The deformation and fracture modes of fine and coarsened NbSS phase in a Nb-20Si-24Ti-2Al-2Cr alloy with a NbSS/Nb5Si3 microstructure

Abstract

The microstructure, deformation and fracture behaviour of a Nb-20Si-24Ti-2Al-2Cr alloy with a ductile/stiffening NbSS/Nb5Si3 structure prepared by spark plasma sintering (SPS) and arc melting (AM) techniques were investigated. An ultra-fine NbSS/Nb5Si3 microstructure, approximately ~2μm 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 NbSS/Nb5Si3 eutectic that was distributed in the primary Nb5Si3 boundaries. Different deformation and failure modes were present in the NbSS phase of the SPS and AM samples. The active dislocation of 〈1 1 1〉/2 operated in the fine SPS NbSS phase, resulting in a dimple failure of the SPS NbSS phase and a fracture toughness (KQ) of the bulk SPS NbSS/Nb5Si3 microstructure as high as 18.4MPa·m1/2. However, the immovable dislocation of 〈1 0 0〉 enhanced {0 0 1} cleavage failure of the coarsened AM NbSS phase, which significantly decreased KQ of the bulk AM NbSS/Nb5Si3 microstructure to 11.5MPa·m1/2.