Solidification Process and Mechanical Behavior of the Nb/Nb₅Si₃ Two Phase Alloys in the Nb-Ti-Si System

Abstract

Design of two-phase alloys consisting of niobium solid solution (A2) and α-Nb₅Si₃ (D8_l) phases in the Nb-Ti-Si ternary system is pursued for ultra-high temperature structural applications. Compositional and annealing conditions are determined for the formation of A2/D8_l lamellar microstructure via eutectoid decomposition of Nb₃Si (tP32) phase in the Nb-Si binary and Nb-Ti-Si ternary system. Addition of titanium is found to result in increased room temperature toughness, but decreased high temperature strength. Enhancement of mechanical properties is achieved by applying the directional solidification technique. Mechanical properties of the alloys are discussed from microstructural point of view.