Formation Kinetics of Light Rare Earth (Ce, Sm)-Fe Intermetallic Compounds

As a part of the program of fundamental study on the formation of light rare earth-transition metal intermetallic compounds, the formation kinetics of Ce-Fe and Sm-Fe compounds was examined in this work. First, diffusion couples of Ce-Fe and Sm-Fe systems containing Mo wires as markers were vacuum-sealed in silica ampules and maintained at 843K and 963K which are just below their eutectic temperatures, respectively. The CeFe2 and SmFe2 were formed between the metal plates, which shows that Ce and Fe were predominant diffusing components in the Ce-Fe and Sm-Fe systems, respectively. Second, an Fe plate was immersed in a Ce-Fe or Sm-Fe melt of which composition was set at each Fe-side liquidus line at a temperature above the eutectic point. The thickness of the compounds formed on the surface of the Fe plate grew in accordance with the parabolic rate law. Only CeFe2 and SmFe2 formed, while the formation of Ce2Fe17, SmFe3 and Sm2Fe17 which were indicated in the phase diagrams could not be confirmed at temperatures lower than 1, 100K. The growth rate of SmFe2 was much higher than that of CeFe2. In each of the Ce-Fe and Sm-Fe systems the growth rate of a compound decreased and showed a greater dependence on temperature with the increase in Fe content. The growth rate of Sm2Fe17 at 1, 300K coincided with that measured in the reduction-diffusion process.