Tungsten carbide (WC) is a well-known material used to increase the wear resistance of iron-based composite materials that exhibit a favorable wettability with iron alloy particles. In this work, two different additive manufacturing technologies, i.e., cold-spray additive-manufacturing (CSAM) and selective laser melting (SLM), were used to fabricate WC/maraging steel 300 (WC/MS300) composites. An investigation comparing the microstructure and tribological behaviors of the composites was carried out. In addition, the evolution of the reinforcement phase during these two processes was characterized by SEM and EDS methods.

In this study, laser glazing is used to densify plasma-sprayed YSZ coatings on carbon steel substrates. Melt pool characteristics are assessed for different laser settings and treatment conditions, including substrate preheating. SEM examination of coating surfaces and cross-sections before and after laser treatment shows how microstructure responds to process parameters. It also shows how preheating widens the melt pool, deepens the laser-glazed layer, and reduces the surface density of cracks, thus improving coating quality.

This study assesses the effects of dry ice blasting on the lifetime and durability of thermal barrier coatings (TBCs). Three sets of TBCs consisting of a CoNiCrAlY bond coat and YSZ topcoat were deposited by air plasma spraying, each set with a different dry ice blasting treatment. Different microstructures were obtained in both the bond coat and topcoat depending on blasting conditions. Bond coat oxidation and thermal shock lifetime of the TBC are also shown to vary with the blasting treatment. TBCs where both the bond coat and topcoat are dry-ice blasted proved to be the most durable with the biggest improvement in lifetime. They also exhibited the most regular surface roughness.

In this work, Fe-40Al coatings are produced by atmospheric plasma spraying using a nanostructured feedstock exhibiting a very low degree of order. The as-sprayed deposits consist of fundamental FeAl phases, Fe3Al phases, and oxides and are found to be ferromagnetic due to the low degree of order and the presence of unmelted nanoparticles retained from the feedstock. The magnetic properties of the coatings are shown to be heterogeneous in the parallel and vertical direction.

This study investigates the effect of dry-ice blasting distance on the deposition of CoNiCrAlY coatings obtained by plasma spraying. Dry-ice blasting was used before, during, and after spraying and its effect on coating quality was measured. The results show how blasting distance influences the deposition efficiency as well as the microstructure, porosity, adhesion strength, hardness, and oxide content of plasma-sprayed coatings. The optimal dry-ice blasting distance was proposed as 25 mm.

Magnesium alloy AZ91D-SiC composite coatings were fabricated by cold spraying to study the effects of SiC particle size and volume fraction on microstructure and mechanical properties. The results show that coatings with large SiC particles have higher microhardness and bonding strength. Mechanically blended powders with fine SiC particles, on the other hand, are difficult to deposit. SiC volume fractions in the starting powders were 15, 30, 45, and 60 vol%, resulting in coatings with SiC volume fractions of 19, 27, 37, and 51 vol%. Based on test results, coating hardness and bonding strength increase with increasing volume fraction of SiC particles.

Dry-ice blasting, as an environmental-friendly method, was used to pretreat the substrate to be coated. In the present paper plasma-sprayed CoNiCrAlY splats were examined on the dry-ice blasted substrate. The cleaning effect of dry-ice blasting was demonstrated accompanying the condensation phenomenon, which is also harmful for the formation of ideal disk-like splat. A solution of ensuring the substrate temperature over dew point temperature was proposed for the proper application of dry-ice blasting during droplet flattening.

Atmospheric plasma spray is considered as one of the most efficient methods for forming FeAl intermetallic coatings. But the performance of plasma-sprayed FeAl coatings was remarkably limited because of oxidation and phase transformation during the preparation. In the present work, FeAl intermetallic coatings were prepared by atmospheric plasma spray combined with dry-ice blasting. The microstructure, oxidation and porosity of FeAl intermetallic coatings were investigated. In addition, XRD measurements were also employed to illustrate the lattice-scale performance, e.g., dislocation density. The temperatures during plasma spray were also measured using an infrared pyrometer system. The results show that a denser B2-FeAl coating with a lower content of oxide and lower phase transformation can be achieved because of the cryogenic effect and the mechanical effect of dry-ice blasting. Moreover, the microhardness of FeAl coating was nearly increased by 72%, due to the lower porosity and higher dislocation density.

A previous study indicated that improved adhesions of plasma-sprayed Al 2 O 3 coatings have been achieved by using dry-ice blasting. Therefore, it is important to understand the mechanisms involved. In this study, the surface roughness of different substrates treated by dry-ice blasting was firstly examined. And then the surface wettability was characterized in order to clarify the effect of dry-ice blasting on the substrate surface properties. The effect of dry-ice blasting on Al 2 O 3 splat morphology with different treatment times was investigated. The residual stress of plasma-sprayed Al 2 O 3 coatings using dry-ice blasting was measured and compared with that of coatings deposited with conventional air cooling. Based on these numerous assessment tests, it could be concluded that the cleaning effect of dry-ice blasting on different organic substances adsorbed on the substrates was the most important influence on the adhesion improvement of Al 2 O 3 coatings.

