Journal of Thermal Spray Technology最新文献

The aim of this study is to investigate the mechanism of the influence of different contents of ceramic-reinforced particles MoB₂ on the microstructure, microhardness, and wear resistance of NiCr coatings. The x (MoB₂)-NiCr composite coatings with varying MoB₂ contents (x = 0,1,5,10, and 15 wt%) were applied to 304 steel using laser cladding. The results suggest the composite coatings consist of γ-(Ni, Cr), γ-(Ni, Fe), Ni_2.9Cr_0.7Fe_0.36, and MoB₂. The hardness of the composite coatings gradually increased as the MoB₂ content increased. The highest average hardness of the composite coatings was achieved when 15 wt% MoB₂ was added, reaching 485.5HV_0.1, which was 61.5% higher than the NiCr coating without MoB₂. The wear resistance of the composite coatings exhibited an initial enhancement followed by a decrease with the MoB₂ content increased. The 10 wt% MoB₂-NiCr coating exhibited the highest wear resistance, and the wear rate decreased by 75.5% compared with the NiCr coating without MoB₂. The wear mechanism of the coatings changed from severe fatigue and adhesive wear to slight abrasive and oxidative wear with the increase of MoB₂.

This study aims to evaluate the tribological performance of copper coatings developed by high-velocity air fuel (HVAF) and cold spray (CS) which are two important low-temperature solid-state deposition processes among spraying techniques. Reciprocating sliding wear tests against alumina balls were conducted at room (25 °C) and high (300 °C) temperatures. HVAF and CS coatings showed similar friction coefficients, both with a greater friction at high temperature. However, they exhibited different wear behaviors, where HVAF coating showed increased wear depth with temperature raise, while wear depth of CS coatings remained similar. Ex situ characterizations performed from the top and cross section of the worn surfaces by SEM, EDX, and Raman spectroscopy indicated profound oxidation occurred inside the wear tracks and higher wear of HVAF coating at high temperature was mainly due to greater oxidation and more cracks inside the tribolayer.

The dynamic impact test of eutectic high-entropy alloy (EHEA) coating composed of alternating arrangement of soft and hard phases is employed to investigate the damage accumulation principles under impact cycles combined with microstructure characteristic. The Fe₂Ni₂CrV_0.5Nb_0.8 EHEA coating presents a typical hypoeutectic alloys structure with the lamellar eutectic colonies of Laves and FCC phase uniformly dispersed within the primary FCC solid solution matrix. The Laves phase, serving as the primary load-bearing constituent, provides exceptional deformation resistance, while the FCC phase accommodates plastic strain to mitigate stress concentration and suppress crack initiation. The coating undergoes plastic deformation during the initial stage (10–1000 cycles), and the impact wear volume increases slowly. The impact energy dissipation under impact loading is predominantly attributed to elastic–plastic deformation. The slight edge damage stage exceeding 5000 cycles is characterized by oxidative wear. The tangential shear force at the edge position induce material spalling and accelerating impact wear volume growth, progressively elevating energy loss via wear. As the impact cycles approaches 15000, the material exhausts its capacity for further plastic deformation, shifting energy dissipation predominantly to wear-driven mechanisms. The high residual stresses formed on the impact crater surface initiate microcracks, promoting oxide layer exfoliation. Fatigue wear governs the failure mechanism, accompanied by a sharp rise in wear rate due to cyclic stress-induced crack propagation.

Laser cladding coatings typically exhibit high strength and wear resistance but limited toughness and ductility. To address this, a composite interface texture inspired by biological tissue was developed, using laser cladding to apply Fe-based coatings onto a 1045 steel substrate. The study evaluated the mechanical properties of these coatings, focusing on how varying the depth of the micro-texture impacts performance. Findings revealed that increased micro-texture depth enhanced the bonding strength and coordinated deformation between the coating and substrate. However, it also led to greater stress concentration, increased defect quantity, and higher martensite content at the interface, causing complex shifts in impact toughness, tensile strength, and ductility. A competitive relationship was identified between the coordinated deformation induced by the micro-texture and the stress concentration at the interface. Optimal results were achieved with a micro-texture depth of 0.2 mm, which significantly improved microhardness, tensile strength, and elongation through a synergistic effect, offering the best overall mechanical properties among the tested parameters. This study provides a novel approach to resolving the trade-off between high strength and high toughness in laser cladding coatings. The insights gained are valuable for enhancing the adaptability of these coatings under challenging conditions, such as impact-sliding wear, and shed light on the mechanisms behind the simultaneous improvement in toughness and strength.

The residual stresses induced by the various process conditions in engineering components can have a significant impact on their structural integrity and performance. It is essential to ensure reliable control of the mechanical properties of structural components during the repair process, as this directly affects their performance and longevity. Cold gas spray, a solid-state deposition technique, involves the high-velocity impact of fine powder particles onto a substrate, resulting in the formation of a dense, metallurgically bonded coating. The aim of this study is to investigate the suitability of cold gas spraying parameters for the repair of large cavities in components made of Inconel 718. Two sets of parameters, approaching the limits of the spraying facility, have been utilized and analyzed using particle diagnostics. Experimental methodologies involve the characterization of residual stress profiles using techniques such as in situ curvature measurement and the incremental hole drilling method after the cold gas spray repair. Additionally, the microstructure and topography of the as-sprayed repair coatings are demonstrated. The results demonstrate the ability of cold gas spray to successfully fill deep repair cavities and adjust the residual stress state of such repair coatings by varying the processing parameters. Lower residual compressive stresses in the layer were achieved by utilizing gas parameters, wherein the particles impact the substrate at an elevated temperature and at a comparatively reduced velocity. Both conditions exhibited coatings with consistent microstructure, good adhesion and uniform topography without major defects. This research demonstrates the potential of cold gas spray as a viable and efficient repair method for large repair geometries, offering a promising avenue for enhancing the reliability and lifespan of critical engineering structures.

