Journal of Thermal Spray Technology最新文献

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 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.

To address the issue of low surface hardness and poor wear resistance of 45# steel, this study applied laser cladding technology to prepare three types of iron-based coatings on the surface of 45# steel: Fe25-30WC, Fe25-30TiC, and Fe25-15WC+15TiC. The microstructure and mechanical properties of the coatings were analyzed using SEM, EDS, XRD, Vickers hardness tester, and a mechanical testing machine. The results indicated that in terms of hardness, the Fe25-30TiC coating exhibited the highest average microhardness of 600 ({HV}_{0.2}), followed by the Fe25-30WC coating (520 ({HV}_{0.2})) and the Fe25-15WC+15TiC coating (480 ({HV}_{0.2})). The bond strength of the Fe25-30WC coating and the Fe25-15WC+15TiC coating to the substrate was roughly the same, about 500 MPa, which is higher than that of the Fe25-30TiC coating (467 MPa). Additionally, the study discussed the abrasive wear characteristics of the three coatings under dry and wet sand conditions. The experimental results showed that under dry sand conditions, the Fe25-30TiC coating had superior wear resistance compared to the Fe25-15WC+15TiC coating and the Fe25-30WC coating. Under wet sand conditions, the Fe25-30WC coating exhibited better wear resistance than the Fe25-30TiC coatings and Fe25-15WC+15TiC coatings.

Dual-phase AlCoCrFeNiSi_0.5 high-entropy alloy powders for thermal spraying were prepared by mechanical alloying (MA). The effect of ball-milling time on MA of AlCoCrFeNiSi_0.5 powder was studied. The formation of solid solution during ball-milling was studied by X-ray diffraction. The grain size (GS), lattice distortion (LS) and dislocation density were calculated. The morphology, microstructure and element content of the powder were analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The GS decreases with the increase in rotating milling time, while the LS and dislocation density change in contrast therewith. The addition of Si increased the hardness and modulus of the powder to 12.33 ± 1.26 and 79.9 ± 6.21 GPa, respectively. The AlCoCrFeNiSi_0.5 powder has BCC and FCC solid solutions, while the FCC phase can be adjusted by annealing treatment. After 2 h solid-solution treatment at 1110 °C, BCC phase content up to 79%, the content of BCC solid solution is much higher than that before solid-solution treatment (46%), the GS increases, the LS and dislocation density decreases, the effects of solid-solution strengthening, dislocation strengthening, and fine-crystal strengthening are significantly enhanced, and the distribution of elements is more uniform. However, due to the reduction of FCC solid solution and σ-phase content, the hardness and elastic modulus of the powder after 1110 °C solid-solution treatment are slightly lower than that beforehand.