Intermetallic compound layer growth at the interface of solid refractory metals molybdenum and niobium with molten aluminum

The growth mechanisms and growth kinetics of intermetallic phases formed between the solid refractory metals Mo and Nb and molten aluminum have been studied for contact times ranging from 1 to 180 minutes at various temperatures in the range from 700 to 1100°C. The growth of the layers of the resulting intermetallic phases has been investigated under static conditions in a saturated melt and under dynamic conditions using forced convection in unsatured aluminum melts. The Nb/Al interfacial microstructure consisted of a single intermetallic phase layer, Al₃Nb, whereas two to four different phase layers were observed in the Mo/Al interface region, depending upon the operating temperature. It was found that, in a satured melt, the intermetallic phase growth process was diffusion-controlled. The parabolic growth constants of the first and second kind and integral values of the chemical diffusion coefficients over the widths of the phases were calculated for both Mo/Al and Nb/Al systems. It also was found that the AlNb₂ phase grew between the Nb and Al₃Nb phases after consumption of the saturated Al phase. Similarly, the AlMo₃ phase grew between the Mo and Al₈Mo₃ phases with diminishing of all the other existing compound phases. In an unsaturated melt, the intermetallic phase layer grows at the solid surface while, simultaneously, dissolution occurs at the solid/liquid interface. This behavior is compared to the growth mechanisms proposed in existing theories, taking into consideration that interaction occurs between neighboring phases. It was found that the intermetallic phase, Al₈Mo₃, adjoining the base metal, was not bonded strongly to the base metal Mo and was brittle; its hardness also was larger than that of the layer near the adhering aluminum and the adjacent phases.     

Structural Changes of High-Temperature Nickel Alloy Containing Rhenium and Lanthanum on Heat Treatment

The properties of high-temperature nickel alloys for manufacturing depend on the thermal stability of the structure, the particle size, the shape, the quantity of strengthening γ' phase, and the strength of the γ solid solution. Such alloys are strengthened by the addition of rhenium and lanthanum. In the present work, the structure and phase composition of high-temperature nickel alloy with added rhenium (0.4 at %) and lanthanum (0.006 at %) are qualitatively and quantitatively investigated. The methods employed are transmission diffraction electron microscopy and scanning electron microscopy. The alloy structure is considered in three states: after directed crystallization (the initial state, sample 1); after directed crystallization, annealing at 1150°C for 1 h, and annealing at 1100°C for 480 h (sample 2); and after directed crystallization, annealing at 1150°C for 1 h, and annealing at 1100°C for 1430 h (sample 3). Primary and secondary phases are observed in the superalloy. The primary phases are γ' and γ. They form the structure of the alloy and are present in the form of γ' quasi-cuboids separated by γ layers. The secondary phases due to the presence of rhenium and lanthanum are β NiAl, AlRe, NiAl₂Re, σ, χ, and Ni₃La₂. The secondary phases seriously disrupt the structure of the γ + γ' quasi-cuboids. The rhenium and lanthanum do not uniformly fill the whole alloy volume, but only appear in local sections. Therefore, in all three states of the alloy, only some volume of γ + γ' quasicuboids is disrupted. Analysis of the secondary phases’ morphology shows that the σ particles are thin needles, whereas the Ni₃La₂ particles have internal structure with characteristic contrast and are relatively thick. Interestingly, the σ phase and Ni₃La₂ are deposited at the same locations. The introduction of rhenium and lanthanum changes the phase composition of the alloy, suppressing the formation of γ phase. The particles of secondary phase are localized in individual sections of the alloy with specific periodicity. The secondary phases are refractory: the melting point is about 1600°C for β phase, 2600°C for σ phase; and 2800° for χ phase. Thanks to the formation of refractory secondary phases and their periodic distribution in the structure, the strength of the superalloy with added rhenium and lanthanum is increased.     

