Microstructure, mechanical properties and fracture behavior of Nb with minor Si addition

• 0.5 at.% Si significantly improves the strength of Nb.
• Addition of 0.5 at.% Si retains the good ductility of Nb.
• 1 at.% Si reduces the elongation rapidly.
• Fracture feature changes from dimple to cleavage with increase of Si.

Controlling the content of elements in niobium solid solution (NbSS) is significant for better comprehensive properties of Nb-Si based alloys. In this paper, the influences of minor Si (0, 0.5, 1, 2 and 3.5 at.%) on microstructures and mechanical properties of arc melted Nb at room temperature have been investigated. The increasing addition of Si would promote grain refinement and increase Si concentration in NbSS. Nb3Si and (NbSS + Nb3Si) eutectic phases are found when Si content is higher than 1 at.%. With the increase of Si concentration in NbSS, the Vickers hardness, ultimate tensile strength (UTS) of NbSS increases while elongation decreases. However, the fracture toughness and UTS decrease from 1 at.% to 3.5 at.% because of the grain boundary precipitation of silicides. In addition, with Si addition from 0.5 at.% to 1 at.%, the fracture feature transforms from dimple to cleavage and reduces the elongation rapidly (23.4% to ~ 0%) because of the embrittlement of NbSS. Controlling Si concentration to 0.5 at.% is beneficial for strengthening the NbSS and retaining its good ductility and fracture toughness.