Microstructure and highly enhanced mechanical properties of fine-grained tungsten heavy alloy after one-pass rapid hot extrusion

One-pass rapid hot extrusion of fine-grained 93W–4.9Ni–2.1Fe–0.03Y (wt.%) alloy with an average grain size of ∼10 μm was performed at 1150 °C with an extrusion speed of ∼100 mm/s and an extrusion ratio of ∼3.33:1. Microstructure and mechanical properties of the as-extruded alloy were investigated. The results show that the tungsten particles of the as-extruded alloy are severely elongated along the extrusion direction and the aspect ratios of these elongated particles are 5–8. Three crystallographic textures {0 0 1}〈1 1 0〉, {1 1 1}〈1 1 0〉 and {1 1 0}〈1 1 0〉 arose after rapid hot extrusion and the total volume fraction of these texture components was approximately 30%. Many lath-shaped subgrains with a small misorientation and low density dislocations could be observed in tungsten phase and γ-(Ni, Fe) phase respectively. These microstructure characteristics indicate that slight dynamic recovery-recrystallization process occurred during rapid hot extrusion. In contrast to as-sintered alloy, the as-extruded alloy possessed much higher ultimate tensile strength and hardness (HRC) but a relatively lower ductility (1570 MPa vs. 995 MPa; HRC48 vs. HRC29 and 6.5% vs. 24%). In addition, the fracture morphology shows that the predominant failure mode for the as-extruded alloy is cleavage failure of the tungsten particles, while the ductile rupture of the γ-(Ni, Fe) phase that can be frequently observed in the as-sintered alloy nearly disappeared after rapid hot extrusion.

Research highlights► The strength of fine-grained WHAs is as high as 1570 MPa after rapid hot extrusion. ► Plastic deformation of fine-grained WHAs during rapid hot extrusion is uniform. ► Slight dynamic recovery-recrystallization process occurred during hot extrusion. ► Fine grains and reserved numerous dislocations contribute to the high strength.