# High-Pressure Sensors Based on Laser-Manufactured Sintered Silicon Carbide
## 2 Materials and Methods  
### Sintered SiC Laser Processing  
Sintered SiC samples (BC-4 SiC, Bettini Textile Division, LC, Italy) used in this work were obtained through dry molding process of high-purity SiC powder. All cylindrical samples, see Figure 1, have a diameter of 5 mm and 2 mm in height. Table 1 summarizes their main characteristics. Figure 1: Sintered SiC samples. All the laser treated samples had a diameter of 5 mm and 2 mm in height. A ns-pulsed fiber Yb:YAG laser source (1064 nm, 30 W, mod. YLP-RA30-1-50-20-20, by IPG Photonics, MI, Italy), with a galvanometric scanning head (by LASIT SpA, NA, Italy) equipped with a flat-focusing F-Theta lens (by LINOS, QIOPTIQ, Goettingen, Germany) with focal length of 160 mm has been used for S-SiC processing. Table 2 summarizes the main characteristics of the laser-treatment apparatus. Preliminary tests were conducted at scanning speeds between 500 and 2000 mm/s, at maximum light power (minimum repetition rate of 30 kHz). In order to evaluate the influence of the process on the manufacturing, three different scanning strategies have been verified: LINE, NET and CROSS, whose meaning is clarified with the scheme reported in Figure 2. High-resolution images of treated samples by scanning electron microscopy (SEM) are illustrated in Figure 3. The smoothest surface was obtained by means of the CROSS strategy at a scan-speed of 1000 mm/s. The other strategies show surfaces with higher levels of damage as well as a higher roughness. Indeed, high scanning speeds (2000 mm/s) do not allow to obtain a uniform surface remaining visible the effect induced by each laser-pulse. Conversely, at lower scan-speed smoother surfaces are gained thanks to a better overlapping of laser pulses. Based on the preliminary investigation, S-SiC samples were laser treated according to the process parameters' combination reported in Table 3. Laser processing was performed in order to ablate each S-SiC cylinder realizing the desired diaphragm diameter and thickness. A picture of an example of laser-processed sample is reported in Figure 4a. In this sample, a 3 mm in diameter hole was realized up a depth of 1.9 mm, hence a membrane 100 \(\upmu\)m thick, with a removal rate of about 3.1 mg/min, which is to be considered for micromachining operations [20; 40]. Moreover, a digital microscope (Hirox KH8700, River Edge, NJ, USA) was used to analyze the morphology of laser-treated regions. The 2D profile reconstruction of treated sample is shown in Figure 4a (bottom). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Characteristics** & **Value** & **Unit** \\ \hline Composition & SiC & 99.6 & \% wt \\  & B4C & 0.6 & \% wt \\ \hline Diameter & \(5\pm 0.2\) & mm \\ Height & \(2\pm 0.2\) & mm \\ Density & 3.4 & g cm\({}^{-3}\) \\ Hardness & \(26.0\pm 0.3\) & GPa \\ Flexural strength & 530 & MPa \\ Elastic modulus & 400 & GPa \\ Compressive strength & 2200 & MPa \\ Fracture toughness & 4 & MPa m\({}^{1/2}\) \\ Thermal conductivity & 110 & W K\({}^{-1}\) m\({}^{-1}\) \\ Max use temperature & 1300 & \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main characteristics of Sintered Silicon Carbide (S-SiC) samples used in this work. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristics** & **Value** & **Unit** \\ \hline Wavelength & 1064 & nm \\ Pulse width & 50 & ns \\ Repetition rate & 30–80 & kHz \\ Pulse energy (30 kHz) & 1 & mJ \\ \hline Beam quality & TEM & 00 \\ M\({}^{2}\) & 1.2–1.5 & \\ \hline Focused beam diameter & 80 & \(\upmu\)m \\ Scan area & \(100\times 100\) & mm\({}^{2}\) \\ Max scan speed & 5000 & mm s\({}^{-1}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main characteristics of the laser system used for S-SiC treatments. _Appl. Sci._**2020**, _10_, 7095  
Figure 3: Scanning electron microscopy (SEM) images of surfaces morphology of laser-processed samples with a pulse frequency of 30 kHz and 20 repetitions. (**a**) 2000 mm/s, LINE strategy; (**b**) 1000 mm/s, NET strategy; (**c**) 1000 mm/s, CROSS strategy.