Microstructure and mechanical properties of super-strong nanocrystalline tungsten processed by high-pressure torsion

作者：Wei Q^*; Zhang H T; Schuster B E; Ramesh K T; Valiev R Z; Kecskes L J; Dowding R J; Magness L; Cho K

来源：Acta Materialia, 2006, 54(15): 4079-4089.

DOI：10.1016/j.actamat.2006.05.005

• nanocrystalline
• tungsten
• grain boundaries
• transmission electron microscopy
• high-pressure torsion

Fully dense nanocrystalline tungsten (nc-W) with extremely high strength (similar to 3.0 GPa under quasi-static compression and similar to 4.0 GPa under dynamic compression) has been obtained by high-pressure torsion (HPT) at low temperature (500 degrees C). The nanocrystalline microstructure is revealed by transmission electron microscopy (TEM). The grain boundaries (GBs) are mostly of the large-angle type. Highresolution TEM (lattice images) suggests that the GBs are clean and well defined (atomically sharp). GBs are non-equilibrium and of a high-energy nature. Edge dislocations are present within the grains. The authors hypothesize that these edge dislocations, combined with a depleted impurity concentrations along pre-existing GBs, contribute to enhance the ductility of nc-W. Under dynamic compression, the specimens exhibit localized shearing followed by cracking and subsequent failure, similar to their ultrafine-grain (UFG) counterparts processed by equal-channel angular pressing plus cold rolling, and to many other body-centered cubic metals with UFG/nanocrystalline microstructures. The shear band width in the HPT-processed nc-W is much smaller (shear band width < 5 mu m) than that observed in the UFG counterparts (shear band width similar to 40 mu m).

• 出版日期2006-9