Optimization of electropolishing parameters for enhancing the surface roughness of powder bed fusion-laser beam NiTi using response surface methodology

Powder bed fusion-laser beam (PBF-LB) is a prominent additive manufacturing technique for fabricating complex, near-net-shape components. However, the high surface roughness of as-built parts, arising from partially melted powder particles and stair-step effects, can adversely affect their fatigue performance and functional properties. This study investigates electropolishing (EP) as a post-processing strategy for improving the surface quality of PBF-LB-manufactured nickel-titanium (NiTi) cuboids. A statistically designed Design of Experiments (DoE) approach was employed to systematically investigate and optimize three key EP parameters: voltage, processing time, and electrolyte flow rate. Surface topography and chemical composition were characterized using three-dimensional optical profilometry, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Electropolishing substantially transformed the initially jagged, peak-dominated surface morphology into a smoother, more plateau-like topography, achieving maximum reductions of 92.85% in Sa and 94.7% in Sz. The results demonstrate that the extent of surface improvement depends on the combined effects of the EP process parameters. An appropriate processing window, characterized by elevated electrolyte flow, extended processing time, and a controlled intermediate voltage, was identified to improve surface uniformity while limiting severe pitting and localized over-etching. These findings provide a systematic optimization framework for improving the surface quality of PBF-LB NiTi components for potential biomedical and industrial applications.