This study compares the performance of different measurement methods for characterizing particles during thermal spraying. The accuracy of double-point and single-point measurements is assessed in the context of HVOF and suspension plasma spraying (SPS) where in-flight particle temperature and velocity are recorded for different powders and suspensions. The results are evaluated by analyzing splats and correlating their size and shape to in-flight particle temperature measurements. It is shown that particle diagnostic systems based on single-point measurements are well suited for SPS and HVOF processes.

This work addresses some of the challenges associated with depositing copper on PEEK by cold spraying. Getting copper powder to adhere to the PEEK substrate is not difficult at first, but deposition efficiency falls rapidly during coating build-up. Without heating the propellant gas, a copper coating will not form, even at the highest gas pressures. Increasing prechamber pressure is necessary, but requires an increase in gas temperature to 400°C to reach a deposition efficiency of 70%. Subjecting PEEK to such heat causes delamination issues that offset the deposition efficiency gained.

Knowledge of thermal interactions between the substrate and deposited particles during cold spraying can shed light on coating formation and bonding mechanisms. In this study, a mathematical model based on the differential quadrature method was used to solve the hyperbolic heat conduction problem to predict the transient thermal evolution associated with the impact of a single particle. In addition, a 2D finite element model was developed to simulate the thermal and dynamic behavior of particle impact. The two models showed good agreement in predicting the maximum temperature at the particle-substrate interface. It was concluded that the proposed mathematical model could be used to predict the transient temperature of metallic and nonmetallic particle-substrate interfaces during cold spray deposition.

In suspension high-velocity oxyfuel (SHVOF) thermal spraying, the suspension is usually injected axially into the combustion chamber. Deposition of oxygen sensitive materials such as graphene can be difficult using this approach as the particles degrade with extended exposure to oxygen at high temperatures. Radial injection outside of the nozzle, however, reduces in-flight particle time thereby accommodating oxygen sensitive nanomaterials. The aim of this study is to investigate how radial injection parameters affect in-flight particle conditions during SHVOF spraying. The models used in this work are shown to accurately predict flame temperature in the combustion chamber for an Al 3 O 2 suspension. Experimental observations of the liquid jet obtained using high-speed imaging are compared to numerically predicted values. The results indicate that in-flight particle characteristics can be improved by more than 30% in SHVOF spraying by optimizing the suspension flow rate and radial injection angle.

In plasma spraying, hydrogen is widely used as a secondary working gas. Under low-pressure conditions, even small amounts of hydrogen can have a significant effect on the plasma jet as mechanisms such as diffusion and recombination come into play. This study investigates the influence of Ar-H 2 mixtures on electron densities, temperature distributions, and local composition in the plasma jet using optical emission spectroscopy. Several mechanisms reported in the literature are consulted to explain the observed phenomena.

In this study, NiCrBSi powders with a size range of 30-50 μm were deposited on mild steel substrates by self-fusing atmospheric plasma spraying. Particle temperatures exceeded 2400 °C and the deposits were remarkably dense with low oxygen content. Based on the results, a novel strategy is proposed to directly deposit dense, oxide-free coatings by plasma spraying without the need of post-spray fusing processes.

The aim of this work is to develop and assess an eco-friendly carbon-based composite coating for piston ring applications. The coatings were produced from sugarcane waste and Mo, NiCr, and CrC powders using high-velocity oxyfuel spraying and thermal chemical vapor deposition. SEM-EDS and XRD analysis confirms the presence of carbides and oxides that cause coating hardness to increase with increasing temperature. At 550 °C, under a 20 N load with a sliding velocity 0.3 m/sec, the friction coefficient of the coating was found to be 0.2, the wear value was 130 μm, and friction force was 4N. The results indicate that the friction and wear properties of the coatings improve with increasing temperature due to the formation of tribo-oxidative films and the effects of graphitization associated with the presence of carbon.

In this study, titanium carbonitride (TiCN) coatings are obtained by atmospheric plasma spray synthesis, or reactive plasma spraying. In order to promote reactions between Ti particles and reactive gases, an extended gas tunnel was mounted at the end of a conventional plasma gun. The oxidation behavior of the TiCN coatings was investigated over a wide temperature range, showing that the coatings suffered severe oxidation at temperatures above 700 °C and were entirely oxidized to the TiO 2 phase at 1100 °C. The principal oxidation mechanism was revealed, indicating that oxygen can penetrate into the TiCN coatings at high temperatures. Changes in microhardness were also investigated as a function of temperature, showing a precipitous drop over the range of 700-1100 °C.

This study investigates the influence of substrate preheating on the microstructure, hardness, and adhesion of detonation sprayed WC-CoCr coatings. Using commercially available powders, coating samples are deposited on low carbon steel substrates, some at room temperature and some having been preheated to 300°C. Test results show that the coatings deposited on preheated substrates are harder, more crack resistant, and better adhered, with no significant differences in microstructure. After tensile testing, fracture surfaces and interfaces were investigated, showing how fracture behavior, along with hardness and bonding strength, correlate with phase composition and particle impact conditions.

In this work, liquid plasma spraying is used to deposit composite coatings for potential use as cathodes in intermediate-temperature solid oxide fuel cells. A suspension containing well-distributed Gd-doped ceria (GDC) nanoparticles in a lanthanum strontium cobalt ferrite precursor solution was used as the feedstock, and GDC concentration was varied to study its effect on phase composition, microstructure, surface morphology, and electrochemical performance. The results are presented and discussed.

