A comparison study on microstructures and fracture behaviours of a single Nb_SS solid solution alloy and a two-phase Nb_SS/Nb₅Si₃ alloy prepared by spark plasma sintering and arc melting

Single Nb_SS phase alloy (Nb-37Ti-13Cr-2Al-1Si) and two-phase Nb_SS/Nb₅Si₃ alloy (hypoeutectic composition of Nb-16Si-24Ti-2Al-2Cr) powders prepared by the plasma rotating electrode atomization technique (PREA) were spark plasma sintered (SPS), and the microstructure, fracture toughness, deformation and fracture mode of the two SPS and arc melting (AM) alloys were characterized. With a coarsened grain size, the AM and SPS single Nb_SS phase alloy had a small difference in fracture toughness and it failed in a cleavage mode. As for the SPS two-phase Nb_SS/Nb₅Si₃ sample containing an ultra-fine ductile/stiffening Nb_SS/Nb₅Si₃ microstructure, approximately 1–2 μm in phase size, a fracture toughness of as high as 16.1 MPa·m^1/2 was obtained, owing to operation of the active dislocation of a/2 〈111〉 and dimple failure of the fine Nb_SS phase. However, the AM two-phase Nb_SS/Nb₅Si₃ microstructure had a coarsened Nb_SS phase and a low fracture toughness of 9.6 MPa·m^1/2, resulting from the movement of a 〈100〉 dislocation in the {001} cleavage planes and a cleavage failure mode of the coarsened Nb_SS phase.