Friction properties of composites of the system TiN−AlN. I. Effect of structure and phase composition of friction and wear of materials of the system TiN−AlN

The tribological properties of ceramic composites of the system TiN?AlN are studied in the concentration range 10–90% AlN. It was found that materials which contain 25, 50, and 75% AlN have a low friction coefficient. Their rate of wear when paired with steel is neglible—2.9–6.0 μm/km (the wear rate of a steel-steel 024 couple is 1000 μm/km). Thin oxide films are formed during friction at high velocities and pressures. These films have relatively high adhesion with respect to materials of the TiN?AlN system and relatively low adhesion with respect to steel. The films may act as a solid lubricant, thus reducing the friction coefficient and wear. This is particularly true of the materials 25% TiN?75% AlN and 50% TiN?50% AlN.     

Overview no. 89 Thermoelasticity and plasticity of composites—II. A model system

A theory of the workhardening and Bauschinger effect in two-phase materials, combining dislocation mechanisms with a continuum model, is extended to high volume fraction of the hard phase by using the mean field theory of Paper I [Acta metall.31, 1795 (1983)]. Application of the extended model to available workhardening data for the simple experimental model system of copper with continuous tungsten fibres reveals a novel workhardening contribution: “elastic friction”. The contribution arises from the interaction of gliding dislocations with the complex spatially fluctuating pattern of internal stresses induced by the applied stress as a result of elastic heterogeneity. Elastic friction is taken into account in a simple model of the Bauschinger effect, the “modified Orowan-Wilson model”, which is substantiated by a new set of experiments on copper-tungsten with large tungsten volume fractions.     

Thermodynamic properties of molten sulfides: Part I. The system Ni−S

The equilibrium partial pressure of sulfur vapor over Ni?S melts has been determined by equilibrating the melts with H₂-H₂S gas mixtures at temperatures from 1100°C through 1600°C and for melt compositions ranging from nickel saturation up to about 27 wt pct sulfur. An optical interferometer was employed to monitor the system’s approach to equilibrium and to analyze the composition of the equilibrium gas phase. A mathematical model was employed to correlate these data with those of Nagamori and Ingraham² for temperatures from 800°C through 1100°C. The model was somewhat complicated but it described the Ni?S melts very well over unusually wide ranges of composition and temperature;e. g. σ (logP _S2 ^1/2 )=0.029.     

The effect of residual stresses on the debonding of coatings—II. An experimental study of a thermally sprayed system

Specimens have been produced by plasma spraying of boron carbide coatings about 1 mm in thickness on to titanium alloy substrates about 3 mm thick. The residual stress distributions in these specimens have been calculated using a numerical process model and also estimated from observed changes in curvature on debonding. Good agreement was observed between the two methods, with both suggesting the average substrate stress to be about + 20 MPa and the average coating stress to be about −60 MPa. In both constituents, there was a significant positive gradient of stress level through the thickness. These specimens were loaded in four point bending until cracks propagated along the interface between substrate and coating. From the load/displacement plots obtained during this testing, and taking account of the effect of relaxation of the residual stresses during debonding, the critical strain energy release rates of the interfaces, G_ic, were estimated to be ∼ 0.2–0.5 kJ m⁻². Substantial errors would have resulted from neglect of the presence of the residual stresses. Also of significance is the effect of the residual stresses on the mode mixity of interfacial loading, as characterised by the phase angle, ψ, since G_ic has been often observed to vary with ψ. The value of ψ for the four point bend test in the absence of residual stress is about 47°, whereas for the specimens tested here it was estimated to cover the complete range from 90° (pure shear) to 0° (pure opening) as the applied load was increased. The quoted values of G_ic were obtained in a regime where ψ ∼ 30°.     

Activation of the immune–endocrine system with lipopolysaccharide reduces affiliative behaviors in voles.

In Experiment 1, individually housed male meadow voles (Microtus pennsylvanicus) and prairie voles (Microtus ochrogaster) were injected with lipopolysaccharide (LPS) and exhibited the expected decrease in testosterone and increase in corticosterone and interleukin- 1β concentrations 3 hr later, indicating activation of the endocrine and immune systems. In Experiment 2, LPS- and saline-injected males were tethered in a 3-chamber partner preference apparatus. The time females spent in each chamber with a male, as well as the amount of time spent in social contact, was monitored. Female prairie voles, but not meadow voles, spent more time in the chamber with saline- than with LPS-injected males. LPS-injected male prairie and meadow voles engaged in less social contact with female conspecifics than did saline-injected males. These data suggest that LPS modifies physiology and behavior in male voles and that females may use these changes to discriminate healthy from potentially infected males. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Diffusional coalescence of island films on the real crystal surface in the case of layer-by-layer growth of islands—II. An open system. Undamped sources of deposited atoms

Coalescence of island films on the real crystal surface in the presence of the sources of deposited atoms is studied in case of layer-by-layer growth of islands. Asymptotic distribution functions and critical radii time dependences with different modes of mass-transport are obtained and analyzed. Restrictions in the sources intensity are given.     

