Nanoquasicrystalline Phase Research Articles

On the Formation of AlNiCo Nano-Quasicrystalline Phase during Mechanical Alloying through Electroless Ni-P Plating of Starting Particles.

A new strategy was applied to develop nano-quasicrystalline phase in well-known AlNiCo ternary system. This approach was based on electroless Ni-P plating of the starting powders and subsequent ball milling in a protective atmosphere without additional annealing or sintering processes. Microstructural evolution and phase transformation of both raw and coated particles were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. After 360 min of mechanical alloying, the peaks demonstrating the formation of nano-quasicrystalline phase appeared in XRD pattern of the coated powders, while those in mechanically alloyed raw powders remained mostly unchanged. The formation of nano-quasicrystalline phase in the vicinity of the primary elements was also confirmed by the corresponding selected area diffraction patterns, and images generated by transmission electron microscope (TEM).

Microstructural transformation of quasicrystalline AlFeCrTi extruded bars upon long thermal treatments

Bulk Al93Fe3Cr2Ti2 bars extruded from gas atomised powder particles present a microstructure of an aluminium matrix reinforced with a spherical nanoquasicrystalline phase. In this work the evolution of the microstructure of Al93Fe3Cr2Ti2 extruded bars upon heating at 400°C for up to 1000h is investigated by means of X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. According to our observations we propose that the quasicrystalline alloy evolves in two steps: a first step consists in the decomposition of the supersaturated solid solution of the matrix and the quasicrystals, and a second step in the transformation of the quasicrystals into the equilibrium phases.

Inverse Hall-Petch Like Mechanical Behaviour in Nanophase Al-Cu-Fe Quasicrystals: A New Phenomenon

The structural and mechanical stability of quasicrystals are important issues due to their potential for possible applications at high temperatures and stresses. The aim of the present work is, therefore, to review the earlier works on conventional crystalline and quasicrystalline materials and also to report the results and the analysis on the Hall Petch and inverse Hall Petch like behavior of nanoquasicrystalline Al62.5Cu25Fe12.5 alloys. It was observed that, at large grain sizes, the hardness increases with decreasing grain size, exhibiting the conventional Hall Petch relationship, whereas for smaller grains, inverse Hall Petch behavior was identified. The inverse Hall Fetch behavior in the nanoquasicrystalline phase could be attributed to thermally activated shearing of the grain boundaries, leading to grain boundary sliding in nanostructures of quasicrystalline grains. These results were analyzed based on the dislocation pile-up model as well as the grain boundary shearing models applicable to nanomaterials.

Nanoquasicrystalline Phase in Mechanically Alloyed and Heat-Treated Al73Cu11Cr16

and Heat-Treated Al73Cu11Cr16 T.A. Sviridovaa,∗, A.P. Shevchukov, E.V. Shelekhov, D.L. Diakonov, M.V. Gorshenkov, S.D. Kaloshkin, V.V. Tcherdyntsev, Z. Li and G. Fan Center for Composite Materials, National University of Science and Technology MISIS , Moscow 119049, Russia Bardin Central Research Institute for the Iron and Steel Industry, Moscow 105005, Russia Int. School of Microscopy, National University of Science and Technology MISIS , Moscow 119049, Russia State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China

Nanostructuration of i-Al64Cu23Fe13 quasicrystals produced by arc-furnace

The Al46Cu23Fe13 quasicrystal phase, prepared by arc-melting and nanostructured using high energy ball milling technique, was studied employing X-ray diffraction, transmission electron microscopy, ferromagnetic resonance and electric transport measurements. Fe local environments were studied by Mossbauer spectroscopy. The resistivity ratio R(4.2 K)/R(300 K) is within the expected values commonly observed in an icosahedral phase. In general, the experimental results show that an appropriate heat treatment of the as-cast alloy prepared by arc-melting makes possible to obtain good quasicrystal samples. On the other hand, for milling time longer than five hours, the average grain-size of quasicrystal phase reduces, but it preserves Fe local atomic orders. It is also observed that the quasicrystalline sample decomposes in an iron rich nano-quasicrystalline phase and a e-Al2Cu3 phase. Electric transport measurements show that at low temperatures the nano-quasicrystalline samples behave strongly different to their solid counterparts, an effect attributed to a long-range order reduction and an increasing of grain boundary regions. The presence of local magnetic moments in the nanostructured sample is also discussed.

