Lattice dynamics and specific heat of Al-Si and Al-Ge solid solutions

A simplified treatment has been proposed to study quantitatively the lattice dynamics of Al-Si and Al-Ge alloy systems by solid-solutioning under pressure. The volume and electron density effects on the lattice dynamics of the pure constituents aluminium, silicon or germanium are considered, and the phonon dispersion relations of the local and band modes were obtained. Then, the concentration dependence of the local and band mode frequencies were calculated for the Al_1–x Si _x and Al_1–x Ge _x systems. Using the local and band mode frequencies, the lattice specific heat at constant volume was determined theoretically, and results obtained for the temperature-dependent specific heat of matrix aluminium were found to be in good agreement with the experimental data. The concentration dependence of the specific heat could then be predicted quantitatively for Al_1–x Si _x and Al_1–x Ge _x alloy systems.     

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.     

Isobaric sections of the aluminium phase field in the Al-Ge phase diagram at high pressures up to 2.6 GPa

The isobaric sections of the aluminium phase field in the Al-Ge system have been obtained experimentally at 0.1 MPa, 2.2 and 2.6 GPa. The solidus and solid solubility lines of the aluminium phase were determined by electron probe microanalysis of alloys quenched after equilibration at known temperatures and pressures. The aluminium phase field of aluminium was observed to expand with increasing pressure. This result was compared with the phase diagrams calculated on the basis of thermodynamic and volumetric data at 0.1 MPa. The calculations are in qualitative agreement with the experimental results.     

On the specific heat of Al-Si and Al-Ge alloys—A simulation study

The large variation in specific heats with concentration between temperatures 50 K and 200 K for Al-Si and Al-Ge alloys are analysed in detail by lattice dynamical and Monte Carlo approaches. The large deviation from linearity at low temperatures does not seem to be due to the Debye’s low temperature contribution. It is shown that an anharmonic vibration in the above solid solutions, particularly at 200 K, is the cause for the small variation in the specific heat.     

Interaction of Al-Si,Al-Ge,and Zn-Al eutectic alloys with SiC/Al discontinuously reinforced metal matrix composites

Interactions between Al-Si, Al-Ge, and Zn-Al eutectic alloys with SiC whisker-reinforced aluminium metal matrix composites were studied as a function of temperature above the eutectic melting temperature. Penetration extended several millimetres into the composite for the Al-Si and Al-Ge alloys but was restricted to a thin surface layer (50 m) for the Zn-Al alloy. The extent of the penetration zone for the aluminium alloys containing silicon and germanium was also affected by the thermal-mechanical treatment of the composite: limited penetration was observed for hot-pressed material whereas extensive penetration was observed for mechanically worked material. Mechanisms for the observed phenomena are discussed in terms of the wettability of the SiC whiskers by the eutectic alloys, the formation of channels during mechanical working as well as the fine grain size of the composite.     

Shape rheocasting of unmodified Al-Si binary eutectic

It is demonstrated experimentally that by using the Council for Scientific and Industrial Research Rheo Casting System and high pressure die casting it is possible to semi-solid process and cast into a shape unmodified Al-Si binary eutectic without a solidification temperature range. Silicon leads the aluminium coupled crystal growth subjected to convection by induction during thermal arrest. The semi-solid structure during thermal arrest is captured after rheo-processing and casting.     

Elastic and superconducting properties of supersaturated Al-Si and Al-Ge solid-solution alloys treated under a 5.4 GPa pressure

Supersaturated Al-Si and Al-Ge solid solutions having up to a 10 at% solute concentration were treated at 5.4 GPa. The variations in the elastic moduli, superconducting transition temperature T _c and other physical properties were obtained. Using the resonance method the moduli of the solid solutions in both alloy systems decreased with increasing solute concentration, in contrast with those of the two-phase states which increased. The maximum value of T _c was determined as 6.6 K for an Al-15 at% Si solid solution. It was confirmed that the dependence of T _c on the valence electron concentration was remarkably greater than that of other non-transition and noble metal alloys. Using low-temperature specific-heat experiments as a basis, the superconducting properties were discussed in terms of the electronic specific heat coefficient and the Debye temperature in comparison with other metallic superconductors.     

