Hierarchical microstructures enabled excellent low-temperature strength-ductility synergy in bulk pure tungsten

Refractory tungsten (W) is notoriously brittle at room temperature, which restricts its workability and narrows the temperature range of critical applications. Here, we report a multi-scale microstructure modulation strategy to achieve an excellent combination of low-temperature ductility and high strength in bulk pure W. Through fast two-step low temperature sintering of the activated W powders and high-energy-rate forging treatments, unique hierarchical microstructures were constructed in pure W, including lamellar elongated matrix grains, with profuse interior fine sub-grains, and high density of mobile edge and mixed dislocations. At room temperature, the hierarchical structured bulk W exhibits a detectable tensile ductility and an ultimate tensile strength (UTS) of 1.35 GPa. The high strength can be maintained at elevated temperatures, i.e., UTS > 1.0 GPa at 200 °C; it also has a remarkable tensile ductility of 15.3% at this temperature. These properties are significantly better than those reported in bulk pure W and W alloys with second phase particles. The shielding and blunting effects from low-angle grain boundaries and highly mobile dislocations, and the lamellar structure reaped delamination toughening effect are the main mechanisms for the improved low-temperature ductility and strength. This study demonstrates a practical route to achieve attractive low-temperature strength-ductility synergy in bulk W without involving any alloying elements, and it is a feasible and low-cost pathway to design high performance refractory metals and alloys.