The effect of Cu on precipitation in Al–Mg–Si alloys

TEM investigations of two alloys isothermally heat treated at 175°C and 260°C show how Cu additions to the Al–Mg–Si system affect precipitation. Both alloys had a solute content Mg?+?Si?=?1.3 at.%, 0.127 at.% Cu, but with Mg/Si 0.8 and 1.25. Cu-containing Guinier-Preston (GP) zones and three types of Q′ precursors are identified as most common phases at peak-hardness conditions, whereas β″ accounts for maximum 30% of the total number of precipitates. The precursors have needle (L and S precipitates) or plate (C precipitate) morphologies. They consist of different arrangements of Al, Mg and Cu atoms on a grid defined by triangularly arranged Si planes parallel with and having the same period as {100} Al planes. The Si grid is composed of nearly hexagonal sub-cells of a?=?b?=?4.05?Å, c?=?4.05?Å. The Cu arrangement on the grid is often disordered in the needle precursors. The plate precursor is ordered, with a monoclinic unit cell of a?=?10.32?Å, b?=?8.1?Å, c?=?4.05?Å, γ?=?101°.     

Effects of minor additions of Mg and Ag on precipitation phenomena in Al–4 mass% Cu

Calorimetric measurements and transmission electron microscopy have been used to study the effects of minor additions of Mg and Ag on mechanism and kinetics of precipitation in Al–4 mass% Cu. Isothermal studies at 30°C show that the rate of Guinier–Preston (Cu) zone formation is progressively reduced by the presence of Mg, or Mg?+?Ag, which is attributed to preferential trapping of vacancies so that their ability to assist diffusion of Cu atoms is reduced. At elevated temperatures, Mg enhances precipitation of θ′, whereas Mg?+?Ag stimulates formation of the Ω phase. Precipitation of S′ follows θ′ if Mg or Mg?+?Ag are present and pre-ageing increases the quantity of θ′ precipitated at the expense of S′. It has been confirmed that secondary precipitation occurs at low temperatures if alloys are first aged at elevated temperatures.     

Adsorption-desorption properties and surface structural chemistry of chlorine on Cu(111) and Ag(111)

The adsorption, desorption, and structural properties of chlorine adlayers on Cu(111) and Ag(111) have been studied by LEED, Auger, Δ?, and thermal desorption measurements. Ancillary experiments were also carried out on cuprous chloride for purposes of comparison with the Cu(111)-Cl data. Chlorine adsorption is rapid on both metals and follows precursor kinetics, the absolute initial sticking probabilities being ~1.0 (Cu) and ~0.5 (Ag). Δ? results suggest that significant depolarisation of the chemisorption bond occurs at high coverages, the maximum values being + 1.2 eV (Cu) and + 1.8 eV (Ag). On Cu(111), adsorption leads to the formation of a sequence of well-ordered phases; in order of increasing coverage, these are as follows: (√3 × √3)R30°, (12√3 × 12√3)R30°, (4√7 × 4√7)R19.2°, and (6√3 × 6√3)R30°. On Ag(111) (√3 × √3)R30°, and (10 × 10) structures are observed. All six structures are susceptible to a straightforward interpretation in terms of coincidence lattices resulting from the progressive uniform compression of a hexagonal layer of Cl atoms. This interpretation is consistent with all the experimental results, and gives values for the nearest-neighbour ClCl spacing on both Cu(111) and Ag(111) which are in good agreement with other work on other surfaces. Chlorine desorbs exclusively as atoms from both metals with first-order desorption kinetics, and apparent desorption energies of 236 (Cu) and 209 (Ag) kJ mol^?1. These values, which depend on an assumed pre-exponential factor of 10¹³ s^?1, are shown to be inconsistent with the thermochemical constraints on the system necessitated by the complete absence of Cl₂ desorption. Lower limits for the pre-exponential factors are then deduced, and the values are found to be consistent with the differences between the CuCl and AgCl systems.     

