Study On Melting Mechanism Simulation Of Alumina Material For EBSM Forming Technology

The Electron Beam Selection Melting?EBSM?technology was used in the forming process of Al₂O₃ in this paper.The melting process of pure Al₂O₃ nanoparticles and the Al₂O₃ nanoparticles with surface defects or impurities,as well as the effect of heating rate on melting points of pure Al₂O₃ nanoparticles were simulated by the Molecular Dynamics?MD?method.The conclusions are:?1?The surfaces of Al₂O₃ samples formed by EBSM technology were rough.Although the samples had a certain strength and density,further research is needed.The most important thing is to simulate the melting process of Al₂O₃ powder to optimize the forming parameters and improve the performance of the samples.?2?The melting points of the Al₂O₃ nanoparticles with radii of 1-2.2 nm were increased with the increasing of the radius,and were lower than the melting point of the mass.By reasonable fitting and extrapolating of the melting points curve,the relationship between the melting point and the radius was as follows:y=2269.53301-783.2726(1+?x.141347?.⁸⁵¹⁴³²),x?.24 y=2310.33636-871.86612(1+?x.140728?^6.90193),x?.24?3?The melting point of the 1.4 nm Al₂O₃ particle increased with the increasing heating rate,and was higher than the equilibrium melting point.There happened superheating.The more surface defects,the lower the melting points of 1.4 nm Al₂O₃particles.Their melting points were less than that of the perfect crystal particle.The melting points of 1.4 nm Al₂O₃ particles gradually decreased with the increasing impurity doping amount.?4?The melting process of the pure 1.4 nm Al₂O₃ particle,the particles contain 5%surface defects,contain5%Zr or 5%Si,and contain5%Zr+5%Si,could all be divided into four stages:thermal expansion stage,surface activation stage,pre-melting stage and melting stage.The pre-melting temperature of the above particles:the particle contain Zr+Si was lowest?1420 K?,the following was the particle with surface defects?1430 K?,particle contain Zr?1450 K?was in the middle,particle contain Si was the highest?1470 K?.They were all lower than that of pure 1.4 nm Al₂O₃ particle?1500K?.The reason was that the more the surface defects,the larger the specific surface area,the great amount of surface active atoms.The doping caused the unequivalent replacement of particles,caused vacancies and lattice distortion,so the stability of particles was reduced.The 3D printing temperature must be higher than the pre-melting temperature,which is very important for obtaining enough strength and density of Al₂O₃ samples.?5?From the Radial Distribution Function?RDF?of O atoms at 1500 K by the conventional method and at heating rate of 5 K/ps can be seen:the internal structure of the crystal changed and the disorder of the crystal increased at the rapid heating rate.?6?By analyzing the MSD at 300 K of Al and O atoms of different kind of Al₂O₃nanoparticles,such as pure Al₂O₃ nanoparticle,the particles solely including Zr or Si,or the ones including both Si and Zr dopants,we could see that:the addition of impurity could effectively promote the atomic migration and diffusion of Al₂O₃ nanoparticles,thereby it promoted the melting process.The influence of the impurities on O atoms was greater than that on Al atoms.?7?According to the RDF of O atoms under 300 K and melting temperature,we could get that the bond broke at the particular position away from the central O atom during the melting process,such as at site of 2.55?for pure Al₂O₃ nanoparticle,at site of 4.65?for particle including 5%Zr,at site of 4.55?for particle including 5%Si,at site of 4.65?for particle including 5%Si+5%Zr.So if the Al₂O₃ nanoparticles contained impurities,the positions easily to broke bond were far away from the central atom.These positions gave us some informations to select the appropriate wavelength of laser or the electron beam for 3D print device.