High-temperature defect kinetics in titanium and zirconium alloys revealed by the dynamic extinction of neutron radiation

Liss, K. D.; Kabra, S.*; Thoennessen, L.*; Harjo, S.   ; Reid, M.*; Yan, K.*; Harrison, R.*; Dippenaar, R. J.*

After + Zr and Ti alloys have fully transformed into single -phase upon heating, the intensities of all -Zr Bragg reflections decrease simultaneously as a function of time. This effect represents a transition from the kinematic to the dynamic theory of diffraction due to the ever increasing crystal perfection driven by thermal recovery of the system, and has been employed to further investigate the kinetics of crystal perfection. Crystal recovery is identified as a process of dislocation annihilation, hindered by lattice friction. Furthermore, intensity increases during plastic deformation due to recreation of dislocations. Upon cooling, precipitating -phase induces strain into the perfect -crystallites, re-establishing the kinematic diffraction intensities. An Avrami analysis leads to an understanding of the nucleation and growth kinetics of the phase in its very early stages.