[en] Highlights: • Nb-Si based alloy powders were prepared by plasma rotating electrode atomization. • A fine Nb_SS/Nb₅Si₃ microstructure (~ 2 μm) was obtained by spark plasma sintering (SPS). • Operation of active 〈1 1 1〉/2 dislocation resulting in a dimple failure of SPS Nb_SS • Immovable 〈1 0 0〉 dislocation developed {0 0 1} cleavage of arc-melting (AM) Nb_SS. • Fracture toughness of the SPS and AM Nb-Si samples was 18.9 and 11.5 MPa·m^1/2 respectively. The microstructure, deformation and fracture behaviour of a Nb-20Si-24Ti-2Al-2Cr alloy with a ductile/stiffening Nb_SS/Nb₅Si₃ structure prepared by spark plasma sintering (SPS) and arc melting (AM) techniques were investigated. An ultra-fine Nb_SS/Nb₅Si₃ microstructure, approximately ~ 2 μm in phase size, was obtained when this Nb-Si based alloy powder prepared by the plasma rotating electrode atomization technique (PREA) was SPSed, and the SPS sample consisted of a continuous Nb matrix with equiaxed- and worm-like Nb₅Si₃ islands. The AM sample contained largely primary Nb₅Si₃ phase and coarsened Nb_SS/Nb₅Si₃ eutectic that was distributed in the primary Nb₅Si₃ boundaries. Different deformation and failure modes were present in the Nb_SS phase of the SPS and AM samples. The active dislocation of 〈1 1 1〉/2 operated in the fine SPS Nb_SS phase, resulting in a dimple failure of the SPS Nb_SS phase and a fracture toughness (K_Q) of the bulk SPS Nb_SS/Nb₅Si₃ microstructure as high as 18.4 MPa·m^1/2. However, the immovable dislocation of 〈1 0 0〉 enhanced {0 0 1} cleavage failure of the coarsened AM Nb_SS phase, which significantly decreased K_Q of the bulk AM Nb_SS/Nb₅Si₃ microstructure to 11.5 MPa·m^1/2.