Al-Ge Alloys Research Articles

Measurement of solid solubility of germanium in aluminum

The solid solubility of Ge in aluminum was determined by resistivity measurement at 77 K of Al-Ge alloys annealed at various temperatures for times sufficient to complete the precipitation of the equilibrium Ge phase. The solid solubility of Ge in aluminum was found to vary from 0.252 at. pct at 533 K to 1.82 at. pct at 693 K. From the temperature dependence of the solid solubilities, the excess entropy of mixing ΔS and heat of mixing ΔH associated with the formation of solid solution of Ge in aluminum were calculated to be 2.77 R and 38.5 kJ mol-1, respectively. Using these values of ΔS and ΔH, the maximum solid solubility of Ge in aluminum was calculated to be 2.08 at. pct at the eutectic temperature 697 K. The magnitude ΔρGe77/Δc due to 1 at. pct impurity was determined to be 8.60 nΩm/at. pct Ge. The resistivity of Al-1.32 at. pct Ge alloys aged at 573 and 623 K was measured at 77 K to determine the time variation of the average concentrationc of the solute in the matrix during coarsening of the Ge precipitates. The value ofc, calculated using the value of ΔρGe77/Δc, decreased linearly in accordance with the t-1/3 law. The concentration of the solute in the matrix, in equilibrium with the Ge particle of infinite size, was determined by extrapolating thec vs t-1/3 plot to infinite time, in excellent agreement with the above solid solubility.

Thermodynamic calculation of phase equilibria in the Al-Ge-Zn system

Phase equilibria in the ternary system Al-Ge-Zn were calculated at 873, 773 and 658 K from thermodynamic data of the constituent binary systems. Quasi-regular solution and shortest distance path equations were employed to estimate the thermodynamic data of liquid Al-Ge-Zn alloys from the binary data. The thermodynamic behaviour of solid alloys was also approximated by a quasi-regular solution model. The interaction parameter for solid Al-Ge alloys was deduced from the binary phase diagram. The calculated isothermal phase diagrams are in reasonable agreement with the experimental data. Tie-lines delineating equilibria between the liquid and solid alloys were generated.

A Transition from DBM to Fractals Generated by Random Successive Nucleation Model

We present a random successive nucleation model to simulate the formation of the dense branching morphology (DBM) found in amorphous Al-Ge alloys. Our simulation shows that the DBM is obtained when the parameter K accounting for the structures of alloy films is small, and that a transition from DBM to fractals is found as K increases.

Elastic stiffness constants of Al-Si and Al-Ge alloys by solid-solutioning under high pressure

The elastic stiffness constants of the Al-Si and Al-Ge alloy systems formed by solid solutioning under high pressure are studied using our previous formalism for the static crystal energy term taking account of the lattice dynamical contributions. The obtained results for the temperature-dependence of the elastic constants for pure solvent Al are consistent with the observed data. Then, the atomic fraction-dependence of the elastic constants for these alloy systems is calculated, and a decrease of the elastic stiffness constants C 11, C 12 and C 44 with increasing concentration of Si or Ge is found for both Al-Si and Al-Ge solid solutions. Numerical results of the concentration x-derivative 1/ C ij ·d C ij /d x of the elastic constants C ij for the Al 1- x Si x and Al 1- x Ge x alloy system are obtained theoretically and found to be nearly constant under pressure and high temperatures. The deviation from the elastic constants of pure Al is larger for the Al-Ge alloy than for the Al-Si system.

Elastic moduli of Al-Si and Al-Ge solid solutions

The elastic moduli of Al-Si and Al-Ge alloys obtained by solid-solution under pressure are investigated theoretically using a previous treatment based on the microscopic electronic theory. The obtained results for elastic coefficients such as bulk modulus, shear modulus, Young's modulus and Poisson's ratio for matrix Al are in good agreement with temperature-dependent experimental data. These moduli of Al-Si and Al-Ge alloys are calculated, and the concentration dependence of the elastic data is presented quantitatively.

Effect of Pressure on Order and Stability in Alloys: The Case of Al-Ge

ABSTRACTA parameter-free approach to phase stability in substitutional alloys is applied to the influence of pressure on order-disorder phenomena in Al-Ge. The methodology is based upon an application of the Generalized Perturbation Method to the Korringa-Kohn-Rostoker scattering formulation of the Coherent Potential Approximation. For fcc-based Al-Ge alloys, it is shown that the tendency towards phase separation at normal pressure originates from a structural difference between the pure species. By applying pressure, the structural energy difference is reduced, and a significant increase in the tendency towards order, especially for Al-rich alloys, is theoretically observed, leading, as an example, to the possible observation of a DO22 ordered state around 25 at. pct. Ge. The electronic origin of the ordering tendencies induced by pressure is discussed and the theoretical predictions are related to experimental facts.

