This paper presents results from recent factory engine testing of simple aluminide coatings produced using pack cementation processes and platinum modified aluminide coatings produced using both pack cementation and chemical vapor deposition processes. These coatings were evaluated on DS nickel base superalloy high pressure turbine blades in a commercial high bypass turbofan engine. Operating conditions were such that turbine inlet air contained up to 3 ppb of sodium. Details of the factory engine testing, coating selection and application, and environmental protection provided by the coatings are highlighted. Future testing plans are also presented.
The goal of all repair processes is to return the hardware to a serviceable condition. Diffusion braze repairs utilize metallurgical processes to achieve economical repairs of expensive gas turbine components, especially in the turbine section. Component repairs often require dimensional restoration and crack repair on the same part. To achieve this goal, a new diffusion braze repair alloy was developed that combines high strength crack repair and dimensional build up into one material. This new material has mechanical property strength approaching that of the base metal. The improved mechanical properties result from a homogenous gamma prime strengthened diffusion braze zone. As part of an FAA approved test plan, the Howmet ESR (Effective Structural Repair) diffusion braze material was evaluated by tensile and stress rupture testing at elevated temperature. The test results showed high tensile strengths and long stress rupture life. In addition, the effect of the diffusion braze thermal cycle was evaluated on the base metal. A comparison was made between the gamma prime size and shape of engine run JT8D LPT vane clusters before and after the thermal cycle. The thermal cycle was shown to have a beneficial effect on the gamma prime size and shape relative to overaged engine run nozzles. The low cycle fatigue (LCF) life of MarM247 was also shown to improve with the ESR thermal cycle relative to a typical LPT nozzle heat treatment.
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