Journal of Thermal Spray Technology最新文献

The application of Finite Element Analysis (FEA) in cold spray (CS) provides valuable information about material deformation and stress distribution. The Johnson–Cook (JC) model is widely used to simulate material behavior, while the particle Flattening Ratio (FR) is commonly used to assess the deformation pattern and mechanism. FR has also been employed to evaluate and select appropriate JC model parameters. Experimental FR values can be obtained from a cross-sectional view of splats; however, the accuracy of these values can be affected by the sectioning location. This study introduces a novel approach for experimental FR observation by integrating top and cross-sectional views of Ti6Al4V and Ti-5553 deposited particle splats, addressing the limitations of the conventional cross-sectional FR method. The influence of the sectioning region on FR values was systematically evaluated through numerical and experimental analyses. Experimental FR results show that off-axis sectioning leads to overestimating FR values, with increases of 25.98% for Ti6Al4V and 15.45% for Ti-5553. The differences in critical velocities obtained using the FEA between the two FR measurement approaches were approximately 24.61% for Ti6Al4V and 32.46% for Ti-5553. The findings highlight the importance of accuracy in FR measurement and its effect on JC parameter selection and FEA results.

The thermal barrier coating (TBC) system is a key technology for protecting the hot parts of many thermal systems. But, the TBC system will not operate normally after a certain life cycle due to the high temperature environment, the mechanical force and the vibration. In this study, a theoretical model composed of TBC, thermally grown oxide (TGO) and the substrate was constructed after verifying the theoretical model against FEA results. In the following step, the TGO growth rate, TGO layer thickness, and TBC thickness were optimized using the ideal point method and the D-optimal method for upgrading the performance of the TBC systems. Then, the magnitude of the induced force and the frequency of the vibration were investigated using design of experiments method. The results show that the strain of the theoretical model has been increased with increased creep. Also, at the same mechanical stress and the experimental points, the strain changes between 10000 and 1000 cycles/min is almost negligible, and the strain increases sharply as the frequency decreases from 100 cycles/min. The constructed temperature-vibration coupled characteristics made a scientific basis for designing the high-performance TBC systems.

Recent research in biomaterials aims to promote a distinct tissue response to create truly biocompatible material. Many modern biomaterials have been developed with different surface energy, size, surface topography, elasticity, etc., to fulfill biocompatibility because the complex process of tissue formation and organization in human is mainly driven by the interaction of cells with their environment. Therefore, it is necessary to understand and control the surface characteristics of biomaterials to optimize their performance in biological environments. In this work, the surface topography of Hydroxyapatite (HAp)-coated polyamide substrate using Pulsed Laser Deposition (PLD) was studied. The topography of the HAp layer produced by PLD was evaluated as a function of substrate temperature, laser pulse energy, and pulse duration because these parameters play an important role in producing a quality layer. The surface topography was evaluated using Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM), the results revealed that the layer produced at different parameters had a smooth apatite coating with some micro- and nanoparticles scattered over the surface, along with some pits and pillar-like structures was also observed. The RMS roughness and thickness of HAp layer decreased, when there was an increase in substrate temperature at the same time laser pulse energy and pulse duration increased, the RMS roughness and thickness of HAp layer also increased. The results suggest that the surface topography of a HAp layer obtained in this work will have a positive effect on bone bonding and facilitate cellular growth and differentiation.

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The dislocation density and recrystallization kinetics in laser-heated cold sprayed SS304L are investigated for the first time via a combination of neutron diffraction, the convolutional multiple whole profile (CMWP) method, differential scanning calorimetry (DSC), and electron diffraction. These results are then coupled with thermal simulations to provide a more complete picture of the rapid recrystallization process in laser-heated cold sprayed SS304L. It was found that the cold sprayed process resulted in a uniform dislocation density throughout the material, and laser heating showed rapid recrystallization in the samples, resulting in reduced dislocation density. Furthermore, it was found that at lower heating rates, the cold sprayed material exhibited distinct recovery and recrystallization temperatures. At high heating rates, the more rapid kinetics of recrystallization at the prior particle interface regions become more pronounced than those at the prior particle interior, leading to the necklacing of recrystallized grain at the prior particle interface around the prior particle interior at 750 °C. Comparison of these results with thermal simulations and measured in situ dislocation density as a function of temperature shows that the resulting microstructure and degree of recrystallization can be approximated by the maximum temperature reached at any location. This allows the optimization of coating properties and tool path geometry using thermal simulations.

Arbon/carbon (C/C) composites have emerged as ideal candidates for thermal protection systems in aerospace vehicles due to their exceptional high-temperature mechanical properties. However, their rapid ablation in high-temperature oxidative environments severely limits engineering applications. To address this bottleneck, this study proposes a ZrC-30vol.%SiC (ZS3) ultra-high temperature ceramic coating system with an SiC transition layer. The composite coating was fabricated on C/C substrates via vacuum plasma spraying technology, and its anti-ablation mechanisms were systematically investigated through multi-scale analytical approaches. A three-dimensional transient thermo-structural coupling model was established using the ANSYS software, incorporating the " birth and death element " technique to simulate dynamic evolution of coating ablation morphology. This enabled quantitative characterization of spatiotemporal temperature distribution and Gaussian-type temperature gradient characteristics under laser irradiation. Transient thermo-structural coupling analysis elucidated the thermal stress evolution mechanisms in the coating-transition layer-substrate system during ablation. Combined CO₂ laser ablation experiments and microstructural characterization revealed that the ZS3 composite coating exhibits significantly superior ablation resistance compared to pure ZrC coatings, attributed to the formation of a dense ZrO₂-SiO₂ oxide layer. The synergistic failure mechanism involving oxidative phase transformation and thermal stress was comprehensively revealed. This research provides theoretical foundations for damage assessment and optimized design of ultra-high temperature ceramic coatings under high-energy laser irradiation.

