Composition-dependent collapse of β {111} planes leading to ω precipitation in Ti-Nb alloys: A first-principles study

The effects of Nb content on the collapse of β {111} planes leading to ω phase precipitation were investigated in binary Ti-Nb alloys by first-principles exact muffin-tin orbitals-coherent potential approximation (EMTO-CPA) method. In accordance with the accepted mechanism of the beta to omega transformation occurring due to the collapse of the bcc {111} planes, the total energies of β Ti-Nb binary alloys containing multiple states corresponding to different Nb concentration ranging from 20at.% to 30at.% were calculated. The results indicated that the total energies for the same Nb content are not monotonically decreasing with the z (z denotes the degree of collapse of β {111} planes) value increasing, but keeping an energy barrier to cross. The energy barrier increases gradually along with increasing Nb content. The density of states (DOS) was given to elucidate the changes of electronic structure during the collapse of β {111} planes.