Surface Alteration in Ti–6Al–4V Extra Low Interstitial With Boric Acid PMEDM

Abstract

Abstract. The current work uses powder-mixed electrical discharge machining (PMEDM) to modify Ti–6Al–4V extra low interstitial (ELI) surface, with boric acid powder suspended in de-ionized (DI) water. The study characterizes surfaces machined by electrical discharge machining (EDM) with pure dielectric and PMEDM (15 g/L) under identical discharge conditions. Voltage–current waveforms were analyzed to evaluate spark behavior, while optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used for analyzing surface morphology. Cross-sectional microscopy was used to assess the thickness of the recast layer, and X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) analyses were utilized to comprehend the surface constituents. The formation of TiB and TiO2 phases was confirmed in the PMEDM sample, demonstrating chemical surface modification due to boron incorporation. TEM showed needle-shaped TiB whiskers with 0.217 nm interplanar spacing, closely matching XRD's 0.210 nm spacing. XPS validated the bonding states between Ti–B and Ti–O, supporting the formation of TiB and TiO2. Vickers microhardness (MH) testing indicated a considerable increase from 435 HV in the unmachined sample to 1125 HV in PMEDM. Dry sliding wear testing showed a significant decrease in the coefficient of friction from 0.549 to 0.292. Wettability analysis indicated a reduction in contact angle from 71.5 deg (unmachined) to 38.1 deg (PMEDM), suggesting a hydrophilic surface. TiB and TiO2 phases increase wettability, which is particularly useful in biomedical applications that need better fluid interaction. Thus, boric acid PMEDM improved Ti–6Al–4V ELI surface integrity, MH, and tribology, with DI water supporting its biomedical and eco-friendly applications.