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 25×25×150 mm3 were processed at 300 °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 ~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 °C, while the tungsten-rich phase begins to recrystallize at near ~800 °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.