63Cu NMR analysis of microstructure evolution in Al–Cu–Mg alloys

⁶³Cu NMR spectroscopy has been used to detect metastable Guinier–Preston–Bagaryatsky (GPB) zones and nanoscale precipitates of equilibrium S-phase (Al₂CuMg) in dilute alloys of aluminium containing copper and magnesium with compositions which lie in the α?+?S phase field. The GPB zones are observed to form rapidly at room temperature with a time development closely related to the Vickers hardness. The final development of S-phase in the alloy has been confirmed by the observation of a line shape in the alloy identical to that observed in a specimen prepared from stoichiometric Al₂CuMg. Analysis of the hyperfine structure of the ⁶³Cu line shape observed for S-phase shows clearly that two Cu sites are present with approximately equal population. This result suggests that possibly two crystallographically distinct Al₂CuMg phases are present. The addition of small amounts of silver to Al–Cu–Mg alloys in the α?+?θ phase field is known to induce the formation of Ω-phase: a slight distortion of tetragonal θ-phase Al₂Cu. A hyperfine-structured ⁶³Cu line shape assigned to Ω-phase, indicating one distinct Cu site, has been observed in two separate Al–1.7?at.%?Cu–0.33?at.%?Mg alloys containing 0.1 and 0.18?at.%?Ag, but not in the same Al–Cu–Mg alloy without Ag.     

The effect of Zn on precipitation in Al–Mg–Si alloys

Effects of addition of Zn (up to 1 wt%) on microstructure, precipitate structure and intergranular corrosion (IGC) in an Al–Mg–Si alloys were investigated. During ageing at 185?°C, the alloys showed modest increases in hardness as function of Zn content, corresponding to increased number densities of needle-shaped precipitates in the Al–Mg–Si alloy system. No precipitates of the Al–Zn–Mg alloy system were found. Using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), the Zn atoms were incorporated in the precipitate structures at different atomic sites with various atomic column occupancies. Zn atoms segregated along grain boundaries, forming continuous film. It correlates to high IGC susceptibility when Zn concentration is ~1wt% and the materials in peak-aged condition.     

Synthesis and characterization of nanocrystalline MgAl2O4 spinel by polymerized complex method

Ultrafine MgAl₂O₄ powder has been synthesized by a polymerized complex method. Heating of a precursor solution containing citric acid (CA), ethylene glycol (EG) and Mg and Al salts with a molar ratio of Mg/Al/CA/EG=1/2/8/32 at 180°C produced a transparent polymeric gel, which have been characterized by FT-IR spectroscopy and TG/DTA. The organic fraction was removed by controlled thermal treatments (350–1200°C) whereby the bimetallic oxide was formed. XRD analysis showed the presence of MgAl₂O₄ at 600°C. TEM observation showed that the spherical nanosized powders with good uniformity was obtained. Furthermore, these powders showed excellent sinterability, relative density up to 99.8% was achieved when sintered at 1550°C for 3 h in air without any sintering additive.     

Atomic Diffusion in Cu/Si （111） and Cu/SiO2/Si （111） Systems by Neutral Cluster Beam Deposition

The Cu films are deposited on two kinds of p-type Si （111） substrates by ionized duster beam （ICB） technique. The interface reaction and atomic diffusion of Cu/Si （111） and Cu/SiO2/Si （111） systems are studied at different annealing temperatures by x-ray diffraction （XRD） and Rutherford backscattering spectrometry （RBS）. Some significant results are obtained： For the Cu/Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃ and 500℃ are 8.5 ×10^-15 cm^2.s^-1 and 3.0 ×10^-14 cm^2.s^-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2//Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 ×10^-16 cm^2.s^-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.     