Formation of dense branching morphology in the crystallization of Al-Ge amorphous thin films.

The crystallization of Al-Ge alloy amorphous thin films reveals a unique, dense branching morphology. Such morphology is found in other systems, i.e., electrodeposition and the Hele-Shaw cell, but so far this is the only known case in the field of materials science. A detailed description is given of the structure, morphology, and composition of the crystallized films and of the material processes that are involved in the crystallization of the Al-Ge alloy, and which are responsible for the unique morphology. The role played by diffusion is particularly emphasized.

Nonequilibrium behavior in the Al-Ge alloy system: Insights into the metastable phase diagram

The competitive formation of metastable and stable phases during nonequilibrium processing of Al-Ge alloys and the corresponding metastable phase equilibria have been investigated. For germanium concentrations in the range 30 to 50 at. pct, it is shown that the four metastable phases can be ranked in order of decreasing stability as follows: monoclinic (P21/c), rhombohedral (R-C), orthorhombic (Pbca), and hexagonal (P6/mmm). Their formation depends not only on the transformation temperature(e.g., the liquid undercooling), but also on the presence of appropriate heterogeneous nucleation sites. For example, the orthorhombic phase has only been observed in amorphous films after rapid annealing/crystallization treatments. It is also shown that all of these phases form metastable equilibria with α-aluminum only,i.e., no metastable phase equilibria appear to exist between any metastable phase and β-germanium or between any two metastable phases. Consequently, it is not possible to draw a single metastable phase diagram that incorporates all of these phases with phase boundaries that represent their metastable equilibria; rather, separate diagrams should be drawn for each metastable phase. It is noted that these diagrams should extend only to the metastable phase field rather than all the way to pure germanium: for compositions richer in germanium, the results indicate that the metastable phase forms and then remelts upon the formation of germanium or a more stable, germanium-enriched metastable phase. Furthermore, it is proposed that this behavior is rather general in nature. Finally, it is concluded that the production of metastable phases in bulk form, in systems such as this where so many reactions occur simultaneously and competitively, might be impossible using solidification processing approaches.

Influence of germanium-clustering on the precipitation behaviour of rapidly solidified AlGe solid solutions

Differences in precipitation behaviour in liquid and solid quenched Al1.3at.%Ge solid solutions were investigated by means of transmission electron microscopy and electrical resistivity measurements. Precipitation behaviour in rapidly quenched Al(Ge) alloys is assumed to depend on the existence of germanium clusters that act as nucleation sites, thus leading to a strong correlation between cluster density and the density of germanium precipitates after annealing. The observed precipitation morphology indicates that such clusters exist in thermodynamically stable solid solutions as well as in slightly superheated melts. At higher temperatures the number of clusters in the superheated melt is drastically reduced. Appropriate high quenching rates have been found to result in the formation of supersaturated solid solutions with a low density of clusters, leading to a distinctly different precipitation morphology and retardation of the precipitation reaction upon ageing compared with solid quenched alloys.

Effects of Precipitation on Recrystallization Textures in Al-Ge Alloy

The recrystallization textures of Al-4.0wt%Ge alloys with the different states of precipitation before cold rolling were determined by means of orientation distribution functions (ODFs). Additionally, measurements of the hardness and the electrical resistivity and optical microscopic observation were carried out to investigate the process of recrystallization and precipitation, and effects of two kinds of precipitates were revealed. Recrystallization textures were strongly dependent on annealing temperature. At higher temperatures, discontinuous recrystallization occurred, while continuous recrystallization predominated at lower temperatures. This was due to the precipitation during annealing. On the other hand, it was found that precipitates which existed before cold rolling randomized recrystallization textures.

Shape Transformations of Ge Precipitates in Al

ABSTRACTGe precipitates in Al-Ge alloys have been observed to undergo a transformation in shape during in-situ temperature cycling in a high voltage electron microscope. Octahedral precipitates with a parallel-cube orientation relationship spheroidized on heating and refaceted to the octahedral shape on cooling. This shape transformation was essentially conservative if the temperature excursions were kept small. These observations are discussed in terms of an interface roughening transformation.

