Principles of physical mesomechanics of nanostructural fatigue of metals. Part II. Subsurface fracture of EP741 heat-resistant alloy

Round EP741NP heat-resistant alloy specimens were tested in the range of fatigue life between 105 and 108 cycles under cyclic tension with heating of the surroundings to 650 °C. It is shown that fracture of the specimens begins with subsurface fracture nucleation from a cluster of inclusions or a formed smooth facet. Further, the process develops along slip planes with intense oxidation of the fracture, whereupon a self-organized discrete transition to fracture in the range of low-cycle fatigue occurs with the formation of fatigue striations and less intense oxidation of the fracture. The proposed model of crack opening in modes III and I during the facet formation and subsequent fracture along slip planes allows explaining the observed mechanisms of fracture and oxidation beneath the material surface.