Creep resistance of high-chromium steel and nickel-based alloy with oxidation-resistant coating for the components in advanced ultra supercritical steam generation

减少温室气体CO2排放的要求推动了使用传统化石燃料的发电工业在高于700摄氏度的温度下运行蒸汽涡轮机，这福尔斯属于所谓的先进超超临界（A-USC）蒸汽涡轮机的范畴。为满足A-USC汽轮机的高温运行要求（750 ℃下100，000小时），与高温蒸汽直接接触的部件，包括管子、喷嘴箱（一级喷嘴）、转子和叶片，均采用镍基合金材料。Inconel 740是最有希望的候选材料之一。另一方面，出于经济原因，不直接受蒸汽影响的部件，例如外壳，优选地由传统的锅炉材料制成，通常是高铬钢F91。对于A-USC蒸汽涡轮机部件，材料都要求在高温下具有高的抗蠕变强度和抗氧化性。现有的材料，无论是高铬钢还是镍基高温合金，由于氧化的干扰，都表现出长期蠕变性能的不足。这些材料的可用蠕变数据大多来自短期试验。这些合金中的蠕变-氧化相互作用尚未被很好地理解，以预测它们在A USC条件下的长期应用行为。为解决这些问题，本研究旨在进一步表征Inconel 740和F91的高温抗蠕变性能，同时通过在其上涂覆MCrAlY（M代表Co、Ni或Co/Ni）涂层来提高其抗氧化性能，并研究涂层对这些基材蠕变性能的影响。由于通过真实的材料蠕变试验进行保证可能需要太长的时间进行材料设计和表征，因此将利用基于变形机制的蠕变建模方法来描述这些材料及其涂层系统的短期蠕变行为并预测其长期抗蠕变性。

The requirement of reducing the greenhouse CO2 emission has pushed the electrical power generation industry using the traditional fossil fuels to run steam turbines at temperatures above 700 degree C, which falls in the category of the so called advanced ultra supercritical (A-USC) steam turbines. To meet the high-temperature operating requirement of A-USC steam turbines (100,000 hours at 750oC), nickel-based alloy materials are to be used for parts that are directly in contact with the high temperature steam, including tubes, nozzle box (first stage nozzle), rotors and blades. Inconel 740 is one of the promising candidates. On the other hand, for economic reasons, parts that are not directly affected by the steam, for example, outer casings, are preferably made of traditional boiler materials, typically high chromium steel F91. For A-USC steam turbine components, the materials are all required to have high anti-creep strength and oxidation resistance at elevated temperatures. The existing materials, whether high Cr steels or Ni based superalloys, all exhibit deficiency in long-term creep performance because of the interference of oxidation. The available creep data for these materials were mostly obtained from short-term tests. The creep-oxidation interaction in these alloys has not been well understood as to predict their long-term behavior for application under the A USC condition. To solve these problems, the proposed research is aimed to further characterize the high-temperature creep resistance of Inconel 740 and F91; and in the meanwhile, to enhance the oxidation resistance of these substrates by applying a MCrAlY (where M represents Co, Ni or Co/Ni) coating on them; subsequently, to investigate the influence of the coating on the creep performance of these substrate materials. Since assurance by real material creep test may take a too long time for material design and characterization; a deformation mechanism based creep modeling approach will be utilized to depict the short-term creep behaviour and predict the long term creep resistance of these materials and their coating systems.