Microstructural characteristics of tungsten-base nanocomposites produced from micropowders by high-pressure torsion

摘要

Micropowder mixtures of W-50 Al, W-50 Ti and W-50 Ni were subjected to severe plastic deformation at 573 K using high-pressure torsion (HPT). The powder mixtures were consolidated and nanocomposites of W/Ti, W/Ti and W/Ni, with average grain sizes as small as ~9, ~15 and ~12nm, respectively, were formed by imposing large shear strains. The nanocomposites exhibited Vickers microhardness as high as ~900 Hv, a level that has rarely been reported for metal-matrix composites. X-ray diffraction analyses together with high-resolution transmission electron microscopy showed that in addition to grain refinement, an increase in the fraction of grain boundaries up to 20, the dissolution of elements in each other up to ~15 mol., an increase in the lattice strain up to 0.6, and an increase in density of edge dislocations up to 1016 m~2 occurred by HPT. The current study introduces the HPT process as an effective route for the production of ultrahigh-strength W-base nanocomposites, fabrication of which is not generally easy when processing at high temperatures because of interfacial reaction and formation of brittle intermetallics.