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

•Synchrotron XRD confirmed the CALPHAD-predicted BCC phase in Cr18Fe27Mn27Ni28 at 700 °C and a BCC phase in Cr15Fe35Mn15Ni35 that was not predicted.•The alloys showed promising strength in tensile deformation, with yield strengths of 155 MPa and 151 MPa at room temperature for Cr18Fe27Mn27Ni28 and Cr15Fe35Mn15Ni35, respectively, falling to 93 MPa, and to 100 MPa, respectively at 500 °C.•Heavy-ion irradiation yielded similar densities of dislocation loops in two-beam conditions, but differences in faulted loop populations were resolved with rel-rod contrast condition.•Cr18Fe27Mn27Ni28 experienced void swelling in the target-dpa plateau region; Cr15Fe35Mn15Ni35 resisted swelling in this region, but small voids nucleated beyond the displacement damage peak.•EDS indicates that vacancies migrate primarily via Mn-exchange, with the counter-diffusion of Ni more strongly affected than Fe or Cr. 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. [Display omitted]