Characterization of magnesium-hydroxyapatite functionally graded composites prepared by rapid microwave sintering technique

The use of the microwave technique for the sintering of materials has been noticed due to the reduction in processing time, the achievement of uniform microstructure, and high effectiveness. In this study, magnesium/hydroxyapatite (Mg/HA) functionally graded materials (FGMs) in the form of a 2-layer, 3-layer, and 4-layer samples with different contents of HA (0, 5, 10, and 15 wt%) and also single-layer pure Mg samples were successfully fabricated by powder metallurgy and rapid microwave sintering technique. For this purpose, the prepared powders were first mixed and then poured into a die in a layer-by-layer manner at a predetermined arrangement. The stacked powders were compacted under a pressure of 300 MPa and sintered via microwave technique at 530 degrees C for 12 min under an argon atmosphere. The samples were investigated by the Archimedes test, optical microscope (OM), scanning electron microscopy (SEM), mechanical and corrosion tests. Achieving high relative densities in a short time for pure Mg (99.5%) and its multi-layer composites suggested the high effectiveness of this technique in processing these materials. In addition to the uniform distribution of HA particles in the Mg matrix, the microstructural studies confirmed the proper inter-layer bonding. The mechanical properties of the samples were evaluated by the microhardness indentation method and the compression test. The results showed that the microhardness and compressive strength of the layered samples is much higher than pure Mg. The highest microhardness (63 +/- 5 Hv) and compressive strength (148 +/- 10 MPa) were observed in the 3-layer sample. The corrosion behavior of the samples was also examined in simulated body fluid (SBF) at 37 degrees C through immersion tests which indicated superior corrosion resistance of layered samples compared to pure Mg. The 3-layer sample exhibited the best corrosion behavior.