Abstract
Titanium alloys owe their superior fatigue performance to a lack of extrinsic nucleation sites for cracking, but this also results in difficulty in developing fine, 10 nm scale precipitates to provide fatigue strength. Conventional Ti alloys used for large components such as jet engine discs must instead develop a hierarchical microstructure through successive waves of nucleation. Here we show that intermediate temperature deformation can result in the nucleation of nanoscale hcp α precipitates in between large μm thick α plates, and observe the precipitation of these in situ in the TEM using 4D-Scanning Transmission Electron Microscopy (4D-STEM) alongside the accompanying partially-relaxed transformation strain fields. This results in an improvement in the high cycle fatigue strength of the material by 95 MPa, to around 920 MPa in un-notched high cycle fatigue at 106 cycles, or 200 MJ kg−1, which is among the highest of all structural materials.
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Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request, a.ackerman14@imperial.ac.uk.
Code availability
Code used for data analysis of the 4D-STEM data can be accessed via GitHub at cophus/py4DSTEM.
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Acknowledgements
The authors acknowledge funding from EPSRC (grant EP/K034332/1), Rolls-Royce plc and Imperial College. The assistance of Dr. Alexander Knowles in discussions surrounding the focused ion preparation process is greatly appreciated. We are grateful to the Electron Physical Sciences Imaging Centre (ePSIC) and Diamond Light Source for access to E02, proposal number EM18190. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors acknowledge use of characterisation facilities within the David Cockayne Centre for Electron Microscopy, Department of Materials, University of Oxford, alongside financial support provided by the Henry Royce Institute (Grant ref EP/R010145/1).
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A.K.A. and D.D. designed the study. A.A. completed thermomechanical testing, mechanical testing and data analysis, as well as SEM. B.S. and C.O. analysed the 4D-STEM data. M.D. performed TEM experiments. P.K. performed TKD experiments whilst A.K.A. analysed the resultant data.
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Ackerman, A.K., Savitzky, B.H., Ophus, C. et al. Defect-assisted refinement of nanoscale alpha in titanium alloys. Commun Mater (2026). https://doi.org/10.1038/s43246-026-01096-y
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DOI: https://doi.org/10.1038/s43246-026-01096-y
