Microstructure and Mechanical Property Evolution during Annealing of a Cold-Rolled Metastable Powder Metallurgy High Entropy Alloy

Li Li,Zhou Zhou,Qiu Qiu,Guo Guo,Liu Liu

doi:10.3390/e21090833

Li Li, Zhou Zhou + Show 3 more

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https://doi.org/10.3390/e21090833

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Abstract

Precipitation strengthening is an effective approach to strengthen high-entropy alloys (HEAs) with a simple face-center-cubic (FCC) structure. In this work, CoCrFeNiMo0.2 HEAs were prepared by powder metallurgy, followed by cool rolling and subsequent heat-treatment at different temperatures. The effects of cold working and annealing on microstructure and mechanical properties have been investigated. Results show the fine and dispersed (Cr, Mo)-rich σ phase with a topologically close-packed structure precipitated in the FCC matrix after the prior cold deformation process, which enhanced the mechanical property of the CoCrFeNiMo0.2 alloy. The HEA annealed at 600 °C for 48 h had a tensile strength of 1.9 GPa but an elongation which decreased to 8%. The HEA annealed at 800 °C for 12 h exhibited a tensile strength of 1.2 GPa and an elongation of 31%. These outstanding mechanical properties can be attributed to precipitation strengthening and fine-grain strengthening.

Highlights

Most traditional alloys, such as steels, Al alloys, and nickel-based superalloys, generally consist of one element as their principal component and other additional minor elements to improve their mechanical properties. This conventional limitation on composition design strategy was broken by high-entropy alloys (HEAs), which were proposed by Yeh et al [1,2]
The CoCrFeNiMo0.2 HEAs were prepared by the powder metallurgy method in this work
The chemical composition of the alloy powder obtained by gas atomization is shown in Table 1; the composition is close to the nominal composition of CoCrFeNiMo0.2

Summary

Introduction

Most traditional alloys, such as steels, Al alloys, and nickel-based superalloys, generally consist of one element as their principal component and other additional minor elements to improve their mechanical properties. This conventional limitation on composition design strategy was broken by high-entropy alloys (HEAs), which were proposed by Yeh et al [1,2]. FCC HEAs exhibit outstanding ductility [3,4,5,6,7,8,9]. It has been reported that appropriate composition design can promote the formation of secondary precipitation in HEAs through heat treatment, as with other conventional alloys [18,19,20,21,22]

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