Abstract
Liquid phase sintered biodegradable Mg-0.6Ca alloy generally exhibits an isotropic microstructure with homogenously restricted grain size of 30 µm, even after long sintering durations of 60 h at 625 °C. Such sintered microstructures reveal the presence of numerous impurity oxide particles at the grain boundaries, which are evident also on the initial gas atomized powder surfaces. However, after a mechanical powder sieving treatment for 20 min, the surface SiO2 concentration dropped from initially 220 ppm to 85 ppm, resulting in heterogeneous grain coarsening after sintering for 18 h at 625°C. For the use of Mg-Ca materials as biodegradable implants, reproducibility of in vitro degradation results is a prerequisite, for which a homogenous grain structure is desired. However, the lowered oxide-pinning effect at certain grain boundaries created heterogeneous grain coarsening and this indicates the necessity for the careful handling of fine powders to ensure repeatability in degradation and mechanical properties.
