Journal of Thermal Spray Technology最新文献

Ni60WC coatings were prepared on 45 steel by laser cladding with different scanning speeds, and the effects of laser scanning speed on the microstructure, phases and hardness were analyzed using a super-depth field microscopy, x-ray diffraction and microhardness tester. The tribological performance of Ni60WC coatings fabricated at the different scanning speeds was analyzed using a ball-on-disc wear tester, and the wear mechanism was discussed. The results show that the hardness of Ni60WC coating fabricated at the laser scanning speeds of 50, 60 and 70 mm/s is 1475.0 ± 129, 1564.9 ± 117 and 1527.2 ± 140 HV_0.5, respectively, showing the coating hardness fabricated at the laser scanning speed of 60 mm/s is the highest. The average coefficients of friction of Ni60WC coatings fabricated at the laser scanning speeds of 50, 60 and 70 mm/s are 0.297, 0.344 and 0.440, respectively, and the corresponding wear rates are 949.2, 854.6 and 881.4 μm³s⁻¹N⁻¹, respectively, showing that the wear resistance of Ni60WC coating fabricated at the laser scanning speed of 60 mm/s is the best. The wear mechanism of Ni60WC coating is combined of abrasive wear and adhesive wear, which is attributed to the WC particle with the high hardness.

Suspension plasma spray (SPS) and solution precursor plasma spray (SPPS) are advanced thermal spraying techniques that enable creation of the coatings with desirable properties. In both techniques, it is necessary to entrain the liquid feedstock into the thermal jet so that it can be effectively transformed into oxide particles. In this study, the suspension containing 3wt.% solid load of 40 nm ZrO₂-7%Y₂O₃ (7YSZ) powder with a medium of zirconium acetate-yttrium nitrate solution (instead of an aqueous or non-aqueous solvent) was used as titled solution medium suspension plasma spray (SMSPS) to produce the YSZ thermal barrier coating (TBC). The microstructure of SMSPS coating exhibited a columnar structure, with an inter-columnar spacing of approximately 5 microns. This columnar structure was attributed to the trajectory of nano-sized particles being affected by the plasma jet and their deposition at shallow angles on surface asperities, resulting in shadowing effect. The presence of vertical cracks within some of the columns in the microstructure of SMSPS coating was similar to the structure observed in SPPS coatings, highlighting the unique nature of this TBC structure. The oxidation testing at 1000°C for 12, 50, 120, and 250 hours revealed the formation of a thermally grown oxide (TGO) layer consisting of aluminum oxide and mixed oxides. The TGO layer growth rate was initially high, but then significantly decreased during the diffusion-controlled and steady-state stages of the test. It was found that the inter-columnar spacing in the coating facilitated oxygen diffusion, resulting in an accelerated oxidation of the bond coat during the initial stages. In addition, the SMSPS coating exhibited an average life of 753 cycles in 1-hours, 1000 ˚C thermal cycling test. The failure mechanism observed involved insular collapsing of adjacent clusters due to crack propagation which was attributed to the presence of vertical cracks and the columnar structure.

Atmospheric plasma-sprayed (APS) copper-nickel-based coatings are commonly used for the prevention of fretting wear of components in aerospace engines. In this study, Cu-Ni alloy was deposited using plasma spraying on different substrate materials such as stainless steel, carbon steel, and aluminum alloy to investigate the influence of the substrate materials as well as the performance (mechanical and tribological behavior) of the coatings. Microstructural studies revealed a homogeneous microstructure with the presence of splats for coatings deposited on each substrate. The porosity and microhardness of coatings deposited on each substrate were found to be within the range of (1.22 ± 0.27-1.65 ± 0.33%) and (117 ± 10-136 ± 23 HV_0.05), respectively. The tribology results also showed an increase in the frictional coefficient for each substrate from 0.41 at 25° to 0.73 at 300 °C. However, a steady state was not obtained at 450 °C. Similarly, the wear rates of coatings for each substrate increased from 300 to 450 °C test conditions, with no significant wear obtained at 25 °C. The results showed that the substrate materials had no significant effect on the performance of the coatings, as the thickness, porosity, surface roughness, and microhardness of coatings for each substrate material were comparable with no remarkable difference.