Formation of metastable phases and nanocomposite structures in rapidly solidified Al–Fe alloys

In the present work the structure and morphology of the phases of nanocomposites formed in rapidly solidified Al–Fe alloys were investigated in details using analytical transmission electron microscopy and X-ray diffraction. Nanoquasicrystalline phases, amorphous phase and intermetallics like Al 5Fe 2, Al 13F 4 coexisted with α-Al in nanocomposites of the melt spun alloys. It was seen that the Fe supersaturation in α-Al diminished with the increase in Fe content and wheel speed indicating the dominant role of the thermodynamic driving force in the precipitation of Fe-rich phases. Nanoquasicrystalline phases were observed for the first time in the dilute Al alloys like Al–2.5Fe and Al–5Fe as confirmed by high resolution TEM. High hardness (3.57 GPa) was measured in nanocomposite of Al–10Fe alloy, which was attributed to synergistic effect of solid solution strengthening due to high solute content (9.17 at.% Fe), dispersion strengthening by high volume fraction of nanoquasicrystalline phase; and Hall–Petch strengthening from finer cell size (20–30 nm) of α-Al matrix.

Formation of nano quasicrystalline and crystalline phases by mechanical alloying

In the present work, the formation of nano quasicrystalline icosahedral phase in Al 86Cr 14, Al 84Fe 16 and Al 62.5Cu 25Fe 12.5 alloys has been investigated by mechanical alloying. Mixtures of quasicrystalline and related crystalline phases have been observed under various milling conditions. The X-ray diffraction, differential thermal analysis and electrical resistivity techniques have been used for characterization and physical property measurements. The particle size was calculated by X-ray profile using Williamson–Hall plot method and it was found to be 25–50 nm size.

Indentation characteristics of metallic glass and nanoquasicrystal-glass composite in Zr–Al (Ga)–Cu–Ni alloys

Indentation characteristics of melt-spun Zr 69.5Al 7.5− x Ga x Cu 12Ni 11 ( x = 0–2.5; in at %) metallic glasses have been investigated. Formation of a nano-quasicrystalline phase by annealing the glass has been found only upto x = 1.5. The substitution of Ga changes the size and shape of this phase. The load dependent hardness behaviour of metallic glasses and nanoquasicrystal-glass composites are reported in detail. It has been observed that substitution of 1.5 at % Ga improved microhardness property of Zr–Al–Cu–Ni alloy. The value of yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. It has been found that microstructural and morphological changes alter the Meyer exponent. Pile up parameters seems to be sensitive to structural and microstructural details.

Effect of Ti addition on the quasicrystalline phase formation and indentation characteristics of Zr69.5Al7.5Cu12Ni11 alloy

The crystallisation behaviour and indentation characteristics of melt-spun (Zr69.5Al7.5Cu12Ni11)100− x Ti x (x = 0–16 at. %) metallic glasses was investigated. Differential scanning calorimetry traces revealed changes in crystallisation behaviour with addition of Ti. Formation of a nanoquasicrystalline phase by annealing the glass was found up to x = 12. Further increase of Ti content gives rise to formation of a Zr2Ni-type crystalline phase. In addition to this, the size of nanoquasicrystals decreases with increasing addition of Ti. The load-dependent hardness behaviour of the metallic glasses and nanoquasicrystal–glass composites is reported in detail. The value of the yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. The formation of shear bands around the indentation periphery was observed. It was found that microstructural and morphological changes alter the indentation characteristics of glasses as well as composites formed after controlled crystallisation.

Effect of Ga substitution on the crystallization behaviour and glass forming ability of Zr–Al–Cu–Ni alloys

The crystallization behaviour of melt spun Zr 69.5Al 7.5− x Ga x Cu 12Ni 11 ( x = 0–7.5; in at.%) metallic glasses has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The DSC traces showed changes in crystallization behaviour with substitution of Ga. Formation of single nano-quasicrystalline phase by controlled crystallization of glasses has been found only for 0 ≤ x ≤ 1.5. Further increase of Ga content gives rise to formation of the quasicrystals together with Zr 2Cu type crystalline phase. In addition to this, the substitution of Ga influences the size and shape of nano-quasicrystals. The glass forming abilities (GFAs) of these metallic glasses were assessed by the recognition of glass forming ability indicators, i.e. reduced glass transition temperature ( T rg ) and supercooled liquid region (Δ T x ). The glass transition temperature ( T g ) has been observed for all the melt spun ribbons.

