Abstract
The liquid phase separation (LPS) behavior in Co-Cr-based high-entropy alloys (HEAs) is an important target for the development of Co-Cr-based HEAs for metallic biomaterials (BioHEAs). The solidification microstructure in Ag-Co-Cr-Fe-Mn-Ni-Ag, Co-Cr-Cu-Fe-Mn-Ni-Cu, and Co-Cr-Cu-Fe-Mn-Ni-B HEAs, which were designed as the combination of the equiatomic CoCrFeMnNi with Ag, Cu, and the interstitial element of B, was investigated as the fundamental research of LPS in Co-Cr-based HEAs. Ingots of equiatomic AgCoCrFeMnNi, equiatomic CoCrCuFeMnNi, non-equiatomic CoCrCuxFeMnNi (x = 2, 3), and CoCrCuxFeMnNiB0.2 (x = 1, 2, 3) with a small amount of B were fabricated using the arc-melting process. A macroscopic phase-separated structure was observed in the ingots of the equiatomic AgCoCrFeMnNi and CoCrCuxFeMnNiB0.2 (x = 2, 3) HEAs. The addition of a small amount of B enhanced the LPS tendency in the Co-Cr-Fe-Mn-Ni-Cu HEAs. The LPS behavior was discussed through the heat of mixing and computer coupling of phase diagrams and thermochemistry (CALPHAD).
Highlights
Co-Cr-based and Co-Cr-Mo-based alloys are commercially used as engineering materials in industry for high wear resistance and superior chemical and corrosion performance in hostile environments
The liquid phase separation (LPS) tendency in the designed alloy system was discussed based on the heat of mixing (∆Hi-j ) of the i-j atomic pair [66], predicted phase diagrams constructed by the Materials Project [67], and thermodynamic calculation using FactSage and SGTE2017
A macroscopically phase-separated structure, which is typical for the solidification microstructure formed via LPS, was observed in the equiatomic AgCoCrFeMnNi High-entropy alloys (HEAs) and B-added CoCrCux FeMnNiB0.2
Summary
Co-Cr-based and Co-Cr-Mo-based alloys are commercially used as engineering materials in industry for high wear resistance and superior chemical and corrosion performance in hostile environments. Co-Cr-based and Co-Cr-Mo-based alloys have been commercially used as metallic biomaterials [1,2,3,4,5,6,7], for surgical implants. Examples of these are ASTM F753, ASTM F1537, and JIS T 7402 alloys. Co-Cr-Mo-based HEAs of Ag-Co-Cr-Fe-Mn-Mo-W HEAs [23] were developed from Co-Cr-Mo metallic biomaterials, and the single solid solution formation for the development of Co-Cr-based HEAs for metallic biomaterials (BioHEAs) was prevented by the σ phase formation and the occurrence of LPS. The σ phase formation was clarified to be related to the valence
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