Understanding the microstructure refinement and mechanical strengthening of dual-phase high entropy alloy during ultrasonic shot peening

The ultrastrong gradient nanostructured dual-phase high entropy alloy (DP-HEA) Fe50Mn30Co10Cr10 has been fabricated by an efficient surface nanocrystallization method, e.g. ultrasonic shot peeing (USP) at room temperature. We investigated the effect of the USP duration on the microstructure of the DP-HEA Fe50Mn30Co10Cr10 by the advanced materials characterization methods, e.g. Electron Backscatter Diffraction (EBSD), X-ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). We found that the microstructure of the USPed DP-HEA Fe50Mn30Co10Cr10 can be refined into several nanometers. Additionally, the FCC c phase is transferred into the HCP e phase during the USP process of the DP-HEA Fe50Mn30Co10Cr10 and the portion of the HCP e phase increases gradually with the increase of the USP duration. Nanoindentation tests indicate that the nanohardness of the nanostructured DP-HEA Fe50Mn30Co10Cr10 can reach as high as 7.49 GPa, suggesting a yield strength of 2.49 GPa, which is 10 times higher than that of the coarse-grained materials. Additionally, nanocrystallization of the DP-HEA Fe50Mn30Co10Cr10 can be triggered with a short peening duration and the transformation-induced plas-ticity (TRIP) effect can benefit the formation of a thick gradient nano-grained layer during USP. Micro-tensile tests revealed that the gradient nano-grained layer can significantly improve the yield strength of the DP-HEA Fe50Mn30Co10Cr10 with sacrificing ductility.& COPY; 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).