Microstructure Evolution And Electrochemical Corrosion Behavior Of Directionally Solidified FeCoNiCr Based Multi-principal-element Alloys

According to multi-principal-element alloys of equal atomic ration design concept, the free solidified FeCoNiCrAl alloy and FeCoNiCrCu alloy were synthesized by vacuum electromagnetic induction method, and directionally solidified FeCoNiCrAl alloy and FeCoNiCrCu alloy were prepared by directional solidification experiment which was carried out at various withdrawal velocitys under the condition of certain temperature gradient. The phase, distribution of element, microstructure evolution and thermal property of multi-principal-element alloys were examined by using optical microscope, SEM, EDS, XRD, DSC. Electrochemical corrosion behaviors of the free solidified alloys and directionally solidified alloys which were prepared under withdrawal velocity of 1μm/s were analysed in 3.5%NaCl solution.The XRD result shows that brittle intermetallics are not observed while only simple phase structures are found in alloys. Only diffraction peak corresponding to a BCC crystal structure is observed for the FeCoNiCrAl alloy while only diffraction peak corresponding to a FCC crystal structure is observed for the FeCoNiCrCu alloy. EDS results indicate that dendritic segregation area is found to be Ni, Al rich and Fe, Cr deplete, while interdendritic segregation area is Fe, Cr rich and Ni, Al deplete, and the distribution of Co is essentially identical in the FeCoNiCrAl alloy. Dendritic segregation area is found to be Fe, Co, Ni, Cr rich and Cu deplete, while interdendritic segregation area is Cu rich and Fe, Co, Ni, Cr deplete in the FeCoNiCrCu alloy.In the experiment, with the increase of growth rate, FeCoNiCrAl alloy steady-state organization has experienced evolution of planar crystal, coarse cell crystal, small cell crystal, coarse dendrite, slender dendrite; FeCoNiCrCu alloy steady-state organization has experienced evolution of planar crystal, cell crystal, cell-dendrite crystal, dendrite crystal. With the solidification rate increased, two kinds of alloys experience grain refinement. FeCoNiCrAl alloy adjusts primary spacing mainly through the way of competitive growth and lateral branches to develop into primary spindle arm while FeCoNiCrCu alloy adjusts primary spacing mainly through the way of competition growth and cutting-edge cracking.In 3.5% NaCl solution, FeCoNiCrAl alloy and FeCoNiCrCu alloy show a similar electrochemical corrosion properties, which is that corrosion resistant property of the directionally solidified alloy prepared at the growth rate of 1μm/s is greater than that of free solidified alloy, because grain number reduces and extent of element segregation decreases for the directionally solidified alloy, reducing the tendency of formation of localized corrosion original battery.