A. G. Kolmakov

Multiparametric optimization of laser cutting of steel sheets

Mathematical models that provide an adequate description of the effect of laser cutting parameters on the roughness of the cut surface with no burr, the extent of the heat-affected area, and the nonperpendicularity of the cut surface are devised. Nomograms that allow one to select the laser cutting regimes designed to minimize the surface roughness, the heat-affected area, and the nonperpendicularity for sheets of St. 3 steel of different thickness are proposed.

Local Elastic Moduli of Particle-Filled B83 Babbitt-Based Composite Materials Prepared by Powder Metallurgy Techniques

We have measured local elastic moduli of particle-filled B83 babbitt-matrix composite materials produced by powder metallurgy techniques and containing silicon carbide (SiC) ceramic and modified shungite rock particles as fillers. The measurements were made by an optoacoustic laser method, whose basic principle is to determine the phase velocities of thermo-optically excited longitudinal and shear ultrasonic waves. The addition of 3 wt % of high-modulus SiC particles tends to increase the Young’s and shear moduli (by 10–12%) and decrease Poisson’s ratio (by 5%) relative to a hot-pressed B83 babbitt sample without fillers.

Role of nucleation in the development of first-order phase transformations

Hypotheses on how first-order phase transitions develop which deny a fundamental element of the classical thermal fluctuation theory, namely, that the nucleation of a new phase must take place when the crystal lattice changes, are considered. It is shown that the thermal fluctuation theory does not work for polymorphic transformations in pure metals, which are accompanied by lattice rearrangement in a macrovolume (over the entire volume of a sample under study) without substance transfer. However, the classical thermal fluctuation theory of new phase nucleation is valid in describing the supersaturated solid solution decomposition in the case where the main pattern of the crystal lattice of the matrix is retained, and a new phase, which differs from the parent one in both crystal structure and chemical composition, precipitates in separate microvolumes.

Properties of nanostructured titanium nickelide and composite based on it

The properties of nanostructured nitinol (Ni, 55.91 wt %; Ti, 44.03 wt %) in the initial state and after mechanical and the thermal treatment and a composite of nitinol with a tantalum surface layer obtained by magnetron sputtering have been studied. Compared with microstructured nitinol, the use of nanostructured nitinol for medical appliances, like stent, has great opportunities due to better corrosion resistance in solutions that model the physiological media of a human organism and the decreased diffusion of nickel ions into solution below the admitted average dietary intake of 200–300 mg/day in solutions of any acidity. Surface mechanical polishing increases its corrosion resistance by two to three times more. Compared with nitinol, the composite of nitinol with a tantalum surface layer is ∼7–11% better by strength, plasticity, and surface microhardness and characterized by the absence of a corrosion processes and diffusion of metal ions into solution.

Mechanical properties of nanostructured nitinol/chitosan composite material

The mechanical properties and degradation behavior of a composite material based on nanostructured nitinol and a biodegradable polymer surface coating of chitosan of various molecular weights are studied. The formation of a biodegradable surface layer of any composition does not change the properties of the base material. The created biodegradable polymer surface coating disintegrates upon applying the yield stress, i.e., within the operating range of loadings on medical items. The base disintegrates with the formation of a neck. Surface layer cracking is observed only near the fracture.

Optimization of NbC Concentration in (Bi,Pb)2Sr2Ca2Cu3O10 + x Superconducting Ceramics Using Multifractal Formalism

The microstructure effect on the superconducting properties of (Bi,Pb)2Sr2Ca2Cu3O10 + x ceramics containing different additions of nanocrystalline NbC powder was analyzed using information interpretation of multifractal formalism. By introducing NbC additions, the midpoint transition temperature Tc of the ceramics can be raised by more than 10 K. The optimal NbC content evaluated with the use of the multifractal parametrization methodology is 0.35 wt %. The corresponding increase in Tc may attain 12–16 K. The crystallite and pore substructures in the ceramics are found to be closely related. The information approaches are shown to have great potential for structural characterization of superconducting materials and optimization analysis of property–structure–composition relationships.

Wear products that form during tribological tests of aluminum-matrix composite materials

The wear products and the friction surfaces of the composite materials fabricated by reactive casting after the addition of commercial-purity aluminum AD1, titanium and nickel powders, and nanosized modifiers to a matrix melt are studied. The dispersity and the chemical composition of the wear products that form an intermediate layer between the contacting surfaces are analyzed, and the dominating wear mechanisms under experimental tribological loading conditions are determined. It is shown that the formation of such a disperse intermediate layer during lubricant-free friction of the synthesized composite materials decreases the temperature in the tribological contact and ensures a transition from weak to intense wear at higher critical loads.

Grain size effect of austenite on the kinetics of pearlite transformation in low- and medium-carbon low-alloy steels

The value of the parameter n from the kinetic Avrami equation is determined for pearlite transformation in low- and medium-carbon low-alloy steels. The grain size effect of austenite on the kinetic curves of pearlite transformation is shown.

FEATURES OF SOFTENING PROCESSES OF ALUMINUM, COPPER, AND THEIR ALLOYS UNDER HOT DEFORMATION

The sequence of the hot-deformation-induced softening processes of aluminum, copper, and their alloys explaining the effect of an elevated plasticity is studied.

Systematic description of nanomaterial structure

The use of systematic approaches ensures significant development of the conventional methods of materials science and efficient use of these methods for objects having complex multidimensional structure, including nanostructured materials. The application of wavelet-based multifractal analysis and multidimensional physicochemical analysis for qualitative and quantitative description of material structures, which allows one to detect that differences that cannot be detected using other individual methods, is shown. The system characteristics of material structures are assessed. The self-organization processes in structures are characterized.