Reactive diffusion in Mg–Gd binary system at 773 K

The reactive diffusion in Mg–Gd binary system was studied at 773 K by optical microscopy (OM), scanning electron microscopy (SEM) and electron probe micro-analysis (EPMA). After annealing at 773 K for 12–48 h, four different intermetallic layers, Mg5Gd, Mg3Gd, Mg2Gd and MgGd, form at the Mg/Gd interfaces in the diffusion couples. The thicknesses of intermetallic layers Δi (i stands for the phases of Mg5Gd, Mg3Gd, Mg2Gd and MgGd, respectively) are proportional to the square root of annealing time t1/2, which indicates that the growth behavior of the intermetallics is controlled by the diffusion rate. The ratio of thickness of each intermetallic layer to the total thickness is constant with increasing the annealing time, which means that the growth behavior is constant at a certain annealing temperature. The diffusion coefficient of Gd in different intermetallics was calculated by Matano method.