Effect of Mn Addition on the Microstructures and Mechanical Properties of CoCrFeNiPd High Entropy Alloy

Abstract

CoCrFeNiPdMnx (x = 0, 0.2, 0.4, 0.6, 0.8) high entropy alloys (HEAs) were prepared and characterized. With an increase in Mn addition, the microstructures changed from dendrites (CoCrFeNiPd with a single face-centered-cubic (FCC) phase) to divorced eutectics (CoCrFeNiPdMn0.2 and CoCrFeNiPdMn0.4), to hypoeutectic microstructures (CoCrFeNiPdMn0.6), and finally to seaweed eutectic dendrites (CoCrFeNiPdMn0.8). The addition of Mn might change the interface energy anisotropy of both the FCC/liquid and MnPd-rich intermetallic compound/liquid interfaces, thus forming the seaweed eutectic dendrites. The hardness of the FCC phase was found to be highly related to the solute strengthening effect, the formation of nanotwins and the transition from CoCrFeNiPd-rich to CoCrFeNi-rich FCC phase. Hierarchical nanotwins were found in the MnPd-rich intermetallic compound and a decrease in either the spacing of primary twins or secondary twins led to an increase in hardness. The designing rules of EHEAs were discussed and the pseudo binary method was revised accordingly.

New Advances in High-Entropy Alloys

“…This phenomenon was revealed by Zhang et al [ 24 ]. Tan et al [ 25 ] then studied the effect of Mn addition on the microstructures and mechanical properties of this CoCrFeNiPd alloy.…”

Thermal–Mechanical Processing and Strengthen in AlxCoCrFeNi High-Entropy Alloys

“…Recently, studies have focused on overcoming the strength-ductility trade off, by introducing high-density nano-twins in the grains (Lu, 2016;Schneider et al, 2020), as processing fine grains combined with nanoscale precipitates even distribution within the grains (Zhao et al, 2020b;Guillot et al, 2020;Yu et al, 2020), controlling the lattice misfit between intermetallic nanoparticles and matrix (Miracle, 2015;He et al, 2016a;Zhang et al, 2019) and producing materials with a heterogeneous structure (Sun et al, 2018;Wu et al, 2019;Du et al, 2020). The successful preparation of eutectic high-entropy alloy (EHEA) provided a new way to optimize the phase structure of HEAs by combining the ductile phase (e.g., fcc solid-solution phase) with the hard phase (e.g., bcc solid-solution phase or intermetallics) (Lu et al, 2014;Tan et al, 2019). This structure design could be realized through a simple and effective way of thermal-mechanical processing, offering a feasible strategy for a new generation of high-strength and high-toughness HEAs.…”