A certain level of porosity is always presented in thermal spray ceramic coatings. LPPS or some specific APS processes can allow to reduce it but it is difficult to obtain coatings with a low thickness (less than 100 m) which are fully gas-tight because of cracks or interconnected pores. This gas-tight property is for example very suitable for the ceramic electrolyte of solid oxide fuel cells (SOFC). Some ZrO 2 -Y 2 O 3 coatings were obtained by the VLPPS process, a LPPS system operating at a pressure of about 100 Pa. The specific structure of these coatings is a mixture of condensed vapors and splats. The results are very satisfying because ZrO 2 -Y 2 O 3 coatings with a thickness of about 70 micrometers are tight under a hydrogen pressure of 2x105 Pa. This paper presents some ZrO 2 -Y 2 O 3 coatings obtained by different processes (APS, LPPS and VLPPS) and their properties.

High temperature protection requires full coating density, high adhesion, minor oxide inclusions, and preferably fine grains, which is not achievable in most thermal spray processes. High velocity oxygen-fuel (HVOF) thermal spray process has been applied extensively for making such coatings with the highest density and adhesion strength, but the existence of not or partially melted particles are usually observed in HVOF-formed coatings because of relative low flame temperature and short particle resident time in the process. This work has investigated the development of an innovative HVOF process using a liquid-state suspension/slurry containing small alloy powders. The advantages of using small particles in a HVOF process include uniform coating, less defective microstructure, higher cohesion and adhesion, full density, lower internal stress and higher deposition efficiency. Process investigations have proven the benefits for making alloy coatings with full density and high bond strength attributing to increased melting of the small particles and the very high kinetic energy of particles striking on the substrate. High temperature oxidation and hot corrosion tests at 800°C have demonstrated that the alloy coatings made by the novel process have superior properties to conventional counterpart coatings in terms of oxidation rates and corrosion penetration depths.

Gas permeation behaviour through atmospheric plasma-sprayed 8 mol% yttria stabilized zirconia (YSZ) electrolyte coating was studied experimentally. YSZ coatings were fabricated using different powder feedstock. The temperature and velocity of in-flight particles during spraying were measured with a diagnostic system. The results showed that particle temperature and velocity were significantly influenced by the size of powders. The gas permeability of these coatings was estimated by a specific instrument with pure O 2 , N 2 and H 2 . It was found that the gas permeability was reduced by decreasing the size of powder. Gas permeation behaviour through plasma-sprayed YSZ coating was studied. Transition flow was compatible to gas permeation behaviour for all three plasma-sprayed YSZ coatings. The relationship between gas permeation behaviour and coating microstructure is discussed in this article.

Grinding applications for the machining of stone and concrete require composite tools where large diamonds are perfectly embedded into a metallic matrix. With the detonation flame spraying process it is possible to manufacture these superabrasive composites. Excellent embedment of the voluminous superabrasive particles into the matrix coating material can be realized in order to produce high quality composite layers for grinding applications of stone and concrete. In this paper different diamond sizes as well as different volume contents of diamond in matrix are compared. Especially, the influence of particle size on its implantation efficiency is investigated and the influence of process and substrate temperature is analyzed. The thermal sprayed grinding tools are evaluated in the sense of their morphology as well as their grinding abilities. Compared to sintered diamond-bronze samples the results of an adaptively designed grinding test for the machining of concrete are presented and analyzed.

Detonation-gun spray technology is a novel coating deposition process which is capable of achieving very high gas and particle velocities approaching 4-5 times the speed of sound. This process provides the possibility of producing high hardness coatings with significant adherence strength. In the present study, this technique has been used to deposit WC-Co coatings on T22 boiler steel. Investigations on the oxidation performance of detonation-sprayed WC-Co coatings in air and in molten salt Na 2 SO 4 -82Fe 2 (SO 4 ) 3 at 700°C under cyclic conditions have been carried out. The thermogravimetric technique was used to establish the kinetics of corrosion. The uncoated boiler steel suffered a catastrophic corrosion in the form of intense spalling of its oxide scale during air, as well as, molten salt induced oxidation. The WC-Co coated specimens showed lesser overall weight gains in comparison to their uncoated counterparts in both the environments. The oxidation kinetics for the coated specimens followed nearly the parabolic rate law. The overall weight gain has been found to be higher in the case of air oxidation as compared to that in salt environment for all the cases. Scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) techniques were used to analyse the corrosion products, which indicated the formation of W and O as main elements in the oxide scales of the coated steel in both the environments.

