Corrosion behavior and in-vitro bioactivity of porous Mg/Al ₂ O ₃ and Mg/Si ₃ N ₄ metal matrix composites fabricated using microwave sintering process

In the present work the corrosion behavior and in-vitro bioactivity of two kinds of porous Mg-metal matrix nano-composites separately reinforced with Al ₂ O ₃ whiskers and Si ₃ N ₄ particles were reported. 10 wt% of reinforcement was mixed with magnesium using high-energy ball milling and ethanol media for 10 min. After that, 10 ml ethylene glycol was added to milled mixture at the final stage of drying on a heater/stirrer at 70 °C. After stirring for 12 h, the powder mixtures were uniaxially pressed at 300 MPa to produce bar-shaped green specimens. The microwave sintering was performed at 650 °C without soaking time in a graphite bed. Porosity of about 50% was measured for both sintered composites using Archimedes principle. The XRD investigations revealed Mg ₂ Al ₃ and MgO phases as the result of reaction between Mg and Al ₂ O ₃ . Moreover, the reaction products in Mg- Si ₃ N ₄ composite were Mg ₂ Si, Mg ₃ N ₂ and Si. The corrosion tests showed that the polarization resistance of both prepared composites is higher than that of pure Mg. Mg-Al ₂ O ₃ composite also showed lower corrosion current density compared to Mg- Si ₃ N ₄ composite (1.42E ⁻⁴ and 1.36E ⁻³ A cm ⁻² , respectively). In-vitro bioactivity analysis of composites showed high level of needle-shaped CA-P inside porosities of Mg-Si ₃ N ₄ composite; while in the case of Mg-Al ₂ O ₃ composite a lower amount and smaller needle-shaped particles were found.