Hardness and microstructure of tungsten heavy alloy subjected to severe plastic deformation and post-processing heat treatment

The hardness and thermal stability of 90W-8Ni-2Fe tungsten heavy alloy (WHA), following severe plastic deformation by equal channel angular extrusion, are reported. Square bars measuring 25 x 25 x 150 mm(3) were processed at 300 degrees C to plastic strains of 2.68. The hardness of WHA increased with increased strain, from 29 Rockwell Hardness C (HRC) in the as-received condition, to similar to 50 HRC. ECAE refined the grain size of the tungsten particles from tens of microns to 270 nm. This decrease in tungsten grain size correlates with the increase in hardness following a Hall-Petch relationship. Annealing results indicate that the matrix phase recrystallizes at 500 degrees C, while the tungsten-rich phase begins to recrystallize at near 800 degrees C. The morphology of the tungsten-rich particles changes from near-spherical to elongated platelets or ellipsoids, depending on processing strain path. The results suggest ECAE is an effective technique for manipulating the microstructure, phase morphology, and mechanical properties of WHA. (C) 2015 Elsevier B.V. All rights reserved.