Microstructure and Phase Evolution of Al4C3-NiCrAlY Composite Powders by Short-term Heat Treatments

Abstract This study proposes an alternative Al 4 C 3 -NiCrAlY composite bond coat (BC) “system” to address the current challenges associated with traditional “stacked-horizontal layer” coating designs featuring linear interfacial thermal grown oxide (TGO) layers. The reactivity of Al 4 C 3 with metallic alloy systems remains largely unexplored. This work establishes an initial baseline for the compositional and microstructural characteristics of this novel composite composition in the powder form. The microstructure and phase evolution of spray-dried Al 4 C 3 -(25-75 vol.%) NiCrAlY composite powders were examined via controlled-atmosphere heat treatments to establish the steady-state composition and microstructure up to 1300 °C. No significant phase interaction was observed below 1250 °C. Above this temperature, Al diffusion from Al 4 C 3 into NiCrAlY enabled nickel aluminide formation, while free carbon facilitated the precipitation of chromium carbides. The final composition of the composite powder comprised nickel aluminide matrices with internal chromium carbide formations. For powders with higher initial Al 4 C 3 content, nickel aluminide phases also formed as external attachments to the main body of the composite particles.