F. Kh. Mirzade

Nonlinear longitudinal strain wave interacting with point defect in metal plates

A model of nonlinear longitudinal strain wave propagation in metal plates with quadratic nonlinearity of elastic continuum, exposed to laser impulses, is developed in view of the interaction with the fields of point defects (vacancies and interstitials). The influence of the recombination-generation processes in a defect subsystem on elastic strain wave propagation is analyzed. The existence of a nonlinear elastic shock wave of low intensity is revealed in the system and its structure is studied. The shock waves can have either an oscillatory or a monotonic profile. The estimations of the wave front depth and velocity are performed. The contributions to the linear elastic modulus, as well as to the lattice dispersion parameters are found, which are due to the interaction of the elastic strain field and the field of defects.

A model for the propagation of strain solitary waves in solids with relaxing atomic defects

A model for the propagation of nonlinear dispersive one-dimensional longitudinal strain waves in an isotropic solid with quadratic nonlinearity of elastic continuum is proposed by taking into account the interaction of the longitudinal displacements with the temperature field and the field of concentration of nonequilibrium (recombining) atomic point defects (vacancies and interstitial atoms). The governing nonlinear equation describing the evolution of the self-consistent strain fields is derived. It is shown that the thermoelastic effect on the strain waves manifests itself in the appearance of dissipative terms, which describe the heat transfer and the thermoelastic interaction caused by the strain-induced heat release due to the recombination of atomic defects. The equation that describes the evolution of the amplitude of nonlinear traveling localized waves with time in the single-wave approximation is derived, and on the basis of this equation, the damping increments of these waves are determined wit...

Finite-amplitude strain waves in laser-excited plates.

The governing equations for two-dimensional finite-amplitude longitudinal strain waves in isotropic laser-excited solid plates are derived. Geometric and weak material nonlinearities are included, and the interaction of longitudinal displacements with the field of concentration of non-equilibrium laser-generated atomic defects is taken into account. An asymptotic approach is used to show that the equations are reducible to the Kadomtsev-Petviashvili-Burgers nonlinear evolution equation for a longitudinal self-consistent strain field. It is shown that two-dimensional shock waves can propagate in plates.

Numerical modeling of laser sintering of two-component powder mixtures

The process of direct sintering of metal powders induced by laser radiation is investigated. A two-component mix of powders consisting of low- and high-melting components is considered. The model is based on a self-consistent nonlinear equation of continuity for volume fractions of low- and high-melting components of the mixture and on the equation of energy transfer in the melt-powder mixture system. It includes the motion of hard particles due to shrinkage associated with the changed density of the powder mixture and with convective fluxes caused by the forces of surface stress and gravitation. The liquid flow is determined by the Darcy law of filtration. The effect of the finite width of the region of phase transition of the high-melting powder has been detected. The rate of melting zone expansion is shown to depend on both the parameters of laser radiation (beam power) and on the physical characteristics of the substance of particles, and to grow with the increase in penetrability or phase transition heat. A diagram of the evolution quality of the melting front is obtained, by which it is possible to predict the solution behavior depending on the parameters of the powder mixture (penetrability and melting heat).

Heat and Mass Transfer under Laser Sintering of a Powder Mixture

A model of heat and mass transfer during the sintering process of a two-component powder mixture under the action of laser beam irradiation was formulated and numerically investigated. The model accounts for the movement of solid particles in a shrinkage caused by the changed density of the powder mixture, as well as for convective fluxes caused by surface forces and gravity. The flow of the liquid phase of the low-melting component of the mixture was described by the generalized Darcy law. The space-inhomogeneous and non-steady distributions of the phase saturations and the temperature field were estimated to predict the dynamics of the phase change process depending on the properties of the powder mixture (porosity, penetration, and thermal properties of components), and depending on the parameters of the laser beam. The effect of surface subsidence of the powder mixture has been considered.

Heat Transfer and Thermocapillary Convection during the Laser Deposition of Metal Powders Implemented in Additive Technologies

Heat-transfer- and thermocapillary-convection macroprocesses observed during direct laser metal deposition (DLMD) with coaxial powder injection are examined. The study is performed using the 3D mathematical model incorporating self-consistent equations for free surface evolution, heat transfer, and hydrodynamics, which allow for powder-particle embedding into the thermocapillary convection zone under DLMD. The processes under consideration refer to the main ones underlying additive laser technologies, which determine the microstructural properties and quality of synthesized parts. The convection-diffusion equations are numerically solved using the final volume method. Calculations are carried out for the thermocapillary convection of H13 steel powder. The influence of laser-radiation characteristics (power, scanning rate, intensity distribution in the beam) and the powder-mass flow velocity on temperature fields, the structure of convective melt flow (including a maximum melt velocity), and the geometric characteristics (height and width) of the object formed is investigated.

Numerical investigation of the microstructure of a clad layer produced via laser cladding with coaxial metal powder injection

The microstructure of a clad layer produced via selective laser cladding with coaxial metal powder injection is studied numerically. The Johnson–Mehl–Avrami–Kolmogorov equation for condensed systems with inhomogeneous rates of nucleation is used to model the phase change kinetics. The impact of the substrate boundary along with interconnected heat transfer and phase change processes on the final microstructure of a built-up layer is demonstrated. The qualitative difference between the behavior of the temperature on the built-up layer’s surface and at the depth of the substrate is established, revealing the inhomogeneous microstructure of the final layer.

Finite-amplitude elastic waves interacting with temperature and nonequilibrium atomic defect fields

Nonlinear dynamics of one-dimensional longitudinal waves in isotropic elastic plates was studied taking into account the interaction of displacement fields, temperature, and concentration of nonequilibrium (relaxing) atomic point defects. A nonlinear evolution equation for describing the self-consistent field of longitudinal thermoelastic strain was derived. The effect of generation-recombination processes on the evolution of nonlinear localized and periodic waves was analyzed. In the single-wave approximation, an equation was derived which describes the amplitude variation of nonlinear waves; based on this equation, characteristic features of damping of these waves were considered taking into account low-and high-frequency losses. The interaction of counterpropagating waves is briefly discussed taking into account dissipative effects.

Wave instability of a molten metal layer formed by intense laser irradiation

Wave structure of a molten metal layer flowing over the walls of a vapor-gas cavern that appears as an intense laser radiation penetrates deep into condensed media is studied theoretically taking into account surface tension, gravitation, thermocapillary effect, and nonuniform evaporation from the free surface of the melt. A long-wavelength evolution equation describing the evolution of nonlinear waves on the free surface of a plane molten layer is derived. The spatially periodic running solution to this equation is obtained, and the main characteristics (amplitude and period) of the nonlinear wave structures are determined.

Using optical diagnostics to determine the melt temperature field in layer-by-layer laser alloying of metal powder

The results of application of optical diagnostics in the estimation of the temperature field at the melt surface in layer-by-layer laser alloying of metal powder are presented. It is demonstrated that surface concavity induced by the thermocapillary effect upon nonuniform heating may distort pyrometry data considerably. The use of external illumination provides an opportunity to determine the shape of the melt surface. The obtained minimum estimate of the temperature gradient in the metal region affected by laser radiation is 2.8 × 104 K/cm.