Journal of Thermal Spray Technology最新文献

Ni60A spraying-cladding coatings were innovatively prepared on the surface of the Q235 steel substrate by plasma spraying-cladding technique. Ni60A powder with a particle size of 30 μm was further selected as the optimum spraying-cladding powder based on preliminary numerical simulation. The spraying-cladding distanceØ was optimized, and the optimum distance was determined as 18 and 16 mm, respectively, for the internal feeding process and external feeding process. The microhardness of the spraying-cladding coating could reach 875.6 HV during the internal feeding process at a spraying-cladding distance of 18 mm, and reach 791.6 HV during the external feeding process at a spraying-cladding distance of 16 mm. Meanwhile, the thermal effect of the plasma spraying-cladding technique on the Q235 steel substrate was less.

The effect of MCrAlY and nano-fly ash additive powders on the mechanical and microstructural properties of mullite coatings was examined in this work. Three distinct mullite-based coatings, namely M (100% mullite), MM (95% mullite − 5% MCrAlY), and MMF (90% mullite − 5% MCrAlY − 5% nano-fly ash), were deposited onto a martensitic stainless steel (AISI 410) substrate through air-plasma spraying. MMF coatings achieved the best coating integrity during the experimental trials, with a porosity of 7.65%, and an optimum fracture toughness of 1.40 MPa m^0.5. The results revealed that incorporating MCrAlY particles into mullite coatings resulted in an optimal hardness of 638 HV₁. The addition of nano-fly ash significantly increased the adherence of MMF coatings to the AISI 410 substrate, which is critical to their durability and efficacy. Furthermore, the MMF coatings demonstrated a remarkable 60% reduction in crystallite size, yielding a finer size of 47 nm. Furthermore, dislocation density increased by 125%, reaching 44.8 × 10⁻⁵ nm⁻², compared to MM coatings. It was also revealed that the presence of MCrAlY and fly ash nanoparticles increased shear resistance by restricting the mobility of the shear plane, obtaining the highest adhesion strength of 76 MPa. These findings show that combining MCrAlY particles with nano-fly ash in mullite coatings provides various benefits, including enhanced hardness, crystal characteristics, adhesion, and shear resistance.

Aviation kerosene is a high-density, high-calorific value fuel widely used in high-velocity oxygen fuel (HVOF) thermal spraying. However, incomplete combustion of aviation kerosene generates CO₂, CO, and unburned hydrocarbons, which are not conducive to sustainable development for industry. Research on new HVOF processes using clean fuels is significant for energy conservation and emission reduction. In this study, a two-dimensional numerical model of JP-8000 spray gun flow field was established based on the computational fluid dynamics method, and the ethanol was blended into aviation kerosene fuel to reduce carbon emissions during spraying. Ethanol-kerosene premixed fuel and WC-12Co particles were injected into spray gun in discrete phase form. The KHRT method and O 'Rourke method in the discrete phase model were used to deal with the breakup and coalescence of fuel droplets. Lagrange tracking method was used to capture the flight trajectory of fuel droplets and sprayed particles, and the gas–liquid–solid coupling calculation of spraying flow field was realized. The results show that adding ethanol to aviation kerosene fuel can effectively reduce CO₂ emissions. When the ethanol proportion is 10%, CO₂ emissions decrease by nearly 30%. Ethanol pyrolysis leads to a slight increase in CO emissions, which can be effectively reduced by appropriately increasing the oxygen/fuel ratio. This study provides an important theoretical basis for the spraying practice of HVOF mixed fuel for energy saving and environmental protection and offers new insights for further optimizing the spraying process.

7-Series aluminum (Al) alloys have been widely used in aircraft and high-speed train manufacturing owing to its excellent mechanical properties and fracture toughness. However, surface problems of corrosion, wear and fatigue failure of Al alloy parts seriously affect the service life. In the present study, the noncontact laser shock peening (LSP) was applied to improve the fatigue life of the substrate before the coating deposited by cold spraying (CS). The effect of LSP on the interfacial bonding behavior between CS Al with 50 vol.% Al₂O₃ composite coatings and 7075 Al alloy substrate was comprehensively investigated. Results showed that after LSP treatment, the tensile strength is reduced from 47 to 34 MPa and 32 MPa when the laser shock energy was 2 and 3 J, respectively. Under the condition of shear strength, it decreases from 41.5 to 30 MPa and 26 MPa, respectively. In addition, numerical simulations were conducted on LSP and CS processes, and the results showed that with the increase of laser shock energy, the plastic deformation dissipation energy of Al particles increases gradually, while the plastic deformation dissipation energy of the matrix decreased. Therefore, the surface hardening caused by LSP treatment is the main reason for the decrease of interfacial bonding strength.

