Defect-assisted refinement of nanoscale alpha in titanium alloys

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 μ m 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 10 6 cycles, or 200 MJ kg −1 , which is among the highest of all structural materials.