Abstract: The microstructural modification for cellular structures can achieve the improvement of dynamic mechanical properties of a selective laser melted FeCoNiCrMo_0.2 high-entropy alloy (SLM-FeCoNiCrMo_0.2 HEA) and can expand its promising applications in the field of high-velocity deformation. In this work, FeCoNiCrMo_0.2 HEAs with cellular structures in different sizes were produced by selective laser melting (SLM) with different process parameters. The dynamic mechanical properties and microstructure of the SLM-FeCoNiCrMo_0.2 HEA were studied. The dynamic mechanical properties of the SLM-FeCoNiCrMo_0.2 HEA increased with decrease of average size of cellular structures, and the values of them were sensitive to strain rates. The energy absorption, compressive strength and yield strength of the SLM-FeCoNiCrMo_0.2 HEAs reached 315.6 MJ/m³, 2.2 GPa and 775.6 MPa, respectively at a strain rate of 2,420 s^-1, under the process parameters of laser power and scanning speed of 330 W and 800 mm/s, respectively, where the corresponding average size of cellular structures in the HEAs was 483.6 nm. The value of strain-hardening rate of the SLM-FeCoNiCrMo_0.2 HEA was about 5.1 GPa at a strain level of 0.1, which was much higher than that of the powder-metallurgy FeCoNiCrMo_0.2 HEA. The cellular structure was formed inside the molten pool with segregation of Mo on the boundary. Deformation localization appeared in the cellular structures, forming several deformation bands after high strain-rate deformation. The elemental segregation strengthening and dislocation strengthening are considered to be the main strengthening mechanisms in SLM-FeCoNiCrMo_0.2 HEA.

Key words: FeNiCr-based HEA, Additive manufacturing, Mechanical property, Cellular structure, Strengthening mechanisms