Diffusional coalescence of island films on the real crystal surface in the case of layer-by-layer growth of islands—I. An isolated system

Necessary conditions for layer-by-layer growth of islands, situated on the real crystal surface, are discussed. The behaviour of an ensemble of sphere- and cylider-shaped islands in the stage of coalescence is considered, provided the supersaturation in the maternal phase near the surface small enough and the conditions for layer-like growth of islands satisfied. It is shown that if the growth processes are controlled by interface transfer, the time dependence of the radius (of surface curvature of the base) of a critical nucleus differs from the one obtained in the case of normal growth of islands. The critical radius and the supersaturation time dependences as well as the asymptotic distribution functions in the presence of damped sources of deposited atoms are derived and their consequences are analyzed.     

Electron microscopy investigation of the ZrO2-ZrN system—I. Formation of an incommensurate superstructure ZrON

The ZrO₂-ZrN system has been investigated in the ZrO₂ rich field using electron microscopy and diffraction. When 2.5 mol% or more ZrN is added to ZrO₂ the monoclinic transformation is partially avoided and a new long period modulated zirconium oxynitride is formed. The modulated structure has a rhombohedral (trigonal) symmetry and is based upon the Zr₇O₁₁N₂ structure which is isostructural with Zr₂Sc₂O₁₃. The structure is closely related to the cubic fluorite phase but the vacancies, introduced by replacing oxygen with nitrogen, are ordered along one of the threefold axes, lowering the symmetry and giving rise to slight distortions of the original cubic lattice. The modulations with a 3 nm wavelength are most probably due to pseudo-periodic composition fluctuations in order to incorporate a deficiency of nitrogen necessary to form the Zr₇O₁₁N₂ structure. The final incommensurate modulated structure can be regarded as a completely coherent mixture of pure Zr₇O₁₄ layers alternating with Zr₇O₁₁N₂ layers perpendicular to the threefold axis. The non-commensurability arises from local deviations in spacing and/or orientation of these layers.     

The deformation behaviour of single crystals of the CuCrSiO2 system—I. Yield and pre-yield behaviour

The yield behaviour and pre-yield behaviour of Cu-0,4% Cr and CuCrSiO₂ single crystals have been studied as a function of aging time for this age hardening system. The stress at the onset of gross plasticity in CuCr is comparable with the stress required for the Orowan process. The dislocation configurations at yield have been examined and found to be determined by the cross-slipping of screw segments.The stress for gross plasticity in CuCrSiO₂ crystals is shown to be controlled by the Cr precipitates and not by the SiO₂ particles which have an immeasureable effect. However, the SiO₂ particles modify both the pre-yield behaviour and the dislocation structures observed in the crystal after small strains.     

Oxidation of Ni — Ta alloys. III. Mechanism of oxidation

The results of an x-ray diffraction and metallographic study of the kinetics of scale formation during the oxidation of Ni(Ta), Ni₃Ta, and NiTa in air at 600–1000°C are analyzed. The free energies, equilibrium oxygen pressures, and mass balances of the oxidation reactions were calculated, and conditions for the formation of NiO·Ta₂O₅ and NiO on the alloy determined. It is shown that the oxidation process is controlled primarily by the diffusion of oxygen and counter-diffusion of Ni⁺² in the scale, and involves oxidation, reduction, and synthesis reactions. A multilayer scale is formed, consisting of an outer layer containing only oxides (NiO, NiO·Ta₂O₅, Ta₂O₅) and an inner one which additionally contains nickel. The protective ability of the outer scale depends upon the concentrations of NiO and NiO·Ta₂O₅ in it. Preferential oxidation of tantalum is responsible for the appearance of a subscale consisting of Ni(Ta) + Ta₂O₅ on the intermetallic Ni₃Ta, and Ni₃Ta + Ni(Ta) + Ta₂O₅ on NiTa. Differences in molar volumes of phases result in the formation of pores and cracks at interphase boundaries, particularly in the inner scale on Ni₃Ta. A change in the oxidation mechanism occurs at T ≥ 850°C as a result of the p → n transition in Ta₂O₅, which leads to retarded oxygen diffusion and the appearance of Ta⁺⁵ diffusion in the intermetallic. This, as well as the diffusion of Ni⁺², promotes the healing of macrodefects in the scale. However, it also results in enrichment of the outer scale in pentoxide, which decreases its protective ability. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 69–78, May–June, 2000.     

Influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f.c.c.-f.c.c. nucleation—III. The influence of elastic strain energy

The influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f.c.c.-f.c.c. nucleation was studied by combining the discrete lattice point non-classical model utilized in paper II of this series with the microscopic theory of strain energy as applied by Cook and de Fontaine to compositional fluctuations in cubic lattices. This permits simultaneous consideration of the influence of anistropic interfacial energy and anisotropic strain energy upon nucleation. This is extremely difficult to do using other models of strain energy because of mathematical problems. The model is applied to f.c.c. nuclei in AlCu and CuCo alloys. Nuclei in AlCu are plates because coherency strain energy predominates in this system. In CuCo alloys, the misfit is smaller and the distortion tensor is cubic; thus the nuclei are essentially spherical. Despite this lesser effect, the influence of strain energy upon the nucleation kinetics of Co-rich precipitates in a Cu-rich CuCo alloy is found to be very important, reducing these kinetics by as much as five orders of magnitude.     

