Amorphous Aluminum Alloys Research Articles

Characterization and corrosion behavior of Al–Co–rare earth (Ce–La) amorphous alloy

A new Al-based amorphous alloy with excellent corrosion resistance and high thermal stability was produced in the Al–Co–RE (Ce–La) system. In this regard, two different amorphous-nanocrystalline ribbons: Al87.6–Co6.4–Ce3.8–La2.2 (M1) and Al82.3–Co10.1–Ce4.8–La2.8 (M2) were prepared using melt spinning. The results reveal the supercooled liquid region (ΔTx) of 218 °C which shows that the M2 alloy has higher thermal stability in comparison to the M1 alloy. The M2 ribbons present the superior corrosion resistance because of the formation of amorphous phase. The icorr, Ecorr, Epit, and Epit – Ecorr values of fully amorphous Al–Co–Ce–La metallic ribbons have a better trend of anti-corrosion performance compared to other crystalline and amorphous aluminum alloys.

Role of the Diffusion of Products of Redox Reactions in the Processes of Corrosion of Amorphous Aluminum Alloys

Role of the Diffusion of Products of Redox Reactions in the Processes of Corrosion of Amorphous Aluminum Alloys

Hardening of Al thin films by Ti[sbnd]C doping

Amorphous aluminum alloys have been evaluated as suitable thin films for protective coatings. Magnetron sputtering deposition may provide the necessary conditions for preparing such alloys due to its far-from-equilibrium deposition conditions. In this work, Al-Ti-C nanocomposite films were deposited by magnetron sputtering technique using TiC and Al targets. The produced films are mainly composed of Al nanocrystallites embedded into an amorphous matrix. Films effective hardness varied in the 6.4–8.2GPa range, while their elastic modulus ranged from 109 up to 134GPa. The higher the TiC/Al target power ratio, the harder the film. Topographic atomic force microscopy (AFM) images showed that films are mainly constituted by unevenly dispersed grains. Also, the dark phase angle fraction calculation derived from the phase angle contrast AFM images could be correlated with the deposited Al–Ti–C films hardness measured by nanoindentation tests; the higher the surface dark phase angle fraction, the harder the Al–Ti–C films.

Low friction mechanism of chlorine-doped amorphous carbon films sliding against an aluminium alloy

The effect of chlorine-doping on the tribological properties of amorphous carbon films was investigated. Chlorine-doped amorphous carbon films were deposited using a plasma-based ion implantation and deposition (PBII&D) method with vaporized tetrachloroethylene as a precursor. During sliding tests with aluminium alloy counter parts, chlorine-doped amorphous carbon films showed lower friction coefficients compared to hydrogenated amorphous carbon films. Both aluminium and a chlorine-based hydrate were observed on the wear track of the carbon films. This hydrate was a tribofilm formed via a tribochemical reaction during sliding between the chlorine-doped amorphous carbon films and aluminium alloy. The viscosity of this tribofilm was similar to polyalpha olefin and we propose that it acted as a lubricant and lowered the friction coefficient.

The effect of minor addition of insoluble elements on transformation kinetics in amorphous Al alloys

Nanocrystalline metallic materials based on partial devitrification of amorphous aluminum alloys show an attractive combination of high strength and low density. A key feature concerning the improved mechanical properties is the high number density of Al nanocrystals (1022–1023m−3) that precipitate within the amorphous precursor structure upon low temperature annealing. For Al87Y7Fe5Pb, the melt-spun ribbons consisted of an amorphous matrix with a dispersion of Pb nanoparticles (10nm diameter). HRTEM images of the Pb–Al interface revealed a good wetting behavior between the Al and the Pb nanoparticles. Isothermal annealing for Al87Y7Fe5Pb showed no transient stage even though the crystallization onset, Tx, was at a much lower temperature (247°C) compared with Al88Y7Fe5 (267°C). For Al(88−x)Y7Fe5Inx (x=0.5, 1.0, 1.5, 2.0), the DSC results indicated that Tx continuously decreased from 232°C to 220°C as the indium level increases from 0.5at.% to 2.0at.%. Under STEM, the image showed a coherent interface between Al and In particles. In the analysis of the transformation kinetics, the addition of minor elements can effectively promote additional nucleation of Al nanocrystals by providing heterogeneous nucleation sites. These developments offer new opportunities for the control of nanoscale microstructures.

