Simultaneous ultrasonic inversion for porosity and texture of additively manufactured polycrystalline metal with differential-Mori-Tanaka model

Traditional ultrasonic testing technologies have difficulty simultaneously achieving non-destructive characterisation of both porosity and texture of additively manufactured metallic polycrystals. Based on an ultrasonic propagation model that comprehensively considers the combined effects of textures and porosity, we propose here an improved regularisation model based on the L1-L2 norm and an improved L-curve method for ultrasonic non-destructive inversion. Using efficient computation strategies based on sensitivity matrix, we achieved simultaneous and high-precision inversion of texture parameter and porosity. Using two selected laser melting Ti-6Al-4 V samples as examples, texture parameters and porosity were measured respectively through electron backscatter diffraction and Archimedes method. These true results are then used for comparing with the ultrasonic non-destructive inversion results of this study. The comparison shows that the mean absolute percentage errors (MAPE) values between the inversion results based on the improved regularisation model and the true values are 6.51% and 6.89% for two AM Ti-6Al-4 V samples respectively, while the MAPE values based on the Tikhonov regularisation model are 13.02% and 8.06%, respectively. These results indicate that the proposed inversion framework is effective and provides a reliable ultrasonic non-destructive testing method for texture parameter and porosity.