Abstract
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.
Highlights
The practical effectiveness of coatings is related primarily to an improvement in the service life of hardened parts
It was determined that the phase composition of Al2O3 coatings during detonation spraying strongly depends on the barrel filling volume with the gas mixture
Based on the experimental data obtained and their analysis, the following conclusions were made: - The method of obtaining multilayer coatings based on NiCr/NiCr- Al2O3/Al2O3, consisting of the lower metal layer, the upper ceramic layer and the transition layer of the mechanical mixture of metal and ceramics, was developed. - It was determined that the phase composition of Al2O3 coatings strongly depends on the technological parameters of detonation sputtering
Summary
The practical effectiveness of coatings is related primarily to an improvement in the service life of hardened parts. For the increasing of the service life of parts, it is necessary to create coatings with complex properties (high strength, corrosion resistance, wear resistance, etc.). A significant increase in coating properties can be achieved by spraying various materials in several layers, allowing the obtaining of coatings with unique characteristics. Such methods of obtaining multifunctional coatings are widely used to apply composite ceramic, metal–ceramic, bio-ceramic and other synthetic compositions [1,2,3]. The presence of porosity and residual thermal stresses in ceramic plasma coatings can decrease their protective and strength properties. The thermal mismatch between the ceramic coating and the steel matrix due to a significant discrepancy in the thermal expansion coefficients leads to a large alteration of stresses at the coating–substrate interface and improves the coating detachment risk [4,5]
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