Effect of heat treatment on the mechanical and microstructural characterization of Mg-AZ91E/TiC composites

Mg-AZ91E/TiC_p composite was fabricated using a spontaneous infiltration technique at 950 °C under an argon atmosphere. The composites produced have 37 vol.% of metal matrix and 63 vol.% of TiC-like reinforcement. The obtained composites were subsequently solution heat-treated at 413 °C during 24 h, cold water quenched, and subsequently artificially aged at 168 and 216 °C during 16 h in an argon atmosphere. Effect of heat treatment on the microstructure and mechanical properties was evaluated. Microstructural characterization was analyzed using different techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). Interface between matrix and reinforcement was examined using transmission electron microscopy (TEM), and mechanical properties were evaluated by measuring the elastic modulus and hardness. Mg, TiC, Al, and Mg₁₇Al₁₂ phases through XRD were detected. Meanwhile, using TEM analysis in heat-treated composites MgAl₂O₄, MgO, and Al₂O₃ were identified. The as-fabricated composite have elastic modulus and hardness of 162 GPa and 316 Hv, respectively. After solution heat treatment and aging at 168 °C during 12 h, the composites reaches values of 178 GPa and 362 Hv for the elastic modulus and hardness, respectively. Time of aging was correlated with measures of elastic modulus and hardness.     

Study of solid-solution hardening in binary aluminium-based alloys

Solid-solution formation in binary aluminium-based alloys is due essentially to the combined effects of the size and valence of solvent and solute atoms, as expected by the four Hume-Rothery rules. The lattice parameter of aluminium in the solid solution of the sputtered Al?Fe films is [Al-a (Å)=4.052?6.6×10^?3Y]. The increasing and decreasing evolution of the lattice parameter of copper [Cu-a (Å)=3.612+1.8×10^?3Z] and aluminium [Al-a (Å)=4.048?1.6×10^?3X] in the sputtered Al-1.8 to 92.5 at. % Cu films is a result of the difference in size between the aluminium and copper atoms. The low solubility of copper in aluminium (<1.8 at % Cu) is due to the valences of solvent and solute atoms in contrast with other sputtered films prepared under similar conditions, such as Al?Mg (20 at. % Mg), Al?Ti (27 at. % Ti), Al?Cr (5at. % Cr) and Al?Fe (5.5 at. % Fe) where the solubility is due to the difference in size.     

Characterization of EUV periodic multilayers

Nanometric Co/Mg, Co/Mg/B₄C, Al/SiC and Al/Mo/SiC periodic multilayers deposited by magnetron sputtering are studied in order to correlate their optical performances in the extreme ultraviolet (EUV) range to their structural quality. To that purpose, our recently developed methodology based on high‐resolution X‐ray emission spectroscopy (XES) and X‐ray and EUV reflectometry is now extended to nuclear magnetic resonance (NMR) spectroscopy and time‐of‐flight secondary ions mass spectrometry (ToF‐SIMS). The analysis of the Co Lαβ and Mg Kβ emission spectra shows that the Co and Mg atoms within the multilayers are in a chemical state equivalent to that of the atoms in the pure Co and Mg references, respectively. But NMR spectra give evidence for a reaction between Co atoms and B and/or C atoms from B₄C. The Al and Si Kβ emission spectra do not reveal the formation of an interfacial compound in Al/SiC and Al/Mo/SiC. Only the roughness limits the optical quality of Al/SiC. The comparative analysis of the ToF‐SIMS spectra of Al/SiC and Al/Mo/SiC indicates that the structural quality is enhanced when Mo is introduced within the stack. Copyright © 2011 John Wiley & Sons, Ltd.     

