**2. Materials and Methods**

#### *2.1. Sample Preparation*

The experimental materials—gas-atomized 17-4PH SS powders—were provided by Nantong Jinyuan Intelligence Manufacturing Technology Co. Ltd (Nantong, China). The particle size range of the powders was 15–53 µm, with an average diameter of 32.85 µm, and the standard deviation was 13 µm (Figure 1a). The scanning electron microscopy (SEM) image shows that the powder (Figure 1b) is almost spherical, making it conducive to SLM forming. The chemical composition of the 17-4PH SS powder is shown in Table 1. The SLM-ed cubic 17-4PH steel with dimensions of 15 <sup>×</sup> <sup>15</sup> <sup>×</sup> 15 mm<sup>3</sup> was fabricated in a nitrogen atmosphere. SLM equipment (SLM-100, Han's Laser Co. Ltd, Shenzhen, China) containing a 200 W fiber laser was used for this experiment. The laser power used for the SLM process was 180 W with a scanning speed of 800 mm/s, and the layer thickness was about 0.03 mm. During the SLM process, the scanning directions for the adjacent forming layers differed by 67◦ . Part of the SLM-ed samples was selected for a 0.5 h solution treatment at 1040 ◦C in a muffle furnace and then air-cooled to 550 ◦C. After that, the samples were aged for 4 h and then air-cooled to room temperature. The oxide layers on the sample surfaces were removed with 80-mesh sandpaper and then cleaned in an ethanol ultrasonic bath for 15 min. Through the use of the Archimedes method, the SLM-ed parts had a density of approximately 99.8%.


**Table 1.** Chemical composition of 17-4PH SS powder (wt %).

**Figure 1.** (**a**) Histogram of the powder's equivalent diameter and (**b**) representative powder image. **Figure 1.** (**a**) Histogram of the powder's equivalent diameter and (**b**) representative powder image.

#### **Table 1.** Chemical composition of 17-4PH SS powder (wt %). *2.2. Laser Processing*

**Fe Cr Ni Cu Mn Nb Si O C P S**  balance 17.01 4.69 4.03 0.59 0.34 0.26 0.05 0.04 0.012 0.007 *2.2. Laser Processing*  After the heat treatment, the samples were textured by a femtosecond laser. The schematic diagrams for the laser treatment are shown in Figure 2. A 520 nm femtosecond laser (Spectra-Physics Spirit HE 1040-30-SHG, Boston, USA) with a pulse width of 300 fs at a 250 kHz pulse repetition frequency was focused onto the sample surface by an F-theta lens with a focal spot size of 16 μm in diameter. Before laser treatment, the SLM-ed metal After the heat treatment, the samples were textured by a femtosecond laser. The schematic diagrams for the laser treatment are shown in Figure 2. A 520 nm femtosecond laser (Spectra-Physics Spirit HE 1040-30-SHG, Boston, MA, USA) with a pulse width of 300 fs at a 250 kHz pulse repetition frequency was focused onto the sample surface by an F-theta lens with a focal spot size of 16 µm in diameter. Before laser treatment, the SLM-ed metal surfaces were pretreated with 80-mesh sandpaper. The optimized processing parameters used for laser treatment are shown in Table 2. The laser processing experiments were conducted both in air and argon atmospheres. To obtain SH surfaces, the laser textured samples were placed on a heated plate to be annealed at 110 ◦C for 2.5 h. Anhydrous ethanol was dripped onto the surface every 30 min during the annealing process.

**Figure 2.** Schematic illustrating the laser surface treatment of the 17-4PH SS.

**Table 2.** Laser processing parameters used in this study.

