Investigation of microstructure, texture, and mechanical properties of FeCrCuMnNi multiphase high entropy alloy during recrystallization

Highlights

• A fully recrystallized microstructure was achieved after annealing at 1273 K.

• Fast elimination of residual strain in FCC1 led to earlier recrystallization.

• D and Cube texture components formed as a result of recrystallization.

• The alloy preserved its strength during partial recrystallization.

Abstract

FeCrCuMnNi multiphase high entropy alloy was cold-rolled to 85% reduction and annealed at different temperatures. Recrystallization behavior of the alloy was investigated using XRD, SEM-EBSD, hardness, microhardness, and tensile tests. The results revealed variation in phase distribution due to annealing and earlier recrystallization of the FCC1 phase. Recrystallization of FCC1 and FCC2 phases initiated at 873 and 1073 K, respectively, and a fully recrystallized microstructure was seen after 1273 K. Deformation texture components eliminated slowly with increase in annealing temperature, and D and Cube components formed as a result of recrystallization. Faster decrease in FCC1 microhardness was seen due to earlier recrystallization. In addition, an excellent combination of strength and elongation was achieved in the partially recrystallized samples compared to conventional alloys. The strength was affected more after annealing at temperatures higher than 1073 K. Fracture behavior of FCC2 phase changed from a brittle fracture to a ductile fracture with increase in annealing temperature; however, FCC1 phase revealed a ductile fracture even at low annealing temperatures.

Introduction

High-entropy alloys (HEAs) are multicomponent equiatomic or near- equiatomic alloys, consisting of at least five elements with amounts in the range of 5–35 at. %. There has been growing interest in HEAs in recent years for their superior mechanical properties, such as high strength, large strain-hardening capabilities, high fracture toughness, and so on. [[1], [2], [3]]. According to Boltzmann's hypothesis, based on the regular solution model, HEAs revealed high entropy of mixing in liquid state or regular solution state [3,4]. Therefore, HEAs with special composition, may consist of simple solid solution structures such as face-centered cubic (FCC), body-centered cubic (BCC), and/or hexagonal closed-pack (HCP) instead of ordered phases or complex intermetallics [[4], [5], [6]]. However, the presence of ordered phases or intermetallics in the microstructure of different HEA systems were reported, and it was seen that these phases significantly affects their properties [1,3,7,8].

Hitherto, most of the studies carried out on HEAs have assessed as-cast or homogenized materials [4,[9], [10], [11], [12]]. However, similar to conventional alloys, there is a great possibility of microstructural control through thermo-mechanical processing (TMP) in HEAs in order to improve their properties [1,2]. Nevertheless, this field has recently attracted the attention of researchers working on different parameters and different alloying systems [7,13,14].

It has been reported that HEAs reveal resistance to grain growth and maintain their deformed microstructure at higher temperatures, compared to traditional alloys [1,15,16]. According to Guo et al. [13], Al_0.5CoCrFeNi HEA resists restoration process and has a high recrystallization temperature (0.8 Tm). These authors have argued that this phenomenon can be attributed to original coarse as-cast grains, severe lattice distortion effect, and sluggish diffusion effect [13]. In addition, Bhattacharjee et al. [5] claimed that dislocation energy and grain boundary energy decreases due to the strain energy related to severe lattice distortion in HEAs; therefore, the driving force for recrystallization decreases.

Moreover, a meaningful combination of tensile strength and elongation for partially-recrystallized and recrystallized HEAs has been reported [1,7,14,17]. Mostly, researchers have reported that the temperature effect evidently influences tensile strength and have reported a linear decline in strength with increasing temperature [18]. Baker et al. [1] showed >800 MPa tensile strength with 20% elongation in recrystallized FeNiMnAlCr alloy. The dual phase nature of the alloy, fine grain size, and solution hardening effect were claimed to be the main reasons for these properties [1]. Additionally, Park et al. [2] have shown that the microhardness of the CoCrCuFeNi alloy decreases with increasing of the fraction recrystallized; however, the microhardness values of partially recrystallized specimens were found to be much higher than those predicted using a simple rule of mixture. They reported that the reasons for this phenomenon were the ultrafine grain size, sluggish diffusion, and two-phase structure of the CoCrCuFeNi alloy [2].

In the present work, the microstructure, texture, and mechanical properties of the FeCrCuMnNi alloy was investigated following cold-rolling and annealing treatments, which has so far not been reported. Therefore, the samples were cold rolled to 85% thickness reduction and annealed for 60 min at different temperatures, and then, examined using X-ray diffraction (XRD), scanning electron microscope-electron backscatter diffraction (SEM-EBSD), and hardness and tensile tests.