Showing papers on "Microstructure published in 1969"

Preparation of High-Purity Submicron Barium Titanate Powders

Abstract: Simultaneous hydrolytic decomposition of barium bis isopropoxide and titanium tetrakis tertiary amyloxide was used to produce stoichiometric BaTiO3. The particle size range was 50 to 150 A. The purity was 99.98+%, the major contaminant being silicon from the glass apparatus. The homogeneity and stoichiometry of the powder were demonstrated by electron microscopy and wet chemical analysis. X-ray and infrared analyses indicate that the material, as-prepared and helium-dried at 5O°C, has the titanate crystal structure. The powder sinters at 1300°C to a high density, translucent body with a uniform microstructure. The experiments suggest that the alkoxy-based preparation of oxides may provide a broad base for improving the quality and reproducibility of electrical and structural ceramics.

Correlations between high-temperature creep behavior and structure.

Abstract: Creep of metals and alloys at high temperatures is usually diffusion-controlled. Nevertheless, the creep behavior is often sensitive to various structural and substructural details. The secondary creep rates, E , of all coarse-grained fcc metals are given by s 6 DGb (a. )n Es = 2.5 x 10 kT \ /G where D = the diffusivity, G = the she'ar modulus of elasticity, b = the Burgers vector, kT = the Boltzmann constant times the absolute temperature, and a = the applied tensile stress, The constant n increases from 4.4 for Al,to 5.3 for Ag in a consistent manner with increasing value of Gb/f where r is the stacking fault energy. Whereas, many alloys give the same trends, others in which the velocity of glide of dislocations is limited by solute atom diffusion, give . E ~ 0,5 DGb s kT At the steady state the substructure consists of subgrains demarked by low-angle boundaries and more or less randomly meandering dislocations within the subgrains. The density, p, of dislocations during steady state creep depends only on the applied stress and is given by the same relationship that applies to metals during low-temperature strain hardening, namely

Defect microstructure and mechanical properttes in shock-hardened metals - The relationship of defect microstructure and mechanical properties in shock-hardened metals and alloys and the comparison with simply compressed and cold-rolled metals was investigated by transmission electron microscopy

Abstract: This paper is concerned primarily with the direct observation of shock-induced defect microstructures in 70/30 brass, 304 stainless steel and copper; and the attempt to relate the microstructural features observed with experimentally determined mechanical properties. The method of direct observation utilizes both bright- and dark-field transmission electron microscopy. Some attention is also given to the relationship of shock-induced defect structures to those resulting from conventional modes of deformation such as simple compression and cold reduction by rolling. It is shown, through the use of the electron microscope, that structures in stainless steel vary greatly with the mode of deformation. Some consideration is also given to the apparent role of stacking-fault energy in determining residual-shock structures in fcc metals and alloys.

The crystallisation of glasses based on the eutectic compositions in the system Li2O-Al2O3-SiO2

Abstract: Structural transformations have been studied in glasses related in composition to the binary eutectic between lithium metasilicate and β-spodumene. Crystallisation processes and changes in microstructure during the controlled heating of the glasses have been followed using X-ray diffraction, electron microscopy, high temperature microscopy, thermal analysis and electron spin resonance spectroscopy. The influence exerted by titanium dioxide on the phase relationships, crystal growth rates and micromorphology of the polycrystalline products of heat-treatment has been investigated and the findings used as a basis for proposals on the role of TiO2 during nucleation and crystal growth.

Structural Dependence of Strain Gauge Effect and Surface Resistivity for Thin Gold Films

Abstract: Gold films of 80 to 500 A thickness were deposited onto 6-mil-thick glass substrates, and continuous measurement of electrical and mechanical properties pertinent to the use of a film as a strain gauge element were made in situ. Gauge factors of greater than 100 for films that are less than 100 A thick have been observed. These are over a factor of 20 greater than reported foil bulk values. The temperature coefficients of resistance for these high-gauge factor films were negative and their microstructure consisted of isolated islands. Increasing the island size and joining of islands, such as occurs in annealing, caused the gauge factor to decrease for films having the same surface resistivity. Straining and relaxing films up to 16 000 times resulted in drift in most specimens although there was no observable microstructure change. Films having high initial surface resistivities and gauge factors drifted to higher values upon cycling, while those with relatively low initial values dropped upon cycling. Surface passivation by silicon monoxide films did not change the film structure, but did increase the resistivity and decrease the gauge factor.

