Insights into the fatigue cracking of Alloy 690TT subjected to fretting wear under partial slip conditions

Fatigue crack initiation and propagation is one of the failure modes of Alloy 690TT when subjected to fretting wear under partial slip conditions. Detail characterization was performed for the fatigue cracks by using transmission electron microscopy (TEM). The results indicated that slip bands, subgrain boundaries, and oxide film contributed to the fatigue crack initiation and propagation. Intergranular and intragranular oxidation accelerated the crack propagation and changed the propagation path. The dislocation interactions and the synergy of oxidation and amorphization were responsible for the formation of nano-cavities. Amorphous structure was formed by the oxidation at crack inner and surrounding the nano-cavities due to severe plastic deformation. The combination of oxidation and amorphization along with the chemical and structural disorder accelerated the crack propagation.