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.     

On the nature of the dispersion hardening of Cu-Al-Co alloys

The authors describe an investigation into the mechanism of strain hardening of Cu-8 at. % Al-2 at. % Co alloy strengthened by particles of the intermetallic compound CoAl. They show that within the range 77–573°K the temperature dependence of the yield point is determined by the temperature dependence of the shear modulus. At T > 573°K the reverse processes gain in importance and cause a sharp decrease in the coefficient of strain-hardening and a loss of plasticity. The investigation of the Bauschinger effect and its reversal showed that distant stresses, generated by Orowan loops, have a considerable effect on the strain-hardening process. The reversal processes and an increase in test temperature produced no qualitative change in the dislocation pattern.     

Ultrasonic hardening of aluminium alloys

The application of cyclic mechanical loading at 22 kHz frequency significantly modifies the kinetics and dynamics of the individual stages of the precipitation hardening process. Therefore, an investigation was initiated where aluminium alloys containing 3.8%, 4.1% and 5.2% (weight) copper were aged at a variety of temperatures with and without simultaneous ultrasonic loading at stress amplitudes approaching the fatigue limit of these materials.     

On the description of isothermal phase transformations in binary alloys

Two effects are considered to influence the time dependence of the transformed volume in a binary alloy: a) the impingement effect (IE), takes into account the mutual impingement of the growing particles and b) the impoverishment effect (PE), which considers the decrease of driving forces and the increase of the diffusion paths in the approximation of an impoverishing matrix. Combining both effects growth equations are obtained analogous toJohnson-Mehl-Avrami only for one-dimensional growth.     

Acoustic study of martensitic-phase aging in copper-based shape memory alloys

An acoustic technique was applied to study aging of the β ₁ ^′ martensitic phase in a number of copper-based shape memory alloys (Cu-Zn-Al, Cu-Al-Ni, Cu-Al-Be) characterized by various degrees of martensitic-phase stabilization. The nonlinear anelasticity of the martensitic phase was studied in wide ranges of temperature (7–300 K) and vibrational strain amplitude (2 × 10^?7 ?2 × 10^?4) at vibrational-loading frequencies of ～100 kHz. It was shown that aging effects of the martensitic phase can have homogeneous and heterogeneous components. The homogeneous component is associated with a change in the degree of atomic order in the crystal volume. The basic heterogeneous mechanisms of martensitic-phase aging are associated with the formation of atmospheres of point defects and local changes (which are greater than those in the crystal volume) in the degree of atomic order in the vicinity of partial dislocations and the boundaries between martensite variants. It is concluded that various stabilization properties of the alloys at hand result not only from the different diffusion properties of quenching point defects but also from the different influence of these defects on the degree of atomic order and the different features of their interaction with partial dislocations and intervariant boundaries.     

De Haas-van Alphen studies of electron-scattering in dilute copper-based alloys

We have used the de Haas-van Alphen (dHvA) effect to study the relaxation times of “neck” and “belly” electrons in copper containing a range of dilute heterovalent and transition-metal solutes. The scattering (Dingle) temperaturex is derived from the variation of signal amplitude with magnetic field at a fixed temperature. Values ofx are believed accurate to within 0.1°K in a range ofx _N(neck) from ≃0.4°K to ≃6°K andx _B(belly) from ≃0.2°K to ≃3°K. Our results may be summarized as follows:Heterovalent solutes (Zn, Cd, Al; up to 0.1 at. %) .Transition-metal solutes (Ni, Co, Fe, Mn, Cr; up to 0.05 at.-%) . An anomalous dependence of dHvA amplitude on magnetic field has been observed for belly oscillations in several very dilute Cu Cr alloys. This anomaly is both concentration and temperature-sensitive, and is probably related to the Kondo effect.     

Phase transitions in films prepared from Alnico-type alloys

Phase transitions taking place in films of an alloy based on Fe-Ni-Co-Al-Cu (YuDNK-24) as a result of a thermomagnetic treatment and which lead to a high coercivity state have been investigated. In this state, three phases are detected in the films: a phase with a bcc lattice, and a phase with a fcc lattice, and a phase based on the compound NiAl (or Ni₃Al).     

Strain hardening of alloys with face-centered cubic lattice

A brief review is given of the peculiarities of the strain hardening of face-centered cubic (fee) alloys as compared with pure metals. The fundamental equations connecting the strain hardening characteristics to the quantitative characteristics of the dislocation structure and the slip trace picture are considered in application to alloys with a high friction stress of a nondislocation nature _F. The shape of the strain hardening curves of alloy mono- and polycrystals is analyzed; it is shown that it depends substantially on the stress level F.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 132–150, August, 1976.     