Microstructure and Magnetic Properties of Lead Ferrite

Abstract: Unoriented lead ferrite specimens were prepared by calcining and sintering techniques. Specimens having an initial composition of Pb0.5Fe2O3 had the best permanent magnet properties (for nondoped material). The effects of small amounts of added oxides on the microstructure and magnetic properties were also determined. Silica and boria were most effective in raising the (BaHa)max to over 1.4 × 106 G.Oe as compared to 0.9 to 1.1 × 105 G.Oe for commercial un oriented barium ferrite magnets. Optical and electron microscopy revealed that silica and boria form low melting phases as the specimens are sintered, which, acting as fluxes (probably by a solution-precipitation mechanism), enhance the densification of the magnets, thereby raising the Br, and (BaHa)max, values. On cooling, these nonmagnetic low-melting phases are retained at the ferrite grain boundaries where they inhibit domain wall motion which would otherwise lead to a reduction in coercive force. Although these magnets are termed “un oriented” to distinguish them from “oriented” ferrites which are purposely aligned before sintering, a slight orientation is imparted to the polycrystalline compact during the pressing operation before sintering. The silica and boria additions increase the degree of orientation by accelerating the rate of densification. The increase in orientation accounts for part of the increase in Br, and (Ba, Ha)max.

The Early Stages of Growth of Second-Phase Particles in an Fe–Ti–Si Alloy

Abstract: The microstructural investigations outlined in this paper represent natural extensions of previous work in investigating precipitation in the Fe–Ti–Si system. The obvious value of the field-ion microscope in enabling pre-peak-hardness microstructures to be defined is established and a correlation between particle size and hardness is given. The observed qualitative changes in microstructure are related to the variation in titanium content of the particles, which are believed to be based on the DO3Fe3Si structure. Quantitative size-distribution data are presented that extend the work performed by other authors to shorter ageing times. For ageing times > 1 h at 600° C a linear time-dependence is found for the cube of the mean particle size, in agreement with bulk-diffusion-controlled coarsening theory and previous work. For ageing times < 1 h deviations in such a plot occur, which are shown to arise from an incomplete precipitation reaction.

Dispersion-strengthened aluminium products manufactured by powder blending*

Abstract: The microstructure of dispersion-strengthened aluminium products manufactured by powder blending has been examined by optical and transmission electron microscopy, and the mechanical properties have been determined at room temperature and at elevated temperatures by tensile- and creep-testing.Powder variables, such as the size of the aluminium-powder particles and the size, volume concentration, and type of oxide (Al2O3, SiO2, ZrO2) used as the dispersed phase, have been investigated, together with manufacturing variables, such as temperature of the extrusion billet, reduction ratio in extrusion, and heat-treatment after extrusion. Major variables are the size of the aluminium particles and the oxide concentration, and generally it has been found that the strength increases and the elongation decreases for decreasing size of aluminium particles and increasing oxide concentration. The elongation measured after extended creep-testing is, however, practically the same for all products, of the order o...

Microstructure, impurity content and critical current density in Nb3Sn

Abstract: Critical current density measurements, transmission electron microscopy and chemical analysis have established a correlation between critical current density Jc, the oxygen content in Nb3Sn and the presence of a fine dispersion of precipitate. As the oxygen content increased from <50 to 1000 p.p.m. by weight, Jc increased from 1 to 6 × 105 A cm−2 at 46 kG. A fine precipitate (particle size similar 50 A) was observed for all oxygen contents greater than 160 p.p.m. It is concluded that the precipitate particles act as flux-pinning centres in Nb3Sn. No correlation was observed between nitrogen content and Jc.

