Tan K. Development of supersonic nozzles for cold spraying

The dissertation is devoted to the creation of an approach to the design of supersonic nozzles of various configurations for cold gas-dynamic spraying and the optimization of spraying parameters in the development of technological recommendations based on numerical modeling of the processes of the acceleration of powder particles in the gas flow and their high-speed deposition with the substrate surface. The object of research is the process of acceleration of powder particles by a supersonic flow in the nozzle channel for cold gas-dynamic spraying and high-speed interaction when the particles impact on the substrate. The subject of the study is the influence of the nozzle geometry and the parameters of the cold gas-dynamic spraying process on the temperature and speed of the powder particles in the flow. The relevance and necessity of research is due to the development of cold gas-dynamic spraying technology in the field of surface engineering, as well as the use of technology to create volumetric additive materials. Increasing the productivity of the process and ensuring high performance indicators of coating quality can be achieved by improving equipment elements and optimizing spraying modes for forming coatings from given powder materials. In addition, the expansion of technological capabilities of equipment for spraying coatings on internal and hard-to-reach surfaces of parts will open new directions of practical application of technology in the field of spraying protective and restorative coatings. The scientific novelty of the obtained results is as follows: 1) for the first time, a method of profiling supersonic single- and multi-channel right-angle nozzles for cold gas-dynamic spraying of coatings on internal and out-off-view surfaces was proposed, which provides the necessary values of the speed of powder particles at the exit of the nozzle for their adhesion to the substrate when the flow is turned by 90°. 2) For the first time, based on the results of numerical modeling, the dependence of the temperature-velocity characteristics of the powder particles at the exit from the right-angle nozzle on the material of the particles, their size, temperature and gas pressure at the entrance to the nozzle was obtained. 3) For the first time, an approach to assigning cold gas-dynamic spraying modes is proposed, based on the planning of a multi-factor experiment, response surface methodology and GA+BPNN, which allows assigning the technological parameters of coating sputtering, which ensure that the powder particles achieve the speed necessary for their adhesion to the substrate. 4) For the first time, on the basis of numerical modeling and the planning methodology of a multifactorial experiment, the dependences of porosity on particle speed, its temperature, and the temperature of the substrate in the studied ranges of values were obtained. The practical significance of the obtained results lies in the fact that the results obtained in the dissertation research can be used in solving a wide class of practical problems when developing technologies and technological recommendations for spraying protective and restorative coatings, in particular: - the proposed method of profiling a right-angle supersonic nozzle for cold gas-dynamic spraying allows to determine the geometric parameters of the nozzle according to the specified characteristics of the used powder material, pressure and temperature of the gas at the nozzle entrance; - the revealed features of the effect of the material of the powder particles, their size, initial values of temperature and gas pressure on the temperature and speed of particles at the exit from the nozzle, expand the understanding of the regularities of gas dynamics processes of two-phase flow in supersonic nozzles for cold gas dynamic spraying; - the results of the study of the processes of acceleration of powder particles in supersonic nozzles and high-speed deposition of particles on the substrate create a theoretical basis for improving the models of these processes, designing and creating equipment for cold gas-dynamic spraying; - the approaches proposed in the dissertation regarding the designation of spraying modes can be used to optimize the parameters of cold gas-dynamic spraying in order to control and ensure the given characteristics of the coatings.