Combined Effect of Calcium and Silicon on the Phase Composition and Structure of Al–10%Mg Alloy

Phase transformations in the Al–Ca–Mg–Si system in the region of aluminum–magnesium alloys are investigated using the Thermo-Calc program. The liquidus projection of the quaternary system is constructed with a Mg content of 10% and it is shown that phases Al4Ca, Mg₂Si, and Al₂CaSi₂ can crystallize (in addition to the aluminum solid solution (Al)) depending on the calcium and silicon concentrations. The crystallization character of quaternary alloys is investigated with the help of a polythermal cross section calculated at concentrations of 10% Mg and 84% Al. Based on the analysis of phase transformations occurring in alloys of this section, the presence of the Al–Al₂CaSi₂–Mg₂Si quasi-ternary section in the Al–Ca–Mg–Si system was assumed. Three experimental alloys were considered from a quantitative analysis of the phase composition, notably, Al–10% Ca–10% Mg–2% Si, Al–4% Ca–10% Mg–2% Si, and Al–3% Ca–10% Mg–1% Si. Metallographic investigations and electron-probe microanalysis were performed using a TESCAN Vega 3 scanning electron microscope. Critical temperatures are determined using a DSC Setaram Setsys Evolution differential calorimeter. The experimental results agree well with the calculated data; in particular, a peak at t ~ 450°C is revealed for all alloys in curves of the nonequilibrium solidus and invariant eutectic reaction L → (Al) + Al₄Ca + Mg₂Si + Al₃Mg₂. It is established that the structure of the Al–3% Ca–10% Mg–1% Si alloy is closest to the eutectic alloy. It is no worse that the AMg10 alloy in regards to density and corrosion resistance and even surpasses it in hardness, which allows us to consider this alloy as the basis for the development of a new cast material: “natural composites.”     

Influence of a Silicon Additive on Resistivity and Hardness of the Al–1% Fe–0.3% Zr Alloy

Isothermal sections of the diagram of the Al–Fe–Si–Zr alloy at temperatures of 450 and 600°C, as well as polythermal sections at concentrations of silicon up to 2 wt % and zirconium up to 1 wt %, are analyzed using computational methods with the help of Thermo-Calc software. It is shown that the favorable phase composition consisting of the aluminum solid solution (Al), the Al₈Fe₂Si phase, and Zr (which completely enters the composition of the solid solution (Al) during the formation of the cast billet) can be attained in equilibrium conditions at silicon concentrations of 0.27–0.47 wt %. To implement the above-listed structural components in nonequilibrium conditions and ensure that Zr enters the (Al) composition, experimental ingots were fabricated at an elevated cooling rate (higher than 10 K/s). A metallographic analysis of the cast structure of experimental samples revealed the desired structure with contents of 0.25 wt % Si and 0.3 wt % Zr in the alloy. The microstructure of the Al–1% Fe–0.3% Zr–0.5% Si alloy also contains the eutectic (Al) + Al₈Fe₂Si; however, the Al₈Fe₂Si phase partially transforms into Al₃Fe. The structure of the alloy with 0.25 wt % Si in the annealing state at 600°C contains fragmented particles of the degenerate eutectic (Al) + Al₈Fe₂Si along the boundaries of dendritic cells. It is established that the Si: Fe = 1: 2 ratio in the alloy positively affects its mechanical properties, especially hardness, without substantially lowering the specific conductivity during annealing, which is explained by the formation of the particles of the Al₈Fe₂Si phase of the compact morphology in the structure. Moreover, silicon accelerates the decay of the solid solution by zirconium, which is evidenced by the experimental plots of the dependence of hardness and resistivity on the annealing step. The best complex of properties was shown by the Al–1% Fe–0.3% Zr–0.25% Si alloy in the annealing stage at 450°C with the help of the optimization function at specified values of hardness and resistivity.     

