A. A. Teplov

Thermodynamic and kinetic properties of an icosahedral quasicrystalline phase in the Al-Pd-Tc system

The properties of a quasicrystalline phase in the Al-Pd-Tc system are studied for the first time. X-ray investigations demonstrate that the quasicrystalline phase in the Al70Pd21Tc9 alloy has a face-centered icosahedral quasi-lattice with parameter a=6.514 Å. Annealing experiments have revealed that this icosahedral phase is thermodynamically stable. The heat capacity of an Al70Pd21Tc9 sample is measured in the temperature range 3–30 K. The electrical resistivity and magnetic susceptibility are determined in the temperature range 2–300 K. The electrical resistivity is found to be high (600 µΩ cm at room temperature), which is typical of quasicrystals. The temperature coefficient of electrical resistivity is small and positive at temperatures above 50 K and negative at temperatures below 50 K. The magnetic susceptibility has a weakly paramagnetic character. The coefficient of linear contribution to heat capacity (γ=0.24 mJ/(g-atom K2)) and the Debye characteristic temperature (Θ=410 K) are determined. The origin of the specific features in the vibrational spectrum of the quasicrystals is discussed.

Composites reinforced by Al—Cu—Fe quasicrystalline particles with a copper matrix and their tribological properties

Copper-based composite coatings with addition of 34 wt % of Al—Cu—Fe quasicrystalline powder of dispersity less than 20 fum, as well as 70 wt % of quasicrystalline powder of dispersity less than 40fum and less than 3 fum, were produced by the cold spray process. The phase composition during annealing of samples at various temperatures was studied by X-ray phase analysis. Tribological properties of each composite coating and pure copper were investigated. The experimental results showed a considerable improvement of the tribological properties of the material at the addition of quasicrystals. The least wear was observed in the composite sample containing quasicrystalline inclusions of less than 3 fum subjected to thermal treatment. In this case the counterbody wear was practically absent.

Tribological and mechanical properties of composites based on ethylene-tetrafluoroethylene and quasicrystalline Al−Cu−Fe filler

Samples of composites, in which ethylene-tetrafluoroethylene copolymer is used as a matrix and quasicrystalline Al−Cu−Fe powder as a filler with 0, 1, 2, 4 and 8 vol % concentrations, are prepared. Electron microscopy studies of the sample structure are carried out. The influence of the filler on the crystallinity and temperatures of sample melting and destruction is investigated. The mechanical and tribological properties of the samples are tested. It is found that an increase in the filler content changes neither the mechanical nor thermodynamic characteristics of the material but significantly improves the tribological characteristics. The friction coefficient decreases twice at 1 vol % of the filler and the wear resistance increases by 40 times at 8 vol %. Experimental data indicate the probability of good adhesion of the filler particles to the fluoropolymer matrix. The composites under investigation may be of interest as promising materials for polymer friction bearings.

Effect of a quasicrystalline filler on the tribological properties of a composite based on ultrahigh-molecular-weight polyethylene

We prepare composites in which ultrahigh-molecular-weight polyethylene (UHMWPE) is used as a matrix and quasicrystalline Al–Cu–Fe powder is used as a filler with concentrations of 1, 10, 30, and 50 vol %. The mechanical and tribological properties of the samples are measured, and electron microscopic studies of fractured regions are performed. It is shown that with increasing concentrations of the filler, the nature of fracturing of the samples changes. The minimum value of the friction coefficient is 0.07. It is assumed that the limiting factor in improving the tribological properties of UHMWPE–quasicrystal composites is the chipping of filler particles from the polymer matrix.

Reflection spectra and optical constants of quasicrystalline Al-Pd-Re films in the IR region

Optical properties of quasicrystalline Al-Pd-Re films have been investigated in the mid and far IR regions. Films were deposited on sapphire substrates using layer-by-layer ion-plasma sputtering with subsequent vacuum annealing. Reflection spectra have been measured in a wide IR spectral range from 50 to 7500 cm−1. The complex dielectric function of the films was determined from the experimental data by dispersion analysis of the reflection spectra. The frequency dependence of the real part of the optical conductivity was calculated.

IR reflectance spectra and optical constants of Al-Cu-Fe quasicrystalline thin films

The optical properties of Al-Cu-Fe quasicrystalline films and, for comparison, crystalline films of similar composition are studied using middle-and far-IR reflectance spectroscopy. Measurements are performed with 0.1-to 0.3-μm-thick films on sapphire substrates. The complex dielectric function of the films is calculated from experimental data. It is found that the real part of the dielectric function is negative for the crystalline films but positive and weakly frequency dependent, except in the range near 245 cm−1, for the quasicrystalline films. The optical conductivity of the quasicrystalline films does not feature the Drude peak observed for crystalline films and exhibits a peak at 245 cm−1, which can be assigned to optical phonon excitations and is absent for crystalline films.

Gamma-resonance study of nanopowders with different dispersion and quasicrystalline phases in the Al-Cu-Fe system

Abstract57Fe Mössbauer spectroscopy has been used to monitor synthesis of quasicrystals in the Al-Cu-Fe system and study the influence of the size of quasicrystalline particles in powder samples of the Al63.1Cu25.6Fe11.3 alloy on the properties of synthesized materials. Quasicrystalline samples of different dispersion with particle sizes from 0.3 to 15 μm have been studied in the temperature range 80–295 K. It is established that iron atoms in an Al63.1Cu25.6Fe11.3 quasicrystals occupy four types of structural positions, which differ in the atomic composition of the nearest environment. The results of the analysis suggest the dependence of the hyperfine-interaction parameters on the degree of sample dispersion. The components corresponding to iron atoms in both the surface layer and bulk of microparticles are isolated in the Mössbauer spectra. No magnetic hyperfine splitting has been found in the Mössbauer spectra in the entire temperature range. This fact suggests that a localized magnetic moment is absent in iron atoms.

Composite Material Based on Polytetrafluoroethylene and Al–Cu–Fe Quasi-Crystal Filler with Ultralow Wear: Morphology, Tribological, and Mechanical Properties

Samples of composites with polytetrafluoroethylene as the matrix and a powder of 0, 1, 2, 4, 8, 16, and 32 vol % Al–Cu–Fe quasi-crystal as the filler are prepared. Electron microscopy studies of the sample structure are carried out, the influence of the filler on the degree of crystallinity and the melting and destruction temperatures of the samples is investigated; mechanical tensile tests and tribological tests are performed. The composite samples with filler contents of 4, 8, 16, and 32 vol % show ultralow wear with the coefficient K < 5 × 10–7 mm3/N m. The highest wear resistance exceeding that of unfilled polytetrafluoroethylene by 2200–3100 times is recorded in composites with 16 vol % filler. An increase in the wear resistance is associated with formation on the friction surface of a thin crust containing quasi-crystal particles 0.2–0.3 μm in size, revealed by scanning electron microscopy in combination with energy dispersive analysis.

Magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by solid-phase diffusion

The magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by solid-phase diffusion as a result of thermal treatment in vacuum and in a hydrogen atmosphere have been studied. The magnetic properties of the samples synthesized in hydrogen were found to be much better than those of the samples synthesized in vacuum. It is shown that an increase in the treatment time in vacuum decreases the number of magnetic nanoclusters and elimninates the time instability of their magnetic properties (magnetic susceptibility and magnetization).