A. A. Uglov

Modelling of pulse-periodic energy flow action on metallic materials

Abstract Heat processes in pulse-periodic energy flow action on metallic materials are considered. Heating. melting, evaporation and solidification are analysed by means of mathematical modelling. Velocities and positions of phase boundaries (both evaporation and melting) are determined over a wide range of operating parameters. The existence of surface temperature, melt thickness and velocities of phase boundaries of different types of oscillation regimes are shown. Relationships between the pulse-periodic energy flow structure and the evolution of heat processes are determined.

Simulation of unsteady-state thermocapillary mass transfer for laser doping of metals

Abstract By imposing the approximation of a shallow melt bath, small reduced Reynolds number and of a plane free surface, unsteady-state thermocapillary flow of melt is considered for the case of melting a metallic solid body by a Gaussian surface heat source. Based on the velocity field obtained, convective mass transfer of the doping impurity is analysed by the method of model particles in the assumption of a small Schmidt number. The feasibility of producing both a relatively homogeneous and an essentially nonmonotonous (layered) structure of concentration fields in the remelted zone is shown. The analysis of the formation of such structures is made and their specific features are revealed in the case of laser doping of metals from the gas (plasma) phase and from previously deposited coatings. Comparison between the predicted concentration profiles and the results of experiments is made and their satisfactory qualitative agreement is obtained.

MOVEMENT OF PHASE BOUNDARIES OF METALS SUBJECTED TO SURFACE PERIODIC ENERGY PULSES

The heat phenomena including heating, melting, evaporation, cooling, and solidification are analyzed by means of mathematical modeling. Velocities and positions of phase boundaries (both evaporation and melting) are determined for different conditions of pulse‐periodic energy flow irradiation of metallic materials. Heat process dynamics, determined by the shape of the single energy pulse, by the energy input per oscillation period, and by the average energy density flow, are discussed.

Mass transfer in the process of pulsed laser alloying of titanium in nitrogen vapors

Thermocapillary mass transfer accompanying pulsed laser alloying of titanium in vapors of liquid nitrogen is studied. The impurity concentration fields are determined by the methods of numerical modeling. The numerical and experimental results are compared.

Modeling the thermal processes of laser synthesis for the nitrides in refractory metals

We examine the thermal processes which include the motion of phase melt and vaporization fronts in the laser synthesis of nitrides in high-melting refractory metals. The integral radiant flux, on reaching the surface of its target, is determined by a longitudinal x-ray method. We demonstrate that the extreme relationship between the thicknesses of the synthesized layers and the pressure of the gas is a result of the competition between the process of surface vaporization in the region of lower pressures and the increase in the optical density of the beam in the region of higher pressures.

Consideration of the nonmonotonic character of the spatial distribution of laser radiation in calculating heat-treatment regimes for massive articles

Conclusions1.A method based on approximation of the real heat source by a combination of Gaussian sources is proposed for calculation of the parameters of the heating of massive bodies by spatially nonmonotonic laser radiation; this makes it possible to represent the desired thermal field as the superposition of known solution.2.The higher the velocity of the beam right down to disruption of the production parameters of the hardening process, the more vigrously the nonmonotonicity of the spatial distribution of laser radiation in the direction perpendicular to the displacement axis will affect the parameters of the temperature field. This influence diminishes with decreasing displacement rate of the laser beam and with increasing depth of penetration of the isotherm under consideration.3.Computations of production parameters of the laser hardening of steel 55SM5FA and ShKh15 articles indicated good convergence with experimental data.

Thermophysical recovery processes during pulse laser heating

We consider thermophysical processes during laser heating of an oxide with account of growth of the metallic phase at the surface.

Nonsteady thermocapillary mass transfer in the laser alloying of metals

This article examines convective mass transfer of an impurity in a shallow bath of molten metal with allowance for the motion of the fusion front during the laser alloying of metals.

Thermocapillary convection in the shallow bath formed when a solid is melted by a concentrated energy flux

The unsteady thermocapillary motion of the liquid phase (motion caused by the temperature dependence of the surface tension and the nonuniform heating of the free surface of the melt) associated with the melting of metals by a concentrated energy flux (CEF) is investigated taking into account the variation of the size and shape of the molten bath with time. It is assumed that the free surface of the liquid is plane, and that the molten bath is shallow, i.e., its radius considerably exceeds the depth. It is shown that the movement of the bottom of the bath into the interior of the metal has an important influence on the hydrodynamic processes and leads to quantitative and qualitative differences from the results obtained for flows with plane and stationary boundaries of the liquid layer.