In this study, the influence of surface states (as-received versus polished state) on the antibacterial and anti-biofilm attachment properties of thermally sprayed Cu-bearing coatings was studied. Findings indicate that the Cu ion release rate remains the predominant factor influencing the short-period antimicrobial efficacy of these coatings in their as-received state. Additionally, the influence of surface states on the antibacterial efficacy varied with Cu distributions (Cu as a segregated phase within a composite versus Cu as a solute element within a single phase). During microbial corrosion testing with Desulfovibrio vulgaris over an extended exposure, Cu addition continues to exhibit a significant inhibitory effect on biofilm attachment in as-received state. In contrast to their polished counterparts, the rough surfaces of the as-received samples significantly enhanced biofilm attachment; however, this facilitating effect diminished over time. The mechanisms leading to reduced facilitation varied with Cu distribution, due to either the formation of Cu₂S in composite coatings or the preferential biofilm attachment in valley areas in coatings containing Cu as solute. Additionally, the results suggest that arc spray has greater advantages over HVOF in preparing antimicrobial corrosion coatings, as it produces more uniformly flattened splats that show inhibiting effect on biofilm attachment.

A finite element (FE) model of a 25-µm Al₂O₃ particle impacting an AISI 1018 steel surface is constructed using the Johnson–Holmquist-2 and Johnson–Cook material definition models, respectively. Particle impact velocities in the range of 200–700 m/sec, obtained using a deLaval nozzle, are considered. Energy, temperature, and strain evolutions over time for varying impact velocities are reported, along with penetration depth into target material. Penetration results are validated against experiments, showing good agreement, with observed depths between 4.8 and 8.2 µm. Penetration, contact pressure, and contact time for varying impact velocities are predicted, along with their effects on the interfacial bonding mechanism between particle and substrate. The threshold velocity for Al₂O₃ particle fragmentation is estimated at 170 m/sec. The stress behavior and the location of failure onset within the particle are predicted and described. The damage and fragmentation behavior of Al₂O₂ particles of different sizes is also analyzed. The implications of obtained results for cold spray deposition of metal matrix composite material are discussed.

The effects of service environment temperature (25, 550, 650, 700, and 750 °C) on the friction and wear properties of (Ti, Cr, V) N composite coatings were investigated. The structure and phase of the coating before and after wear at wide temperature ranges were analyzed by scanning electron microscopy, XRD, transmission electron microscopy, and Raman spectroscopy. A wide temperature range wear test was carried out at room temperature, 550, 650, 700, and 750 °C for 20 min using a reciprocating friction and wear tester. The results show that the (Ti, Cr, V) N composite coating overcomes the shortcomings of single nitride, which is the initial oxidation temperature is low in a wide temperature range. The surface oxides produced at 25-750 °C have an important influence on the wear behavior and wear resistance. At room temperature and 550 °C, the main phase of the coating is the TiCrVN hard phase, which can reduce the wear rate of the coating at room temperature. At higher temperatures of 700 and 750 °C, dense oxide hard films of Cr₂O3, TiO₂, V₂O₅, and TiVO₄ formed on the wear scar surface play a key role during friction and wear. 650 °C is a critical temperature for wear behavior change. The mechanical properties of the coatings at 700 and 750 °C are significantly higher than those at 650 °C, and H_IT³/E^*2 is increased by 76%, which improves the wear resistance and reduces the wear rate. The coating is mainly oxidative wear at high temperatures above 700 °C. It is shown that the wear resistance and oxidation resistance of the composite coating can be improved by the mutual doping of Ti, Cr, and V elements in a wide temperature range.

This study explores the mechanical and tribological behavior of IN625 and IN718 coatings deposited on Ni-based IN718 alloy substrates using the high-velocity air fuel, HVAF technique. Microstructural analysis revealed that the IN625 coating exhibited more visible splats, weaker bonding, and a greater presence of unmelted and partially melted regions than IN718. Both IN625 and IN718 coatings retained the original constituent phases from the powder. The IN718 coating, however, demonstrated superior mechanical properties, with its hardness and adhesion strength surpassing those of IN625 by 56% and 30%, respectively. Notably, the adhesion strength was highest in a 0.5 mm thick IN718 coating, reaching 63 MPa. At room temperature, both the coatings had significant coefficient of friction (COF) values, while the wear volume loss for IN718 was reduced by 52% compared to IN625, although IN625 showed wider wear scars with more pits, deeper grooves, and peeling. IN718 formed a glaze layer, enhancing its wear resistance. These findings suggest that optimally thick IN718 HVAF coatings hold significant promise for improving performance in various repair and cladding applications.

Previous own works revealed that novel partially amorphous Fe-based alloys have a combination of properties that are beneficial for the application in liquid hydrogen (LH2) tanks, such as low thermal diffusivity, little porosity, and good adhesion. The influence of cryogenic temperatures or hydrogen on coating tensile strength, on the other hand, has not been investigated yet for this material. However, this is crucial for the long-term durability of the coatings under hydrogen and other alternative fuels. Thus, in this work, tubular coating tensile (TCT) tests were performed at room temperature, cryogenic temperatures and after hydrogen charging. For this, a methodology for hydrogen charging was developed to identify a possible regime being sufficient for inducing a measurable amount of hydrogen. Subsequently, the fracture surfaces were evaluated analytically, optically and profilometrically. Under cryogenic conditions, a significant increase in tensile strength and finer structures of the fracture surfaces were observed. The TCT tests with ex-situ hydrogen charging revealed a small reduction in tensile strength and ductility compared to specimens tested at room temperature, proven by the coarse structure of the fracture surface.