Surface & Coatings Technology最新文献

Numerous peening techniques exist can effectively modify the sample surface, although at the expense of severe surface damage and high capital investment. Ultrasonic-assisted abrasive peening (UAP) is a superior option that can peen the surface with minimal deterioration using a basic probe sonicator. In this paper, the influence of UAP parameters (i.e., beaker size and fluid volume, power, abrasive concentration, and time) on the surface integrity of Ti-6Al-4V and OFHC Cu was studied experimentally. The process is capable of inducing significant compressive residual stress at around 84 % and 280 % of yield strength in Ti-6Al-4V and OFHC Cu, respectively. The study examined the change in surface roughness (ΔR_a), ΔR_a = roughness before - roughness after peening. As peening intensities increase, ΔR_a reaches +7 nm, showing a surface finish in Ti-6Al-4V. The dislocations density calculated from the Williamson-Hall equation exhibited a 20 and 4.5-fold augmentation in peened Ti-6Al-4V and OFHC Cu in comparison to their un-peened state. EBSD analysis revealed a 28 % and 40 % reduction in grain size in Ti-6Al-4V and OFHC Cu after peening. This work validates the efficacy of the proposed UAP technique and supports the selection of optimized UAP process parameters.

This study investigates the microstructural and mechanical characteristics of chromium carbide‑nickel rich alloy coatings produced through laser cladding, detonation spraying, and plasma spraying techniques. While all three processing techniques used the same feedstock powder, each method yields coatings with unique microstructures encompassing varying compositions and length scales. Employing Field Emission Scanning Electron Microscopy (FE-SEM) in combination with Energy Dispersive Spectroscopy (EDS) and nanoindentation mapping, local microstructure and mechanical properties were assessed at the micrometre length scale. Laser-clad coatings exhibit a typical metal matrix composite microstructure with high carbide content, distinct (MoNb)C₂ phases, and Fe in the metallic matrix, while the thermal sprayed coatings showed carbides of varying sizes and metallic matrix with varying degrees of chromium dissolved in it. The instrumented indentation technique helped precisely record the microstructural features in all the coatings. Chromium carbide consistently emerges as the hardest phase across all coatings, with variations in metallic matrix hardness. Higher matrix hardness in thermal sprayed coatings correlates with increased Cr content, attributed to extended solid solubility of Cr and the presence of Mo and Nb. Energy dispersive spectroscopy and transmission electron microscopy provided clearer insight into the microstructure. This study highlights a direct one-to-one correlation between microstructure and mechanical properties mapped using instrumented indentation techniques in chromium carbide‑nickel rich coatings across different deposition methods.

This paper employs numerical simulation to investigate the influence of thermal barrier coatings' (TBCs) thickness and surface roughness on the cooling and flow resistance characteristics of turbine blades. The results indicate that the application of TBCs significantly enhances the surface cooling efficiency of the blades. Turbine blades coated with a 0.4 mm thickness of TBC compared to blades without thermal barrier coatings, the average cooling efficiency of the blade surface increases by 12.3 %, and the maximum temperature drop at the leading edge(LE) is 317.8 K. However, the small increment in TBCs thickness leads to an increase in aerodynamic losses in the vane passage. The static pressure coefficient continuously decreases in the suction side(SS) within the interval 0.3 < x/C < 1.0. The average flow coefficient of the film holes exhibits distinct variations in different regions of the blade. As surface roughness increases, the cooling efficiency on the SS and pressure side(PS) of the blade decreases, while the heat transfer enhancement at the LE and cooling efficiency improve. Compared to a smooth coated surface, when the surface roughness height increases to 20 μm, the blade surface cooling efficiency decreases by 1.12 %, and the average temperature rise is 10.3 K. Simultaneously, the energy loss coefficient and total pressure loss coefficient in the vane passage rise with the increase in surface roughness, while the variation in the average flow coefficient of the film cooling holes remains relatively small.