Numerical simulations focused on the impacting behavior of cold-sprayed particles are usually conducted with the Lagrangian method. However, the calculated output is much dependent on the mesh size due to the mesh distortion and/or the element-averaged variables in simulations. While the Eulerian method is attractive to overcome the mesh distortion. In this study, an investigation on the impacting behavior of cold-sprayed particles using the Eulerian formulation available in ABAQUS/Explicit was conducted with typical copper material. The results show that a jet can not be formed at the impacting velocities of 200-300m/s, but a continuous and smooth jet composed of the particle and substrate materials can be formed as the impacting velocity is in the extent of about 300-400 m/s which could be a theoretical value of the critical velocity for a successful bonding. At this velocity extent, the maximum PEEQ almost keeps unchanged accompanying with a temperature fluctuation. In addition, the jet presents discontinuous and the splashing causes the loss of material as the impacting velocity exceeds this velocity extent. Therefore, this model could be also used to predict the critical velocity of other materials besides the copper.

Magnesium coatings were deposited upon aluminum and stainless steel substrates by cold spraying. Three Mg powders with different particle size distributions were used as feedstock. The microstructures of as-sprayed coatings were evaluated by optical microscopy, and scanning electron microscopy. The coating observations show that a main gas temperature has an important effect on the deposition behaviour of particles. Changing the gas temperature from 350°C to 630°C involves an increase of the deposition efficiency from 1.57% to 19.57%. The effects of the particle size distribution and substrate material on the deposition efficiency of particles were also investigated. The results show that the particle size distribution has a significant effect on the deposition efficiency of particles which increases from 19.57% to 59% when the mean particle size decreases from 63 µm to 38 µm under gas temperature of 630°C. However, the deposition efficiency of particles was slightly influenced by the substrate material. In addition to these experimental results, the in-flight particle velocities were simulated by FLUENT software to point out the effects of the gas temperature and particle size distribution.

In this paper, a commercial AZ91D magnesium alloy powder and its mixture with 30 vol.% SiC powder were used to deposit coatings by cold spraying. Two types of converging-diverging nozzles with different cross-sectional shapes were employed. The velocity and temperature of in-flight particles under different operating conditions were simulated using the FLUENT software. The simulated results show that the particle velocity through the rectangular cross-section nozzle is the same with that through the circular one. However, the coating observation shows that the AZ91D coating and its composite could only be deposited using the rectangular cross-section nozzle. The increase of gas temperature has little effect on the coating microstructure, porosity and microhardness. Furthermore, the observation of the composite coating produced under the gas temperature of 600°C shows that the SiC content in the composite is about 23 vol.%. The microhardness of the composite is improved to about 140 HV 0.3 due to the enhancement of SiC particles, compared to that of about 100 HV 0.3 for the AZ91D coating.

Effective properties of TBCs may be quantified thanks to different measurement techniques. Image-based analysis represents an alternative method for predicting these effective properties. During the last 10 years, 2D modelling was intensively applied to estimate the thermal conductivity from coating cross-sectional images. However, real coatings present a complex 3D architecture so that the use of 2D computations based on cross-sections has to be validated. In the recent decade, 3D imaging approaches were applied for capturing 3D images of thermal spray coatings with relatively high resolution (up to 1 micrometer). Nevertheless, high resolution brings very large computational systems for which finite-element (FE) methods seem to be unsuitable due to high requirements in terms of computer memory (RAM) capacity. In the present study, a three-dimensional finite-difference-based heat transfer model was developed for analyzing the heat transfer mechanisms through a porous structure by saving RAM usage. An artificial 3D coating image, containing 300×300×300 voxels, was generated from microstructural information measured for a real coating cross-sectional image. In particular, this 3D artificial pore network was generated so that calculations performed on its cross-sections present similar results in comparison with those concerning SEM images of real coating cross-sections. Then, the results computed for the 3D image were compared with those obtained from 2D computations performed on cross-sections of the same 3D image, revealing the differences between 2D and 3D image-based analyses. Finally, the results were then compared with those computed by FE packages (OOF2 and ANSYS).

A previous study indicated that dense thick Cu-4Cr-2Nb coatings could be formed by cold spraying, and the post-spray heat treatment could significantly influence the microstructure and microhardness of the as-sprayed Cu- 4Cr-2Nb coatings. In this study, the tensile strength and fracture performance of the Cu-4Cr-2Nb coatings after annealing were investigated. The vacuum heat treatment was conducted under 10-2 Pa at 850°C for 4 h. Results showed that the heat treatment had a great contribution to the healing-up of the incompleteness of the interfaces between the deposited particles. In addition, the coating microhardness decreased from 156.8±4.6 Hv0.2 for the as-sprayed coatings to 101.7±4.5 Hv 0.2 for the annealed ones. The mean tensile strength of the annealed coatings was approximately 298.8±31.5 MPa compared to that of 45±10.5 MPa for the as-sprayed ones, which results from the partially metallurgically bonded zones between the deposited particles inducing by the heat treatment process.

