Consolidation of blended powders by severe plastic deformation to form amorphous metal matrix composites

Warm equal channel angular extrusion (ECAE) in 90° tooling is used to consolidate Vitreloy 106a plus tungsten powders. A fully dense amorphous matrix composite showing good infiltration of the amorphous phase in between crystalline particles and uniform consolidation is achieved after one ECAE extrusion in the supercooled liquid temperature region of the amorphous phase. The results demonstrate that ECAE appears to be a viable processing method for producing bulk metallic glass matrix-crystalline particle composites.     

Study on local structure in amorphous SbS films by Raman scattering

A stoichiometric Sb₄₀S₆₀ film contains SbSb and SS bonds in addition to SbS bonds in an SbS₃ unit. The amount of the SbSb bond rapidly decreases with an increase in the S content beyond the stoichiometric value. On the other hand, as the S content decrease beyond the stoichiometric value, the SbS bond decreases and the SbSb bond increases. Annealing at temperatures near the glass transition decreases the fraction of the SbSb bond in the Sb₄₀S₆₀ film.     

Role of twinning in plastic deformation

A new concept of the structure of yttrium-aluminum garnet (Y₃Al₅O₁₂) has demonstrated the possibility of forming inversion twins in the (111) plane. The twinning processes are shown to be responsible for stress relaxation during the growth and plastic deformation of Y₃Al₅O₁₂ single crystals. This way of stress relaxation can be used to describe the plastic deformation of other crystals, at least cubic ones.     

Plastic deformation behavior of amorphous Fe78Si9B13 alloy at elevated temperature

The plastic deformation behavior of amorphous Fe₇₈Si₉B₁₃ alloy was investigated under uniaxial tension and gas pressure bulging. The deformed specimens were studied by means of XRD and SEM. It is shown that amorphous Fe₇₈Si₉B₁₃ ribbon has good deformation ability in the temperature range from 450 °C to 500 °C. The elongation of 36.3% and the relative bulging height (RBH) of 0.45 were obtained at 500 °C. In the uniaxial tension test, the amount of the crystalline α-Fe phase increases with deformation temperature below the crystallization temperature, which also suggests that the tensile stress promotes the crystallization of amorphous Fe₇₈Si₉B₁₃ ribbon. The suitable gas pressure bulging conditions for the specimens are 500 °C, 3.4 MPa and 30 min.     

Pulling CsI(Na) single crystals from melt by continuous method without plastic deformation

It is established that bromine impurity in CsI(Na) crystals not only facilitates the homogeneous incorporation of an activator into the lattice and prevents complex activator clusters from forming, but it also significantly hinders (at certain concentrations) the action of the primary and secondary dislocation slip systems. It is shown that the automatic pulling of large CsI-based crystals can be provided by the introduction of a single Br impurity into the charge; this impurity, to a large extent, strengthens only the top part of the crystal. The absence of plastic deformation in CsI-CsBr(Na) crystals with a diameter Ø300 mm and height h = 600 mm (grown by the continuous method) and Ø500 mm and h = 200 mm (grown by the automatic Kiropulos method) has been experimentally confirmed.     

A simple method for forming amorphous rare earth-transition metal alloy nanotube arrays

Arrays of rare earth-transition metal alloy Co₆₈Nd₃₂ and Co₉₆Sm₄ nanotubes, with amorphous structures and outer diameters of ca. 270–330 nm and with lengths of over 30 μm, have been fabricated for the first time by direct current electrodeposition with a mercury cathode via anodic aluminum oxide (AAO) template. The using of mercury cathode is a crucial condition for the growth of nanotubes and the co-reduction of Co²⁺, Nd³⁺ and Sm³⁺ in aqueous solution without any chemical modification of the pores of AAO, since the liquid mercury has characters of excellent conductivity and fluidity, high surface tension, high photoelectric work function, and high over-potential. A possible growth mechanism for the nanotubes is proposed. The as-prepared nanotube arrays display low coercivity and uniaxial magnetic anisotropy, and the easy magnetization direction is perpendicular to the nanotubes axes.     

Quantum effects in low temperature plastic deformation

A quantum mechanical calculation of the transition rate of a dislocation segment across an obstacle of finite width is performed. Compared with previous theories the achievement of the new treatment is that the finite compliance of the force distance profile is taken into account in the evaluation of the oscillatory modes. As a consequence, not only the DEBYE temperature of the dislocation line but also the obstacle compliance enters the transition rate and determines the temperature regime in which quantum effects become observable. Furthermore, the results of classical thermal activation theory that is valid at high temperatures are for the first time derived from first principles.     

Study of layered and defective amorphous solids by means of thermal wave method

In this work the thermal properties and the thickness calibration in layered thick acrylic films using the thermal wave method are reported. The results from acrylic films on two different substrates showed that thermal diffusivity and conductivity can be measured for both supports, metallic and glassy. The experimental applicability of a 1-D model and accuracy of the thickness measurement are also discussed.     