Method for solidifying while rubbing the solid-liquid interface

Abstract: The microstructure and the impurity distribution in a solid which has been directionally solidified from a melt or solution can be strongly influenced by rubbing the solid-liquid interface during solidification. If the solid has two or more phases, a major effect will be the production of a fine-grain microstructure. The grains in addition to being small will be roughly equiaxial and not possess the usual columnar, dendritic and substructures. If the solid is single phase, the rubbing should break up the diffusion layer in the liquid, which is, typically, enriched in one or more of the constituents, and the equilibrium segregation coefficient between the solid and the liquid should be realized in normal freezing. Fine-grained microstructures have recently become of interest in the field of superplasticity and an important application of normal freezing of a single-phase material is in the desalination of water.

Two-phase cobalt iron alloys prepared by powder metallurgy

Abstract: A DUCTILE COBALT ALLOY CONTAINING ABOUT 15 TO ABOUT 15% BY WEIGHT IRON AND BALANCE COBALT AND BEING FABRICATED BY POWDER METALLURGY METHODS FROM COBALT AND IRON POWDERS THE ALLOY HAS A TWO-PASE MICROSTRUCTURE IN WHICH THE IRON CONTENT OF ONE PHASE IS HIGHER THAN THE IRON CONTENT OF THE OTHER PHASE AND HAS A PREDOMINANTLY FACE-CENTERED CUBIC CRYSTAL ALLOTROPIC STRUCTURE AND SUPPRESSED TRANSFORMATION FROM SAID FACE-CENTERED CUBIC CRYSTAL STRUCTURE TO A HEXAGONAL CRYSTAL STRUCTURE AT ROOM TEMPERATURE

Soft magnetic thin-film memory materials

Abstract: Thin-film deposition techniques as applied to magnetic memory applications are reviewed. The relationship between the microstructure of the film and the fabrication technique and pertinent parameters is discussed in terms of the atomistics of film nucleation and growth. The dependence of the magnetic properties governing switching of a magnetic storage element is qualitatively discussed in terms of the microstructure and ripple theory; literature data is used to elucidate this by showing the effects of composition, temperature, thickness, and substrate morphology on the magnetic properties. The literature values for the anisotropy field, coercivity field, and dispersion of various classes of ternary alloys is reviewed, extending previous papers reviewing elemental and binary alloys.

Electrical contact material

Abstract: ELECTRICAL CONTACT MATERIAL CONSISTING ESSENTIALLY OF SILVER AND CADMIUM OXIDE IS DISCLOSED WHEREIN THE MATERIAL IS CHARACTERIZED BY HAVING A PRE-OXIDIZED MICROSTRUCTURE WHEREIN THERE IS A FINE CADMIUM OXIDE PARTICLE SIZE AND A SUBSTANTIALLY UNIFORM DISTRIBUTION OF CADMIUM OXIDE THROUGHOUT THE MATERIAL INCLUDING THE CORE THE MATERIAL HAS A LOWER ARC EROSION RATE THAN POST OXIDIZED MATERIAL OF THE SAME COMPOSITION WHEN TESTED UNDER SIMILAR CONDITIONS A BACKING, FOR EXAMPLE OF FINE SILVER MAY BE PROVIDED FOR THE CONTACT MATERIAL

Physical and mechanical properties of reactor materials.

Abstract: High temperature (to 3000 deg C) physical and mechanical properties for commercially available and newly developed materials being considered for use in high temperature reactors were measured. Creep, stress rupture, ductility, microstructure, and failure mechanism for tungsten were determined. Values were found for creep of as cast Mo; creep rupture of Re, Mo - Re - W, Mo - W, and Re - W; thermal conductivity and electrical resistivity of Re - W; and enthalpies, heat content and heat capacity of W. (F.S.)

