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并减少其二氧化碳排放。虽然用于A-USC的高铬钢可以承受约600摄氏度的温度，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，这些合金通常涂敷有Stellite合金（Stellite 6）硬面。然而，近年来发现，钨铬钴合金6耐磨堆焊在A-USC条件下会发生劣化，并在使用一段时间后失效。因此，阀门行业的需求强劲，例如，Velan Inc.，以获得一种有效的耐磨堆焊材料，该耐磨堆焊材料可以承受高温，同时它们具有耐磨性和耐腐蚀性。本研究尝试将一种新开发的高性能Tribaloy合金T-400 C应用于Inconel 740或Haynes 282表面，通过等离子转移弧（PTA）焊接或激光熔覆。堆焊试样将在氧化和蠕变试验下进行研究。另一方面，为了降低直接作用在镍基合金上的温度，将在Inconel 740或Haynes 282上施加热障涂层（TBC）;涂层系统由金属粘合涂层和由氧化钇稳定的氧化锆（YSZ）组成的陶瓷顶涂层组成。涂层试样的抗氧化性和抗蠕变性将在650至850 ℃的高温下进行研究。长期蠕变试验时间太长，不可能在实验室内进行。因此，基于变形机制的蠕变模型，这些涂层/基体系统将开发描述其短期蠕变行为，同时预测其长期蠕变阻力。本研究成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.