The effect of operating gas temperature and powder type on microstructure and mechanical characteristics of cold spraying coatings deposited on EZ33A-T5 magnesium alloy was studied. Three aluminum-based cold spraying powder mixtures Al + Zn, Al + Al2O3 and Al + Zn + Al2O3 were used for the investigation. Deposition was performed using D423 low-pressure cold spray system at operating gas pressure of 1.0 MPa and different temperatures – 300 °C, 450 °C, and 600 °C. The coatings microstructure was investigated with optical and scanning electron microscopy. Mechanical properties of the coatings were characterized through standard test methods for adhesion and cohesion strength, and standard test methods for Vickers hardness of thermal spray coatings. The results demonstrate that with increasing initial gas temperature at spraying nozzle inlet from 300 °C to 600 °C, an increase in the porosity of the coatings of all investigated powder mixtures can be observed. Microstructure characterization showed an increase in porosity from 2.3 % to 4.1 % for Al + Zn powder mixture, from 2.1 % to 3.5 % for Al + Al Al2O3 powder mixture, and from 2.5 % to 5.6 % for Al + Zn + Al2O3 powder mixture. The minimum porosity was obtained at 450 °C for all investigated powder mixtures. Adhesion and cohesion strength and microhardness of coatings were reach their maximum value at 450 °C. The best performance was obtained for Al + Al2O3 powder mixture: coating adhesion – 31.9 MPa (was limited by the bonding strength of the glue), cohesion – 93.5 MPa, microhardness – 81 HV0.15. The influence of Al2O3 particles in the powder mixture on the above-mentioned parameters was also established. The results show that the presence of ceramic particles in powder mixtures can positively affect porosity level and mechanical characteristics.
Modern technologies for producing carbon nanostructures are based on many years of experience in the development of coating methods. The latest trends in the formation of carbon nanostructures are associated with complex technological processes of physical and technical treatment, when microstructures are obtained based on traditional methods, which are then completely or partially modified into nanostructures. In this case, the possibility of the formation of a part of nanostructures in a gas flow is considered in order to use them as islands of growth of other nanostructures on the treated surface. The conditions for formation of the specified structures are characterized by the energy state of particles, physical and mechanical properties of particles and substrate materials. The paper presents the results of numerical simulation for determination of velocity and temperature of nanocomposite metalmatrix powder particles in a supersonic nozzle. The necessity to determine parameters of solid particles of powder in a two-phase supersonic flow is determined. Particles velocity and temperature are the crucial parameters which allow for formation of coatings and impact their physical and mechanical properties. The contour plots of velocity and temperature distribution in the nozzle and free space from the nozzle exit to the substrate are obtained. Coating application and its characteristics are considered when selecting coating materials. The numerical simulation is performed for the particles of boron carbide (B4C) and nickel (Ni) powders. The dependence of velocity and
The study of flow of gas with solid particles in a flat nozzle is performed. The parameters of flow of gas with particles of powder in the flow passage of the flat supersonic nozzle are studied, as well the parameters of interaction between the solid particles of the spray deposited material and surface of the target backing plate by means of mathematical modelling of the threedimensional constant-property flow of the viscous compressed real gas with solid particles. During the mathematical modelling of the process of flow of gas with solid particles by using highly specialized CFX-Pre 16.2 and CFX-Solver Manager 16.2 software packages the fields of parameters in the nozzle's flow passage and near the target backing plate are obtained.
The effect of temperature and air pressure at the supersonic nozzle inlet, as well as the distance from the nozzle outlet to the surface of the substrate (stand-of-distance) on the powder usage rate of nickel-based powder in low pressure cold gas-dynamic spraying (inlet pressure up to 1.0 MPa) was analyzed. One of the most important parameters characterizing the deposition efficiency of the spraying process is the powder usage rate. This parameter is the ratio of the mass of the coating to the mass of the powder used to obtain this one. For the process of cold gas-dynamic spraying, implemented on the equipment using air pressure up to 1.0 MPa, the main disadvantage is the relatively low-powder usage rate. To increase it (but not limited to it), a ceramic component, such as alumina Al2O3, is added to pure metal powders. In this study a nickel-based powder mixture, in which the content of Al2O3 powder is about 10% mass., was used. Titanium alloy plates BT9 were used as the substrate material. Based on the multifactor planning of the experiment, the effect of the complex parameters of the low-pressure cold gas-dynamic spraying on the powder usage rate was studied. After the coating deposition according to the matrix of the experiment, the samples with coatings were weighed. According to the known mass of the samples before spraying and the increase in their mass, the powder usage rate was calculated. From the analysis of the obtained statistical data, the dependence of the effect of the complex parameters of the deposition process on the powder usage rate was developed. The maximum value of the powder usage rate were obtained up to 35 %. It was confirmed that the air temperature at the nozzle inlet has the greatest effect on the above-mentioned parameter. The explanation of this is the increase in gas flow temperature and velocity, and as a result, the increase in the velocity and temperature of the powder particles in this flow. Higher values of the velocity and temperature of the particles lead to more intense plastic deformation of particles during impact with the substrate and their adhesion to it.
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