To increase the service life of a sink roll in a continuous galvanizing line has been an important issue in steel industry. It was shown that sink rolls are vulnerable to molten zinc corrosion and can be improved by thermal spraying with WC-Co coatings. Four WC-12Co thermal sprayed coatings were investigated in this study. Samples were immersed in Al-added zinc bath (460°C) for testing. The results show that the conventional coatings are more resistant to molten zinc corrosion than the nanostructured ones. It was also found that coatings containing η- phase have longer life in the zinc bath. Accumulation of Al on the coating surface was also observed.

Electrically conductive and flexible Aluminium coatings using powder and wire flame spraying were successfully deposited onto diverse textiles. The influence of different process parameters as well as the fabric materials on the electrical conductivity and microstructure of the metal-fabric composites were studied. Preliminary results show that in order to obtain excellent coating surface conductivity values, a specific coating quantity higher than 20 mg/cm 2 is necessary. After further optimization of the spraying parameters, a very good specific surface conductivity (~500 S i ) could be obtained even with reduced coating quantities. This corroborates that by performing an adequate parameter optimization a reduction of the specific coating quantity could be done while still keeping high conductivity values. Furthermore, when the coating quantity is reduced, the flexibility of the fabric substrates is better conserved. This study illustrates that optimized electrically conductive composites with flexible fabric substrates can be produced, without any preliminary thermal or chemical fabric specifications.

In the production line of glass sheets, the 8%Y 2 O 3 -ZrO 2 thermal spray coatings have put into practical uses. These coatings have under layers of metal Cr 3 C 2 -Ni/Cr cermets, to improve their bonding strength. In forming process of glass, non-oxygenated atmosphere containing sulfur dioxide is selected continually to improve the surface condition of glass sheets. Degradation and pealing of these coating have been observed frequently due to increasing of SO 2 concentration. In this study, effects of SO 2 on decay durability of the 8YZ coating having meta cermet under coat are examined. Interactions between the atmosphere and the top-layer or the under layer are clarified individually by some basic examinations and analysis. It is clarified that peeling of the bi-layer coating was occurred at the boundary region between top coat and under coat. By exposure test of the coated sample and some powders for N 2 -SO 2 at 113K, following results obtained, 1) Some cracks and fine streaks are observed also, in the bottom region of the ZrO 2 top layer after the exposure test of coated sample.. 2) Main components of these streaks are Cr and S. 3) Sulfur contents of Cr 3 C 2 cermet and Cr 3 C 2 are increased remarkably by the exposure test. 4) By the exposure, Cr 3 C 2 can be converted into a Cr 2 O 3 or a CrSx. due to reaction with SO 2 . As peeling of the coating on carrying roll is induced by oxidation and sulfurization of Cr 3 C 2 , the under layer of Cr 3 C 2 cermet is not suitable especially as its under coat.

SrTiO x is an expected oxide thermoelectric material, which performance can be improved by doping Y 3+ in place of Sr 2+ . However, the maximum content of Y 3+ is limited to about 10% because of the phase transformation in the equilibrium sintered material. By contrast, plasma sprayed (Sr, Y)TiO x , which was essentially rapidly quenched, could solve Y up to 20% of Sr-site without the second phase, and produce the increase in the electric conductivity and the decrease in the thermal conductivity. But the absolute value of Seebeck coefficient decreased with an increase of Y content. As the result, the ZT value, which showed the performance for thermoelectric power generation, was reached only 0.1 in the Y content range 10% to 25% of Sr site.

High purity oxide ceramic powders of alumina (Al 2 O 3 ) and yttria (Y 2 O 3 ) for plasma spraying have been developed to apply to semiconductor and flat-panel-display (FPD) production equipments. The ceramic coatings onto inside chamber wall of the equipments are required to have highly erosion resistance against CF containing plasma, widely used in dry etching process for micro-fabrications of the devices. Yttria is increasingly used in this application due to the high resistance compared to alumina. It is found that the yttria coating formed from agglomerated-and- sintered powder consisting of large primary particle has smoother eroded surface. Considering that particle deposition onto the devices, this coating will be effective to decrease generation of large sized particle, which is easily deposit onto the devices. Electric insulating properties of the coatings are also investigated to apply to electrostatic chuck. Electric breakdown voltage of yttria coatings is almost comparable to that of alumina coatings. However, yttria is difficult to apply due to its lower mechanical strength. Using smaller powder as feedstock is effective to improve the electric properties and influence of coating purity is lower than the powder size.