Fatigue crack propagation in single- and bicrystals of a ferritic stainless steel

The effect of crystallographic orientation on fatigue crack propagation has been investigated in Fe-30%Cr alloy single- and bicrystals. It was found in the single crystals that crystallographic-orientation dependences of strength were different between tensile and fatigue crack growth tests. This is because the properties of the propagating crack could be affected not only by tensile axis but also by notch directions. The fatigue cracks were grown in the manner of shear decohesion along slip bands, thus having a preferential growth direction at individual tensile axes. In order to examine effect of grain boundary on the fatigue crack growth, the bicrystal specimens were also prepared. In the bicrystal experiments, occurrence of intergranular fatigue crack propagation was related to a geometrical relationship between the abovementioned preferential growth directions in constituent grains. It was also recognized that slip continuity between adjoining grains played an important role on crack growth retardation at the grain boundary.