Interfacial reaction in (Mg-37.5Al)/(Mg-6.7Nd) diffusion couples

The solid-state diffusion reaction between Mg-37.5Al and Mg-6.7Nd was studied in the 623-673 K temperature range. A solid-liquid contact method was employed to produce diffusion couples. The Al₄Nd, Al₁₁Nd₃, Al₃Nd and Al₂Nd intermetallic compounds form in the diffusion reaction layers of the couples. The formation of intermetallic compounds in the diffusion reaction layers is rationalized using the Miedema model. The local average compositions through the diffusion reaction layer were determined, and used to construct a semi-quantitative diffusion path on the isothermal Mg-Al-Nd ternary phase diagram at 673 K. The growth constants of the entire diffusion reaction layers were determined as 8.91 (±0.94)×10^-14 m²/s, 1.39 (±0.15)×10^-13 m²/s and 1.93 (±0.38)×10^-13 m²/s at 623 K, 648 K and 673 K, respectively. The activation energy Q for the growth of the entire diffusion reaction layers was 54±4.6 kJ/mol.