Structure of nanocomposites of Al-Fe alloys prepared by mechanical alloying and rapid solidification processing

Structures of Al-based nanocomposites of Al-Fe alloys prepared by mechanical alloying (MA) and subsequent annealing are compared with those obtained by rapid solidification processing (RSP). MA produced only supersaturated solid solution of Fe in Al up to 10 at.% Fe, while for higher Fe content up to 20 at.% the nonequilibrium intermetallic Al5Fe2 appeared. Subsequent annealing at 673 K resulted in more Al5Fe2 formation with very little coarsening. The equilibrium intermetallics, Al3Fe (Al13Fe4), was not observed even at this temperature. In contrast, ribbons of similar composition produced by RSP formed fine cellular or dendritic structure with nanosized dispersoids of possibly a nano-quasicrystalline phase and amorphous phase along with α-Al depending on the Fe content in the alloys. This difference in the product structure can be attributed to the difference in alloying mechanisms in MA and RSP.

Nanoindentation Studies on Amorphous, Nanoquasicrystalline and Nanocrystalline Zr80Pt20 and Zr75Pd25 Alloys

Nanoindentation studies on rapidly solidified Zr80Pt20 and Zr75Pd25 binary alloys with nanocrystalline, nanoquasicrystalline, and amorphous microstructures are reported. The results indicate that the hardness and elastic modulus are the highest for a mixture of amorphous and nanoquasicrystalline state among the various microstructures studied. Nanoquasicrystalline phase has high hardness and elastic modulus in comparison to amorphous and nanocrystalline phases. The hardness to modulus ratio is close to 0.1 in both the alloys, irrespective of the phase/phase mixture studied indicating that the bonding in these alloys is of covalent nature. In Zr80Pt20, all the phases/phase mixtures have higher hardness and modulus in comparison to similar microstructures in Zr75Pd25 due to higher bond energies caused by more negative heat of mixing in the former case.

Phase Stability of Crystalline and Amorphous Phases and Formation of Nanostructure in Zr-Pd and Zr-Pt Alloys Under Electron Irradiation

AbstractElectron irradiation induced phase transition behavior of Zr-Pd and Zr-Pt alloys was investigated focusing on phase selection in crystallization by thermal annealing and electron irradiation. Nano quasi-crystalline (QC) phase was formed by thermal crystallization in Zr66.7Pd33.3 and Zr80Pt20 alloys, while nano two-type f.c.c. super-saturated solid solutions were formed by irradiation induced crystallization at 298K. In Zr66.7Pt33.3 alloy, polycrystalline Zr5Pt3 and Zr9Pt11 phases transformed to two-type f.c.c. nano-crystalline phase through an amorphous state by crystal-to-amorphous-to-crystal (C-A-C) transition during electron irradiation. Nano-composite phase composed of f.c.c. super-saturated solid solution and residual amorphous phase was stable rather than an amorphous single phase, thermal equilibrium crystalline phase and quasi-crystalline phase under 2.0MV electron irradiation at 298K, resulting in the formation of nano-composite structure by irradiation induced amorphization and crystallization.

Surface oxides and their effect on the oxidation behavior of amorphous and nanoquasicrystalline Zr–Pd and Zr–Pt alloys

The oxidation behavior of melt-spun Zr75Pd25 and Zr80Pt20 alloys with nanoquasicrystalline phase embedded in amorphous matrix has been studied isothermally as well as nonisothermally in static air. The nature of oxides formed during oxidation has been studied by x-ray diffraction and scanning electron microscopy, and a transition in the structure of the oxides has been shown as one of the primary reasons for the difference in the oxidation behavior of the alloys.

Study of formation of nano-quasicrystals and crystallization kinetics of Zr-Al-Ni-Cu metallic glass

The formation of nano-quasicrystals on isothermal annealing of melt-spun ribbons of Zr69.5Al7.5Ni11Cu12 metallic glass has been investigated using transmission electron microscopy (TEM). The crystallization study of this metallic glass has been carried out using differential scanning calorimetry (DSC) in non-isothermal (linear heating) mode. It exhibits two-stage crystallization where the first stage corresponds to the precipitation of icosohedral nano-quasicrystalline phase. This has been confirmed with the help of TEM investigations. The crystallization parameters like the activation energy (Ec) and frequency factor (k0) have been derived using the Kissinger peak shift analysis. The activation energies for the first and second crystallization peak are found to be 278 and 295 kJ mol-1, respectively. The frequency factors obtained for the two peaks are respectively 7.16·1019 and 1.42·1020 s-1. Ec, k0 and the Avrami exponent (n) have also been derived by fitting the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation for the transformed volume fraction (x) to the crystallization data. JMAK results of Ec for the first and second crystallization peak turn out to be 270 and 290 kJ mol-1 respectively. However, k0 and n are found to be heating rate dependent as reported in similar studies. The values of n for the first crystallization stage ranges between 1.66 and 2.57 indicating diffusion-controlled transformation in agreement with earlier reports.

