Characterization of non-metallic inclusions in Co46Cr30Mn7.5Fe7.5Ni7.5V1.5 dual-phase high entropy alloy with trace amount of Hf addition

초록

This study systematically investigates the effect of trace hafnium (Hf) addition (0.069 wt%) on the microstructure evolution and inclusion characteristics in V-alloyed Co-based dual-phase high-entropy alloys. The trace amount of Hf addition was found to mainly form HfO<inf>x</inf> inclusion in the matrix. This phase replaces the conventional oxide formation and could stabilize the V element in the matrix and against its oxidation. Compare with the Hf-rich HEAs, where Hf segregates at grain boundaries within an FCC-dominant matrix and forms lamellar HCP precipitates. However, Co<inf>46</inf>Cr<inf>30</inf>Mn<inf>7.5</inf>Fe<inf>7.5</inf>Ni<inf>7.5</inf>V<inf>1.5</inf> with a trace amount of Hf enhances the blocky HCP phase formation and increases the HCP fraction from 15 % to 26 %. Non-metallic inclusion analysis here reveals that V-HEA contains HfO<inf>x</inf> alongside MnS and HfO<inf>x</inf>-MnS. In situ observations by high-temperature confocal laser scanning microscopy demonstrate that inclusion motion in the liquid matrix is governed by liquid surface flow and fluctuations. When inter-inclusion distances approach a critical value, attractive capillary force triggers the increase in velocity and acceleration and leads to a rapid collision of inclusions. Smaller inclusions exhibit a weaker attraction and are obviously influenced by the surface flow of liquid. While the larger inclusions are more prone to coarsening through agglomeration. This work provides theoretical and experimental insights into tailoring inclusion characteristics and microstructure evolution in HEAs through trace amounts of critical element addition. © 2025 Elsevier Inc.

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