Compositional ordering kinetics of epitaxial growth of fcc alloy systems

The kinetics of ordering in fcc alloys during the epitaxial growth is investigated by the kinetic mean field method. There are various evolution behaviors during the growth of the system. The kinetic phase diagrams for the epitaxial alloy of an fcc multilayer are calculated. We have found that there is a kinetic induced oscillatory ordered phase in addition to the equilibrium ordered phase in the kinetic phase diagrams.     

Microstructural analysis of Fe-Si-Al alloy powders and films by Mössbauer spectrometry

The powder, plate and films of Fe-Si-Al alloy were prepared by gas atomizer, extrusion, sputtering, and quenching. The characteristics of these alloy materials were studied by Mössbauer spectrometry, and estimated on the base of iron configuration. The magnetic hyperfine fields were dependent on each preparation process. Quenched ribbon gave a perfect DO₃ structure.     

Metastable phase diagrams of Cu-based alloy systems with a miscibility gap in undercooled state

Some Cu-based alloy systems with a large positive enthalpy of mixing display a eutectic or peritectic phase diagram under equilibrium conditions, but show a metastable liquid miscibility gap in the undercooled state. When the melt is undercooled below certain temperature beyond the critical liquid-phase separation temperature, it separates into two liquids with different compositions. The compositions of the two liquids change successively upon the metastable phase diagram before solidification occurs. The shape and position of the metastable miscibility gap are dependent of the alloy components and their interaction features. This study reviews the metastable phase diagrams of Cu-based alloy systems, which are derived from experiments and thermodynamic calculations.     

Experimental and theoretical phase diagrams of the iron-rich Fe-Si-Ge ordering system

The phase separation in iron-rich Fe-Si-Ge ternary alloys was investigated by means of transmission electron microscopy. The phase separations into A2 and D0₃ were recognized in several alloys in addition to the phase separation into B2 and D0₃ which has already been found in Fe-Si and Fe-Ge binary systems. On the basis of TEM observations, isothermal section diagrams are proposed for the iron-rich corner at 823, 873, 923 and 973 K. The A2 + D0₃ two-phase field exists in a band-shaped region at 823 K. With increase in temperature,the A2 + D0₃ field gradually shrinks and is eventually replaced at 973 Kwith the B2 + D0₃ field, which extends from both the Fe-Si and Fe-Ge binary sides. The phase diagrams were well reproduced by the calculations based on the so-called Bragg-Williams-Gorsky approximation, taking account of the chemical and magnetic pair interactions up to the second nearest neighbour. The effects of the magnetism on the equilibria are discussed.     

Phase diagrams of thin films and wires

Starting from a relation between phonons, defects and surfaces, a model is developped, dealing with the stability of crystalline phases. It is shown that:

• 1.1) the disordering temperature decreases with decreasing thickness;
• 2.2) phase diagrams of thin films might differ from bulk ones;
• 3.3) surface and interface contributions might modify the previous effects.

     

Phase separation and ordering in the Fe-Co system

The Fe₅₀Co₅₀, Fe₆₅Co₃₅, and Fe₃₅Co₆₅ alloys heat-treated between 500 and 1300°C were characterized by x-ray diffraction and transmission electron microscopy. The surface layer of the alloys was found to phase-separate in the range 900–1300°C, leading to the formation of alternating α and γ zones on the order of 0.5 μm in thickness. Phase separation in the bulk of the alloys led to precipitation of an fcc phase, with a volume fraction no greater than 0.1. In the ordering region, the volume fraction of the B2 phase was also no greater than 0.1. The phase-separation region was shown to be divided from the ordering region by a solid-solution phase. Below 550°C, the alloys undergo a phase transformation accompanied by a slight increase in lattice parameter. Comparison with a similar transformation of the Fe₆₀Cr₃₀Co₁₀ alloy suggests that, under certain conditions, this transformation may lead to a significant rise in coercivity. The results are represented in a modified Fe-Co phase diagram.     

