Observation of hydrogen distribution in high-strength steel

The diffusible hydrogen in Cr-Mo steels are observed with autoradiography technique. Specimens with the diffusible hydrogen are prepared by an electrochemical cathodic charging method and those without the diffusible hydrogen by annealing at 373 K after charging hydrogen. TEM autoradiographs suggests, by the developed silver grains, that the hydrogen trapping sites are the grain boundary and internal interface of ferrite-cementite and ferrite-lath structure. After keeping the sample at 373 K, the silver grains disappeared. Most of hydrogen trapping sites release almost all the hydrogen at 373 K. It is clear that these sites of high-strength steels supplies the diffusible hydrogen. Hydrogen absorption characteristics of quench hardening tempering Cr-Mo steels have been evaluated by thermal desorption spectrometry (TDS). From tritium electron microscopic autoradiography and TDS analysis, the lower temperature (360 K–370 K) peaks show the diffusing hydrogen which is released a few days. The diffusible hydrogen from trapping sites such as the internal interface of ferrite-cementite or ferrite-lath structure are distinguished to the diffusing hydrogen.     

A comparison of exact first order and spring boundary conditions for scattering by thin layers

In scattering problems for time-harmonic elastic waves, thin elastic layers are often of interest, e.g., in laminates. Various ways of substituting such layers by some effective boundary conditions have been proposed, and these are briefly reviewed. A rational way of obtaining boundary conditions that are exact to first order in the layer thickness is then described. For a thin spherical layer numerical comparisons are performed between these exact first order boundary conditions, the commonly used spring boundary conditions and the exact solution, and it is shown that the exact boundary conditions are far superior to the spring boundary conditions in most situations. A drawback with the exact boundary conditions is that they are quite complicated.     

An electron microscopic study of nickel sulfide inclusions in toughened glass

It has been known since the early sixties that nickel sulfide inclusions cause spontaneous fracture of toughened (thermally tempered) glass, but despite the considerable amount of work done on this problem in the last four decades, failures still occur in the field with regularity. In this study we have classified (by viewing through a 60× optical microscope) inclusions into two groups, which are classic and atypical nickel sulfides. The classics look like the nickel sulfide inclusions found at the initiation-of-fracture of windows that have broken spontaneously. We have compared the structure and composition of the atypical inclusions with the structure and composition of the classics. All of the classic and atypical nickel sulfide inclusions studied in this work were found to have a composition in the range of Ni₅₂S₄₈to Ni₄₈S₅₂. Inclusions on the nickel rich side of stoichiometric NiS were found to be two-phase assemblies, and inclusions on the sulphur rich side of NiS were single phase. It had been proposed that the atypicals were passive, and of a different composition to the classics. However, we found that the difference between passive and dangerous nickel sulfide inclusions was not a difference in composition but rather a difference in the type of material in the internal pore space. The passive's had carbon char in their internal pore space, whereas the pore space of dangerous inclusions contained Na₂O. The presence of Na₂O and carbon char with the inclusions indicates that the formation of the inclusions results from a reaction of a nickel-rich phase with sodium sulphate and carbon.     

A new acoustic spectroscopy: Resonance spectroscopy by the MIIR

Recent and remarkable advances in the experimental study of acoustic scattering from targets immersed in water are leading to a new spectroscopy: resonance acoustic spectroscopy. The discovery and improvement of an intriguing method, the Method of Isolation and Identification of Resonances (MIIR), has made possible experimental determination of the eigenfrequency spectra of aluminum-elastic cylinders and cylindrical shells. This method gives a quasilinear resonance spectra. In addition, it shows the importance of circumferential waves which generate standing waves. They allow us to explain the reradiation of targets after the end of insonification. The MIIR has numerous applications, especially in underwater acoustics and nondestructive testing.     

Fatigue crack growth behaviour of tungsten carbide-cobalt hardmetals

Fatigue crack propagation studies have been carried out on a range of WC-Co hardmetals of varying cobalt content and grain size using a constant-stress intensity factor double torsion test specimen geometry. Results have confirmed the marked influence of mean stress (throughK _max), which is interpreted in terms of static modes of fracture occurring in conjunction with a true fatigue process, the existence of which can be rationalized through the absence of any frequency effect. Dramatic increases in fatigue crack growth rate are found asK _max approaches that value of stress intensity factor ( 0.9K_IC) for which static crack growth under monotonic load (or static fatigue) occurs in these materials. Lower crack growth rates, however, produce fractographic features indistinguishable from those resulting from fast fracture. These observations, and the important effect of increasing mean free path of the cobalt binder in reducing fatigue crack growth rate, can reasonably be explained through a consideration of the mechanism of fatigue crack advance through ligament rupture of the cobalt binder at the tip of a propagating crack.     

