Phase Stability of the CoxMn2-xCrFeNi High Entropy Alloys
TIAN Mengyun1, WU Changjun1,2, LIU Ya1,2, PENG Haoping1, WANG Jianhua1,2, SU Xuping1,2
1 Jiangsu Key Laboratory of Materials Surface Science and Technology, School of Materials Science and Engineering, Changzhou University,Changzhou 213164,China 2 Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Changzhou 213164, China
Abstract: The phase stability of arc-melted CoxMn2-xCrFeNi (x=0.25—1.75) high entropy alloys in as-cast and 800 ℃ or 1 000 ℃ annealed states were investigated using XRD, SEM, EDS, and DSC. It was found that the CoxMn2-xCrFeNi alloy with more than 15at% Co had a FCC single phase in as-cast state or after annealing at 800 ℃ or 1 000 ℃ for 720 h. The as-cast Co0.25Mn1.75CrFeNi alloy was composed of FCC+BCC two-phase. However, after annealing at 1 000 ℃ or 800 ℃ for 720 h, the BCC phase disappeared, and the Cr element enriched and transformed into FCC+σ phases. In 800 ℃ annealed Co0.5Mn1.5CrFeNi alloy, not only σ phase but also Cr-rich BCC phase was precipitated from the as-cast FCC matrix. DSC measurements showed that the transition point of FCC phase increased with the increasing of Co content, and the σ phase would decompose at 1 097—1 120 ℃. In addition, although thermodynamic calculation based on TCFE database could accurately predict the stability of FCC phase, it could not accurately predict the stability of BCC phase and σ phase. That is to say, the thermodynamic parameters of the σ and BCC phases in Co-Cr-Fe-Mn-Ni system still need to be further optimized.
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