Cu-C and Al-Cu-C phase diagrams and thermodynamic properties of c in the alloys from 1550 °C to 2300 °C

The Cu-C and Al-Cu-C phase diagrams were determined at 1550 °C to 2300 °C by chemical and X-ray diffraction analyses of alloys saturated with carbon within sealed graphite crucibles. Isothermal sections for the ternary system were determined at intervals of 150 °C over the range of temperatures investigated. The univariant points in atomic percent on the 1700 °C, 1850 °C, and 2000 °C isotherms are 70.7Al-28.9Cu-0.4C, 74.4Al-24.0Cu-1.6C, and 78.3Al-17.0Cu-4.7C, respectively, as determined by metallographic examination of rapidly cooled alloys. Graphite and Al₄C₃ (decomposition temperature 2156 °C) were the only solid phases observed at these temperatures. The excess partial Gibbs energy for dissolved carbon in the liquid Al-Cu-C solutions in equilibrium with C, as calculated from the experimental solubilities, isˉ G _c ^e = - RT lnx =y ²[176,860 - 55.42T - (224,200 - 110.84T)x] +z ²[237,000 - 48.61T] +yz[320,510 - 36.77T + (30,180 + 35.10T)z + (51,570 - 74.13T)yz + (246,400 - 88.04T)yz ² - 60,000], J/g atom where R is the gas constant,T is the temperature in K, andx, y, andz are the atomic fractions of C, Al, and Cu, respectively. The equation also is a good approximation for liquid solutions in equilibrium with A1₄C₃.     

The tensile properties of a particulate reinforced al alloy in the temperature range -196–300 °c

The tensile properties of a particulate reinforced Al- Si-Mg alloy were determined in the temperature range — 196–300 °C. Microstructural coarsening of a peak aged (T61) material occurs at the higher temperatures (i.e. 200 and 300 °C), which, together with the test temperature, results in a considerable decrease in flow strength for both the composite and unreinforced alloy. However, the strengthening ratio (i.e. the ratio of composite to matrix strength, σ_c/σ_m actually increases with temperature. This effect is also observed when investigating the influence of test temperature alone (i.e. a stable matrix microstructure over the full temperature range). These results suggest that the primary relaxation mechanisms are damage accumulation and relaxation by plastic deformation of the matrix. There is no evidence of unrelaxed behaviour, even at −196 °C, and the strain rate used during testing is likely to be too high to allow diffusional relaxation to be operative at the higher temperatures     

Solubility of iron in liquid selenium below 585°C

Abstract

With the use of a JXA-3A microprobe the diffusion characteristics of indium in lead single crystals were determined in the temperature range from 160 to 200°C. For the temperature dependence of the heterodiffusion coefficient of indium in lead in dilute solid solution the relation

D = 33.exp {?(26.79 ± 0.76)/RT} cm²/sec

was found. A special technique for measuring the concentration gradient was developed. This enables one to eliminate the influence of surface relief, formed during the microtome preparation of the sample, on the microprobe measurements.

Résumé

Au moyen d'une micro-sonde JXA-3A les auteurs ont détermine les caractéristiques de diffusion de l'indium dans des cristaux uniques de plomb, entre 160°C et 200°C. En solution étendue, le coefficient de diffusion hétérdgène de l'indium dans le plomb est relié à la température par la relation

D = 33.exp {?(26.79 ± 0.76)/RT}cm²/sec

Une technique nouvelle mise au point par les auteurs élimite l'influence de la rugosité de surface produite au cours de la préparation d'éprouvettes par microtome.     

