High-Cycle Fatigue of Metastable β Ti-12Mo-6Zr-2Fe Alloy – Effects of Hydrogen Absorption Caused by Surface Modification

Metastable β Ti-12Mo-6Zr-2Fe (TMZF) alloy offers a low elastic modulus for biomedical applications, yet its fatigue performance following surface bioactivation is a major concern. This study utilized the staircase method to evaluate the high-cycle fatigue response of untreated, chemical surface treated (CST), and anodized nanopore (Np) specimens. Untreated samples exhibited a fatigue resistance of 730 MPa (maximum stress). Conversely, CST and Np treatments caused a drastic reduction in fatigue resistance, exceeding 50%. Polishing CST samples only partially recovered this loss, maintaining a 25% decrease compared to untreated specimens. Fractographic evidence, characterized by Wallner lines and brittle fracture, pointed to hydrogen embrittlement. Mechanisms identified include, mainly, stress-induced TiH 2 hydride formation, which increases local dislocation density, alongside hydrogen-induced decohesion (HEDE). While CST and anodization is recognized to enhance osseointegration, they compromise structural reliability through hydrogen-induced degradation, highlighting hydrogen uptake during surface modification as a critical challenge for titanium alloys in hydrogen-rich environments.