Stress Corrosion and Corrosion Fatigue of Biodegradable Mg-Zn-Nd-Y-Zr Alloy in In-Vitro Conditions

Lilach Elkaiam,Orly Hakimi,Eli Aghion

doi:10.3390/met10060791

Abstract

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.

Highlights

Mg alloys have attracted significant attention as potential structural materials for biodegradable implants due to their excellent biocompatibility, degradation capabilities in physiological environments, and appropriate mechanical properties [1,2,3,4]
The present study aims to evaluate the effect of the addition of up to 3% Nd on the stress corrosion performance of a Mg-5% Zn alloy in terms of slow strain rate testing (SSRT) analysis and low cycle corrosion fatigue (LCCF)
The results of the stress corrosion analysis obtained by the SSRT in a phosphate-buffered saline (PBS) solution in terms of stress–strain curves is shown in Figure 2, while a summary of the results of the UTS and elongation versus strain rate is shown in Figures 3 and 4, respectively

Summary

Introduction

Mg alloys have attracted significant attention as potential structural materials for biodegradable implants due to their excellent biocompatibility, degradation capabilities in physiological environments, and appropriate mechanical properties [1,2,3,4]. The accelerated corrosion of Mg alloys can produce an accumulation of hydrogen gas through the following chemical reaction: Mg(s) + 2H2 O(l)→Mg(OH) (s) + H2 (g). Guangling Song [6] reported that the human body can tolerate hydrogen gas emissions of up to 0.01 mL/cm2 /day. This means that the hydrogen evaluation rate during the degradation process of Mg based implants should be lower than this value, in practice

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Conclusion