The influence of surface treatments on the degradation behaviour of Mg-5GdFriday (09.06.2017) 10:40 - 11:00 Förde II Part of:
Mg is susceptible to deformation during processing, which in turn, will change the microstructural properties near the surface region of the material by the introduced stress. This leads to different degradation kinetics of surface and bulk material. Mg has an extremely low electrochemical potential, thus, high potential differences between the Mg matrix and other phases like precipitates and impurities, but also mechanically influenced regions, usually occur. This leads to accelerated degradation by microgalvanic degradation and possibly also pitting. Therefore, in this study extruded and milled Mg-5Gd samples were treated by acid etching to remove different depths of machined surfaces to achieve a linear and homogeneous degradation. The relationship between depth of removed surface and degradation behaviour was investigated. The microstructure of cross sections parallel to the extrusion direction were analysed before and after acid etching by OM. The surface perpendicular to the extrusion direction was analysed by SEM and EDS to evaluate the amount of GdH2 and cathodic impurities from the manufacturing of the samples. For phase determination small angle XRD was used. After acid etching the samples were immersed in DMEM + Glutamax + 10% FBS + 1% Streptomycin/Penicillin. The surface after acid etching and after degradation in physiological solution were characterised by interferometry, OM, SEM and μXRF to correlate the influence of microstructure and chemical composition on the degradation behaviour. It was shown that acid etching leads to the removal of accumulation of twins and GdH2 associated with a decrease of degradation rate.