In situ investigation of the deformation behaviors of Fe₂₀Co₃₀Cr₂₅Ni₂₅ and Fe₂₀Co₃₀Cr₃₀Ni₂₀ high entropy alloys by high-energy X-ray diffraction

In situ synchrotron-based high-energy X-ray diffraction (HE-XRD) technique was employed to investigate the mechanical behaviors and microstructural evolution of face-centered cubic (FCC) Fe₂₀Co₃₀Cr₂₅Ni₂₅ and Fe₂₀Co₃₀Cr₃₀Ni₂₀ high entropy alloys (HEAs) during tensile deformation. Fe₂₀Co₃₀Cr₃₀Ni₂₀ HEA has a good combination of strength (ultimate tensile strength of 864 ± 35 MPa) and ductility (elongation of 0.627 ± 0.021). The HE-XRD investigation reveals that Fe₂₀Co₃₀Cr₃₀Ni₂₀ HEA has the transformation-induced plasticity (TRIP) effect, which starts at a critical stress of ~555 MPa. Transmission electron microscopy confirmed this deformation-induced new phase is hexagonal-close-packed structured ε-martensite, which follows an orientation relationship of {111}_γ//(0001)_ε, and ⟨110⟩_γ//[112¯0]_ε with the FCC γ matrix. The observation of deformation twins in the deformed samples of the two studied HEAs proves that twinning-induced plasticity (TWIP) effect occurs in both HEAs. The combination of TRIP and TWIP effects lead to the high strength, large ductility and improved strain hardening behavior of Fe₂₀Co₃₀Cr₃₀Ni₂₀ HEA.