoelectron spectroscopy revealed that Ni/Ti on the sample surface was changed with an evident oxidization of titanium element under different laser energies. This investigation provides a new approach to improve the biocompatibility of NiTi-based implant devices.