Microstructural characterization of Nb–B–Si alloys with composition in the Nb−Nb5Si2B (T2-phase) vertical section

Multiphase alloys of the Me–B–Si (Me=refractory metal) systems have been considered for structural applications at high temperatures. In this work, the solidification pathway and phase stability of Nb-rich Nb–B–Si alloys were evaluated from arc-melted and heat-treated samples. The primary phases observed in the region of study were Nbss, T2-phase and D88-phase. The as-cast microstructure of all the alloys indicates formation of an Nbss+T2 eutectic in the last part to solidify. From the heat treatment of several alloys, the Nbss−T2 two-phase field was observed to exist at 1700 °C. Based on DTA experiments, the Nbss−T2 two-phase field should be stable up to 2150 °C.