Effect of Sc on the microstructure and room-temperature mechanical properties of Nb-Si based alloys

Abstract The microstructure and room-temperature mechanical properties of directionally solidified and heat-treated Nb‑16Si‑23Ti‑4Cr‑2Al‑2Hf‑0/0.3/0.5Sc (at.%) alloys were investigated. All alloys consisted of Nb-based solid solution (Nb ss ), α‑Nb 5 Si 3 and γ‑Nb 5 Si 3 with preferred 〈001〉 orientation for the first two phases, and Sc was enriched in γ‑Nb 5 Si 3 phase. Sc-added alloys showed a more continuous Nb ss matrix in which the finer Nb 5 Si 3 phase distributed uniformly. The volume fraction of both α‑Nb 5 Si 3 and γ‑Nb 5 Si 3 phase was decreased by Sc addition. Sc alloying reduced the Young's modulus and nano-hardness of Nb ss phase. 0.50 at.% Sc addition enhanced the fracture toughness and tensile strength from 9.88 MPa m 1/2 and 430.3 MPa to 25.95 MPa m 1/2 and 1119.7 MPa. The improvement in fracture toughness was due to the better deformability of Nb ss phase. The high tensile strength was attributed to the dispersed and refined Nb 5 Si 3 phase, which was not degraded by the increased Nb ss volume fraction since dislocations were not open within most Nb ss phase. Besides, the strong interface cohesion was preferable for the strength of Sc-added alloys.