Cryogenic Treatment of CoCrFeMnNi(NbC) High-Entropy Alloys
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JMEPEG https://doi.org/10.1007/s11665-019-04439-8
Cryogenic Treatment of CoCrFeMnNi(NbC) High-Entropy Alloys Erfan Abbasi and Kamran Dehghani (Submitted July 25, 2019; in revised form October 25, 2019) The effect of cryogenic treatment on the microstructure and mechanical properties of CoCrFeMnNi and CoCrFeMnNi(NbC) high-entropy alloys was investigated during annealing. The heat-treated samples were characterized by optical microscopy, scanning electron microscopy–wavelength-dispersive x-ray spectroscopy, x-ray diffraction technique, differential scanning calorimetry, Vickers hardness testing and tensile testing. The results showed a single-phase FCC crystal structure matrix in both alloys during cryogenic treatment and annealing. Cryogenic treatment altered the recrystallization behavior of CoCrFeMnNi highentropy alloy, while it did not influence the recrystallization of CoCrFeMnNi(NbC) high-entropy alloy. It was also found that cryogenic treatment changed the precipitation behavior of CoCrFeMnNi(NbC) highentropy alloy during annealing. In both studied high-entropy alloys, the mechanical testing indicated that the cryogenic treatment can effectively reduce the yield strength of cold-rolled samples after annealing. This was primarily attributed to the effect of cryogenic treatment in enhancing crystalline defects annihilation. Furthermore, the cryogenic treatment increased the ultimate tensile strength of CoCrFeMnNi(NbC). A lager plastic deformation and precipitates were considered as the main reasons for the higher ultimate tensile strength. Keywords
annealing, cryogenic treatment, high-entropy alloys, hardness, microstructural evolution, Nb-C addition
1. Introduction High-entropy alloys (HEA) have shown outstanding mechanical properties at cryogenic, room and high temperatures (Ref 1-3). This has been primarily attributed to their chemical composition and microstructure, consisting of a solid solution matrix with a high mixing entropy, lattice distortion and sluggish diffusion (Ref 4, 5). The microstructure of HEAs are mainly manipulated through thermomechanical processing after casting, e.g., annealing, hot/cold rolling followed by aging (Ref 6-8). It has been shown that the solid solution matrix of HEAs is normally stable during thermomechanical processing, despite the possible formation of secondary phases in matrix (Ref 911). The formation of secondary phases and precipitates in HEA can enhance their mechanical properties. In this context, ‘‘compositionally complex alloys (CCA)’’ have been introduced as a new generation of HEAs that consist of two or more phases with a high-entropy matrix (Ref 12). Conventional thermomechanical processing does not change the configurational entropy of matrix and consequently the characteristics of solid solution (Ref 13). However, it is not still
Erfan Abbasi, Department of Materials and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran; and IranÕs National Elites Foundation, Tehran, Iran; and Kamran Dehghani, Department of Materials and Metallurgi
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