Proposal of fractographic analysis method coupled with EBSD and ECCI

Fracture surface contains key information to analyze the crack propagation behavior and identify the causes of fracture in post-mortem specimens/structural parts. For instance, fatigue crack propagation rate and the associated ΔK can be estimated from a fractographic feature, i.e., the striation spacings. However, the current fractography-based methods for the estimation of fatigue crack propagation rate and ΔK require the presence of striations. This requirement limits the capacity for the quantitative analysis of the fracture surface. Therefore, further advancement of fatigue fractography is required to facilitate the quantitative assessment of fracture, using post-mortem specimens/structural parts. In this study, we propose fractography coupled with microstructural evolution underneath the fracture surface. Microstructural characterization was performed, using electron backscattering diffraction (EBSD) and electron channeling contrast imaging (ECCI). In this study, we used a Fe-3Al bcc single crystalline alloy. EBSD-based grain reference orientation deviation analysis showed discrete plastic zones appearing along the crack propagation direction, with spacings corresponding to the crack propagation rate. Furthermore, it was confirmed via ECCI that underneath the fracture surface low- and high-ΔK regions showed vein-like and labyrinth structures, respectively. This information is expected to be useful for microstructure-based estimation of fatigue crack propagation rate and ΔK.