Synthesis of nanocrystalline/quasicrystalline Mg32(Al,Zn)49by melt spinning and mechanical milling

In the present investigation we have made an attempt to synthesize T-Mg32(Al,Zn)49 Frank Kasper phase and investigate the mechanical properties of the T-Phase in micro and nano scale. Single T-Phase (bcc, a = 1.42 nm) has been prepared by conventional casting with a proper combination of flux in order to avoid the loss of magnesium from the melt. Chemical analysis by energy dispersive X-ray microanalysis system attached to scanning electron microscope has confirmed the desired composition for T-phase. The as-cast material was then rapidly solidified by melt spinning and mechanically milled using a high-energy ball mill. The samples were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction techniques. The rapidly solidified foils showed the presence of mostly nanoquasicrystalline phases coexisting with a minute amount of crystalline phases in the thin region where the cooling rate is expected to be high. The dark field imaging in electron microscopy clearly confirms the existence of nano phases. Mechanically milled powder exhibited the evolution of nanophases at higher milling time. Microhardness measurement at low load was carried out in both the as-cast and nanophase materials in order to understand the influence of nanophases on the mode of deformation and cracking at low load.

On the criteria for the formation of nanoquasicrystalline phase

The formation of nanoquasicrystalline phase is reported directly from the liquid on melt spinning over a wide range of wheel velocities of 10–30 m/s in Zr–Pd system at the eutectic composition (Zr75Pd25 alloy). The earlier studies in the Zr–Pd system (Zr70Pd30 and Zr65Pd35 alloys) showed nanoquasicrystallization on annealing of the amorphous phase obtained by melt spinning. Based on the existing results in various systems, a large negative enthalpy of mixing and/or existence of Frank–Kasper-type phases appear to be the crucial criteria for the formation of nanoquasicrystalline phase in any system.

Oxidation behavior of Al–Cu–Fe nanoquasicrystal powders

A nanoquasicrystalline phase was synthesized by a mechanical alloying process. The thermal stability and oxidation behavior of this phase were investigated in different environments using X-ray diffraction and X-ray photoelectron spectroscopy. The results show that the nanoquasicrystalline phase is stable up to temperatures greater than 1173 K in an inert gas atmosphere, while they are stable up to 873 K in air. The X-ray photoelectron spectroscopy results show three distinct chemical states of Al in Al–Cu–Fe, Al (3+), Al (0) and Al (hydroxide).

Corrosion and oxidation behavior of amorphous and nanoquasicrystalline phases in Zr 70Pd 30 and Zr 80Pt 20 alloys

The corrosion behavior of melt-spun amorphous and nanoquasicrystalline Zr 80Pt 20 ribbons and amorphous Zr 70Pd 30 ribbons has been investigated using a potentiodynamic polarization study in a neutral NaCl solution. All three alloys are susceptible to chloride attack, and pitting is observed. The pitting corrosion behavior of these alloys has been compared with zirconium (98% pure). The oxidation behavior of the amorphous Zr 70Pd 30 alloy and the partially nanocrystalline Zr 80Pt 20 alloys has been studied non-isothermally by a thermo-gravimetric analysis in static air at different heating rates up to 773 K. It was observed that the amorphous Zr 70Pd 30 alloy readily oxidizes. Zr 80Pt 20 alloys in the nanoquasicrystalline state are more resistant to oxidation.

Synthesis and devitrification of glassy Zr–Ti–Ni and Zr–Hf–Ni ternary alloys

Two alloys of nominal compositions Zr 41.5Ti 41.5Ni 17 and Zr 41.5Hf 41.5Ni 17 have been melt spun at 40 ms −1 wheel speed. Under this processing condition Zr–Ti–Ni alloy becomes amorphous and the Zr–Hf–Ni alloy precipitates a cubic phase with 4.95 Å lattice parameter in the amorphous matrix. The Zr–Ti–Ni alloy, upon annealing, precipitates a nanoquasicrystalline phase, which at the later stages of crystallisation transforms into cF96 NiZr 2 phase. The amorphous phase in Zr–Hf–Ni alloy upon annealing precipitates the same cubic phase with 4.95 Å lattice parameter. The lower glass forming ability of Zr–Hf–Ni compared to Zr–Ti–Ni and nanoquasicrystallisation in Zr–Ti–Ni alloy can be explained by taking into consideration the atomic size differences among Ti, Zr and Hf.