Ultrasonic nonlinear evaluation of tensile plastic damage in Nickel based single crystal superalloy

The tensile interruption tests of Nickel-based single crystal (NBSX) superalloys at room temperature were carried out to artificially introduce controllable levels of plastic damage, and linear and nonlinear ultrasonic nondestructive methods were used to evaluate it. The results indicate that ultrasonic nonlinear parameter β shows hypersensitivity to early tensile plastic damage compared with traditional linear parameters. Transmission electron microscope (TEM) and X-ray diffraction (XRD) measurements of dislocation string length and dislocation density were conducted to calculate the theoretical predicted values of β by ultrasonic nonlinearity dislocation monopole model, and they are in well agreement with experimental results. In addition, the actuation of slip systems and evolution of dislocation configuration were observed under optical microscope (OM) and TEM. From the perspective of element distribution and energy, it is revealed that the plastic deformation mechanism of the NBSX superalloys at room temperature is anti-phase boundary (APB) dislocation pairs shear γ′ phase. The measurement results of macro mechanical properties manifested that accumulative tensile plastic deformation lead to increase of strength and decrease of plasticity.