The nature of the brittle-to-ductile transition of ultra fine grained tungsten (W) foil

The aim of this work is to answer the question of whether an ultra fine grained (UFG) microstructure has an impart on the nature of the brittle-to-ductile transition (BDT) of tungsten. Therefore, four-point bend tests were performed using unnotched 100 mu m UFG tungsten foil and annealed coarse-grained polycrystalline tungsten foil (2073 K for 2 h in vacuum) with exactly the same chemical composition and dimensions. The reported results for coarse-grained tungsten foil show a strain-rate dependent BDT that occurs between 350 and 450 K. The activation energy of the BDT, E-BDT, for the coarse-grained material was deduced to be 2.9 (+ 2.6/-0.9) eV. The results obtained from UFG tungsten foil indicate a strain-rate independent BDT at relatively low temperatures 77 K). The strong disparity in the nature of the BDT can be attributed solely to the presence of microstructural differences. The possible mechanism controlling the BDT in tungsten for both tungsten foil conditions will be discussed against this background and in the light of previous studies performed on the nature of the BDT of tungsten reported in pertinent literature. (C) 2014 Elsevier Ltd. All rights reserved.