Mechanical and tribological characteristics of nickel-rich CoCrCu_xFeNi₂ high entropy-alloys

This research explores the potential to enhance the copper solubility limit in high-entropy alloys (HEAs) within the CoCrCuFeNi system by increasing the nickel content twofold and applying additional heat treatment. The CoCrCu_xFeNi₂ HEAs were synthesized through mechanical alloying of elemental powders followed by hot pressing. The study investigated the microstructure and phase composition of CoCrCu_xFeNi₂ HEAs in relation to varying copper concentrations (x = 0; 0.25; 0.5; 0.75; 1.0). The evaluation of the alloy matrix's chemical composition, which is based on the FCC solid solution, enabled the determination of copper solubility. It was found that doubling the nickel content, relative to the equiatomic ratio, facilitated the formation of HEAs with a homogenous FCC structure for copper concentrations up to x ≤ 0.75. Further heat treatment of these HEAs resulted in an enhanced copper solubility of up to 17.5 at.%. The mechanical and tribological properties of CoCrCuxFeNi_y HEAs were also assessed, revealing significant improvements in tensile strength (ranging from 910 to 1045 MPa) and hardness (285–395 HV) for the CoCrCu_xFeNi₂ alloys. Despite the increased copper solubility limit, the heat treatment process caused a decline in mechanical properties by 35–50 %, attributed to grain size enlargement to 5.5 μm. The CoCrCu_0.75FeNi₂ and CoCrCuFeNi₂ alloys exhibited the lowest wear rates when tested against Al₂O₃ counterbody, with wear rates of 1,58·10^–5 and 1,48·10^–5 mm³/(N·m), respectively.

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