Fiber-reinforced polymer composites are prominent structural components in various industries such as aerospace, automotive, and wind energy. These materials are considered due to their high strength-to-weight ratio and relative ease of fabrication. However, fiber composites possess low electrical and thermal conductivities and are prone to impact-induced damage. Metallization of fiber-reinforced polymer composites has become an area of interest as a means to prevent abrasive and corrosive damage while also improving other physical properties including thermal and electrical conductivity. The possibility of using cold spray as a novel composite metallization approach has been investigated in this work. The significance of cold spray for metallization is due to relatively low process temperatures which effectively protect the underlaid substrate from potential temperature degradation. As a practical approach to further reduce the possibility of cold spray-induced damage, the present study explores the impact and failure mechanics of metal particles coated with a thin polymeric shell, hence the term polymer-coated metal particle. The thorough model-based analyses presented herein indicate that the so-called polymer-coated metal particles can be cold spray deposited without imposing significant damage to the composite substrate mainly due to the ‘cushioning’ effect of the thin polymer shell. The results discussed here also provide guidelines for the surface metallization of high-performance fiber-reinforced thermoplastic composites in practice.

High velocity air fuel (HVAF) technique, an innovative thermal spraying method, has proven more promising than traditional methods for both coating and repairing surfaces. This study focuses on the application of different thicknesses of IN625 superalloy coatings using HVAF to assess its potential for repair and cladding applications. Detailed coating characteristics of IN625 superalloy coating have been examined based on various techniques like nanoindentation, adhesion, micro-tensile and flexural strength of the coated samples. Within the coating, γ (NiCr rich), secondary peaks γ″ and carbide phases were identified. Particle deformation under impact and rapid cooling resulting in the formation of γ″ precipitates enhances the coating strength. However, the decrease in the adhesion strength with increasing coating thicknesses results from the defects formed at the coating–substrate interface and also influenced by thermal stresses and oxidation. Coating microstructure revealed a strong particle-to-substrate adhesion and varied splat morphologies dependent on degree of particle melting—at higher particle velocities in-flight oxidation of the powders was also minimal. Furthermore, the in-plane cohesive strength of the coating approaches 50% of the wrought alloy's yield strength, attributed to strain hardening from the peening effect. However, decrease in flexural strength as coating thickness increases due to compressive residual stress and coating delamination. The flexural strength of the as-sprayed coating exhibits up to 70% of the flexural strength of the wrought material with thicker coatings exhibiting lower strength.

Wear and erosion wear represent primary failure mechanisms in flow passage components, and proactive preventive maintenance can effectively extend their service life. This study investigates the utilization of laser metal deposition technology for the additive manufacturing of 17-4PH stainless steel (17-4PHss) followed by solid solution aging treatment. Structural transformations before and after the solution aging treatment, along with the dry wear and erosion wear properties of 17-4PHss post-heat treatment, were examined. During the heat treatment process, the solid solution treatment fully transformed the microstructure to martensite, alleviating the stress generated by the additive process, and refined the microstructure to 0.64 μm. The subsequent aging treatment further refined the grains, ultimately reducing the grain size from 0.68 μm in the additive state to 0.62 μm. Compared to traditional casting, the grain size of 17-4PHss was reduced by 6.83%. Additionally, NbC was uniformly distributed in the sample, playing a secondary phase strengthening role, resulting in high microhardness (455.5 HV_0.2). Simultaneously, the solid solution-aged (SSA) sample exhibited robust wear resistance, manifesting abrasive wear at low loads. With increasing load, a transition to abrasive wear and adhesive wear occurs, accompanied by oxidative wear and fatigue wear. At a 30 N load, the specific wear rate of the SSA sample decreased to 0.17 × 10⁻⁵ mm³/Nm, attributed to the more stable microstructure of the SSA sample under high loads. In the erosion wear test, the cumulative mass loss of the sample after heat treatment was the lowest (10.71 mg/m²h), with the erosion wear mechanism attributed to plastic deformation and micro-cutting.

This study investigates the feasibility of using cold spray for repair of Inconel 718 (IN718) components. The effect of cold spray parameters on the particle velocity, splat morphology, deposition efficiency (DE), thickness, and porosity was evaluated. Thick coatings of approximately 4 mm were deposited onto ground and polished IN718 substrates using N₂ gas heated to 1000 °C with gas pressure of 5 and 7 MPa. The coatings were subjected to standard double aging (DA) and a combination of solutionizing and double aging (STDA) heat treatment. The microstructure, hardness, porosity, tensile strength, and adhesive strength of as-sprayed and heat-treated coatings were evaluated. Additionally, the tensile properties of the coating–substrate combination (sandwich samples) were also evaluated. It was observed that higher gas pressure led to increased particle velocity, decreased porosity, enhanced hardness, and improved adhesion/tensile strength. The splat size increased with higher particle velocity, indicating greater particle deformation. The DE decreased with increase in number of deposited layers and increased with increase in gas pressure. The AS coating microstructure exhibited a deformed powder microstructure having fine dendritic/cellular structure. Following the DA treatment, the dendritic features were preserved, accompanied by the precipitation of γ′, γ′′, and δ phases. After STDA treatment, a homogeneous microstructure with the presence of γ′, γ′′, and Nb and Ti carbides without any δ phase was observed. The most favorable outcomes were achieved with the 7 MPa STDA sample, yielding a minimal porosity level of 0.4 ± 0.1% and a tensile strength of 1325 ± 10 MPa with a failure strain of 6.1 ± 0.6%. The tensile strength of 7 MPa sandwich sample was found better (1049 ± 8.5 MPa) compared to stand-alone coating (965 ± 24 MPa) after DA treatment.

