Microstructures and properties of ultrafine-grained tungsten produced by equal-channel angular pressing at low temperatures

The ultrafine-grained tungsten was fabricated by equal-channel angular pressing (ECAP) at 800 degrees C and 950 degrees C, respectively, and was characterized by electron microscopy and Vickers microhardness measurement. The average grain size of W decreases with the increasing number of ECAP extrusion passes and can be refined from the initial value of about 6 mu m to 0.9 mu m after two ECAP extrusion passes at 800 degrees C, while it is refined to 1.5 mu m after three ECAP extrusion passes at 950 degrees C. Small angle tilt grain boundaries consisting of edge dislocations are formed in the 950 degrees C extrusion. Intergranular fracture mode dominates the fracture failure of the W after 800 degrees C extrusion while transgranular facture mode together with intergranular fracture mode play an important role in the fracture failure of the W after 950 degrees C extrusion. The Vickers microhardness increases from about 510 HV for the as-received W to about 560 HV for the W extruded at both 800 degrees C and 950 degrees C. However, the thermal conductivity was affected only a little by the ECAP processing. (c) 2012 Elsevier B.V. All rights reserved.