In order to improve the performance of 45 steel, Fe-Cr-Mo-B-C amorphous composite coatings were fabricated on 45 steel substrates using a synergistic technique of laser cladding (LC) followed by laser remelting (LR). To further refine the microstructure of the coatings, laser remelting was applied with varying scanning speeds. The influence of different laser scanning speeds during laser remelting on the microstructure (including amorphous content, porosity, and phase composition) and properties of the coatings, including Vickers hardness, tribological behavior, and corrosion resistance, was systematically investigated in this study. Scanning electron microscopy (SEM), x-ray diffraction (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) were employed to characterize the microstructure, phase composition, amorphous/nanocrystalline coexistence, and thermal stability, respectively, and the wear and corrosion morphologies were analyzed to evaluate the surface integrity. The results indicate that a scanning speed of 20 mm/s is optimal, as it significantly enhances the amorphous content of the coatings (up to 48%), reduces porosity (to 0.474%), improves their microstructure, and strengthens their mechanical properties (maximum Vickers hardness of 1520.36 HV and minimum wear volume of 0.00315 mm³) as well as corrosion resistance (corrosion current density as low as 7.876 × 10⁻⁷ A/cm² and corrosion potential of  −215 mV in 3.5 wt.% NaCl solution). This study provides valuable insights into optimizing laser processing parameters to enhance the performance of Fe-based amorphous composite coatings for demanding industrial applications such as automotive, petrochemical, and marine engineering.

This study investigates the effects of high-velocity oxy-acetylene flame treatment (FT) and along with high pressure (4 MPa) air jet compression (AC) on the microstructural and mechanical properties of Ni-based superalloy coatings, specifically Inconel 718 (IN718), which were applied using high-velocity air fuel (HVAF) methods. Quantitative analyses revealed a ~ 40 % reduction in porosity and a refinement of dendritic structures from coarser to finer morphology. The coatings largely showed a compressive residual stress, but the stresses were reduced with the post-treatment, nevertheless maintaining phase stability. Field emission scanning electron microscopy (FESEM) showed improved interlamellar cohesion and fewer defects. Following flame treatment, hardness increased from 3.23 GPa (IN718 AS) to 10.99 GPa (IN718 FT), with elastic modulus enhancements of 232%. In contrast, under flame treatment with high-pressure air jet compression (FT + AC), hardness values reached an intermediate level, increased to 6.8 GPa, while the elastic modulus improved by ~ 43%. The lower hardness and elastic modulus in FT + AC compared to FT resulted from localized plastic deformation and stress relaxation induced by high-pressure air compression. This research highlights oxyacetylene flame treatment as a novel, effective, yet inexpensive solution for optimizing HVAF coatings, emphasizing its potential to enhance the performance and durability of Ni-based superalloys in advanced engineering applications.

Diesel-type engines utilizing heavy crude oil as fuel often experience accelerated erosion and corrosion within their combustion exhaust ducts. To address this issue, this study proposes various surface reclamation techniques and materials for depositing coatings to rebuild the wall thickness of gray cast iron. Laser cladding and several thermal spray techniques are considered, chosen for their low heat input and limited heat-affected zone (HAZ). The evaluation encompasses various Ni-based alloys (Inconel-718 and NiCrBSiFe) and hard metals (WC-CoCr and CrC-NiCr) under high-temperature erosion conditions. The investigation employs the ASTM G211-14 (modified) standard experimental method as a reference for conducting erosion tests using Al₂O₃ particles. The samples are tested at 500 °C, simulating the actual working temperature of the engine. Remarkably, the resistance of Inconel-718 coatings produced by laser cladding and HVOF processes was outstanding, exhibiting a volumetric erosion rate one-third less than that of the original cast iron. WC-CoCr coatings demonstrated brittle behavior but still a superior resistance compared to the cast iron. The obtained results are thoroughly discussed within the framework of the characterized microstructures, mechanical properties, and erosion mechanisms inherent to each of the proposed coating solutions.

Understanding the coefficient of thermal expansion (CTE) of thermal barrier coatings (TBCs) used in gas turbines is essential for determining the thermal cycle life of the coatings and preventing their catastrophic failure. In this work, an attempt is made to measure CTE of TBCs using in situ high-temperature x-ray diffraction in the temperature range of 298 K to 1273 K at every 100 K increment. For this study, single-layer yttria-stabilized zirconia (YSZ), single-layer gadolinium zirconate (GZ) coatings, YSZ/GZ bilayer coating (Bilayer YSZ/GZ), and functionally graded GZ coating (FGC) were deposited on a NiCrAlY bond coat using the atmospheric plasma spray method with an overall coating thickness of ~ 300 µm. The structural and microstructural changes were studied using XRD and SEM, respectively. The linear CTEs of YSZ, GZ, bilayer YSZ/GZ, and FGC at 1273 K were found to be 10.1 × 10^-6 K^-1, 9.9 × 10^-6 K^-1, 10.1 × 10^-6 K^-1, and 9.1 × 10^-6 K^-1, respectively. An isothermal oxidation test (IOT), thermal cyclic fatigue test (TCT), and thermal shock resistance tests of the YSZ, GZ, YSZ/GZ, and FGC were conducted at 1273 K and analyzed using XRD and SEM to evaluate the performance of the coatings. The bilayer YSZ/GZ TBC system has shown better isothermal oxidation resistance and thermal cyclic and thermal shock resistance.