Effect of minor Zr addition on γ′ and η phase precipitation and tensile properties of A286 superalloy

Abstract

In this study, the mechanisms of Zr on microstructure and tensile properties of A286 Fe-based superalloy were investigated. Cellular η phases precipitated homogenous at approximately all the grain boundaries in the modified Zr-A286 superalloy but heterogeneous in Zr-free alloy. Detailed microstructural analysis revealed that with the addition of Zr to the alloy; the grain size reduced, η volume fraction decreased and the growth and dissolution of γ′ phase accelerated. The mechanism of Zr in Ni and Fe-based superalloys is different. The mechanism in Fe-based superalloy is segregation of Zr at grain boundaries and occupation of Ti sites for η phase formation. In Ni based superalloy, Zr stabilizes the γ′ phase and retards the γ′ to η transformation. Zr addition led to improvement of room temperature tensile strength by replacement of the primary relatively smooth grain boundaries by new jagged grain boundaries after the η phase precipitation.