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

Abstract

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.