Growth and characterisation of single grain Al-Cu-Ru icosahedral quasicrystals from self-fluxes

ABSTRACT

In order to obtain high-quality single grains of the Al-Cu-Ru icosahedral quasicrystal (iQC), suitable for a structure analysis, the crystal growth conditions with the self-flux method have been studied. The melts of the master alloys with the compositions of Al_57.0+xCu_39.5-xRu_3.5 (x?=?0, 2.5, 5, 7.5, 10) and Al_62.0Cu_34.0+y Ru_4.0-y (y?=?0, 0.5, 1.5) were held at 1150°C for 2?h, then cooled down to 800, 900, or 1000°C at a rate of ?2?K/h, and subsequently retained for various durations, up to 750?h. Single grain iQCs having several millimetre-sizes, which were evaluated their quality by powder X-ray diffraction (XRD), were grown throughout this study. The peak of (664004) reflection in powder XRD of the iQCs grown at 1000°C has approximately 50% narrower width than that grown at 800°C. The inhomogeneity of the compositions intra- as well as inter-grains grown at 800°C was observed. High-quality single grains with homogeneous composition could be achieved with a long-time annealing at 900°C or regardless of the annealing time at 1000°C. By changing the Al/Cu ratio of the master alloys, the composition could also be controlled for the iQCs grown at 1000°C. Single-crystal XRD experiment with synchrotron radiation on Al_66.6Cu_16.4Ru_17.0 iQC, grown at 1000°C, resulted in the collection of 2680 independent Bragg reflections that confirms the high-quality of the sample. The phase retrieval of the diffraction data resulted successfully in obtaining the structure solution, which reveals some characteristic features of this face-centred iQC structure.     

合金元素对Ag/Al界面性质影响的第一性原理研究

采用基于密度泛函理论的第一性原理方法,计算和分析Ag(111)/Al(111)界面体系的能量与电子结构,讨论Ag中加入的Be、Mg、Al、Ca、Ni、Sn合金化元素对Ag/Al界面性质的影响.结果表明:Ni原子倾向于界面处的取代位置,而Be、Mg原子倾向于靠近界面处的取代位置,Al、Ca、Sn原子倾向于远离界面处的取代位置;合金元素Be、Mg、Al、Ca、Ni、Sn的加入均会使Ag/Al界面的稳定性降低,其中Ca元素的影响程度最大,分离功降低到0.923 J/m~2,界面能增至0.703 J/m~2;通过电子结构计算结果分析认为,导致界面稳定性下降的主要原因应是合金化元素的加入使界面间形成的Ag-Al共价键强度降低引起.     

Leed,aes and photoemission measurements of epitaxially grown GaAs(001), (111)A and (1̄1̄1̄)B surfaces and their behaviour upon cs adsorption

Epitaxially grown GaAs(001), (111) and (1?1?1?) surfaces and their behaviour on Cs adsorption are studied by LEED, AES and photoemission. Upon heat treatment the clean GaAs(001) surface shows all the structures of the As-stabilized to the Ga-stabilized surface. By careful annealing it is also possible to obtain the As-stabilized surface from the Ga-stabilized surface, which must be due to the diffusion of As from the bulk to the surface. The As-stabilized surface can be recovered from the Ga-stabilized surface by treating the surface at 400°C in an AsH₃ atmosphere. The Cs coverage of all these surfaces is linear with the dosage and shows a sharp breakpoint at 5.3 × 10¹⁴ atoms cm^?2. The photoemission reaches a maximum precisely at the dosage of this break point for the GaAs(001) and GaAs(1?1?1?) surface, whereas for the GaAs(111) surface the maximum in the photoemission is reached at a higher dosage of 6.5 × 10¹⁴ atoms cm^?2. The maximum photoemission from all surfaces is in the order of 50μA Im^?1 for white light (T = 2850 K). LEED measurements show that Cs adsorbs as an amorphous layer on these surfaces at room temperature. Heat treatment of the Cs-activated GaAs (001) surface shows a stability region of 4.7 × 10¹⁴ atoms cm^?2 at 260dgC and one of 2.7 × 10¹⁴ atoms cm^?2 at 340°C without any ordering of the Cs atoms. Heat treatment of the Cs-activated GaAs(111) crystal shows a gradual desorption of Cs up to a coverage of 1 × 10¹⁴ atoms cm^?2, which is stable at 360°C and where LEED shows the formation of the GaAs(111) (√7 × √7)Cs structure. Heat treatment of the Cs-activated GaAs(1?1?1?) crystal shows a stability region at 260°C with a coverage of 3.8 × 10¹⁴ atoms cm^?2 with ordering of the Cs atoms in a GaAs(1?1?1?) (4 × 4)Cs structure and at 340°C a further stability region with a coverage of 1 × 10¹⁴ at cm^?2 with the formation of a GaAs(1?1?1?) (√21 × √21)Cs structure. Possible models of the GaAs(1?1?1?) (4 × 4)Cs, GaAs(1?1?1?)(√21 × √21)Cs and GaAs(111) (√7 × √7)Cs structures are given.     

