Chemical Ordering as a Precursor to Formation of Ordered δ-UZr2 Phase: A Theoretical and Experimental Study

A combination of special quasi-random structure (SQS) analysis, density functional theory (DFT) based simulations and experimental techniques are employed to determine transformation pathway for disordered γ-(U,Zr)→chemically ordered δ-UZr2phase transformation (PT). A novel Monte-Carlo based strategy is developed to generate SQS structures to study β→ω displacive PT in A1-xBx binary random alloy. Structures generated with this strategy and using DFT calculations, it is determined that (222)bccplane collapse mechanism is energetically unfavorable in chemically disordered environment at UZr2composition. A mechanically and dynamically stable 24 atom SQS structure is derived which serves as a structural model of chemically ordered δ-UZr2structure. Finally, a thermodynamic basis for the mechanism of the γ to δ transformation has been established which ensures chemical ordering is a precursor to the subsequent displacive transformation to form chemically ordered δ-UZr2structure.