Effect of Ta addition on solidification microstructure and element segregation of IN617B nickel-base superalloy

Abstract

IN617B nickel-base superalloy is considered as a good candidate material in 700 °C advanced ultra- supercritical coal-fired power plants. The effect of Ta addition on solidification microstructure and element segregation of IN617B alloy was investigated by OM, SEM, TEM, EDS, EPMA and thermodynamic calculation. The results showed that the solidification microstructure exhibited a dendritic segregation pattern with many primary carbides distributed in interdendritic regions, such as network M6C, lath M23C6 and granular Ti(C,N). The addition of Ta promoted the precipitation of Ta-rich MC significantly inhibiting the precipitation of M6C and M23C6, and reduced the segregation degree of Al, Mo and Ti alloying elements. The addition of Ta decreased the melting temperature of MC carbide, but did not impact the solidification path, that was, L→ γ matrix → MC or Ti(C,N) → M6C → M23C6, where MC and Ti(C,N) tended to form symbiotic microstructure with M6C. This study will provide theoretical basis and data support for the alloy optimization and casting structure control of IN617B nickel-based superalloy.