Complex Metallic Alloy Research Articles

Metadislocation configurations and novel phason defects in the complex metallic alloy T-Al-Mn-Pd

Metadislocations (MDs) are linear defects enabling plastic deformation in complex metallic alloys, a class of materials with large lattice parameters. We systematically investigate MD configurations in plastically deformed T-Al-Mn-Pd using aberration-corrected scanning transmission electron microscopy. Atomic-resolution imaging reveals that MDs in the T-phase can dissociate into energetically more favorable partials through a pure glide process. The analysis of MD dissociations allows for an estimate of the energy of the associated stacking faults. Adjacent MDs with opposite signs in the T-phase are found to interact and form dipolar configurations connected by shared chains of phason defects. We furthermore report on a new type of phason defect, which we identify as anti-phason. We discuss structural variants of anti-phasons, their role in the deformation- and MD-interaction processes and their energetical impact.

Electrochemical characterization of rapidly solidified Al-(Cr,Cu,Ni,Y,Zr)-Fe alloys

The aim of this work was to investigate the multiphase structure of new Al71(Cr, Cu, Ni, Y, Zr)24Fe5 and Al65(Cr, Cu, Ni, Y, Zr)20Fe15 alloys, and the influence of chemical composition on their corrosion behavior. Samples were prepared using two different cooling rates: slowly cooled (master alloys), and rapidly solidified by high-pressure die casting into a water-cooled copper mold (plates). The structure of the studied alloys were investigated by X-ray diffraction (XRD), light microscopy, and Mössbauer spectroscopy. The crystallization mechanisms are described based on differential scanning calorimetry (DSC) heating and cooling curves. Electrochemical potentiodynamic measurements were conducted in 3.5% NaCl solution at 25 °C, and electrochemical impedance spectroscopy (EIS) tests were also carried out. The alloys were characterized by a multiphase crystalline structure, except Al65Cu20Fe15 and the plate form of Al71Ni24Fe5 alloy, for which a quasicrystalline phases were identified. Moreover, the complex metallic alloy (CMA) phase was detected for Al-Cr-Fe alloys. For samples in the form of plates, structure fragmentation was found. On the basis of the experimental polarization curves, extrapolation of Tafel curves and EIS results, the best corrosion properties were found for alloys with zirconium additions, while the alloys with addition of yttrium showed the least resistance.

Deformation of Mg-γMg17Al12in situ composites: Room temperature mechanical behaviour, microstructures and mechanisms

Deformation tests at room temperature have been carried out on a series of in situ Mg-γMg17Al12 composites with volume fraction of γMg17Al12 phase varying between 20% and 60%. Regardless of the phase volume fraction, these Mg-γMg17Al12 composites that are prepared by solidification consist in magnesium-rich dendrites and a eutectic mixture. The eutectic mixture is made of magnesium fibres embedded in a matrix formed by the γMg17Al12 phase, a hard and brittle complex metallic alloy. Compression tests at room temperature have shown that a global plastic deformation is observed even though the soft phase is always enclosed in the brittle one. According to the strain-stress curve, deformation proceeds in two stages: a first stage at low stress (σ ~ 100 MPa) and low strain (Δε < 0.01) almost similar for all the composites and a second stage characterized by a strain hardening effect along with a significant deformation for composites with γ phase volume fraction smaller than 40%, whereas no or little additional deformation is observed for composites with volume fraction higher than 40% that break at high stress (~400 MPa). Microstructural observations of the deformed samples have evidenced dislocations in the γMg17Al12 matrix and their localization as pile-ups and slip bands as well as the transmission of deformation across the eutectic mixture. The plasticity of the γMg17Al12 phase and the mechanical behaviour of the Mg-γMg17Al12 composites are discussed with respect to the microstructure characteristics and to the specific atomic features of complex metallic alloy phases.

