Microstructure and room temperature fracture toughness of Nb-Si-based alloys with Sr addition

Nb-Si-based alloys show great potential to surpass the widely used Ni-based superalloys.The element Sr is widely applied in aluminum and magnesium alloys,but reports about the effects of Sr on Nb-Si-based alloys are quite rare.So,Nb-Si-based alloys with nominal compositions of Nb-15Si-24Ti-4Cr-2Al-2Hf-0/0.05/0.15Sr(at%)were prepared by directional solidification and heat treatment.The microstructural characterization and room temperature fracture toughness of Nb-Si-based alloy were systematically investigated.Results show that all these alloys consist of Nb_5Si_3 phase embedded within Nb solid solution(Nb_(ss)) matrix.The Nb_(5)Si_(3) phase becomes refined and more discontinuous after adding minor Sr.As for the fracture toughness,0.05 at% and 0.15 at% Sr additions do not cause significant change.The discontinuous and refining mechanism of Sr element was studied,and the analysis of toughness decreasing with Sr addition reveals that the size of Nb_(ss) phase plays a crucial role in determining the fracture toughness.