Residual stresses arising during high-velocity oxyfuel (HVOF) spraying usually impose a limit on coating thickness. In this work, dry-ice blasting is used in combination with HVOF spraying to produce thick WC-Co coatings characterized by compact microstructure, crystal refinement, high hardness, and excellent sliding wear resistance.

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.

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.

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.

Dry-ice blasting, as an environmental-friendly method, was used during atmospheric plasma spraying for improving coating properties. This process is believed to be capable to reduce the porosity and the oxide of the coating and to increase the deposition efficiency, etc. Considering dry-ice pellets are carried and accelerated by compressed air through a convergent-divergent nozzle, the computational fluid dynamic (CFD) approach was firstly employed in this study to evaluate the effects of nozzle geometry, accelerating gas conditions as well as properties of pellets, on the pellet velocity variation and further to optimize the process. Moreover, the experiment with a steel powder was then carried out and the results indicate that a denser coating with a lower content of oxide can be achieved with the application of dry-ice blasting during the plasma spraying.

A statistical study of the Spraying Xplorer AMT system was undertaken in order to check that if it can be used as a means of assistance for on-line production control. A patented procedure of the system calibration is explained and some results are presented.

The development of High Velocity Oxy-Fuel (HVOF) process shows a clear trend toward the design of new gun in which high pressure and large power are expected in order to obtain a stable flame and a high powder feed rate for industrial applications. In this work, a new HVOF gun, AMT-200, was used to prepare NiCrAlY and WC-Co-Cr coatings. To optimise the spraying parameters, i.e., flux rates of oxygen and fuel gas and spraying distance, the on line control system AMT Spraying Xplorer was used. The results show that the spraying parameters play significant roles on the properties of NiCrAlY coatings. Employing optimized parameters, a dense NiCrAlY coating, with a high coating/substrate bonding strength and low oxygen content, could be obtained by this system. Moreover, thermal treatment could reduce significantly the coating porosity and increase greatly coating/substrate bonding strength. The preliminary tests on WC-Co-Cr coating indicate that dense cermet based coatings could be deposited with this system.

The aim of this work is to produce titanium dioxide coatings doped with silicon dioxide nanoparticles. Nanoscale SiO 2 powders are prepared in an induction plasma reactor, then spray-dried to obtain a homogeneous mixture of micro- and nano-crystalline oxide powders suitable for dc plasma spraying. A test case based on conventional aluminum oxide powder is presented. Paper includes a German-language abstract.

Today, powder particles diameter used for thermal spraying is generally comprised between 5 and 100µm with a preferred range around 40µm for APS applications. Actually, the future trends in plasma spraying are directed to the use of fine or ultrafine powders and the reduction of the steps between raw materials and coatings. So, the present paper investigates the way to use directly spray dried ceramic powders in suppressing the sintering stage. AI2O3 based powders were obtained by the spray drying process. By optimizing the parameters (slurry composition and injection as well as drying characteristics), a narrow grain size distribution was achieved. Chemical composition and shape of synthesized powders were analyzed by scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). The crystallographic structure was identified by X-ray diffraction (XRD). Demonstration was made that it is possible to obtain coatings using directly spray dried ceramic powders. The plasma spray process parameters (such as current intensity, gas flow rate, powder feed rate and injection mode, cooling stage,...) have to be managed to achieve cohesive coatings. The structure and chemical composition of these coatings were studied. In this way, the direct use of spray dried powders appears as a promising way to realize ceramic coatings.

In general, thermal spraying involves high temperatures that can be deleterious for the microstructure and deformation of the substrate. As a consequence, the use of a cooling system during spraying is often necessary. Meanwhile, in some cases, a too low surface temperature can induce a loss of properties, in particular concerning adherence and coating density. Therefore, it would be sometimes interesting to combine pre-heating and cooling stages with the plasma spray. A specific process, named HeatCool, was developed and patented to ensure a precise control of the temperature at the spraying location. The present work was focused on the study of the influence of pre-heating and cryogenic cooling conditions on the microstructure and mechanical characteristics of NiCrFeBSi self-fluxing alloy deposited by d.c. plasma spray technique. Firstly, a comparison between air and CO2 cooling was conducted to assess the efficiency corresponding to the specific use of cryogenic CO2. The main characteristics studied were the microhardness, roughness, porosity, mechanical deformations, morphology and crystallographic structures. Optimising the cooling methods and conditions combined with the process parameters improved microhardness of the plasma sprayed metal alloy and induced lower strain deformation of the substrate. Secondly, the pre-heating system was added to the device and the HeatCool process was evaluated. The process was demonstrated to be an efficient mean to enhance the structural and mechanical characteristics of coatings made of self-fluxing alloy.

A new family of spherical powders produced by the spray drying route has been developed. This paper describes as an example the manufacturing method of an Y2O3-coated aluminum powder. Atmospheric Plasma Spraying (APS) was used to test the corresponding coatings. Morphology and phases of powders and coatings were investigated by optical and scanning electron microscopy while the level of porosity was evaluated using image analysis. Results show that homogenous composite coatings can be obtained from cladded spray dried powders.

Thermal spraying involves high temperatures which can be a serious problem for some applications. Among different possibilities existing to cool down a specimen during spraying, the use of liquid CO 2 is one of the most attractive. However, care has to be taken to obtain good results due to the specific characteristics of CO 2 . Moreover, there are still some remaining problems which limit the growth of such system. One of the most important is the condensation of air humidity at the exit of the atomising nozzle. Therefore, a new design of the nozzle has been developed. This design avoid ice building up and can be easily fixed on any kind of spraying set up. Examples of working conditions are presented.