Influence of the sintering conditions on the densification of manganese-zinc ferrites

Abstract: In order to prepare reproducibly high permeability manganese-zinc ferrites, it is necessary to carefully control the sintering schedule for obtaining both a homogeneous chemical composition and the desired microstructure. The latter should consist of big pore-free crystals, the remaining porosity being a few number of big pores situated at the grain boundaries. In our theoretical analysis of the densification, a volume diffusion model is used taking into account the geometrical parameters of the average crystal in thermodynamical equilibrium in the polycrystalline material. In the intermediate stage of sintering, the grain growth and densification are correlated, the densification rate being approximately inversely proportional to the grain volume. Sintering experiments have been carried out under various conditions of temperature and duration, the atmosphere composition being adjusted for maintaining the same stoichiometry. These results permit one to define isoporosity curves. It is then possible to compute the activation energies Q and Q 1 responsible for grain growth and for densification. The values found are Q = 82 \pm 5 kcal/mole and Q_{1} = 85 \pm 5 kcal/mole, in agreement with the previous measurements of Paulus [5] and Ogawa [3]. The experimental results show that both processes are controlled by the diffusion energy of oxygen anions which are the slowest diffusing species. The variation of the porosity versus time follows a (t)^{-n} law, n being roughly equal to 0.5 in good agreement with our predicted model. The experimental results also confirm that the use of a more oxidizing atmosphere increases the grain growth rate but decreases the densification rate. A sintering schedule leading to very high permeability ferrites is determined taking into account these results. The microstructure is obtained during a first soak at high temperature under oxidizing atmosphere. This leads to big crystals and open porosity while preventing zinc losses. This first treatment is followed by a second soak under a more reducing atmosphere leading to a high density ferrite and an homogeneous chemical composition possessing a ferrous iron content so as to obtain a maximum permeability at room temperature.

Elastic Behavior of Arc-Cast Zirconium Carbide-Graphite Alloys

Abstract: : The Young's modulus and shear modulus of arc-cast zirconium carbide-graphite alloys were measured as a function of graphite content and were found to be dependent upon the microstructure of these alloys. Attempts to fit several theoretical analyses to the data were not successful. The simplified physical models from which these analyses were derived limit their usefulness in predicting elastic behavior for materials having complex microstructures. (Author)

Sigma phase formation and its effect on stress-rupture properties of IN-100

Abstract: Sigma phase formation and its effect on stress rupture properties of nickel base alloy IN-100

Nickel-chromium eutectic alloy

Abstract: A nickel-chromium alloy consisting of about 50 percent of nickel and 50 percent of chromium and having an oriented lamellar microstructure which is obtained by directional solidification.

Al-1.3%Mg2Si合金の二段時効について

Abstract: The effect of pre-ageing on artificial age-hardening of an Al-1.32%Mg2Si alloy at 170°C was investigated. Hardness was measured and it was found that there was some correlation between the hardness and microstructure revealed by transmission electron microscopy. The following results were obtained.(1) When the pre-ageing was made at below the room temperature, the maximum hardness after ageing at 170°C was about 10% lower than that of no pre-ageing. On the contrary, when the pre-ageing was made at above 50°C, the maximum hardness after ageing was about 10% higher than that of no pre-ageing. However, in the latter case, the maximum hardness was lower when the pre-ageing was made for a very short time.(2) The critical temperature for pre-ageing, at which the two-stepped ageing effect changed from positive to negative, was about 36°C.(3) The observation of the structure by electron microscopy showed that coarse acicular precipitates were disperssed after the pre-treatment at 0°C for 7 days; while, fine acicular precipitates were very homogeneously distributed after the pretreatment at 100°C for 24 hrs.(4) As the results of hardness reversion experiments, it was suggested that the thermal stability of G. P. zones formed by the pre-treatment was higher in the aging of at 100°C for 24 hrs. than that of at 0°C for 7 days.Most of the above results of experiments can be interpreted by Pashley's kinetic model.