Glassy magnetic state and negative temperature coefficient of resistivity in Mn3+δIn

The complex metallic alloy ${\mathrm{Mn}}_{3}\mathrm{In}$ has recently attracted attention for being a probable candidate for the fully compensated half-metallic ferrimagnet. The compound is associated with a rather unusual negative coefficient of resistivity approximately above the ferrimagnetic, ${T}_{C}=80\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Our investigation indicates that that the ground state of the alloy is spin-glass like, which possibly coexists with the ferrimagnetic state. The carrier density obtained from the Hall-effect measurement shows a jump below ${T}_{C}$; afterward, it gradually increases with lowering temperature and shows a saturating tendency at the lowest temperature. The electronic structure calculations indicate that, at the Fermi energy, dominant contributions come from minority-spin channels with larger bandwidth. In contrast, very weak but nonzero states arise from the majority-spin channel, and half metallicity can be ruled out. The calculations also found that the antiferromagnetic alignment of Mn spins with nonzero resultant magnetic moment confirms the ferrimagnetic nature consistent with the experimental results. The high-temperature phase with negative temperature coefficient of resistivity can be related to the localization of charge carriers through electron-phonon interactions.

The Study of A New Symmetrical Rod Phase in Mg-Zn-Gd Alloys

Quasicrystal alloys have a wide application prospect because of excellent performances and characteristics; meanwhile, magnesium alloys are known as green engineering materials because of their high specific strength and light weight. Therefore, the study of Mg-Zn-Gd quasicrystal alloys is of great significance for the development of new materials. In this paper, Mg(70-x)Zn30Gdx(x=3,4,5) alloys were prepared by a conventional casting method and the morphologies and properties of these alloys were studied. There was a new symmetrical rod phase found in the Mg66Zn30Gd4 alloy and the symmetrical rod phase was identified as a ternary phase by mapping scanning and energy dispersive spectroscopy (EDS) analysis. The Zn/Gd ratio of the symmetrical rod phase was found to be 4.8 and the TEM images obtained were different from the typical diffraction spots patterns of quasicrystalline, which means it is unlikely to be quasicrystalline. With different melt holding time, the symmetrical rod phase evolved gradually over time from a lamellar eutectic structure; differential scanning calorimetry (DSC), heat treatment, and microhardness tests showed that the melting temperature of the rod phase was 453 °C and that its thermal stability and microhardness are better than quasicrystalline. Hence, the symmetrical rod phase is a new kind of complex metallic alloy phase whose composition and properties are close to those of quasicrystals but is not quasicrystalline.

Low-temperature synthesis of a graphene-based, corrosion-inhibiting coating on an industrial grade alloy

The use of graphene materials as protective coatings for metallic substrates has received much attention because of graphene’s ability to seal a metal and prevent the diffusion of most corrosive species to the metal surface. The application of graphene-based coating technology to industrially relevant samples, however, is hindered by the high growth temperatures required to prepare functional and efficient protective graphene layers. The growth temperatures typical for popular catalysts and precursors are incompatible with most relevant alloys. Here, we present a low-temperature synthesis route to a graphene-based coating, using a complex metallic alloy, Inconel 625, as an example substrate. We demonstrate that the coating reduces the sample corrosion current by two orders of magnitude and also shifts the open circuit potential from −308 mV to + 129 mV. We present an extensive characterisation of the coating and the coating synthesis procedure. The procedure relies on a surface-activated, thermally-induced polymerisation reaction and the method should be transferable to other metallic alloys.

Ca12 [Mn19 N23 ] and Ca133 [Mn216 N260 ]: Structural Complexity by 2D Intergrowth.

Two new calcium nitridomanganates, Ca12 [Mn19 N23 ] (P3, a=11.81341(3) Å, c=5.58975(2) Å, Z=1) and Ca133 [Mn216 N260 ] (P3‾ , a=39.477(1) Å, c=5.5974(2) Å, Z=1), were obtained by a gas-solid reaction of Ca3 N2 and Mn with N2 at 1273 K and 1223 K, respectively. The crystal structure of Ca12 [Mn19 N23 ] was determined from high-resolution X-ray synchrotron powder diffraction data, whereas single-crystal X-ray diffraction was employed to establish the crystal structure of the Ca133 [Mn216 N260 ] phase, which classifies as a complex metallic alloy (CMA). Both crystal structures have 2D nitridomanganate layers containing similar building blocks but of different levels of structural complexity. Bonding analysis as well as magnetic susceptibility and electron spin resonance measurements revealed that only a fraction of the Mn atoms in both structures carries a localized magnetic moment, while for most Mn species the magnetism is quenched as a result of metal-metal bond formation.

