Nonlinear ultrasonic evaluation and simulation of precipitation coherence change in thermal aging damage of P91

The thermal aging damage of P91 steel was assessed using nonlinear ultrasonic detection technology. Acoustic nonlinear parameters demonstrate high sensitivity to thermal aging damage. The variation in acoustic nonlinearity during the early thermal aging period results from the interplay between a reduction in dislocation density and the coarsening of carbide precipitation. In the late thermal aging period, a loss of precipitation coherence leads to a reduction in acoustic nonlinear parameters. Based on the existing prediction model, dynamic mismatch parameters are added, and the precipitation size distribution is coupled with the corresponding mismatch parameters. This model effectively captures the contributions of both the precipitation size distribution and coherence variations to acoustic nonlinearity. Based on the molecular dynamic method, the contribution of precipitation coherence to acoustic nonlinearity is explored from a microscopic perspective. Both experimental and simulation studies demonstrate the potential of nonlinear ultrasonic detection technology for detecting changes in precipitation coherence.