Since Dye sensitized solar cell (DSC) is a solar cell which uses anatase film as photo voltaic device, production cost of DSC can be very low in comparison with that of silicon solar cell. Besides, according to some theoretical discussion on DSC, the electric power conversion efficiency can be raised to 30%. Therefore, DSC will be mainly used in future. In this study, in order to develop a low cost fabrication process for photo voltaic device of DSC, photo-catalytic titanium oxide film depositions were carried out by thermal plasma CVD (TPCVD) and thermal spraying. As working gas for plasma jet, and substrate, Ar gas and 20mm×40mm×1mm copper plate were used. Feedstock materials were titanium tetra butoxide in TPCVD and rutile powder in thermal spraying. In the DSCs using these films, cathodes (titanium oxide coated electrodes) were located beneath the transparent anodes. Consequently, in the case of TPCVD, anatase dominant film could be deposited and the DSC using this TPCVD film could generate 50 mV in electro motive force. Furthermore, even in case of thermal spraying, though rutile powder was used, photo-catalytic coating (anatase and rutile mixture coating) could be obtained by cooling substrate during coating and post heat treatment. It was confirmed that the electromotive force of the DSC using this thermal spray coating was almost the same as that of the DSC using the TPCVD film. From these results, these thermal plasma processes was found to have high potential for DSC fabrication.

In order to develop a functional film deposition process with high deposition rate, as a basic study, deposition of zinc oxide film by thermal plasma CVD (TPCVD) in the air was carried out. As ingredient, working gas and substrate, ethanol diluted zinc acetate solution, Ar and 430 stainless steel were used. As for deposition condition, Ar gas flow rate was fixed at 20SLM, deposition distance (distance between substrate surface and nozzle outlet of plasma torch) was varied 50 to 200 mm, zinc acetate concentration in the ingredient was varied 20 to 50 vol%, and ingredient feed rate was varied 30 to 200 ml/h. Consequently, with varying deposition distance, not only crystallized film but also amorphous film could be deposited. In the case of crystallized film, photo-catalytic properties could be confirmed in the films by methylene blue decoloration testing and wettability testing. Besides, in this case, film structure could be changed from lamellar to columnar by decreasing zinc acetate/ ethanol ratio. From these results, this process was found to have high potential for high rate functional film deposition process conducted in the air.

The aim of this preliminary investigation was to ascertain the synergetic potential of two process technologies of thermally spraying and HIPing (Hot Isostatic Pressing) for tribological applications and address the key design factors, which need to be considered for successful applications of HIPed thermal spray WC-NiCrBSi coatings. The relative performance of the as-sprayed and hot isostatically pressed WC-NiCrBSi functionally graded coatings was investigated in sliding wear conditions. Results indicate that HIPing post-treatment can improve the sliding wear resistance of WC-NiCrBSi coatings. These coatings were deposited by a High Velocity Oxy-Fuel - JP5000 system and HIPing process was carried out at two different temperatures of 850°C and 1200°C. This study shows that un-capsulated HIPing can be successfully applied to functionally graded WC-NiCrBSi coatings, which has economical as well as technical incentives for industrial applications. Sliding wear tests were carried out using a high frequency reciprocating ball on plate rig using steel and ceramic balls. Results are discussed in terms of powder manufacture method, microstructural investigations, phase transformation, mechanical properties and residual stress investigations. Phase analysis by X-ray diffraction revealed transformations, which altered the phase composition such as the elimination of secondary phase W2C and metallic W and the formation of new phases containing Ni, Si and B after the post-treatment. The measurements of hardness, Young’s modulus and residual stress indicate that substantial improvements can be achieved due to simultaneous application of temperature and pressure during the HIPing post-treatment. Hardness and Young’s modulus measured by indentation method, increased after the HIPing process due to the transformations in the morphology and phase composition of the coatings. The residual stress evaluations by sin2Ψ technique using synchrotron x-ray diffraction showed a relaxation of residual stress fields in the coating with increasing temperature of the HIPing process.

