Nondestructive evaluation for thermally degraded co-base superalloy by scanning acoustic microscope

This research investigates the feasibility of ultrasonic microscope for nondestructive assessment of thermal degradation in artificially aged commercial Co-base superalloy, FSX414. This alloy has been used for high temperature structure applications such as stationary gas turbine blade and nozzle chamber in fossil plant. Microstructural change was found that the fine carbides became coarser and spheroidized in matrix as aging time increased. The leaky surface acoustic wave velocity gradually decreases by a maximum of 4.7% with increasing aging time up to 4,000 hours. However, the longitudinal wave velocity has a little change. Also, it has a good correlation between leaky surface acoustic wave velocity and vickers hardness. Consequently, LSAW can be used to examine the degree of degradation in thermally aged Co-base superalloy