Vojnarovych S. Development of technology for microplasma spraying of bioceramic coatings.

The thesis is dedicated to development of the technology for microplasma spraying of bioceramic coatings of hydroxyapatite (HA) by providing the required phase composition and structure of the coatings. Main technological peculiarities of the microplasma spraying processes were identified. Factors exerting the highest effect on the spraying process and properties of the HA coatings were defined. Volt-ampere characteristics of microplasmatron with an external anode were determined. The effect of process parameters on the efficiency of the plasmatron was investigated. Mean-mass initial enthalpy and temperature of the plasma, velocity and temperature of the spraying powder particles, and powder utilization factor were determined for the microplasma spraying conditions. Dependence of phase composition of the HA-based bioceramic coating upon the microplasma spraying parameters (current, spraying distance, consumption of plasma gas and powder) was derived by using the method of mathematical planning of multifactor experimental design. Mathematical processing of the resulting data allowed the development of linear regression models, showing the effect of these parameters on formation of a combination of characteristics of the HA coatings. This will make it possible to find the ways of controlling structure and phase composition of HA under the microplasma spraying conditions. It is shown that phase composition of the HA coatings within the HA crystalline phase content of 88...98 %, amorphization degree of 0...7 %, and ?-TCP content (degree of decomposition of HA) of 0...6 %, and, as a result, formation of the HA coating with the required phase composition can be controlled by varying the plasma spraying parameters, thus leading to changes in the heating conditions and motion of the spraying material particles. The coating to substrate adhesion strength was determined, depending upon the presence of a sub-layer and type of its material. Technological recommendations were worked out for deposition of the HA coatings on different types of endoprostheses.