The investigation of α/β interface structure in Ti-5Al-6Nb(V/Cr) model titanium alloys

The structure of the α/β phase interface, which includes component such as interface misfit, dislocations, and step structures, critically influences the mechanical strength and stress distribution in titanium alloys. Pursuing an in-depth understanding of these characteristics, Ti-Al-Nb (V, Cr) ternary alloy system were ingeniously developed utilizing the Exact Muffin-Tin Orbitals (EMTO)-Coherent Potential Approximation (CPA) method to vary interface misfits. The study revealed that Ti-5(at.%)Al-6(at.%)Cr exhibited the highest misfit, followed by Ti-5Al-6 V and Ti-5Al-6Nb demonstrating the lowest. Misfits were experimentally characterized at various aging temperatures through selected area electron diffraction (SAED), aligning closely with theoretical predictions. High-resolution transmission electron microscopy (HRTEM) facilitated a detailed examination of Ti-5Al-6 V and Ti-5Al-6Nb, uncovering a shared broad interface step structure: the broad face of the α precipitate consists of areas of coherent terrace planes on 11¯00_α‖112_βand ledge planes on 01¯10_α‖110_β. Besides, the height of the ledges characterized is twice the 112_βinterplanar spacing. Upon comparison with the initial phase transition, the equilibrium state α/β interface misfit was observed to increase, with a reduction in coherent regions. Notably, the Ti-5Al-6Nb alloy, with its lower misfit, presents broader terrace widths and reduced step density compared to Ti-5Al-6 V, suggesting an intrinsic link to the distinct transformation strains induced by V and Nb component.