Crystallization study of the melt spun Al70Fe13Si17 glass

The crystallization of a melt spun amorphous Al based alloy (Al₇₀Fe₁₃Si₁₇) has been studied by various techniques. In situ Transmission Electon Microscopy (TEM) combined with Scanning Transmission Electron Microscope microanalysis (STEM) and high resolution TEM provide most of the information on the crystallization sequences, while their representativity and kinetics are controlled and precised by “bulk” techniques [Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC) and Small Angle X-ray Scattering (SAXS)]. The crystallization occurs in two steps: it first appears a very small volume fraction of tiny Al particles (less than 2%) before the complete crystallization of the metallic glass in two intermetallic compounds (called β and τ₄). Both phases β and τ₄ are in epitaxy and form a multisliced sandwich. On about 0.25 nm² surface microanalyses, the global composition of β + τ₄ containing Al particles corresponds to the initial glass composition. By in situ annealing of electropolished Al₇₀Fe₁₃Si₁₇ amorphous samples, another crystallization occurs just within the thin parts of samples: a phase called α or τ₅ surrounded by aluminium. Such transformation can be considered as an artefact; nevertheless its study related to crystallographic studies has represented the basis of another work aimed to a structural modelling of the AlMn and AlFe quasicristalline phases.     

Influence of small additives of calcium on the structure and properties of ML5 alloy (AZ91)

The influence of the calcium additive (from 0.1 to 1.0 wt %) on the phase composition and solidus temperature of ML5 magnesium alloy is investigated. Calcium transfers into the intermetallic compound of the variable composition during alloy crystallization. This compound contains Al (53.4–57.4%), Ca (42.6–42.8%), and Mg (0.002–3.8%) and is transformed with a decrease in temperature into the Al₂Ca compound. The influence of calcium on the amount of phases Mg₁₇Al₁₂ and Al₂Ca and its distribution in the casting and thermally treated ML5 alloy structures are investigated. It is revealed with the help of the electron probe microanalysis that calcium and aluminum are concentrated along the boundaries of the magnesium solid solution. It is shown that, in order to acquire satisfactory mechanical properties and pouring of calcium-containing magnesium alloys should be performed according to the production process preventing the contamination of metal of the coarse inclusions. It is established that small additives of calcium (up to 1 wt %) increase the ignition temperature and lower the alloy oxidability at elevated temperatures (up to 715°C). The influence of the sulfur hexafluoride (SF6) for the calcium loss during flux-free melting was established.     

Microstructure of a complex Nb–Si-based alloy and its behavior during high-temperature oxidation

A in-situ composite Nb–Si–Ti–Hf–Cr–Mo–Al composite material alloyed with yttrium and zirconium is studied. The evolution of the structure–phase state of the alloy during oxidation under dynamic and isothermal conditions is considered on samples prepared by vacuum remelting and directional solidification. The phase composition and the microstructure of the alloy are examined by the methods of physico-chemical analysis, and the distribution of alloying elements in initial samples and the products of oxidation is estimated. Thermogravimetric experiments are performed on powders and compacted samples during continuous (in the range 25–1400°C) and isothermal (at 900 and 1100°C) heating in air. The directional solidification of an Nb–Si–Ti–Al–Hf–Cr–Mo–Zr–Y is found to cause the formation of an ultradispersed eutectic consisting of α-Nb_ss and γ-Nb₅Si_3ss cells. The as-cast sample prepared by vacuum remelting has a dendritic structure and contains Nb₃Si apart from these phases. Oxidation leads to the formation of a double oxide layer and an inner oxidation zone, which retain the two-phase microstructure and the ratio of alloying elements that are characteristic of the initial alloy. Diffusion redistribution is only detected for molybdenum. The cyclicity of heating at the initial stage of oxidation weakly influences the oxidation resistance of the alloy.     

Construction of Phase Diagrams for Al<Subscript>x</Subscript>HfNbTaTiZr Refractory High Entropy Alloy

This work involves construction of phase diagrams of Al_xHfNbTaTiZr refractory high entropy alloy (RHEA) with an objective to understand the phase stability of the alloy at different concentrations of Al, which is expected to stabilize the body-centred cubic (BCC) structure. The constructed hexanal phase diagrams of Al_xHfNbTaTiZr RHEA shows that continuous BCC solid solution forms up to 1.5 mol of initial concentration of Al and any further increase in the Al concentration results in the formation of intermetallic phases. Further, the phase stability of Al_xHfNbTaTiZr RHEA as a function of Al concentration has been discussed in correlation with the concerned Valence Electron Concentration parameter.     

