Nb–Si alloys are highly promising for aero-engine applications because of their high melting point, low density, and excellent high-temperature creep resistance. However, producing Nb–Si alloy components via investment casting is very challenging due to the alloy’s high reactivity with ceramic molds and the required strict process control. In this study, a 30 kg Nb–Si ingot was created using vacuum levitation melting (VLM) and vacuum arc remelting (VAR), achieving a near-nominal composition and minimal macrosegregation. Microstructural analysis showed a dual-phase Nb solid solution Nbss/γ-Nb5Si3 structure, with Nbss/γ-Nb5Si3 cellular eutectic colonies exhibited a preferred orientation of \(\left\langle {{1 1 1}_{{{\text{Nb}}_{{{\text{ss}}}} }} } \right\rangle ||{ }\left\langle {{0 0 0 1}_{{\gamma {\text{ - Nb}}_{{5}} {\text{Si}}_{{3}} }} } \right\rangle\) and \(\left( {1 1 0} \right)_{{{\text{Nb}}_{{{\text{ss}}}} }} ||\left( {1{ }0{ }\overline{1}{ }0} \right)_{{\gamma {\text{ - Nb}}_{{5}} {\text{Si}}_{{3}} }}\) . Four ceramic shells were designed to cast turbine shroud segments, and the shell consists of Y2O3-based face-coat and silica-zircon reinforcement was applied because of its best balance of strength, low roughness, and thermal stability. ProCAST simulations refined the directional solidification parameters, identifying a pulling speed of 2 mm/min and an outward flange arrangement as optimal for minimizing defects and ensuring microstructural uniformity. Casting trials at 1850 °C confirmed that these conditions allowed effective mold filling, produced a minimal (10–30 µm) interfacial reaction layer, and resulted in shroud segments with excellent surface integrity. These findings demonstrate the feasibility of industrial-scale Nb–Si alloy casting and provide insights into manufacturing Nb–Si-based ultrahigh-temperature components.
Graphical abstract
