## 2 Ultrasonic Testing of Materials
For this purpose, 10 measurements of ultrasonic wave parameters were made for 25 mm thick specimens. The amplitudes of the first two pulses obtained from the bottom of the sample were recorded, and then the value of the damping coefficient was determined (Figure 3). The damping coefficient was determined based on the relationship:  
\[\alpha_{f}=\frac{20}{2\cdot h}.log\left(\frac{H_{1}}{H_{2}}\right) \tag{2}\]  
where: \(H_{1}\), \(H_{2}\)--percentage height (the amplitude value) of the first and second pulse from the bottom of the tested element, respectively, \(h\)--thickness of the element. The gain of the ultrasonic wave pulse was also varied in the 1 dB from 20 to 35 dB range. This was the range that allowed us to obtain diagnostically useful ultrasonic longitudinal wave pulses. In this stage of ultrasonic testing, 160 measurements of wave parameters were made for the material Ti6 Al4V-AM (10 measurements for each ultrasonic wave gain). Based on the results, it was concluded that the effect of changing the pulse gain of the ultrasonic longitudinal wave on the damping coefficient is small and does not significantly affect the obtained measurement results. Moreover, this influence will also be negligible during the test of materials and joints made with additive manufacturing technology. Therefore, in the last stage of the acoustic properties study, the damping coefficients for Ti6 Al4V and Ti6 Al4V-AM material were determined. Damping tests were conducted for all three thicknesses of material made by additive manufacturing and conventional technology. As in the earlier stage of ultrasonic testing, relation 2 was used to determine the damping coefficient. For both materials and each ultrasonic head, 20 measurements of this coefficient were made. Due to the high frequency of the wave beam generated by the GE20 ultrasonic transducer, it was not possible to obtain a sequence of return echoes for the 25 and 40-mm-thick material. This high damping of the wave beam causes the lack of imaging of the second pulse of the ultrasonic wave on the screen of the ultrasonic flaw detector. The results of all damping coefficient measurements for Ti6 Al4V and Ti6 Al4V-AM materials, depending on the frequency of the ultrasonic transducer, are shown in Figures 4 and 5. Figure 3: Dependence of the gain of the wave pulse on the attenuation of an ultrasonic wave in a material. An increase in the damping coefficient for the material made with additive manufacturing technology relative to conventional manufacturing technology was noted in each of the tested samples. The largest increase in damping coefficient for the material made with additive manufacturing technology relative to conventional technology was observed for the frequency of 2 MHz and amounted to 68%. However, for the other frequencies of ultrasonic heads, the values of the damping coefficient were at similar levels, regardless of the manufacturing process of the sample. The differences ranged from about 5% to 12%, with the material made by the conventional manufacturing process always having lower  
Figure 4: Dependence of the ultrasonic transducer frequency on damping coefficient for Ti6 Al4V material. Figure 5: Dependence of the ultrasonic transducer frequency on damping coefficient for Ti6 Al4V-AM material. values for this parameter. The detailed differences in the damping coefficient determined for the two tested materials and ultrasonic heads at different frequencies are as follows:  
* MB2S \(\rightarrow\) 67.87%,
* KD1-6 \(\rightarrow\) 9.84%,
* KD0.8-3 \(\rightarrow\) 6.12%,
* MB4S \(\rightarrow\) 11.60%,
* KD4-12 \(\rightarrow\) 12.46%,
* KD6-16 \(\rightarrow\) 4.60%,
* GE20 \(\rightarrow\) 6.67%. The damping coefficient results are similar for the Ti6 Al4V-AM and Ti6 Al4V materials. Nevertheless, higher damping coefficient values were always determined for Ti6 Al4V-AM.