Solidification Pathway, Phase Stability, and High-Temperature Deformation Mechanisms of a Dual-Phase High-Entropy Alloy

Abstract High-entropy alloys (HEAs) offer a pathway for designing microstructures suited to extreme conditions. Eutectic HEA’s leverage a combination of phase ordering, interfacial strengthening, secondary phase strengthening, and heterodeformation induced (HDI) strengthening to achieve high strength and ductility at elevated temperatures. Maintaining these properties past 700 °C has proved challenging due to limitations in phase stability and breakdown of work hardening mechanisms. This paper set out to produce a dual-phase HEA with enhanced high-temperature stability and work hardenability by leveraging the enhanced HDI strengthening. We have designed a dual-phase hierarchical AlCoCrFeNi(CuTiZr) HEA comprised lamellar composite regions containing FCC(L1 2 ) lamella in a continuous BCC(B2) matrix which is surrounded by coarse FCC(L1 2 ) grains. A Cr-rich fine scale spinodal phase forms within the BCC regions, in addition to slow forming coarse FeCr-type σ phases in the lamellar FCC and minor NiZr intermetallic phase at the coarse FCC-BCC boundaries. Annealing of the cast samples at 1100 °C for 50 h and quenching breaks down the cast lamellar structure, disorders the FCC, and dissolves the coarse σ phases, while preserving the near equal ratio of FCC to BCC and the Cr-rich spinodal phase. Under compression at 800 °C (1/s strain rate), both the as-cast and high-temperature annealed structures display high strength and work hardening. With increasing temperature, a higher degree of strain partitioning is observed in the annealed structure than the as-cast, resulting in an increase in the peak flow and sustained work hardenability at 900 °C and early onset of strain softening in the annealed structure at 1000 °C due to localized activation of dynamic recrystallization. The persistence of this strain partitioning in the annealed samples corresponds to the enhanced thermal stability of the spinodal Cr phase strengthening the BCC(B2) regions. Above 800 °C, this spinodal phase is consumed in the as-cast structure to fuel the growth of coarser σ and α-Cr phases. The absence of these coarser phases in the annealed condition results in the growth of the spinodal phase and enhanced high-temperature strength of the BCC(B2) regions and enhanced heterodeformation at elevated temperatures. These findings deepen understanding of high-temperature deformation in dual-phase HEAs, offering pathways for optimizing alloy design in extreme environments.