A study on delamination behavior of coating thermally sprayed with Ni-based self-fluxing alloy under fatigue loadings

In order to examine the mechanisms of delamination between coating layer and substrate under fatigue loading in steel thermally sprayed with Ni-based self-fluxing alloy, three types of specimens with different coating thickness were prepared. The fusing was performed by using an induction heating system in order to change the stress distribution. Rotating bending fatigue tests and observations of fracture surfaces were carried out. With all fracture surfaces, the delamination between the coating and the substrate occurred. However, the coating thickness strongly affected the fatigue properties ; the thicker the coating, the lower the fatigue strength. In order to clarify the mechanism of delamination, the differences of strain on the interface between the coating layer and the substrate were performed by using FEM analysis. The differences of strain strongly affected the delamination between the coating and substrate ; the thinner the coating, the smaller the differences of strain. Considering these results and observing the interface during the cyclic loading in detail, it is considered that the greater the differences of strain on the interface between the coating and the substrate, the earlier the delamination occurred and propagated, and a lower fatigue strength resulted.