Titan g2 60 300 chemistem

As-extruded Zn-0.8Li alloys were cut into 1 mm thickness disk followed by grounding and polishing with 0.25 µm diamond slurry. Polished samples were etched with 4% HNO₃/alcohol solution for 5-10 s and pictured by a scanning electron microscopy (Hitachi S-4800, Japan). An X-ray diffractometer (XRD, Rigaku DMAX 2400, Japan) was used to examine the intermetallic phases with scanning range from 10° to 90° at a scan rate of 2° min⁻¹ and step of 0.02°. Polished samples were further processed into 60 µm thickness, followed by punching into 3 mm diameter disks, and ion-beam milling using Gatan PIPS 691 with 10 KeV at −25 °C to −30 °C. Samples were plasma cleaned by Gatan SOLARUS 950 before visualized under a high-resolution high-angle annular dark-field mode (HAADF) at 300 kV using a scanning transmission electron microscopy (FEI Titan G2 60–300 ChemiSTEM).

For HAADF-STEM the samples were polished the slices to 50-70 μm, punched to discs with 3 mm in diameter, and then ion-beam milled using Gatan PIPS 695 at approximately −70 °C. Atomic-resolution HAADF-STEM images and EDS maps were acquired from a FEI Titan G² 60–300 ChemiSTEM operating at 120 kV, equipped with a Cs probe corrector and a Super-X EDS with four windowless silicon-drift detectors. A convergence semi-angle of 15 mrad, collection semi-angle of 45–262 mrad and spot size 9 were used. The count rate is in the range of 180 to 500 cps when acquiring atomic-resolution EDS maps. HAADF-STEM image simulations were conducted using xHREM software. The atomic-resolution HAADF-STEM images were Fourier filtered using Gatan DigitalMicrograph. The atomic-resolution EDS maps were appropriately adjusted for brightness, contrast and gamma value in Esprit software, without any other manipulations.

Thin specimens for TEM and HAADF-TEM observation were prepared by mechanical polishing from 500 μm to 60–80 μm, punching into 3 mm diameter discs, and ion-beam milling using Gatan 695. TEM was carried out on FEI Tecnai G² F20. HAADF-STEM and EDS were performed on FEI Titan G² 60–300 ChemiSTEM. Microstructure and crystallographic orientations were analyzed by TKD-EBSD on SEM (JEOL JSM-7800) equipped with an HKL-EBSD system using a step size of 0.09 μm. The sample preparation process for TKD-EBSD mapping was similar to that for TEM. Electron channeling contrast image and EDS maps were recorded on Zeiss Auriga SEM-FIB. The surface suitable for electron channeling contrast imaging was sputter-cleaned with an argon gun Gatan 697. Because precipitates are invisible on the surface of corroded regions, samples were re-etched in an acetic picral solution (2 ml acetic acid + 1 g picric acid + 2 ml of H₂O + 16 ml of ethanol) to show the second phase. In-situ corrosion process and corrosion morphology were observed under a stereo optical microscope (Keyence VHX 2000) to obtain 2D and 3D images. The chemical states of corrosion products were determined by XPS (ESCALAB250Xi, Thermo Fishes Scientific, USA) using Al K_α X-ray corresponding to 1486.71 eV photons.