Journal of Thermal Spray Technology最新文献

As cold spray transitions from a coating technology to an additive manufacturing process, the variety of part shapes and sizes is significantly increasing while the drive to optimize the mechanical properties of cold-sprayed deposits has emerged. This study investigates the effect of substrate characteristics, a variable typically neglected, on copper cold-sprayed deposit hardness and tensile properties before and after deposit heat treatment. Substrate material, shape and size were varied, resulting in a range of substrate process temperatures as evaluated using IR camera measurements. Deposits sprayed on the smallest parts, i.e., those displaying the highest temperatures, exhibited lower hardness due to spontaneous in situ annealing caused by the thermal energy rise intrinsic to the cold spray process. Smallest parts also presented the best ductility from a combination of spontaneous in situ annealing and improved interparticle cohesion. The as-sprayed deposit strength was rather optimized at an intermediate substrate size and temperature where partial spontaneous in situ annealing was combined with improved interparticle cohesion. After deposit heat treatment, differences among tested substrate sizes vanish. Deposit heat treatment at 350 °C causes softening, a decrease in strength and an increase in ductility due to the annealing effect. The sintering effect becomes predominant for deposit heat treatment at 600 °C, leading to an increase in ultimate tensile strength and further improvement in deposit ductility. This work has important implications for cold spray process scale-up, as one cannot assume the properties achieved after process optimization on small laboratory-size coupons will be maintained on larger parts.

Atmospheric plasma spraying (APS) is an attractive method for metal-supported solid oxide fuel cells (MS-SOFCs). In this study, NiO-Gd_0.2Ce_0.8O_1.9 anodes are fabricated by APS. Different spraying distances of 80-120 mm are adopted to investigate the effect on the microstructures and properties of anode coatings. The temperature, velocity and deposition morphology of the anode particles indicate that at a suitable spray distance of 100 mm, the anode particles are fully melted and accelerated under the plasma jet to form an optimal anode coating on the substrate. As a result, the full cell based on the 100-mm anode coating shows a maximum output power density of 940.45 mW/cm² and an open-circuit voltage of 1 V at 800 °C. The polarization resistance of the cell is 0.234 Ω·cm². It demonstrates that controlling the APS spraying distance can effectively adjust the anode deposition state and obtain high-performance MS-SOFCs.

In this study, we developed a ~ 2 mm thick deposit of CoCrFeNiMn high entropy alloy (HEA) from cold spray. After cold-spraying, annealing at 600, 800 and 1000 °C for 5 hrs was conducted to improve and consolidate the microstructure. The influence of the annealing treatment on the microstructure, hardness and tensile strength of the HEA deposit was studied. The results showed that annealing treatment increased the fraction of metallurgical bonded areas due to diffusion, which resulted in enhanced mechanical performances of the deposit. The examined fractured surfaces of the tensile test samples revealed that the annealing treatment changed the failure behavior of the as-sprayed deposit from mostly particle-particle interface failure to void coalescence (ductile failure). Interestingly, a distinct microstructure was observed for the deposited annealed at 600 °C; a partially recrystallized microstructure with a small volume fraction of Cr-rich phase formed along grain boundaries, whereas fully recrystallized microstructure at higher two temperatures. The strengthening effect of partial recrystallisation, with a small volume fraction of the Cr-rich phase led to a greater reduced modulus and tensile strength (~196.7 GPa and 51.7 MPa) of the deposit annealed at 600 °C when compared with that annealed at 800 °C (~182.5 GPa and 43.6 MPa). It is believed that the small volume fraction of the Cr-rich phase partly constrained the deformation of the surrounding FCC HEA matrix during mechanical loading, leading to better mechanical properties as compared to the deposit annealed at 800 °C.

Cold spray deposition of SiCp/Al composite coatings shows great potential in the field of material protection. However, the strengthening effect of single-scale reinforcement on the composite coating’s performance is limited. To further enhance the mechanical properties of the composite coating, a dual-scale reinforcement model with both micron and nanoparticles was adopted. The addition of nanoparticles further enhances the individual scale advantages and coupling effects of SiC particles, resulting in a composite coating with excellent comprehensive properties, thus meeting the combined requirements for strength and wear resistance. Micro-nano-SiCp/6061Al composite coatings were designed and prepared using high-pressure cold spray technology. The preparation process, microstructure, and property changes of the micro-nano-reinforced composite coatings were systematically studied. The results indicate that cold spray can successfully produce micro-nano-dual-scale SiCp/6061Al composite coatings. The SiC/Al nano-composite coating exhibits a dense structure with micron and nano-SiC particles uniformly dispersed throughout the 6061Al matrix. Compared to single micron-reinforced SiCp/6061Al composite coatings, the addition of nano-SiC particles significantly strengthen the 6061Al matrix. The hardness of cold-sprayed micro-nano-reinforced SiC/6061Al composite coatings increased by 21.9% and the wear resistance has been improved substantially, while the wear rate reduced by 41.92%. With the content of nano-SiC particles increasing, the hardness and wear resistance of the micro-nano-reinforced SiC/6061Al composite coatings initially increase and then decrease. When the mass fraction of nanoparticles reaches 5%, the hardness peaks at 100.64 Hv, while the wear rate decreases to 1.0390 × 10⁻⁴mm³/N m. The proposed cold spray method for preparing dual-scale SiC/6061Al composite coatings could provide data support for future applications of SiC particle-reinforced aluminum matrix composite coatings.

