This study investigated the effects of repeated flux-cored arc welding deposition on the dilution, microstructure, bending integrity, and electrochemical corrosion behavior of Inconel 625 weld overlays on AH36 steel by comparing single-layer and three-layer multipass conditions. Both overlays exhibited dendritic solidification structures; however, qualitative SEM observations indicated differences in the morphology and spatial distribution of the interdendritic constituents, with a relatively continuous or semi-continuous network observed in the single-layer overlay and a more discontinuous and dispersed distribution in the topmost multipass layer. These qualitative morphological differences coincided with substantial compositional recovery; the Fe content decreased from 36.29 wt.% in the single-layer overlay to 4.77 wt.% in the third multipass layer, whereas the Ni, Cr, and Mo contents increased toward nominal Inconel 625 filler-metal values. Local Nb and Mo enrichment persisted within interdendritic regions under both conditions, with no consistent reduction in local Nb enrichment following multipass deposition. The spatial distribution of the interdendritic constituents also differed between the two conditions, while Mo exhibited a more uniform overall distribution at the mapping scale in the multipass third layer. One of the three single-layer specimens developed a large open crack after 180° side bending, whereas none of the three multipass specimens exhibited visible open cracking or fracture. The multipass overlay further exhibited a lower anodic current density, and higher film and charge-transfer resistance, consistent with a more stable passive electrochemical response.
Synthesis of multilayer graphene oxide (GO) was achieved through a Hummers method with meticulous control over the addition of the oxidizing agent. Precursors were immersed in an ice bath during the synthesis to maintain a temperature of approximately 275 K in oxidation stages I and II, temperature was measured with a thermocouple inside the cooling bath, in direct contact with the vacuum filter flask at the level of the reactants. In contrast to the variety of Hummers synthesis methods—where the system is maintained at certain temperature during the initial oxidation stage and heat continues to be supplied during the second stage—our setup operates at low temperature from the beginning to the conclusion of the process. A detailed analysis of the compositional, structural, and optical properties of the fabricated GO was conducted, revealing a notable photoluminescent band in the 380–480 nm region. This property is of interest for a potential future application in the field of optoelectronics. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) revealed that the structure of the material consists of a sp3 matrix with sp2 domains. Raman spectroscopy revealed an ID/IG ratio of 2.7, which could indicate a high density of structural defects or extremely small sp2 graphitic domains. Furthermore, deconvolution of the 2D band suggests the presence of multilayers in the GO. Fourier transform infrared spectroscopy (FTIR) analysis revealed the presence of all functional groups associated with the GO. Upon observation of the photoluminescence exhibited by the material, a broadband centered on the violet-blue emission, with a possible mechanism consistent with the literature associated with the transitions between sp2 domains and localized states in the basal plane defects or it might be caused by quantum confinement effects. The diminished contribution from the green emission could be caused by the transitions between localized states sp2 and the functional groups associated with oxygen.
Long-afterglow self-luminous road marking coatings are promising for improving nighttime visibility, but their application is restricted by the poor water stability of SrAl2O4:Eu2+,Dy3+ phosphors and weak interfacial compatibility with polymer matrices. In this study, SrAl2O4:Eu2+,Dy3+ phosphor was modified using a silane coupling agent and incorporated into a two-component methyl methacrylate coating. The modification mechanism and durability performance were investigated through SEM, FTIR, fluorescence spectroscopy, afterglow decay, abrasion, water immersion, and UV aging tests. Results showed that silane modification formed an organic protective layer on the phosphor surface, improving interfacial bonding and water stability while maintaining the intrinsic luminescent properties. Modified and unmodified phosphors exhibited similar excitation and emission peaks at approximately 360 and 520 nm, respectively, with comparable two-stage afterglow decay behavior. The coating containing modified phosphor and glass beads showed the best performance, with an abrasion loss of 27.9 mg and a skid resistance value of 69 BPN after 1000 abrasion cycles. After 7 days of water immersion and UV aging, the coating maintained good mechanical and luminescent stability. This study demonstrates that the synergistic reinforcement of modified phosphor and glass beads is an effective strategy for durable self-luminous road markings.
The increasing demand for thermal protection materials in new energy vehicle (NEV) systems has stimulated the development of lightweight coatings capable of simultaneously providing thermal insulation and fire resistance. In this study, a lightweight ceramic-like inorganic coating was prepared by incorporating hollow glass microspheres (HGMs), expanded vermiculite, and ceramic fibers into a sodium silicate matrix. The expanded vermiculite/ceramic-fiber ratio and coating thickness were varied to evaluate their effects on thermal protection. Among the investigated formulations, Formulation C showed the lowest mean thermal conductivity, with a value of 0.0649 ± 0.0004 W m−1 K−1 for the 1-mm-thick C-1 coating. The apparent density of the representative Formulation C coating was 0.54 ± 0.02 g cm−3 (n = 3). During representative single-specimen direct butane-flame exposure tests, the spatially averaged backside temperature of the 2-mm-thick C-2 specimen was 147.1 °C after 600 s, compared with 420.1 °C for the uncoated aluminum plate, corresponding to a temperature difference of 273.0 °C. Cross-sectional SEM showed non-uniform structural evolution after flame exposure, with more pronounced morphological changes near the flame-facing region and greater retention of microspherical structures in the inner region. The representative Formulation C coating also retained more than 80% of its mass at 800 °C in both nitrogen and air. These results indicate that the combined presence of HGMs, expanded vermiculite, ceramic fibers, and the sodium silicate matrix provides effective resistance to heat transfer under high-temperature exposure. The coating therefore offers a lightweight inorganic approach for high-temperature thermal protection.
In this study, a stepwise strategy was adopted to regulate and control the complexing agent system of the cyanide-free alkaline zinc–nickel (Zn-Ni) electroplating solution. A Zn-Ni coating containing a quaternary complexing agent was successfully prepared on the surface of low-carbon steel to enhance the flatness and corrosion resistance of the coating. The investigated complexing agents included triethanolamine (TEA), tetraethylenepentamine (TEPA), ethylene diaminetetraacetic acid (EDTA), and potassium sodium tartrate (PST). By fixing other parameters and testing the four complexing agents one by one, TEA was finally determined to be the best single complexing agent. This substance can effectively stabilize the metal-ion deposition process. The synergistic effects of TEPA, EDTA and PST were systematically studied, and the independent contributions of each complexing agent to performance were clarified. This design enables performance differences to be directly attributed to the inherent characteristics of each complexing agent category. The surface morphology of the sample was characterized by scanning electron microscopy (SEM). The cross-sectional morphological characteristics were analyzed by a laser scanning confocal microscope (LSCM). The chemical composition and phase composition of the samples were determined by X-ray diffraction (XRD), while the corrosion behavior of the samples was studied by electrochemical techniques, including electrochemical impedance spectroscopy (EIS) and Tafel curves. Characterization shows that when the molar ratio of EDTA to PST is 1:4 and TEA and TEPA are used in combination, the grain size of the coating is smaller, the surface is smoother, and the number of surface micropores is significantly reduced compared with coatings prepared by other complexation systems, thereby improving the flatness and corrosion resistance of the coating.
