Characterization of Aluminum Foam Impact Response

Strength of Materials - The paper addresses the investigation of high-strain rate compressive behavior of Al foams subjected to impact at the intermediate striking velocity ranged from 40 to...     

Characteristic features of microhardness determination in assessing the structural strength of coatings

A critical analysis of the results of microhardness measurement, which were obtained by subjecting surface layers to various loading schemes, is conducted for a broad circle of protective strengthening coatings. Characteristic features of the deformation and failure are investigated experimentally within the region of indenter penetration during elastoplastic contact of coatings formed from brittle high-strength materials. For a more accurate and reliable estimate of the structural strength of coatings, notions concerning microhardness as the limiting strength of the material are developed, and the test conditions required to obtain H values comparable with respect to their own physical significance are indicated.Translated from Problemy Prochnosti, No. 9, pp. 44–54, September, 1995.     

Theory of Initial Microcavity Growth in a Liquid Metal Around a Gas - Releasing Particle. Part 2. Bubble Initiation Conditions and Growth Kinetics

A theory is presented that includes capillary, hydrodynamic, and diffusion aspects. The main attention is devoted to capillary and hydrodynamic effects. The hydrodynamic process (bubble growth) is governed by a nonlinear integrodifferential equation, whose coefficients are dependent on the surface tension, density, and viscosity of the liquid, and also on the difference between the pressure in the gas within the bubble and that in the surrounding liquid. The gas pressure in the bubble is dependent on the rate of gas release from the inclusion (source). An expression is derived for the bubble radius as a function of time. The theory can be useful for developing the technology of powder materials and foam metals.     

Application of carbide coatings to hard-metal tools

Conclusions A study was made of the deposition of coatings of titanium, zirconium, vanadium, and niobium carbides on VK8 and T15K6 alloy surfaces. The kinetics of growth, structures, phaseTranslated from Poroshkovaya Metallurgiya, No. 7(223), pp. 36–40, July, 1981.     

Semisynthetic flavocytochromes based on cytochrome P450 2B4: reductase and oxygenase activities

Endurance exercise training induces a rapid increase in the GLUT-4 isoform of the glucose transporter in muscle. In fasted rats, insulin-stimulated muscle glucose transport is increased in proportion to the increase in GLUT-4. There is evidence that high muscle glycogen may decrease insulin-stimulated glucose transport. This study was undertaken to determine whether glycogen supercompensation interferes with the increase in glucose transport associated with an exercise-induced increase in GLUT-4. Rats were trained by means of swimming for 6 h/day for 2 days. Rats fasted overnight after the last exercise bout had an approximately twofold increase in epitrochlearis muscle GLUT-4 and an associated approximately twofold increase in maximally insulin-stimulated glucose transport activity. Epitrochlearis muscles of rats fed rodent chow after exercise were glycogen supercompensated (86.4 +/- 4.8 micromol/g wet wt) and showed no significant increase in maximally insulin-stimulated glucose transport above the sedentary control value despite an approximately twofold increase in GLUT-4. Fasting resulted in higher basal muscle glucose transport rates in both sedentary and trained rats but did not significantly increase maximally insulin-stimulated transport in the sedentary group. We conclude that carbohydrate feeding that results in muscle glycogen supercompensation prevents the increase in maximally insulin-stimulated glucose transport associated with an exercise training-induced increase in muscle GLUT-4.     

Thermophysical Properties and Preparation of Slag-Forming Mixtures

The phase and chemical transformations in slag-forming mixtures used in continuous casting and the ladle treatment of steel over a broad temperature range are studied. By physicochemical analysis, data are obtained regarding the relations between the endo- and exothermal effects and the time for silicate and slagmelt formation. The thermal diffusivity is determined by an improved method in which heat sources and sinks in the heated material are taken into account. On the basis of these results and preliminary values of the specific heat and density, the temperature dependence of the thermal conductivity is found for the slag mixtures. The results permit prediction of the economic consequences (including the thermal costs) of using slag mixtures, in selecting the initial materials for granule production and in casting the steel.     

Theory of Initial Growth of a Microcavity in a Liquid Metal Around a Gas-Releasing Particle. Part 1. Physical and Mathematical Models

Certain inhomogeneities in a liquid can act as bubble nucleation centers. If such a center is a source of gas on a considerable scale, the bubble can grow rapidly to an appreciable size. The following model is proposed for analyzing this process: a solid sphere (compound containing a gas-forming element such as hydrogen) is surrounded by a liquid metal. The initial equations are as follows: the Navier-Stokes equation, in which there are terms containing the concentration of the gas component; the equation of continuity; and the equation for the convective diffusion of the gas component in the liquid metal. The growth of the bubble obeys an integrodifferential equation derived here, which reflects the effects of the hydrodynamic, diffusion, and capillary factors.

     

Structure and mechanical properties of iron after surface severe plastic deformation under friction with simultaneous nitrogen saturation: II. The mechanical properties of nano- and submicrocrystalline iron saturated with nitrogen during deformation

The effect of structure refinement of iron to submicro- and nanograins during intense plastic deformation under friction (SPDF) with simultaneous nitrogen saturation on the mechanical characteristics (hardness, plasticity, Young??s modulus) has been studied by nanoindentation. The nitrogen saturation of iron during SPDF is shown to increase the hardness of micro- and submicrocrystalline regions of the surface layer as compared to SPDF in argon as a result of solid-solution hardening. A high nitrogen concentration in an ??-Fe[N] solid solution weakly affects the mechanical properties of nanocrystalline iron with grain sizes d < 50 nm, in which deformation is controlled by grain-boundary sliding.     

Influence of wettability on bubble formation in liquid

This paper presents experimental results of the surface phenomena effect on bubble formation from a single orifice in water and at nozzle in liquid aluminium with gas blowing at small flow rates. The usage of coated orifice in water and nozzles of different materials in the melt realized wide range of contact angles. The meaningful stages, termed (1) nucleation period, (2) under critical growth, (3) critical growth and (4) necking, were identified during bubble formation in a regime referring to simultaneous forced flow and surface tension control. It was revealed that bubble formation is substantially dominated by hysteresis of contact angle. Evolution of interface equilibrium and force balance conditions distinctive for bubble formation is clarified. X-ray fluoroscope was used to carry out in-situ observation of bubble formation in the melt. It was shown that bubble volume increased with wettability worsening both for aqueous and metallic systems. A further insight into the mechanism of the bubble formation was obtained by comparison of the bubble behaviour at the tip of the injection devices in liquid aluminium and at the orifice in water.     

Structure and mechanical properties of iron after surface severe plastic deformation under friction with simultaneous nitrogen saturation: I. structure formation

The structure of armco iron after severe plastic deformation under friction with simultaneous nitrogen saturation has been studied by microstructure analysis, X-ray diffraction, and transmission and scanning electron microscopy. A gradient surface layer, in which the grain size varies from micro- to submicro- and nanometer-scale values, is found to form. A mutual intensifying effect of the deformation-induced refinement of a grain structure and the diffusion of nitrogen atoms in iron is shown. The formation of a nanocrystalline state is discussed as a result of dynamic recrystallization.