Coatings

High-entropy alloys (HEAs) represent one of the most promising emerging material families, particularly for advanced surface engineering applications. In this work, a near-high-entropy alloy (near-HEA) coating was produced on a 316L stainless steel substrate using laser metal deposition (LMD) from a powder mixture of Inconel 625, Cr and Mo, without the intentional addition of Fe. Due to dilution from the substrate, the resulting alloy contained elevated Fe content while maintaining Cr, Ni and Mo concentrations within the generally accepted compositional range of HEAs. The deposited layer exhibited a dual-phase microstructure consisting of a face-centered cubic (FCC) phase and a highly distorted tetragonal phase forming a periodic network with a characteristic length scale of several hundred nanometers. The hardness of the coating increased to approximately three times that of the substrate, reaching values of 600–700 HV. To further modify the surface properties, laser-induced periodic surface structures (LIPSS) were generated on the polished coating using femtosecond pulsed laser irradiation at different energy densities. The morphology and subsurface structure of the resulting periodic patterns were investigated by scanning electron microscopy. LIPSS with characteristic dimensions ranging from the micrometer to nanometer scale were successfully produced. Cross-sectional analyses revealed that the underlying dual-phase microstructure remained continuous within the laser-structured regions, indicating that LIPSS formation occurred predominantly via metallic ablation without significant phase transformation or amorphization. These results demonstrate the combined applicability of LMD and femtosecond laser structuring for producing mechanically enhanced, micro- and nanostructured near-HEA coatings with potential for advanced surface-related functionalities.

The bottleneck of service stability of perovskite solar cells is rooted in the mechanical failure of its active layer materials at the micro scale. In order to deeply understand this process, the nano-indentation mechanical response of all-inorganic perovskite CsPbBr₃ under pre-stress was studied by molecular dynamics simulation at the atomic scale. The core of this research work is to systematically reveal the quantitative influence of prestress, an inevitable initial stress state in the preparation and service of practical devices, on the near-surface mechanical behavior of materials. Firstly, the stress–strain response of the CsPbBr₃ model at 300 K, 350 K, and 400 K was verified. The temperature dependence of its mechanical properties and the consistency with the experimental values confirmed the reliability of the force field and simulation method. In addition, by applying a series of uniaxial pre-strains, we analyzed the influence of prestress on the evolution of the force-depth curve and indentation strain during nano-indentation. The results show that the introduction of pre-strain will induce the material to have a significant “softening effect” and systematically reduce its ability to resist the intrusion of the indenter. More importantly, this study quantitatively reveals the asymmetric influence of prestress direction: tensile prestress leads to more serious softening than compressive prestress with the same amplitude, indicating that materials are more prone to plastic deformation under tensile preload. This work clarifies the key regulation function of prestress on the mechanical properties of perovskite thin films and provides a crucial theoretical basis for constructing accurate cross-scale mechanical models and designing perovskite photoelectric devices with high reliability and fatigue resistance.

Solar energy stands as one of the most promising green energy sources today. This paper proposes a symmetrical gap-type separated solar absorber and radiator (SETR) featuring a dielectric layer of Al₂O₃ and metal W as separation columns. Its unique structure enhances absorption within the effective solar energy spectrum, thereby alleviating solar energy absorption challenges. The finite difference time domain method (FDTD) results show that the SETR achieves an absorption rate of more than 90% in the 280–2096 nm band, which perfectly covers the visible light band range. The weighted average absorption in the 280–2500 nm band is 95.22% under AM1.5 conditions. The thermal emission efficiency at 1500 K is 95.13%, and the thermal radiation loss is less than 5%. Beyond analyzing the results, we also investigated the overall band absorption efficiency of the SETR under varying conditions by adjusting its structural parameters and physical parameters such as materials. This approach enables effective control over the absorption spectrum. Additionally, the proposed SETR is independent of polarization conditions. Both the TM and TE modes are insensitive to large incident angles. In the future, broadband SETRs can be applied to solar energy harvesting, thermoelectric conversion, and imaging fields, as it holds broad application prospects.