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The mechanisms of lath decomposition and dispersion were hitherto rarely explained due to limited understanding into the heterostructure deformation between two phases and associated interactions. In this work, the lath decomposition and dispersion were systematically investigated in a wide subtransus processing range of 0.001 s−1–1 s−1 and 745 °C–820 °C with the consideration into the heterostructure deformation and associated interactions. The relationship between flowing behavior and microstructure evolution were discussed. Results indicated that the initial buckling of α laths caused high peak strength. The rotation and twist of α laths are helpful to decrease the flow stress, but it caused serious extra deformation and dislocation storage in the β matrix. The lath decomposition dominated by the ablation was greatly contributed by the adiabatic temperature rise (ATR) near boundaries with high energies. The α laths could rotate under low strain rates, and numerous residual laths (RLs) could be obtained. The increment in strain rates to 0.1 s−1 resulted in earlier lath decomposition and softening, as well as to disperse α p particles and homogenize the β matrix. But an overhigh strain rate of ∼1 s−1 caused adiabatic shear bands. The low temperatures are unfavorable to the lath decomposition, while over-high temperatures diminished the extra deformation and ATR. On this basis, a deformation mechanism map for the subtransus processing of lamellae Ti-55531 alloy was established. This investigation sheds deeper insight into the tailoring of microstructure and prediction of flowing behavior for the subtransus processing of lamellae metastable-β Ti alloys. [ABSTRACT FROM AUTHOR]

In this work, an (α + β) TRIPLEX heat treatment process was designed, as well as its impact on the microstructures and high–temperature mechanical properties of 2.5 vol% (TiB + TiC)/Ti–6Al–4Sn–7Zr–1Nb–1Mo–1W–0.2Si (wt.%) was carefully investigated. The results show that the microstructures of heat–treated TMCs consist of the primary α phase (α p) and the transformed β (β t) with a large number of nano–scale secondary α phases (α s). The TRIPLEX heat treatment encourages the effect of structural heredity, causing the residual α p lamellae to develop adequately and even mature into lamellae clusters with the same orientation, which induces a visible strengthening of the variant selection for the α phase. After the TRIPLEX heat treatment, the increase in content and size of silicides is mainly due to the process providing favorable sites and sufficient time for nucleation and growth. The longitudinal axes of some silicides exhibit an approximate 40° angle or parallel arrangement with the β/α p interfaces, which means that the silicides will grow preferentially along a specific orientation to minimize the strain energy. The (α + β) TRIPLEX heat treatment significantly increases the high–temperature strength of the TMCs with no appreciable elongation loss (as–cast TMCs: UTS = 487.6 MPa, EL = 17.4%; HT–4#: UTS = 558.1 MPa, EL = 11.5%). The strength improvement of HT–4 # is mainly related to the combined effects of α p content reduction, α s precipitation, obstruction of dislocations by the β t /α p interface, hetero–deformation strengthening, silicides precipitation strengthening, and α 2 dispersion strengthening. [ABSTRACT FROM AUTHOR]