Comparative Site-Specific Study on Partitioning of Solutes in Structural Alloys and Rare-Earth Magnets
DOI:
https://doi.org/10.71448/jme2026122Keywords:
solute topology; short-range order; atom probe tomography; grain-boundary segregation; boundary cohesion; grain-boundary diffusion; Nd–Fe–B magnets; alloy designAbstract
The choice of the physical site is crucial to atomic scale alloy design since the state is defined relative to its location in a material. For the fcc Co-Cr-Ni system, the key physical site is the nearest-neighbor one; for the ferritic iron material, it is the pairing within the grain boundary plane; while for the Pr-Al-diffused Nd-La-Ce-Fe-B magnets, it is the shell-boundary region where the magnetism is preserved. The research problem is the identification of the appropriate among six possible states on the basis of the analysis of their behavior relative to the failure condition of their respective physical site. The material set includes equiatomic Co-Cr-Ni after heat treatment at 1200∘C/24 h and at 500∘C/500 h; Mo/W-containing and Cu-containing paired solute states at Σ3(111), Σ3(112), Σ9(221), and Σ11(332) ferritic iron boundaries; and Pr-Al diffusion states in Nd-La-Ce-Fe-B magnets processed at 900∘C/6 h + 480∘C/4 h. In Co-Cr-Ni, the 1200∘C/24 h condition acts as the weak order comparison condition due to the proximity of its local signal to the interval of the random state of −0.00022 to +0.00022. In ferritic iron, Mo- and W-containing boundary pairs need cohesion-sensitivity test, while Cu paired with Ti, V, Cr, Mn, Co, or Ni is excluded under the hypothesis of pairing occupation associated with the bad cohesion. In the magnet, the useful diffusion depth does not lie in the maximum detectable one of the Pr or Al signal; it corresponds to the deepest zone with the Pr-Al-rich shell and high-Al rare-earth boundary phase still coupled. At about 100 μm, the boundary phase consists of the following composition: Nd 5.20 at.%, Pr 22.30 at.%, Ce 1.61 at.%, La 0.72 at.%, Fe 53.07 at.%, Co 1.86 at.%, Al 13.75 at.%, and B 1.48 at.%. Chemically visible solute states direct the alloy design only under all four criteria satisfaction.
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