94 PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 94 NR 7/2018 Darya ALONTSEVA 1 , Yuri BORISOV 2 , Sergii VOINAROVYCH 2 , Oleksandr KYSLYTSIA 2 , Tatyana KOLESNIKOVA 1 , Nadezhda PROKHORENKOVA 1 , Albina KADYROLDINA 1 D. Serikbayev East Kazakhstan State Technical University, Kazakhstan (1), E. O. Paton Electric Welding Institute, Ukraine (2) doi:10.15199/48.2018.07.23 Development of technology of microplasma spraying for the application of biocompatible coatings in the manufacture of medical implants Abstract. This paper describes the equipment design of E. O. Paton Electric Welding Institute and technology of microplasma spraying of coatings from powder and wire materials for applying biocompatible coatings for medical implants. The given equipment was introduced at an experimental robotics complex for microplasma spraying at D. Serikbayev East-Kazakhstan State Technical University By this example the authors discuss the challenges and prospects of the development and implementation of microplasma spraying technology Streszczenie. W artykule opisano konstrukcję sprzętu w E. O. Paton Electric Welding Institute oraz technologię natryskiwania mikroplazmy powłok z proszków i materiałów drucianych w celu nanoszenia biokompatybilnych powłok na implanty medyczne. Dany sprzęt został wprowadzony do eksperymentalnego kompleksu robotyki do natryskiwania mikroplazmy na Uniwersytecie Technicznym D. Serikbayev East-Kazakhstan. Na tym przykładzie autorzy omawiają wyzwania i perspektywy rozwoju i wdrażania technologii mikroplazmatycznej Technologia natryskiwania mikroplazmy powłok z proszków i materiałów drucianych w celu nanoszenia biokompatybilnych powłok na implanty medyczne Keywords: microplasma spraying, biocompatible coatings, medical implants. Słowa kluczowe: rozpylanie mikroskopowe, biokompatybilne powłoki, implanty medyczne, Introduction The multi-purpose methods of Thermal Coating Spraying, such as: Plasma Spraying, Combustion Flame Spraying, Arc – Spraying have become popular all over the world [1, 2]. Thermal spray coatings effectively increase the wear resistance and the corrosion resistance of the surface and its resistance to oxidation and corrosion at high temperatures. It is significant that thermal spraying is a relatively “cold” process, and the substrate is usually not heated above 65°C, which ensures its minimal thermal degradation [2]. The treatment of surfaces of complex configurations presents a challenge for the implementation of the thermal spraying technology and requires automated manipulations of the jet and/or the substrate along with robotic control for appropriate treatment of a surface [1, 2]. Summarizing the results presented in [1-4], we can note that the technologies of thermal spraying include the selection and use of equipment (guns, power supplies, manipulators, etc.), materials (powders, wires or rods), as well as technical and technological know-how (experience). Only when all these key technology components are used correctly, one can get a desirable coating with controlled structure and satisfactory adhesion. One of the major methods of gas-thermal deposition of coatings is plasma spraying. Plasma guns that generate a turbulent plasma jet with the electric power up to 200 kW and a spot diameter of the sprayed material of 15...30 mm are most commonly used for this purpose. The use of such plasma guns for spraying small-sized parts or thin-wall parts can lead to their overheating and distortion due to high heat power of a plasma jet. In addition, in the case of spraying small parts or local areas of surfaces (5...10 mm or less) there is a considerable loss of the sprayed material. Besides, masking the areas that are not to be treated requires additional operations. These circumstances have led to the development of a new method of thermal coating, microplasma spraying (MPS), by the E. O. Paton Electric Welding Institute (EWI) [5, 6]. The microplasma spraying method is characterized by a small diameter of a spraying spot (1 ... 8 mm) and low (up to 2 kW) power of plasma, which results in low flow of heat into the substrate [5-7]. These characteristics are very attractive for the deposition of coatings on small parts or in case high accuracy is required, in particular for applying biocompatible coatings in the manufacture of medical implants. The aim of this work was to develop such technology for automated micro plasma deposition of metal coatings using an industrial robot that is suitable for producing biocompatible coatings for medical implants. Experimental procedure A series of design and technological works which resulted in developing a number of microplasma deposition plants (MPS-001, MPS-002, MPS-003) has been carried out by E. O. Paton EWI. MPS-004, a latest generation plasma spraying plant, includes a power supply unit with a water cooling unit, a control box, a microplasmotron with an offset rotating cooled anode (the design of the microplasmotron is patented [8]), an interchangeable mechanism for feeding wire, and a MP-004 microplasmotron (Fig.1 a). The process of microplasma spraying is distinctive of low power consumption (microplasmotron MP-004 power is up to 2.5 kW) and the possibility of coating deposition in a laminar jet flow mode using pure argon as a plasma gas. The sprayed materials utilization rate at MPS is established as 0.6...0.9. In this regard, and according to the design of the microplasmotron, the MPS process has the following distinctive characteristics: - since the expansion angle of a laminar plasma jet makes only 2...6° (instead of 10...18° for turbulent plasma jets), and the nozzle diameter is small (1...2 mm and less), it is possible to reduce the size of the deposition spot to 1...8 mm; - low thermal power of a microplasma jet allows reducing the heating of a substrate, which provides the possibility of applying coatings on small-sized and thin-walled products without excessive local overheating and warpage; - the use of a microplasmatron with an offset anode allows for the flow of the sprayed material directly into the arc discharge, the highest temperature area of the plasma jet, which is advantageous for coating deposition on such high- melting-point material as Al 2 O 3 , ZrO 2 , W; - the use of a jet of protective gas, argon, helps reduce the degree of oxidation of the sprayed material; - a laminar plasma jet has a low sound level (30...50 dB),