Theoretical analyses of 〈111〉 pencil glide in b.c.c. crystals

A new theoretical analysis of 〈111〉 pencil glide in b.c.c. crystals is proposed. Complete sets of equations are given for one, two, three or four active slip systems. The yield surface for b.c.c. single crystals deforming by pencil glide is described, and the closed subspaces are listed. The cases where stress or shear rate and rotation ambiguities occur are also detailed. A correspondence is shown to exist between the plastic deformation rates that are induced by the classical eight solutions in pencil glide, and those associated with the Bishop and Hill vertices for {110}〈111〉 slip. Each six-fold vertex in groups B and D is related to a particular three-system pencil glide solution, and each eight-fold vertex in groups A, C, and E with one four-system solution as well as four three-system solutions. The analysis shows that the cones of normals of the Bishop and Hill vertices have very different extensions, the solid angle pertaining to the group C vertices being an order of magnitude greater than those of group A. The Taylor (prescribed strain) problem for b.c.c. crystals is treated in this way and it is shown that the necessary calculations are reduced by factors of three to six when compared with the previous methods. In particular the number of three-system solutions to be analyzed, which require a special numerical procedure, is reduced to a minimum. The Taylor factor for isotropic aggregates of b.c.c. crystals with pencil glide is also calculated for various imposed strain rates. Finally, the well known analyses of pencil glide available in the literature are compared; the correspondence between the notations is tabulated, and the approaches and sets of results obtained are evaluated and discussed in turn.     

Study of creep deformation of irradiated zircaloy cladding by isothermal heating of irradiated PHWR fuel pins in temperature range 700°C–900°C

Fuel pins removed from actual irradiated fuel bundles discharged from Pressurised Heavy Water Reactors (PHWRs) have been used for experimental study of high temperature creep deformation as functions of cladding temperature and internal fission gas pressure. Experiment consisted of localized heating of 100 mm long segment of the fuel pins in a furnace in inert atmosphere at temperatures 700°C, 800°C, 850°C and 900°C for 10–15 minutes. The internal pressure and the total void volume in the fuel pins were estimated by puncture test on sibling pins from the same fuel bundle. After the heating experiment the diameter of the pin along the length was measured to obtain the diameter increase due to high temperature creep. Analysis of the experimental data for fuel pins with internal pressure 0.55 ± 0.05 MPa, provided the following empirical correlation for creep rate of the cladding as a function of temperature Creep rate (s^?1) = 2.23 × 10¹⁰ × exp (?305500/RT), for temperatures in the range of 800°C–900°C, where, R is gas constant, 8.314 J/mol K and T is temperature in K. For fuel pins with different internal fission gas pressures, the correlation obtained for the cladding strain as a function of internal pressure (at room temperature) was $$ \begin{gathered} Cladding strain = 118.22 \times 10^{ - 3} exp (0.53P), for temperature = 900^\circ C \hfill \\ where, P is the internal pressure in MPa at room temperature. \hfill \\ \end{gathered} $$ This paper presents the details of the experiment and the results.     

Electrochemical study of the catalytic influence of Sulfolobus metallicus in the bioleaching of chalcopyrite at 70 °C

The catalytic influence of Sulfolobus metallicus in bioleaching of chalcopyrite at 70 °C and pH 1.7 was characterized from studies of anodic dissolution of a chalcopyrite concentrate at constant potential. Experiments were conducted in iron-free nutrient medium which minimized the influence of jarosites formation on the process. The use of a novel electrochemical technique enabled the simultaneous determination of copper dissolution rate and the number of electrons involved in the dissolution reaction. This experimental approach permitted to monitor the degree of the oxidation of reduced sulfur compounds and assess its influence on the copper dissolution kinetics.Experimental results showed that in bioleaching of chalcopyrite with S. metallicus there is an efficient process of oxidation of residual sulfur compounds, i.e. sulfur and polysulfides, formed during the chemical dissolution of the sulfide. This oxidative process contributes to a dramatic increase in copper dissolution rate with respect to that obtained in chalcopyrite dissolution under simple indirect bacterial action. Oxidation of reduced sulfur compounds in the presence of S. metallicus involves the participation of a mechanism of chemical catalysis triggered by the presence of dissolved oxygen in solution.     

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.     

Solubility of silver in the K–KCl melt at 850°C

The solubility of silver in K–KCl melts at 850°C is studied in varying the potassium content from 0 to 100 mol %. It is shown that the solubility linearly increases as the alkali metal content increases; the solubility of silver in potassium melt is 6.0 mol %.     

