Seminaire Julia Pürstl, vendredi 19 septembre 11h : "Oxygen-Guided Phase Evolution in Metastable Ti–50Nb Systems"
Salle des séminaires de l'Im2np, campus de Saint-Jérôme, 1er étage Bâtiment Poincaré
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Julia Pürstl
Materials Department, University of California, Santa Barbara, 93106, CA, USA
Oxygen-Guided Phase Evolution in Metastable Ti–50Nb Systems
The development of refractory high-performance alloys traditionally requires costly oxygen-free production processes, as oxygen has historically been associated with grain boundary embrittlement and detrimental secondary phase formation. However, recent observations in Ti-containing refractory multi-principal element alloys suggest that controlled oxygen incorporation can enhance both strength and ductility, opening pathways toward more sustainable alloy production.
The observed improvements in mechanical properties have previously been linked to oxygen-induced nanoscale chemically ordered domains, which facilitate enhanced dislocation cross-slip. Given the emerging evidence that these nanodomains influence multiple physical phenomena, it becomes essential to systematically investigate their evolution and transformation pathways under different external stimuli. Our present work investigated nanodomain evolution under both thermal annealing and mechanical loading in a model bcc Ti–50Nb–1 at% O alloy, using complementary TEM, in-situ 4D-STEM, and μ-Laue diffraction techniques.
Under thermal processing, the precursor nanodomains transform into orthorhombic O′, α″, and hcp α phases, following the bcc–hcp transformation pathway. The phase landscape is thus altered in a manner not accessible in oxygen-free alloys, and the ensuing oxygen-stabilized microstructures enhance strength and modify dislocation activity. Within the established energy landscape, we further explore to which extent such transformations could also be triggered by externally applied stress, similar to superelastic β-Ti alloys.
Our findings establish that interstitial oxygen can access complex transformations and refined microstructures not accessible in oxygen-free alloys, while simultaneously enhancing the performance of the model Ti–Nb system. This demonstrates the potential for controlled oxygen incorporation to improve refractory alloy performance, paving the way for more sustainable production processes.
The observed improvements in mechanical properties have previously been linked to oxygen-induced nanoscale chemically ordered domains, which facilitate enhanced dislocation cross-slip. Given the emerging evidence that these nanodomains influence multiple physical phenomena, it becomes essential to systematically investigate their evolution and transformation pathways under different external stimuli. Our present work investigated nanodomain evolution under both thermal annealing and mechanical loading in a model bcc Ti–50Nb–1 at% O alloy, using complementary TEM, in-situ 4D-STEM, and μ-Laue diffraction techniques.
Under thermal processing, the precursor nanodomains transform into orthorhombic O′, α″, and hcp α phases, following the bcc–hcp transformation pathway. The phase landscape is thus altered in a manner not accessible in oxygen-free alloys, and the ensuing oxygen-stabilized microstructures enhance strength and modify dislocation activity. Within the established energy landscape, we further explore to which extent such transformations could also be triggered by externally applied stress, similar to superelastic β-Ti alloys.
Our findings establish that interstitial oxygen can access complex transformations and refined microstructures not accessible in oxygen-free alloys, while simultaneously enhancing the performance of the model Ti–Nb system. This demonstrates the potential for controlled oxygen incorporation to improve refractory alloy performance, paving the way for more sustainable production processes.
