Microstructure of the novel biomedical Mg–4Y–3Nd alloy prepared by spark plasma sintering

Abstract

One of the prominent applications of magnesium alloys, thoroughly investigated in recent years, is medicine. The commercial WE43 (Mg-4wt.%Y-3wt.%mischmetal) alloy was reported to exhibit superior in vitro and in vivo performance, however, the presence and possible harmful effect of rare earth (RE) elements mischmetal in this alloy have been vastly debated. For this reason, the RE mischmetal was substituted in this study by pure neodymium, which exhibits rather low toxicity. In this way, a novel WN43 (Mg-4wt.%Y-3wt.%Nd) alloy was prepared, with well-defined composition. In order to attain a good control over the grain size and phase distribution, a modern spark plasma sintering (SPS) method was employed. The main objective of this study was to examine the effect of sintering parameters on the resulting microstructure (type and morphology of secondary phases, grain structure, and residual strain) and microhardness (Hv). The application of relatively high pressure (100 MPa) during consolidation leads to the production of practically fully compact final material. Increasing sintering temperature (from 400 up to 500 °C) stimulated homogenization and stabilization of the microstructure and reduction of the internal strain. On the other hand, the effect of sintering time (3 or 10 min) was rather negligible. Furthermore, the microhardness experiments revealed that the softening effect due to homogenization and decrease in the dislocation density at higher sintering temperatures was well-compensated by precipitation hardening as the hardness values were comparable in all the samples. The understanding of microstructure evolution as a function of sintering parameters can be of particular importance for subsequent mechanical, corrosion and in vivo degradation testing of this novel biomedical magnesium alloy.