Microstructural development of nickel-based alloys oxidised in high temperature air and steam environments over a range of pressures

Environmental and regulatory constraints on the global energy market are driving the need to improve conventional power generation methods to meet commitments made to reduce carbon emissions set out in the Kyoto Protocol.To maintain security of supply and ensure competitive energy prices, fossil fuels will play a vital role in the energy market over the next century, however, in order to comply with regulations it is necessary to improve on current conventional power generation technologies. Improvements in security of supply and environmentally deleterious emissions can be realised via increases in plant efficiency. A major route to achieving a considerable increase in efficiency in conventional coal fired power station is via elevating the operating conditions of the working steam to benefit from enhanced thermal cycle efficiencies. It has been proposed that increasing the operating steam parameters from the current typical levels of ~540°C/~190 bar to ~700°C/~300 bar could lead to an increase in plant efficiency of up to 15%. The major challenges to increasing steam parameters need to be met by advanced materials. Increasing the steam temperature and pressure to the suggested levels would push traditional materials beyond their acceptable oxidation and creep resistances. One strategy to accommodate the proposed steam conditions is to substitute traditional steel based materials at key regions of the steam cycle for alternative nickel-based superalloys. [Continues.]