Tuning the Microstructure and Mechanical Properties of Cold Sprayed Equiatomic CoCrFeMnNi High-Entropy Alloy Coating Lay
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Tuning the Microstructure and Mechanical Properties of Cold Sprayed Equiatomic CoCrFeMnNi High-Entropy Alloy Coating Layer Ji‑Eun Ahn1 · Young‑Kyun Kim1 · Sang‑Hoon Yoon2 · Kee‑Ahn Lee1 Received: 30 July 2020 / Accepted: 20 September 2020 © The Korean Institute of Metals and Materials 2020
Abstract An equiatomic CoCrFeMnNi high entropy alloy (HEA) coating layer was prepared via a cold spray (CS) process. In order to control the microstructure and nano-indentation properties of the CS HEA, heat treatments were employed. CS HEA coating layer showed a heterogeneous microstructure where ultra-fine grains were formed at the particle interfaces, while coarse grains were formed inside the particles. Furthermore, deformation twins (DTs) were also formed inside the particles due to severe plastic deformation (SPD) in each particle generated during the CS deposition. For the 550 °C heat treatment (HT), fine Cr-rich precipitates were additionally formed at the grain boundary and particle boundary. By contrast, recrystallization occurred during 850 °C HT, while the size of the Cr-rich precipitate increased. The nano-indentation hardness of the CS HEA coating layer was 10.9 GPa, which was ~ 3 times higher than that of the conventional cast HEA. The superior hardness of the CS HEA might has been enabled due to the combination of the high dislocation density, DTs, and ultra-fine grains. Based on the results above, the strategy to control the microstructure and mechanical properties through HT of the equiatomic CoCrFeMnNi HEA coating layer prepared via the CS process has been discussed. Keywords High-entropy alloy · Cold spray · Coatings · Microstructure · Nanoindentation · Heat treatment
1 Introduction High entropy alloy (HEA) or compositionally complex alloy (CCA), with unique properties, is a mixture of at least 5 principal elements, unlike conventional alloys, and each element exists at the mole fraction of 5–35 at% [1–4]. In addition, the HEA is characterized as not forming an intermetallic compound owing to its high configurational entropy. In particular, the equiatomic CoCrFeMnNi HEA (referred to as cantor alloy), which has been firstly developed among HEAs, has received extensive attention in the past 10 years due to its excellent tensile strength-ductility combination at Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12540-020-00886-4) contains supplementary material, which is available to authorized users. * Kee‑Ahn Lee [email protected] 1
Department of Materials Science and Engineering, Inha University, Incheon 22212, Republic of Korea
Industrial Materials Research Group, Research Institute of Industrial Science and Technology, Pohang 37673, Republic of Korea
2
cryogenic temperatures, high fracture toughness and corrosion resistance; therefore, numerous studies have been conducted [5–12]. Recently, due to the excellent physical and chemical properties of cantor alloy, its application as a coating layer as well as a bulk material is emerging [13, 14, 17].
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