Physiopathologie du syndrome des jambes sans repos

Two methods were used to obtain amorphous aluminium alloy powder: gas atomization and melt spinning. The sprayed powder contained only a small amount of the amorphous phase and therefore bulk composites were prepared by hot pressing of aluminium powder with the 10% addition of ball milled melt spun ribbons of the Al84Ni6V5Zr5 alloy (numbers indicate at.%). The properties were compared with those of a composite containing a 10% addition of Al2O3 ceramic particles. Additionally, a composite based on 2618A Al alloy was prepared with the addition of the Al84Ni6V5Zr5 powder from the ribbons used as the strengthening phase. X-ray studies confirmed the presence of the amorphous phase with a small amount of aluminium solid solution in the melt spun ribbons. Differential Scanning Calorimetry (DSC) studies showed the start of the crystallization process of the amorphous ribbons at 437 °C. The composite samples were obtained in the process of uniaxial hot pressing in a vacuum at 380 °C, below the crystallization temperature of the amorphous phase. A uniform distribution of both metallic and ceramic strengthening phases was observed in the composites. The hardness of all the prepared composites was comparable and amounted to approximately 50 HV for those with the Al matrix and 120 HV for the ones with the 2618A alloy matrix. The composites showed a higher yield stress than the hot pressed aluminium or 2618A alloy. Scanning Electron Microscopy (SEM) studies after compression tests revealed that the propagation of cracks in the composites strengthened with the amorphous phase shows a different character than these with ceramic particles. In the composite strengthened with the Al2O3 particles cracks have the tendency to propagate at the interfaces of Al/ceramic particles more often than at the amorphous/Al interfaces.

Aluminium based composites strengthened with metallic amorphous phase or ceramic (Al2O3) particles

Two methods were used to obtain amorphous aluminium alloy powder: gas atomization and melt spinning. The sprayed powder contained only a small amount of the amorphous phase and therefore bulk composites were prepared by hot pressing of aluminium powder with the 10% addition of ball milled melt spun ribbons of the Al84Ni6V5Zr5 alloy (numbers indicate at.%). The properties were compared with those of a composite containing a 10% addition of Al2O3 ceramic particles. Additionally, a composite based on 2618A Al alloy was prepared with the addition of the Al84Ni6V5Zr5 powder from the ribbons used as the strengthening phase. X-ray studies confirmed the presence of the amorphous phase with asmall amount of aluminium solid solution in the melt spun ribbons. Differential Scanning Calorimetry (DSC) studies showed the start of the crystallization process of the amorphous ribbons at 437°C. The composite samples were obtained in the process of uniaxial hot pressing in a vacuum at 380°C, below the crystallization temperature of the amorphous phase. A uniform distribution of both metallic and ceramic strengthening phases was observed in the composites. The hardness of all the prepared composites was comparable and amounted to approximately 50 HV for those with the Al matrix and 120 HV for the ones with the 2618A alloy matrix. The composites showed a higher yield stress than the hot pressed aluminium or 2618A alloy. Scanning Electron Microscopy (SEM) studies after compression tests revealed that the propagation of cracks in the composites strengthened with the amorphous phase shows a different character than these with ceramic particles. In the composite strengthened with the Al2O3 particles cracks have the tendency to propagate at the interfaces of Al/ceramic particles more often than at the amorphous/Al interfaces.