The aim of this experimental study was to comprehend the relative performance and failure modes of WC-NiCrBSi Thermal Spray coatings in As–Sprayed and HIPed (Hot Isostatically Pressed) conditions in rolling/sliding contact. Recently a number of scientific studies have addressed the fatigue performance and durability of Thermal spray coatings in rolling/sliding contact, but as of yet there have been no investigations on Thermal Spray Coatings which have undergone the post treatment HIPing. The understanding of the mechanisms of failure in rolling /sliding contact after HIPing is therefore critical in optimising the parameters associated with this post treatment to achieve superior performance. Coatings were deposited by a JP5000 system and HIPing was carried out at two different furnace temperatures of 1123K and 1473K. At both HIPing temperatures the rate of cooling was kept constant at 8°C/minute. Rolling Contact Fatigue tests were conducted using a modified four ball machine under various tribological conditions of contact stress, configuration and lubrication. Results are discussed in terms of as-sprayed and HIPed surface examination of rolling elements using Scanning Electron Microscope (SEM) and Light Microscope.

Hot isostatic pressing has been shown to be an effective post treatment for thermal spray coatings, improving hardness, density, and microstructure as well as metallurgical bonding between splats. In this study, the sliding wear resistance of as-sprayed and post-treated WC-Co deposited by HVOF is evaluated by means of ball-on-disk testing and the effects of HIPing are assessed based on SEM and XRD analysis, hardness measurements, and fracture toughness tests. Changes observed in the WC-Co layers, including the precipitation of carbides and the elimination of secondary phase W 2 C, are also discussed. Paper includes a German-language abstract.

This work evaluates the microstructure and composition of zirconia films produced by thermal plasma chemical vapor deposition (TPCVD). The results show that TPCVD has the potential to produce durable ceramic films with columnar structure, even in open air. Paper includes a German-language abstract.

Turbine entrance temperatures in the latest high-efficiency jet engines rise to more than 1773 K, which significantly raises the bar for thermal barrier coatings (TBCs). This paper describes a ternary coating system consisting of a vacuum plasma sprayed NiCrAlY bond coat, an atmospheric plasma sprayed ZrO 2 top coat, and a MoSi 2 middle coat. The middle layer inhibits oxidation of the nickel-chromium bond coat, thus extending the service life of the TBC system. Paper includes a German-language abstract.

To improve wear resistance of the atmospheric thermal plasma sprayed molybdenum coating, diamond deposition on the molybdenum plate and the atmospheric plasma sprayed molybdenum coating by the combustion flame chemical vapor deposition (CVD) was carried out. Diamond has excellent properties such as low surface energy, hardness, chemical corrosion resistance ability and so on. Besides, since the combustion flame CVD is the process carried out in the air, diamond/ molybdenum complex coating can be deposited without any vacuum facilities by using this technique if molybdenum coating is deposited by atmospheric thermal spray. In this study, acetylene welding torch was used as diamond synthesis apparatus and mass flow ratio C 2 H 2 /O 2 was varied from 0.9 to 1.3. Consequently, many diamond particles which were 10 micrometer in diameter respectively were deposited on the molybdenum plate by only 20 minutes combustion flame irradiation in the case of 1.2 in mass flow ratio of C 2 H 2 /O 2 . Especially, the molybdenum coating was covered with diamond films consists of 10 micrometer diameter particles in the case of over 1373K in deposition temperature. Besides, according to the results of wear testing, wear mass loss of diamond deposited coatings were much lower than that of original thermal sprayed molybdenum coatings. From these results, this process was found to have a high potential in order to improve wear resistance of thermal sprayed coating.

Importance of coating adhesion in a corrosive environment was studied experimentally. Tensile adhesion strength of HVOF sprayed 316L stainless steel and Hastelloy C coatings were tested in as-sprayed condition as well as after immersion in seawater. It was found that the adhesion strength of the stainless steel coatings degraded rapidly whereas that of the Hastelloy coatings remained almost intact. Specimens with an artificial defect were also immersed in seawater. The cross sectional observation after the test revealed that the corrosion at the coating-substrate interface proceeded much faster with the stainless steel coating as compared to the Ni-base alloy coating. A model experiment to simulate the galvanic corrosion of a coating-substrate couple was carried out and no significant difference in the galvanic current density was found between the two coatings when coupled with the steel substrate. The tightness of the coating-substrate interface was then tested with a fluorescent dye penetration test. The dye could penetrate the boundary between the stainless steel coating and the substrate whereas the boundary between the Ni-base alloy coating and the substrate was so tight that no penetration occurred. The size of the micro-gaps at the coating-substrate boundary was discussed from the viewpoint of classical Washburn-Ridiel theory. It was concluded that such micro-gaps between the coating and substrate must be eliminated for these barrier-type coatings to be used in corrosive environments. Heat treatment was highly effective for suppressing the preferential corrosion at the coating-substrate boundary.