Nanowire array fabricated by Al-Ge phase separation

Phase-separated Al-Ge films, composed of Al nanowire array with diameters ranging from less than 10 to 18 nm embedded in an amorphous Ge matrix, have been prepared by a sputtering method. Similar to lateral phase separation of Al-Si system, sputtered Al and Ge form an Al nanowire array surrounded by a Ge matrix during film growth when the preparation conditions are optimized. Removal of the Al nanowires from the phase-separated Al-Ge films by etching in acid solution provides nanoporous films with a pore density on the order of 10¹⁵ pores/m². Template-assisted growth of Ni nanowires into the nanopores was carried out to increase the potential applications of the phase-separated Al-Ge films.     

Approximations in using solubility products for B,N, Ti and Al

Abstract

The addition of boron in just a few parts per million can influence the hardenability of steel, provided it remains in solid solution. To protect boron from forming nitrides, titanium and aluminium which have a strong affinity for nitrogen are added in optimised proportions. The amount of soluble boron in such multicomponent systems can be estimated using commercial software available based on thermodynamic databases. Alternatively, the so called simultaneous and sequential methods permit the soluble boron concentration to be estimated using solubility products. The reliability of these methods has been investigated and compared with a different approach, the stepwise method based on the solubility product of various nitrides under equilibrium conditions.     

Non-equilibrium microstructure of hyper-eutectic Al-Si alloy solidified under superhigh pressure

The non-equilibrium microstructures of hyper-eutectic Al-26.6wt%Si solidified under superhigh pressure (5.5 GPa) have been investigated. The results show that there exists a great deal of primary phase in hyper-eutectic Al-Si alloy. The non-equilibrium microstructure for hyper-eutectic Al-Si alloy is composed of primary phase, phase and ( + ) eutectic phase. The solid solubility of Si in phase and the solid solubility of Al in phase increase significantly. The effects of high pressure on the solidification structures of Al-Si alloy are discussed.     

Effect of alloying with zinc on SFE of aluminium by study of lattice imperfections in cold worked Al-Zn alloys

A detailed X-ray Fourier line shape analysis has been performed on three compositions of Al-Zn alloys viz. Al-3.55 wt% Zn, Al-14.7 wt% Zn and Al-19.3 wt% Zn infcc phase. It has been found that deformation stacking faults, both intrinsic ά and extrinsic α are absent in the cold worked state and twin fault β is found to be slightly present in the deformed lattice of the two initial compositions of the alloys. Similar to the effect of solute germanium and copper, respectively in Al-Ge and Al-Cu systems, hexagonal zinc also fails to impart faulting infcc Al-Zn system. This corroborates the fact that aluminium has high stacking fault energy.     

机械合金化W-Cu固溶体的形成机理

采用W-15%Cu和W-25%Cu两种复合粉,开展了机械合金化诱导W-Cu固溶度扩展机制的研究.研究表明:两种粉末经8 h高能球磨后,Cu固溶入W中形成固溶体.机械合金化诱导W-Cu固溶度扩展的主要机制,一方面是高能球磨过程中所引起的粒子纳米化,形成大量的纳米界面,许多原子"储存"在这些纳米晶界上,诱导W-Cu固溶浓度扩展.另一方面是机械合金化过程晶格严重畸变,晶粒内部生成高密度缺陷,成为溶质快速扩散的网络通道,诱导过饱和固溶体的形成.     

Crystallographic orientation relationships between primary silicon and aluminium crystals

Crystallographic orientation relationships between the primary silicon crystal and the aluminium crystal heterogeneously nucleated on the silicon surface in hypereutectic Al-Si alloys, were studied by the micro-focus X-ray diffraction analysis. The apparently random orientation relationships obtained by X-ray analysis have been classified into simple relationships by taking the twinning in the primary silicon crystals into consideration. The epitaxial relationships between silicon and aluminium crystals in untreated alloys, and that in sodium-treated alloys, are found to be distinctly different.     

Phase studies in the system mercury selenide - manganese selenide

HgSe forms solid solutions with MnSe while retaining the sphalerite structure. The solubility limit as determined from lattice constant measurements is 38.5 mol % MnSe at 700°C. No detectable solubility of HgSe in rocksalt type MnSe could be observed. The phase relationships within the region of HgSe solid solution are given based on DTA and X-ray diffraction.     

