Exploration of phase structure evolution induced by alloying elements in Ti alloys via a chemical-short-range-order cluster model

The prominent comprehensive properties of solid-solution- and intermetallic-based Ti alloys are derived from their diverse microstructures induced by multi-component alloying, which results in a chemical composition complexity. A cluster-plus-glue-atom model, characterizing the chemical short-range orders, was introduced to explore the relationships among the local atomic distributions of alloying elements in different phase structures of Ti alloys, including α-Ti, β-Ti, ω-Ti, α2-Ti3Al, γ-TiAl, O-Ti2AlNb, and B2-Ti(Al,Nb). Specific cluster structural units, i.e., cluster formulas, for these phases were determined with the guide of the Friedel oscillation theory for electron-structure stabilization. It is due to the change of cluster structural units that induces the phase transformation, which is attributed to the amounts of primary alloying elements of Al and Nb. The total atom number (Z) values in these cluster structural units, calculated by the Fermi vector kF, are all very close to the integer of Z = 16. Furthermore, the composition rules of industrial multi-component Ti alloys based on these phases were generalized in light of the cluster formula approach, which will open up a new route towards designing high-performance Ti alloys with complex compositions.