Compared with conventional laser cladding (CLC), extreme high-speed laser cladding (EHLA) offers substantially enhanced cladding efficiency and improved coating properties. In this study, (CoCrNi)₈₂Al₉Ti₉ high-entropy alloy (HEA) coatings were prepared via CLC and EHLA. The coatings were also characterized and tested. Results indicated that the thickness of the EHLA coating was 261.9 μm, the microstructure of the cladding layer consisted of alternating lamellar FCC matrix and strengthening phases (B2 and L2₁), and the average grain size was 5.3 μm. The EHLA coating has approximately three times more strengthening phases than the CLC coating. Thus, the microhardness of the EHLA coating in the range of 25–650 °C is approximately twice that of the CLC coating, and the wear rate of the former at 650 °C is 61 % lower than that of the latter. EHLA markedly improves the wear resistance of HEA coating at room temperature and 650 °C.

Molybdenum disulfide (MoS₂) is a two-dimensional material that exhibits unique interfacial interactions with metals, making it potential coating material for improving material properties of metals. In this work, the effects of multilayer MoS₂ coating on the mechanical properties and deformation behaviours of copper (Cu) and gold (Au) substrates are investigated by nanoindentation experiments and molecular dynamics (MD) simulations. Specifically, our experimental results indicate that the MoS₂ coating greatly increases the Young's modulus and hardness of Au substrate throughout the indentation process. In the MoS₂/Cu system, however, the MoS₂ coating exhibits inverse effects at diffident indentation depths, which, specifically, has the weakening and enhancing effects at the early and late stages of the indentation process, respectively. MD simulations indicate that the different effects of the MoS₂ coating on the mechanical properties of Au and Cu substrates are attributed to the different interfacial adhesion properties between the MoS₂/Cu and MoS₂/Au systems, as the binding energy of the MoS₂/Au system is much larger than that of its MoS₂/Cu counterpart. Moreover, it is also revealed in MD simulations that the load-bearing area of metal substrates can be significantly enlarged by the MoS₂ coating, which leads to the dense dislocations distributed in metal substrates and thus the strain-hardening in MoS₂/metal composites.

Superhydrophobic (SH) coatings have great potential to protect metals by reducing the contact area between metals and corrosive media. However, the poor mechanical stability of SH coatings restricts their potential applications. In this study, a nickel underlayer with a multi-hierarchical structure was deposited on the substrate using two-step electroplating in a nickel-plating bath. Finally, the SH coating was obtained by electrodeposition in an octamethyltrisiloxane solution. The morphology, composition, hydrophobicity, and corrosion resistance of SH coating were characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), contact angle measurement, and electrochemical workstation. The prepared coating, with a water contact angle (WCA) of 157.5 ± 0.5° and a sliding angle (SA) of 4.3 ± 0.4°, exhibited excellent hydrophobicity due to the multi-hierarchical rough structure and low surface energy of the coating. The porous structure of the coating allowed its hydrophobic properties to be maintained even after 240 cm of sandpaper abrasion testing. After 20 days of immersion in 3.5 wt% NaCl solution, the coating still exhibited excellent corrosion resistance (i_corr ∼ 1.01 × 10⁻⁸ A⋅cm⁻²) and hydrophobic properties (∼ 148.5 ± 0.5°), providing long-lasting protection to the substrate and prolonging its lifespan. This study introduces a strategy for preparing long-term corrosion-resistant SH coating on metallic surfaces.

High-performance coatings are crucial for improving the overall lifetime of molds. In this study, multi-scale microstructure evolution in nano Ni–Co–C alloy coatings was induced through cryogenic treatment, and various strengthening mechanisms were employed to enhance their comprehensive properties, particularly wear resistance. Specifically, it was observed that lattice contraction occurred in the coatings due to stress during cryogenic treatment, accompanied by strain and dislocation accumulation. As the cryogenic treatment duration increased, the texture of the coatings exhibited a random distribution, and the emergence and subsequent increase of copper texture were identified as crucial for enhancing coating performance. Additionally, TEM results revealed a typical nano-polycrystalline structure in the coatings, with grain sizes becoming more refined and uniformly distributed after cryogenic treatment. Simultaneously, a significant increase in stacking faults was noted, which facilitated the formation of complex dislocation structures and hindered dislocation mobility. Moreover, cryogenic treatment was found to enhance coating hardness and improve fracture toughness, primarily due to dislocation strengthening and secondarily to grain refinement. Furthermore, the wear rate of the coatings was significantly reduced, and the dominant wear mechanism shifted from oxidation wear to abrasive wear with prolonged cryogenic treatment duration.

