# Evaluating the Reliability of Powder Bed Fusion for Biomedical Materials: An Experimental Approach
## 2 Materials and Methods
### Physical-Mechanical Measurements  
The experimental research conducted using the methodology described above allowed us to obtain 16 sets of specimens, which were evaluated for their tensile strength, hardness, and roughness characteristics. For each material and SLM process parameter (laser power) as described in Table 4, a minimum number of five specimens were tested. The values presented in the following tables are the mean values. The standard deviation was under 10% from the mean value, with a higher scattering for the specimens manufactured with a low laser power.  
\begin{table}
\begin{tabular}{l c c c c} \hline \multirow{2}{*}{**Material**} & **Laser Power** & **Scanning Speed** & **Layer Thickness** & **Hatch Distance** \\  & **[W]** & **[mm/s]** & **[\(\mu\)m]** & **[mm]** \\ \hline \multirow{3}{*}{Ti} & 100 & & & \\  & 120 & & & \\  & 140 & & 500 & 50 & 0.12 \\  & 160 & & & \\ \hline \multirow{3}{*}{Ti6 AI7 Nb} & 50 & & & & \\  & 70 & & & \\  & 100 & & & & \\  & 160 & & & & \\ \hline \multirow{3}{*}{CoCr} & 70 & & & & \\  & 85 & & 500 & 50 & 0.10 \\ \cline{1-1}  & 90 & & & & \\ \cline{1-1}  & 100 & & & & \\ \hline \multirow{3}{*}{CoCrWMo} & 70 & & & & \\ \cline{1-1}  & 85 & & 500 & 50 & 0.10 \\ \cline{1-1}  & 90 & & & & \\ \cline{1-1}  & 100 & & & & \\ \hline \end{tabular}
\end{table}
Table 4: SLM process parameters to produce testing samples.  
The ultimate tensile strength (R\({}_{\rm m}\)), Young's modulus (E), and Poisson's ratio were measured using the Instron 3366 (10 kN) and Instron 8801 (100 kN) testing machines, along with a unidirectional extensometer (Instron 2620-602; Instron Corporation, Norwood, MA 02062, USA) and a bidirectional extensometer (3560-Epsilon Tech; Epsilon Technology Corp., Jackson, WY 83001, USA). The testing parameters for the Instron equipment were set to a pulling speed of 2 mm/min and 50% humidity at ambient temperature.  
The specimens were designed in accordance with ISO 6892:2019 [43] and were anchored using block supports with square lines of 1-2 mm in dimension. The cross-section of the parts was rectangular (see Figure 1). In some cases, it was challenging to grip the specimens with the extensometer, so a strain gauge technique was used to achieve the most accurate results for determining the elastic constants, particularly the Poisson's ratio. A bidirectional strain gauge (C2A-06-062 LT-120), supplied by VISHAY Micro-Measurements (Wendell, NC 27591, SUA), was used to measure the transverse contraction strain and longitudinal extension strain. These transducers are suitable for a wide range of deformation analyses and were directly connected to the recording device, an Amplifier Spider8.  
Using a Mitutoyo SJ-2010 contact profilometer, the surface roughness of PBF samples was assessed on the top side. Roughness parameters Ra and Rz were calculated in accordance with ISO 4287 [44]. The arithmetical mean of the absolute values of the parameter deviations from the mean profile line is represented by the Ra roughness. The arithmetic mean value of the surface profile's average highest and lowest peaks is denoted by Rz.  
The hardness of the specimens was measured using the Vickers method with the Wilson Tukon 1102 equipment. Surface preparation involved wet grinding with silicon carbide disks and abrasive paper up to 600 grit. Micro-indentation hardness tests were conducted by applying a force of 9.81 N across the surface with a dwell time of 5 s, following the ASTM E384-17 standard [45]. A total of 15 successive trials were performed on the parts of the specimens that had previously been used for tensile tests.