Surface degradation mechanisms in a eutectic high entropy alloy at microstructural length-scales and correlation with phase-specific work function

Vahid Hasannaeimi,Saideep Muskeri,Aditya V Ayyagari,Riyadh Salloom,Sundeep Mukherjee

doi:10.1038/s41529-019-0079-0

Vahid Hasannaeimi, Saideep Muskeri + Show 3 more

Open Access

https://doi.org/10.1038/s41529-019-0079-0

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Abstract

High entropy alloys represent a new paradigm of structural alloy design consisting of (near) equal proportions of constituent elements resulting in a number of attractive properties. In particular, eutectic high entropy alloys offer a remarkable combination of high strength and good ductility from the synergistic contribution of each phase in the eutectic, thereby circumventing the strength-ductility trade-off in conventional structural materials. In the present study, wear and corrosion behavior were evaluated for the AlCoCrFeNi2.1 eutectic high entropy alloy consisting of BCC (B2), and FCC (L12) lamellae. A transition from adhesive to oxidative wear was observed in reciprocating wear analysis. The L12 phase with lower hardness preferentially deformed during the wear test. The ratio of hardness to modulus was almost two times higher for the B2 phase as compared to L12. The overall corrosion resistance of the eutectic high entropy alloy was comparable to 304 stainless steel in 3.5 wt% NaCl solution. However, detailed microscopy revealed preferential dissolution of the B2 phase. Phase-specific scanning kelvin probe analysis showed relatively higher electropositivity for the B2 phase as compared with L12, supporting the selective corrosion and higher coefficient of friction of B2.

Highlights

Multi-principal element alloys represent a new paradigm in the design of advanced materials consisting of equal proportions of constituent elements
Complex-phase high entropy alloys (HEAs) are finding increasing research interest as they bring together the superior properties of singlephase HEAs and precipitation strengthening effects of superalloys. In some of these alloys, the secondary phase is in the form of uniform dispersoids in a single-phase matrix,[1,2] while for others it is in the form of lamellae as in the case of eutectic HEAs (E-HEAs) such as AlCoCrFeNi2.1,3 Nb25Sc25Ti25Zr25,4 and CoCrFeNiNbx.[5]
Among the reported eutectic HEAs, AlCoCrFeNi2.1 E-HEA in particular has been found to be highly tunable, where a wide range of microstructures and excellent mechanical properties have been obtained by thermomechanical processing

Summary

INTRODUCTION

Multi-principal element alloys represent a new paradigm in the design of advanced materials consisting of (near) equal proportions of constituent elements These are often termed as high entropy alloys (HEAs) because high configurational entropy suppresses the formation of intermetallic compounds and leads to simple microstructures and attractive engineering properties. Complex-phase HEAs are finding increasing research interest as they bring together the superior properties of singlephase HEAs and precipitation strengthening effects of superalloys In some of these alloys, the secondary phase is in the form of uniform dispersoids in a single-phase matrix,[1,2] while for others it is in the form of lamellae as in the case of eutectic HEAs (E-HEAs) such as AlCoCrFeNi2.1,3 Nb25Sc25Ti25Zr25,4 and CoCrFeNiNbx.[5] These alloys demonstrate a unique combination of excellent tensile/compressive strength, good ductility, high hardness, and good oxidation resistance. Phase-specific response in the eutectic was quantified using SKP microscopy to

Hasannaeimi et al 2

RESULTS AND DISCUSSION

METHODS