Abstract
The precipitation hardening mechanisms and their dependence on precipitate size (rp) and precipitate/matrix lattice misfit (δ) in γ'/γ systems were studied in nickel-base superalloy using micro-indentations experiments and theoretical models. Metallurgical states were characterized by TEM, SEM-EBSD, XRD and APT. For the precipitate size range studied (radius rp smaller than 110 nm), γ' precipitates are ordered spherical Ni3(Al,Ti) phase, the volume fraction remains relatively constant and equal to 20 % and lattice misfit δ is lower than 0.45 %. Prevalence of order strengthening by anti-phase boundary formation and Orowan bypassing was observed in various rp range, whereas chemistry and coherency strengthening were found insignificant in the nickel-base superalloy studied (Waspaloy®). Shearing by weakly coupled dislocations was dominant for fine precipitates, i.e. rp lower than 18 nm, shearing by strongly-coupled dislocations for an intermediate rp range, i.e. from 18 nm to 98 nm and Orowan bypassing for coarse precipitates with a rp larger than 98 nm.
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