Effect of plasma nitriding on high-cycle fatigue properties and fracture behaviors of GJS']JS700 nodular cast iron under cyclic bending loading

In this article, the influence of plasma nitriding on the fatigue behavior and fracture mechanisms of the GJS700 nodular cast iron has been investigated. Factors contributing to this influence, which included the microstructure, the phase detection, the surface roughness, and the hardness of the plasma-nitrided specimens were discussed. Moreover, rotating-bending high-cycle fatigue testing was also done on standard samples, and then the field-emission scanning electron microscopy was also utilized to find the failure mechanism on fracture surfaces. Obtained results demonstrated that the average surface roughness and the Vickers micro-hardness increased by plasma nitriding, compared to the base material. However, fatigue lifetimes decreased in plasma-nitrided samples due to the increase in the surface roughness and the formation of a compound layer. On the fracture surface, micro-cracks, cleavage planes, and fatigue striations were observed. Debonding of the graphite from the matrix in all specimens was a dominant cause of the failure.