## 2 Ultrasonic Testing of Materials  
Modern machines and vehicles increasingly use components made of titanium. Therefore, the research was conducted on the material Ti6 Al4V, both made by additive manufacturing technology (Ti6 Al4V-AM bars manufactured by laser bed fusion (LPBF) method) and conventionally (drawn rod--Ti6 Al4V). Both materials made with different technologies had similar densities. The density for the material made with additive manufacturing technology equals 4.43 g/cm\({}^{3}\) and the density for the material made with conventional methods was 4.40 g/cm\({}^{3}\). LPBF-made Ti6 Al4V bars were manufactured using an SLM 280 2.0 machine (SLM Solutions Group AG, Lubeck, Germany) and SLM Solutions Ti6 Al4V ELI (Grade 23) powder with a powder size distribution of 20-63 \(\upmu\)m. Bars were printed vertically using process parameters provided by the powder and machine supplier, i.e., layer height of 60 \(\upmu\)m, laser power of 350 W, scanning speed of 1100 mm/s, hatch distance of 0.12 mm, and stripe length of 10 \(\upmu\)m. LPBF-made Ti6 Al4V bars were tested in as-built conditions. A rod with a diameter of 25 mm and three different thicknesses (10, 25 and 40 mm) was used. This diameter was selected taking into account the ultrasonic heads used in the laboratory and industrial conditions--the possibility of generating a beam of ultrasonic wave in the tested material. Heads with frequencies from 2 to 20 MHz and a maximum transducer diameter of 12 mm were selected. The basic parameters of the ultrasonic heads used in the study, as well as the selected values of the propagating wave beam in the material, are summarized in Tables 1 and 2. The diameter of the ultrasonic wave beam for the selected heads was determined based on the relationship:  
\[B=2\cdot s\cdot tg\left(arc\,\sin\left(k\cdot\frac{c}{f\cdot 0.97\cdot D} \right)\right) \tag{1}\]  
where:  
\(B\)--beam diameter mm,  
\(s\)--distance from the ultrasonic transducer mm,  
\(k\)--coefficient of amplitude decrease across the beam width by 6 dB (\(k\) = 0.5) and by 10 dB (\(k\) = 0.87),  
\(c\)--wave velocity in the material m/s,  
\(f\)--head frequency 1/s,  
\(D\)--transducer diameter mm. The \(k\) factor is the coefficient of amplitude decrease across the width of the beam. In industrial tests, \(k\) = 0.5 is assumed, which means a 6 dB decrease in amplitude value. In more accurate laboratory tests, \(k\) = 0.87 can be assumed, which means a decibel drop of 10 dB in the amplitude value. The data in Tables 1 and 2 allowed us to calculate the diameter of the ultrasonic wave beam for all tested samples and all used ultrasonic transducers. The results of calculations using relation (1) are shown in Table 3.  
It can be seen from Table 3 that the largest beam diameter was 20.4 mm for the additively manufactured specimens, which means that the specimen diameter of 25 mm was chosen correctly. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Parameter/Head Name** & **MB2S** & **KD1-6** & **KD0.8-3** & **MB4S** & **KD4-12** & **KD6-16** & **GE20** \\ \hline
**Number of Ultrasonic** & **1** & **2** & **3** & **4** & **5** & **6** & **7** \\ \hline frequency MHz & 2.00 & 2.40 & 2.75 & 4.00 & 12.5 & 14.00 & 20.00 \\ transducer diameter mm & 10.00 & 12.00 & 12.00 & 10.00 & 6.00 & 3.00 & 3.00 \\ effective diameter of the beam mm & 9.70 & 11.64 & 11.64 & 9.70 & 5.82 & 2.91 & 2.91 \\ mean wave velocity in & 5418 & 5418 & 5418 & 5418 & 5418 & 5418 & 5418 \\ wavelength mm & 2.71 & 2.26 & 1.97 & 1.36 & 0.43 & 0.39 & 0.27 \\ near field mm & 8.00 & 14.40 & 16.70 & 17.00 & 19.40 & 5.40 & 7.70 \\ decibel drop ratio K & 0.87 & 0.87 & 0.87 & 0.87 & 0.87 & 0.87 & 0.87 \\ sin beam divergence angle & 0.24 & 0.17 & 0.15 & 0.12 & 0.06 & 0.12 & 0.08 \\ divergence angle\({}^{\circ}\) & 14.06 & 9.71 & 8.47 & 6.98 & 3.71 & 6.64 & 4.65 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of the ultrasonic heads used in the study of basic acoustic parameters of Ti6 Al4V manufactured in conventional process.