Delineating hardening contributions of secondary and tertiary γ′ particles in an aged Alloy 693

Bi-modal and tri-modal distribution of γ′ particles in Alloy 693 can be produced by inducing the precipitation of different generations of particles during slow cooling after an annealing treatment. In the present work, an attempt has been made to quantify hardening contributions of different generations of particles and to identify change in the dominant hardening mechanism when particle distribution changes from mono-modal to multi-modal. This has been carried out by first establishing a functional dependence of the hardening behaviour of mono-dispersed (first generation) particles on their size and volume fraction to identify particle size range for different hardening mechanisms. Governing hardening mechanisms were validated by transmission electron microscopy on the basis of experimentally observed interaction of dislocations with precipitate particles. Functional dependence of first generation particles has been utilized to identify hardening mechanisms and contributions of later generations of particles.