Journal of Thermal Spray Technology最新文献

This study proposes an alternative Al₄C₃-NiCrAlY composite bond coat (BC) “system” to address the current challenges associated with traditional “stacked-horizontal layer” coating designs featuring linear interfacial thermal grown oxide (TGO) layers. The reactivity of Al₄C₃ with metallic alloy systems remains largely unexplored. This work establishes an initial baseline for the compositional and microstructural characteristics of this novel composite composition in the powder form. The microstructure and phase evolution of spray-dried Al₄C₃-(25-75 vol.%) NiCrAlY composite powders were examined via controlled-atmosphere heat treatments to establish the steady-state composition and microstructure up to 1300 °C. No significant phase interaction was observed below 1250 °C. Above this temperature, Al diffusion from Al₄C₃ into NiCrAlY enabled nickel aluminide formation, while free carbon facilitated the precipitation of chromium carbides. The final composition of the composite powder comprised nickel aluminide matrices with internal chromium carbide formations. For powders with higher initial Al₄C₃ content, nickel aluminide phases also formed as external attachments to the main body of the composite particles.

In this study, (FeCoNiCrMo + Ti_X) alloy coatings (x = 0, 0.5, 1.0, 1.5) were successfully deposited on carbon fiber-reinforced polymer (CFRP) substrates via plasma spraying. The objective was to enhance the surface hardness and wear resistance of CFRP, while systematically investigating the effects of Ti content on the coating’s microstructure and mechanical performance. The results show that the (FeCoNiCrMo + Ti_X) coatings significantly improve the surface hardness and wear resistance of CFRP. The addition of Ti leads to the formation of a dark region in the coating due to its high reactivity, which promotes reactions with certain metallic elements. Consequently, the FCC2 phase disappears, and new phases such as BCC, Laves, and trace amounts of TiO₂ are formed, affecting the oxidation behavior of elements like Cr and Fe. These phase transitions and solid solution strengthening effects not only improve the coating’s hardness and wear resistance, but also impact the interfacial bonding strength. The Ti_1.5 coating achieved a microhardness of 838.8 HV_0.1, representing a 13.3% improvement over the original coating, and demonstrated approximately 53.4 times greater wear resistance, with the wear rate reduced to 8.17 × 10⁻⁶ mm³ N⁻¹ m⁻¹.The Ti_0.5 coating showed the lowest porosity (1.27%) and the highest interfacial bonding strength (26.2 MPa). Overall, the (FeCoNiCrMo + Ti_1.0) coating exhibited relatively balanced performance across key metrics.

Strain gauges were fabricated on steel surfaces via a 100 µm thick insulating alumina layer, followed by wire-arc deposition of Ni–Cr through a 3D printed polymer mask. The metallic serpentine traces, 100 µm thick and 0.75 mm wide, were designed to produce small (240 mm²) and large (900 mm²) sensors with unloaded resistances ranging from 17 to 30 Ω. Tensile and four-point bending tests demonstrated a linear correlation between the electrical resistance of the resistive track and applied strain. Samples subject to cycling presented hysteresis, wherein the resistance of the gauge did not return to its original value, which could be attributed to densification or crack formation in the coating. Upon sequential loading, however, gauge resistances reached a steady state. Moreover, strain gauges were deposited on the outer wall of a steel pressure vessel to investigate responsiveness following injection of a hydraulic fluid. The gauges were sensitive enough to detect individual step changes in internal cavity pressure. Finally, to differentiate between changes due to strain and temperature, a surface thermocouple was fabricated using the steel substrate and an insulated constantan wire through the sample as the thermocouple materials. A Ni–Cr coating was sprayed on the surface to electrically connect the wire to the surrounding substrate, forming a thermocouple junction. The empirical findings in this study demonstrate the feasibility of manufacturing strain gauges with masked deposition for structural health monitoring.

This study presents a three-dimensional non-axisymmetric numerical model to investigate the effect of the pressure differential (ΔP) between the powder carrier gas and the main working gas, arranged at a 45° angle, on the flow field distributions inside and outside the spraying gun, as well as on the Al particle accelerating and heating behavior during the cold spraying process. The numerical results indicate that, under a non-axisymmetric gas arrangement, an increase in ΔP significantly lowers the temperature of the mixed gas upstream of the spraying gun, consequently reducing the Al particle impact temperature. However, ΔP has a negligible effect on both the gas velocity and the Al particle impact velocity. Furthermore, the extent of Al particle dispersion within the spraying gun and the Al particle distribution on the substrate remain unaffected by ΔP variations, contrasting sharply with the behavior observed in coaxial gas arrangements. To validate the numerical predictions, single-pass cold spraying experiments were conducted to deposit Al coatings. Experimental results demonstrate that the width of the Al particle impact area on the substrate closely coincides with the simulation data and the coating width is invariant to adjustments in ΔP, hence verifying the numerical simulations.