To investigate the effect of the multi-phase Ti-containing oxides on the ablation behavior of (Hf-Zr-Ti)C coating, the (Hf_0.25Zr_0.25Ti_0.5)C coating was prepared on the SiC-coated C/C composites, and their ablation resistance was investigated. After ablation, Ti-poor and Ti-rich areas appeared on the coating surface, corresponding to the Ti-doped m-(Hf, Zr)O₂ and o-(Hf, Zr)TiO₄, respectively. Their interface interaction on the ablation resistance, microstructural evolution and defect initiation of the coating during ablation was discussed. The combination of the experimental results (SEM/TEM), first-principle calculation (VASP) and finite element simulation (ABAQUS) indicated the latter had poor plastic deformation to resist crack initiation and propagation compared to the former. The mechanical denudation produced the stress concentration, which resulted in some damaged areas appearing at the phase interface between Ti-doped m-(Hf, Zr)O₂ and o-(Hf, Zr)TiO₄, as well as the grain boundaries of different o-(Hf, Zr)TiO₄ grains, in the forms of phase interface cracks and intergranular pores/cracks, respectively. Although these ablative defects accelerated the damage to the coating, without exposed carbon fibers and broken SiC coating after ablation for 120 s, the intact interface between SiC and C/C composites indicated that (Hf_0.25Zr_0.25Ti_0.5)C coating had good ablation protection for C/C composites.

Y₂O₃ coatings are widely applied in semiconductor etching machines to protect the inner walls of aluminum alloys. This study reports the preparation of yttria-based coatings on aluminum alloy substrates using atmospheric laminar plasma spraying (ALPS) methods. In this study, four yttria-based coatings were designed and tested for their thermal performance, plasma etching resistance, and resistance to laser ablation. The rare-earth-zirconia (RE-ZrO₂) doped Y₂O₃ coating exhibited the best thermal insulation performance, with a thermal conductivity of approximately 0.6 W m⁻¹ k⁻¹ at 600 °C. Plasma etching experiments demonstrated that more rare-earth fluorides were generated on the surface of the RE-ZrO₂ doped Y₂O₃ coating, which weakened the plasma energy. Finally, the lowest etching rate was achieved. Laser ablation experiments demonstrated that the depth of the ablation pit on the surface of the RE-ZrO₂ doped Y₂O₃ coating was shallow, indicating good laser ablation resistance. These results indicate that rare-earth-doped yttria-based coatings provide excellent corrosion protection against plasma etching and laser ablation.

High-temperature turbine airfoils and combustion chamber walls in jet engines require sufficient cooling via cooling holes and thermal barrier coating systems (TBCs) to protect them from hot combustion gases. As the demand for greater efficiency and higher firing temperatures in jet engines increases, there is a corresponding need for more advanced film cooling methods, such as the use of more complex hole geometries. The use of Additive Layer Manufacturing (ALM) techniques allows the production of such intricate cooling holes, enhancing the flow of cooling air onto component surfaces. Conventional TBC deposition techniques, for example Atmospheric Plasma Spraying (APS) or Electron Beam Physical Vapor Deposition (EB-PVD), often lead to partial or complete blockage of cooling holes. This study compares the blockage of TBCs deposited on conventionally-sheet alloys with standard cooling holes and ALM alloys with more complex cooling holes using APS as a baseline process. Additionally, alternative plasma spray deposition technologies such as Suspension Plasma Spraying (SPS) and Plasma Spray-Physical Vapor Deposition (PS-PVD) were explored. The aim was to determine the effectiveness of these processes in preventing blockage compared to the traditional APS process. The experimental results showed that the formation of the coating, whether originating from splats or from the vapor phase, the feedstock particle size, and the cooling hole geometry can all affect the blockage. It was demonstrated that PS-PVD, with its vapor-induced deposition, is highly effective in minimizing blockage, regardless of the cooling hole geometry.