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DOE OSTI2020

Materials Data on Ti3Al by Materials Project

Ti3Al is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ti is bonded to eight equivalent Ti and four equivalent Al atoms to form TiTi8Al4 cuboctahedra that share corners with four equivalent AlTi12 cuboctahedra, corners with fourteen equivalent TiTi8Al4 cuboctahedra, edges with six equivalent AlTi12 cuboctahedra, edges with twelve equivalent TiTi8Al4 cuboctahedra, faces with four equivalent AlTi12 cuboctahedra, and faces with sixteen equivalent TiTi8Al4 cuboctahedra. There are a spread of Ti–Ti bond distances ranging from 2.82–2.93 Å. There are two shorter (2.84 Å) and two longer (2.88 Å) Ti–Al bond lengths. Al is bonded to twelve equivalent Ti atoms to form AlTi12 cuboctahedra that share corners with six equivalent AlTi12 cuboctahedra, corners with twelve equivalent TiTi8Al4 cuboctahedra, edges with eighteen equivalent TiTi8Al4 cuboctahedra, faces with eight equivalent AlTi12 cuboctahedra, and faces with twelve equivalent TiTi8Al4 cuboctahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ti3Al by Materials Project

Ti3Al is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a distorted body-centered cubic geometry to four equivalent Ti and four equivalent Al atoms. All Ti–Ti bond lengths are 2.80 Å. All Ti–Al bond lengths are 2.80 Å. In the second Ti site, Ti is bonded in a distorted body-centered cubic geometry to eight equivalent Ti and six equivalent Al atoms. All Ti–Al bond lengths are 3.23 Å. Al is bonded in a distorted body-centered cubic geometry to fourteen Ti atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ti3Al by Materials Project

Ti3Al is Magnesium-derived structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded to twelve Ti atoms to form TiTi12 cuboctahedra that share corners with six equivalent TiTi12 cuboctahedra, corners with twelve equivalent AlTi6Al6 cuboctahedra, edges with eighteen TiTi12 cuboctahedra, faces with two equivalent AlTi6Al6 cuboctahedra, and faces with eighteen TiTi12 cuboctahedra. There are six shorter (2.86 Å) and six longer (2.93 Å) Ti–Ti bond lengths. In the second Ti site, Ti is bonded to nine Ti and three equivalent Al atoms to form TiTi9Al3 cuboctahedra that share corners with eighteen equivalent TiTi9Al3 cuboctahedra, edges with six equivalent AlTi6Al6 cuboctahedra, edges with twelve TiTi12 cuboctahedra, faces with six equivalent AlTi6Al6 cuboctahedra, and faces with fourteen TiTi12 cuboctahedra. All Ti–Ti bond lengths are 2.93 Å. All Ti–Al bond lengths are 2.86 Å. Al is bonded to six equivalent Ti and six equivalent Al atoms to form AlTi6Al6 cuboctahedra that share corners with six equivalent AlTi6Al6 cuboctahedra, corners with twelve equivalent TiTi12 cuboctahedra, edges with six equivalent AlTi6Al6 cuboctahedra, edges with twelve equivalent TiTi9Al3 cuboctahedra, faces with six equivalent AlTi6Al6 cuboctahedra, and faces with fourteen TiTi12 cuboctahedra. All Al–Al bond lengths are 2.93 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Mechanisms of Ti 3 Al precipitation in hcp α -Ti

Here, nucleation and growth of Ti3Al α( 2 ) ordered domains in alpha-Ti-Al-X alloys were characterised using a combination of transmission electron microscopy, atom probe tomography and small angle X-ray scattering. Model alloys based on Ti-7Al (wt.%) and containing O, V and Mo were aged at 550 °C for times up to 120d and the resulting precipitate dispersions were observed at intermediate points. Precipitates grew to around 30nm in size, with a volume fraction of 6-10% depending on tertiary solutes. Interstitial O was found to increase the equilibrium volume fraction of α 2 , while V and Mo showed relatively little influence. Addition of any of the solutes in this study, but most prominently Mo, was found to increase nucleation density and decrease precipitate size and possibly coarsening rate. Coarsening can be described by the Lifshitz-Slyozov-Wagner model, suggesting a matrix diffusion-controlled coarsening mechanism (rather than control by interfacial coherency). Solutionising temperature was found to affect nucleation number density with an activation energy of E f = 1.5 +/- 0.4 eV, supporting the hypothesis that vacancy concentration affects α 2 nucleation. The observation that all solutes increase nucleation number density is also consistent with a vacancy-controlled nucleation mechanism.

36 MATERIALS SCIENCE↗