Nondestructive evaluation of creep and fatigue damages in nickel-base superalloys using a scanning blue laser microscope

A new nondestructive evaluation method for detecting both creep and fatigue damages of Ni-base superalloy used in advanced gas turbine systems has been proposed by applying a scanning blue laser microscope. The change of the microtexture in a grain of the alloy due to creep and fatigue damages can be observed clearly by using this microscope. The reflectance of the γ′ (Ni3Al) phase of the alloy was found to be less than that of the γ (Ni-base alloy) phase, when a laser beam of wavelength shorter than 500 nm was radiated to the alloy. Since the microtexture of the alloy varies significantly during damage progress, it is possible to evaluate the damages quantitatively and nondestructively by observing the change of the microtexture using the laser beam with wavelength 410 nm.