Small-scale analysis of brittle-to-ductile transition behavior in pure tungsten

Abstract

l Small-scale and non-destructive approach to figure out the BDT behavior of pure W. l Development of practical fracture analysis diagram for estimating the BDT regime utilizing nano-indentation and atomistic simulation. l Good agreement between the present BDT prediction and direct observation of failure responses in macroscopic mechanical tests. l Lower pop-in activation energy and higher macroscopic shear strain rate in cold-rolled tungsten. l Decrease in BDT temperature after cold-rolling caused by the dominant presence of mobile edge dislocations. Tungsten as a material exhibits broad and increasingly important applications; however, the characterization of its ductile-to-brittle transition (BDT) is currently limited to large-scale scenarios and destructive testing. In this study, we overcome this challenge by implementing small-scale techniques to provide a comprehensive understanding of the BDT behavior of pure tungsten. In order to predict the failure mode at various temperature ranges, the practical fracture analysis diagram has been proposed to describe the resistance to shear flow and cracking behavior with temperature. High temperature nano-indentation tests have provided the inherent mechanical responses corresponding to the maximum shear stress at various temperatures, which is required for dislocation activities in an atomic scaled activation volume. On one hand, atomistic simulations have provided the temperature dependence of brittle fracture stress, where the atomic bonds break due to intergranular or intragranular fracture. We considered four tungsten specimens having various microstructures prepared using different processing conditions of cold-rolling and post-annealing, and their BDT ranges were inferred using the obtained fracture analysis diagram with the statistical data processing. The fracture analysis diagram of each specimen obtained were compared with the direct observation of fracture responses in macroscopic mechanical tests, which conclusively indicated that the small-scale inherent mechanical properties are greatly relevant to the macroscopic BDT behavior in pure tungsten. Based on the BDT estimations by small-scale characterization, we provided further insights into the factors affecting the BDT behavior of tungsten, focusing on the contributions of different types of dislocations. .