Environmental barrier coatings (EBCs) are required to protect SiC based composites in high temperature, steam containing combustion environments found in the latest generation of high efficiency gas turbine aeroengines. Ytterbium disilicate has shown promise as an environmental barrier coating, showing excellent phase stability at high temperature and a coefficient of thermal expansion close to that of SiC; however, its performance is dependent on the conditions under which the coating was deposited. In this work, a parametric study was undertaken to demonstrate how processing parameters using a widely used Praxair SG-100 atmospheric plasma spraying torch affect the phase composition, microstructure and mechanical properties of ytterbium disilicate environmental barrier coatings. Ytterbium disilicate coatings were deposited using 5 sets of spray parameters, varying arc current and secondary gas flow. The phases present in these coatings were quantified using X-ray diffraction with Rietveld refinement, and the level of porosity was measured. Using this data, the relationship between processing parameters and phase composition and microstructure was examined. Abradable coatings are used throughout gas turbine engines to increase efficiency in the compression and combustion phases of the turbine. Abradable coatings are soft enough to be worn away by turbine blade tips (without damaging the tip itself), allowing for tighter clearances to be used, limiting leakages and increasing efficiency. Using the optimum process parameter window determined in this work, a low density abradable Yb 2 Si 2 O 7 layer will be deposited in future research.

Environmental degradation of thermal barrier coatings (TBC) by molten deposits such as calcium magnesium alumino-silicates (CMAS) is one of the most vital factors resulting in the failure of thermal barrier coatings, while turbine engine inlet temperatures are kept increasing for higher fuel efficiency. A new phase composite ceramic had been developed and evaluated for the topcoat of a durable thermal barrier coating (TBC) system with low thermal conductivity property and improved erosion resistance. The present work is to continue the effort to exploring the behavior of CMAS resistance of the phase composite TBC at high temperatures. The effects of CMAS attack and thermal exposure on the TBC degradation were investigated in experimental runs. In addition, a YAG-modified layer over the top of the TBC was applied with the attempt to improve CMAS resistance of the TBC system. The evaluation of CMAS resistance was focused on the most important characteristics of coating microstructure, CMAS penetration, and failure mode and test condition factors. The mechanisms for the CMAS infiltration and the TBC damages were discussed based on the analyses of the CMAS corroded samples in details.

Silicon coatings have been developed for environmental barrier coatings by thermal spraying. Until now, these coatings have been produced almost exclusively by Atmospheric Plasma Spraying (APS). High Velocity Oxy-Fuel (HVOF) spraying is commonly used to produce dense metallic and carbide-based coatings due to high particle velocities. However, there have been no scientific reports on HVOF-sprayed silicon coatings in the literature. This study was conducted to investigate the feasibility of fabricating silicon coatings by HVOF using a DJ2600 spray system. Both the spray powders and the parameters were varied. The coatings were investigated on their surfaces and cross-sections using scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The hardness and indentation modulus of the silicon coatings were also determined. The results show that the particle size distribution and the stand-off distance are important influencing factors. Dense coatings could be produced by HVOF spraying, confirming the feasibility.

This article illustrates the application of various cold spraying technologies for aircraft equipment of different countries. Presentation slides only; no full-text paper available.

This study aims to develop a metal-based compatibilizing sublayer on a Carbon Fiber-Reinforced Polymer (CFRP) composite to overcome the erosion issue of polymer substrate using the cold spray deposition technique. The objective is to contribute to the in-situ repair of aircraft structures. Two cases of sublayers, i.e., Al-based sublayer (1126 μm thick) and Cu-based sublayer (547 μm thick), have been prepared and co-cured with the CFRP substrates by pressure assisted molding process. Gas-atomized copper powders were deposited on a reference sample of aluminum panel (A-0) and on two functionalized composite substrates (A-1 and C-1) by a high-pressure cold spraying (HPCS) process. The results show that cold spray deposition onto the Al-based sublayer leads to a coating formation whereas the Cu-based sublayer is strongly eroded by the supersonic collision of copper powders. Scanning electronic microscope (SEM) morphologies were used to investigate the HPCS deposition mechanisms on various configurations of substrates. It was found that the high deposition efficiency of case Cu/A-0 was achieved by metallic bonding, evidenced by the significant flattening powders and agglomeration phenomenon of multiple particles. The copper particles of case Cu/A-1, encapsulated by the deformed aluminum powders, could anchor to the substrate via mechanical interlocking, whereas only pure localized fracture of epoxy and exposed broken carbon fibers were observed on the substrate of case Cu/C-1. The results demonstrated the feasibility of an Al-based sublayer-assisted cold spray process for the thermosetting CFRP composite to achieve a successful deposition of copper powders, which also emphasized the necessity to search an optimal material coupling between sublayers and coatings.

The HVOF sprayed WC-CoCr coatings are widely spread due to their excellent resistance against wear and corrosion. These coatings are one of the most suitable alternatives for hard chromium in many applications. Within the research project, the most suitable hard chromium alternative for hydraulic devices in aircraft is being developed and tested. This application is highly demanding not only on the functional properties of applied coatings but also on the surface quality. Grinding and polishing of the coating are not sufficient, to achieve the necessary surface properties. This study aims to optimize the superfinishing process of HVOF sprayed WC-CoCr coating. The achieved surface quality is primarily measured using profilometry. With optimized surface preparation, the tested parts for aircraft hydraulic parts are treated and tested for leakage of operating fluids and high cyclic lifespan.