Interdiffusion and impurity diffusion behavior in polycrystalline Mg-Y binary system

Abstract

The diffusion behavior in binary Mg-Y system was investigated using polycrystalline Mg/Y diffusion couples at temperatures ranging from 573 to 823 K. For all diffusion couples, electron microprobe analysis was utilized for the measurement of concentration profiles. The interdiffusion coefficients in Mg solid solution and intermetallic phases were determined via the Boltzmann-Matano and Heumann-Matano method, respectively. In addition, the Hall method was employed to extrapolate the impurity diffusion coefficients of Y in pure polycrystalline Mg and Mg in pure polycrystalline Y. The results showed that the interdiffusion coefficient in Mg solid solution increased with an increase of Y concentration, and the corresponding pre-exponential factor and activation energy both increased nearly linearly. The pre-exponential factor and activation energy for Y impurity diffusion in Mg were determined to be 2.36×10−8 (±9.0×10−9) m2/s and 85.61 (±2.0) kJ/mol, while those for Mg impurity diffusion in Y were determined to be 3.47×10−7 (±7.6×10−7) m2/s and 95.90 (±6.7) kJ/mol. Simultaneously, the pre-exponential factor and activation energy for interdiffusion in intermetallic phase Mg24Y5 were determined to be 9.96×10−9 (±2.9×10−9) m2/s and 68.98 (±2.0) kJ/mol；while those for Mg2Y were determined to be 1.18×10−9 (±9.0×10−10) m2/s and 64.54 (±3.2) kJ/mol. Additionally, the vacancy diffusion was dominant mechanism above 723 K, while the grain boundary diffusion mechanism dominated below 723 K in polycrystalline Mg-Y binary system.