High-pressure phase diagram of an aluminium-rich Al-Li alloy at a pressure of 5.4 GPa

The high-pressure phase diagram of an aluminium-rich Al-Li alloy at a 5.4 GPa pressure was investigated. To determine the equilibrium state under high-pressure and high-temperature conditions, the quenching method was applied and a phase analysis of the sample was performed using X-ray diffraction and microscopic observations. The experimental results were then compared with a thermodynamic theoretical calculation and good agreement was found. The resultant solid solubility of lithium in aluminium was subsequently increased up to 20 at % and the eutectic temperature increased up to 800 °C.     

Effect of iron on the solubility of hydrogen in tantalum

Pressure-composition-isotherms for Ta–Fe–H systems have been investigated in the temperature range 673–873 K. Tantalum–iron alloys (Ta–xFe, x = 0, 1.6 and 3.2 atom  % Fe) were prepared by arc melting using high purity elements. The equilibrium solid solubility of hydrogen in the alloys decreases with an increase of iron content. Thermodynamic parameters of the solution process—the Gibb’s free energy, enthalpy, and entropy, for each of the solutions have been calculated. The relative partial molar enthalpy becomes less negative with increase in iron content, whereas the entropy values are nearly constant for these alloys. The solubility changes were explained on the basis of change in lattice strain energy of tantalum due to iron addition.     

Microstructural transitions in an RS Al-4La alloy

The use of rapid solidification (RS) techniques to increase the thermal stability of aluminium and aluminium alloys is considered a promising processing route. The Al-La equilibrium binary system tends to form a high melting temperature intermetallic compound on the aluminium rich side. The limited solid solubility of solute, high solubility in the liquid and the relatively low solid state diffusivity, in general, of rare earth (RE) elements in aluminium suggests this system (as well as other Al-RE systems) as a suitable lightweight, dispersion-strengthened alloy candidate for elevated homological temperature applications. RS processing promotes the formation of a relatively finer microstructure in an Al-4La alloy, as well as the formation of a finely dispersed metastable phase. This metastable phase, is fairly stable up to 400° C. Lanthanum concentration in the ribbon bulk matrix, is considerably increased via RS process ing, and the formation of a heavy eutectic is suppressed.     

Splat cooling of aluminium-manganese alloys

The gun technique of splat cooling is utilized to extend the solid solubility of manganese in aluminium by a factor of four above that at the eutectic temperature. The supersaturated solid solutions can be retained up to 250° C without any significant decomposition. Isochronal and isothermal studies of the variation of the lattice parameter of the 6.4 wt % manganese solid solution yield a value for the activation energy of 30 kcal mol^?1 which is considerably higher than that for the splat cooled aluminium-silicon alloys. The decomposition of the supersaturated solid solution leads to the precipitation of the equilibrium Al₆Mn phase.     

Alloy formation in the Fe-Ni system during cold mechanical activation by pressure shear

Binary alloys of the Fe-Ni system were used to study the regularities involved in the cold mechanical synthesis realized by pressure shear in Bridgman anvils. The alloy formation was found to depend on the crystal lattice symmetry: the solid solution is formed in mixtures of components having a similar symmetry of the crystal lattice but the alloy formation is retarded or does not occur altogether in mixtures of components having different symmetries of the crystal lattice. The kinetics of the alloy formation in mixtures of Fe-Ni solid solutions with a FCC lattice was determined. The phase transformations were found to affect the kinetics and the alloy formation mechanism in mixtures whose components are pressure- and strain-unstable.     

Evolution of microstructures and phases of Al–Mg alloy under 4 GPa high pressure

Optical microscope (OM), energy dispersive X-ray (EDX) analysis, differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscope (TEM) were applied to investigate the solidification microstructures and phases of Al–9.6 wt.% Mg alloy which solidified under 4 GPa high pressure with the melting temperature 1,153 K. Fine dendritic microstructures were obtained, and the second dendritic arm spacing reduced. Area fraction of the primary α-Al phase increased and that of the second phase decreased. In addition, the solid solubility of Mg in α-Al phase increased. The lattice constant of α-Al phase increased. Specially, the new double phase regions (α-Al′ + Al _x Mg _y ) formed besides a small amount of Al₃Mg₂ phases under high pressure. The Al _x Mg _y phase presented a mean size of about 20 nm, and had the hexagonal structure with the lattice constant of a = 0.288 nm, c = 0.8165 nm probably. Wherein the lattice constant of α-Al′ phase differed from that of α-Al phase greatly. Moreover, evolution mechanism of microstructures and phases under 4 GPa high pressure was discussed.