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Optimising heat treatment of gas turbine blades with a Co-C fixed point for improved in-service thermocouples.

Pearce, J V; Machin, G; Ford, T*; Wardle, S* (2008) Optimising heat treatment of gas turbine blades with a Co-C fixed point for improved in-service thermocouples. Int. J. Thermophysics, 29 (1). pp. 222-230.

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Improvement of energy efficiency of aircraft is achieved by operating gas turbine engines at higher temperatures. To facilitate this gas turbine engine manufacturers are continuously developing new alloys for hot zone turbine blades that will withstand the increased in-service temperatures. A critical part of the manufacture of these blades is heat treatment to ensure that they attain the necessary metallurgical characteristics. The next generation of turbine blades undergo heat treatment at over 1310 °C to attain the required properties. In the project described here the heat treatment, which is controlled by noble metal thermocouples, is performed at Bodycote, Derby. The process has exacting control requirements (±3 °C), at the limits of the lowest accredited uncertainty currently available from thermocouple manufacturers. The heat treatment is therefore limited by available uncertainties, and additional detailed inspection is required to verify the process efficacy. Ideally Bodycote would like to attain ±1 °C temperature uncertainty in-process, but this is currently not possible because even the best accredited uncertainties attainable for noble metal thermocouple calibration (by NMIs) at these temperatures are around ±1 °C.
We report on a project that will allow thermocouple manufacturer CCPI Europe Ltd. to realise uncertainties of ±1 °C, or better, in the calibration of its noble metal thermocouples. This will be realised through implementing a Co-C eutectic fixed point in CCPI¿s calibration chain. As this melts at 1324 °C, very close to the heat treatment temperatures required, low uncertainties will be obtained. This should yield an increase in effectiveness of the heat treatment process at Bodycote, allowing them to respond effectively to the increasingly stringent demands of engine manufacturers.
Outside the current project, there is strong requirement by industry for lower uncertainties at and above 1300 °C. Successful implementation of the current fixed point in an industrial setting is likely to result in rapid take-up by other companies, probably through the supply of ultra-low uncertainty thermocouples, looking to improve their high temperature processes.

Item Type: Article
Keywords: metrology, heat transfer, temperature, phase transitions, melting, phase control
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4084

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