Surface Modification of Medical-Grade Ni55.6Ti44.4 alloy via enhanced machining characteristics of Zn Powder Mixed-μ-EDM

Abstract The surface modification via subtractive manufacturing intends to localize the desired properties on the produced surface during the machining. In the case of miniaturized components, the powder mixed-micro-electric discharge machining (PM-μ-EDM), a potential variant of EDM, can achieve superior microfeatures such as dimensional accuracy and surface integrity, and a noteworthy surface modification on the hard and tough materials such as titanium and nickel alloys. Besides, the increasing demands for microfabricated devices used in tissue engineering and therapeutics delivery encourage their production with improved surface characteristics and biocompatibility. The superelastic nickel‑titanium alloy (Nitinol) has recently emerged as one of the most desirable biomaterials primarily in the vascular and prosthetic applications. However, the microfabrication followed by surface modification of Nitinol by the PM-μ-EDM has been rarely recorded. Hence, this research aimed to modify the Medical-grade Ni55.6Ti44.4 alloy surface with the least machining time and dimensional deviation using zinc PM-μ-EDM. A comparative study between the μ-tool electrodes (copper and brass) and Zn powder particle concentrations (PPCs: 0, 2, 4, 6, 8, and 10 g/l) revealed that the copper μ-tool electrode in association with 6 g/l PPC, could achieve the most improved machinability and modified layer on the Ni55.6Ti44.4 alloy surface. A field emission scanning electron microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDS) investigated the dimensional, morphological, and compositional features of the modified Ni55.6Ti44.4 alloy surface and reported significant improvements. The X-ray diffraction (XRD) analysis of the modified surface detected a remarkable impact of the thermally induced variations on the crystalline phases of Ni55.6Ti44.4 alloy. Further, the lactate dehydrogenase (LDH) and CellTiter-Blue assays determined improved cytocompatibility characteristics and Drop Shape Analyzer (DSA) ascertained the hydrophobicity of the modified Ni55.6Ti44.4 alloy surface.