Evaluation of the Ferromagnetic Cold-Sprayed Coating Peeling Process at the Interface Based on Magnetic Barkhausen Noise Testing

As a type of novel surface engineering technology, the application of cold spraying in the manufacturing and remanufacturing of high-end precision parts is very suitable. However, the disadvantage of low interface bonding strength can easily induce coating peeling at the coating/substrate interface under the effect of applied loads. Therefore, finding a suitable nondestructive testing method is significant to evaluate the cold-sprayed coating peeling process and provide prediction results. To achieve this aim, magnetic Barkhausen noise (MBN) testing was used in this paper because of its high sensitivity to microstructure variation. The Ni-Zn-Al₂O₃ ferromagnetic coating deposited on the ductile cast iron substrate was prepared by cold spraying. Based on the wavelet coherence analysis, the frequency of MBN signals induced by magnetic domain movement was mainly concentrated in the range of 1–4 kHz. The spectrum power between 1 kHz and 4 kHz was extracted as the characteristic value, and the linear fitting relationship between the characteristic value and applied load was established. When the power reaches the threshold value range of 3.106×10⁻⁸–3.557×10⁻⁸ W, the probability that the interfacial stress exceeds the coating/substrate bonding strength and that Ni-Zn-Al₂O₃ coating peeling occurs is 95%. Combined with the microstructure and morphology analysis, the mechanism of cold-sprayed coating peeling was revealed, and the underlying reason for MBN signal variation was explained. This research can accurately evaluate the ferromagnetic cold-sprayed coating peeling process and the interface bonding strength.