*2.2. Experimental Calibration*

#### 2.2.1. Materials, Equipment and Plan of Experiment

The experimental part of this study was conducted using the EOS-supplied IN625 powder and an EOSINT M280 LPBF system (EOS GmbH, Munich, Germany) equipped with a 400 W ytterbium fiber laser (beam radius *rf* = 50 μm). The initial temperature of the substrate (build platform) *T0* = 60 ◦C. To design the plan of experiments, the analytical model represented by Equations (1)–(4) was used first. To this end, the following physical properties of an irradiated body: thermal conductivity *k*<sup>0</sup> [22], specific heat *Cp*<sup>0</sup> [23], and electrical resistivity *ρ*<sup>0</sup> [24] need to be calculated, taking into account the effective powder bed density *ϕ*, the latter being the powder morphology and spreading mechanism-dependent:

$$k = k\_0 \times \frac{\varphi}{0.5(3-\varphi)}; \ C\_p = C\_{p0} \times \varphi; \ \rho = 0.696 \times \frac{4}{\varphi} \times \rho\_0 \tag{5}$$

In this work, the density *φ* of IN625 powder spread by a standard EOS metal doctor blade and measured using the encapsulated samples method [25] was found to be close to 60%. Given the preceding, the IN625 alloy properties used for calculations are shown in Table 1. They were taken at room temperature, and it is considered that the preceding layer cools down to 60 ◦C between two scanning runs.

**Table 1.** Physical properties of IN625 powder [26,27].


The temperature distribution map shown in Figure 2 represents an example of calculations using Equations (1)–(5). It corresponds to the following set of LPBF processing parameters: *P* = 270 W, *v* = 1000 mm/s, and *t* = 40 μm applied to IN625 powder (Table 1). From this temperature map, the melt pool width, depth and length are delimited by the alloy melting temperature of 1350 ◦C: *W* = 173 μm, *D* = 89 μm, and *L* = 806 μm, which correspond to the following dimensionless metrics: *D/t* = 2.2 and

*L/W* = 4.7 (since only a single track is modeled, the hatching space *h* is not considered at this stage). This calculation procedure can be repeated for any material and any given set of processing parameters.

**Figure 2.** Melt pool dimensions for IN625 powder when *P* = 270 W, *v* = 1000 mm/s, and *t* = 40 μm; the melt pool width and depth are delimited by the alloy melting temperature.