In this research, large gas-atomized copper powder was selected as the feedstock. Some powder was annealed in a vacuum circumstance to avoid to the greatest extent the effect of grain boundaries on the high velocity impact behavior of particles during cold spraying. Some powder was oxidized in a resistance furnace to clarify the effect of surface oxide films. Both the annealed and the oxidized Cu powders were deposited by cold spraying with respect to the single impacts and coating deposition under the same gas condition. In addition, the rebounded copper particles were collected for morphology analysis compared to the adhered particles. The results show that the average size of the rebounded particles is apparently increased compared to the starting powder because of the rebound of the larger particles and the intensive plastic deformation of particles. For the deposited particles, obvious plastic deformation causes the higher hardness of the coatings. The last but not the least finding in this study is the rebounded particles also experienced large deformation and possible shear instability at the impact interfaces.

In order to improve the ionic conductivity of lanthanum silicates, which have been considered as the new electrolyte candidates for intermediate temperature solid oxide fuel cells (IT-SOFCs), the feedstock powders are prepared by sintering the mixed oxide powders in different temperatures and sintering times. The main phase of all the samples is the hexagonal apatite structure. The apatite-type ceramic coatings with a typical composition of La 10 (SiO 4 ) 6 O 3 are deposited by atmospheric plasma spraying (APS). The influence of sintering time of feedstock powders on the electrical properties of La 10 (SiO 4 ) 6 O 3 electrolyte coatings is reported here. The highest conductivity of the dense composite electrolyte coatings reaches 6.8×10 -6 S·cm -1 at 435 °C in air which is comparable to other apatite-type lanthanum silicate (ATLS) conductors.

In this study, La 10 (SiO 4 ) 6 O 3 coatings deposited on aluminum substrates by atmospheric plasma spraying were investigated for potential for use as electrolyte layers in solid oxide fuel cells. By proper selection of spraying parameters, particularly the hydrogen gas flow rate, the La 10 (SiO 4 ) 6 O 3 ceramic layers showed good densification. The results suggest that atmospheric plasma spraying may be an appropriate method for the production of SOFCs.

Being the 7th most abundant element on the earth, magnesium and its alloys have become very promising in numerous industrial applications because of some of their distinguished properties, including high thermal conductivity, high strength/weight ratio, good machinability etc. However, some inferior properties especially the poor wear and corrosion resistance have obstructed a widespread use. As one of the most effective solutions, thermal spraying can deposit an adequate protective coating on the substrate, but the necessary grit-blasting operation before spraying leads to high grit-residues on the magnesium surface therefore degrading the deposit performance. The PROTAL® process, combining a laser surface preparation with the deposition stage, can avoid this kind of disadvantage. This paper presents the possibility of employing PROTAL® to prepare a resistant Ni-Cr coating on a magnesium substrate. The coating adhesion and interface microstructure were especially investigated.

Although it is widely used prior to the spraying stage to eliminate the surface contaminants and to improve the splat contact with substrate, a preheating operation should be precisely controlled to keep the metallic substrate away from an excessive oxidation. In most cases, the oxide scale can deteriorate the interface adhesion. A nanosecond pulsed laser treatment is a powerful tool to remove the surface oxide layers. It is also the fundamental principle of the PROTAL process that combines a laser surface preparation and the thermal spraying process. In this paper, a nanosecond pulsed laser was used to remove the thermally induced oxide while keeping the advantage of preheating. It is shown that the particle splashing was suppressed and the deposit adhesion was significantly improved resulting from the laser cleaning effects. The mechanism of oxide removal is also investigated.

Thermal spray coatings are formed by successive molten droplets impinging onto a substrate. It is commonly admitted that the flattening behavior determines the interaction of splats with the substrate or previously deposited under layer and hence governs the overall quality of the sprayed deposit. Therefore a number of works have been devoted to explain the splashing mechanisms and the flattening behavior from different aspects, such as fluid dynamics, solidification behavior, surface wettability or surface adsorbates/condensates. It was thus shown that surface conditions such as surface roughness, contaminants, adsorption, etc. play a very important role in controlling the splat flattening behavior. In this study, the role of the substrate condition as well as that of the impinging particle parameters are emphasized in the case of a copper deposit formed on a titanium base alloy and on a stainless steel substrates. The plasma sprayed copper splats were examined for different surface conditions. It was thus confirmed that favorable surface conditions tend to suppress splashing and to promote the occurrence of disc-shaped splats while the substrate nature and particle parameters also affect the splat flattening behavior. Results also indicated that disc-shaped copper splats prepared on a cold substrate have a smaller flattening degree than those obtained on a preheated substrate.