The effect of local textures on microcrack propagation in fatigued f.c.c. metals

The individual crystallographic orientation of the grains in fatigued specimens with f.c.c. lattice (nickel and austenitic steel) was determined with the help of electron backscattering diffraction (EBSD). From the orientation data, the misorientation of neighboured grains was calculated (angle-axis pairs). In nickel specimen, twin boundaries are preferred sites for microcrack initiation and propagation. The observed damaged twin boundaries agree with Neumannʹs model of additional incompatibility stresses. In austenitic steel, a greater portion of microcracks propagate in random grain boundaries. The probability of microcrack propagation can be given by a misorientation crack factor, which takes into account the incompatibility of the grain rotation during the plastic deformation of misoriented grains.