Formation of AlSi and AlGe solid solutions and equation of state

The pressure effect on the solid solubility of the AlSi and AlGe systems is studied using the electronic theory based on pseudo- potentials and the virtual crystal approximation for the disordered alloy. The atomic concentration x-dependence of the equilibrium volume satisfying energy-minimum condition for Al 1− x Si x and Al 1− x Ge x solid solutions with fcc lattice is in good agreement with an available experimental data. The equation of state of these alloy systems is presented quantitatively and the compression effect on the heat of solution is investigated. The heat of solution ΔE S ( x, P) for Al 1− x Si x and Al 1− x Ge x solid solutions under pressure P is small for the Al-rich region and decreases as the crystal is compressed. Consequently, using the Helmholtz free energy of formation under pressure F' s ( x, P, T), we predict the extended solid solutions under pressure in AlSi and AlGe alloy system is consistent with the experimental tendency.

Vibration Damping Characteristics of Al–Ge Alloys

The logarithmic decrement δ and the rigidity modulus G were investigated for heat-treated and cold-worked Al-Ge alloys containing 2 to 20 mass% Ge. The δ and G values were measured by an inverted torsion pendulum method. The δ values upon furnace-cooling were somewhat higher than those upon water-quenching, which were as low as 0.007. By cold-working after heat treatment, the δ values of all alloys were increased considerably

Al-Ge合金の振動減衰能

The logarithmic decrement δ and the rigidity modulus G were investigated for heat-treated and cold-worked Al-Ge alloys containing 2 to 20 mass%Ge. The δ and G values were measured by an inverted torsion pendulum method.The δ values upon furnace cooling were somewhat higher than those upon water quenching, which were as low as 0.007. By cold working after heat treatment, the δ values of all alloys were increased considerably. With increasing Ge concentration, the δ upon cold working increased abruptly to 5 mass%Ge and then increased gradually. Moreover, in alloys cold worked after furnace cooling, the δ became higher than those cold-worked after water quenching.With increasing Ge concentration, the G increased, and cold working after heat treatment caused G to decrease. The ΔG effect increased abruptly up to 5 mass%Ge and then increased gradually, and high δ values were obtained in the alloys with a large ΔG effect.

Lattice imperfections studied by x-ray diffraction in deformed aluminum-base alloys: Al-Ge alloy

In the present analysis, which is part of a series on a study that has been undertaken on aluminum-base alloys, a detailed X-ray diffraction study of deformation[1–5] is made on aluminum-base germanium alloys in four different compositions: Al-3.10 at. pct Ge, Al-3.80 at. pct Ge, Al-4.16 at. pct Ge, and Al-4.60 at. pct Ge. The alloys were prepared from spectroscopically pure metals supplied by Johnson-Matthey and Co. Ltd., London, by melting them in graphite crucibles sealed under vacuum in quartz capsules. The alloys were homogenized for 15 days at 400 °C in the face-centered cubic phase (Figure 1), and cold working was performed by careful hand filing at room temperature. The diffractometer samples were prepared in the usual manner,[3,4] and X-ray diffraction profiles were recorded in a Siemens Kristalloflex-4 X-ray diffractometer using Cu Kα radiation. A portion of the powder obtained by hand filing from each alloy was annealed at 400 °C to relieve strain and was taken as standard for line shift, line asymmetry, and line shape analyses in light of recent developments.[3,4,6–8] The microstructural parameters, such as coherent domain size (D e, microstrain 〈∈L〉, stacking faults α′ and a" (both intrinsic and extrinsic), deformation twin fault β, dislocation density ρ, and stacking fault energy parameter γ/μ, were determined by adopting the same method of analysis and following the same equations that were used before.[3–7]

Microdiffraction analysis of precipitate crystallography and morphology in Al alloys

Electron microdiffraction has been used to determine the crystallography of precipitation in Al-Cu-Mg-Ag and Al-Ge alloys for individual precipitates with dimensions down to 10 nm. The crystallography has been related to the morphology of the precipitates using an analysis based on the intersection point symmetry. This analysis requires that the precipitate form be consistent with the intersection point group, defined as those point symmetry elements common to precipitate and matrix crystals when the precipitate crystal is in its observed orientation relationship with the matrix.In Al-Cu-Mg-Ag alloys with high Cu:Mg ratios and containing trace amounts of silver, a phase designated Ω readily precipitates as thin, hexagonal-shaped plates on matrix {111}α planes. Examples of these precipitates are shown in Fig. 1. The structure of this phase has been the subject of some controversy. An SAED pattern, Fig. 2, recorded from matrix and precipitates parallel to a <11l>α axis is suggestive of hexagonal symmetry and a hexagonal lattice has been proposed on the basis of such patterns.

