Atomic Simulations Of TiAl Alloy Nanoparticles During Their Melting And Coalescing

As a high-temperature structural material,γ-TiAl alloy has applications in the fields of aviation,spacecraft and automobiles due to its excellent comprehensive performance.At present,100nm powders are used in additive manufacturing.With the further decrease of particle size,especially in the sintering process,when considering the influence of temperature,these nanoparticles will exhibit different properties from their bulk materials.The diameter,contact spacing and contact mode affect the combination of particles as the temperature increases,and affect the microstructure and mechanical properties of the formed parts.Therefore,it is of great significance to study the thermal stability and atomic packing structures of nanoparticles during the heating and coalescing in order to understand the relationship between microstructure and properties in sintering process.In this paper,the molecular dynamics simulations based on embedded atom method is used to analyze the atomic average energy,atomic packing structure and local stress variation of atoms in the systems separately containing one,two,and multi-TiAl alloy nanoparticles.The combination of alloy nanoparticles with different particle sizes and the thermal stability and microstructure changes during continuous heating are studied at the atomic scale.During the continuous heating process of one particle,as the number of atoms contained in the particle increases,the thermal stability of the particle increases,and the alloy particle is transformed from a nearly spherical type with some small facets to an irregular polyhedron.When the temperature reaches a certain point,the irregular accumulation of atoms rapidly spreads through the entire particle,the particles melt into a spherical shape,and the melting point increases as the particle size increases.During the heating process,the lighter Al atoms are more susceptible to stress,in which the surface atoms are subjected tensile stresses and the internal atoms are mostly compressive.The higher the temperature,the more the number of atoms that apparently under stress.For a two-particle system,the larger the particle size at room temperature,the larger the spacing of the particles allowed to merge;the different contact facets also affect the combined distance,but as the particle size increases,this effect will significantly weakened;during the process of coalescing,the particles will rotate.For the three-particle and four-particle systems,the effect of the contact facets on the merge is consistent with the two-particle system,and the spacing has a greater effect on the merge mode.When the spacing is small,the particle rotation and relative misalignment slide will squeeze the contact area.The atoms form more defects,and the gap area after coalescing is larger when the spacing is larger,and the particles slide to the position to complete the combination.During the continuous heating process of the newly formed particle,the evolution of the atomic packing structure being away from the connection zone conforms to the evolution law of the single particle structure,the connection zone will continue to grow and grow through the slip of the atom as the temperature increases.The interface between particles that appears at room temperature disappears with increasing temperature.As the temperature increases,all atoms leave their lattice positions,the particles melt into a sphere and their atomic arrangement becomes completely disordered.