Abstract
In order to explore a refurbishment technology for advanced gas turbine components, the cellular formation in microstructurally-controlled Ni-based superalloys, CMSX-4 and CM247LC, have been studied. The cellular formation can be seen accompanied with a γ/γ' microstructure coarsened in lamellar or equiaxed arrays, when the superalloys are previously subjected to a damage associated with local plastic deformation, followed by re-heat treatment. During this study special attention was paid to the effect of the cellular formation on the high cycle fatigue strength at high temperature. The experiments indicated that once the cellular formation was reached, the fatigue strength was remarkably reduced, compared with the healthy, or virgin material. The methods to reduce and prevent the above unfavorable effect have been explored. It was strongly suggested by the fatigue tests that the addition of grain boundary strengthening elements would be a promising technique. The application of the surface modification technique, or protective coating, might be also a useful technique. Moreover, nondestructive detection of the cellular formation was also studied, employing ultrasonic technique.
