Transformation induced plasticity (TRIP) effect in high entropy alloys (HEAs) overcomes the strength–ductility “trade-off” and leads to the synchronous improvement of strength and ductility. In this work, we studied a TRIP Fe₆₀Mn₂₀Co₁₀Cr₁₀ HEA with a dual-phase structure consisting of face-centered cubic matrix and hexagonal close-packed (HCP) martensite. By warm-rolling and subsequent annealing, three samples with different recrystallization conditions and HCP phase volume fractions were obtained. The alloys exhibit a good combination of ultimate tensile strength (∼700–900 MPa) and elongation (∼45%–55%), representing sustainable strain hardening behavior over extended deformation regime. To reveal the deformation mechanism of the present TRIP HEA, the method to determine the stacking fault energy (SFE) via a regular solution model was discussed, and the SFE of Fe₆₀Mn₂₀Co₁₀Cr₁₀ alloys at 300 K was estimated as 15.3 mJ/m². The low SFE promotes the formation and overlapping of stacking faults via dislocation interaction, which provides nucleation sites of HCP martensite and further contributes to the striking strain hardening capacity upon tension.

Cold rolling with subsequent annealing can be used to produce the recrystallized structure in high entropy alloys (HEAs). The Al_0.25CoCrFeNi HEAs rolled to different final thickness (230, 400, 540, 800, 1000, 1500 μm) are prepared to investigate their microstructure evolutions and mechanical behaviors after annealing. Only the single face-centered cubic phase was obtained after cold rolling and recrystallization annealing at 1100 °C for 10 h. The average recrystallized grain size in this alloy after annealing ranges from 92 μm to 136 μm. The annealed thin sheets show obviously size effects on the flow stress and formability. The yield strength and tensile strength decrease as t/d (thickness/average grain diameter) ratio decreases until the t/d approaches 2.23. In addition, the stretchability (formability) decreases with the decrease of the t/d ratio especially when the t/d ratio is lower than about 6. According to the present results, yield strength can be expressed as a function of the t/d ratio.

The tribological behavior of hot-rolled and boronized Fe₄₀Mn₂₀Cr₂₀Ni₂₀ high-entropy alloys (HEAs) sliding against a Si₃N₄ ball was investigated in the air, deionized water and seawater. The results showed that the hot-rolled Fe₄₀Mn₂₀Cr₂₀Ni₂₀ HEA was composed of an FCC (face-centered cubic) phase. In addition, the boronized HEA was composed of a great number of borides, including CrB, FeB, MnB, Fe₂B, Fe₃B and MnB₂. The hardness increased from 139 HV to 970 HV after boronizing. In air, the wear rate decreased from 4.51 × 10⁻⁴ mm³/Nm to 0.72 × 10⁻⁴ mm³/Nm after boronizing. The wear mechanism transformed from abrasive wear and oxidative wear to the polishing effect. After boronizing, in the deionized water, the wear rate decreased from 1.27 × 10⁻⁴ mm³/Nm to 8.43 × 10⁻⁵ mm³/Nm. The wear mechanism transformed from abrasive wear and delamination wear to delamination wear. In the seawater, the wear rate decreased by about ten times that of hot-rolled alloy.