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21Ta-CONTAINING MATERIALS BY SHS
O. K. Kamynina*", S. G. Vadchenko", A. S. Shchukin", and V. G. Salamatov"
aMerzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Moscow, 142432 Russia *e-mail: sci-secretary@ism.ac.ru
DOI: 10.24411/9999-0014A-2019-10054
As is known, tantalum exhibits a number of unique properties such as high melting point (2996°C), good ductility, hardness, heat resistance, and exceedingly high corrosion resistance in aggressive media. Moreover, tantalum as a biocompatible metal that does not cause irritation of living tissues and is inert toward long-term exposure to the liquid medium of human body. In view of this, Ta is getting more and more widely used in implant surgery to replace damaged bones and stitch nerves or tendons. The unique properties of tantalum afford for its various industrial applications in mechanical engineering, electronics, aerospace industry, nuclear power engineering, and medicine [1, 2]. However, the use of ductile tantalum as a structural and functional material is restricted by its large density and high production cost. Basic intention of this work was the SHS-assisted design of light-weight and inexpensive Ta-based materials whose service parameters would be close to those of modern structural and functional materials. In contrast to earlier attempts [3 -5] to SHS produce Ta-based ceramic materials, we explored the preparation of Ti-Ta-Al intermetallics and sandwich-like Ta-(Ti + 0.65C)-(5Ti + 3Si)-Ta layered structures.
One of task objectives was the preparation Ti-Ta-Al alloys by SHS method in a mode of thermal explosion, with special emphasis on the influence of particle size/morphology of starting blends and their mechanical activation.
In a study on joining Ta foil with ceramics, we used commercial powders of Ti (PTS brand), carbon black (P804T), and Si (d < 10 p,m, 99.4% pure) to prepare the 30 x 12 x 5.5 mm pellets of Ti + 0.65C and 5Ti + 3 Si blends. Combustion experiments under 1 atm of Ar were performed in the geometry schematically presented in Fig. 1. Tantalum foils 1 used as substrates were 100 |im thick. Prior to ignition with coil 7, the assembly was uniformly warmed up to 700°C with heaters 4. Load 6 was placed on firebrick 5. The combustion process was video filmed with a MIRO M310 camcorder (5000 frames per second).
5
2
3
Fig. 1. Experimental setup: 1 Ta foils, 2 pellet of Ti + 0.65C blend, 3 pellet of 5Ti + 3Si blend, 4 electric heaters, 5 chamotte brick, 6 load (1240 g), and 7 igniting coil.
ISHS 2019 Moscow, Russia
Burned samples were characterized by SEM/EDS (Carl Zeiss ULTRA Plus microscope equipped with EDS accessory INCA 350 Oxford Instruments) and three point bend testing (Instron-1195 machine).
Figure 2 presents still frames of combustion at different time moments. As could be expected, burning velocity (11 cm/s) in the Ti-C system (pellet 2 in Fig. 1) was higher (see Fig. 2) than that (7.5 cm/s) in the Ti-Si system (pellet 3 in Fig. 1). Formation of the liquid phase during combustion is evidenced by marked shrinkage of burned samples, down to about 32 x 14.5 x 6 mm.
918 ms 1000 ms
Fig. 2. Still frames of combustion taken at different time moments (indicated).
Strong joining was observed between Ta (upper foil 1) and burned pellet 2, as well as between burned pellets 2 and 3. No joining happened at the interface between pellet 3 and lower Ta foil 1. This can be explained by a lower combustion temperature at the sample bottom: Tad = 2130°C for 5Ti + 3Si and 2240°C for Ti + 0.6C mixture.
In this work, the possibility of producing Ti-Ta-Al based matrerials in SHS mode was demonstrated. We studied the dependence of product structure on the green mixture composition and the effect of preliminary mechanical activation. In the experiments, it was shown that formation of TaAh phase begins during mechanical activation. The Ta-Ti and Ta-Ti-C layers formed on the Ta substrate can be regarded as multifunctional coatings. The materials based on (Ta,Ti)C and TaCx known for their high-temperature strength, corrosion resistance, and hardness are recommended for use as protective coatings onto the items operating in extreme conditions (above 1500°C, in aggressive media, etc.).
Our results open up new horizons for further studies and fabrication of materials based on Ta alloys with desired structure and properties.
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