Transmission electron microscopy studies and modeling of 3D reciprocal space of ω forming alloy.

Initial stage of ω phase formation and associated anomalous features that appear in diffraction patterns of a metastable β transition metal alloy have been investigated in this study with the aid of transmission electron microscopy, simulation and modeling. The paper explores discrete features that emerge in selected area diffraction patterns of quenched Ti-15wt%Mo alloy and analyzes the correlation between ω reflections and diffuse arcs by considering all variants of ω phase as per the formation kinetics of ω phase in β matrix while quenching. Superimposed simulated diffraction patterns have been compared with experimental counterparts and it is deduced that there is lack of congruence between ω reflections and diffuse arcs even after considering trigonal ω with varying degrees of displacement. Direct lattice imaging of trigonal ω in β matrix has been demonstrated by phase contrast microscopy coupled with Fourier filtering techniques. By investigating the nature of ω reflections and diffuse arcs with the aid of electron diffraction pattern calculations and phase contrast microscopy, it is shown that, existing model of three-dimensional (3D) reciprocal space of ω forming alloy at quenched stage is not complete. A new model incorporating a patterned intensity distribution is fitted at the octahedral sites of an fcc reciprocal lattice whose planar intersections with Ewald's sphere show a better fit with the observed experimental diffraction patterns.