H.-I. Kim, H.-S. Park, J.-M. Koo, C.-S. Seok, S.-H. Yang, M.-Y. Kim
The Journal of Mechanical Science and Technology, vol. 26, no. 7, pp.2019-2022, 2012

Abstract : To enhance the gas turbine efficiency, the inflow temperature of the first-stage blade of the turbine system is raised to an ultra-high temperature of more than 1300􀔨. When the gas turbine blade is used at high temperature for a long time, its base material can become damaged. To prevent such damage, regenerative maintenance is performed after the equivalent operating hours so that the quality of the part may be restored for its reuse. After the first-cycle operation, nondestructive testing and a durability diagnosis of material quality are performed to determine whether the gas turbine blade should be reused or scrapped. For the recovery of the material properties, heat treatments are performed. So, this study aimed to analyze the condition of the heat treatment and to evaluate the influence of microstructure variation with this heat treatment for degraded superalloys. We studied the influence of HIP (hot isostatic processing) and post-heat treatment. HIP treatment has the effect of the elimination of cavities and cracks. The heat treatment processes removed the inhomogeneity of the creation and the growth of the γ` phase due to the temperature gradation during the welding.

Keyword : GTD 111DS; Gas turbine; Ultra-high temperature; Regenerative maintenance; Nondestructive testing; Hot isostatic processing; Welding