Antierosion coatings development for power units of space crafts
Аuthors*, **, ***, ****, *****
Siberian State University of Science and Technology named after academician M.F. Reshetnev, 31, Krasnoyarsky Rabochy av., Krasnoyarsk, 660014, Russia
Article type: Research and practical
Objective: Experimental investigation on the study of protective properties of Microarc oxidation (MAO) coatings
Subject: Development of anti-erosion coatings for spacecraft power elements
Object of research: MAO coatings on aluminum alloys
For the operation of the spacecraft (SC) during the entire period of lifetime need that degradation of a number of parameters of the equipment and systems in the operation will not lead to a breach of its intended use. Stricter requirements on weight, available power, and increased resource demands and the reliability of spacecraft lead to compact its layout scheme. As a consequence, the erosive effect of stationary plasma thrusters (SPT), which are used as correction thrusters, on the elements of the spacecraft structure is increasing.
Erosive effect of plasma jets SPT consisting in ablation material of construction as a result of long-term gas ion bombardment leading to a reduction in the thickness and contamination of the external surfaces of spacecraft. The main characteristic of this type of exposure is the depth of erosion, in another words the thickness of the sputtered layer.
Another negative effect of plasma jets SPT is erosion of conductive layer from thermal control coating of spacecraft, which leads to the accumulation of static electricity on the surface and occurrence electrical breakdown of surface SC.
Thus, in order to improve the quality of manufacturing products of space technology the development and application of critical spacecraft surfaces coatings with improved resistance to erosive action of plasma SPT is required.
A preliminary analysis showed that substance which has a high resistance to the plasma jet of inert gas (argon, xenon) is aluminum oxide (Al2O3).
Assessment calculations show that the required thickness of the protective coating of Al2O3 for active existence SC 15 years should not be less than 30 microns.
In this paper we propose to protect the spacecraft design elements fall under the plasma SPD the thin (100 micron) aluminum foil coated with aluminum oxide thickness up to 30 microns, applied microarc oxidation (MAO), which is acceptable for weight characteristics. On the spacecraft design, made from aluminum alloys, the coating may be applied directly to the surfaces to be protected.
The methodology of the study. Coatings were deposited on the IAT -T installation, power supply which allows independent adjustment of the anodic and cathodic current components and simultaneously stabilize the average values of these currents, which greatly simplifies the process of MAO and leads to an improvement in the quality of the coatings.
Source has the following specifications: range of adjustable voltage — (0-800 V), the range of regulated currents — ( 0-120 ) A/dm2 ; error stabilization of current to 5%.
As substrate samples used foil AD 160×130 mm size and a thickness of 100 microns.
Microarc oxidation of samples was carried out in slightly alkaline aqueous electrolytes of various compositions.
The coatings were formed at a ratio of Ik / Ia from 0.6 to 1.4, the current densities in the range of 10 to 40 A/dm2, the treatment time was 10-60 min.
The findings of research. For testing of protective coatings on the impact factors of storage and operation the specimens with protective coating on aluminum foil AD GOST 4784 74 microarc surface oxidation were prepared. The sample size is 100×100 mm.
The following tests were carried out:
— Cyclic bending at a diameter of 20 mm;
— Accelerated environmental testing;
— Radiative exposure;
— Thermal cycling.
Studies samples obtained showed that after exposure to plasma samples from the aluminum foil with surface microarc oxidation appearance remained unchanged. Maximum weight and thickness changed in samples polyamide film. MAO samples lost weight greater than the samples of aluminum foil; it is possible to explain some hygroscopic MAO coatings. Coating thickness remained virtually unchanged. Studies have shown that coatings obtained by MAO may be used as protective coatings for spacecraft.
Keywords:spacecraft, antenna reflectors, radio reflection coatings, antierosion protection, microarc oxidation
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