Carbon Diffusion Measurement in Austenite in the Temperature Range 500 °C to 900 °C

Carbon diffusion in austenite plays a critical role in phase transformation in steel. However, it can only be estimated in the fully austenitic range and has then to be extrapolated to the temperature range of the phase transformation. Therefore, published data are limited to temperatures above 750 °C. In this study, new experiments are carried out to determine the carbon diffusion coefficient in austenite at temperatures as low as 500 °C. Carburization experiments are performed in the austenitic range for a Fe-1.5 pct Mn 0.13 pct C and a Fe-31 pct Ni alloy (wt pct). Composition profile measurements, which are done using glow discharge optical emission spectrometry (GDOES), show that the surface composition is not constant with time. A methodology has been developed to assess the diffusion coefficient of carbon in austenite combining the measured carbon profiles and a numerical method to compute the diffusion profile taking into account the time evolution of the boundary condition. This method is first validated on the Fe-C-Mn steel. Carburization experiments are carried out on a Fe-31 pct Ni alloy at 900 °C, 800 °C, 700 °C, 600 °C, and 500 °C. The carbon diffusion coefficient is assessed using the method described above and fitted with the following expression (T in Kelvin): \( D = 1.23\cdot10^{{ - 6}} \cdot e^{{ - \frac{{15,050}} {{T{\left( {\text{K}} \right)}}}}} ({\text{m}}^{{\text{2}}} {\text{/s}}) \). The new expression is compared with previous experimental results measured for comparable nickel content at higher temperatures, and it shows a reasonable agreement. The model proposed by Ågren for carbon diffusion has been modified to take into account the thermodynamic contribution of nickel. This model also shows good agreement with the present experimental results, even if it was fitted to experiments performed at higher temperatures.     

Phase equilibria in the tungsten-rich field of the W-Fe-Ni system in the 800–575°C

Conclusions In the W-Fe-Ni system subjected to annealing at 800 and 575°C, isostructural phases FeW and NiW form a continuous series of (Fe, Ni)W-type solid solutions.At 800 and 575°C, the phases NiW₂ and (Fe, Ni)W or a solid solution of nickel in the FeW phase are in equilibrium with the tungsten-based -solid solution and (Ni, Fe)W or a solid solution of iron in the NiW phase exists in equilibrium with the NiW₂ phase.It is assumed that an invariant eutectoid equilibrium + + (Fe, Ni)W exists in the system under study at a temperature of approximately 1130°C ( is the Fe₇W₆ phase; and and are the tungsten and the nickel-based solid solutions).Depending on the temperature, the phase composition of the binder present in the tungsten-based heavy alloys subjected to long-term annealing can undergo changes: at temperatures exceeding 1110°C, the binder consists of a nickel-based solid solution; in the 1100–1000°C range, an intermediate (Fe, Ni)W phase is present along with this phase; and at temperatures below 1000°C, it consists of the intermediate phases (Fe, Ni)W and NiW₂.Translated from Poroshkovaya Metallurgiya, No. 8(344), pp. 61–67, August, 1991.     

Fracture toughness of f.c.c. nickel and strain ageing b.c.c. iron in the temperature range 77–773 K

