Microstructural and fractographic analysis of non-equiatomic alloy of Co – Cr – Fe – Mn – Ni system

In the present work, the microstructure of Co20Cr20Fe10Mn30Ni20 high-entropy alloy with increased Mn content and decreased Fe content, which was obtained by vacuum induction melting, was studied. The study evaluates the effect of Fe and Mn content percentages on the microstructure and mechanical properties of high entropy alloy (HEA). The relationship between the microstructure (formation of solid solution phases) and mechanical properties of HEA in comparison with the high-entropy equiatomic Cantor alloy is investigated. Studies of the structure, phase and chemical composition of the material were obtained using X-ray diffraction and scanning electron microscopy. It is shown that the studied alloy is a material consisting of a single-phase solid solution with a face-centered cubic lattice and a structure represented in the form of dendrite branches of the first, second and third order. Energy dispersive X-ray spectroscopy revealed that the dendrite axes are enriched with chromium, iron and cobalt atoms, while manganese and nickel predominate in the interdendritic areas. It is likely that during crystallization process, such elements as manganese and nickel have time to be redistributed and released in the form of second-phase particles in the interaxial spaces of dendrites. Destruction of the material is represented by ductile fracture with the content of deep fracture holes, indicating high plasticity of the material, as well as the presence of globular oxide inclusions, which are more enriched in manganese, oxygen and chromium atoms. According to the conducted tensile tests, it was found that the samples of Сo20Cr20Fe10Mn30Ni20 mainly have high (more than 80%) plasticity and σ0.2 = 236 MPa, σlim = 478 MPa, respectively. The result also shows that the decrease of Fe and increase of Mn in the alloy increases the strain hardening rate, which further increases the embrittlement degree. It is found that the composition of the area containing non-metallic inclusion in Co20Cr20Fe10Mn30Ni20 alloy is more enriched in manganese, oxygen and chromium. The study was funded by the Russian Science Foundation grant No. 23-49-00015, https://rscf.ru/project/23-49-00015/.