Effect of Hf addition on evolution of microstructure and strengthening behavior in Ni-based ODS superalloy

In this study, two kinds of Zr-containing Ni-based ODS superalloys, ODS-Zr (Ni-20Cr-0.5Ti-0.3Al-0.6Zr-0.6Y ₂O ₃, wt%) and ODS-Zr+Hf (Ni-20Cr-0.5Ti-0.3Al-0.6Zr-0.8Hf-0.6Y ₂O ₃ , wt%), were prepared by high-energy milling and hot isostatic pressing (HIP) process. Evolution of microstructure and tensile property caused by Hf addition was analyzed and discussed. The result showed that the addition of Hf changes significantly oxide type and refines oxide size. Y ₄Zr ₃O ₁₂, Y ₂TiO ₅ and three-type Y-Al oxides including monoclinic-structure Y ₄Al ₅O ₁₂ (YAM), orthogonal and hexagonal YAlO ₃(YAM and YAH) are found in ODS-Zr. In contrast, only Y ₂Hf ₂O ₇, Y ₄Zr ₃O ₁₂ and Y ₂TiO ₅ but no Y-Al oxides are viewed in ODS-Zr+Hf. The average diameter of oxides in ODS-Zr and ODS-Zr+Hf is 16.6 nm and 13.0 nm, respectively. The size difference between two alloys is ascribed to different oxide constitution in two alloys. Moreover, Hf addition enhances tensile strength of alloys at 25 °C and 700 °C meanwhile improves tensile ductility at 700 °C.