Abstract
Microstructural features and their effects on yield strength at high temperatures in the P/M HGN200 Ni–Co-base polycrystalline superalloy, subjected to a standard double aging treatment, have been clarified using both Thermo-Calc® and a unified approach. The matrix γ possesses a very fine grain size due to the used processes and pinning by primary γ'. The calculated antiphase boundary energy is very high, resulting in high yield strength. Dispersion of fine tertiary γ′ phases is remarkable to increase the yield strength compared with those of primary and secondary γ′; the contribution of the primary γ′ to the yield strength is negligible. The stoichiometric composition of primary and secondary γ′ is (Ni,Co)3(Ti,Al) and that of tertiary γ′ is (Ni,Co,Cr)3(Ti,Al) and the excellent high temperature strengthening is related to homogeneous dispersion of both the secondary and tertiary γ′.
Published Version
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