Investigation of oxidation and creep resistance of nickel-based alloy with superalloy hardfacing and thermal barrier coating

先进的超超临界(A USC)技术可以将蒸汽温度提高到700摄氏度，以提高燃煤发电的效率，减少其二氧化碳排放。虽然用于A-USC的高铬钢可以承受600摄氏度左右的温度，但这种向更高温度的转变需要采用高性能材料，如镍基合金。对于A-USC发电厂的锅炉、管道和汽轮机中运行的各种阀门，已选择Inconel 740和Haynes 282作为阀体或基础材料。为了提高表面的耐磨性，通常在这些合金表面涂覆一层钨铬钴合金(钨铬钴合金)堆焊。然而，近年来发现，钨铬钴合金6堆焊在A-USC条件下会发生退化，并在一段时间后失效。因此，阀门行业(例如Velan Inc.)对一种有效的耐磨堆焊材料的需求很大，这种堆焊材料既能承受高温，又能抵抗磨损和侵蚀。本研究试图通过等离子转移弧(PTA)焊接或激光熔覆在Inconel 740或Haynes 282表面应用新开发的高性能Tribaloy合金T-400C。堆焊试件将在氧化和蠕变试验下进行研究。另一方面，为了降低直接作用于镍基合金的温度，将在Inconel 740或Haynes 282上应用热障涂层(TBC)；涂层系统由金属粘结涂层和由Y稳定的氧化锆(YSZ)组成的陶瓷面层组成。涂层试件的抗氧化性和蠕变性能将在650-850℃的高温下进行研究。长期的蠕变试验需要太长的时间，不可能在实验室实施。因此，基于变形机理的蠕变模型将被用来描述这些涂层/基材体系的短期蠕变行为，同时预测它们的长期蠕变抗力。这项研究的结果将有助于降低燃煤发电行业的材料和设备维护成本，提高发电技术的效率。

Advanced ultra supercritical (A USC) technology allows the steam temperature raised to 700 degree C in order to increase the efficiency of coalfired power generation and reduce its CO2 emission. While the high-Cr steel used for A-USC can withstand temperatures around 600 degree C, this move to higher temperatures requires the adoption of high performance materials such as Ni based alloys. For various valves operating in boiler, pipework and steam turbines of A-USC power generation plants, Inconel 740 and Haynes 282 have been selected for the body or base materials. To enhance the surface wear/erosion resistance, theses alloys are usually coated with Stellite alloy (Stellite 6) hardfacing. However, it has been found in recent years that Stellite 6 hardfacing degrades in the A-USC conditions and fails in service after a period of time. As a result, there is a strong demand from the valve industry, for example, Velan Inc., for an effective hardfacing material which can sustain the high temperature while they are resistant to wear and erosion. The proposed research attempts to apply a newly developed high performance Tribaloy alloy T-400C on Inconel 740 or Haynes 282 surface via plasma transferred arc (PTA) welding or laser cladding. The hardfacing specimens will be investigated under oxidation and creep tests. On the other hand, in order to reduce the temperature that directly acts on the Ni based alloy, thermal barrier coating (TBC) will be applied on Inconel 740 or Haynes 282; the coating system consists of a metallic bond coat and a ceramic topcoat composed of yttria-stabilized zirconia (YSZ). The oxidation and creep resistance of the coating specimens will be investigated at high temperatures between 650 and 850 degree C. Long-term creep test takes too long time and is impossible to be implemented in laboratory. Therefore a deformation mechanism based creep model for these coating/substrate systems will be developed to depict their short-term creep behaviour and meanwhile predict their long term creep resistance. The outcomes of this research will help reduce the costs of materials and equipment maintenance of the coal-fired power generation industry, with improving the efficiency of power generation technologies.**************************