Oxidation parameters determination of Cu–Al–Ni–Fe shape-memory alloy at high temperatures

In this study, isothermal oxidation behavior of a Cu–Al–Ni–Fe shape-memory alloy between 500 and 900 °C was investigated. Alloy samples were exposed to oxygen by TG/DTA for 1 h at a constant temperature, allowing for calculation of the oxidation constant and activation energy values of the oxidation process. The oxidation constant value increased with temperature, reaching saturation at 800 °C. The effect of oxidation on crystal structure, surface morphology and chemical composition of the Cu–Al–Ni–Fe alloy was determined by X-ray diffractometer (XRD) and scanning electron microscope (SEM)–energy-dispersive X-ray (EDX) analyses. With increasing oxidation temperature, number and intensity of the characteristic 18R martensite phase peaks were reduced while Al₂O₃ phase peaks were increased. In parallel to the XRD results, the same variations were also detected by SEM–EDX measurements.     

Mössbauer and XRD Comparative Study of Host Rock and Iron Rich Mineral Samples from Paz del Rio Iron Ore Mineral Mine in Colombia

The local environment of implanted ¹¹¹Ag (t _1/2 = 7.45 d) in single-crystalline [0001] ZnO was evaluated by means of the perturbed angular correlation (PAC) technique. Following the 60 keV low dose (1 × 10¹³ cm⁻²) ¹¹¹Ag implantation, the PAC measurements were performed for the as-implanted state and following 30 min air annealing steps, at temperatures ranging from 200 to 1050°C. The results revealed that 42% of the probes are located at defect-free S_Zn sites (ν _Q ∼ 32 MHz, η = 0) in the as-implanted state and that this fraction did not significantly change with annealing. Moreover, a progressive lattice recovery in the near vicinity of the probes was observed. Different EFGs assigned to point defects were furthermore measured and a general modification of their parameters occurred after 600°C. The 900°C annealing induced the loss of 30% of the ¹¹¹Ag atoms, 7% of which were located in regions of high defects concentration.     

Preparation of Cu–Ag core–shell particles with their anti-oxidation and antibacterial properties

Cu–Ag core–shell particles were fabricated from Cu particles and silver sulphate with the environmental-friendly TA (tartaric acid, C₄H₆O₆) as reducing and chelating agent in an aqueous system. The influences of [TA]/[Ag] and [Ag]/[Cu] molar ratios on the formation of Ag coatings on the Cu particles were investigated. The SEM images and SEM–EDS analyses showed that [TA]/[Ag] = 0.5 and [Ag]/[Cu] ≥0.2, the Cu particles were coated with uniform Ag nanoparticles. XRD analyses revealed that for these Cu–Ag particles heated at 250 °C, the oxidation of Cu was significantly reduced. Both anti-Staphylococcus aureus (Gram-positive) and anti-Escherichia coli (Gram-negative) characteristics of this Cu–Ag composite particles showed satisfactory antibacterial ability. The characteristics of the composite Cu–Ag particles were discussed in detail.     