Ca12[Mn19N23] and Ca133[Mn216N260]: Structural Complexity by 2D Intergrowth

AbstractTwo new calcium nitridomanganates, Ca12[Mn19N23] (P3, a=11.81341(3) Å, c=5.58975(2) Å, Z=1) and Ca133[Mn216N260] ( , a=39.477(1) Å, c=5.5974(2) Å, Z=1), were obtained by a gas–solid reaction of Ca3N2 and Mn with N2 at 1273 K and 1223 K, respectively. The crystal structure of Ca12[Mn19N23] was determined from high‐resolution X‐ray synchrotron powder diffraction data, whereas single‐crystal X‐ray diffraction was employed to establish the crystal structure of the Ca133[Mn216N260] phase, which classifies as a complex metallic alloy (CMA). Both crystal structures have 2D nitridomanganate layers containing similar building blocks but of different levels of structural complexity. Bonding analysis as well as magnetic susceptibility and electron spin resonance measurements revealed that only a fraction of the Mn atoms in both structures carries a localized magnetic moment, while for most Mn species the magnetism is quenched as a result of metal–metal bond formation.

Comparative study of SPEX and planetary milling methods for the fabrication of complex metallic alloy nanoparticles

The objective of the present work is the comparison of two common milling methods for the production of complex metallic alloy nanoparticles. γ-Al12Mg17 nanoparticles were fabricated using both a planetary ball mill and a SPEX mill. The produced nanoparticles have been compared on the basis of the phase and microstructural characterisations by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The crystallite size, lattice strain, and lattice parameter have been calculated from the XRD data followed by an investigation on the powder morphology and particle size by FESEM. It has been indicated that the higher milling speed in the SPEX milling method leads to a higher milling energy and consequently lower particle size. For the same milling time of 2 h, the particle size decreases down to nano-scale using a SPEX ball mill whereas the planetary ball mill products contained a varied size in the range of micron and submicron regimes. Furthermore, the results showed approximate crystalline sizes of 12 and 85 nm for the Al12Mg17 in SPEX and planetary ball mills after 2 h of milling time, respectively.

Probing Single Pt Atoms in Complex Intermetallic Al13Fe4.

The atomic structure of a 0.2 atom % Pt-doped complex metallic alloy, monoclinic Al13Fe4, was investigated using a single crystal prepared by the Czochralski method. High-angle annular dark-field scanning transmission electron microscopy showed that the Pt atoms were dispersed as single atoms and substituted at Fe sites in Al13Fe4. Single-crystal X-ray structural analysis revealed that the Pt atoms preferentially substitute at Fe(1). Unlike those that have been reported, Pt single atoms in the surface layers showed lower activity and selectivity than those of Al2Pt and bulk Pt for propyne hydrogenation, indicating that the active state of a given single-atom Pt site is strongly dominated by the bonding to surrounding Al atoms.

Softening non-metallic crystals by inhomogeneous elasticity

High temperature structural materials must be resistant to cracking and oxidation. However, most oxidation resistant materials are brittle and a significant reduction in their yield stress is required if they are to be resistant to cracking. It is shown, using density functional theory, that if a crystal’s unit cell elastically deforms in an inhomogeneous manner, the yield stress is greatly reduced, consistent with observations in layered compounds, such as Ti3SiC2, Nb2Co7, W2B5, Ta2C and Ta4C3. The mechanism by which elastic inhomogeneity reduces the yield stress is explained and the effect demonstrated in a complex metallic alloy, even though the electronegativity differences within the unit cell are less than in the layered compounds. Substantial changes appear possible, suggesting this is a first step in developing a simple way of controlling plastic flow in non-metallic crystals, enabling materials with a greater oxidation resistance and hence a higher temperature capability to be used.

