Ductilization of tungsten (W) through cold-rolling: Correlation of microstructure and mechanical properties in UFG-W sheetsThursday (29.09.2016) 12:15 - 12:30 Part of:
Tungsten exhibits outstanding thermomechanical properties for high-temperature applications in oxygen-free environments. However its brittle behavior at low temperatures and a difficult manufacturing process still impede the application as a structural material. Wei and Kecskes showed the possibility of tailoring tungsten down to the ultrafine-grained (UFG) regime by severe plastic deformation (SPD). This leads to much higher strengths, a reduction in strain rate sensitivity and an increase in ductility. Furthermore a significant toughness and a decrease of the BDTT were demonstrated by Pippan and Reiser for thin cold-rolled foils, validating their potential for the use in structural applications. But despite a few interesting findings, a systematic study of the various aspects of plastic deformation of SPD processed ultrafine grained (UFG) W is still lacking.
A batch of Tungsten sheets with different thicknesses has been produced out of a single sintered compact of commercially pure tungsten by subsequent cold-rolling. This unique batch of samples allows investing the mechanical properties without an influence of the chemical composition or fabrication differences in the production of the sintered compact. The presentation shall comprise an EBSD analysis of the evolution of the microstructure with increased true strain, as well as tensile- and strain rate jump tests of foils with different thickness, performed over a wide range of temperatures. The mechanical properties can thereby be correlated to the grain size and cold-work induced defects.
A grain refinement well down to the UFG regime could be verified, reaching a grain refinement of 240 nm perpendicular to the rolling direction. The grain refinement leads to a continuous increase of hardness up to 700 HV0.1. Tensile tests reveal peculiar characteristics in the stress strain curves and yield strength for the samples with UFG grain structure. The advanced tensile strain rate jump tests allow a precise determination of the strain rate senistivity (SRS), revealing for the UFG tungsten samples a decreasing SRS towards the critical temperature, followed by an increasing SRS above this temperature.