Thermal-stress Study Of In-situ Fabrication Process Of Novel Al₂O₃-Fe Coating By Laser Cladding

Alumina ceramics have a wide range of applications in the field of thermal protective coatings for aerospace materials due to their excellent properties of heat resistance,hardness,and corrosion resistance.However,the disadvantages of alumina ceramics such as brittleness,low toughness and thermal stress sensitivity can limit the application of them.The problems of brittleness and toughness of particle-reinforced alumina ceramics fabricated using laser melting in-situ manufacturing technology have been improved.In order to fabricate excellent particle-reinforced alumina coatings,this paper presents a thermodynamic analysis study of the in-situ fabrication process of Al2O3-Fe particle-reinforced composite coatings on titanium alloy substrates using a mixture of ferric tetroxide and aluminum powders to provide a technical reference for actual engineering fabrication.The main studies are as follows:In order to obtain the effect of the induced aluminothermic reaction of the mixed powder under the action of laser on the coating formation,a thermodynamic coupled numerical simulation model applicable to the in-situ fabrication process of Al2O3-Fe laser melting was established in this paper.The model was based on the theory of temperature field and stress field analysis of the laser cladding process,and reveals the evolution of the temperature field during the manufacturing process of the composite coating.The representative volume element model was established in combination with the microstructure of the coating to obtain the property parameters of the coating for model calculation.To simulate the laser-induced reactions occurring during the coating fabrication process,a combined heat source acting simultaneously with a hemispherical Gaussian heat source was established by combining the internal heat-generating heat source model and the raw-dead cell technique.In order to obtain the effect of the induced aluminothermic reaction of the mixed powder under the action of laser on the coating formation,a thermodynamic coupled numerical simulation model applicable to the in-situ fabrication process of Al2O3-Fe laser melting is established in this paper.The model is based on the theory of temperature field and stress field analysis of the laser cladding process,and reveals the evolution of the temperature field during the manufacturing process of the composite coating.A representative volume element model is established in combination with the microstructure of the coating to obtain the property parameters of the coating for model calculations.To simulate the laser-induced reactions occurring during the coating fabrication process,a combined heat source acting simultaneously with a hemispherical Gaussian heat source is established by combining the internal heat-generating heat source model and the raw-dead cell technique.In the temperature field study of the in-situ fabrication process of Al2O3-Fe laser cladding,the influence of the reaction heat on the distribution and evolution of the temperature field and the effect of different laser processing parameters on the maximum melt pool temperature and melt pool morphology were obtained.In order to obtain the distribution of thermal stresses in the fabrication of equivalent composite coatings under the action of different laser processing parameters,further experimental studies on the in-situ fabrication of Al2O3-Fe laser melting were carried out in this paper on the basis of thermodynamic coupling simulations.Numerical simulations were performed to predict the distribution of equivalent stresses and the magnitude and type of stresses in each direction at the end of coating melting by different laser processing parameters.The macroscopic morphology of the experimentally prepared coatings was analyzed to verify the stress field simulation results.In order to produce Al2O3-Fe coatings with regular coating morphology and low substrate thermal deformation,this paper proposed the use of laser scanning point cloud method to obtain the coating morphology and substrate thermal deformation data,and reveals the relationship between them and laser processing parameters.The point clouds of the substrate on both sides of the upper coating were linearly fitted to achieve quantitative analysis of substrate thermal deformation under different parameter combinations.The coating and substrate data were split to obtain the melt height and width data to analyze the morphological changes.The analysis was summarized and the parameter combinations were optimized to obtain good coating samples.