CREEP CHARACTERIZATION OF SUPERALLOY IN-738 USING ULTRASONIC NONLINEARITY MEASUREMENT

Abstract

The higher harmonic generation technique has been presented to investigate the creep characteristics of nickel-based superalloy. The primary γ′ precipitates became coarsened preferentially in the direction perpendicular to the applied stress axis during the creep deformation and the Vickers hardness decreased with creep time due to loss of interfacial strain between γ matrix and γ′ precipitate. The increase in ultrasonic nonlinearity with increasing creep time is discussed in relation to the directional coarsening of the γ′ precipitates, which was closely related to the scattering and distortion of the ultrasonic wave.