Trends of turbine blades of advanced aircraft gas turbine engines are to increase output power of the engines, to increase engine efficiency, and to reduce environmental emission, and thus, higher operating temperatures of the engines are required. One of the technologies for increasing the operating temperature is a thermal barrier splayed coating. A research paper claims that molybdenum silicide in a splayed coating has a self-healing capability for cracks formed in the coating by embedding the cracks with silicon dioxide formed from molybdenum silicide at high temperatures. This article discusses the methods for the extension of life of thermal barrier sprayed coatings by incorporating molybdenum silicide. It discusses monitoring method for detecting cracking conditions in heating and cooling cycles by signals of acoustic emission. A possibility of estimating fatigue life by utilizing an X-ray method for measuring residual stress is also considered.

Since plasma jets, which have been used as heat sources of thermal plasma spraying process, expand adiabatically under a low pressure environment, the plasma temperatures drastically fell down to 2000K at the nozzle out let at 30Pa chamber pressure. However, the plasma jets still had enough reactivity to form hard nitride layer on the surface of the titanium samples by only a few minutes treatment. In this study, in order to obtain useful information for the practical applications of this plasma as low temperature and high rate surface modification processes, nitriding of nitriding steel and carbon steel using supersonic expanding hydrogen/ nitrogen mixture plasma jets were carried out. Consequently, though surface hardening was occurred slightly in the case of carbon steel, surface hardening was obviously promoted in the case of nitriding steel. In both cases, surface hardening was promoted with increasing hydrogen flow rate and thermal damages of the samples due to heat transfer from plasma jets weren't observed. Besides, according to the results of wear testing, wear mass loss of nitrided samples were much lower than that of non-nitrided samples. From these results, this process was found to have a high potential even in the case of surface modification of steel materials.

Microscopic and macroscopic residual stress measurements and a finite element method (FEM) for stress analysis of thermal spray coatings have been carried out to investigate the residual stress generation mechanism. The residual stresses of one splat, laminated two splats and coatings were measured by a micro-beam x-ray stress measurement system and the macroscopic residual stresses were measured in-situ by the curvature change of the thin substrate plate during and after spraying. Two coating materials were employed in this study to deposit the coatings. One is molybdenum of which the coefficient of thermal expansion (CTE) is smaller than that of steel substrate and the other is 80%Ni-20%Cr alloy which has higher CTE than steel. The substrate was preheated up to 550°C just before spraying. The residual stresses of the splat and a coating are fundamentally the same level. The FEM analysis on the residual stress was also useful and by the comparison of two measurement results of microscopic and macroscopic residual stresses, the generation mechanism was discussed.

A non-destructive experimental approach was adapted to investigate the variations in residual stress fields within thermal spray coatings. WC-Co coatings produced by a HVOF technique were considered for concentrated rolling sliding contacts in this study. These coatings were produced in various thicknesses on various substrates. Residual stress measurements were made using an x-ray diffraction technique, along and across the rolling direction. A modified four-ball machine was used to conduct rolling contact fatigue tests under various tribological conditions of contact stress, lubrication and contact configuration. Residual stress measurements were made before and after the tribological tests. Failed rolling elements were analyzed using scanning electron microscopy, electron probe microscopy and surface interferometry. Results indicate that the magnitude of compressive residual stress attenuates during fatigue failure. The magnitude of attenuated residual stress was dependent upon the type of tribological failure. This attenuation of residual stress was attributed to the microcracking of coating under the influence of contact stress.

In this paper, as a basic study of the plasma jet process under a low pressure, the nitriding of titanium plates and atmospheric plasma sprayed titanium coatings are carried out using nitrogen and hydrogen added nitrogen plasma jets at 30Pa. The plasma torch used in this paper is equipped with a supersonic expansion nozzle to improve the acceleration efficiency of plasma jets. The effects of ambient pressures and supersonic expansion nozzles on transformation of plasma particles are examined from gas-dynamical viewpoints. It was observed that from the results, the supersonic plasma jet process under a low pressure was proved to have a high potential for nitriding. Paper includes a German-language abstract.

