Em res102

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 material used in this study was the 25CrMo4 steel supplied by the CRRC Industrial Academy Co., Ltd. The original microstructure of the steel is shown in Figure 1a, and the chemical composition, as shown in Table 1, was provided by the manufacturer. Compressed specimens were prepared in accordance with ASTM E209 [31 ]. Cylindrical specimens were machined with a diameter of 10 mm and a height of 15 mm. Isothermal compression tests were performed on Gleeble-3800 thermal simulator at four different temperatures (950, 1000, 1050, and 1100 °C) under different strain rates (0.01, 0.1, 0.5, and 1 s⁻¹). As shown in Figure 1b, the specimens were heated to compression temperatures at a heating rate of 20 °C/s and held for 3 min, and the temperature of the sample was precisely controlled by a thermocouple. The specimens were compressed to a true strain of 0.8 and then quenched by water immediately.
Figure 1c,d shows the sampling position and the compressed specimens, respectively. The hot deformed specimens were sectioned along the longitudinal compression axis. Then the sections were mechanically polished with sandpaper and polished by Ion thinner (Leica EM RES102 from German) at 2 kv for 4 h. EBSD was measured by scanning electron microscope (Hitachi SU3500 from Japan) with a scan step size of 0.35 μm. HKL Channel5 software was used for the experimental data analysis.

Thin foils for STEM observations were prepared by a conventional method that includes mechanical polishing of the sample back and then ion-beam milling. The ion-beam milling was carried out using argon ion milling (Leica EM RES102) with an acceleration voltage of 5 kV until a hole was made. Finally, low-voltage (0.8 kV) milling was carried out to reduce the irradiation-damaged layers.