High-rate sputter deposition and heat treatment of thick Nb-Al-Ge and Nb-Al superconductors

Crystal structures, microstructures and critical temperatures were determined for Nb-Al-Ge and Nb-Al sputter-deposits in order to evaluate their dependence on sputter-deposition conditions, heat treatment procedures and composition. High-rate sputter deposition techniques were used to make the deposits at rates up to 1 Μm/min. Compositions studied were Nb₃(Al_0.6Ge_0.4), Nb₃(Al_0.75Ge_0.25), Nb₃Al, Nb_2.52(Al_0.84)Ge_0.16), Nb_2.33Al, Nb_3.07(Al_0.75Ge_0.25), and Nb_4.15(Al_0.71Ge_0.29). The investigation indicated it is feasible to make practical A-15 phase superconductors by high-rate sputter deposition. Of all the deposits studied, Nb₃(Al_0.75Ge_0.25),i.e., Nb₂Al₃Ge, deposited at 15°C and heat treated at 750°C for 1 to 5 days had the highest critical temperature (18.5 K), and it had a very high critical current density;e.g., 4.4 × 10⁵ A/cm² at 100 kOe and 4.2 K. Deposits having the highest critical temperatures consisted only of undecomposed metastable A-15 phase. The high current density was attributed to the presence of very small A-15 phase grains, which were observed to be about 350å in diameter by transmission electron microscopy. The crystal structures for deposits made at 15°C were not always clearly defined, but probably were all body-centered-cubic. Body-centered-cubic phases were transformed by heat treatment for short times at 550°C to 850°C to an A-15 phase that was supersaturated with Al and Ge. If heat treatment temperatures were too high or heat treatment times were too long, however, minor phases formed as the A-15 phase decomposed. Nb₃(Al_0.75Ge_0.25) deposits made at elevated temperatures (485°C and 750°C) predominantly consisted of the A-15 phase, but the presence of minor phases even before heat treatment indicated Al and Ge were not completely retained in the A-15 phase solid solution during deposition. Deposits made with-20 V substrate-anode bias had nearly the same composition as the sputtering target, but deposits made with -50 V and -75 V bias had significantly lower Al and Ge contents than the target. The compactness of the A-15 crystal structure relative to the bcc structure was noted in a comparison of average atomic volumes for the two structures in Nb₃Al. The average atomic volume in the A-15 phase formed by heat treatment was 1.36 pct less than the average atomic volume in the bcc phase that existed before heat treatment in sputter-deposited Nb₃Al made at 15°C.     

Role of Si on the Diffusional Interactions Between U-Mo and Al-Si Alloys at 823?K (550?��C)

U-Mo dispersions in Al-alloy matrix and monolithic fuels encased in Al-alloy are under development to fulfill the requirements for research and test reactors to use low-enriched molybdenum stabilized uranium alloy fuels. Significant interaction takes place between the U-Mo fuel and Al during manufacturing and in-reactor irradiation. The interaction products are Al-rich phases with physical and thermal characteristics that adversely affect fuel performance and result in premature failure. Detailed analysis of the interdiffusion and microstructural development of this system was carried through diffusion couples consisting of U-7 wt pct Mo, U-10 wt pct Mo and U-12 wt pct Mo in contact with pure Al, Al-2 wt pct Si, and Al-5 wt pct Si, annealed at 823 K (550 °C) for 1, 5 and 20 hours. Scanning electron microscopy and transmission electron microscopy were employed for the analysis. Diffusion couples consisting of U-Mo in contact with pure Al contained UAl₃, UAl₄, U₆Mo₄Al₄₃, and UMo₂Al₂₀ phases. Additions of Si to the Al significantly reduced the thickness of the interdiffusion zone. The interdiffusion zones developed Al- and Si-enriched regions, whose locations and size depended on the Si and Mo concentrations in the terminal alloys. In these couples, the (U,Mo)(Al,Si)₃ phase was observed throughout the interdiffusion zone, and the U₆Mo₄Al₄₃ and UMo₂Al₂₀ phases were observed only where the Si concentrations were low.     

