Ivas 3

The elemental compositions of the alloys were characterized by APT using a Cameca LEAP^TM 5000XR instrument. APT samples were prepared in a FIB workstation by annular milling, where the current was gradually decreased with decreasing specimen diameter. The last milling parameters used were 5 kV and 41 pA, followed by 2 kV and 23 pA. APT data were collected in high-voltage pulsing mode at 15% pulse fraction and a detection rate of 0.2%, under a high vacuum of around 3 × 10⁻¹¹ mbar, at a temperature of 60 K. The Cameca integrated visualization and analysis software IVAS 3.8.4 was used for data analysis and three-dimensional atom map reconstruction. The 1D compositional profiles were obtained from 5-nm-diameter cylinders with a bin width of 0.2 nm.

The synchrotron X-ray diffraction (SXRD) of the samples at room temperature was collected in Advanced Photon Source (APS, λ = 0.1173 Å), USA. The elements mapping and the microstructure orientation of the samples were measured by using a scanning electron microscope (SEM, Zeiss Geminisem 500), and an electron backscattering diffraction device (EBSD, TESCAN MIRA 3 LMH SEM, and Symmetry EBSD). The brightfield images, SAED, and high-resolution transmission electron microscopy (HRTEM) were conducted at FEI Tecnai F30 transmission electron microscopy (TEM). The HAADF-STEM and ABF-STEM images were obtained on ARM 200CF (JEOL, Tokyo, Japan) transmission electron microscope operated at 200 kV and equipped with double spherical aberration (Cs) correctors. CAMECA Instruments LEAP 5000XR was used for the APT characterizations. The data were collected in voltage mode at a specimen temperature of 50 K, a pulse repetition rate of 200 kHz, a pulse fraction of 15%, and an ion collection rate of 0.5% per-field evaporation pulse. The APT data was reconstructed using Cameca IVAS 3.8.4, and the reconstruction was calibrated using crystallographic elements retained in the data as represented by spatial distribution maps. The lattice mismatch of the two phases is based on the following formula (2): $\mathrm{\Delta }=\frac{a_L-4a_{\alpha }}{a_L}\times 100\%$

Microstructural characterization was performed using back-scattered electron (BSE) imaging in FEI Nova-NanoSEM 230^TM and transmission electron microscopy (TEM) using an FEI Technai G² TF20^TM operating at 200 kV. Chemical composition of the alloy, phases and local regions was determined using energy dispersive spectroscopy (SEM-EDS) and atom probe tomography (APT). Atom probe experiments were performed using a local electrode atom probe (LEAP 3000x HR^®) from Cameca Inc. The TEM foils and the atom probe tips were prepared using Focused Ion Beam (FIB) (FEI Nova 200 NanoLab). All atom probe experiments were conducted in the temperature range of 40–60K, using a voltage evaporation mode with 0.5–1.0% evaporation rate and pulsing voltage maintained to 20% of the steady-state voltage at a frequency of 200 kHz. Raw data from the atom probe experiments were analyzed using Cameca’s IVAS 3.6.8^® (Integrated Visualization and Analysis Software).

To analyze the microstructure of the material after processing, pieces were cut and metallographically polished in stages. Final mirror surface finish was achieved by 0.02 µm colloidal silica gel VibroMet^TM polishing. The crystal orientations and elemental composition were characterized by electron backscattered diffraction (EBSD) and energy dispersive spectroscopy (EDX), respectively, in a FEI Nova Nano scanning electron microscope (SEM). Lift-out samples for transmission electron microscopy (TEM) and atom probe tomography (APT) were prepared using an FEI Nova 200 dual beam focused ion beam (FIB). TEM analysis was conducted using an FEI Tecnai F20 operated at 200 kV fitted with a STEM-EDS detector. To measure the composition, energy dispersive spectroscopy (Super-X system) equipped on an FEI-TITAN G2 TEM microscope was used in the HAADF STEM mode operating at 300 kV and the results were analyzed with FEI’s ES vision software version 6. The APT experiment was performed with a local electrode atomprobe (LEAP 3000X) with a target evaporation rate of 0.5% per pulse at 45 K. APT data reconstruction and quantitative analysis were performed using a CAMECA visualization and analysis software (IVAS) 3.6.8.

An instrument called Cameca LEAP 3000X HR was employed to carry out the atom probe tomography analysis for the cWY alloy. The related test conditions include an ultrahigh vacuum of about 2.5 × 10⁻¹¹ torr, an ultralow test temperature of 80 K, and a target evaporation rate of 3 ions for 1000 pulses on average in high-voltage pulsing mode at a 15% pulse fraction. A dual-beam FEI Helios 600 was used to prepare the specimens for the test via the focused ion beam milling. The CAMECA integrated visualization and analysis software IVAS 3.6.8 was used for three-dimensional atomic reconstruction and data processing.