| Diffusion bonding technique is indispensable in the fields of aviation, aerospace and so on because of the base metals without melting. Diffusion bonding defects will degrade the service performance of bonding structures seriously. Therefore, it is necessary to carry out the nondestructive testing. Mostly, the defects are only a few micrometers in size. Meanwhile, there are always kissing bonds in diffusion bonding. It is very difficult to detect the defects by radiographic testing and conventional ultrasonic testing. With the development of the theory in nonlinear ultrasonic, nonlinear ultrasonic testing has been widely in the detection of tiny defects in solids. Signal processing was adopted in this paper in order to study the nonlinear behavior of ultrasound in diffusion bonding.First of all, diffusion bonding samples which contain typical defects were made by controlling the surface treatment before welding and changing the welding process. Ultrasonic testing was performed to obtain the data of ultrasonic signal which correlate with the joint states.Based on the theory of contact acoustic nonlinearity, the smooth interface model and the rough interface model were used to compare the ultrasonic nonlinear effects of different states in the joints of solid-phase connection.Nonlinear ultrasonic imaging of diffusion bonding was applied by two algorithms. The better algorithm was selected by comparison. Ultrasonic nonlinear images and C-scan images were compared to analyze the difference of bonding quality.With the results of destructive experiments, characteristics of time domain and frequency domain of the ultrasonic echo signals were analyzed in different joint states. Features of unbonded, kissing bond and perfectly bonded area were represented from the points of view of ultrasonic signal feature, ultrasonic interface nonlinear effect, microstructure and shear strength. The results showed that nonlinear ultrasonic testing was more sensitive to kissing bonds in diffusion bonding. |
PDF Full Text Request