Stress corrosion and corrosion fatigue of biodegradable mg-zn-nd-y-zr alloy in in-vitro conditions

Mg alloys are attractive as a structural material for biodegradable implants due to their mechanical properties, biocompatibility and degradation capability in physiological environments. However, their accelerated corrosion degradation, coupled with their inherent sensitivity to stress corrosion, can cause premature failure and consequently loss of mechanical integrity. This study aims to evaluate the potential of a Mg-5% Zn alloy with up to 3% Nd as an implant material in terms of stress corrosion performance in in vitro conditions. Stress corrosion behavior was evaluated under static loading conditions using slow strain rate testing (SSRT) analysis and under low cycle corrosion fatigue (LCCF). Both the SSRT analysis and LCCF testing were carried out in a simulated physiological environment in the form of a phosphate-buffered saline (PBS) solution. The obtained results indicate that the addition of up to 3% Nd to Mg-5% Zn alloy did not have any substantial influence on the stress corrosion susceptibility, beyond the inherent different mechanical properties of the tested alloys. This was attributed to the limited effect of the Nd on the passivation layer and due to the fact that the secondary phases produced by the Nd additions—W-phase (Mg₃(Nd,Y)₂Zn₃) and T-phase (Mg₄(Nd,Y)Zn₂)—did not create any substantial micro-galvanic effect.