Cold spray is a feasible option to repair the versatile yet heat-sensitive Ti-6Al-4V (Ti64) alloy which has been widely used in aerospace, biomedical, marine and automotive industry. Nevertheless, the high yield strength of Ti64 makes it difficult to deform and attain dense coatings during cold spray deposition. While different process parameters have been investigated during cold spray deposition of Ti64 powders, the effect of powder size on the Ti64 deposits’ microstructure and wearability is not clear. Therefore, the influence of powder size on the cold-sprayed Ti64 deposit’s microstructure, residual stress, adhesion strength, coefficient of friction (CoF) and wearability have been investigated in this work. Three types of spherical Ti64 powders with median diameters (D₅₀) of 23.1, 30.3 and 41.8 µm were deposited on Ti64 substrates using a common set of spray parameters. Their microstructure and wear performance were compared against those of Ti64 bulk coupon. The powders with the smallest D₅₀ of 23.1 µm are found to result in the highest deposition efficiency (DE, 78.5%) and the lowest porosity (2.7%). Conversely, the powder with the largest D₅₀ of 41.8 µm exhibits the lowest DE of 19.6%, highest porosity 14.6%, highest compressive residual stress and poorest adhesion to the substrate. With the understanding of the influence of powder size on deposits’ properties and wear performance, deliberate choices can be made regarding powder selection to achieve desired properties for specific cold spray applications.

To address the issues of poor wear resistance and frequent failure in 65Mn steel used for agricultural machinery rotary tillage parts, an Fe/Ni-WC gradient composite coating was deposited on the surface of a 65Mn steel substrate via plasma cladding technology. The surface crack formation of the coating was evaluated, and the variations in elemental composition, phase structure, and crystal structure across the coating were analyzed. Additionally, the hardness distribution and tribological properties of the coating were investigated. The results indicated that the gradient composition of the Fe/Ni-WC coating reduced crack incidence by 98.53%. Interlayer diffusion of the primary elements led to the formation of γ-Fe, γ-(Fe, Ni), Fe–Cr, W₂C, and other carbides and borides. The average hardness of the Fe/Ni-WC top functional layer reached 785.97 HV_0.5, approximately 2.79 times higher than that of the substrate. Wear tests revealed that the gradient coating exhibited a lower friction coefficient, narrower wear width, shallower wear depth, and reduced material loss compared to the substrate. In conclusion, plasma cladding of the Fe/Ni-WC gradient composite coating improved coating integrity and significantly enhanced the hardness and wear resistance of the 65Mn steel substrate.

Liquid cold spray (LCS) is an innovative technique for applying coatings, restoring parts, and enabling cost-effective, high-volume solid-state additive manufacturing. This method uses high-speed superheated liquids, which possess much greater density than the typical gases used in conventional cold spray (CS) systems, in order to propel much coarser solid particles (60-250 µm). The process involves pressurized water, ranging between 300 and 500 MPa, passing through a high-pressure tube and reaching temperatures of approximately 200-400 °C. Subsequently, this heated water is directed through an orifice into a mixing chamber. Within the chamber, rapid depressurization leads to flash boiling, causing some of the water to evaporate. Solid particles are then injected into the chamber. This chamber is connected to a converging nozzle, which accelerates the three-phase flow toward the substrate. The present study uses a Eulerian–Lagrangian approach to investigate the impact of liquid temperature on the behavior of steam, water, and solid particles both inside and outside the nozzle. The Lee’s evaporation–condensation model and the Re-Normalization Group (RNG) k-epsilon turbulence model handle the water-steam flow, while particle’s behavior is modeled considering drag force and heat transfer from the mixture. Different values for mass transfer relaxation coefficients are tested to find the most relevant one for the LCS process. The particle velocity obtained from numerical simulations is compared and validated against the experimental results, as it plays a crucial role in the formation of coatings.

Copper-based materials are extensively utilized in advanced high-power electric slip rings, yet the relatively poor wear resistance limits their service life. To address this issue, this study proposed cold-sprayed Cu/B₄C composite coatings to enhance the wear resistance of copper-based materials. Three types of Cu/B₄C spray powders with Cu:B₄C volume ratios of 1:1 (0.5CBC), 2:1 (CBC), and 4:1 (2CBC), along with pure copper coatings, were fabricated via high pressure cold spray method (HPCS). The friction and wear behavior of coatings against 5mm Al₂O₃ balls under a load of 5 N for 20000 cycles were systematically investigated. Surface morphologies and sheet resistance of different materials were characterized, and the wear evolution mechanisms were analyzed. Results revealed that B₄C constitutes 2.66 ~ 4.58 vol.% in the composite coatings, and sheet resistance as low as 11.75-17.00 μΩ/□. The CBC coating exhibits significantly higher hardness compared to copper coating and copper bulk. Additionally, it demonstrates a friction coefficient of 0.26 (copper bulk: 0.37) and a wear rate of 1.51 × 10⁻⁵ mm³ N⁻¹ m⁻¹, both of which are notably lower than those of copper coating and copper bulk. The incorporation of B₄C particles effectively enhances the frictional and mechanical properties of the copper coating by distributing the applied load and mitigating direct wear, thereby significantly improving durability and extending service life.

Cold spray (CS) is a progressive method for the deposition of metals and alloys whose principles involve considerable plastic deformation of the produced material at extreme strain rates. Positron annihilation spectroscopy (PAS) is an analytical technique capable of studying deformation on the atomic scale level, even in extremely deformed materials. In our study, the PAS method was used to characterize the microstructure and quantify the open-volume defects in four cold sprayed metals: Al, Cu, Ni, and Ti. As counterparts, bulk samples of these materials with ultra-fine-grained structures were also produced by high-pressure torsion (HPT), a process exceeding cold spray in the total deformation, but having several orders of magnitude smaller strain rates, and by a traditional cold rolling process. The results show that the CS and HPT processes lead to the formation of similar lattice defects (dislocations and vacancy clusters), and both exhibit significantly higher dislocation densities than conventionally cold-rolled materials. Further, the vacancy clusters present in CS and HPT materials were not present in the rolled counterparts due to the lower vacancy production rate.