This study investigates the effects of gas composition on cold-sprayed titanium coatings deposited under nine different spray conditions. Experiments show that higher levels of gas purity translate to higher particle velocities and measurable improvements in bending strength. The influence of gas temperature, pressure, and chemical composition is considered in the study along with interactions between carrier gases and sprayed particles. In addition to bending strength, the resulting coatings are assessed in terms of porosity and oxygen content.

Alumina splats were deposited on the polished single crystal alumina substrates with two different crystalline facet orientations of [001] and [110] by atmospheric plasma spraying (APS) at a substrate preheating temperature of 900°C to examine the epitaxy during splat cooling. The cross-sectional samples for high resolution transmission electron microscopy examination was prepared by focused ion beam assisted scanning electron microscopy (FIB-SEM). The results show that the whole splats with a thickness ranging from ~600 to ~1000nm exhibited the same crystalline structure as the substrate. Moreover, the splat deposited on the single crystalline alumina substrates exhibited exactly the same orientation as the substrate. The results evidently indicate that the epitaxial grain growth occurs after alumina droplets impact on single crystal alumina substrate. The present results suggest that the crystalline structure of alumina deposit formed by plasma spraying can be possibly controlled by the substrate preheating temperature.

This paper presents the results of long-term thermal cycling tests on plasma-sprayed thermal barrier coatings, including coating samples produced with functionally graded materials. The role of oxidation is also considered based on the results of elemental analysis. The authors explain how the coatings were produced and tested and present and analyze the test results. The thermal barrier coatings formed with functionally graded materials were found to be relatively unaffected after the long-term thermal cycling test and showed no signs of oxidation. Paper includes a German-language abstract.

As applications of thermal spray processes are expanding, the importance of computer-aided design systems and computer-aided engineering systems for these processes has been growing. The principal objective of this study is to propose a new analytic method for the prediction of coating thickness and deposition efficiency. This method is called the particle tracing method and is based on the Monte Carlo simulation method. In order to evaluate the validity of this model, several tests were carried out. The same stainless steel 316L layers coated by the HP/HVOF process (TAFA JP-5000) were used throughout each test. First, spray patterns were observed which had formed on flat-plate specimens from various spray gun angles. Coating thickness distributions on several curved planes were consequently investigated. Finally, the coating process for a blade of a compressor in a gas turbine was simulated. In the right of the results of these experiments, it is summarized that the calculated values of the coating thickness obtained by our method are in good agreement with experimental values. The accuracy is within 10% of the maximum thickness value in each specimen, except for at the edge of the work-piece. In conclusion, the particle-tracing method can be applied to the fundamental analytic model in the CAD or CAE system for thermal spray processes.

Thermal barrier coating (TBC) is a technology for preventing the rise in surface temperature of the metal substrate by coating a ceramic with low thermal conductivity for the hot section components such as blades, nozzles and combustion chambers. In this paper, for some types of thick TBC specimen which had zirconia based ceramic top coat of 600 micrometer in order to improve the thermal insulation performance, thermal cycle property and heat flux are examined by using thermal simulating facility by gas burner heating. The paper also discusses fracture mechanism of the thick TBC. Paper includes a German-language abstract.

Multi-layered thermal barrier coatings (TBC) having different functions were proposed for the hot section components of land-based gas turbines. This paper describes the multi-layered TBC with an oxidation resistant layer. A conventional duplex TBC and a triplex TBC, in which an aluminized layer was added to the conventional duplex TBC to increase oxidation resistance, was prepared. It was confirmed by a burner rig test that the triplex TBC with the aluminized layer is resistant to oxidation and shows high durability in a thermal cycle test, compared with the conventional duplex TBC. The spalling in the thermal cycle test of each TBC specimen occurred at the same position and when the thickness of the oxidation layer was 11-13 μm. The mechanism of spalling of the coating in the thermal cycle test was discussed in terms of stress in the coating. Stress in the direction of spalling occurs by an uneven interface between the bond coat and top coat, and increases with growth of the oxidation layer. It is thought that the high durability of the triplex TBC in the thermal cycle test is derived from suppressing the growth of the oxidation layer and decreasing the stress due to the addition of the aluminized layer.