Vacuum 192 (2021) 110481 Available online 21 July 2021 0042-207X/© 2021 Elsevier Ltd. All rights reserved. Short communication Double-stage hardening behavior of a lightweight eutectic high entropy alloy in the course of low cycle fatigue M.H. Asoushe a , A. Zarei Hanzaki a, ** , H.R. Abedi b, * a Hot Deformation and Thermomechanical Processing Laboratory of High-Performance Engineering Materials, School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran b School of Metallurgy & Materials Engineering, Iran University of Science and Technology (IUST), Tehran, Iran A R T I C L E INFO Keywords: High entropy alloys Fatigue Deformation and fracture Dendritic structure ABSTRACT A unique crack growth behavior was detected during room temperature cyclic loading of a eutectic high entropy alloy, which caused the occurrence of two-stage cyclic hardening under the low cycle regime in tensile and compressive half cycles. This was attributed to the crack trapping between the dendritic branch, which caused retardation of the growth stage until the crack sheared and pass through the dendrite. The mechanical frag- mentation of the dendrite and distribution through the microstructure could effectively resist crack propagation. This led to higher stress levels during cyclic loading compared with monotonic loading under both tensile and compressive modes of deformation. 1. Introduction High-entropy alloys (HEAs), which usually consist of fve or more elemental constituents with a nearly equal ratio, possess attractive properties such as high hardness, oxidation/corrosion resistance, and outstanding structural stability. In this respect, they have attracted extensive attention from theoretical and industrial points of view. Interestingly, the properties of these compositionally complex alloys can also be tuned in a wide range by changing the type and concentration of their constituents [1,2]. The presence of casting defects within the developed microstructures, such as micro-segregation or cavities, may serve as stress concentration regions and lead to the formation of dis- continuities and micro-crack, thereby deteriorating the mechanical strength and ductility values [3,4]. To overcome such problems, the eutectic HEAs alloys have been developed in which owing to the occurrence of eutectic isothermal transformation and elimination of solidifcation temperature range, both segregation and shrinkage cavity can be alleviated and cast-ability is improved [3]. The concept of eutectic high entropy alloy (EHEA) was frst introduced by Lu et al. through considering the composition of AlCoCrFeNi 2.1 , consisting of both FCC and BCC phases arranged as eutectic structure [5]. The majority of previous researches regarding the deformation behavior of high entropy alloys have focused on the microstructure evolution in the course of monotonic loading. In this respect, Hemphill [3] showed that in Al0.5CoCrCuFeNi alloy the aluminum-oxide-rich particles have been formed during the melting and solidifcation and subsequent homogenization processes, and provide nucleation sites for micro-cracks due to the stress concentration at the particles-matrix interfaces. It is worth to mention that the damages may be more seriously accumulated through the cyclic fatigue loading, which is known as a crucial property for any structural component in servicing condition. However, only a few studies have been directed to investigate the fa- tigue behavior of HEAs. Apparently, in the case of EHEAs, reduction of the casting defects can signifcantly affect the mechanical properties, especially in the course of cyclic loading where the crack initiation and crack propagation are more prominent [6]. In addition, the eutectic cast structure characteristics (such as dendrite morphology and dendrite arm spacing) would play an important role in determining the fatigue behavior of EHEAs. In this context, the present work has been steered toward studying the effect of casting structure characteristics resulting from eutectic solidifcation and on the cyclic behavior of the suscepti- bility for crack initiation and propagation with special emphasizing on the effect of dendritic morphology. * Corresponding author. ** Corresponding author. E-mail addresses: zareih@ut.ac.ir (A.Z. Hanzaki), habedi@iust.ac.ir (H.R. Abedi). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum https://doi.org/10.1016/j.vacuum.2021.110481 Received 14 June 2021; Received in revised form 13 July 2021; Accepted 19 July 2021