Brittle fracture and the brittle-to-ductile transition of tungsten

The aim of this paper is to shortly review the experimental observations and the theoretical understanding of the fracture behaviour of tungsten in the brittle and semi-brittle regime. Advances in the understanding of the mechanisms of fracture processes are made by direct comparison of microscopic modelling and carefully designed experiments. While atomistic simulations are needed to analyse the brittle fracture regime, dislocation simulations are helpful in analysing the dependence of the intrinsic fracture toughness on pre-deformation, temperature or loading rate in the semi-brittle regime below the brittle-to-ductile transition (BDT). By such comparison of fracture experiments on tungsten single crystals with simulations it is shown that dislocation nucleation is the limiting factor at low temperatures, while the dependence on loading rate at intermediate temperatures requires that dislocation mobility takes control. Furthermore, it is shown that the intermediate temperature regime up to the BDT temperature scales with one unique activation energy. At last the results are compared to selected data on polycrystalline tungsten. (C) 2003 Elsevier B.V. All rights reserved.