Spin hydrodynamic equations with external disturbances and suitable Green's functions for superfluid3He-B. New onsager relations

The spin hydrodynamic equations for superfluid³He-B have been obtained for the case of external, time-dependent fields. On the basis of a microscopic approach, expressions are found for additional terms in equations containing these fields. Considering the linear response of the system to the switching on of external fields, formulas are found for suitable Green's functions (magnetization-magnetization, rotation-rotation, magnetization-rotation, rotation-magnetization). The rotation-rotation Green's function has the 1/q ² singularity characteristic of superfluid systems. Connections between Green's functions lead to relations among kinetic coefficients v, ₁, and ₂. It is also shown that there is a conserved quantityQ ^(B) = div v _s ^(B) that describes sources or magnetic type charges (monopoles) of the superfluid velocity v _s ^(B) . Comparison with the phenomenological approach suggests thatQ ^(B) is proportional to a pseudoscalar giving the projection of the spin density onto the vector describing the axis of rotation.     

Phase Diagrams at Different Fillings of the Effective Extended Hubbard–Holstein Hamiltonian for a Four-Site Ring of Variable Length

The effective fermionic Hamiltonian derived from the extended Hubbard–Holstein model by a sequence of generalized displacement and squeezing transformations, contains new, long-range, intersite charge interactions. By exact diagonalization on a four-site ring with equally spaced sites, followed by variational optimization of the energy, we obtain the phase diagrams for 2, 3, and 4 electrons by using interaction parameters expressed as functions of the interatomic distance. Depending on the filling, the new charge interaction can modify the phase diagram appreciably.     

On the structure of some precipitated calcium alumino-sulphate hydrates

The chemistry of the calcium alumino-sulphate hydrates has been reassessed using the methods developed in a previous paper [10]. Ettringite does not have a constant solubility product. The rise in the ionic activity product of solutions in equilibrium with ettringite as a function of pH and sulphate activity is attributed to disordering of the crystal structure. This is due to removal of aluminium from the calcium aluminate hydrate columns which form the framework of the ettringite structure. The columns are terminated by these defects and estimates of the expected column length under various conditions are made. Qualitative explanations of changes in the stability of ettringite with respect to calcium aluminate monosulphate hydrate and of the action of certain admixtures on Portland cement are made on this basis.     

Uncertainty of a measured result and confidence error of measurements

An analysis is made of the known information concerning the concepts of error and uncertainty and it is concluded that they are identical.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 14–17, August, 1994.     

Cyclic crack resistance of ferritic-pearlitic steels and their weld joints

The cyclic crack resistance of ferritic-pearlitic steels and their weld joints is determined. On the basis of an analysis of our own and literature data a method of evaluation of the endurance of welded structures in the area of multicycle fatigue is proposed. The endurance limit _e, the parameter K_th ^*, and other parameters have been introduced into this method. The concepts of repairless structures and safely damaged structures are proposed.Translated from Problemy Prochnosti, No. 7, pp. 25–30, July, 1991.     

Fluctuating collective oscillations and electric field penetration into superconductors

The spectrum of collective oscillations and the penetration of a constant longitudinal electric field into a superconductor are investigated based on microscopic Gor'kov equations integrated over the energy variable of one-particle excitations. The influence of the anharmonicity of collective oscillations upon the attenuation of these oscillations and upon the penetration of the longitudinal electric field into the superconductor has been studied as well. We investigate the problem of the self-attenuation of fluctuating collective oscillations in the vicinity of the critical temperature.     

The tensile properties of carburized and uncarburized low carbon mild steel

The properties of a low carbon mild steel in monotonic tension loading were compared in the plain normalized and the carbo-nitrided slowly cooled conditions. The application of a carbo-nitriding process raised the yield strength of the steel to that of the nominal tensile strength in the uncarburized samples, and increased the nominal tensile strength to a value 45% above that of the plain normalized steel, whilst still retaining a good measure of ductility. The fractures for the plain samples were cup and cone type whilst those for the reinforced samples revealed slant mode fractures.     

Irreversibilites in science and technology networks: An empirical and analytical approach

The theory of autopoiesis, i.e., self-referentiality in the operation of the system, provides us with a production rule for change in the structure of the network. Using information theory, a model system is developed to study the relative likelihood of dynamic transitions: various senses of irreversibility (emergence, and path dependency) are disinguished. A test for path dependency is applied to two sets of empirical data which supposedly reflect historical discontinuities: the budget of theFraunhofer Gesellschaft, and the citation network among AIDS research related journals. The model for the interaction between self-referential developments and goal-referential boundary conditions is further specified, using the example of technological trajectories and selection environments.     