Phase Constituents and Microstructure of Interaction Layer Formed in U-Mo Alloys <Emphasis Type="Italic">vs</Emphasis> Al Diffusion Couples Annealed at 873 K (600 °C)

U-Mo dispersion and monolithic fuels are being developed to fulfill the requirements for research reactors, under the Reduced Enrichment for Research and Test Reactors program. In dispersion fuels, particles of U-Mo alloys are embedded in the Al-alloy matrix, while in monolithic fuels, U-Mo monoliths are roll bonded to the Al-alloy matrix. In this study, interdiffusion and microstructural development in the solid-to-solid diffusion couples, namely, U-15.7 at. pct Mo (7 wt pct Mo) vs pure Al, U-21.6 at. pct Mo (10 wt pct Mo) vs pure Al, and U-25.3 at. pct Mo (12 wt pct Mo) vs pure Al, annealed at 873 K (600 °C) for 24 hours, were examined in detail. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron probe microanalysis (EPMA) were employed to examine the development of a very fine multiphase interaction layer with an approximately constant average composition of 80 at. pct Al. Extensive TEM was carried out to identify the constituent phases across the interaction layer based on selected area electron diffraction and convergent beam electron diffraction (CBED). The cubic-UAl₃, orthorhombic-UAl₄, hexagonal-U₆Mo₄Al₄₃, and cubic-UMo₂Al₂₀ phases were identified within the interaction layer that included two- and three-phase layers. Residual stress from large differences in molar volume, evidenced by vertical cracks within the interaction layer, high Al mobility, Mo supersaturation, and partitioning toward equilibrium in the interdiffusion zone were employed to describe the complex microstructure and phase constituents observed. A mechanism by compositional modification of the Al alloy is explored to mitigate the development of the U₆Mo₄Al₄₃ phase, which exhibits poor irradiation behavior that includes void formation and swelling.     

The AI-Ali8Mo3 section of the binary system aluminum-molybdenum

The constitution of the partial system Al-Al₈Mo₃ is investigated using differential thermal analysis (DTA) and X-ray diffraction data. Ten (10) intermetallic phases are observed, and their stability ranges with respect to composition as well as temperature are determined. The crystal structures of Al₁₂Mo, Al₅Mo(h), Al₄Mo(h), and Al₈Mo₃ are corroborated, confirming literature data. The crystal structures of the phases Al₅Mo(ht), Al₅Mo(r), Al_3+xMo_1-x(h), and Al₃Mo(h) are newly determined. For the phases “Al₂₂Mo₅” and “Al₁₇Mo₄,” powder diffraction patterns are obtained. The revised phase diagram Al-Mo (up to 28 at. pct Mo) is presented.     

Structural study of electrodeposited aluminum-manganese alloys

Aluminum-manganese alloys with compositions ranging between 0 and 27 wt pct Mn were electrodeposited at 150°C onto copper substrates from a chloroaluminate molten salt electrolyte with a controlled addition of MnCl₂. The specimens were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction. The addition of small amounts of Mn results in the formation of a supersaturated fcc solid solution of Mn in Al. At the higher Mn content, an amorphous phase is established. The highly faceted crystalline surface of pure Al and Al−Mn solid solution becomes smooth and nearly specular when the amorphous phase is present. The amorphous phase appears in the form of rounded grains and has a lower limit of Mn concentration close to the Al₆Mn composition. There is a concentration discontinuity between the above limit and the higher Mn concentration limit of the fcc phase (about 9 wt pct). Appearance of the amorphous phase in the alloy results in a decrease in the Mn concentration in solid solution to about 2 wt pct. Crystallization of the amorphous phase starts at the fcc-amorphous phase interface at 230°C. As a result of treatment at 230 °C to 340 °C, the amorphous phase completely transforms into Al₆Mn, while the fcc phase is unaffected. Prior to crystallization, the amorphous phase shows a modification that could be interpreted as the formation of a fine-grained icosahedral phase. The formation and distribution of phases by electrodeposition and rapid solidification are discussed.     

