Application of Diffraction-Amalgamated Grain Boundary Tracking to Fatigue Crack Propagation Behavior in High Strength Aluminum Alloy

Abstract

Fatigue crack propagation behavior in a 7075-type Al alloy (Al-5.6%Zn-2.5%Mg-1.6%Cu) was investigated by applying DiffractionAmalgamated Grain Boundary Tracking (DAGT), which provides grain morphologies and crystallographic orientations in three dimensions (3D). 3D crack morphologies at different propagation stages in the bulk of the sample were successfully obtained using synchrotron radiation X-ray microtomography (SRCT) technique. The apparent crack growth rate, da/dN, which varies significantly along a crack front line, was calculated. There are rapid acceleration and deceleration regions of da/dN due to the interaction with grain boundary (GB) and crack closure segments. Typical crack morphology under the influence of Mode II (in-plane shear) and Mode III (out-of-plane shear), such as crack deflection and twist, is detected by the observation of 2D tomographic slice image. A detailed direct assessment of microstructure-crack interaction behaviors has been achieved by applying the DAGT technique.

Diffraction-amalgamated grain boundary tracking for mapping 3D crystallographic orientation and strain fields during plastic deformation

“…The combination of 4D morphological information on grains and 4D strain mapping has enabled a direct understanding of fundamental deformation mechanisms in polycrystalline materials [14,15,17]. Further details of the GBT process are available elsewhere [14].…”

“…Its first application to tensile deformation of an aluminium alloy revealed highly heterogeneous deformation in individual grains [14], contrary to the conventional understanding, which deformation is attributable to the complex and heterogeneous structures of actual polycrystals. In order to produce a physical interpretation of the complex deformation , the GBT technique has been modified to measure the crystallographic orientation of grains, by adding an X-ray diffraction experiment in the preliminary studies [16,17]. Determining which grain has produced which diffraction spot has been a fundamental problem when interpreting XRD images.…”

Construction of Finite Element Meshes for Polycrystal Grains Model from X-ray CT Image

“…Even in X-ray CT, synchrotron radiation CT (SRCT), which is available in a synchrotron radiation facility, achieves the highest spatial resolution. The SRCT permits us to investigate the presence of an inner defect 1) , nucleation of void during deformation 2,3) , crack initiation and propagation [4][5][6][7] , etc., in metallic material because of the penetrating power by high energy and high ux X-ray. It is possible to observe a change process depending on time because X-ray CT inspection is non-destructive.…”