The effects of a trace addition of silver upon elevated temperature ageing of an Al–Zn–Mg alloy

Microalloying additions of Ag (0.1 at.%) increase the hardening response of Al–Zn–Mg alloys to elevated temperature ageing in the range 100–200°C due to the formation of a high density of very fine η′ precipitate plates. The present study employed transmission electron microscopy (TEM) and three-dimension atom probe (3DAP) to study the early stages of ageing in the alloy Al–1.8Zn–3.4Mg–0.1Ag (at.%) in an attempt to identify the role of Ag in stimulating precipitation hardening. During isothermal ageing at 90°C, the hardening response is attributed to a high density of Zn–Mg–Ag rich solute clusters and GP zones. During ageing at 150°C, η′ precipitates nucleate at Zn–Mg–Ag rich solute clusters, the former growing as {111} platelets with an average composition of approximately 20 at.% Zn, 20 at.% Mg and 1.4 at.% Ag. The 3DAP data indicates that the co-segregation of Zn and Ag and subsequently Zn and Mg atoms precedes the formation of the Zn–Mg–Ag rich solute clusters. The GP zones and η′ precipitates were observed to possess a Zn:Mg ratio close to 1:1, whereas the equilibrium η precipitates possessed compositions consistent with MgZn₂. Furthermore, partitioning of Ag was observed inside all precipitate phases, viz. G.P. zones, η′ and η.     

Long-range chemical interactions in solid-state reactions: effect of an inert Ag interlayer on the formation of L10-FePd in epitaxial Pd(0 0 1)/Ag(0 0 1)/Fe(0 0 1) and Fe(0 0 1)/Ag(0 0 1)/Pd(0 0 1) trilayers

The effect of 0, 0.5, and 1?μm-thick Ag interlayers on the chemical interaction between Pd and Fe in epitaxial Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1)/MgO(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1)/MgO(0?0?1) trilayers has been studied using X-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy, and magnetic structural measurements. No mixing of Pd and Fe occurs via the chemically inert Ag layer at annealing temperatures up to 400?°C. As the annealing temperature is increased above 400?°C, a solid-state synthesis of an ordered L1₀-FePd phase begins in the Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1) film trilayers regardless of the thickness of the buffer Ag layer. In all samples, annealing above 500?°C leads to the formation of a disordered Fe_xPd_1?x(0?0?1) phase; however, in samples lacking the Ag layer, the synthesis of Fe_xPd_1?x is preceded by the formation of an ordered L1₂-FePd₃ phase. An analysis of the X-ray photoelectron spectroscopy results shows that Pd is the dominant moving species in the reaction between Pd and Fe. According to the preliminary results, the 2.2?μm-thick Ag film does not prevent the synthesis of the L1₀-FePd phase and only slightly increases the phase’s initiation temperature. Data showing the ultra-fast transport of Pd atoms via thick inert Ag layers are interpreted as direct evidence of the long-range character of the chemical interaction between Pd and Fe. Thus, in the reaction state, Pd and Fe interact chemically even though the distance between them is about 10⁴ times greater than an ordinary chemical bond length.     

LEED study of the epitaxial growth of the thin film Au(111)/Ag(111) system

An analysis of LEED data from the Ag(111) surface at room temperature and 5° ? Θ ? 16°, φ = 12° has been carried out in order to test three different model potentials for the exchange and correlation part of the one-electron LEED potential. Clean Au(111) surfaces have been grown on Ag(111) at room temperature at a deposition rate of 0.15 Å s^?1. Similar method of calculation and potentials have been employed for the Au overlay er on Ag(111). After the deposition of ? 2.5 monolayers of Au/Ag(111) the growth of Au can proceed in two different ways. One of them matches satisfactorily with the theoretical calculation for the Au(111) overlayer on Ag(111) following the fcc sequence. The other seems to be concerned with the diffusion of Ag during the Au growth. Similar curves have been obtained during the diffusion of Ag through 350 Å of Au(111).