Enhancing the surface finish and corrosion resistance of laser powder bed fusion NiTi surfaces through chemical polishing

Abstract

NiTi alloys exhibit significant potential for biological applications, and the fabrication of customized NiTi geometries is greatly facilitated by the use of laser powder bed fusion (LPBF) processing. However, there are several challenges with post-processing NiTi specimens processed via LPBF, such as uneven, loosely packed, weakly corrosive surfaces, and low dimensional precision. Therefore, solving the surface problem of metals prepared by LPBF has become the key to the application. In this paper, the influence of the solution and parameters on surface roughness, surface shape and size, composition, and corrosion resistance was studied by adjusting the composition of the polishing solution and polishing parameters. The results show that polishing for 2 h in S2 solution (HNO3: HF: H2O = 40:10:50) produces the smoothest surface with the roughness characteristics Sa is 10.41 ± 0.63 μm and Ra is 0.39 ± 0.30 μm. At the same time, the corrosion resistance of polished samples has been significantly improved in simulated body fluids (SBF), and the corrosion current density (Icorr) reduced by up to one order of magnitude, reaching 5.38 ± 0.24 × 10−8. By altering the polishing process duration, it is possible to achieve a micron-level roughness surface while maintaining dimensional accuracy, making LPBF-NiTi more suitable for implant applications. Ultimately, we conclude with a brief discussion of how chemical polishing affects the handling of materials with complex structures. Between 30 and 1 h, LPBF-NiTi scaffolds were polished in S2 solution to provide porosities and dimensional accuracy that best matched the design parameters.