Microstructures of rapidly-solidified binary TiAl alloys

The microstructures of rapidly-solidified binary TiAl alloys containing 46–70 at.% Al have been studied using optical and analytical transmission electron microscopy (AEM). The phases present in the alloys and their distribution were found to be a sensitive function of composition. Essentially single-phase microstructures were seen for alloys with 46 at.% Al, 50–52 at.% Al and 60–65 at.% A. The primary solidification phases present in these alloys were α-Ti, ordered γ-TiAl and disordered cubic TiAl, respectively. The 60–65 at.% Al alloys showed indications of the solid-state formation of long-period superlattice structures based upon γ-TiAl, due to the excess Al. In other composition ranges, two-phase microstructures were seen. The 48 at.% Al alloy contained α₂-Ti₃Al + γ-TiAl, with α₂-Ti₃Al as the primary solidification phase. Alloys from 53 to 55 at.% Al were also α₂-Ti₃Al + γ-TiAl, but with γ-TiAl as the primary solidification phase. The 70 at.% Al alloy was two phase TiAl₂ + TiAl₃. A strong effect of interstitial oxygen content on the α₂-Ti₃Al + γ-TiAl phase relations was also seen. Comparison of these results with the equilibrium phase diagram and with ingot studies of the same alloys showed that most of the microstructures produced by rapid solidification were metastable. A possible metastable phase diagram for TiAl which is consistent with the results is proposed.     

Microstructural Aspects of Second Phases in As-cast and Homogenized 7055 Aluminum Alloy with Different Impurity Contents

The microstructural factors such as type, area fraction, morphology, distribution, and size of second phases in as-cast and homogenized 7055 aluminum alloy and the influence of impurity content variations have been investigated by using optical microscope (OM), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDS), and X-ray diffraction (XRD). In as-cast microstructures, the dominant second phases of η [Mg(Al, Cu, Zn)₂] with extended solubility of Cu and Al, a small amount of impurity phases of Al₇Cu₂Fe and Al₃Fe with a little solubility of Cu and Si, and trace Mg₂Si are identified. The variations of Fe and Si contents have no significant influence on the area fraction of η phases, but the area fraction of Fe-rich phase decreases from 0.231 to 0.102 pct with Fe content decreasing from 0.080 to 0.038 wt pct. Decreasing Fe contents reduces the size parameters of Fe-rich phases and refines their morphology correspondingly. After being homogenized at 753 K (480 °C) for 24 hours, η phases are largely dissolved, but the coarse impurity phases are insoluble. Compared with as-cast microstructures, the area fraction and composition of Fe-rich phases change a little but their morphologies are slightly coarsened.     

Stable and metastable phase equilibria in the Al-Mn system

The aim of the present investigation was resolution of certain obscure features of the Al-Mn phase diagram. The experimental approach was guided by assessment of the previous literature and modeling of the thermodynamics of the system. It has been shown that two phases of approximate stoichiometry “Al₄Mn” (λ and μ) are present in stable equilibrium, λ forming by a peritectoid reaction at 693 ± 2 °C. The liquidus and stable equilibrium invariant reactions as proposed by Goedecke and Koester have been verified. A map has been made of the successive nonequilibrium phase transformations of as-splat-quenched alloys. Finally, the thermodynamic calculation of the phase diagram allows interpretation of complex reaction sequences during cooling in terms of a catalogue of all the metastable invariant reactions involving (Al), Al₆Mn, λ, μ, ?, and Al₁₁Mn₄ phases.     

