Inclusion engineering in Co-based duplex entropic alloys

Highlights: • First time to investigate inclusion characteristics in Co-based entropic alloys. • Quantitatively discuss size evolution of different inclusions in the proposed alloys. • Experimental findings of inclusion agglomeration potency is predicted by the theory. Co-based duplex entropic alloy is designed very recently to replace pure Co as a major component of the binder phase for cemented carbide cutting tools. This work aims to provide a fundamental study of oxide inclusion characteristics in the duplex fcc + hcp Co-based entropic alloys. It is found that the Co_85−xCr_xFe_7.5Ni_7.5 (x = 15, 30 at.%) alloys hold the highest liquidus (T_liq) and solidus (T_sol) temperatures, compare with the Co_85−xCr_xMn_7.5Ni_7.5 (x = 15, 30 at.%) and Co_77.5−xCr_xFe_7.5Mn_7.5Ni_7.5 (x = 15, 30 at.%) alloys. For each grade, the increasing Cr content leads to a decrease of T_sol and T_liq temperatures. It is also noted that there is an approximate 100 °C of undercooling exists in each grade during the solidification. The stable oxide inclusion in the Co_85−xCr_xMn_7.5Ni_7.5 and Co_77.5−xCr_xFe_7.5Mn_7.5Ni_7.5 alloys is the MnCr₂O₄ type, while Cr₂O₃ is the main stable inclusion in the Co_85−xCr_xFe_7.5Ni_7.5 alloy. Furthermore, the size range of the MnCr₂O₄ particles is larger than that of Cr₂O₃. The theoretical calculation shows that MnCr₂O₄ has a higher coagulation coefficient than Cr₂O₃ does. This is due to the influence of the thermo-physical parameters, i.e. the interfacial energy between the oxide and the alloy and the viscosity of liquid alloy. The theoretical calculation fits well with the experimental findings.