Aluminum-base amorphous and nanocrystalline materials

Results of long-term studies of the author are generalized and compared to works of other researchers of amorphous aluminum alloys and nanostructured materials obtained by crystallization of amorphous aluminum alloys and directly by cooling of the melt.

Specific features of sample preparation from amorphous aluminum alloys for transmission electron microscopy

An aluminum amorphous alloy doped with transition (Fe and Ni) and rare earth (La) metals has been used as an object of systematic study of the structural transformations that are characteristic of different methods of sample preparation for transmission electron microscopy (the mechanical tearing of ribbons, electrochemical thinning, and Ar+-ion etching under different conditions). The results of X-ray diffraction analysis and a calorimetric study of the structure in comparison with electron microscopy data made it possible to determine the optimal method of sample preparation, which ensures minimum distortions in the structure of metastable amorphous alloys with a low crystallization temperature.

Vacancy-type defects in amorphous and nanocrystalline Al alloys: Variation with preparation route and processing

Positron annihilation spectroscopy was performed in order to study the influence of preparation route and processing on atomic free volumes in amorphous and nanocrystalline aluminium alloys. In melt-spun amorphous Al 88 Y 7 Fe 5 , structural free volumes smaller than a lattice vacancy are predominant, whereas in amorphous Al 92 Sm 8 prepared by repeated cold rolling larger free volumes occur. In the early stages of nanocrystallization of Al 88 Y 7 Fe 5 , an indication of Y enrichment at interfacial free volumes in the growth front of the Al nanocrystallites is found.

Enhanced thermal stability of amorphous aluminum alloys through microalloying

Amorphous aluminum alloy powders with compositions of Al 85Y 7Fe 8, Al 83Y 7Fe 8Ti 2, and Al 79Y 7Fe 8Ni 3Ti 2Nd 1 were synthesized with crystallization temperatures of 342 °C, 446 °C, and 457 °C, respectively. In-situ high-temperature synchrotron diffraction results were correlated with differential scanning calorimetry studies to investigate the structural evolution during the crystallization. The results show that, through microalloying, the onset-of-crystallization temperature was increased by 115 °C, and the resulting crystalline products changed from a mixture of fcc-Al and an intermetallic phase in the case of Al 85Y 7Fe 8 to only intermetallic phases.

The Effect of As-quenched Structure on Primary Phase Crystallization in Amorphous Aluminum Alloys

AbstractFrom the reported experience, primary nanocrystallization in amorphous Al alloys involves transient kinetic behavior that is sensitive to the initial as-quenched structural arrangements. In order to examine the precursor effects, systematic studies outlining the evolving growth kinetics of primary aluminum nanocrystals (nc) during pre-crystallization annealing treatments, and investigations on the microstructure refining effect of specific alloying substitutions represent new approaches for an analysis of primary phase crystallization kinetics. In Al88Ni8Sm4 melt-spun ribbon (MSR), incremental substitutions of Cu for Ni (0 − 1at%) affect the thermal stability of the material (crystallization onset shifts to lower temperature) and refine the size of the primary phase nanocrystals. However, continuous heating calorimetry measurements indicate that the primary crystallization enthalpy remains approximately constant with increased Cu substitution. From a structural analysis standpoint, quantitative microstructure examinations applied in parallel with calorimetry measurements have been employed to characterize the as-quenched volume of MSR samples. The increased primary Al nanocrystal particle density with Cu substitution reflects the modification of local structural arrangements, necessitating an understanding of the local structure of the as-quenched sample in order to develop a description of primary phase nanocrystal growth kinetics.