Usually small samples are used to test corrosion resistance of a coating, it is sometimes difficult to make a coating on the small samples. When a cylindrical sample is used and the coating is formed on whole of the surface, three or four times coating processes are required. Thus an abacus bead type sample is proposed in this paper. In this sample, only two times coating processes are required to make coating on whole of the surface. In this paper, the high-temperature corrosion resistance of a novel coating made of Cr-based alloys for use in waste incineration plants is tested and compared with the coating made of a Ni-based alloy. Paper includes a German-language abstract.

This paper focuses on the mechanism responsible for crack expansion and contraction: the behavior of cracks in the ceramic bed of zirconium dioxide membranes formed by plasma spraying, and the thermal stresses caused by differences in thermal expansion factors between the base material and sprayed bed, under a thermally cyclic environment. The test sample was prepared by spraying NiCrAlY on a stainless-steel base material to form a substrate membrane, then covering it with sprayed 8YSZ (zirconium dioxide-type ceramic). To clarify the self-recoverability of fatigue cracks caused during the thermal cycle, membrane cracking and crack expansion/contraction is studied. Paper includes a German-language abstract.

It is pointed out that properties corresponding to 3 to 5 % of gross domestic products are lost by corrosion in every year in advanced countries. Corrosion including oxidation is still one of the biggest technical problems which human beings are facing. The application of thermal spray coatings is one of the strongest weapons to prevent corrosion of steel and iron structures. The thermal spray coatings, however, are not panaceas to prevent corrosion. They involve many problems and it is important to understand the proper ways to apply the thermal spray coatings for corrosion resistance. In this paper, a state-of-the-art review on the science and technology against corrosion, oxidation and hot corrosion by the thermal spray coatings is presented.

The development of corrosion resistant sprayed coating without sealing is required to increase reliability of the thermal spray coating method and to expand the field of application for the wet corrosion environments. The conventional wire flame sprayed Al coating on the steel substrate without sealing has poor resistance against aqueous corrosion, so as to be restricted in use in practical fields. A duplex coating composed of sprayed Al on a 80Ni-20Cr alloy undercoat was proven to have sufficient resistance in a hot, near neutral aqueous environment through a trial use in a vegetable oil process. In this paper, mechanism of the corrosion resistance of the duplex coating is clarified by electrochemical measurements of the corrosion potential and the anodic polarization characteristics.

Microscopic fracture mechanisms of thermal spray coatings under bending stress are investigated. Samples of thermally sprayed coatings were made using three distances. The sprayed powder was pure molybdenum. Vertical microcracks occur in lamellae and subsequently, these cracks join together and form vertical macrocracks in the samples sprayed with a short spraying distance. On the other hand, horizontal microcracks occur at the lamellae interfaces, and these cracks link together in the samples sprayed with a long spraying distance. These tendencies can be explained in terms of the hardness of the lamella and the bonding strength between each lamella. It is clarified that the bonding strength between each lamella corresponds to the applied strain at the point of rapid increase of the acoustic emission (AE) event. The amplitude and rate of AE beyond the point of rapid increase are high in the coatings which formed macrocracks. It is concluded that the coating which has high resistance to crack formation has a high point of AE increase, low AE amplitude and low AE increasing rate.

Corrosion behavior of a flame sprayed titanium coating sealed by some resins was investigated in 3.5% NaCl solution by an electrochemical polarization measurement and an immersion test. The composition and structure of the sprayed film was also analyzed by SEM and EPMA. Although an as-sprayed titanium had no resistance to the corrosion because of its porosity, the sprayed titanium sealed with epoxy or silicon resin showed an excellent resistivity against the chloride corrosion. In spite that almost half amount of the titanium changed to oxide, nitride and carbide through the gas flame spraying, the conversion of the metal to the compounds had little effect to decrease the corrosion resistivity. The sprayed and sealed titanium coating obtained by a conventional onsite thermal spraying is expected as an economical material for chloride containing environments.