The Nd-Mg system was studied using differential thermal analysis (DTA), X-ray examination, metallography, and microprobe analysis. The following intermetallic compounds were found to exist and their crystal structures confirmed or determined: NdMg (cubic, cP2 CsCl type, melting point 800 °C), NdMg2 (cubic, cF24 MgCu2 type, peritectic formation ∼755 °C), NdMg3 (cubic, cF16 BiF3 type, melting point 780 °C), and Nd5Mg41 (tetragonal, tI92 Ce5Mg41 type, decomposes peritectically at 560 °C). The NdMg2 phase undergoes a eutectoidal decomposition at 660 °C. Three eutectic equilibria were observed to occur at 42.5 at. pct Mg and 775 °C, 64.5 at. pct Mg and 750 °C, and 92.5 at. pct Mg and 545 °C, respectively. In the Nd-rich alloys, previously determined data[15] concerning the Mg solubility in α-Nd (8.2 at. pct Mg, ≈550 °C) were accepted. The Mg solubility in β-Nd was evaluated as 34 at. pct Mg at 775 °C. The β-Nd phase was observed to decompose eutectoidally at 17 at. pct Mg and 545 °C. Moreover, in the Mgrich alloys, a metastable NdMg12 phase (tetragonal, tI26 ThMn12 type) was observed in samples quenched from the liquid. The general properties of the Nd-Mg phases are compared with those of the R-Mg compounds and briefly discussed. © 1990 The Metallurgical of Society of AIME

The successful applications of magnesium-based alloys as biodegradable orthopedic implants are mainly inhibited due to their high degradation rates in physiological environment. This study examines the bio-corrosion behaviour of Mg-2Zn-0.2X (X = Ca, Mn, Si) alloys in Ringer's physiological solution that simulates bodily fluids, and compares it with that of AZ91 magnesium alloy. Potentiodynamic polarization and electrochemical impedance spectroscopy results showed a better corrosion behaviour of AZ91 alloy with respect to Mg-2Zn-0.2Ca and Mg-2Zn-0.2Si alloys. On the contrary, enhanced corrosion resistance was observed for Mg-2Zn-0.2Mn alloy compared to the AZ91 one: Mg-2Zn-0.2Mn alloy exhibited a four-fold increase in the polarization resistance than AZ91 alloy after 168 h exposure to the Ringer's physiological solution. The improved corrosion behaviour of the Mg-2Zn-0.2Mn alloy with respect to the AZ91 one can be ascribed to enhanced protective properties of the Mg(OH)(2) surface layer. The present study suggests the Mg-2Zn-0.2Mn alloy as a promising candidate for its applications in degradable orthopedic implants, and is worthwhile to further investigate the in vivo corrosion behaviour as well as assessed the mechanical properties of this alloy.

No abstract

No abstract

No abstract