The influence of solute distribution on the high nucleation density of Al crystals in amorphous aluminum alloys

An extension of a previous model that describes the role of solute atoms on glass formability leads to the conclusion that solute distribution plays an important role in the formation and stability of amorphous metals. A random distribution of solutes is shown to produce local solute-depleted regions (on the size scale of the mean inter-solute spacing) that provide preferred sites for the formation of crystalline nuclei. The possibility that these solute-depleted regions are responsible for the exceptionally high number density of critical Al nuclei is explored for three Al–Y binary alloys using a computer simulation. Up to 10 7 Y atoms were placed at random locations in the system, and the number of solute-free regions were counted as a function of the size of these regions. The experimentally observed number density of critical nuclei (∼3 × 10 21 m −3) is reproduced for a critical nucleus about 5 Al atoms in diameter, containing ∼60 Al atoms in an fcc array. Good agreement with previous suggestions of the size of a critical nucleus (about 6 atoms in diameter, containing about 100 atoms) support the conclusion that the current model provides a reasonable physical explanation for the quenched-in features responsible for the exceptionally high nucleation density in some amorphous Al alloys.

Nanocrystallization Reactions in Amorphous Aluminum Alloys

Primary crystallization is the key reaction that controls the synthesis of nanostructured bulk volumes comprised of a high density (1021–1023 m−3) of nanocrystals (7–20 nm) within an amorphous matrix. The primary crystallization kinetics in response to the annealing and the deformation of amorphous Al alloys are assessed in specific sample types and selected thermal treatments to evaluate primary nanocrystallization reactions. All amorphous Al alloy compositions are hypereutectic so that the initial phase selection of primary Al proceeds at a reduced driving free energy compared to thermodynamically favored intermetallic phases. Differential scanning calorimetry (DSC) studies on powders and melt spun ribbon (MSR) samples based upon thermal cycling and annealing below the glass transition, Tg, demonstrate a strong sensitivity of the primary crystallization onset and reaction enthalpy to thermal history and the as-quenched state. Microcalorimetry investigations and careful analysis of nanocrystal size distributions for Al92Sm8 MSRs following sub-Tg anneals reveal a partial nanocrystallization reaction resulting from a transient, decaying nucleation rate and a limited supply of heterogeneous nucleation sites. While crystallization is generally thought of as a thermally activated process, it can also be induced in response to external forcing such as irradiation or mechanical alloying. Intense deformation of amorphous Al88Y7Fe5 MSR, for example, yields a distribution of Al-nanocrystallites in the amorphous matrix without thermal annealing. Moreover, the results of cold-rolling experiments with melt-spun amorphous Al85Ni10Ce5 ribbons show that the deformation process can alter the phase selection upon annealing. These results suggest that the shear process during rolling effects a local rearrangement of atoms in the amorphous matrix. The kinetics behavior highlights the important role of the as-synthesized amorphous structure, reaction pathways and transient conditions on the evolution of nanoscale microstructures during primary crystallization.

Amorphous aluminum alloys—synthesis and stability

Recent innovations in metallic glasses have led to new alloy classes that may be vitrified and a re-examination of the key alloying factors influencing glass formation and stability. The new alloy classes are usually at least ternary systems and often higher order that can be grouped into two general categories. In one case, large, bulk volumes may be slowly cooled to the glassy state, which signifies a nucleation controlled synthesis. The other important class is represented by aluminum- and iron-based glasses that can be synthesized by rapid solidification processes such as melt spinning. These glasses are often called marginal glass formers that are synthesized under growth-controlled kinetic conditions. Glasses in both alloy classes can also be synthesized by intense deformation of crystalline multilayer arrays. These developments represent a major level of microstructure control that has an impact on the structural performance and stability.

Analysis of Primary Crystallization in Amorphous Aluminum Alloys

ABSTRACTThe annealing response of amorphous Al based alloy samples were investigated to assess the role of the as-quenched state on primary crystallization of Al nanocrystals(nc). Continuous heating differential scanning calorimetry (DSC) traces of amorphous Al87Ni10Ce3powders were compared to those from melt spun ribbon (MSR) to examine the effect of sample subdivision on primary crystallization. While the powders exhibited the same onset temperature as MSR, thermal cycling experiments show fine powder sizes reacting at the onset temperature and coarse powder sizes with the lowest melt quench rate transforming at the highest primary reaction temperature. In Al92Sm8MSR, a kinetics analysis of Al nc distributions indicates a notable effect of the as-quenched state on primary crystallization during isothermal annealing. With Al88Y7Fe5MSR intense deformation can induce thedevelopment of an Al nc distribution without thermal annealing. In each case examined, the results support the inclusion of quenched in clusters in the analysis of primary crystallization reactions.

