Composition, Structure, Microhardness, and Ion-Release Behavior of Zn-Modified Ti-35Nb-2Ta-3Zr Alloy After Friction Stir Processing and Compression Plasma Flow Treatment

Ti-35Nb-2Ta-3Zr (TNTZ) β-titanium alloy is attractive for biomedical applications because of its relatively low elastic modulus and composition based on nominally non-cytotoxic alloying elements; however, its surface hardness and intrinsic bioactivity remain limited. In this study, Zn nanoparticles were incorporated into the near-surface region of TNTZ by friction stir processing (FSP), followed by compression plasma flow (CPF) treatment in nitrogen. Cross-sectional scanning electron microscopy and energy-dispersive X-ray spectroscopy, X-ray diffraction, microhardness testing, and inductively coupled plasma mass spectrometry after 60 days of immersion in simulated body fluid were used to characterize the modified layers. CPF treatment produced a distinct surface-modified layer approximately 10–15 μm thick, increased the Zn signal within the upper approximately 11 μm, and generated diffraction peaks assigned to Ti2N. The fitted β-phase lattice parameter decreased with nominal X-ray penetration depth, and tensile residual stresses were calculated for all CPF-treated conditions. Sample 1 exhibited the highest microhardness at the lowest applied load. After 60 days of immersion, the mean Zn concentration was 261.87 ± 0.0031 μg/L for FSP and 102.41 ± 0.0063 μg/L for FSP + CPF, corresponding to an approximately 60.9% lower mean cumulative Zn concentration after CPF treatment. Electrochemical, tribological, and biological testing is still required to establish corrosion, wear, and biological performance.