Microstructure refinement and wear resistance enhancement of cost-effective Fe_50−2xMn₃₀Co₁₀Cr₁₀Ni_xCu_x (x = 0, 5 at%) high-entropy alloys through cyclic closed-die forging process

Novel low-cost Fe_50−2xMn₃₀Co₁₀Cr₁₀Ni_xCu_x (x = 0, 5 at%) high-entropy alloys (HEAs) were produced by vacuum melting and then processed by the cyclic closed-die forging (CCDF) process. It was found that both the as-homogenized and CCDF-processed specimens primarily consisted of a single face-centered cubic (FCC) structure, and the severe plastic strain through CCDF did not result in phase transformations. The microstructure of the CCDF-processed Fe₅₀Mn₃₀Co₁₀Cr₁₀ alloy after the sixth pass demonstrated a uniform structure with ultrafine grains measuring 285 nm in size, whereas for the CCDF-processed Fe₄₀Mn₃₀Co₁₀Cr₁₀Ni₅Cu₅ alloy, the grain size was 135 nm, with a relatively uniform distribution. The CCDF-processed Fe₅₀Mn₃₀Co₁₀Cr₁₀ and especially the Fe₄₀Mn₃₀Co₁₀Cr₁₀Ni₅Cu₅ alloy exhibited significantly higher microhardness compared to the as-homogenized state, with microhardness values being 2.42 and 2.72 times higher, respectively. Furthermore, the wear test results indicated that the CCDF processing effectively increased the wear resistance of the alloys, which was attributed to the changes in morphology and distribution of as-cast dendrites, along with the grain refinement of the matrix phase during CCDF. The CCDF-processed Fe₄₀Mn₃₀Co₁₀Cr₁₀Ni₅Cu₅ alloy exhibited the lowest wear rate, i.e., (1.2 ± 0.2) × 10^–5 mm³.N⁻¹.m⁻¹, whereas that for the Fe₅₀Mn₃₀Co₁₀Cr₁₀ alloy was (2.4 ± 0.1) × 10^–5 mm³.N⁻¹.m⁻¹. Analysis of wear surfaces indicated that the wear mechanisms of the as-homogenized HEAs were adhesive wear and abrasive wear with some delamination, while plastic deformation and adhesive wear were significantly reduced in the CCDF-processed specimens, especially in the Fe₄₀Mn₃₀Co₁₀Cr₁₀Ni₅Cu₅ alloy. These findings suggest that CCDF has the potential to achieve cost-effective nanostructured HEAs and to implement them in engineering applications.