Effects of ultrasonic surface finishing on wear and corrosion resistance of wire-EDM produced titanium alloy parts

This experimental study aims to examine the test specimens of a Ti6Al3MoSiZr titanium alloy produced by WEDM at various energetic modes before and after surface finished by high-frequency mechanical impact (HFMI) treatment using ultrasonic equipment. SEM, EDS, TEM, and XRD analyses were used to analyse the surfaces integrity, chemical composition, stress state, and microstructure. After WEDM and HFMI, the recast/white layer and nanostructured surface layer causing the surface hardening by ∼16% (to 5.8 GPa) were respectively observed by SEM, TEM, and nanoindentation. Corrosion rate in 3.5%NaCl elucidated based on dynamic and static polarization tests increases with the WEDM energy growth up to 19.4 μm/y and diminishes after HFMI by 56% (to 8.6 μm/y). Wear resistance assessed using multi-pass scratch tests was shown to increase after HFMI by 40–85%. A nanoscale grain structure and compressive residual stresses (1.4–1.7 GPa) promote a higher wear resistance and facilitate the formation of a protective passive oxide film decelerating corrosion. A good correlation is observed between the experimentally assessed wear and corrosion resistance and theoretically evaluated parameters accounting for surface roughness and hardness supported by near-surface microstructure. The WEDM innovative technology could be integrated into the production process, provided the surface morphology and surface contamination issues are solved by applying appropriate cutting wire and surface finishing techniques like the HFMI post-processing.