Tenupol 5

The microstructure of both alloys was investigated using scanning electron microscope (SEM) FEI Quanta 200F (Hillsboro, OR, USA), equipped with EDAX energy-dispersive X-ray spectroscope (EDS) and EDAX electron backscatter diffraction (EBSD) camera (EDAX, Pleasanton, CA, USA), and transmission electron microscope (TEM) Jeol 2200FS (Tokyo, Japan) equipped with Gatan EDS. Samples for SEM were prepared by mechanical polishing with decreasing particle size down to 50 nm. Samples prepared for EBSD were subsequently ion-polished using Leica EM RES102 (Wetzlar, Germany) ion-beam milling system. Samples for TEM were mechanically thinned and subsequently electrochemically polished using Struers Tenupol 5 (Cleveland, OH, USA) in a solution of perchloric acid and methanol. The crystallographic texture was measured by X-ray diffractometer (XRD) PANalytical XPert MRD (Malvern, UK). Cu_K radiation and polycapillary in the primary beam were employed during the measurements. Pole figures from 6 reflections, ( $0002$ ), $10\overline{1}0$ , ( $10\overline{1}1$ ), ( $10\overline{12}$ ), ( $10\overline{1}3$ ), and ( $11\overline{2}0$ ), were measured. Inverse pole figures were calculated using the MTEX toolbox implemented in the Matlab 2020a software [24 (link)].

The materials used in this study are commercially pure Ti (99.999 at.%), and such a low level of impurity was found to have a negligible effect on HCP-FCC phase transition^{32 (link)}. The as-received materials show an equiaxed grain structure with the grain size ranging from 20 to 30 μm. Small bars with a dimension of 20 × 10 × 1 mm were cut from the as-received plates, and then were cold-rolled at room temperature for multiple times with a thickness reduction of 0.5 mm per pass to reach a thickness reduction of 50%.
The TEM specimens were prepared using a double-jet electrolytic polisher (Struers TenuPol-5) and a solution of 60% methanol +35% butanol +5% per chloric acid at −30 °C with an applied voltage of 30 V. TEM and high-resolution TEM observations were performed using a FEI Titan G2 60–300 Cs-corrected microscope operated at 300 kV.

Cross-sectional slices with a thickness of ~100 μm were cut from the rods and ingots. These slices were ground to a final thickness of about 50 μm and small disks with a diameter of 3 mm were punched out. In the current study, both twin-jet electrolytic thinning and ion-milling were employed to prepare the TEM specimens. The results shown in the publication were all obtained from electrolytically thinned specimens. Twin-jet electrolytic thinning of the TEM specimens was performed in a Struers TenuPol-5 using a solution of 30 ml perchloric acid +175 ml 1-butanol +295 ml methanol at 248 K and a constant voltage of 20 V. After perforation, the TEM specimens were cleaned with ethanol. For ion-milling, the disks were dimpled using a Gatan dimpler grinder (Model 656) until the thickness of the centre reached a value of about 10 μm. The dimpled disks were then ion-milled in a Gatan 691 or Gatan 695 (PIPS II) precision ion polishing system with liquid nitrogen cooling. The disks were first ion-milled at 3.5 kV, 10 mA and an angle of 8 ° up to perforation, then the disks were ion-milled at 3.0 kV, 10 mA and an angle of 4 ° for 20 min. Additionally, the TEM samples were treated in a Fischione plasma cleaner (model 1020) for 10 min to remove possible amorphous layers at the surface, which might form during ion-milling. All TEM specimens were stored in high vacuum prior to TEM observation.