Journal of Thermal Spray Technology最新文献

To investigate the molten pool dynamics and defect formation mechanisms during the laser cladding of FeCoNiCrMo high-entropy alloys on Ti6Al4V substrates, a three-dimensional coupled temperature and flow field model for a single-track cladded coating was established. The influence of varying laser energy densities (80, 90, 100, 110, and 120 J/mm²) on the geometric characteristics of the cladded coating was systematically analyzed to elucidate the relationship between processing parameters and cladding morphology. The results reveal that the presence of pronounced Marangoni convection significantly influences the morphological characteristics of the FeCoNiCrMo cladded coating. At a laser energy density of 120 J/mm², the molten pool flow velocity reaches up to 48 mm/s, leading to the maximum observed values of cladded layer dimensions. Conversely, at a lower energy density, the molten pool demonstrates limited flowability and promotes bubble entrapment at the solidification front and contributes to the formation of porosity defects. Elevated laser energy densities (Led = 110 and 120 J/mm²) were observed to enhance the dilution rate of the cladded coatings, thereby promoting the diffusion of alloying elements from the molten pool into the Ti6Al4V substrate. However, the increased energy input also led to higher residual tensile stresses within the cladded coatings, which serve as a driving factor for crack initiation at the fusion interface between the substrate and cladded materials.

This paper systematically investigates the impact of cold spraying temperature on the microstructure and high-temperature oxidation resistance of Cr coatings. Three types of Cr coatings are prepared using different temperature parameters. The results show that as the spraying temperature increased from 500 to 700 °C, the average grain size decreased from 3.4 to 0.5 μm. The refinement of grains promoted the rapid formation and continuous growth of the Cr₂O₃ oxide layer by increasing the grain boundary density. The study reveals the mechanism by which cold spraying temperature optimizes the oxidation resistance of coatings through the regulation of grain size.

This study investigates the use of cold spray additive manufacturing (CSAM) to fabricate Permalloy ferromagnetic components using two ferromagnetic iron-nickel FeNi50 alloy powders with particle sizes of D50 = 13 µm and 35 µm. By varying spraying distance and gas temperature, the research evaluates how process parameters influence deposition efficiency, microstructure, and functional properties. The highest deposition efficiency (62%) was achieved using the coarser powder at 640 °C and 35 mm distance. Microstructural analysis showed compact, low-porosity deposits, with the fine powder reaching porosity below 1%. All samples retained the FCC γ-phase structure of the feedstock without forming new phases. Microhardness was highest near the substrate, with the fine powder reaching 247 ± 5 HV. Magnetic characterization revealed superior performance from coarse powders, with higher saturation magnetization (1.06 T), lower coercivity (2239 A/m), and higher permeability (653), while fine powders led to increased magnetic losses due to ultrafine grains and internal defects. Overall, CSAM demonstrates strong potential for producing soft magnetic Permalloy components with tunable properties, particularly when using coarser powders.

This study investigates the relationship between microstructure, hydrogen diffusion, and corrosion resistance in cold sprayed (CS) 410L stainless steel (CS410L). Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used for microstructural analysis, while electrochemical methods assessed hydrogen transport and corrosion performance compared to wrought 410L (W410L). Although studies on the hydrogen trapping steels exist in literature, understanding the influence of the CS microstructure on hydrogen diffusion is crucial before implementation. Analysis of the CS microstructure revealed grain refinement at prior particle boundaries (PPB), while grains among the interior remained coarse though highly strained. Hydrogen permeation results indicated a significant drop in diffusivity in CS deposit, due to increased defect density and heterogenous microstructure. Significant hydrogen trapping at PPB was revealed by silver decoration in CS deposit, while trapping in W410L occurred at precipitate/matrix interfaces. Electrochemical results of CS410L exhibited no passivity and corroded actively in 0.1 M NaCl, while W410L exhibited passivity. Immersion studies demonstrated corrosion initiation and significant propagation along PPBs in CS deposit, in contrast to limited surface degradation in W410L. However, under high alkaline conditions (pH > 12) CS410L exhibited a comparable corrosion performance. Findings highlight CS-induced microstructural defects govern both hydrogen transport and corrosion resistance.

In this study, addressing the challenge of poor mechanical properties in cold spray additive manufacturing (CSAM) deposits, typical thermal-mechanical effects (Friction stir processing-FSP and Hot rolling-HR) were introduced into the deposit. The results indicate that multiple passes of FSP can eliminate defects caused by poor flow within the deposit, resulting in an initial decrease followed by an increase in porosity. However, the bonding quality between metal and ceramic deteriorates after three passes of FSP. Post-FSP, there is an increased disparity in microstructure, with smaller grain size and lower dislocation density observed on the advancing side compared to the retreating side, while the precipitates in the stir zone approaches the solid solution state. The optimal mechanical properties of the deposit are achieved at a traverse speed of 150 mm/min and a rotational speed of 1000 rpm, with a 43% increase in tensile strength and tensile strength and elongation reaching 406 MPa and 2.7%, respectively. After HR, the tensile strength and plasticity of the deposit increased to 439 MPa and 3.93%, respectively. The fundamental reasons for the mechanical property improvement of HR and FSP are both the conversion of mechanical interlocking between particles into metallurgical bonding.

Marine equipment continues to face the threat of marine biofouling, and the large-scale preparation of antifouling coatings using thermal spray technology has been emerging as one of the effective strategies. Polyimide coatings were prepared by flame spraying precursor liquid materials, and the spraying distance and substrate temperature were altered to obtain optimal coating structure. A novel antifouling agent NH₂-ZIF-8@BITEP was synthesized by using a zinc-based metal-organic framework ZIF-8 as a nanocarrier to bond epoxidized BIT. This antifouling agent was mixed with polyamide solution, and the MOF-based coatings were fabricated via flame spraying. The coating showed a sterilization rate of over 99.99% after co-incubation with Escherichia coli and Staphylococcus aureus for 24 h, and effectively reduced the adhesion of diatoms after 14 days of co-culturing. This new MOF-loaded polyimide coating would open a new window for designing and constructing marine antifouling coating for long-term applications.

