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Abstract For decades the poor mechanical properties of Ti alloys were attributed to the intrinsic brittleness of the hexagonal ω-phase that has fewer than 5-independent slip systems. We contradict this conventional wisdom by coupling first-principles and cluster expansion calculations with experiments. We show that the elastic properties of the ω-phase can be systematically varied as a function of its composition to enhance both the ductility and strength of the Ti-alloy. Studies with five prototypical β-stabilizer solutes (Nb, Ta, V, Mo, and W) show that increasing β-stabilizer concentration destabilizes the ω-phase, in agreement with experiments. The Young’s modulus of ω-phase also decreased at larger concentration of β-stabilizers. Within the region of ω-phase stability, addition of Nb, Ta, and V (Group-V elements) decreased Young’s modulus more steeply compared to Mo and W (Group-VI elements) additions. The higher values of Young’s modulus of Ti–W and Ti–Mo binaries is related to the stronger stabilization of ω-phase due to the higher number of valence electrons. Density of states (DOS) calculations also revealed a stronger covalent bonding in the ω-phase compared to a metallic bonding in β-phase, and indicate that alloying is a promising route to enhance the ω-phase’s ductility. Overall, the mechanical properties of ω-phase predicted by our calculations agree well with the available experiments. Importantly, our study reveals that ω precipitates are not intrinsically embrittling and detrimental, and that we can create Ti-alloys with both good ductility and strength by tailoring ω precipitates' composition instead of completely eliminating them. 

Strain-transformable Ti-based alloys are known to display a superior combination of strength, ductility and strain-hardening and attracted considerable interest on recent years. They generally still display, however, a limited yield strength that can be possibly overcome by further precipitation strengthening of the developed systems. In that work, we developed a design strategy to reach a forged dual-phase (α+β) microstructure with TRIP/TWIP properties in a Ti–10V–2Fe–3Al alloy. The results showed an excellent combination of mechanical properties due to the strain-transformable deformed β-matrix. The investigation on the deformation mechanisms in the Ti–10V–2Fe–3Al alloy was accurately performed by means of both in-situ synchrotron XRD, mechanical testing followed by SEM/EBSD mapping and “post mortem” TEM microstructural analyses. Combined Twinning Induced Plasticity (TWIP) and Transformation Induced Plasticity (TRIP) effects were shown to be intensively activated in the alloy. The particular role of stain-induced martensite α″, acting as a relaxation mechanism at the α∕β interfaces, as well as the strong interactions between mechanical twins and primary α nodules were particularly highlighted.