Surface fatigue cracking of plasma nitrided cast iron D6510 under cyclic inclined contact stresses

Abstract The mechanical mating components (e.g., gear teeth and stamping dies) usually have an inclined contact which introduces additional tangential forces and accelerates the formation of the surface fatigue cracking. To study such effects on the surface fatigue behaviours of engineering materials and coatings, an inclined sliding test was adopted to have varying ratios of tangential to normal loads at different positions inside the wear scar during each cyclic loading. In this study, a plasma nitrided ductile cast iron (D6510) was tested under various contact angles, which led to different ratios of tangential to normal loads. The results demonstrated that subsurface cracks occurred at the low ratio while the surface cracks dominated at the high ratio when the inclined sliding contact stresses were very high. Severe surface fatigue failure like chipping could occur as soon as the surface cracking density is higher than 0.13.