Severe-service materials in cracking reactors face complex corrosion-fouling phenomena driven by sulfur-rich heavy oil. Nickel-based alloys (Inconel 718—IN718) and cobalt-based coatings (Wallex 50—W50) are common materials in petrochemical equipment, but their degradation behavior under heavy oil cracking conditions is seldom explored. Bare IN718 and high-velocity oxygen fuel (HVOF) sprayed W50 were exposed to cracking environments—445 °C and > 11 MPa, varying hydrogen, catalyst, and agitation—simulating realistic refinery environments. Optical imaging of the surface allowed to semi-quantitatively assess the surface fouling intensity, while SEM-EDS analysis of cross-sections and surfaces offered new perspectives about the sulfidation mechanism, and XRD identified oxides and sulfides in the degradation scale. W50 formed scales with reduced coke accumulation, especially on smoother surfaces. In contrast, IN718 developed more unstable, delaminating scales with severe grain boundary corrosion, particularly under catalytic hydrocracking conditions. The findings suggest that IN718 fouling is primarily governed by the kinetics of sulfidation-induced chemical reactions, whereas W50 fouling is controlled by mass transfer of sulfur-containing species. A phenomenological model is proposed to describe the interplay between the sulfidation mechanism and scale microstructure evolution.

Air plasma-sprayed (APS) environmental barrier coatings (EBCs) is presently a well-established technology. Even so, there are still unexplored process–property relationships. For example, it is notionally understood that rare-earth silicates before impacting the substrate will undergo an in-flight, in situ chemical shift. It is hypothesized among the community that the free silica in the molten droplets vaporizes, leading to chemically shifted individual splats. The available literature is divided on whether the presence of hydrogen or the plasma power drives this chemical shift. This work established two spraying conditions (at nearly equivalent plasma power) with Ar-H₂ and Ar-He plasma gases. Process diagnostics revealed the two plasmas yield particles of nearly equivalent melt state to directly address the question—what drives the chemical shift of APS EBCs, and how does the chemical shift influence the properties of the coating? The results in this paper will show there is a measurable optical emission signature to indicate the in-flight decomposition when hydrogen is used. Moreover, for equivalently-molten spray streams at similar plasma powers, the phases, crystallization, and thermal expansion properties vary largely depending on the presence or absence of hydrogen in the plasma.

Wear-induced failure represents the predominant degradation mechanism in brake disks. Laser cladding technology provides a rapid and environmentally sustainable approach to enhance wear resistance. In this study, extreme-high-speed laser cladding (EHLA) was employed to fabricate a 316L steel matrix composite coating containing 16% TiC (comprising a 316L transition layer and a wear-resistant layer of 316L steel reinforced with 16 wt.% TiC particles) on gray cast iron (GCI) brake disks. The microstructure and mechanical properties were systematically characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray diffraction (XRD), Vickers microhardness testing, and pin-on-disk tribometry. Phase analysis confirmed the predominant presence of TiC carbides and γ-Fe in the coating. Microhardness measurements revealed a 1.41-fold enhancement in the wear-resistant layer (318.2 HV_0.3) compared to the substrate (225.6 HV_0.3). Tribological evaluations under room temperature (RT) and elevated (300 °C) temperatures demonstrated distinct friction behavior: The substrate exhibited a friction coefficient (COF) increase from 0.282 to 0.498 (1.77-fold rise) with temperature elevation, while the coating showed a more moderate COF increase from 0.241 to 0.331 (1.37-fold rise), demonstrating superior thermal stability. Wear mass loss measurements further confirmed the coating's enhanced performance: At RT, the substrate and coating exhibited mass losses of 3.6 mg and 2 mg, respectively, while at 300 °C, these values increased to 9.6 and 6 mg. In both temperature conditions, the coating demonstrated 44.4-37.5% lower wear mass loss than the substrate. These results conclusively validate the coating's exceptional wear resistance and temperature-adaptive performance.

Stainless steel–tungsten carbide (WC) composite layers were fabricated via laser metal deposition (LMD) and then treated by low-temperature plasma nitriding at 425 °C to improve wear and corrosion resistance. This thermochemical process resulted in the formation of nitrogen-supersaturated expanded austenite (S-phase) and chromium nitride (CrN) phases. To investigate the effects of alloying elements on the nitrided layers, a combination of experimental characterization, statistical analysis, and computational simulation was used. Ordinary least squares (OLS) analysis indicated that chromium might negatively influence nitrided layer thickness (regression coefficient = –0.40, p < 0.01), possibly due to its strong affinity for nitrogen. This trend was further supported by Monte Carlo simulations and density functional theory (DFT) calculations. Among the alloying elements studied, tungsten showed a potential positive correlation with surface hardness, increasing it by 21.85 HV per 1 wt.% increment. This effect may be attributed to the formation of eutectic carbides from the interaction between WC particles and stainless steel during LMD, which may contribute to hardening the nitrogen-enriched matrix. Anodic polarization testing suggested a possible positive correlation between the ferrite-to-austenite phase ratio in the as-deposited layers and the corrosion current density (p < 0.01, R² = 0.71). These results provide preliminary insights suggesting that controlling both the chromium content and ferrite phase ratio might be important for optimizing nitrided layer formation and improving corrosion resistance. Additionally, the formation of eutectic carbides could enhance surface hardness in the nitrided WC composite layers.