Metastable crystalline and amorphous structures formed in the Cu-W system by vapor deposition

The possibility of producing nonequilibrium amorphous and crystalline phases in the Cu-W system is of interest because, under equilibrium conditions, no mutual solubility is expected between Cu and W. Triode sputtered coatings (45 to 150 μm thick, produced at deposition rates between 20 and 150 Å/s) consisted of amorphous and metastable crystalline phases. The latter remained decomposition-resistant on heating to various temperatures between 340 °C and 600 °C (the maximum temperature of exposure). The amorphous phase in such coatings crystallized on heating into a metastable body-centered cubic (bcc) phase, and the crystallization temperatureT _x was found to decrease across the phase diagram from 450 °C to 340 °C as the percentage of W increased from 26 to 60 at. pct. Samples containing amorphous phase regions, when subjected to heating between 150 °C and 250 °C, showed an unusual rapid precipitation of Cu at the sample surface, indicating an easy diffusion of the Cu component. This occurred without crystallization of the remaining slightly tungsten-enriched amorphous matrix. Microhardness measurements in sputtered two-phase amorphous and bcc regions have shown that in alloys of the same composition, the amorphous phase was always softer than the bcc solid solution phase. X-ray, microprobe, and optical evidence suggests that the amorphous films deposited at very low temperatures(i.e., at liquid N₂) may subsequently undergo a phase separation upon heating to room temperature and prior to crystallization. Earlier work and present studies of vapordeposited alloys in this system confirm that the observed phases and microstructures can be related to free energy trends estimated from thermodynamic considerations and to specific deposition parameters, such as the substrate temperature and the deposition rates, which influence the kinetics.     

Etude par analyse en profondeur de l'interdiffusion en couches minces du couple AlCu: Cinetique de croissance des phases entre 200 et 300

This paper deals with thin layers interdiffusion of AlCu at annealing temperatures in the range of 200–300°C. The use of a method for depth analysis based upon the thermal ionization of sputtered material allows one to determine the composition of phases from the very beginning of their formation. Departure from stoichometry of about 1 % are measured for most observed phases. Comparison with thermal equilibrium diagram known at 600°C confirms the existence of the γ phase and shows that the γ₂ phase is in fact a mixture of two compounds Cu₃₂Al₁₉ and Cu₉Al₄. The main results to be mentioned are large diffusion coefficients (~ 10⁻¹⁶cm²/s at 220°C) and the formation of well defined compounds, with no appreciable composition range, growing in successive strates parallel to the plan of the interface of diffusion.     

Effect of lead on the structure and phase composition of an Al–5% Si–4% Cu casting alloy

The phase transformations in the Al–Cu–Si–Pb system have been studied using calculations. It is shown that the aluminum-based solid solution is in equilibrium only with the Al₂Cu, (Si), and (Pb) phases, which correspond to the relevant binary systems. Reported polythermal and isothermal sections show that the Al–Cu–Si–Pb system is characterized by a significant liquid miscibility gap. The effect of lead on the structure and phase composition of an Al–5% Si–4% Cu alloy in the as-cast and annealed states is studied. Lead inclusions are located at the boundaries of dendritic (Al) cells and are globular in the as-cast alloy and after annealing at 500°C. The presence of lead phase does not affect the precipitation hardening upon quenching and aging.     

Excess aluminium effect on the composition and microstructure of Mo–Al alloys from aluminothermic reduction of MoO3

The effect of aluminium excess on the composition and microstructure of Mo–Al alloys from aluminothermic reduction of metallurgical-grade MoO₃ was investigated. Aluminium excess ranged from 0 to 30% (in wt-%) with respect to the stoichiometric amount. The results showed that molybdenum yield increases for higher excess aluminium. The microstructure and composition of the alloys were investigated using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD). The following phases were observed in the microstructures: Mo_ss, Mo₃Al, and Mo₃Al₈, besides particles of Al₂O₃. The results also showed that metallurgical-grade MoO₃ leads to a product containing significant amounts of silicon.