The influence of heat treatment and plastic deformation on the bio-degradation of a Mg-Y-RE alloy

In this study the bio-degradation behavior of a Mg-Y-RE alloy in different heat treatment states with respect to the alloy's potential application as biodegradable implant material was investigated by etectrochemical impedance spectroscopy in two body-similar fluids. The heat treatments increase the degradation resistance of the alloy and lead to the formation of a thermal oxide layer on the sample surface and to a change in microstructure such as the distribution of yttrium. The varying Y distribution in the alloy does not significantly influence the degradation behavior, and all samples show a similar low polarization resistance. However, samples with a thermal oxide layer, which consists mainly Of Y2O3, degrade much more slowly and feature remarkably high polarization resistance. Nevertheless, in some cases localized corrosion attack occurs and drastically impairs performance. Cracks in the oxide layer, intentionally induced by straining of the samples and which in practice could originate from the implantation process, reduce the corrosion resistance. However, these samples perform still better than polished specimens and show a macroscopically homogeneous degradation behavior without localized corrosion. Microscopically, corrosion attacks start at the cracks and undermining of the oxide layer occurs with time. For all the material conditions a remarkable dependence of the degradation rate on the electrolyte is noted. (C) 2009 Wiley Periodicals, Inc. J Biomed Mater Res 92A: 409-418, 2010