Microstructure and Mechanical Properties of CoCrFeMnNiSn_x High-Entropy Alloys

The objective of this study is to investigate the effect of Sn content on the microstructure and mechanical properties of the CoCrFeMnNiSn_x high entropy alloys. The microstructure and mechanical properties of the alloys have been studied by X-ray diffraction, scanning electron microscopy, room-temperature compressive tests and Vickers hardness tests. It has been found that Sn has a great effect on the microstructure and mechanical properties of the alloys. The CoCrFeMnNi alloy has a simple FCC phase structure, while a few white precipitations (MnNi₂Sn-like) are observed in the Sn_0.03 and Sn_0.07 alloys. With further additions of Sn, the microstructure of Sn_0.1, Sn_0.3 and Sn_0.5 changes to a typical dendrite structure, the dominated dendrite region has a lattice of FCC structure which is enriched with Cr, Co and Fe, and the interdendritic region is enriched with Mn, Ni and Sn. The volume of the MnNi₂Sn-like phase increases with Sn content increasing. The addition of Sn enhances the formation of the MnNi₂Sn-like phase in the CoCrFeMnNiSn_x alloys, and improves the hardness and strength of as-cast alloys, but reduces the ductility of the alloys. The strengthening mechanism of alloys was solid solution strengthening and formation of the MnNi₂Sn-like phase. In the CoCrFeMnNiSn_0.03 and CoCrFeMnNiSn_0.07 alloys, the solid solution is the dominant mechanism. With the Sn content increasing, the second phase strengthening is the dominant mechanism.