Assessment of heat-treated INCONEL alloy 690 using third-order ultrasonic nonlinearity parameter measured by the pulse-echo method

The ultrasonic nonlinearity parameter has been demonstrated in numerous studies to be an effective indicator of material degradation. In most such studies, the second-order nonlinearity parameter, defined using the second harmonic component generated during the ultrasonic propagation, is measured via the through-transmission method. However, the pulse-echo method is highly advantageous in field applications. Unfortunately, the second harmonic component is difficult to receive using the pulse-echo method due to the phase inversion effect. To address this difficulty, we measure the third-order nonlinearity parameter, defined using the third harmonic component that is free from phase inversion, using the pulse-echo method to assess heat-treated INCONEL alloy 690. For experimental verification, INCONEL alloy 690 specimens were prepared with up to 200 h of heat treatment at 700 degrees C. For comparison, the second-order nonlinearity parameter was measured via the throughtransmission method. Additionally, the ultrasonic velocity and attenuation coefficient, which are linear parameters, were also measured to compare their change rates with those of the nonlinear parameters. Subsequently, the tensile and yield strengths were obtained through the destructive tensile test, and the results were correlated with the measured parameters. Our results indicate that the third-order nonlinearity parameter showed the strongest correlation to the measured strengths. The second-order nonlinearity parameter showed the same trend as that of the third-order nonlinearity parameter but with lower change rate and the attenuation coefficient showed a tendency, but the change rate was greatly reduced. The ultrasonic velocity showed almost no change. These results show that the third-order nonlinearity parameter is an effective indicator of thermal aging of INCONEL alloy 690 material, and this methodology is expected to be highly applicable to field applications.