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A technique to analyse low concentration elements, i.e. Sulphur, by Glow Discharge Optical Emission Spectroscopy (GDOS) was developed. Sulphur and other trace elements like Boron or Phosphorus can be detrimental to the performance of oxidation resistance coatings. GDOS is a quick an convenient method to analyse multi-component diffusion layers. Other standard methods of material analysis like EDS or EPMA have a lower detection limit of ~1%. IOPW performed analysis of Hafnium and Sulphur with contents in the range down to few a ppm.
The results show that GDOS is a promising technique for diffusion layer analysis. Nevertheless a very precise calibration of the method is necessary to guarantee excellent results. It is foreseen that standards will be developed for several layer compositions. These standards have to be established by a measurement circuit of several laboratories. With this the precision and flexibility of the GDOS method can be improved significantly. An international standardisation will be a need in the future, which could be based on this GDOS technique.
A CVD-method for co-deposition of Hafnium enriched Aluminium diffusion layers onto super alloy substrates were developed. The process uses the fluoride route to generate vapour phase metal halide precursors. The evaporation temperatures of the fluorides determine the partial pressure of Hafnium and, ultimately, the Hafnium content in the diffusion layer and the layer thickness. Values up to 30µm thickness and contents up to 1at% Hf were obtained at a total system pressure of 100 hPa. The distribution perpendicular to the surface was very inhomogenous, therefore an annealing technique or an improved precursor feed has to be developed to get a smoother distribution of Hf in the layer.
Improved oxidation resistance of turbine blade super alloys allow higher combustion temperatures and longer maintenance intervals. Protective coatings containing reactive elements like Hf, Y, La, etc. improve the resistance against oxidative degradation. This was already obtained with additional active elements containing PtAl-diffusion layers. It was performed with the chloride route to serve the precursors. A 4-fold increased oxidation resistance has been reported. Similar effects can be expected by the technique developed by IOPW. It is applicable for simple Al layers but also for PtAl- diffusion layers. A code-position with Yttrium due to the projects master plan is under development.
CRF as research centre has not any "Industrial" exploitation from the project. CRF is involved in the project mainly to characterise coating performances. The increasing of knowledge on single crystal alloys and protective coating can be considered an exploitable results. CRF will be able to offer a more reliable Laboratory Service Activity in the field of aircraft engine and gas turbine for the production of electricity due to the "technical skill" improvement.
CRF has also an educational function: post-graduated students supported by skilled personal have the possibility to work on aircraft engine materials. In this way CRF can promote the employing of young engineers in the aerospace industry.
A process has been developed to deposit Platinum/Aluminide coatings with improved properties onto single crystal Nickel super alloy substrates such as turbine blades. Although the Pt/Al anti-oxidation coating system has been in use in the gas turbine industry for some years, there was a need for a cost effective method, using less expensive coating equipment, which would produce superior oxidation and thermo-mechanical fatigue (TMF) properties.
This has now been achieved.
The coating is deposited in two stages. First Platinum is deposited on the super alloy substrate by a traditional Platinum electroplating process at low temperature. The Platinum coating thickness after plating is typically about 5 microns. Coated samples are then heated treated in a vacuum furnace at high temperature (>1000 C) to achieve adequate diffusion of the Platinum into the super alloy substrate.
Samples are then transferred to a high temperature Aluminium coating reactor of the "out of pack" type. Aluminising takes place at high temperature in conditions conducive to producing a "single phase" Pt/Al diffusion coating. By careful selection of the coating parameters it is possible to produce "single phase" Pt/Al coatings and to modulate the properties of these coatings depending on the desired balance of oxidation/fatigue performance required of the coating.
Laboratory studies indicate that improvements in oxidation performance (when compared to benchmark Pt/Al coatings) of up to 50% can be achieved and improvements in fatigue performance of 200 - 300% can be achieved using this ORDICO coating method.
It is expected that these coatings, when used in service, will result in significant extensions to the "on wing" life of turbine components and to a significant reduction in scrap page rates at engine overhaul.
This new process will be an important technical and commercial advantage to the industrial partners in the ORDICO project.
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