The effect of non-planar substrate surface on homogeneity and quality of cold-sprayed (CS) deposits was studied by scanning acoustic microscopy (SAM). Fe coatings were cold-sprayed onto Al substrates containing artificially introduced grooves of square- and trapezoid-shaped geometries, with flat or cylindrical bottoms. The Al substrates were either wrought or cold-sprayed, to comprehend their prospective influence on the Fe coatings buildup. SAM was then used to assess morphological properties of the materials from the cross-view and top-view directions. The microstructure below the surface of the studied samples was visualized by measuring the amplitudes of the reflection echoes and the velocity of the ultrasonic waves. The SAM analysis revealed that the regions of coating imperfections around the grooves are larger than what is suggested by standard scanning electron microscopy (SEM) observations. Furthermore, we found that the seemingly non-influenced coating regions that appear perfectly homogeneous and dense in SEM do, in fact, possess heterogeneous microstructure associated with the individual CS nozzle passes.

This study explores the potential of cold spray technology for repairing high-strength Al7075 alloy components, particularly in the aerospace industry. The gas-atomized powder contains a dendritic cell structure with solutes segregated at the dendritic cell boundaries. Thus, direct aging of atomized powder fails to induce the formation of strengthened precipitates. Therefore, the effect of different powder pre-treatments on the deposition efficiency, microstructure, and aging behavior of the coatings was investigated. Cold spray coatings were deposited using as-received powder, solutionized, and solutionized + aged powders, revealing a significant improvement in thickness for coatings obtained using solutionized (110%) and solutionized + aged (80%) powders compared to the coating from the as-received atomized powder. Further, coatings deposited using as-received, solutionized, and solutionized + aged powders, were aged at 120 °C for various durations and the aging response of different coatings were studied. Microstructural studies revealed that gas-atomized powders exhibited dendritic structures with segregated solutes. Solutionizing eliminated the dendritic features, promoting deposition efficiency upon cold spraying. Aging of the coating from the solutionized powder led to the formation of ultrafine η' precipitates (29 ± 8 nm length, 2 ± 1 nm diameter) at peak-aged condition (after 8 h). These findings demonstrate the effectiveness of powder pre-treatment in tailoring the microstructure and deposition behavior of cold-sprayed Al7075 coatings, offering a promising approach for repair applications.

This study examined the influence of Bacillus subtilis adhesion on the corrosion and cavitation erosion resistance of high-velocity oxy-fuel (HVOF) sprayed WC-10Co-4Cr coatings. The polished HVOF-sprayed WC-10Co-4Cr coatings were divided into two groups: one immersed in artificial seawater (ASW) and the other immersed in ASW containing Bacillus subtilis (BASW). Following an immersion period of 42 days, chromium oxide was detected on the ASW-immersed coating according to x-ray diffraction, while the BASW-immersed coating showed no signs of oxidation or corrosion. Electrochemical testing indicated compromised corrosion resistance in both the coatings. Nonetheless, the corrosion resistance of the BASW-immersed coating was much better than the ASW-immersed coating, suggesting that the Bacillus subtilis biofilm protected the coating surface from the corrosive substances in ASW, such as chloride ions and oxygen. Cavitation erosion testing revealed that prior immersion in ASW accelerated the erosion process, while the BASW-immersed coating displayed better resistance to cavitation erosion due to the inhibited corrosion attained by the Bacillus subtilis biofilm.

The impact and adhesion mechanics of two-phase block copolymers during high-velocity impacts are studied experimentally and computationally to understand the effect of the rubbery phase on bonding behavior in cold spray additive manufacturing. Micron-scale (10-20 μm) spherical particles of polystyrene-block-polydimethylsiloxane with varying rubbery phases are impacted on a silicon substrate by using a laser-induced projectile impact test setup with impact velocities in the range of 50-600 m/s. Experiments indicate that the minimum impact velocity for polymer particles adhering to the substrate decreases with increasing rubbery phase content. A strain rate- and temperature-dependent constitutive model and cohesive zone model are calibrated for each material by comparing the deformed and computed deformed particle shapes and coefficient of restitution values of the rebounding particles. Computational results show that increasing the rubbery phase content in block copolymers increases plastic energy dissipation from 89 to 96% and the critical strain energy release rate from 1.87 to 9.3 J/m² at 140 m/s, and thus contributes to the observed decrease in the minimum impact velocity required for block copolymers to adhere to substrates. The discovered direct relationship between soft phase content and critical strain energy release rate implies that increased soft-rubbery PDMS content in block copolymers enhances adhesion through improved chain mobility, better surface asperities coverage, and enhanced wetting, due to its lower surface energy and greater adiabatic heating.