Microstructure and microhardness of carbonate apatite particle-reinforced Mg composite consolidated by warm compaction for biodegradable implant application

Magnesium-based composites with carbonate apatite reinforcement are attractive biodegradable implant materials. In this study, we observed the effect of carbonate apatite content (5, 10, and 15% wt.) and milling time (3, 5, and 7 h) on the microstructure and microhardness of magnesium-carbonate apatite composites fabricated by powder metallurgy. The consolidation process involved warm compaction without sintering. Characterization was achieved through density testing, x-ray diffraction (XRD), optical microscopy, SEM-energy dispersive x-ray spectroscopy (EDS), and microhardness testing. The powder milling time affects the distribution of apatite carbonate; adding carbonate apatite can increase the hardness of magnesium-based composites. In the XRD spectrum, we identify the dominant magnesium peak but not the magnesium oxide peak. Carbonate apatite powder is distributed at the grain boundaries. The hardness range is 40.26-44.82 Hv or increase by 8.21%-20.23% compared to the hardness of consolidated pure magnesium. The relative density is around 95.92%-98.71%, whereas the relative density of pure magnesium is 99.58%. The obtained optimal conditions for fabricating magnesium composites are the following: content of 10 wt% carbonate apatite (milled for 5 h) with a hardness of 43.58 Hv.