The influence of the fabrication route on the microstructure and surface degradation properties of Al reinforced by Al9Co2

Al-7 (wt. %) Co alloys have been prepared by conventional casting (Cast), vacuum arc melting (VAM) and free sintering (FS), with the objectives to: a) determine an effective fabrication route (in terms of low cost, ease of manufacture and property boosting) and b) exploit the benefits that the combination of a complex metallic alloy (Al9Co2) with Al at the Al-rich end of the Al-Co phase diagram can offer, corrosion- and wear-wise, whilst at the same time, specific weight and raw material costs remain at relatively low levels. All the attained microstructures consist of Al9Co2 in an Al matrix. However, the main microstructural features are strongly affected by the preparation method. The VAM alloy presents the finest microstructure, which is also highly directional. All the microstructures are analytically being discussed and explained with respect to the fabrication method. Porosity and hardness data are correlated with the fabrication route and the corresponding microstructures. All alloys, regardless of the preparation method, exhibit high resistance to localized corrosion in 3.5 wt% NaCl. The potentiodynamic and potentiostatic polarization performances are analysed. The sliding wear resistance of the Al-Co alloys is notably improved as compared to commercially pure Al and common Al-alloys. A wear mechanism is proposed and the role of Al9Co2 is clarified. The superiority of the VAM alloy with respect to the surface degradation behavior is noted and correlated with its microstructure.

In-situ synthesis of Al76.8Fe24 complex metallic alloy phase in Al-based hybrid composite

The complex metallic alloy (CMA), Al76.8Fe24, was in-situ synthesized in the Al-based hybrid composite by powder metallurgy technique. The structural analysis by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated that the Al76.8Fe24 CMA phase was formed by diffusion of Fe atoms into the Al matrix during the sintering stage. The formation of the CMA phase was mainly determined by the sintering temperature which was just above the eutectic temperature of Al–Fe. Moreover, the fully dense Al-based hybrid composite was obtained and exhibited ultrahigh strength ∼1100MPa, indicating that this method is expected to be effective in producing CMA particle reinforced Al-based hybrid composite.

Fullerene adsorption on intermetallic compounds of increasing structural complexity

Abstract Compared to elemental crystals (Al, Cu, Ag, etc.), the local atomic arrangement within Al-based complex intermetallics is usually best described by highly symmetric clusters decorating the unit cell. With the latter containing tens to several thousand atoms (or an infinite number for the case of quasicrystals), this translates to structurally complex surfaces exhibiting unique potential energy landscapes. This review will focus on the different studies reporting the adsorption of C60 molecules on such complex metallic alloy surfaces, aiming to benefit from this complexity to create exotic molecular nanostructures. First, we will recall the main adsorption mechanisms and surface phases that have been identified when fullerene adsorption is carried out on single crystal surfaces. Second, we will discuss how surfaces of increasing structural complexity impact the film properties. The presence of five-fold symmetric adsorption sites is another intrinsic property of these complex intermetallic surfaces. As will be presented in this review, this leads to specific molecular orientations to maximize substrate–adsorbate symmetry matching, hence introducing another degree of freedom to create new 2-D molecular architectures. The local electronic interactions at the adsorption site interface will also be introduced. Furthermore, the different fullerene structures formed upon adsorption on aperiodic surfaces of varying chemical composition and on Bi allotropes will be discussed. Finally, suggestions will be given for future work along with the foreseen area of interests.

Preparation, microstructure and properties of magnesium-γMg17Al12 complex metallic alloy in situ composites

Magnesium based alloys containing γ Mg17Al12 complex phases have been prepared by solidification. Owing to a methodology based on Scheil Gulliver calculation, a series of composites with controlled volume fraction of γ phase has been obtained. According to SEM and TEM observations, the microstructures of the Mg-γ composites consists in magnesium rich dendrites in various fraction embedded in a eutectic mixture formed by γ phase and Mg rich fibers. Preliminary investigations of the mechanical and electrical behaviors of the composites have been carried out. Microstructures and properties of the Mg-γMg17Al12in situ composite series are discussed with respect to in situ composites containing Bulk Metallic glasses.

Packing of Russian doll clusters to form a nanometer-scale CsCl-type compound in a Cr–Zn–Sn complex metallic alloy

A new cubic complex metallic alloy phase, Cr22Zn72Sn24, with a lattice parameter near 2.5 nm was discovered in crystals grown using a Zn/Sn flux. The structure consists of Russian doll clusters or a 3-d network of Cr-centered icosahedra (shown) with bcc-metal fragments in void spaces.

