Авіаційно-космічна техніка та технологія (Dec 2018)
COLD SPRAY DEPOSITION EFFICIENCY CONTROL OF PROTECTIVE AND RESTORATIVE COATINGS ON MAGNESIUM ALLOYS
Abstract
The crucial task of developing the technology of low pressure cold gas–dynamic spraying and its wide application in the aviation, automotive and other industries is the possibility of obtaining coatings with given properties and deposition efficiency as great as practicable. To do this requires it is necessary to study the effect of complex parameters on coating deposition. An important characteristic of cold gas–dynamic spraying is deposition efficiency – the ratio of weight increment of the sample (weight of the coating) to the weight of powder used to produce the coating. Dependence of the deposition efficiency on the parameters of cold spraying, such as gas stagnation temperature and total pressure, material, shape and size of the powder particles, stand–of–distance, etc., allows a deeper understanding of the nature of the cold gas–dynamic spraying process, and as a consequence, to establish how these parameters effect on coating properties. The effect of stagnation temperature, total pressure and stand–of–distance on the cold spraying coating deposition efficiency on magnesium alloy utilized powder mixture based on aluminum was established. As a result of the deposition efficiency calculation, the optimal sputtering parameters ensuring the maximum deposition efficiency were established. It is shown that changing of the stagnation temperature has the greatest effect on the efficiency of coating formation. Stand–of–distance is the second most influential parameter, and the change in working pressure has the least effect. It is shown that with increasing temperature, the particle velocities increase during the deposition process, since the local speed of sound in the nozzle depends on the local flow temperature. The obtained results are the basis for the development of technological recommendations and processes for the formation of protective and restorative coatings on aeronautical part made of magnesium alloys during maintenance, repair and overhaul. Further optimization of the geometry of the nozzle, the composition of the powder mixture and the particle size is necessary to obtain deposition efficiency as great as practicable.
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