Phase relations and ordering in the dysprosia-zirconia system

The phase diagram in the subsolidus for the system Dy₂O₃-ZrO₂ has been established. The areas of existence of the high temperature solid solutions based on ZrO₂ and Dy₂O₃ were determined using the precision lattice parameter method. At low temperature, long-range ordering occured in the Dy₂O₃-rich region (>50 mol% Dy₂O₃) and two hexagonal compounds of an M₇O_11.5- and M₇O₁₁-type were found. The first of these compounds is formed at about 55 mol% Dy₂O₃ and possesses a very narrow homogeneity range. At approximately 1750° C this compound undergoes a transformation into cubic solid solutions of fluorite and C-type. The second is formed within the Dy₂O₃ concentration range between ~65 and 90 mol% Dy₂O₃. Above 1700° C the hexagonal compound Dy₆ZrO₁₁ undergoes a transformation into a cubic solid solution of C-type.     

Phase equilibria and ordering in the erbia-zirconia system

The phase diagram for the system ZrO₂-Er₂O₃ was redetermined. At high temperatures, the system is dominated by wide regions of solid solution based on ZrO₂ and Er₂O₃ separated by a two-phase field which appears to extend to the solidus. The range of existence of these solid solution fields was determined using the precision lattice parameter method. A low-temperature (<1800° C) long-range ordering occurred between 20 and 90 mol % Er₂O₃, and three ordered phases were found: the first compound was present at 40 mol % Er₂O₃ and corresponds to the ideal formula Er₄Zr₃O₁₂ with rhombohedral symmetry (space group R¯3), is isostructural with UY₆O₁₂, and decomposes at about 1500° C into fluorite solid solution by an order-disorder process; the second ordered phase is formed at about 55 mol % Er₂O₃, its formula is close to Er₅Zr₂O_11.5, and it decomposes at about 1650° C into cubic solid solutions of the fluorite and C-type; the third compound is formed at 75 mol % Er₂O₃, its formula is Er₆ZrO₁₁, it has a wide homogeneity range, and it decomposes above 1700° C into a cubic solid solution of the C-type. Liquidus determination indicated the existence of a peritectic at 62 mol % Er₂O₃.This work is based on the Ph.D. thesis of C. Pascual, Madrid University, 1980.     

Fe-rich border and activation energy of phase decomposition in a Fe–Cr alloy

Concentration of Cr in the Fe-rich α-phase, x, resulted from a phase decomposition caused by an isothermal annealing at T = 415 and 450 °C of a non-irradiated (NR) Fe–Cr14 EFDA sample and that of a He-ions irradiated one (IR) annealed at 415 °C was determined with Mossbauer spectroscopy. The x-value in the latter was by ∼3 at% higher than the one in the NR-counterpart. The activation energy for the phase decomposition in the NR-sample was 122 kJ mol⁻¹. In the IR-sample its value was by 12 kJ mol⁻¹ lower. Avrami exponents for the NR-samples were close to 0.5, and that the IR-sample had a value of about 1.     

Maximizing the opening of eye diagrams for slow-light systems

We present a data-fidelity metric for quantifying distortion in slow-light optical pulse delay devices. We demonstrate the utility of this metric by applying it to the performance optimization of gain-based slow-light delay systems for Gaussian and super-Gaussian pulses. Symmetric Lorentzian double-line and triple-line gain systems are optimized and achieve maximum delay of 1.5 and 1.7 times the single-line gain system delay, respectively. The resulting double-line gain system design is qualitatively similar to the double-line gain system designed with a previous metric, but is tuned specifically to constrain data fidelity.     

Extrusion limit diagrams containing structural and topological information for AA 6063 aluminium alloy

Abstract

The limits of extrusion can be high temperature flow stress related, surface related, or microstructure related. It is shown that the quantification of these features allows convenient representation within the extrusion limit diagram framework. This potential metallurgical process control is most important in the high strength structural alloys of the 2000, 5000, and 7000 series. It is the commonly extruded alloy, AA 6063, that has been considered in the work reported here. While mechanical properties remain an important consideration, the cosmetic appearance represents a special product requirement, particularly regarding the occurrence of the surface defects, pickup and die lines. It is shown, using experimental data from AA 6063 extrusion trials, that pressure requirements, microstructural features, and the surface defects, pickup and die lines, can be characterised through mathematical formulae and, therefore, represented within the limit diagram framework. Limit diagrams containing microstructural and topological information are presented.