In this work, Al_9.9Co_18.18Cr_18.18Fe_18.18Mo_18.18Ni_18.18 (at.%) high-entropy alloy was laser-cladded on the surface of H13 steel to extend the operating temperature range. Due to the dilution of substrate, coating with a composition of Al_3.63Co_10.58Cr_13.41Fe_51.28Mo_12.15Ni_8.95 (at.%) was achieved, which was a multi-phase system composed of FCC + BCC + σ + μ. Moreover, the phase transformation and the solidification behavior of the coating were studied in detail by utilizing phase diagram calculation. Oxidation resistance of the coating was also investigated and compared with that of H13 steel over temperature range of 600-800 °C. Both the coating and H13 steel show excellent oxidation resistance at 600 °C. After holding at 700 °C and 800 °C, the oxidation rate (the increment in oxide layer thickness per unit of time) of the coating is significantly smaller than that of H13 steel. It indicates that Al_3.63Co_10.58Cr_13.41Fe_51.28Mo_12.15Ni_8.95 coating has an advantage over H13 steel when oxidized over the temperature range of 700-800 °C. Based on the research in this work, the service temperature of H13 steel can be effectively extended by the Al_3.63Co_10.58Cr_13.41Fe_51.28Mo_12.15Ni_8.95 coating.

The present study focused on optimizing the cold spray (CS) process parameters for depositing Fe₂₀Cr₂₀Mn₂₀Ni₂₀Co₂₀ (Cantor alloy) coatings using mechanically alloyed (MA) powder. A two-step design of experiments approach was employed, beginning with the initial screening of input variables using the L8 Taguchi method, followed by the refinement of process parameters through the Box–Behnken design of experiments. Key performance indicators included deposition efficiency (DE), coating thickness per pass, and microstructural parameters including porosity, cracks, and interfacial defects/delamination. The study identified process gas temperature as the primary factor influencing both DE and thickness per pass. Higher gas temperature and pressure, combined with increased scanning speed, resulted in higher DE. The DE of the MA Cantor alloy powder peaked at around 14-15%, with a deposit density greater than 99% achieved at the highest process gas temperature and pressure (1000 °C and 60 bar, respectively). The average hardness of the optimal CS coating deposited using MA powder was found to be 679 ± 17 HV_0.1, which is approximately 90% greater than the average hardness reported for CS coatings deposited using atomized powder.

In engineering applications, it is crucial to extend service life by reducing the coefficient of friction (COF) and wear rate to improve dry wear resistance. This work investigates the tribological properties of NiCrAlY-Cr₃C₂-Ti₂SnC coatings with different Ti₂SnC additions over a wide temperature range. Composite coatings with varying Ti₂SnC concentrations were deposited onto TC4 titanium alloy substrates using atmospheric plasma spraying. Pin-on-disk wear tests were utilized to evaluate the tribological performance of the coatings, including the friction coefficient and wear rate, from room temperature to 800 °C. The wear mechanism of the coating was determined using SEM and a 3D profiler. The results demonstrate that the coating containing 30 wt.% Ti₂SnC (NC-30TSC) exhibits the lowest friction coefficient (0.29) and wear rate (4.89 × 10⁻⁵ mm³·N⁻¹·m⁻¹) at 800 °C. The composite coatings containing Ti₂SnC exhibited a decreased coefficient of friction and wear rate due to the high-temperature decomposition products of Ti₂SnC, such as TiO₂ and TiC. The wear mechanisms of the NC-30TSC coating were adhesive and fatigue wear at 300 °C, adhesive and oxidation wear at 600 °C, and oxidation wear at 800 °C. Additionally, the prefabricated cracks on the surface of the NC-30TSC coating healed after isothermal treatment, demonstrating excellent self-healing performance.