Investigation of small crack behaviour under cyclic loading in a dual phase steel with an FIB tomography technique

摘要

Damage accumulation is investigated in the early stage of fatigue life in a ferritic martensitic dual phase steel. Microcrack initiation and propagation are influenced by microstructure, such as grain boundaries, grain orientation and/or phase distribution morphology. The dominant crack initiation pattern is one in which microcracks are generated in a ferrite grain along slip bands inclined at a certain angle with respect to the loading direction. Subsurface observation with a focused ion beam (FIB) device and additional crystallographic characterization by means of the electron backscatter diffraction (EBSD) technique show that a slip system having a high Schmid factor value is activated and results in a crack nucleus. The FIB tomography technique with the help of EBSD measurement allows a three-dimensional investigation of small crack behaviour to be performed.