Experimental determination of phase equilibria in the Co–Cr–Si ternary system

Kazushige Ioroi; Shunya Mochimaru; Xiao Xu; Ryosuke Kainuma; Toshihiro Omori

doi:10.1016/j.jallcom.2026.190321

ジャーナル論文 Experimental determination of phase equilibria in the Co–Cr–Si ternary system

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Kazushige Ioroi, Shunya Mochimaru, Xiao Xu, Ryosuke Kainuma, Toshihiro Omori. Experimental determination of phase equilibria in the Co–Cr–Si ternary system. Journal of Alloys and Compounds. 2026, 1080 (), 190321. https://doi.org/10.1016/j.jallcom.2026.190321

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(abstract)

The phase equilibria of Co–Cr–Si ternary alloys at 1000 and 1200 °C were comprehensively investigated using X-ray diffraction (XRD) analysis, microstructural observations, and quantitative compositional analysis by field-emission electron probe microanalyzer equipped with wavelength dispersive X-ray spectroscopy (FE-EPMA/WDS). The γ(Co)/ε(Co) phase boundary and solubility ranges of binary and ternary intermetallic compounds were determined. Electron backscatter diffraction (EBSD) analysis enabled distinction between the ε(Co) microstructure retained by water quenching and the massive-like ε(Co) microstructure obtained via transformation from γ(Co) during quenching; this helped estimate the γ(Co)/ε(Co) two-phase regions at 1000 and 1200 °C. Several binary silicide phases exhibited well-defined solubility ranges. The β-Co2Si phase was stabilized by Cr addition and could dissolve up to 24.7 at.% Cr at 1000 °C and 29.6 at.% Cr at 1200 °C. The solubility range of the χ phase expanded toward the Cr–Si-rich region with increasing temperature, whereas that of the R phase contracted. FE-EPMA/WDS and XRD analyses revealed that the N phase exists as a ternary compound adopting the Mn5Si3-type structure, with solubility of 30.5–38.3 at.% Cr at 1200 °C. However, the N phase decomposed into β-Co2Si and a eutectoid microstructure consisting of the (Co,Cr)Si and Cr3Si phases, indicating that it is stable only at elevated temperatures. Based on these results, isothermal sections of the Co–Cr–Si phase diagram at 1000 and 1200 °C were constructed.

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