Strengthening by customizing microstructural complexity in nitrogen interstitial CoCrFeMnNi high-entropy alloys

Interstitial alloying has been proved to be a promising option to improve the mechanical properties in various commercial alloys. Herein, we systematically investigate the microstructure evolution and mechanical property change of CoCrFeMnNi high-entropy alloys (HEAs) with varied nitrogen contents as an interstitial alloying element. To equilibrate the thermal history, all the alloys are heat-treated as follows: homogenization (1100 degrees C for 20 h), cold-rolling (reduction ratio of 60%), and subsequent annealing (900 degrees C for 3 min). In N1 alloy (CoCrFeMnNi HEA with 1 at% of nitrogen doping), we could observe fully recrystallized grains with a small amount of Cr2N precipitates. As the nitrogen contents increased to 3 at% (N3 alloy), the recrystallization was significantly retarded by the formation of 3 different types of Cr2N precipitates, leading to having similar to 60% of non-recrystallized grains. Furthermore, the various precipitates let the alloy have a heterogeneous complex microstructure. With increasing nitrogen contents, the yield strength and ultimate tensile strength can be improved without significant reduction of ductility, which exceeds those of Cantor HEA by nearly a factor of two. The effect of each strengthening mechanism on the improved strength in heterogeneous complex microstructure is systematically discussed. These results are expected to provide a novel guideline on how to effectively control key properties of HEAs by interstitial alloying through tailoring of heterogeneous microstructure as well as the inherent complexity of HEAs. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study systematically investigates the microstructure evolution and mechanical property change of CoCrFeMnNi high-entropy alloys (HEAs) with varied nitrogen contents as an interstitial alloying element. The results show that increasing nitrogen contents can improve the yield strength and ultimate tensile strength of the alloy without significant reduction of ductility, exceeding those of Cantor HEA by nearly a factor of two.