Hao Liu

To overcome the intrinsic trade-off between wear and corrosion resistance in multiphase high-entropy alloys under tribocorrosion conditions, a nanoscale eutectic microstructure regulation strategy was developed to synergistically tailor mechanical load-bearing capability and electrochemical response. CoCrFeNi(MoNbTi)x high-entropy alloy coatings with systematically regulated eutectic architectures were fabricated by laser cladding to elucidate the relationships among microstructural evolution, electrochemical behavior, and tribocorrosion performance. Composition-mediated regulation of the eutectic microstructure drove the transition from a hypoeutectic structure to a fully eutectic nano-lamellar structure, while the formation and interfacial energies obtained from first-principles calculations elucidated the energetic origins of the phase and interface stability underlying this evolution. The hypoeutectic microstructure, characterized by densely distributed heterogeneous soft/hard phase interfaces, promoted stress concentration and local electrochemical activation, thereby establishing unfavorable coupled mechanical-electrochemical damage pathways that accelerated crack-induced spalling and localized corrosion. In contrast, the fully eutectic nano-lamellar coating exhibited a microhardness of 647.3 HV and the lowest Icorr of 1.480×10-6 A/cm2, together with the best tribocorrosion resistance. This improvement primarily originated from the synergistic reconstruction of damage pathways by the globally distributed nano-lamellar architecture: the nanoscale periodic FCC/Laves structure suppressed sustained ploughing, plastic localization, and crack propagation; the globally submicron FCC anodic characteristic scale inhibited the development of stable localized corrosion and reduced coarse-scale electrochemical heterogeneity; and the structurally well-matched FCC/Carbide interface mitigated hard-particle debonding and the resulting secondary abrasive wear. Perturbation-induced pitting theory further clarified the influence of characteristic anode/cathode spacing on pit nucleation in eutectic high-entropy alloys, establishing a quantitative correlation between lamellar spacing and local corrosion stability. Overall, this study reveals the strong coupling among microstructural scale, electrochemical response, and mechanical damage, and demonstrates that nanoscale eutectic regulation can reconstruct tribocorrosion damage pathways to achieve synergistic improvements in wear and corrosion resistance.

Wear-resistant compositions optimized at a single temperature often fail to maintain stable performance across a wide temperature range because load-bearing capacity, oxidation behavior, and wear mechanisms evolve with temperature. Here, a machine-learning model linking alloy composition, processing parameters, tribological conditions, and volumetric wear rate (VWR) was combined with a genetic algorithm to design wide-temperature wear-resistant high-entropy alloy coatings. Among the evaluated algorithms, random forest exhibited the best predictive performance (R² = 0.838). A fitness function integrating VWRs at 25, 200, 400, and 600 °C identified Al9Co16Cr20Fe17Ni14Mo16Ti8 (S1) and Co16Cr24Fe17Ni17Mo17Nb9(S2) as candidate alloys. Their experimental mean VWRs were 30.89×10-6 and 30.17×10-6mm3·N-1·m-1, respectively, with prediction errors of 17.8% and 17.7%. The coatings exhibited distinct temperature-adaptation mechanisms. The high-hardness multiphase structure of S1 resisted indentation, plastic deformation, and ploughing at low temperatures. The continuous FCC matrix of S2 provided greater deformation compatibility and promoted a dense, stable tribo-oxide layer at elevated temperatures, suppressing crack propagation and spallation. Accordingly, the VWR of S2 at 600 °C was approximately 12.5% lower than that of S1. These results show that wide-temperature wear resistance arises from the coupled effects of load-bearing capacity, deformation compatibility, tribo-oxide-layer stability, and subsurface damage evolution. This work connects machine-learning-assisted composition design with temperature-dependent wear mechanisms and provides a data-driven strategy for designing high-entropy alloy coatings for wide-temperature service.

Coherent high-entropy alloy (HEA) coatings strengthened by nanoscale ordered precipitates are promising for surface protection. However, conventional laser cladding is often limited by coarse columnar grains, elemental segregation, and insufficient control over precipitate evolution. In this work, a CoCrFeNi2Al0.4Ti0.4 coherent HEA coating was fabricated by ultrasonic-assisted laser cladding to systematically investigate the effect of ultrasonic power on microstructural and mechanical evolution. Results show that ultrasonic vibration preserves the face-centered cubic (FCC) and L12 phase constitution but significantly regulates L12 precipitation and grain morphology. With increasing ultrasonic power, the nanoscale L12 precipitates transition from quasi-spherical to polygonal, and their volume fraction exhibits a non-monotonic trend. At an optimal power of 700 W (V2), the L12 fraction peaks at 2.10%, the average grain size is refined from 52.2 μm to 22.2 μm, and the elemental distribution is homogenized with a weakened preferred orientation. Benefiting from robust FCC/ L12 coherent interfaces and high-density grain boundaries, the V2 coating achieves a peak microhardness of 264.50 HV0.3, a low wear rate of 0.83 × 10-4 mm3/(N·m), and a maximum ultimate tensile strength of 768 MPa with 21.5% elongation. Conversely, an excessive power of 900 W (V3) induces molten-pool instability and porosity, deteriorating the mechanical performance. These findings demonstrate an optimal ultrasonic window for tailoring coherent precipitates, refining grains, and balancing the strength-ductility trade-off in laser-clad HEA coatings.