Ductile initiation fracture toughness J_IC of b.c.c. Armco iron and f.c.c. nickel has been measured in the temperature range 77–773 K. Armco iron exhibits dynamic strain ageing (DSA) in the temperature range 383–573 K while nickel of the purity used does not evince DSA. Load vs load line displacement (LLD) plots during fracture toughness testing of Armco iron show serrations in the temperature range 383–573 K similar to those observed in the tensile stress-strain curves. DSA is found to have a beneficial effect on the fracture toughness J_IC. A marked increase in tensile strength and fracture toughness occurs in Armco iron in the DSA regime. The strain hardening exponent, known to have a bearing on the plastic zone size and the void growth rate, seems a clear parameter in terms of which the observed J_IC variation with temperature can be understood. Remarkably, the variation of n with temperature is found to closely follow the observed trend in _IC. However, the slope of the J-R curve, dJ/da, decreases in the DSA regime with a minimum at 423 K. The decrease has been related to the fracture propagation process which is shown to occur by an alternate fast fracture and the ductile dimpled mode in the DSA regime. In the case of nickel, free from DSA, J_IC or dJ/da are found to be largely unaffected by the test temperature. At room temperature f.c.c. nickel, at closely matching strength levels, possesses higher fracture toughness as compared to b.c.c. Armco iron. The crystal structure effect is more pronounced at temperatures below the ambient. At 77 K, the fracture toughness of iron is drastically reduced due to the onset of cleavage while nickel, not prone to a change in the fracture mode, maintains the same level of J_IC, as at the ambient.     

CFD Predictions and Experimental Comparisons of Pressure Drop Effects of Turning Vanes in 90° Duct Elbows

This paper presents new results for numerical predictions of air flow and pressure distribution in two commonly used elbows: (1) 90° mitered duct elbows with turning vanes having 0.05 m radius, 0.038 m vane spacing and (2) 90° mitered duct elbows without turning vanes, in 0.2×0.2?m (8?in.×8?in.) duct cross section using the STAR-CD computational fluid dynamics (CFD) code. A k-ε turbulence model for high Reynolds number and k-ε Chen model were used for that purpose for comparative purposes. The simulation used 13 different Reynolds numbers chosen between the range of 1×105 and 2×106. To validate the CFD results, the results of two experimental papers using guided vanes were compared with simulated vane runs under the same condition. The first experimental study used a 0.6×0.6?m (24?in.×24?in.) square elbow with 0.05 m radius, 0.038 m vane spacing and air velocities at 2.54 m/s (500 fpm) and 25.4 m/s (5,000 fpm), the second experiment used a 0.81×0.2?m (32?in.×8?in.) rectangular elbow geometry with 0.05 m radius, 0.038 m vane spacing with air velocities from 10.16 m/s (2,000 fpm) to 13.97 m/s (2,750 fpm). For Reynolds numbers (1.00–2.00)×105 the pressure drop difference between vaned and unvaned elbows was found to be 35 Pa as compared to 145 Pa. The simulations also agreed reasonably well with published experimental results. For the 0.6×0.6?m (24?in.×24?in.) square elbow and 0.81×0.2?m (32?in.×8?in.) rectangular elbow with vanes, the difference in pressure drop was 3.9 and 4.1% respectively and indicates that CFD models can be used for predictive purposes in this important HVAC applications area.     

Influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f.c.c.-f.c.c. nucleation—IV. Comparisons between theory and experiment in CuCo alloys

A discrete lattice point model (Cook, de Fontaine and Hilliard) which incorporates strain energy (Cook and de Fontaine), described in earlier papers, has been used to determine the ranges of temperature and composition at which homogeneous nucleation kinetics of f.c.c. precipitates in CuCo alloys would be neither too fast nor too slow to be measured. These predictions proved successful and it was possible to measure experimentally nucleation kinetics in CuCo alloys containing from 0.5 to 1.0 at.% Co within 50°C temperature ranges. Experimental results were compared with theoretical values obtained from the discrete lattice point, the Cahn-Hilliard continuum and the classical theories of homogeneous nucleation. Very good agreement was obtained between the experiments and all three theories. Although surprising at first, the good matching between classical theory and experiments was explained by showing that the calculated concentration profiles of critical nuclei at the temperatures and alloy compositions experimentally studied did show distinct “volumes” and “interfaces” i.e. the solute concentration did not vary continuously throughout the nuclei. In this case, as pointed out in effect by Cahn and Hilliard, classical nucleation theory indeed applies. These findings provide the first strong support for the essential correctness of homogeneous nucleation theory.     

