Research on surface integrity and corrosion performance in high-speed ball-end milling of NiTi shape memory alloys

Abstract Nickel-titanium (NiTi) shape memory alloy, widely used as an artificial bone due to its excellent corrosion resistance and biocompatibility, often requires high-speed ball-end milling to achieve complex curved surfaces. This study investigated how changes in surface integrity during ball-end milling affect the corrosion resistance of NiTi alloy in a simulated body fluid environment. Using potentiodynamic polarization, electrochemical impedance spectroscopy, and scanning electron microscopy, we found that cutting speed has a complex impact on corrosion resistance. Specifically, the corrosion resistance decreased with increasing cutting speed from 60 to 150 m min −1 , attributed to a 47.8% reduction in plastic deformation depth and a 9.5% decrease in surface microhardness, as well as a shift in residual stress from compressive to tensile. Pitting and crevice corrosion on the milled surface were predominantly observed at peak and cutting mark locations. However, further increases in cutting speed from 150 to 180 m min −1 enhanced corrosion resistance through reduced surface roughness. These findings elucidate the intricate relationship between surface integrity and corrosion resistance, providing theoretical insights for optimizing high-speed ball-end milling processes and improving the corrosion resistance of NiTi alloy.