Microstructures of (Fe_0.88Co_0.12)₈₂La₇Si₁₁ prepared by arc-melting/melt spinning and subsequent annealing

Abstract

In this study, we carried out a systematic investigation of the microstructures of (Fe_0.88Co_0.12)₈₂La₇Si₁₁ prepared by arc melting/melt spinning and subsequent annealing. The arc-melted sample contains 36 wt. % of the desired La(Fe,Co,Si)₁₃ phase (denoted by 1:13 in the following). Annealing of the arc-melted ingot at 1273 K for 200 h leads to a single 1:13 phase. Melt spinning enhances formation of the 1:13 phase. As the wheel speed reaches or is greater than 15 m/s, over 50 wt. % of 1:13 is directly formed in the melt-spun ribbons. A subsequent annealing of these melt-spun samples at 1273 K for 20 min results in a nearly single phase 1:13 structure. The samples prepared under different conditions were systematically studied by transmission electron microscopy in order to elucidate possible origins of the enhanced formation of the 1:13 phase when using the new technique. The presence of a high density of La-Fe-Co-Si clusters in the undercooled liquid is believed to contribute to the formation of the 1:13 phase in melt-spun ribbons. The enhanced atomic diffusivity as a result of structural refinement in melt-spun samples accounts for the subsequent fast transformation of the 1:13 phase during the annealing process.