## 2 Experimental  
After electron beam evaporation of tantalum powder, it was deposited onto the aluminum 300-450 \({}^{\circ}\)C substrate. Tantalum powder (product No. 73 MR-0001, lot No. IAM1283 TAM, grain size 5 \(\upmu\)m, \"Inframat Advanced Materials,\" Manchester, ST, USA) was pressed to obtain \(50\times 30\) mm cylindrical briquettes, and before evaporation it was melted in vacuum by electron beam. A flat aluminum (A6, 99.6% Al, \(120\times 280\times 2\) mm, \"Auremo,\" Kiev, Ukraine) plate was used as a substrate, on which a temperature gradient was created in the range of 100-550 \({}^{\circ}\)C using a molybdenum furnace on one side and water cooling on the other.  
The experimental part of the study was carried out on an electron-beam installation under high vacuum of (3.99-5.32) \(\times 10^{-2}\) Pa resulting in coatings without undesired impurities.  
The vacuum system consists of a BH-6 for a vacuum pump, ABII-8 and ZEISS vapor-oil diffusers and a BH-3 booster pump. \(1.33\times 10^{-2}\) Pa vacuum is achieved in the vacuum system within an hour. The system is controlled with an ionization-thermocouple vacuum gauge VIT-2 (BHT-2, \"Mayak,\" Kursk, Russia).  
The unit is equipped with two separate electron beam guns. Each gun has an autonomous power supply and control system, allowing the use of two different electron beams, each with controlled power and beam orientation. Automatic control systems provide continuous maintenance of the electron beam power throughout the cycle.  
The design of the camera ensures independent pumping of air from technological and gun areas, resulting in a stable vacuum of \(10^{-2}\) Pa in the range of the electron beam section, and smooth operation of electronic guns.  
The original material is evaporated from a water-cooled copper crucible (Figure 1). The distance between the evaporator and the substrate is approximately 300 mm. The focused electron beam can evaporate most of the refractory metals, alloys and chemical compounds with adjustable speed, completely eliminating the need of selection the source material based on its melting or evaporation temperature. It should be noted that water-cooled copper crucibles and vacuum processes ensure complete environmental safety and high purity of the steam flow and consequently, of the final product.  
Samples of tantalum coatings (coating thickness of 1 \(\upmu\)m) on aluminum substrate were cut out of three temperature zones (\(t_{\mathrm{Cond}}\) = 300-350 \({}^{\circ}\)C, \(t_{\mathrm{Cond}}\) = 390-420 \({}^{\circ}\)C, and \(t_{\mathrm{Cond}}\)\(\approx\) 450 \({}^{\circ}\)C).  
The surface morphology and elemental composition were studied on a JSM-5610 LV scanning electron microscope equipped with the EDX JED-2201 chemical analysis system (JEOL, Akishima, Japan). Accelerating voltage was 20 keV. The estimated depth range of electrons does not exceed 0.98 \(\upmu\)m.  
For determining the quantitative composition the characteristic X-ray fluorescence lines of Al K\(\alpha\) and Ta M\(\alpha\) with energies of 1.486 keV and 1.709 keV were used. It should be noted that the energy resolution of the detector is about 0.137 keV.  
The phase composition was studied by X-ray diffraction (XRD) on a DRON-3M diffractometer (Bourevestnik, St. Petersburg, Russia) in the Cu K\(\alpha\) radiation. Microhardness of the coating surface was measured on a CASON-59 HV microhardness tester (Jinan Kason Testing Equipment Co, Jinan City, Shandong Province, China).  
The adhesion between Ta coatings and the aluminum substrate was investigated by the scratch method based on applying a scratches grid on the surface of testing coatings. The adhesion test was carried out in accordance with the interstate standard [6].