Synthesis and Properties of Al-Based Amorphous and Microcrystalline Thin Films

ABSTRACTAmorphous metal alloys are ideally suited for interconnects in micro-electromechanical sys- tems (MEMS) because of their resistance against stress- and electromigration, and their stability in chemically aggressive environments, which should both lead to a substantial improvement of lifetime and reliability of robust sensors. While amorphous refractory metal alloys and amor- phous silicides are excellent interconnect materials for devices operating at elevated tempera- tures, these systems lack the cost-effective and easy interconnect processing of the prevalent polycrystalline aluminum alloy metallizations. Amorphous aluminum alloys are applicable to devices operating at up to 200°C, and their stressmigration resistance and chemical stability is far superior to conventional polycrystalline aluminum alloys. These new metallizations are very promising for processing interconnects, in particular because of their high strength and ductility, though having low density, and their relatively low electrical resistivity compared to other amor- phous metal alloys. Therefore these metallizations are especially suited for surface acoustic wave (SAW) sensors, where the interconnects are exposed to considerable mechanical strains. In this work amorphous Aluminum Yttrium alloy thin film metallizations deposited on appropriate sub- strates at room temperature (R.T.) by ultra-high vacuum (UHV) electron beam evaporation will be presented, and their mechanical and electronic properties together with their temperature sta- bility will be investigated.

XAFS Study of Amorphous Aluminium Alloy Thin Films

Al-Ta and Al-Nd alloy films are studied by x-ray absorption fine structure (XAFS) spectroscopy, x-ray diffraction (XRD) spectroscopy and the spectral simulations (EXCURV92, Cerius2) in order to make clear the relatinship between the metal content of Ta or Nd, the heat treatment temperature and the structure of intermetallic compounds (e.g. Al3Ta or Al4Nd) in the films. The experimental results indicate that the Al100-xTax (x>11) and/or Al100-yNdy (y>8) alloy films have amorphous structure, and that their intermetallic compounds are in the form of crystallite or quasi-compound structures.

Aleaciones de aluminio amorfas y nanoestructuradas

The work carried out in CENIM on amorphous and nanostructured aluminium alloys is described. Results about Al-LTM-ETM, Al-Fe-Nb and Al-Cu-Zr, and Al-LTM-RE, Al-Fe-Nd (LTM = Late Transition Metal, ETM = Early Transition Metal y RE = Rare Earth) alloys obtained by rapid solidification, inert gas atomization and melt-spinning, as well as mechanical alloying are presented.

Mechanically reinforced and corrosion-resistant sputtered amorphous aluminium alloy coatings

Aluminium alloy coatings are potentially interesting candidates for the cathodic protection of construction steels. This paper reviews the main features of Al−TM−(N) metallurgical coatings (TM: transition metal = Cr, Ti) deposited by reactive magnetron sputtering of composite Al−TM targets in Ar−N 2 reactive gas mixtures. In particular, both binary and ternary amorphous coatings always present the best compromise between mechanical properties and corrosion resistance. Generally, they present favourable intrinsic compressive stress associated with good compactness, a microhardness around 6000 MPa, a Young modulus of at least 110 GPa, better ductility and wear resistance than crystallized alloys, while maintaining a corrosion potential around that of iron, and an excellent pitting resistance in a chlorine environment. The thermal stability of such coatings is guaranteed for applications up to 300 °C. Their crystallization at higher temperature yields stable (Al 4Cr) or metastable (disordered AlTi) phases.