In this study, we found that well-developed α₂′ martensite was formed in a Ti-40Al-10V (atomic percent or at.%) alloy after air-cooling from a β phase field, rather than the traditional α₂/γ lamellar colonies. The martensitic laths were produced according to the Burgers orientation relationship (OR), the same as those during quenching. Local variant selection detected that three (or six) α₂′ variants sharing one (or two) common [11.0]_α2′ axes were predominant, while no global variant selection was observed. Subsequent to the martensitic transformation, the retained β phase was decomposed mainly via a β→γ transformation. The γ laths always nucleated at the α₂′/β interface according to a Blackburn orientation relationship. In order to stabilize the microstructure, the air-cooled samples were tempered at 800–1000 °C. During tempering, the microstructure decomposed mainly via an α₂′→γ transformation. The martensite was almost completely transformed after tempering at 1000 °C for 4 h, and hence a fine β-γ microstructure was obtained. Such a treatment resembling the quenching–tempering in steels may be a new strategy for the microstructural design of TiAl alloys, while an unexpected quenching process can be avoided.

Interdiffusion coefficients of the β single-phase in the Ti-rich portion of the binary Ti–X (X = Al, Mo, V, Cr, Fe) systems at 1 523 K were determined by annealing infinite diffusion couples between appropriate pairs of alloys. The values were derived from the concentration profiles by electron probe microanalysis coupled with the Boltzmann–Matano method. The comparison of the interdiffusion coefficients in these binary Ti–X (X = Al, Mo, V, Cr, Fe) systems show that the Mo diffuses the least while the Fe diffuses fastest in titanium alloys. Furthermore, the values of the interdiffusion coefficients of the Ti–Al, Ti–V and Ti–Cr binary systems were similar.

We introduce a new strategy that extends the established diffusion couple approach for efficient mapping of microstructural and mechanical properties in bulk samples. The featured diffusion couples undergo an interdiffusion annealing followed by a thermal/mechanical treatment for creating a blended spectrum of phases and microstructures in the well-grooved continuous composition gradients, which is then further accessible to local high spatially resolving microanalysis probing. The strategy is demonstrated on two diffusion couples, Ti/Ti-7.58Al-4.97Mo and Ti-5.04Al/Ti-1.52Mo, by surveying the spectrums of microstructural and mechanical characteristics created through an appreciation of the β-to-α phase transformation with such microanalysis techniques as electron probe microanalysis, electron backscatter diffraction analysis, and nanoindentation. The examined microstructural characteristics and mechanical properties reveal the variation of phase, morphology, and microhardness based on the changes of the compositions of the overall alloys and the individual phases in these near-β Ti alloys.

In this study, the deformation behavior of a Ti-40Al-10V (at.%) alloy within β single phase field was examined by means of isothermal compression at 1300 °C under strain rates of 2 s⁻¹, 0.2 s⁻¹, and 0.02 s⁻¹, as well as its effect on the subsequent β→α transformation. The results showed that the alloy behaved steady-state flow with dislocation creep as the predominant rate-controlling process. Dynamic recrystallization (DRX) evidently occurred during deformation, and its volume fraction was dramatically increased so that at the lowest strain rate (0.02 s⁻¹), a full-DRX β structure was obtained. The preferentially dynamic migration of grain boundaries with orientation was demonstrated to be the major DRX mechanism. The texture was characterized by a + double-fiber at 2 s⁻¹, but gradually transformed into a simple rotated cube orientationunder 0.02 s⁻¹, accompanied by a decreasing texture intensity. During the subsequent β→α transformation, two types of α morphology wereproduced with evident variant selection, namely, the Widmannstatten colony and martensitic laths. Texture simulation revealed that the α texture was solely determined by parent β texture, despite of the variant selections.

The effect of the changing of the local composition of the β matrix on the precipitation of the α phase has been investigated by electron backscatter diffraction (EBSD) to obtain more insight in the nucleation and variant selection of these α plates based on the Ti‐5.04Al/Ti‐1.52Mo (at.%) diffusion couple. The results showed that the composition gradient was formed from one side of the diffusion couple to another side after diffusion annealing. Followed by a secondary heat treatment process, it was found for the first time that all 12 variants formed in a single β grain in the diffusion zone in the Ti‐5.04Al/Ti‐1.52Mo diffusion couple, which indicated that the changing of the local composition of the β matrix significantly weakened the α variants selection behavior.

The atomic mobility for the bcc phase of the Ti-Al-Mo ternary system was developed by critical assessment of the experimental diffusion data by using the DICTRA software. The results shown the calculated diffusion coefficients presented the good agreements by the comprehensive comparisons with the experimental diffusion coefficients. The developed Ti-Al-Mo ternary atomic mobility was then subsequently validated by appropriate prediction of the interdiffusion behavior with comparison of the diffusion-couple experiments in the literature.