The Influence of Cr on the Solidification Behavior of Polycrystalline γ(Ni)/γ'(Ni_3AI)-δ(Ni_3Nb) Eutectic Ni-Base Superalloys

摘要

In the current investigation, the effect of Cr on the solidification characteristics and as-cast microstructure of pseudobinary γ-δ eutectic alloys based on a near-eutectic composition (Ni-5.5Al-13.5Nb at. pct) was investigated. It was found that Cr additions promote the formation of a higher volume fraction of γ-δ eutectic microstructure in the interdendritic region. Increasing levels of Cr also triggered morphological changes in the γ-δ eutectic and the formation of γ-γ'-δ ternary eutectic during the last stage of solidification. A detailed characterization of the as-cast alloys also revealed that Cr additions suppressed the liquidus, solidus, and γ' precipitation temperature of these γ/γ'-δ eutectic alloys. A comparison of the experimental results with thermodynamic calculations using the CompuTherm Pandat database (Compu-Therm LLC, Madison, WI) showed qualitative agreement.