Characterizing the magnetic memory signals on the surface of plasma transferred arc cladding coating under fatigue loads

The metal magnetic memory signals were measured during dynamic tension tests on the surfaces of the cladding coatings by plasma transferred arc (PTA) welding and the 0.45% C steel. Results showed that the slope of the normal component Hp(y) of magnetic signal and the average value of the tangential component Hp(x) reflect the magnetization of the specimens. The signals increased sharply in the few initial cycles; and then fluctuated around a constant value during fatigue process until fracture. For the PTA cladding coating, the slope of Hp(y) was steeper and the average of Hp(x) was smaller, compared with the 0.45% C steel. The hysteresis curves of cladding layer, bonding layer and substrate were measured by vibrating sample magnetometer testing, and then saturation magnetization, initial susceptibility and coercivity were further calculated. The stress-magnetization curves were also plotted based on the J-A model, which showed that the PTA cladding coating has smaller remanence and coercivity compared with the 0.45% C steel. The microstructures of cladding coating confirmed that the dendritic structure and second-phase of alloy hinder the magnetic domain motion, which was the main factor influencing the variation of magnetic signal during the fatigue tests.