The hypothalamo-hypophysial system in Acipenseridae. V. Ecological-histophysiological analysis of the neurohypophysis of the female sturgeon Acipenser güldenst?dti Brandt during up-stream migration and after spawning

Neurohypophyses from sexually mature female sturgeons, Acipenser guldenstadti Brandt, killed before, soon after spawning, and during down-stream migration were studied light and electron microscopically. Ovaries were examined only under a light microscope. A large amount of neurosecretory material (3.5-4.5 arbitrary units) is found in the neurohypophysial "roots" during up-stream migration to spawning grounds. Neurosecretory fibres and their terminals are replete with elementary neurosecretory granules. Side by side with the latter some terminals contain single residual granules and few "synaptic" vesicles. Soon after spawning the amount of neurosecretory material decreases markedly in most individuals (content up to 1-3 units), and elementary granules are few in the fibres and their terminals. The number of residual granules increases, and "synaptic" vesicles are especially numerous. Granulated, disintegrating neurosecretory granules and granule-shadows occur in the preterminal parts of the fibres. The number of pituicytes increases becuase some "light" tanycytes seem to migrate from the ependymal into the subependymal layer. The restoration of neurosecretory material (reaching again up to 3.5-4.5 units) occurs within a month after spawning. The number of elementary granules increases in fibres and terminals while that of residual granules and "synaptic" vesicles decreases. These changes in the neurohypophysis of females after spawning are due to discharge of great amounts of peptide neurohorsmones into the general circulation after spawning. Spawning is regarded as a "physiological" stress for these females.     

Simulation of tuyere–raceway system in blast furnace

Abstract

A uniform distribution of the blast is an important prerequisite of a balanced blast furnace operation, because the blast is the main source of the hot gases that are needed to preheat, reduce and melt iron ores. The supply of hot gas from the raceways is not necessarily uniform along the furnace periphery, but depends on flow resistances encountered on the individual bustle main tuyere–raceway–raceway boundary routes. A model for this system has been developed in order to study and analyse the effects of changes in tuyere parameters and boundary conditions. Variables such as the total blast volume, blast pressure, tuyere diameter and the combustion degree of injected reductants in the tuyeres can be studied. An online version of the model has also been developed to track how the conditions on the tuyere level change with time in operating blast furnaces.     

Atomic mechanisms of precipitate plate growth in the AlAg system—II. High-resolution transmission electron microscopy

High-resolution electron microscopy was used to study the interfacial structure of γ′ precipitates in an Al-15 wt% Ag alloy aged at 350°C. The results of these studies show that:

• 1.(1) all ledges are multiples of two {111} planes high, supporting the theory and conventional transmission electron microscopy observations that plate thickening occurs by passage of Shockley partial dislocations on alternate {111} planes
• 2.(2) most ledges are more than just two planes high, indicating a strong tendency toward diffusional and/or elastic interactions
• 3.(3) the terraces between ledges are atomically flat and ledges are uniformly stepped-down from the centers to the edges of isolated precipitates as predicted by the general theory of precipitate morphology
• 4.(4) the {111} planes are continuous across the edges of ledges, indicating that they are largely coherent and not disordered as treated in most kinetic analyses, and
• 5.(5) the edges of precipitate plates appear to be composed of similar two-plane ledges arranged vertically above one another and hence, may grow by the same mechanism of atomic attachment as ledges on the broad faces.

Examination of γ′ plates during early stages of growth indicates that their aspect ratio may deviate from the equilibrium value almost immediately, probably due to the ledge mechanism of growth. Lastly, an atomic model of a γ′ precipitate was used to test the high-resolution images obtained, and illustrate possible atomic growth mechanisms of the ledges.     

Report of the… .

Asummary of a report containing "information about subdoctoral training programs,… questions the committee deemed relevant and important,… and appropriate recommendations." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f.c.c.-f.c.c. nucleation—V. The origin of GP zones in AlAg and AlCu alloys

GP zone formation in aluminum-base alloys has been proposed, by previous investigators, to take place by spinodal decomposition or by homogeneous nucleation and growth. The possibilities of these two mechanisms are examined here for two alloy systems, AlAg and AlCu, representing two extreme cases, a narrow and a (potentially) very wide miscibility gap, respectively, resulting in low and high interphase boundary energies. The coherent spinodal and the temperature-composition curve corresponding to abundant homogeneous f.c.c.-f.c.c. nucleation were calculated for both systems. In AlAg alloys, the nucleation barrier is so low that negligible undercooling is needed to achieve abundant nucleation. Hence cooling into the spinodal region with ordinary quenching rates is virtually impossible. In AlCu, however, the inverse situation is present and GP zone formation by (or aided by) spinodal decomposition should be feasible if the diffusivity remains sufficiently high in the spinodal region. Detailed evaluation of the latter proposal is prevented, however, by the incompleteness of thermodynamic information on f.c.c. AlCu alloys.