Journal
MATERIALS TODAY
Volume 61, Issue -, Pages 11-21Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.mattod.2022.10.026
Keywords
China; FCC Ti; Additive manufacturing; Interstitial strengthening; Mechanical properties
Categories
Funding
- Australia-US Multidisci-plinary University Research Initiative (AUSMURI) program
- Australian Research Council [DP190102243, DP150104719, DE180100440, DP200100940]
- Research Office of The Hong Kong Polytechnic University [P0041361, P0039966]
- Sydney Microscopy & Microanalysis-a core research facility of the University of Sydney
- University's node of Microscopy Australia
- Australian Government under the NCRIS program
- Australian Research Council [DE180100440, DP200100940] Funding Source: Australian Research Council
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An oxygen-rich FCC Ti phase was successfully engineered in a Ti-6Al-4V alloy via additive manufacturing. The presence of this FCC phase significantly increased the local yield strength without sacrificing ductility. Additive manufacturing holds great potential for microstructural design of titanium alloys.
An oxygen-rich face-centred cubic (FCC) Ti phase was engineered in the microstructure of a Ti-6Al-4V alloy via additive manufacturing using laser powder bed fusion. Designated 'C', this oxygen-rich FCC phase has a lattice parameter of 0.406 nm and exhibits an orientation relationship with the parent a0 phase as follows: (000 1)a0//{1 1 1}C, and h1 2 10ia0 //h1 1 0iC. We propose that the formation of the C phase is facilitated by the combined effect of thermal gradients, deformation induced by the martensitic transformation, and local O enrichment. This enables an in-situ phase transformation from the hexagonal close-packed a0 phase to the C phase at elevated temperatures. Our density functional theory calculations indicate that oxygen occupancy in the octahedral interstices of the FCC structure is energetically preferred to corresponding sites in the a0 phase. The in-situ mechanical testing results indicate that the presence of the FCC phase significantly increases the local yield strength from 1.2 GPa for samples with only the a0 phase to 1.9 GPa for samples comprising approximately equal volume fractions of the a0 and FCC phases. No loss of ductility was reported, demonstrating great potential for strengthening and work hardening. We discuss the formation mechanism of the FCC phase and a pathway for future microstructural design of titanium alloys by additive manufacturing.
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