MST/1626     

Calculation of phase diagrams of binary fcc and ideal hcp alloys undergoing ordering transitions

The tetrahedron approximation of the cluster variation method (CVM) has been employed to investigate phase diagrams having fcc-based ordered and disordered phases. This approximation is also applicable to the binary hcp ordered structures with ideal axial ratio. The CVM developed by Kikuchi consists of calculating approximate expressions for the number of configurations and hence entropy of a crystal lattice having definite distribution of clusters (points, pairs, triangles, tetrahedra, etc.) of lattice points which in general may be occupied by one of a given set of atomic species. Tetrahedral multi-atom interactions denoted by α and β are utilized for expressing the configurational energy. The equilibrium cluster distribution is then found by minimizing the free energy by utilizing the natural iteration method developed by Kikuchi. The effect of α and β parameters on the topology of the resulting phase diagrams is observed by assigning several negative and positive values to them. The invariant reactions were also determined in each case. Finally a study was made on the Cd-Mg diagram.     

Concentration inhomogeneities and phase diagrams of eutectic systems

We show that it is possible to determine the regions of compositions with developed concentration inhomogeneities in the liquid phase by analysis of the phase diagrams of binary eutectic systems.     

Block diagrams for information measuring systems of physicochemical composition and substance properties

Block diagrams for information measuring systems of physicochemical composition and substance properties are considered and it is noted that within their composition there should be first level systems that are either independent measuring systems, or measuring sub-systems of a second level system, or management information measuring systems. Translated from Izmeritel’naya Tekhnika, No. 10, pp. 57–60, October, 2008.     

Optimal batch ordering policies for assembly systems with guaranteed service

For a supply chain modelled as a multi-echelon inventory system, effective management of its inventory at each stock is critical to reduce inventory costs while assuring a given service level to customers. In our previous work, we used the guaranteed-service approach (GSA) to design optimal echelon batch ordering policies for continuous-review serial systems with Poisson customer demand and fixed order costs. The approach assumes that the final customer demand is bounded and each stock has a guaranteed service time in the sense that the demand of its downstream stock can always be satisfied in the service time. This paper extends this work by considering more general assembly systems. We first derive an analytical expression for the total cost of the system in the long run. The problem of finding optimal echelon batch ordering policies for the system can then be decomposed into two independent sub-problems: order size decision sub-problem and reorder point decision sub-problem. We develop efficient dynamic programming algorithms for the two sub-problems. Numerical experiments on randomly generated instances show the effectiveness of the proposed approach.     

Phase equilibrium and interphase transition layer as an ordering problem

The model of a binary ordering alloy, developed previously based on the conventional distribution method, is used for describing spatially inhomogeneous multiphase equilibrium systems of gas-solid, liquid-gas or crystal-liquid types, including the structure of an interphase transition layer. General results are illustrated by specific predictions for a two-phase crystal-gas system.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Belarussian Academy of Sciences, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 2, pp. 198–206, August, 1993.     

The clusterization parameters of neon, argon, krypton, and xenon calculated using their P-V diagrams

The parameters of clusterization for neon, argon, krypton, and xenon were calculated based on a thermodynamic analysis of the corresponding P-V diagrams. The calculated clusterization parameters agree well with experimental values of the evaporation heat.     

A computational study of kinetic phase diagrams for CoPt alloy films during epitaxial growth

We have studied the kinetic processes of the epitaxial growth for CoPt alloy films using the master equation method. The kinetic phase diagrams of CoPt alloy films which show the phase formation conditions during the epitaxial growth are determined. From the kinetic phase diagrams, we find that the [001] ordered structure is much easy to be grown at high temperature while the [100] ordered structure is easy to be grown at low temperature although both the [001] and [100] ordering could be the equilibrium ground states. The atomic deposition, ordering and surface segregation lead to a rich variety of phases in epitaxial growth. The surface segregation is found to enhance the [001] ordering and leads to the formation of the [001] ordered phase at high temperature.