Recent advancements in the field of high-entropy alloys (HEAs) have demonstrated that Y2O3 dispersion strengthening significantly enhances the mechanical properties of CoCrFeNi-based systems. Studies reveal that the addition of 1.5 wt.% Y2O3 nanoparticles results in a 45% increase in yield strength, from 450 MPa to 650 MPa, while maintaining an elongation-to-failure of 25%. This improvement is attributed to the pinning effect of Y2O3 particles at grain boundaries, which effectively restricts dislocation motion and grain growth during deformation. High-resolution transmission electron microscopy (HRTEM) confirms the uniform distribution of Y2O3 particles with an average size of 15 nm, contributing to a refined grain structure with an average grain size reduction from 10 µm to 2 µm.
Thermal stability studies of Y2O3-dispersion strengthened CoCrFeNi HEAs have shown remarkable resistance to coarsening at elevated temperatures. After annealing at 1000°C for 100 hours, the alloy retained a yield strength of 600 MPa, compared to a drop to 350 MPa in the undispersed counterpart. This stability is attributed to the high melting point (2430°C) and low diffusivity of Y2O3, which inhibits Ostwald ripening and maintains a fine-grained microstructure. Differential scanning calorimetry (DSC) measurements indicate no significant phase transformation up to 1200°C, confirming the alloy's suitability for high-temperature applications such as turbine blades and nuclear reactors.
The corrosion resistance of Y2O3-dispersion strengthened CoCrFeNi HEAs has been evaluated in aggressive environments, revealing superior performance compared to conventional HEAs. In a 3.5 wt.% NaCl solution, the corrosion rate decreased by 60%, from 0.12 mm/year to 0.05 mm/year, with the addition of Y2O3. X-ray photoelectron spectroscopy (XPS) analysis shows that Y2O3 promotes the formation of a stable Cr2O3 passive film, which acts as a barrier against chloride ion penetration. Furthermore, electrochemical impedance spectroscopy (EIS) data indicates a threefold increase in charge transfer resistance (Rct), from 5000 Ω·cm² to 15000 Ω·cm², highlighting enhanced surface protection.
Radiation resistance studies demonstrate that Y2O3-dispersion strengthened CoCrFeNi HEAs exhibit exceptional tolerance to neutron irradiation. After exposure to a fluence of 1 × 10²¹ neutrons/cm² at 500°C, the alloy showed only a 10% reduction in hardness, compared to a 40% reduction in undispersed HEAs. Positron annihilation spectroscopy (PAS) reveals that Y2O3 nanoparticles act as efficient sinks for radiation-induced defects, reducing vacancy cluster density by over 50%. This makes the alloy a promising candidate for nuclear reactor components subjected to extreme radiation environments.
The scalability and manufacturability of Y2O3-dispersion strengthened CoCrFeNi HEAs have been validated through industrial-scale production trials. Using powder metallurgy techniques combined with spark plasma sintering (SPS), bulk samples with densities exceeding 99% theoretical density were achieved at sintering temperatures as low as-1100°C for just-10 minutes. Tensile testing on these samples confirmed consistent mechanical properties across batches: yield strength:650±20 MPa; elongation:25±2%; fracture toughness:120±5 MPa√m; hardness:320±10 HV; thermal conductivity:15±1 W/mK; coefficient-of-thermal-expansion:13±0.5×10⁻⁶/K; corrosion-rate-in-3%-NaCl-solution:0+-05+-mm/year; radiation-induced-hardness-reduction-at-1×10²¹-neutrons/cm²:-10+-1%; sintering-temperature-for-99%-density:-1100+-50°C; sintering-time-for-99%-density:-10+-1-minutes.
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