Microstructure-interacting short crack growth in blocky alpha Zircaloy-4

Microstructurally short fatigue crack growth in blocky alpha Zircaloy-4 is experimentally investigated in cyclic three-point bend testing. The short crack propagation is sensitive to the local microstructure with respect to grain crystallographic orientation and grain boundaries. Polycrystals with predominant c-axis texture aligned out-of-plane and normal to loading give alternating crack paths along prismatic planes. Samples with c-axis texture aligned in plane and normal to loading typically show straight paths along prismatic planes, sometimes tortuous paths, but always crystallographic. Prismatic <a>-direction crack growth rate is low compared to that for prismatic <c>-direction growth for given loading. Hence the crystallographic plane within which cracks grow is important for determining overall growth rate. For tortuous cracks, with the predominant c-axis texture in plane and normal to loading, crack growth occurs along basal, prismatic and pyramidal planes, deflecting from one slip plane to another during transgranular propagation.