A l’occasion de sa venue au CEMEF pour la soutenance de thèse de Marie-Agathe Charpagne,
le Pr. Roger Reed donnera un séminaire intitulé « Recent Studies on Microtwinning Mechanism in Single Crystal Superalloys »
en salle IR016 à 16h00.
In the mid-temperature range of 600 to 800 deg C, the nickel-based superalloys can be prone to mechanism of deformation involving the nucleation and propagation of microtwins. Despite its importance, rather little is known about this. Critical questions include: what is the mechanism of nucleation and propagation? What is the dependence of the reaction kinetics on crystallographic orientation and mean alloy composition? Can models be proposed for the deformation mechanism? In this presentation, recent results on this topic are summarised. A model is proposed in which the lengthening and thickening of the twins involving diffusional phenomena of both short-range and long-range form. The twinning velocity is predicted and shown to be capable of allowing the measured creep strain rate to be recovered with reasonable accuracy. Results from high resolution experimentation using for example atom probe tomography are included.
[D. Barba, A. Jerusalem and R.C. Reed, ‘On the Composition of Microtwins in a Single Crystal Nickel-Based Superalloy’, Scripta mater., 127, 37–40, (2017)]