Vania Vassileva

Simulation of the heat transfer process through treated metal, melted in a water-cooled crucible by an electron beam

A two-dimensional axisymmetrical steady-state base thermal model is developed for electron beam (EB) melting and refining. A computer simulation is carried out, according to the proposed model, for various powers of EB heat source. Temperature distributions and heat flows in a cylindrical copper ingot, confined in a copper water-cooled crucible are calculated. The calculated and experimental observed shapes and/or depths of the metal pools are compared and a reasonable agreement is observed.

Investigations of refining processes during electron beam melting

Abstract The improvement of impurity contamination and extraction of non metallic inclusions during electron beam (EB) refining involves a better understanding of heat exchange mass transport and chemical interactions among the alloy components, the contaminants and residual gases in the technological vacuum chamber. A physical description of the EB refining process and a computer simulation code for evaluating the kinetics of the refining of copper, titanium and cobalt base alloys are developed and applied. The data for the calculated approximation parameters of the partial processes during refining are given. Such evaluations are applicable to an optimization of the fabrication of pure metals and alloys.

Thermal Processes in Electron-Beam Treatment of Metals

An amended quasi-stationary model of heat transfer in a metallic ingot hardening in a water-cooled crucible after electron-beam melting and refining of the metal is suggested. The processes of heat transfer and heat flows through different interfaces are considered for aluminum and tantalum under the assumption of three mechanisms of heat transfer. The model allows for the temperature dependences of the thermal conductivity and specific heat capacity. Experimental results are used for estimating the distribution of energy in beam heating of the metal and the losses of heat to radiation and evaporation from the upper surface of the ingot. Data on the shape of the hardening front, on the geometry of the molten zone, on the heat flow at various treatment parameters (electron beam power, casting rate, etc.) are obtained and discussed.

Experimental and numerical investigation of the refinement of Hf by EBM

Electron beam melting (EBM) in vacuum is one of the most promising technologies for refining and recycling of metals that react with oxygen when heated. Hf is such a metal. Pure Hf (with a small content of gas and metal impurities) is needed for a variety of applications in the aerospace industry and metallurgy, in the production of components of nuclear reactors, microprocessors, optical components etc. We conducted experiments with the ELIT-60 equipment on Hf ingots at electron beam powers of 12, 15, 17 kW and obtained data about the concentration of impurities by the ICP-MS method. For further understanding and optimizing the Hf refining processes, a non-stationary heat model was applied for numerical simulation of the heat transfer processes. Simulation data about the liquid pool variation during the e-beam treatment was thus obtained. The flatness of the crystallization front shape, which is connected to the structure quality, was investigated by optimization criteria related to the curvature of the liquid/solid boundary curve. We also describe an algorithm for calculation of the criteria. One of the criteria was applied to EBM of Hf for different electron beam powers; the results obtained were confirmed by the experimental data. Combining experimental, theoretical and simulation results, a proper technological regime is proposed for better Hf refining.

Refining effect of electron beam melting on recycling of nickel wastes

Experimental and theoretical investigations and results on refining of nickel scrap materials applying electron beam melting (EBM) are presented and discussed. Different technological regimes (different e-beam powers and melting rates, single and double EBM) are realized and the refining effect on the recycling of nickel wastes is studied. Thermodynamics conditions and mechanisms as possibilities for the refining process of nickel are evaluated and analyzed. Data for the refining kinetics of EMB of Ni wastes is calculated using Monte Carlo methodology. For the performed experiments the best purification of Ni (99.99%) is obtained at 15 kW beam power and 63.8 g/min melting rate. The accumulated data, the obtained experimental results and evaluation of the kinetics coefficients allow identification of the refining process mechanisms and process optimization for e-beam recycling of nickel wastes.

Obtaining Multiple Metals Through Electron Beam Melting of Refractory Metal Wastes

Investigations and results on the refining of tungsten scrap applying electron beam melting (EBM) in vacuum are presented and discussed. In this work EB melting experiments were performed in single or double-melt operations with different power inputs and refining times for tungsten purification and recovery of multiple metals (including refractory and other metals such as Mo, Nb, Cu, Zn, etc.), which are alloyed elements or impurities with high concentrations in the initial materials. Evaluations for extraction of some valuable metals, generated in the condensate at their removal from the liquid metal during the refining process are provided. Efficient technological regimes for e-beam melting and refining that enable the simultaneous production of pure metal ingots and condensates that can be used directly or can be used for subsequent extraction of expensive and valuable metals are presented.

Electron Beam Deposition of High Temperature Superconducting Thin Films

Some results of characterization of prepared high temperature super-conducting HTS (namely YBa2Cu3O7) thin films by electron beam physical vacuum deposition (EB PVD) are given. An approach for the use of high rate EB PVD of the (HTS) depositing layers is discussed. A need of clarification of: (i) the role of the used electron beam energy distribution at the melted and vaporized material surface on the molten metal stirring, (ii) the effect of the temporal (not continuos) thermal contact between evaporated material and crucible as well as (iii) the consequences of the processes of the beam interaction with the vapors on the obtained evaporating rate is discussed.