Abstract: A device, for non-destructive testing of a mechanical part made of a polycrystalline material, includes: an ultrasonic probe including a two-dimensional array of transducers capable of emitting and receiving signals at different excitation angles; and a processing module suitable for controlling the emission and the reception of the transducers, for processing the signals received by the transducers so as to express the signals received by the ultrasonic probe in two planar wave planes constructed from the emission and reception wave vectors of the probe, and for deducing therefrom information representative of the three-dimensional orientation of the fiber structure of the mechanical part.