A study on the evolution of ω-phase in Zr-20Nb alloy under the influence of electron irradiation

Abstract

In-situ TEM investigations are carried out on the Zr-20Nb alloy to study the evolution of ω phase under the influence of 2 MeV electrons at different temperatures. The Selected Area Diffraction (SAD) patterns taken during the irradiation show characteristic features of ω phase formation like diffuse scattering and streaking of the diffraction spots. Continuous shifting of the peak intensity maxima is observed during the course of transformation. This behaviour is rationalised in terms of the existence of sub-units of ω phase like ω3, ω5, ω7 predicted through Monte-Carlo simulations. Simulated SAD patterns also show the effect of ordering and the aspect ratios of these sub-units on the streaking behaviour. Density functional theory based simulations predict an increasing ω phase formation tendency with decreasing Nb concentration in the alloy. The deviation in the peak shift as a function of irradiation time establishes that with increasing irradiation temperature and electron energy, the ω phase destabilises after certain duration of irradiation which is attributed to the increased vacancy concentration in the alloy induced by 2 MeV electrons.