Molecular Dynamics Simulation And Interface Analysis On Mechanism Of Dip-coating Aluminum On Ceramics

Successful application of ceramics in many devices and structures requires some type of ceramic-metal joining.This kind of composite is widely used in the field of mechanical and electronic devices.However,because of the big differences of the physical properties and mechanical properties between ceramic and metal,wettability between the two materials is poor,thus influencing the performance and quality of connection between ceramics and metals.Our group invented a novel dip-coating process can make it possible to coat aluminum film evenly on the substrate of alumina,aluminum nitride and silicon carbide ceramics under the protection of nitrogen atmosphere,"super wetting" phenomenon occurred between aluminum and ceramics.In this paper,to explore the mechanism of the "supper wetting" phenomenon based on the product from the dip-coating process,we studied the interface of aluminum between aluminum nitride ceramic or silicon carbide ceramic especially the microstructure and orientation of the interfaces.Theoretically,by molecular dynamics simulation calculation,we studied the mechanism of dip-coating aluminum on alumina ceramics.A large amount of literatures reported that the contact angles between aluminum and alumina,using the improved sessile drop method,are greater than the requirement in dip-coating experiments,in which alumina substrate can be perfectly wetted by aluminum.In this paper,Al and Al2O3(0001)interface was studied using molecular dynamics simulations.Based on the ES+potential function calculation model,the effectiveness of the model was first verified by comparing the contact angle results between simulation calculation and experimental measurement in the temperature range of 1000 K to 1200 K.It was revealed that the error of contact angles between simulation and measurement was within 7%,which suggested good consistency.Further improvement of the simulation model focused on the process of receding contact angle measurement in dip-coating process.Under the temperature of 1073 K,the obtained contact angle in the molecular dynamics simulation significantly reduced to 45 Observations showed that oxygen atoms form Al2O3 substrate surface diffused into the liquid aluminum,making the relative density of O atoms in this layer form oxygen vacancy.The surface of alumina substrate reconstructed to improve wettability In addition,it was reported that the surface tension of liquid aluminum could decrease from 1.122 J/m2 to 0.869 J/m2 through the adsorption of oxygen in the atmosphere.By molecular dynamics simulation,we made an adsorption of a layer oxygen atoms on the surface of liquid aluminum and then obtained that when the aluminum liquid surface tension decreased to 0.912 J/m2,the contact angle can be reduced to 0°.The system reached to "perfect wetting".Compared with the model without oxygen adsorption,the ceramic substrate was observed with an increase in the oxygen atoms diffusion the liquid aluminum from the substrate.The diffusion distance is shorter and the aluminum droplet was more compact,spreading more evenly.Analysis of the relevant energies from simulation revealed that the adsorption of oxygen atoms could form a new Al-O bond to reduce total potential energy of Al/Al2O3 system,making the surface tension of the liquid aluminum reduce and the contact angle decrease in macro scope.Respectively,we prepared interface observation samples of aluminum nitride and silicon carbide dip-coated with aluminum film.Then we used HRTEM to analyze the microstructure between the interfaces.By applying SAED,we further analyzed the orientation relationship between aluminum and ceramics.Interface observation in Al/AlN system revealed good quality of matching with a slight tilt.SAED analysis showed an orientation relationship of Al(111)[01(?)]|| AlN(20(?)0)[01(?)]with a tilt of about 90.Al/SiC system showed a smooth and straight connection line on the interface.No Al4C3 was found.At the same time,we found twin phase in Al area.The orientation between single-phase aluminum and silicon carbide was Al(111)[01(?)]||SiC((?)012)[01(?)0],which matched good.Relatively,aluminum with a twin-phase matched poor with silicon carbide.The orientation relationship was approximately Al(1(?))[01(?)]|| SiC((?)021)[01(?)0].