Ductile-Phase Toughening in Niobium-Niobium Silicide Powder Processed Composites

Abstract

AbstractThe Nb-Si system offers a possibility of ductile-phase toughening of the brittle Nb5Si3 intermetallic with the terminal niobium-silicon solid solution. Powder composites have been made in which the volume fraction of the terminal Nb-Si phase is systematically varied in a matrix of Nb5Si3 in order to study the extent of toughening. The Nb-Si solid-solution phase was observed to exhibit cleavage failure under both as hot pressed and heat treated conditions, thereby limiting the toughening attained by the presence of this phase. Hot working of the composite results in a dramatic improvement in toughness because of a change in the plastic behavior and fracture mode of the terminal Nb-Si phase from brittle cleavage to a mixed mode of cleavage and ductile microvoid growth and coalescence (dimpled) fracture.