Investigation on the as-cast microstructure of Nb–Nb silicide based multicomponent alloys

Refractory metal intermetallic composites (RMICs) based on the Nb–Ti–Si–Cr–Hf quinary are candidate materials for ultra-high temperature applications beyond 1200 °C. In this investigation, minor additions of Al, B, Y and Mo were introduced into the Nb-22Ti-(15–18)Si-6Cr-4Hf (at.%) base alloy for potential enhancement of the mechanical and environmental properties. The phases, phase compositions and morphologies in the as-cast microstructure of the base alloy with or without minor Al, B, Y and Mo additions were investigated using X-ray diffraction (XRD), optical metallography (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS) and electron probe microanalysis (EPMA). The experimental results obtained from several selected alloys were found to agree with the solidification paths calculated from the Scheil model using established thermodynamic properties of all the phases in the Nb–Ti–Si–Cr–Hf–Al system.