Effect of Zr and Hf addition on microstructure and tensile properties of high-Al Ni-based ODS superalloys

Abstract

In this paper, three kinds of high-Al Ni-based oxide dispersion strengthening (ODS) superalloys, ODS-Z (Ni–20Cr–4.5Al–0.5Ti–0.6Y2O3–0.6Zr, wt.%), ODS-H (Ni–20Cr–4.5Al–0.5Ti–0.6Y2O3–0.8Hf) and ODS-ZH (Ni–20Cr–4.5Al–0.5Ti–0.6Y2O3–0.6Zr–0.8Hf), were prepared by mechanical alloying (MA) and hot isotropic pressing (HIP). The effect of Zr and Hf addition on grains, oxides, γ′ phases and mechanical properties of Ni-based ODS superalloys was investigated. The result exhibited that grain size is refined by Hf addition. The addition of Zr or Hf significantly varies the type and distribution of oxides. The mean size and number density of oxides are 11.8 nm and 6.64 × 1021 m−3 for ODS-Z, 9.5 nm and 7.86 × 1021 m−3 for ODS-H, 10.7 nm and 7.53 × 1021 m−3 for ODS-ZH, respectively. The oxides formed in ODS-Z are hexagonal δ-Y4Zr3O12 and YAlO3 perovskite (YAP). The oxides in ODS-H consist of cubic-structure Y2Hf2O7, YAP and monoclinic Y4Al2O9 (YAM). However, only Y2Hf2O7 and Y4Zr3O12 are observed in ODS-ZH. The addition of Zr and Hf does not change average size and volume fraction of γ′ phases. Compared with the addition of Zr or Hf alone, the co-addition of Zr and Hf exhibits high tensile strength while improves significantly ductile at room temperature and 700 °C.