We have developed a coal-fired advanced-ultra super critical steam turbine system (A-USC) for several years. The temperature of re-heated steam in the A-USC system is 700-720 °C. Many high temperature components in the A-USC system should be produced by Ni-based superalloys. Nozzle box is one of the hot components in the high pressure turbine. We have investigated feasible TBCs to reduce the thermal stress in the nozzle box. Since a remarkably high heat resistance is required, the target values of the thermal conductivity and the thickness of the topcoat are 1 W/mK and over 3 mm, respectively. In order to satisfy the specification, we have developed the TBCs with a porous and ultra-thick YSZ topcoat by APS process. The processing parameters are carefully controlled to suppressing the thermal stress during deposition process. As results of the tests for fundamental properties in laboratory, the ultra-thick TBCs shows a enough performance as the TBCs applied to the nozzle box. The several coating tests by the use of mock-up specimens were also carried out.
展开▼
