Magneto-elastic softening in cold-sprayed polycrystalline nickel studied by resonant ultrasound spectroscopy

Cold-sprayed metallic deposits are additively manufactured materials containing high levels of compressive residual stress. Here we show that the presence and intensity of this stress can be analyzed using laser-ultrasonics, provided that the sprayed material is ferromagnetic and magnetostrictive, as in the case of pure nickel. Contactless resonant ultrasound spectroscopy is used to monitor the evolution of shear modulus and internal friction parameter of two polycrystalline Ni deposits with temperature over the Curie point, which enables a direct assessment of the strength of magneto-elastic softening that is known to be strongly stress-dependent. In addition, the proposed methodology is also shown to be suitable for in-situ observation of the recrystallization process in the vicinity of the Curie point, as well as inspecting the homogeneity of the residual stress level across the thickness of the cold-sprayed deposit. Finally, a methodology for room-temperature probing of the magnetoelastic coupling is proposed and tested on the examined materials.