Influence of grain aspect-ratio on the fracture properties of ultrafine-grained tantalum.

[Display omitted] • Ta was used as a model material to study the effect of rolling on the fracture toughness of ultrafine-grained materials. • Cold Rolling induces a pronounced grain elongation and leads to a significant increase of the fracture toughness. • The origin of the fracture toughness enhancement is mainly based on the activation of a delamination fracture mechanism. The fracture characteristics of severely plastically deformed (SPD) materials exhibit large variations in the quasi-static fracture resistance depending on factors such as the investigated material, testing temperature and grain aspect ratio. Especially the latter one is considered to control the frequently observed orientation dependent fracture toughness. A question that arises thereby is how the fracture properties for certain testing directions could be actively tuned by tailoring the grain aspect ratio. In this contribution this issue has been investigated by changing the aspect ratio of ultrafine-grained tantalum processed by high pressure torsion through post-rolling operations which induced a substantial increase of the grain length while keeping the strength on a comparable level. Samples in interesting testing directions were manufactured and tested. The increase of the aspect ratio results in the technically significant testing directions to an enhancement of the fracture toughness. Delamination toughening, which is promoted by the change of the aspect-ratio, has been indentified to be the main cause for the toughness enhancement and represents therefore a feasible pathway for optimizing the damage tolerance of SPD-processed materials. [ABSTRACT FROM AUTHOR]