C-Ni and Al-C-Ni phase diagrams and thermodynamic properties of C in the alloys from 1550 °C to 2300 °C

The C-Ni and Al-C-Ni phase diagrams were determined by chemical analysis of alloys saturated with carbon within sealed graphite crucibles. The solubility of carbon in nickel over the temperature range 1550 °C to 2300 °C is given by log (at. pct C)=2.0376−1874.68/T, where T is temperature in kelvin. Isothermal sections for the ternary system were determined at intervals of 150 °C over the range of temperatures investigated. The univariant points on the 1700 °C, 1850 °C, and 2000 °C isotherms were determined by metallographic examination of rapidly cooled alloys to be about 67.2Al-1.1C-31.7Ni, 70.3Al-2.3C-27.4Ni, and 82.5Al-7.0C-10.5Ni, respectively, where all concentrations are in atomic percent. Graphite, Al₄C₃ (decomposition temperature 2156 °C), and AlNi (decomposition temperature 1638 °C) were the only solid phases observed within the temperature range investigated. The excess partial Gibbs energy for dissolved C, , in liquid Al-C-Ni solutions in equilibrium with C, as calculated from the experimental solubilities and thermodynamic data on Al-Ni, is

The crystallography of fatigue crack initiation in coarse grained astroloy at 20°C

The effects of crystallographic orientation on fatigue crack initiation has been examined for coarse-grained Astroloy at 20°C. Specimens were cycled by three-point bending at stress ranges between 5 and 95% of the proportional limit until fatigue cracks were detected. The crystallographic orientation of individual grains within which fatigue cracks initiated was determined by use of selected area electron channeling. Grains forming cracks were found to have surface normals near the 〈100〉, 〈011〉, and 〈113〉 directions. Conversely, grains which did not initiate cracks were not similarly grouped in orientation. Calculations of the Taylor factor using the Bishop-Hill approach revealed that fatigue crack initiation in Astroloy occurred at grains with low values of the Taylor factor.     

Kinetics of the martensitic f.c.c.→ h.c.p. transformation in CoCrMo alloy powders

The kinetics of isothermal martensìtìc nucleation in CoCrMo alloy powders is monitored. It is shown that a linear relation exists between the activation energy for martensite formation and the chemical free energy for the f.c.c. → h.c.p. transition. The nucleation kinetics is governed by the thermally activated motion of partial dislocations and the interaction between the Shockley partials and short range obstacles (stacking faults intersections and solute clusters).     

A mechanism for fault formation in fine particles and implications for theories of annealing twins in f.c.c. metals—II

A mechanism is proposed for fault structure formation in annealed f.c.c. metals on the basis of experimental observations during annealing of gold particles in a fused silica matrix. The proposed model is an extension of the ‘growth accident’ model of Gleiter and accounts for particle-particle impingement and coalescence. The model explains how the high angle boundaries formed upon impingement and coalescence of two or more particles migrate to form metastable twin boundary structures. All structures observed are explained successfully by the modified growth accident model. Other theories were critically examined, but fail to explain the observed morphologies. The gold particle-fused silica matrix system may be viewed as a model system for understanding the nature of particle impingement, grain boundary migration, and annealing twin formation. The observations made and mechanism developed may be extended to recrystallization, grain growth, and annealing twin formation in bulk, polycrystalline materials.     

Structure of surface layers of boron carbide after friction in the temperature range 20–1400°C

Conclusions The experimental results show that, starting from 800°C, friction of the boron carbide is characterized by high ductility associated with the formation of planar defects. The results show that the depth of the deformed layer to temperatures of 800–1000°C is determined by the grain size and in the regions of the coarse-grained material the layer is 10–15 m deep which is 3–5 times greater than in the areas of the fine-grained material. The products of wear do not form a continuous layer on the friction surface of the Bi₄C-B₄C pair and are distributed in the form of individual clusters. Friction of this pair in air at temperatures above 600°C is accompanied by the formation of quasiamorphous oxide films.Translated from Poroshkovaya Metallurgiya, No. 8(284), pp. 93–97, August, 1986.