Kyslytsia O. Microplasma wire spraying.

The thesis is dedicated to development of the technology for microplasma spraying of coatings by using wire consumables. The calculation-theoretical analysis of the process of dispersion of a neutral wire material melt under microplasma spraying conditions showed that the requirement for detachment of a drop of the melt from the wire tip is achievement of a certain velocity of the microplasma jet, which depends on the properties of the wire material and, primarily, on the value of surface tension of the melt. Diameter of the wire and speed of its feeding to the arc zone during MPS depend on the thermal-physical properties of its material, which determine its stable melting within the arc zone. Volt-ampere characteristics and efficiency of the miroplasmatron were determined for the microplasma wire spraying conditions. Enthalpy and temperature of the plasma jet were calculated. The effect of process parameters on the character of outflow of the plasma jet was studied. The degree of impact of different factors of the wire spraying process on the average size of particles for different materials in dispersion of the wire melt by the plasma jet, as well as on the material utilization coefficient was determined by using the multifactorial experiment design. Linear regression models were developed, showing the effect of the most significant process parameters (current, plasma gas flow rate, spraying distance, wire feed speed) on formation of a jet of the spraying material particles and a set of characteristics of the W, NiCr and Ti coatings. Velocities of the spraying material particles in MPS, which depend on the current and plasma gas flow rate and are inversely proportional to the specific weight of the spraying material, were determined. The metalizing figure for MPS by using the NiCr wire was investigated. Sizes of the spraying spot and micrplasma jet opening angle were determined. It was shown that a lower content of oxide and nitride phases could be achieved in a coating owing to the possibility of decreasing the spraying distance in wire MPS. Establishing the possibility of controlling macroporosity of Ti-coatings in wire MPS and correspondence of the value of their adhesion to the Ti-alloy substrate in tensile and shear tests to the ASTM C633 requirements, as well as the data of testing these coatings "in-vivo" proved the efficiency of applying them for manufacture of various-purpose endoprostheses (hip joint, dental, etc.).