Phase stability, mechanical properties, and ion irradiation effects in face-centered cubic CrFeMnNi compositionally complex solid-solution alloys at high temperatures

Two CrFeMnNi face-centered cubic complex concentrated solid-solution alloys (CSA) have been evaluated for phase stability, mechanical properties, and radiation damage effects from heavy ions. Cr₁₈Fe₂₇Mn₂₇Ni₂₈ and Cr₁₅Fe₃₅Mn₁₅Ni₃₅ were predicted by thermodynamic calculations to phase separate and maintain a single phase at 700 °C, respectively. Aging experiments at this temperature confirmed varying degrees of precipitation of a body-centered cubic phase in both Cr₁₈Fe₂₇Mn₂₇Ni₂₈ and Cr₁₅Fe₃₅Mn₁₅Ni₃₅. The alloys showed promising strength in tensile deformation at room temperature, with yield strengths of 155 MPa and 151 MPa for Cr₁₈Fe₂₇Mn₂₇Ni₂₈ and Cr₁₅Fe₃₅Mn₁₅Ni₃₅, respectively. At 500 °C, the yield strength of Cr₁₈Fe₂₇Mn₂₇Ni₂₈ fell to 93 MPa, and to 100 MPa in Cr₁₅Fe₃₅Mn₁₅Ni₃₅. Unlike Cr₁₈Fe₂₇Mn₂₇Ni₂₈, Cr₁₅Fe₃₅Mn₁₅Ni₃₅ gained some ductility at 500 °C compared to room temperature. The two CSAs were irradiated to 75 dpa at 500 °C in the plateau region of the displacement curve using 3.7 MeV Ni²⁺ ions, alongside model alloy 709 as a reference. Irradiation results produced similar densities and sizes of dislocations loops in the two CSAs compared to the reference. However, while large voids form in the plateau region of Cr₁₈Fe₂₇Mn₂₇Ni₂₈, small voids form just beyond the displacement peak of Cr₁₅Fe₃₅Mn₁₅Ni₃₅. Atom probe tomography and energy dispersive X-ray spectroscopy-equipped scanning transmission electron microscopes were used to characterize the alloys for changes in chemical distribution.