Nanocrystalline Ternary Fe-Co-X Alloys Produced by Ball Milling or Rapid Solidification

Several ternary soft magnetic Fe-Co-X alloys were produced by ball milling or rapid solidification (melt spinning) with the goal of obtaining nanocrystalline structures. The ternary alloy additions investigated include: Zr, Y, Ce, Ag, Sb, Au, and Cu in the range of 0% (50Fe50Co) to 6 at. %. The mechanically alloyed powder samples exhibited grain sizes ranging from approximately 10 to 250 nanometers based on X-ray diffraction analyses. Upon annealing for up to 10 hrs., the alloys with Zr and Y additions were the most resistant to grain growth, maintaining grain size below ~30 nm at 500°C and below ~60 nm at 750°C. TEM of the FeCo-Zr alloys confirmed the small grain size and indicated regions of Zr-rich phase at grain boundaries and possible formation of Laves phase during annealing. The FeCo-Y alloys displayed similarly fine grain size with TEM but in this case the Y-rich regions appear to be Y-oxide particles. Spark plasma sintering (SPS) of ball-milled powders is being explored as a means of consolidation into centimeter-sized specimens for further microstructure characterization and property measurement. Melt-spun ribbons of the same FeCo-X alloys were produced at Ames Laboratory. TEM analysis of the FeCo-Zr alloy ribbons indicated a cellular solidification structure with cell size or grain size on the order of 1 micron. Zr-rich regions were observed randomly distributed as well as along grain boundaries. This preliminary study points out interesting differences between alloys produced from the melt vs. those produced by powder processing.

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