Some advances on precipitation hardening in Waspaloy: Critical review on the contribution of shear, Orowan and coherency mechanisms

The precipitation hardening mechanisms and their dependence on precipitate size (rp) r p ) and precipitate/matrix lattice misfit (delta) delta ) in gamma'/gamma / gamma 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 p smaller than 110 nm), gamma' precipitates are ordered spherical Ni3(Al,Ti) 3 (Al,Ti) phase, the volume fraction remains relatively constant and equal to 20 % and lattice misfit delta is lower than 0.45 %. Prevalence of order strengthening by anti-phase boundary formation and Orowan bypassing was observed in various rp p range, whereas chemistry and coherency strengthening were found insignificant in the nickel-base superalloy studied (Waspaloy (R)). (R)). Shearing by weakly coupled dislocations was dominant for fine precipitates, i.e. rp p lower than 18 nm, shearing by strongly-coupled dislocations for an intermediate rp p range, i.e. from 18 nm to 98 nm and Orowan bypassing for coarse precipitates with a rp p larger than 98 nm.