In situ TEM studies of the mechanisms of crack nucleation and propagation in fully lamellar microstructures

The mechanisms of crack nucleation and propagation of the lamellar microstructures found in pearlite were studied by in situ transmission electron microscopy. It was found that, in addition to the predominant mechanism of cleavage fracture in the cementite plates, ductile fracture of the cementite plates is another crack nucleation mechanism. The process of failure in the fully lamellar microstructure studied in the present investigation consists of four stages: dislocation pile-ups; single crack nucleation; distribution of crack nucleation; and crack growth, followed by final fracture. Through this study, a description of the lamellar microstructure fracture mechanism has been developed for numerical simulation in future studies. [Material: AISI 1080.]