Correlation of gamma-gamma prime mismatch and strengthening in Ni/Fe-Ni base alloys containing aluminum and titanium as hardeners

Various authors have invoked coherency strains and disregistry between the crystal lattices of the matrix and γ′ phase to account for considerable hardening in γ′-strengthened superalloys. Hagel and Beattie correlated the mode of precipitation with the degree of its lattice mismatch. Heydt and Whitney used this approach during the development of an Fe-Ni base high temperature alloy. To understand the role of such a relationship, an investigation of a few experimental Ni-base/Fe-Ni base alloys was carried out. These alloys were strengthened by variable titanium, aluminum, and molybdenum additions and contained chromium. Lattice parameters of the solution treated and aged samples were measured. The γ′ phase was electrolytically extracted for lattice parameter determinations, and γ?γ′ mismatch calculated. The γ?γ′ mismatch calculated. The γ?γ′ mismatch was correlated with room temperature hardness and stress rupture properties at 1200°F. The influence of alloying additions, matrix and γ′ lattice parameters were interrelated.