Preparation and Characterization of NiCr/NiCr-Al2O3/Al2O3 Multilayer Gradient Coatings by Gas Detonation Spraying

This paper investigates the influence of the technological parameters of detonation spraying on the phase composition of NiCr- and Al2O3-based coatings. It was determined that the phase composition of Al2O3 coatings during detonation spraying strongly depends on the barrel filling volume with the gas mixture. The acetylene–oxygen mixture, which is the most frequently used fuel in the detonation spraying of powder materials, was used as a fuel gas. To obtain a ceramic layer based on Al2O3, spraying was performed at an acetylene–oxygen O2/C2H2 mixture ratio of 1.856; the volume of filling of the detonation gun barrel with an explosive gas mixture was 63%. To obtain a NiCr-based metallic layer, spraying was performed at the O2/C2H2 ratio of 1.063; the volume of filling of the detonation gun barrel with an explosive gas mixture was 54%. Based on a study of the effect of the detonation spraying mode on the phase composition of NiCr and Al2O3 coatings, NiCr/NiCr-Al2O3/Al2O3-based multilayer coatings were obtained. Mixtures of NiCr/Al2O3 powders with different component ratios were used to obtain multilayer gradient coatings. The structural-phase composition, mechanical and tribological properties of multilayer gradient metal–ceramic coatings in which the content of the ceramic phase changes smoothly along the depth were experimentally investigated. Three-, five- and six-layer gradient coatings were obtained by alternating metallic (NiCr) and ceramic (Al2O3) layers. The phase composition of all coatings was found to correspond to the removal of information from a depth of 20–30 μm. It was determined that the five-layer gradient coating, consisting of the lower metal layer (NiCr), the upper ceramic layer (Al2O3) and the transition layer of the mechanical mixture of metal and ceramics, is characterized by significantly higher hardness (15.9 GPa), wear resistance and adhesion strength.

Development and Application of Thin Wide-Band Screening Composite Materials

The paper is dedicated to the development of effective composite coatings with the use of carbon fillers of different morphology, their research, and application in the broadband frequency range. Electromagnetic loss studies were performed according to international standards ASTM D4935, IEEE-STD-299, and the US Department of Defence standard MIL-STD 461F. The impact of hybrid carbon nanomaterial "graphene/nanotubes" on the electrophysical properties of the composite material has been analyzed. As a result, the research laboratory technologies of production of composite coating on water and non-water (alcohol) basis are developed based on the carbon fillers of various morphology and also magnetite. The shielding properties of most of the created composites are estimated in the frequency range from 50 MHz to 30 GHz. The state enterprise “All-Ukrainian center for standardization, metrology, certification, and consumers’ rights protection” (here and after “Ukrmetrteststandart”) conducted comparative tests of the developed coating (in the form of paint) with a protective coating # 842 MG Chemicals (Burlington, Ontario, Canada) based on silver microparticles. Developed water-based composites can be used for interior decoration, in the formation of electromagnetic screens, thin gradient coatings to protect people from electromagnetic radiation in the microwave range.

Inter-Relationship between Coating Micro/Nanostructure and the Tribological Performance of Zr–C Gradient Coatings

The research presented in this article concerns Zr–C gradient coatings that were deposited on HS6-5-2 steel by reactive magnetron sputtering from the Zr target in appropriately programmed C2H2 mass flow rate, resulting in various profiles of atomic carbon concentrations in the coating and consequently in spatial change of the properties (H, E, …) and behavior (H/E, H3/E2, We). In particular, the characteristic changes in hardness and Young’s modulus in the Zr–C coatings represented approximately by the bell curve, which has a maximum at the content of about 50 at.% C, were an inspiration to study the behavior of gradient coatings with carbon content in the range of 0–50 and 50–85 at.% with the same hardness change profile. The obtained results indicate that, firstly, the gradient of spatial changes in the coating composition increases their resistance to cohesive damage in comparison to non-gradient coatings, and, secondly, the results show that high hardness is a desired property but not sufficient to ensure adequate coating performance. Independently, an appropriate nano/microstructural structure is necessary, which determines their tribological behavior. In particular, in the case of the tested Zr–C coatings, the obtained results indicate that gradient coatings with a carbon content in the range of 50–85 at.% have better properties, characterized by the critical force Lc2, wear, coefficient of friction, H/E and H3/E2 ratios.

Technology for the production of nanostructured coatings from nanoparticles of tungsten carbide and metal chromium

This paper presents results of a study of complex processes for producing composite powder materials from tungsten carbide and metallic chromium. Technological methods for the formation of functionally gradient coatings with high microhardness up to 426 HV through microplasma spraying technology are disclosed.