Features of the Structure of Layered Epoxy Composite Coatings Formed on a Metal-Ceramic-Coated Aluminum Base

Abstract

Difficult, extreme operating conditions of parabolic antennas under precipitation and sub-zero temperatures require the creation of effective heating systems. The purpose of the research is to develop a multilayer coating containing two metal-ceramic layers, epoxy composite layers, carbon fabric, and an outer layer of basalt fabric, which allows for effective heating of the antenna, and to study the properties of this coating. The multilayer coating was formed on an aluminum base that was subjected to abrasive jet processing. The first and second metal-ceramic layers, Al₂O₃ + 5% Al, which were applied by high-speed multi-chamber cumulative detonation spraying (CDS), respectively, provide maximum adhesion strength to the aluminum base and high adhesion strength to the third layer of the epoxy composite containing Al₂O₃. On this not-yet-polymerized layer of epoxy composite containing Al₂O₃, a layer of carbon fabric (impregnated with epoxy resin) was formed, which serves as a resistive heating element. On top of this carbon fabric, a layer of epoxy composite containing Cr₂O₃ and SiO₂ was applied. Next, basalt fabric was applied to this still-not-yet-polymerized layer. Then, the resulting layered coating was compacted and dried. To study this multilayer coating, X-ray analysis, light and raster scanning microscopy, and transmission electron microscopy were used. The thickness of the coating layers and microhardness were measured on transverse microsections. The adhesion strength of the metal-ceramic coating layers to the aluminum base was determined by both bending testing and peeling using the adhesive method. It was established that CDS provides the formation of metal-ceramic layers with a maximum fraction of lamellae and a microhardness of 7900-10,520 MPa. In these metal-ceramic layers, a dispersed subgrain structure, a uniform distribution of nanoparticles, and a gradient-free level of dislocation density are observed. Such a structure prevents the formation of local concentrators of internal stresses, thereby increasing the level of dispersion and substructural strengthening of the metal-ceramic layers' material. The formation of materials with a nanostructure increases their strength and crack resistance. The effectiveness of using aluminum, chromium, and silicon oxides as nanofillers in epoxy composite layers was demonstrated. The presence of structures near the surface of these nanofillers, which differ from the properties of the epoxy matrix in the coating, was established. Such zones, specifically the outer surface layers (OSL), significantly affect the properties of the epoxy composite. The results of industrial tests showed the high performance of the multilayer coating during antenna heating.

Keywords: cumulative detonation spraying; dislocation density; epoxy composites; hardening; microstructure; multilayer coatings; nanoparticles; oxide coating layer; subgrain structure; temperature.

Figure 1

Photos of powders for spraying a metal-ceramic coating layer: (a) Al₂O₃ (×600); (b) Al (×300).

Figure 2

Schematic representation of a multilayer coating: 1—product base–substructure (aluminum sheet); 2—metal-ceramic layer Al₂O₃ + 5% Al (applied by high-speed multi-chamber cumulative detonation spraying, porosity less than 1%); 3—metal-ceramic layer Al₂O₃ + 5% Al (applied by high-speed multi-chamber cumulative detonation spraying, porosity 20–25%); 4—epoxy composite with Al₂O₃ filler; 5—heating layer (carbon fabric impregnated with epoxy resin); 6—epoxy composite with Cr₂O₃ + SiO₂ filler; 7—basalt fabric; 8—carbon fabric.

Figure 3

Structural diagram of the technological process for forming multilayer epoxy composite coatings formed on metal–ceramic spraying on an aluminum substrate.

Figure 4

Model of a device for high-speed multi-chamber cumulative detonation spraying (a) and general view of this device mounted on a manipulator during detonation-gas spraying of a coating (b): 1—nozzle chamber; 2, 3—main and cylindrical chambers; 4—three-axis manipulator.

Figure 5

Photograph of an aluminum substrate that was subjected to abrasive blasting with corundum.

Figure 6

Microstructure of the coating (Al₂O₃ + 5% Al) in the fusion zone, ×500 magnification (a), and the first layer, ×1000 magnification (b).

Figure 7

Outer surface layers (OSL): (a,c,e)—when Cr₂O₃ is introduced; (b,d,f)—Al₂O₃; (g,h)—SiO₂; (a,b,g,h)—individual particles, (c–f)—OSL overlap and their convergence.

Figure 8

Substructure (a,b) and nanoparticles of phases (c,d) in the material of the first coating layer (Al₂O₃ + 5% Al), the fusion zone (F/L) of the coating with the substrate, and in the substrate material ((a–d)—×52,000; (e,f)—×35,000).

Figure 8

Substructure (a,b) and nanoparticles of phases (c,d) in the material of the first coating layer (Al₂O₃ + 5% Al), the fusion zone (F/L) of the coating with the substrate, and in the substrate material ((a–d)—×52,000; (e,f)—×35,000).

Figure 9

Fracture surface patterns of the Al₂O₃ + 5% Al coating layer: (a,b)—×1200; (c,d)—×2400.

Figure 10

Photograph of the outer layer (basalt fabric) of a multilayer coating.