Using coupled micropillar compression and micro-Laue diffraction to investigate deformation mechanisms in a complex metallic alloy Al13Co4

In this study, we have used in-situ micro-Laue diffraction combined with micropillar compression of focused ion beam milled Al13Co4 complex metallic alloy to investigate the evolution of deformation in Al13Co4. Streaking of the Laue spots shows that the onset of plastic flow occurs at stresses as low as 0.8 GPa, although macroscopic yield only becomes apparent at 2 GPa. The measured misorientations, obtained from peak splitting, enable the geometrically necessary dislocation density to be estimated as 1.1 × 1013 m−2.

Adsorption of O2 and C2Hn (n = 2, 4, 6) on the Al9Co2(0 0 1) and o-Al13Co4(1 0 0) complex metallic alloy surfaces

Oxidation of the Al9Co2(001) and Al13Co4(100) surfaces has been performed in a wide range of temperatures at 2×10−8 or 1×10−7mbar oxygen pressure. Only AlO bonding is observed. The oxidation kinetics are controlled by the quantity of oxygen sticking on the surface. Oxidation results from a competition between several effects: formation of an oxide film, dissolution of the film, oxygen desorption and oxygen dissolution into the bulk. For temperatures lower than 710K for the Al9Co2(001) surface and 925K for the Al13Co4(100) surface, a ∼5Å thick oxide film is formed which does not show any long-range order and desorbs upon annealing. When oxidation is performed at higher temperatures, oxygen diffusion into the bulk is observed. A poorly ordered oxide film having a sixton structure is formed on the Al9Co2(001) surface when oxidation is performed at 775K, which is dissolved when annealing at higher temperatures. On the Al13Co4(100) surface, only a weak streaky polar circle is observed following annealing at 925K the film formed at room temperature, which corresponds to an hexagonal network of O atoms into small ultrathin oxide layers domains. The oxidation behaviour of the Al9Co2(001) and Al13Co4(100) surfaces has been ascribed to the strong covalent character of bonds present in these AlCo phases, which prevents aluminium diffusion. C2Hn molecules (n=2, 4, 6) do not adsorb on the Al13Co4(100) surface in the experimental conditions used in this study, thus suggesting that this surface might not be the active one in the semi-hydrogenation of acetylene.

Size effect on the melting temperature depression of Al12Mg17 complex metallic alloy nanoparticles prepared by planetary ball milling

This research investigates the synthesis and size-dependent melting point depression of complex metallic alloy (CMA) nanoparticles. Al12Mg17 which belongs to this new category of intermetallic materials was initially produced as pre-alloyed ingot, then homogenized to achieve single phase compound and crushed into small size powder and finally, mechanically milled in a planetary ball mill to synthesize nanoparticles. Phase and microstructural characterizations of the as-crushed and milled powders were performed using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Effects of the mechanical milling on thermal behavior of the Al12Mg17 nanoparticles in comparison with as-cast Al12Mg17 ingot has been investigated by differential scanning calorimetry (DSC) measurement. It was found that an average particle size of 24nm with crystallite size of 16nm was achieved after 20h of ball milling process. The size- dependent melting point depression of the Al12Mg17 nanoparticles has been experimentally observed and also comparison of the obtained results with theoretical models was carried out.

Effect of temperature on the initial stages of oxidation of γ-Al4Cu9(110)

Combined X-ray photoemission spectroscopy and low energy electron diffraction investigations have been performed to study the influence of temperature on the first stages of oxidation of the (110) surface of γ-Al4Cu9 complex metallic alloy in the pressure range 2–6×10−7mbar. The oxidation mechanism is driven by aluminium segregation. At 115K, a pure aluminium oxide film is formed, which does not present any long range order. CuO bonds are never observed. The lower oxidation kinetics compared to that previously observed at room temperature is due to blocking of the oxygen dissociation and/or a decrease in the aluminium segregation. However, aluminium segregation is still observed, even for this very low temperature, due to the low energy value of the activation energy for aluminium diffusion in γ-Al4Cu9 (0.65±0.12eV) which is related to the presence of two vacancies in the crystal structure. At 925K, fast aluminium segregation and possible oxygen diffusion into the bulk leads to the formation of domains or clusters of γ-like alumina either on top of or, more likely, below the surface.