Modelling work hardening of aluminium alloys containing dispersoids

The influence of dispersoids on tensile deformation behaviour has been studied by comparison of aluminium alloys containing different dispersoid densities. It was found that a fine dispersion of non-shearable particles led to an increased work hardening at the initial plastic deformation, but the effect was opposite at higher strains. The reason has been attributed to the generation of geometrically necessary dislocations (GNDs). A new model has been proposed for the evolution of GNDs based on a balance of storage and dynamic recovery of GNDs. The model predicts a rapid saturation of GNDs and a reduced work hardening at small strains, consistent with the experimental results.     

Lattice dynamics of some binary alloys

Summary The phonon dispersion frequencies for Cu₃Au, Cu₃Zn and Ni₃Fe alloys have been calculated using the model potential approach. The contribution of a short-range three-body interaction to the dynamical matrix has also been included in the present study. The theoretically computed phonon dispersion curves of these alloys are found to be in good agreement with the experimental data.     

Superconducting state parameters of binary alloys

The theoretical investigation of the superconducting state parameters (SSP) viz. electron–phonon coupling strength $\lambda$, Coulomb pseudopotential μ^*, transition temperature T_C, isotope effect exponent α and effective interaction strength N_OV of large numbers of binary alloys have been made extensively in the present work using a model potential formalism for the first time with pseudo-atom-alloy (PAA) model. A considerable influence of various exchange and correlation functions on $\lambda$ and μ^* is found from the present study. The present results of the SSP are found in qualitative agreement with the available experimental data wherever exist.     

Behaviour of positrons in binary alloys

The pseudopotential picture of the positron in a binary alloy is developed. It is shown that the positron is usually preferentially attracted to one sort of atom in the alloy. This relative positron affinity is associated with the positron pseudopotential difference between the different sorts of atom and calculations of this quantity are presented for a number of 50 at % alloys.     

Quantitative analysis of binary alloys by XPS

A rapid method for a quantitative analysis of a multielement alloy is discussed. This method is independent of surface-roughness and contaminations. Co     

Superconducting state parameters of indium-based binary alloys

Our well-recognized pseudopotential is used to investigate the superconducting state parameters viz: electron-phonon coupling strength λ. Coulomb pseudopotential μ*, transition temperature T _c, isotope effective exponent α and interaction strength N ₀ V for the In_1−x Zn _x and In_1−x Sn _x binary alloys. We have incorporated six different types of local field correction functions, proposed by Hartree, Taylor, Vashistha-Singwi, Ichimaru-Utsumi, Farid et al and Sarkar et al to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of the various exchange and correlation functions is concluded from the present study. The comparison with other such theoretical values is encouraging, which confirms the applicability of our model potential in explaining the superconducting state parameters of binary mixture.     

Dimensional crystal geometry of binary intermetallic alloys

The present work is devoted to a search for general crystal geometry laws of AB and A₃B binary alloys. Histograms of distribution of the B2, L1₀, B19, L1₁, L1₂, D0₂₂, D0₂₃, D0₁₉, D0₂₄, and A15 structures versus the dimensional factor, space filling factor, and superstructure contraction are constructed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 34–43, January, 2006.     

Thermodynamic properties of some gallium-based binary alloys

We have studied the concentration dependence of the free energy of mixing, concentration-concentration fluctuations in the long-wavelength limit, the chemical short-range order parameter, the enthalpy and entropy of mixing of Ga-Zn, Ga-Mg and Al-Ga binary alloys at different temperatures using a quasi-chemical approximation for compound forming binary alloys and that for simple regular alloys. From the study of the thermodynamic quantities, we observed that thermodynamic properties of Ga-Zn and Al-Ga exhibit positive deviations from Raoultian behaviour, while Ga-Mg exhibits negative deviation. Hence, this study reveals that both Ga-Zn and Al-Ga are segregating systems, while chemical order exists in Ga-Mg alloy in the whole concentration range. Furthermore, our investigation indicate that Al-Ga binary alloy have a tendency to exhibit ideal mixture behaviour in the concentration range 0?c_Al?0.30 and 0.7?c_Al?1.     

Work hardening of alloys with short range order of atoms

The study presents analysis of the experimental flow curves for polycrystals of fcc concentrated solid solutions Ni-Cr and Ni-Mn. It was demonstrated that the flow curves of these alloys can be divided into a number of stages of work hardening, and stage II bisects into two substages: with parabolic, and linear hardening. It was demonstrated that the shape of the curves of work hardening is determined by the type of dependence L = f(σ), where L is the average path length of the motion of the dislocation;σ is flow stress. Some possible critical stresses of transition from stage to stage are discussed.     

Superhydrophobic surfaces prepared from water glass and non-fluorinated alkylsilane on cotton substrates

Superhydrophobic surfaces have been successfully prepared by sol-gel method using water glass as starting material. Such surfaces were obtained first by dip-coating the silica hydrosols prepared via hydrolysis and condensation of water glass onto cotton substrates, then the surface of the silica coating was modified with a non-fluoro compound, hexadecyltrimethoxysilane (HDTMS), to gain a thin film through self-assembly, superhydrophobicity with a water contact angle higher than 151° can be achieved. The morphology and surface roughness were characterized by SEM and AFM.