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The coating process is an essential part of stereolithography technology to mold alumina paste, achieved using a scraper. The characteristics of the scraper (geometry and roughness) are investigated to discover the potential influence mechanism on the coating process. To complete the analysis, the bidirectional gated recurrent unit (BiGRU) optimized by the marine predator algorithm (MPA) is proposed to provide a predicted model for the rheological data instead of the traditional fitting by using the known rheological equations. Then, a pseudo-lattice Boltzmann (pseudo-LB) method is proposed to conduct the coating flow simulation without a specific rheological equation, where the predicted rheological model is applied to obtain the relaxation time for each iteration. Based on the above MPA-BiGRU pseudo-LB method, three geometries and different roughnesses are explored for the coating process. The results indicate that the rectangle geometry suits the large coating speed, and the trapezium geometry is recommended for conditions with the small coating speed. The roughness significantly affects the coating process with the rectangle geometry, and the smoother scraper generates a minor disturbance. However, it is almost ineffective in the cases with trapezium geometry. [ABSTRACT FROM AUTHOR]

The aircraft serving in the marine environment is easy to cause the corrosion of its structure due to the long-term influence of the harsh environment such as seawater and salt mist. In order to improve the corrosion resistance of aircraft structure, plasma spraying and laser cladding were used to prepare Fe-based amorphous coatings on the surface of 304 stainless steel. The microstructures of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and their microhardness was tested using a Vickers hardness meter. The corrosion behavior of Fe-based amorphous coatings in the simulated seawater environment was studied by potentiodynamic polarization curve measurement and electrochemical impedance spectroscopy. The results showed that the Fe-based amorphous coatings prepared by these two surface technologies have good corrosion resistance, and can reduce the corrosion rate of aircraft structure, so as to ensure the safety of flight operation. [ABSTRACT FROM AUTHOR]

In this paper, AlCoCrFeNi high-entropy alloy composite coatings using the AlCoCrFeNi matrix with Ni-coated-Al2O3 reinforcement were prepared by laser cladding to investigate the effect of Ni-coated-Al2O3 addition on slurry erosion resistance. Microstructure and microhardness of all high-entropy alloy (HEA) composite coatings were characterized by using x-ray diffraction, scanning electron microscope and Vickers hardness measurement. The slurry erosion test was carried out by using an abrasive waterjet method to evaluate the erosion performance of all coatings. The results show that AlCoCrFeNi HEA composite coatings present the typical equiaxed crystal structure with the single body-centered cubic (BCC) phase. After adding the Ni-coated-Al2O3 reinforced powders, the grains of composite coatings are gradually refined with increase in Ni-coated-Al2O3 mass fraction. The average microhardness of composite coatings increases with the increase in the Ni-coated-Al2O3 powder content. The cumulative mass loss of the composite coatings is lower than that of martensitic stainless steel substrate and gradually decreases with the increase in Ni-coated-Al2O3 mass fraction, which proves the addition of Ni-coated-Al2O3 particles can effectively enhance the slurry erosion resistance. Ploughing and micro-cutting are the primary erosion mechanisms of AlCoCrFeNi-x Ni-coated-Al2O3 composite coatings at low erosion angle, while the erosion mechanisms of composite coating material loss are dominated by ploughing and craters at high erosion angle. [ABSTRACT FROM AUTHOR]

BACKGROUND: 3D printing provides a new way of molding chocolate with complex geometrical structures. The screw extruder can efficiently transport the liquid chocolate, which has been adopted to investigate the effect of the profile of the screw flight on the flow. First, the rheological behavior of the liquid chocolate is measured and the Cross equation is demonstrated as the proper rheological model. Then, based on the rheological behavior, an improved lattice Boltzmann method is creatively proposed, for which the effectiveness is validated by the classical Poiseuille flow. Third, the geometrical structure of the screw extruder is analyzed and transformed. The possible changes in the profiles of the screw flights are listed. Finally, the fluid analysis is conducted and the necessary streamlines figures, cloud charts and velocity distributions are obtained. RESULTS: The large dip angle in straight cases has an obvious effect on the velocity distribution and the common flow area. The position of the convex point is the additional important factor, whereas the concave profiles are the most moderate in the proposed cases. CONCLUSION: The changes in the profiles will affect the chocolate flow. The work is significant for extrusion theory in 3D printing. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]