Control of cleanliness in sustainable high entropy alloys: A comparison study of non-metallic inclusion behaviors in CoCrFeMnNi alloys produced by pure metals and low-cost feedstocks

초록

Commercial ferroalloys offer a resource-efficient alternative to high-purity elemental feedstocks for high-entropy alloy production, but impurity-derived inclusions require the systematic evaluation. Two CoCrFeMnNi high-entropy alloys were produced by high-frequency induction melting using high-purity elemental metals (Cantor-P) and commercial FeMn, FeCr, and FeNi ferroalloys supplemented with Ni and Co (Cantor-F). Inclusion chemistry, formation, and evolution were investigated using equilibrium and Scheil-Gulliver solidification calculations, scanning electron microscope equipped with energy dispersive X-ray spectroscopy (SEM-EDS), automated inclusion analysis, electrolytic extraction, and high-temperature confocal laser scanning microscopy (HT-CLSM). FeMn mainly contained MnO and MnO-SiO2 inclusions, FeCr contained Cr2O3 and Cr2O3-MnO inclusions, and FeNi contained abundant MnS, providing the potential precursors for complex inclusions in Cantor-F. The higher Si content in Cantor-F promoted SiO2-MnO-rich outer layers around Cr2O3-MnO based inclusions and increased the spheroidization of Cr2O3-MnO-Mn(S, Se)-SiO2 inclusions. The initial inclusion number densities were 617.1 and 673.4 mm-2, and the mean inclusion sizes were 1.73 and 1.81 μm in Cantor-P and Cantor-F alloys, and the sizes of most inclusions in both alloys were smaller than 2 μm. During HT-CLSM measurements, small Si-bearing inclusions in Cantor-F began to agglomerate at a separation of approximately 10 μm and exhibited a slightly higher apparent migration velocity. After remelting, the mean retained inclusion number densities were 45.3 mm−2 in Cantor-P and 32.4 mm−2 in Cantor-F. These results indicate a stronger apparent agglomeration and flotation tendency in Cantor-F, although the decrease cannot represent directly the measured inclusion removal efficiencies.

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