Cold spray is a dynamic additive manufacturing process which results in a unique microstructure and mechanical properties. This work investigates cold spray deposited material under high strain-rate dynamic loading, and specifically the influence of post-build heat treatment on the material strength when subjected to incipient spallation. As-deposited and heat-treated samples were characterized and subjected to shock loading with a plate impact apparatus; the free-surface velocity was measured during the experiment, and the samples were recovered for postmortem analysis. The test results show that the as-deposited material has little to no strength under high strain-rate tensile loading and breaks into pieces. After a short heat treatment, the material recovers some of its tensile strength (compared to wrought copper) but does not exhibit the expected damage morphology and void distribution. When the heat treatment time is extended to several hours and the temperature is increased, the material exhibits ramp-like shock rise and damage formation that is widely distributed within the sample. This work contributes to a better understanding of the influence of heat treatment on the microstructure and subsequent material strength properties under high strain-rate loading, which is crucial for applications where cold spray is a technique of interest.

Yttria-stabilized zirconia (YSZ), a typical thermal barrier coating, faces challenges in meeting the stringent service requirements of critical components such as aero-engine blades due to high-temperature phase transitions and susceptibility to sintering. In the short term, optimizing the coating structure provides an effective and cost-efficient solution to this problem. This study deposited a multi-modal YSZ coating using supersonic atmospheric plasma spraying. The evolution of the microstructure and thermal-mechanical properties of the coating during sintering was systematically studied. The results showed that the multi-modal YSZ coating mainly comprised crystalline regions and unmelted particles, which remained stable after sintering at 1200 °C for 100 h. During sintering for less than 20 h, micro-defects such as cracks and pores rapidly healed by forming sintering necks, significantly enhancing hardness and elastic modulus of the coating. After 50 h, rapid sintering of the unmelted particles led to the formation of interfacial cracks between these particles and the crystalline regions. This effectively reduced the coating's thermal conductivity by inhibiting heat transfer, which slowed down sintering behavior and maintained the stability of hardness and elastic modulus.

Two WC-10Co-4Cr and WC-12Co coatings were deposited on the surface of AZ91 magnesium alloy using high velocity oxygen fuel (HVOF) technology aiming to improve the wear resistance and corrosion resistance. The hardness and organization of the surface and cross section of the coating and substrate were compared. The differences in wear resistance and corrosion resistance between the coatings and the substrate were compared. The wear experiments showed that the wear volumes of WC-10Co4Cr, WC-12Co and AZ91 substrate were 2.7 × 10^-3 mm³, 1.1 × 10^-3 mm³ and 6.1 × 10^-1 mm³, respectively. The coatings mainly exhibited abrasive wear and adhesive wear. The better wear resistance of the coatings than the AZ91 substrate is due to the high hardness of the coatings. The corrosion resistance of the coatings was better than that of the substrate, and the corrosion resistance of WC-10Co-4Cr was better than that of WC-12Co. The corrosion currents density of WC-10Co4Cr, WC-12Co and AZ91 substrates are 4.02 μA cm^-2, 34.31 μA cm^-2 and 46.79 μA cm^-2, respectively. The Cr element is favorable for further improving the corrosion resistance.

The in-flight behavior of quasicrystal (QC) particles during the high-velocity oxygen fuel (HVOF) process across four distinct operational settings was analyzed using computational fluid dynamics (CFD) simulations. A three-dimensional two-way coupled Eulerian–Lagrangian approach was used to simulate the process. The gas phase was modeled by solving equations governing mass, momentum, energy, and species, alongside the shear stress transport (SST) k-ω turbulence model, while the oxygen-propylene premixed combustion was simulated using the eddy dissipation model. Following the gas flow modeling, the trajectory and thermal evolution of QC particles were tracked within the computational domain, utilizing accurate correlations for drag coefficient and Nusselt number that cover a wide range of Mach, Knudsen, and Reynolds numbers. The analysis revealed that large particles do not melt due to their mass and the low thermal conductivity of QC materials. These particles typically attain impact velocities around 400 m/s. In contrast, smaller particles with diameters less than 20-25 μm reach temperatures of 1200 °C or higher, transitioning into a molten state with impact velocities reaching approximately 600 m/s. Moreover, it was found that approaching stoichiometric conditions with reduced mass flow rates of QC powder resulted in elevated particle temperatures and velocities upon impact, consequently leading to a reduction in porosity. To verify this finding, experiments were conducted under varying oxygen-to-fuel ratios and powder loadings, with subsequent measurement of the coating porosity. An in-flight particle diagnostic system was also used to assess the particle velocity. The numerical study agrees closely with the experimental observations.

In order to combine the anti-friction performance of micro-texture with the lubrication effect of solid self-lubricating phase, and further improve the tribological performance of the coating under dry friction conditions. Fe₅/10%WC/5% MoS₂ self-lubricating coating was prepared by laser cladding technology, and then elliptical micro-textures with different arrangement angles (0°, 45°, 90°) were processed on the surface of the coating by laser micro-texture technology. The friction and wear behavior of the micro-texture coating was investigated from the perspectives of friction coefficient, volume wear loss, and wear morphology. The improvement effect of micro-texture on the wear resistance of the coating was discussed, and the synergistic anti-friction mechanism of the self-lubricating coating and surface micro-texture was explored. The results show that the friction coefficient and volume loss of the 0° textured coating are the smallest under the external load of 70 N, and the wear mechanism is characterized by slight abrasive wear. The 45° textured coating exhibits local adhesive traces in addition to a few micro-cutting furrows, suggesting a combination of slight abrasive wear and adhesive wear. The friction coefficient and volume loss of the 90° textured coating are the largest and the volume loss is greater than that of the non-textured coating. The wear mechanism is dominated by fatigue wear, accompanied by slight abrasive wear and adhesive wear. During the friction and wear process, the elliptical micro-pits can promptly capture wear debris, reducing the continuous damage to the coating. Additionally, the solid lubricant (MoS₂) stored in the micro-pits can provide continuous lubrication to the friction contact area and effectively decrease the friction coefficient.