Development of New Co-Base Superalloys Precipitaion Hardened by an Intermetallic Phase for Gas Turbine Application

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Commercial Co-base superalloys are inferior in their high temperature strength and creep properties to the Ni-base superalloys because an effective strengthening phase such as gamma-prime in the latter alloys has not been found and utilized. In the present work, two phase alloys consisting of Co solid solution matrix and an intermetallic compound Co_3AlC_<0.5> are investigated for the development of a new class of precipitation strengthened Co-base superalloys. The crystal structure of the intermetallic compound resembles the L1_2, having interstitial carbon atoms in the fcc base ordered crystal structure. Critical assessment of the crystal structure of the compound by electron diffraction analyses, orientation relationships between the matrix and the compound, room to high temperature mechanical properties, and elevated temperature creep properties of the two phase alloys with various volume fraction of the intermetallic phase are examined. It is shown that the alloys with proper dispersion characteristics of the compound have comparable creep properties with commercial Ni-base superalloys and exhibit fairly good room temperature tensile ductility.