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.

The role of phase morphology in controlling the high-temperature oxidation of a dual-phase FCC + B2 + BCC AlCoCrFeNi(CuTiZr) high-entropy alloy was investigated using as-cast (AC) and high-temperature annealed (HTA) conditions, identical in composition and phase constitution with near-equal phase fractions and differing only in the spatial arrangement of the two phases. Cyclic oxidation was conducted at 850 °C and 1050 °C, representing diffusion-limited and spallation-dominated regimes, respectively. At 850 °C, the AC condition recorded a parabolic rate constant of 27.0 × 10 ⁻¹³ g ² cm ⁻⁴ s ⁻¹ compared with 102.0 × 10 ⁻¹³ g ² cm ⁻⁴ s ⁻¹ for the HTA condition, and at 1050 °C, subsurface voiding extended to 100–200 μm in the AC condition compared with 500–600 μm in the HTA condition. Neither Al nor Ti reaches the surface in sufficient quantity to form a continuous external Al₂O₃ scale, leaving protection to a Cr₂O₃ framework that codominant spinel renders discontinuous. Oxidation performance is therefore governed by the rate and spatial uniformity with which the B2 + BCC phase supplies Al and Ti to the advancing front. The pathway by which morphology acts switches with temperature: supply path length in the diffusion-limited regime and local composition at the front in the spallation-dominated regime. Spot friction processing refined both phases to approximately 1.9 μm without phase transformation or change in phase balance and reduced mass loss at 1050 °C by more than 50% relative to the AC and HTA conditions within a 20-h window. These results establish phase morphology as an independent and controllable design parameter for high-temperature oxidation resistance in multiphase high-entropy alloys.

High-entropy alloys (HEAs) offer a platform for designing microstructures suited to extreme conditions. Dual-phase HEAs show promising strength-ductility combinations at high temperatures, but maintaining phase stability above 800°C remains challenging. This study introduces a novel dual-phase HEA (FCC + BCC) with microstructural evolution driven by spinodal decomposition and intermetallic stabilization. The alloy transitions from initial FCC to mixed FCC-BCC laths, with spinodal nanophases in the BCC matrix. Coarse σ (FeCr-type) and NiZr-rich intermetallics form at phase boundaries, enhancing stability. Post-solidification analysis shows σ phase consuming spinodal BCC at high temperatures, while retained nanoscale BCC spinodal contributes to strain incompatibility and HDI hardening. This interplay balances phase stability and mechanical performance. Compressive tests at 800-1000°C (strain rate 1/s) reveal phase stability and deformation mechanisms. Behavior is governed by lamellar morphology and σ/α-Cr ↔ B2 interactions. Retained GNDs and enhanced twinning sustain work hardening up to 900°C. At 1000°C, FCC-dominated strain localization triggers rapid softening via dynamic recrystallization. These findings deepen understanding of high-temperature deformation in dual-phase HEAs, offering pathways for optimizing alloy design in extreme environments.