In this study, yttria films with high thermal shock resistance were synthesized from a metal-EDTA complex by means of combustion flame spraying. A rotating stage and various cooling agents were used to control substrate temperature during deposition. Although thermally extreme environments were employed during synthesis, the obtained films showed only a few cracks and some minor peeling in their microstructures. In the case of a Y 2 O 3 film synthesized using substrate rotation and water atomization, the porosity was found to be 22.8% and the temperature of the film immediately after deposition was 453 °C, owing to a high heat of evaporation in the cooling water.

This study investigates the effects of laser remelting on plasma sprayed YSZ thermal barrier coatings using a pulsed laser with and without induction preheating. It is shown that induction preheating decreases the laser threshold energy required for full remelting, which effectively reduces crack density. Induction preheating also helps in developing a steadier melt temperature and in decreasing thermal gradients between successive remelting passes. XRD analysis shows that it can reduce the amount of monoclinic phase as well.

In plasma spray-physical vapor deposition (PS-PVD), deposition takes place not only from liquid splats, but also from nanosized clusters as well as the vapor phase. As a result, thin, dense, and porous ceramic coatings can be produced for special applications using this method. In this study, columnar-structured YSZ coatings were deposited by PS-PVD on graphite and zirconia substrates and the effect of substrate temperature on coating microstructure was investigated. A deposition mechanism of heterogeneous nucleation is presented based on the observations and findings of the study.

A plasma torch with a converging-diverging nozzle has been developed for low pressure plasma spraying. This study investigates the current-voltage characteristics of the plasma arc for argon and argon-hydrogen plasma gases and the effect of hydrogen volume percentage on the plasma jet. Emission spectroscopy is used to analyze the plasma spectra and electron temperatures in the center of the plasma jet are determined based on a Boltzmann distribution. The results show that an increase in input power considerably increases electron temperature and that gas composition has a significant effect on current-voltage characteristics. The impact of detection distance is also addressed.

In this study, a mathematical model based on 2D heat conduction was developed to determine the temperature distribution within different substrate materials during cold gas dynamic spraying. Heat transfer between the hot gas and substrate was estimated theoretically and experimentally and the results were compared with those obtained from numerical studies. The heat transfer coefficient was found to be dependent on the distance from the stagnation point of the impinging air jet. It was also concluded that at higher air jet temperatures, the Nusselt number of the spreading air film near the stagnation point could be affected by external heat exchange with colder ambient air.

The temperature of in-flight particles in plasma spraying is one of the main parameters affecting the coating microstructure. Temperature measurement has been carried out before for inflight particles in air plasma spray (APS) and other thermal spraying processes. Suspension plasma spray (SPS) is an emerging coating deposition technology that permits the deposition of nanostructured coatings with unique structural characteristics. The aim of this work is to evaluate the influence of radiation emitted by the plasma and metallic vapors on temperature measurement of SPS particles performed by two-color pyrometry. To do so, spectroscopic analysis in the visible to near-infrared range is carried out on the jet stream when suspension of 20wt% YSZ particles in ethanol is sprayed. The analysis takes into account the radiation scattered by the particles (Mie scattering) as well as the radiation directly detected from the jet stream, and it was found that the effect of the scattered radiation by the particles on temperature measurement is 1 degree at its melting point (2700°C) and 16 degrees at 2500°C.

Different directions characterize the advances being made in thermal spraying today. On the one hand, spray processes are becoming colder, on the other hand, high-performance systems are being designed which enable a higher powder throughput, thus making production faster and more efficient. The current spectrum of substrate materials is much broader and even more versatile, as can be seen with new materials which prevent thermal stresses from arising during the production process. More and more applications require the use of special cooling methods to increase the cooling efficiency and, in turn, optimize the process. An ongoing objective of the gas industry is to offer the user hardware which not only exploits all the advantages of CO 2 , for example, but which is also suited to new applications.

This study investigates the influence of substrate temperature on the adhesion strength of cold spray coatings. Copper, aluminum, and iron powders were deposited on preheated substrates similar in composition with the respective powder. Adhesion strength was determined by shear adhesion testing. The results show that substrate preheating improves adhesion strength for specific combinations of coating and substrate materials, likely due to the relief of thermal stress and the formation of an oxide layer on the substrate surface.

In earlier experiments, plasma-sprayed Al 2 O 3 coatings were deposited on preheated Al 2 O 3 substrates to study the effect of substrate temperature on splat formation and phase transformations. The aim of the present work is to develop a model to better understand the factors that affect phase selection during the solidification of Al 2 O 3 splats. A model based on one-dimensional heat transfer and classic nucleation theory is presented and used to simulate the rapid solidification process and the influence of process parameters on phase selection. The model accounts for under-cooling phenomena, heterogeneous nucleation, and nucleation kinetics. The findings indicate that the relationship between initial substrate temperature and phase selection is primarily based on the catalytic effect of the alumina substrate on the nucleation of Al 2 O 3 phases as a function of contact angle.

Thermal cycling tests were performed on thermal barrier coatings (TBCs) to evaluate the influence of temperature gradients in the ceramic topcoat on overall lifetime and performance. The coating system tested consists of an Inconel 738 substrate, a cold-sprayed NiCoCrAlTaY bond coat, and an atmospheric plasma sprayed YSZ topcoat. YSZ surface temperatures were 1150, 1200, and 1250 °C, corresponding to temperature gradients of 150, 200, and 250 °C across the 250 µm thick layer. Heating and cooling times were set at 120 sec for each thermal cycle. The results of the study show that lifetime decreases with increasing temperature gradient, although the gradient has little effect on the failure mode.