Simultaneous Strength-Ductility Enhancement of a Nano-Lamellar AlCoCrFeNi2.1 Eutectic High Entropy Alloy by Cryo-Rolling and Annealing

T Bhattacharjee,S Guo,N Tsuji,S Sheikh,T Okawa,I S Wani,I T Clark,P P Bhattacharjee

doi:10.1038/s41598-018-21385-y

Abstract

Nano-lamellar (L12 + B2) AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) was processed by cryo-rolling and annealing. The EHEA developed a novel hierarchical microstructure featured by fine lamellar regions consisting of FCC lamellae filled with ultrafine FCC grains (average size ~200–250 nm) and B2 lamellae, and coarse non-lamellar regions consisting of ultrafine FCC (average size ~200–250 nm), few coarse recrystallized FCC grains and rather coarse unrecrystallized B2 phase (~2.5 µm). This complex and hierarchical microstructure originated from differences in strain-partitioning amongst the constituent phases, affecting the driving force for recrystallization. The hierarchical microstructure of the cryo-rolled and annealed material resulted in simultaneous enhancement in strength (Yield Strength/YS: 1437 ± 26 MPa, Ultimate Tensile Strength/UTS: 1562 ± 33 MPa) and ductility (elongation to failure/ef ~ 14 ± 1%) as compared to the as-cast as well as cold-rolled and annealed materials. The present study for the first time demonstrated that cryo-deformation and annealing could be a novel microstructural design strategy for overcoming strength-ductility trade off in multiphase high entropy alloys.

Highlights

High entropy alloys (HEAs) have emerged as a novel class of multicomponent alloys containing five or more elements in equi-atomic or nearly equi-atomic compositions[25]
Cryo-rolling has been investigated in single phase HEAs37,38, we have found a remarkable effect of cryo-rolling on tensile properties of the eutectic high entropy alloy (EHEA) for the first time
The microstructure shows remarkable heterogeneity due to the presence of the fine lamellar regions consisting of FCC and B2 lamellae, and the coarse non-lamellar regions consisting of FCC grains and coarse B2 www.nature.com/scientificreports/ Figure 2

Summary

Introduction

High entropy alloys (HEAs) have emerged as a novel class of multicomponent alloys containing five or more elements in equi-atomic or nearly equi-atomic compositions[25]. Despite having a large number of components, HEAs can show simple phases such as FCC, BCC and FCC + BCC25,26, presumably due to their high configurational entropy, which decreases the free energy sufficiently to stabilize simple solid solution phases. In order to further enhance the properties of HEAs, dual and multi-phase HEAs having mixture of soft and hard phases are suggested. Non-equiatomic AlCoCrFeNi2.1 eutectic HEA is a noteworthy example of such multiphase HEAs34. Cryo-rolling has been investigated in single phase HEAs37,38, we have found a remarkable effect of cryo-rolling on tensile properties of the EHEA for the first time

Methods

Results

Conclusion