Katia Vutova

Calculation of weld parameters and thermal efficiency in electron beam welding

Abstract Using the model of quasi-steady thermal distribution in a solid sample, generated by a linear heat source, moving at constant welding velocity, values of the weld depth at a given weld width are calculated and compared with the experimental data. A discussion for thermal efficiency and an analysis concerning the correlation between the weld depth and weld width and the process parameters are given. The results show that the steady operating, moving linear heat source can be assumed as an approximation in the simulation of electron beam welding with a deep penetrating beam.

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.

Experimental investigation of the weld depth and thermal efficiency during electron beam welding

Abstract The results are given of an investigation of electron beam welding, concerning the correlation between the process parameters such as weld depth, focusing parameter and thermal efficiency. Weld quality data for various welding velocities, beam powers and positions of the focusing plane relative to the sample surface are given. The goal was to achieve practical and reliable optimum process parameters and to estimate the efficiency of the electron beam welding.

Photoelectron signal simulation from textured samples covered by a thin film

Abstract In this paper we propose a mathematical model for calculating the XPS intensity distribution from textured sample surfaces covered with a thin film. The surface roughness is approximated using triangular prisms. Analytical expressions for calculation of the angular photoelectron intensity distribution are given. The obtained results allow an understanding of the relation between the escape depths of emitted photoelectrons and the angular XPS intensity distribution. The results show that the X-ray photoelectron signals vary significantly with a change in surface overlayer thickness and prism slope angle α . The maximum of the XPS intensity distribution does not correspond to the maximum escape depth of emitted photoelectrons. The ejected photoelectron ejection angle characterizes the maximum location depth of the investigated component or chemical bond. This model is useful when evaluating the surface roughness and the film thickness.

Sensitivity, contrast and development process in electron and ion lithography

Abstract The dependence of the resist solubility rate S on the average exposure dose D (or on the adsorbed energy per 1 U resist volume) makes it possible to optimise the used sensitivity (or the dose requirements) to achieve the needed contrast at chosen development conditions for an arbitrary combination of resist–developer (i.e. at a given molecular weight, resist density and radiation efficiency of the charged particles). Two cases of this relation S ( D ) are distinguished. In the first of them a universal dependence S ( D ) is obtained during the development process with one and the same solubility rate. In the second case the obtained dependence S ( D ) is a multi-valued function of a non-linear solubility rate during the development process for a different developing time. The contrast parameter value γ s (proportional to the traditionally used contrast parameter γ d ) is determined by the slope of the dependence S ( D ). One and the same resist–developer couple can show high sensitivity at a low contrast value and a high contrast value at lower sensitivity for different conditions. The contrast is a function of the developing time and the dose in the case of a non-linear S ( D ) dependence. A mathematical model and results for the resist surface evolution in electron and ion beam lithography are also presented.

The role of ingot–crucible thermal contact in mathematical modelling of the heat transfer during electron beam melting

The heat exchange of different interfaces between the casting ingot and both the water-cooled crucible and the pulling mechanism is studied. Computer simulations of the process of electron beam melting and refining and regression equations for the heat flows through the boundary surfaces, as well as for the volume of the molten metal pool on the top part of the casting ingot have been performed. They are considered as functions of the coefficients of the heat transfer and the width of the heat contact ring between the casting ingot and the copper crucible. The response surface plots are drawn to visualise these dependences. They can be used for the choice of proper process conditions and for the optimisation of the heat flows, according to the requirements of the process.

Computer simulation of the heat transfer during electron beam melting and refining

Abstract A computer model and software for simulation of electron beam melting are developed. A two-dimensional modeling is done, for an ingot, casted in a cylindrical copper water-cooled crucible. Melting of copper, titanium and aluminum were simulated. The pouring of the molten material increases the energy input and the depth of the molten pool. In the case of titanium, due to the molten metal stirring an assumption for limitation of upper surface ingot temperatures was done. The important role of the temperature distribution, near to cooled crucible wall contact zone, in the process of thermal balance is discussed. Some qualitative conclusions for non-steady thermal transfer in this zone are made.

Electron Beam Melting and Refining of Metals: Computational Modeling and Optimization

Computational modeling offers an opportunity for a better understanding and investigation of thermal transfer mechanisms. It can be used for the optimization of the electron beam melting process and for obtaining new materials with improved characteristics that have many applications in the power industry, medicine, instrument engineering, electronics, etc. A time-dependent 3D axis-symmetrical heat model for simulation of thermal transfer in metal ingots solidified in a water-cooled crucible at electron beam melting and refining (EBMR) is developed. The model predicts the change in the temperature field in the casting ingot during the interaction of the beam with the material. A modified Pismen-Rekford numerical scheme to discretize the analytical model is developed. These equation systems, describing the thermal processes and main characteristics of the developed numerical method, are presented. In order to optimize the technological regimes, different criteria for better refinement and obtaining dendrite crystal structures are proposed. Analytical problems of mathematical optimization are formulated, discretized and heuristically solved by cluster methods. Using important for the practice simulation results, suggestions can be made for EBMR technology optimization. The proposed tool is important and useful for studying, control, optimization of EBMR process parameters and improving of the quality of the newly produced materials.

Photoelectron signal simulation from textured overlayer samples

In this paper we propose a mathematical model for calculating XPS intensity distribution from a textured sample surface covered with a thin film. The surface roughness is approximated using triangular prisms. Analytical expressions for XPS intensity calculation are given. The results show that the XPS signals vary significantly in the cases of thin overlayers and high values of the prism slope angle. This model is useful when evaluating the surface roughness together with the film thickness.

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.