13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Metallic melt fracture and fragmentation under the high-current electron irradiation Polina N. Mayer.1,*, Alexander E. Dudorov1, Alexander E. Mayer 1, 1 Department of Physics, Chelyabinsk State University, 454001, Russia * Corresponding author: polina.nik@mail.ru Abstract Action of the high-current electron beam leads to an intensive heating of a surface layer of the irradiated metal. Rapid temperature increase can cause melting of the surface layer and generate intensive stresses in it. Release of these stresses induces fast expansion of the molten metal and, on the contrary, results in tension. Tension of the melt activates nucleation, growth and coalescence of vapor bubbles, it means, fracture and fragmentation of the metallic melt. In present work we numerically investigate kinetics of the liquid metal fracture and fragmentation under the dynamic tension initiated by the powerful electron irradiation. Metal is treated as a two-phase medium consisting of vapor bubbles in liquid metal at the first stage of the evolution and of liquid drops in vapor at the second stage. Two-level approach is used: on the macroscopic level, the irradiated metal is treated as a two-phase heterogeneous medium in the one-velocity approximation, while on the microscopic level, the exchange of energy, mass and volume between both phases are described including grow or decrease of size of the vapor bubbles or liquid drops. Generation of ultra-dispersed particles of copper at the high-current electron beam irradiation is numerically investigated. Keywords Liquid metal, Dynamic fracture, Electron irradiation, Heterogeneous medium, Vapor bubbles 1. Introduction Action of the high-current electron beam on the metals can be used for production of the ultrafine metal particles [1,2]. The process of particles formation passes through several stages. At the first stage, during the irradiation, fast beam electrons lose their energy in the substance, which leads to the metal heating and formation of the high pressure region inside the energy release zone [3-5]. The next stage is an expansion of the heated and “compressed” layer of metal, which generates tensile stresses (negative pressure) in it. Destruction of the expanded metal begins at the expense of nucleation and growth of cavities. The higher temperature of the surface layer leads to the lower threshold of the negative stress, required for the destruction [6,7]. Complete destruction of the liquid phase takes place when the cavities grow up thus much to coalescence with each other forming a singly connected vapor phase, while the remaining liquid is fragmented on drops. The following expansion of the vapor-drops mixture (aerosol) is accompanied by the metal evaporation and condensation on drops. At the sufficient level of the enclosed energy, the liquid drops can be fully evaporated with formation of pure vapor. In turn, the adiabatically expanding vapor can become oversaturated, which result in the nucleation of liquid drops in it. In the paper [8] the condensation of the metal particles from the pure vapor, obtained at the complete evaporation under the action of the high-current electron beam, was numerically investigated; it was shown, that the homogeneous nucleation and the coagulation of the drops determine the size of the produced metal nanoparticles. Meanwhile, the electron beam irradiation leads to the incomplete evaporation in the most cases. A part of metal remains condensed in the form of liquid drops. During the adiabatic expansion these drops become the centers of condensation; their quantity determines the quantity and size of the formed ultrafine metal particles. In this report a mathematical model of the ultrafine metal particles formation in the case of incomplete evaporation is described. Kinetics of evaporation and condensation of metal irradiated by the high-current electron beam is numerically investigated.
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