Biodegradable Mg-Ca-Zn alloys synthesized by powder metallurgy

Abstract

Mg-Ca-Zn biodegradable alloys were synthesized by powder metallurgy processing using foaming agent CaCO3 coated with Na2SiO3 and dolomite CaMg(CO3)2. The microstructure was investigated using SEM/EDS, S-TEM, and XRD analyses. The in-vitro degradation behavior was determined via measuring the hydrogen evolution rate using immersion test in Hanks' solution. The microstructure examinations of the sintered samples by SEM/EDS revealed the formation of three intermetallic Mg-Ca-, Mg-Zn- and Ca-Si-phases. The S-TEM observations indicated the formation of secondary phases of CaSi2, MgZn2, and MgO, whereas XRD results showed the corrosion products of Mg(OH)2, MgO, and apatite-CaOH. The hydrogen evolution rate decreased with increasing material density. The material density could be directly correlated with the coalescence of porosities at higher sintering temperatures. However, also the amount, continuity and type of the secondary phases were associated to the degradation behaviour. Further, it was observed that the degradation rate of the Mg-Ca-Zn alloy sintered with dolomite CaMg(CO3)2 was significantly lower than the degradation rate of the magnesium alloy sintered with CaCO3. The magnesium diffusion from the dolomite into the alloy matrix during sintering was presumably related to this observation.