**2. Experimental Details**

The experimental system consists of a 4 kW semiconductor laser (LDM 4000-100, Laserline, Mülheim-Kärlich, Germany), a 6-axis KUKA robot (KR 16-2), a high precision powder feeder, a side powder feeding nozzle, and an inert gas (Ar) protection box.

The substrate was a piece of ductile iron (ISO 1038/JS/500-7) with a size of 100 mm × 50 mm × 15 mm. The powder used in the experiment was Ni-based self-fluxing alloy powder (Wall Colmonoy Corporation, Madison Heights, MI, USA). The chemical compositions of the ductile iron and the powder are listed in Tables 1 and 2, respectively.

**Table 1.** Chemical composition of ductile iron (mass fraction (%)).



**Table 2.** Chemical composition of cladding materials (mass fraction (%)).

Before the experiment, the powder was dried in a vacuum at 100 ◦C for 2 h to remove water vapor adsorbed on the surface. The substrate's surface was polished with sandpaper (180–400 grit sandpaper) and cleaned with acetone. The main process parameters used in the experiments are as follows: laser power of 1.6–2.5 kW, scanning speed of 8 mm/s, powder feeding speed of 20 g/min, gas flow rate of 12 L/min, laser spot diameter of 5 mm, and deposition thickness of 0.2 mm. Table 3 shows the deposition parameters in the experiment. After each cladding layer was completed, each interlayer cooling specimen was cooled to room temperature (about 5 min), and each non-interlayer cooling specimen was cladded without waiting time. The cladding equipment and one of the samples are showninFigure 1.


**Table 3.** Experimental parameters, thickness of layers, and depth of penetration.

The height of the cladding layers was measured by a micrometer. The cross-section of the specimen was cut by a wire-cut electrical discharge machine (EDM, DK7763, CHENGHONG, Jiangsu, China) along a vertical laser path. Metallographic specimens were prepared by mechanical polishing. The polished specimens were etched by a solution (200 mL H2O + 200 mL HCl + 40 g CuSO4). The heat-a ffected zone (HAZ) was etched by a solution (HF and HNO3 1:1 mixing). The microstructures of the powder and the layers were analyzed by optical microscopy (OM, Axio Vert.A1, ZEISS, Oberkochen, Germany), and a scanning electron microscopy (SEM, SIGMA 04-03, ZEISS, Oberkochen, Germany) equipped with an energy-dispersive spectroscopy (EDS). The penetration data in Table 3, which indicate the distance from the deepest position of the substrate's melting part to the surface of the substrate, as schematically illustrated in Figure 2, were also measured by an optical microscopy. Meanwhile, the dilution ratio in Figure 2 is the ratio of penetration to thickness of layers. Phase constitution was identified by X-ray di ffraction (XRD, D/MAX 2500/PC, Neo-confucianism, Tokyo, Japan). The microhardness of the single tracks was measured with a HV-5ACL microhardness tester (HENGYI, Shanghai, China) and a Vickers pyramidal-shaped diamond indenter under the load of 0.5 kg for 15 s of loading.

**Figure 1.** Pictures of the cladding equipment and specimens: (**a**) cladding equipment; (**b**) picture of one specimen.

**Figure 2.** Overview of the cladding.
