Peculiarities of the Formation of Defects Initiating Fatigue Faults in Granular Alloy EP741NP

The EP741NP alloy samples destroyed during fatigue testing have been studied by transmission electron microscopy, energy-dispersive X-ray microanalysis, and electron diffraction. The composition and crystal structure of defects detected at the fatigue crack boundaries have been thoroughly examined. It has been shown that these defects have mainly the morphology of elongated flat “carpets” containing NiO, CTi_xNb \(_{{1 - x}}\) , amorphous AlO_x, HfO₂, α-Al₂O₃, β-Al₂O₃, Al₂MgO₄, Co₇Mo₆, Co₃O₄, S₄Ti₃, NbO₂, TiO₂, and amorphous regions containing C, O, Ca, S, Na, and Cl. Assumptions concerning the source and time of formation of the investigated defects have been made.