Molecular Dynamics Study On The Structure And Phase Transition Properties Of Ag-Cu Alloy Particles

Nanoparticles these have a size of 1-100 nm play an important role in metallurgy,chemical industry and aviation industry because of their complex structures.The properties of the nanoparticles vary by their size,components,surface effect and control parameters,such as temperature,pressure,the cooling rate.At present,the structural characteristics of nanoparticles in the cooling process are becoming a hot spot in the research.In this paper,we applied molecular dynamics simulation by LAMMPS package(the large-scale atomic/molecular massively parallel simulator)to explore the properties of Ag-Cu particles in cooling process.Our simulations use the embedded atom method(EAM)potential,Nose-Hoover thermostat in canonical NVT ensemble at a time step of 1 fs under periodic boundary conditions with a quench rate of 2×1011 K/s.And the potential energy analysis,radial distribution function analysis,crystal and local polyhedrons analysis are used for the results discussion.Through simulation,several conclusions we have achieved:(1)The AgxCu(500-x),(x=0,100,125,200,250,300,375.400,500)alloy particles tend to be Ag-shell/Cu-core structure.When the number of Ag atoms is few,Cu atoms cannot be completely covered by Ag atoms which only appear in the surface.But if there are 200 Ag atoms,Cu atoms are almost completely covered by them.When there are too many Ag atoms,Cu atoms are completely covered by Ag atoms,and other Ag atoms are mixed with Cu atoms in the inner particle.(2)In AgxCu(500-x);particles,the disorder degree of Ag300Cu200 particle is still very high after the liquid-solid phase transition.There is no obvious step phenomenon in the potential energy curve,and there is no significantly change except for the height of the peak in the radial pair distribution function curve during the cooling process.So the binary Ag-Cu alloy particle with stoichiometry Ag3Cu2 is favorable for producing amorphous phase at a cooling rate of more than 2×1011 K/s.(3)The phase transitions temperature of Ag-Cu alloy particles are typically less than or close to the lower phase transition temperature of the Ag particle compared with Cu particle at the same size.(4)In the cooling process,the coordination polyhedral in code 13 is the characteristic of liquid phase and amoiphous phase particles;At equilibrium,the body atoms generally have the coordination polyhedron in code 12I(hexagonal close-packed)in crystal particles,but in the amorphous particles the coordination polyhedron is generally in code 13.The coordination number of the atoms in the surface is generally 7?9.(5)The degree of amoiphization of Ag-Cu nano-alloy particles can be directly judged by the average coordination number.The larger the average coordination number,the higher the degree of amorphization.The results in this paper enrich the microstructure mechanism of Ag-Cu nano-alloy particles,and set up a bridge between experiment and theory,providing a theoretical basis for the preparation and application of Ag-Cu nano-alloy particles with different properties.