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

点击翻译按钮获取中文摘要

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.**************************