Fabrication of melt-texture growth YBCO samples using a simple muffle furnace

In our previous work we showed that gradients of temperatureT inside the heating chamber andT/t are the necessary conditions for growing oriented crystal layers inside bulk samples. Using a simple muffle furnace, we have successfully fabricated layers of YBCO samples. Powder layers of Y-123 and Y-211 in different structures were compressed to make sample pellets before heat treatment in order to create internal temperature gradients inside the samples when they were heated. SEM observation proved that the crystal layers grew from both the top and bottom surfaces of the sample independently of the original powder layers before heat treatment. Moreover, we found that the crystal layers are not true layers but bulk crystal with gap lines. EDX analysis confirmed that the 123 and 211 phases coexist in almost all of the samples. Using the concept of internal temperature gradients, we show that it is possible to carry out modified melt-texture growth even in a muffle furnace.     

A simplified method of generating layer sequences for SiC polytypes

According to the principle that high-temperature phases of SiC should not have 1 in the Zhdanov notation of their layer sequences, a simplified method of generating the layer sequences has been designed. This method is described in order that all of the possible layer sequences without 1 may be generated systematically. By utilizing this method, full sets of the possible layer sequences of SiC polytypes up to 20-layers are produced.     

On the “Metallurgiya” Department of the Mining-Metallurgical Section of Russian Academy of Natural Sciences

A background of Russian Academy of Natural Sciences' (RANS) organization and the main scientific task of activities of the Metallurgiya department of Mining-Metallurgical Section are described.     

Plasma spraying of ferrites

The production of thick films (> 20 m) of polycrystalline ferrite by the arc plasma deposition process is described. Operating conditions of a plasma torch of the authors' own design are quoted. As-sprayed films have high electrical conductivity and low magnetic permeability, but these parameters are restored close to the bulk values by annealing. The surface finish of the films is coarse and unaffected by the particle size of the powder sprayed.     

Synthesis of aluminum infiltrated boron suboxide drag cutters and drill bits

Synthesis of boron suboxide (B₆O) was made by reactive sintering of crystalline boron and zinc oxide powders at 1450 °C, in argon, for 12 h. After sintering, Vickers microhardness testing was performed on the material synthesized and an average hardness value of 34 GPa was obtained. Sintered suboxide (in crushed and ground powder form) was then analyzed through optical and scanning electron microscopies and X-ray diffraction. Following the completion of the analyses, consolidation of the powder was performed. Two different routes were carried out: (1) explosive consolidation which was performed in double tube (with a density value of 2.22 g/cm³) and single tube (with a density value of 2.12 g/cm³) canister design arrangements and (2) hot pressing which was performed in a graphite die assembly, at 1600 °C, in vacuum, for 2 and 4 h (with density values of 2.15 and 2.18 g/cm³ respectively). Consolidated samples of both routes showed different levels of mechanical attachment, agglomeration, porosity, fracture toughness and fracture strength values, whereas microhardness values and X-ray diffraction plots (as shown in Table I and Figs 6 and 8 respectively) were determined to be similar. Following characterizations, compacts of both routes were then given a high temperature sintering treatment (pressureless sintering) at 1800 °C, in vacuum, for full densification. Both in the as consolidated and densification sintered stages test results revealed the most desirable and well-established properties for the explosively consolidated double tube design compacts (with densification sintered density, microhardness and fracture toughness values of 2.46 g/cm³, 38 GPa and 7.05 MPa m^1/2 respectively). Consolidation and desification sintering steps were then followed by a pressureless infiltration step. Aluminum was infiltrated into densification sintered double tube design consolidated and 4 h of pressed samples (better-compacted and better-sintered compacts) in the temperature range 1100–1250 °C, in argon, for 10 h. During infiltrations, the optimum temperature of the infiltration process was determined to be 1200 °C. Characterization results revealed the most uniform and well established properties once more for the double tube design explosively consolidated compact (with aluminum infiltrated density, microhardness and fracture toughness values of 2.55 g/cm³, 41 GPa and 8.70 MPa m^1/2 respectively).     

Universal behavior of an isolated phase-slip center: Extension to high pair-breaking parameters

For the first phase-slip center in superconducting whiskers of zinc and zinc-silver alloys the normalized normal-like length and zero-voltage intercept are plotted as a function of the pair-breaking parameter, which ranges between 4 × 10³ and 2 × 10⁴. A comparison is made with results from aluminum microbridges and the prediction of the time-dependent Ginzburg-Landau theory.     

Quantitative estimation of “big” and “little” science interrelation

Qantitative analysis of the interrelation of big and little science on the example of Research and Development of higher education in the USA has been made. The difference in the growth rates of big and little science is explained with the help of scientometric index of capital expenditures per researcher. An attempt has been made to compare the dynamics of efficiency of big and little science on the base of mean duration of a research project. Possibilities of an alternative index of a relative amount of preliminary researches (preprojects) are pointed out.