Resistance scaling in media with fractal-like structure in the vicinity of a metal-insulator transition

Scaling relation between residual R 0 and temperature-dependent R 1 parts of the sample electrical resistance in the vicinity of a metal-insulator transition can be a guide in examining the structure of the material. Three possible values of the exponent ν in the relation R 1 ∝ ( R 0) ν are discussed. ν = 1 is typical for a random mixture of metallic and insulating domains, ν = 0 for granular metals. A special case ν = 0.75 which has been observed recently corresponds to a fractal structure of the insulating phase with the classical size effect governing the conductivity of the metallic channels. Experimental data on ZnSb and AlGe alloys are presented.

The morphology of precipitates in an AlGe Alloy—I. experimental observations

The morphology and crystallography of Ge precipitates formed in a quenched and aged Al-4 wt% Ge alloy have been characterized using transmission electron microscopy and electron microdiffraction. Five different precipitate forms have been distinguished in a sample aged 3 h at 200°C: (i) triangular plates on {111} Al, (ii) laths parallel 〈100〈 Al, (iii) rods parallel 〈110〉 Al, (iv) hexagonal plates on {111} Al, and (v) small regular tetrahedra with {111} Al facets. The cube-cube orientation relationship, (111) Ge//( 1 11) Al and [110] Ge//[110] Al, has been assocaited with three separate forms of precipitate: the triangular and hexagonal plates on ( 111) Al andthe tetrahedra. A second type of twinned hexagonal plate has been observed on ( 111) Al with an orientation relationships deviating from cube-cube by a rotation of 30° about the habit plane normal, [ 111] Ge . The 〈100〉 Al laths have [110] Ge//[100] Al along their long axis and ( 111) Ge //(001) Al ; the long axis is an approximately invariant line. Rods parallel to 〈110〉 Al have in common a rod axis [110] Ge//[110] Al, but several orientation relationships have been detected, differing by a rotation about this axis. A summary is presented of all precipitate forms and associated orientation relationships observed in the AlGe system.

The morphology of precipitates in an AlGe alloy—II. Analysis using symmetry

The range of morphologies observed for Ge precipitates in quenched and aged AlGe alloys (4.0 wt% Ge) has been analysed in terms of the symmetry of precipitate and matrix phases and the orientation relationship between them. For precipitates in the form of (i) laths parallel to 〈100〉 Al, (ii) rectangular plates on {100} Al, (iii) hexagonal plates on {111} Al, and (iv) rods parallel to 〈110〉 Al, each precipitate shape is found to be consistent with the symmetry of the intersection point group defined by point symmetry elements common to precipitate and matrix structures in the observed orientation relationship. For those precipitates which exhibit an identity or “cube-cube” relationship with the matrix phase, there is a correspondence between translational elements of symmetry in the two structures and a complete analysis requires the determination of the full space group defined by the intersection of the individual space groups of the precipitate (Ge) and matrix (Al) structures. Those precipitates in the form of regular tetrahedra with {111} Al facets are found to be consistent with the intersection space group ( F 43m )_describing the lattice obtained by superposition of the Ge and Al lattices in an identity relationship, with a Ge atom site somewhere coincident with an Al atom site. However, it remains impossible to account for those Ge precipitates occurring as triangular plates on {111} Al in terms of this analysis. It seems likely that such precipitates nucleate heterogeneously and that it will be necessary to incorporate the symmetry of the nucleating defect in a complete symmetry analysis. One possible analysis is outlined briefly.

Solute Trapping of Ge in Al

AbstractPartitioning during rapid solidification of dilute Al-Ge alloys has been investigated. Implanted thin films of Al have been pulsed-laser melted to obtain solidification at velocities in the range of 0.01 m/s to 3.3 m/s, as measured by the transient conductance technique. Previous and subsequent Rutherford Backscattering depth profiling of the Ge solute in the Al alloys has been used to determine the nonequilibrium partition coefficient k. A significant degree of lateral film growth during solidification confines determination of k to the placing of an upper bound of 0.22 on k for solidification velocities in this range. We place a lower limit of 10m/s on the “diffusive velocity,” which locates the transition from solute paritioning to solute trapping in the Continuous Growth Model.