Influence of plastic deformation on the photoconductivity of CdTe

Investigation of photoconductivity have been performed on p-type phosphorus doped CdTe (5 × 10¹⁵ cm⁻³) deformed by compression at room temperature. Using a technique of axial illumination, the contribution of the surface to the photoconductivity is suppressed. In the investigated energy range (0.08–1.54 eV), and at room temperature, a maximum of the signal of the non-deformed material is of found at 1.312 ± 0.009 eV, with a half width of 0.100 eV, whereas the 0.3% deformed material presents a maximum at 1.348 ± 0.009 eV with the same half width. At 223 K these peaks are shifted to higher energies, the half width remaining unchanged, and the amplitudes being ∼ 30 times higher.     

On the character of local electric fields in amorphous semiconductors

On the basis of the agreement of calculated and measured parameters of some amorphous semiconductors, an argument is stated in favour of the central-symmetric type of random local electric fields. A possible mechanism of the transport of electrons is discussed.     

Study of the local structure of CuZr amorphous alloys by exafs. Effect of a structural relaxation

A structural investigation of Cu_xZr_1?x amorphous alloys has been made using EXAFS (x = 0.33, 0.46, 0.60). The partial radial distribution functions of the first shell of neighbours were derived from the study of the Cu and Zr K absorption edges. The distribution of the CuCu pairs remains almost constant in the whole range of concentration while the distribution of the unlike atom pairs varies drastically, becoming more asymmetric with increasing Cu content. In the meantime, the chemical ordering increases.A study of structural relaxation has been done for the Cu₆₀Zr₄₀ and Cu₄₆Zr₅₄ glasses by DTA and EXAFS. An additional endothermic phenomenon appears at T_g on DTA curves after annealing. No drastic change was observed by EXAFS. A slight increase of the spectrum was however obtained on the Cu edge for Cu₆₀Zr₄₀.     

The network structure of amorphous silicon-carbon alloy

The network structure of amorphous silicon-carbon alloy (a-Si_1−xC_x) has been studied over a wide range of x. The a-Si_1−xC_x thin films were prepared by sputtering silicon and carbon target with argon in radio-frequency magnetron sputtering equipment. The films were characterized by X-ray photoelectron spectroscopy, optical absorption, infrared absorption, and mechanical measurements. The results showed that the network structure could be classified neither as the random covalent network nor as the chemically ordered covalent network. The structure as a whole was close to the random covalent network, but the Si-Si combination at x>0.5 showed a feature of the chemically ordered covalent network. The film at 0.6<x<0.8 was hard and showed a high energy gap, due to the sp³ configuration in Si-C combinations.     

Pressure-induced crystallization in a bulk amorphous Zr-based alloy

Crystallization of multi-component on amorphous Zr-based alloy (Zr₄₁Ti₁₄Cu_12.5Ni₉Be_22.5C₁) is investigated at different pressures and temperatures. We have previously found that the primary crystallization temperature decreases with increasing pressure below 6 GPa, and the crystallization follows a different process under high pressure when compared to that at ambient pressure. In this work, pressure-induced crystallization is observed by in situ X-ray diffraction (XRD) using synchrotron radiation in a diamond anvil cell at ∼25 GPa and room temperature. This phase transition between amorphous and crystalline is reversible and the crystallized sample returns to the amorphous state during decompression. The mechanism for pressure-induced crystallization is discussed. We suggest that the crystallized phases under high pressure are interstitial solid solution phases formed from the amorphous matrix without long-range atomic rearrangements.     

Inhomogeneities of the plastic deformation of MgZn2 single crystals

Single crystals of the Laves phase MgZn₂ of different chemical composition within the range of homogeneity were deformed by dynamic compression at temperatures from 300 to 500°C. The surfaces of the specimens were observed by light microscopy. Special types of inhomogeneities of deformation (Lüders bands, macro-slip steps) are described and first conclusions are drawn concerning the behaviour of dislocations in this substance.     

Defect recovery after 77 K plastic deformation in bismuth

Dopplerbroadening measurements were performed in 77 K deformed bismuth in the temperature range between 80 K and 410 K. An important trapping effect was observed. Two recovery stages were found, one at 230 K and the other at 380 K. The measurements were compared with the results obtained from positron annihilation lineshape measurements in as-received polycrystalline bismuth samples of different purities, and in room temperature deformed bismuth samples. In all samples a recovery stage at 380 K was found, which is ascribed to the annealing of dislocations. Lifetime measurements were performed in the as-received bismuth samples. For dislocations a lifetime of 289 ps was found.     

Crystallization of metastable phases in the Pd83Si17 amorphous alloy

The crystallization of the Pd₈₃Si₁₇ amorphous alloy started by formation of small crystallites. By comparisons of selected area electron diffraction patterns from the crystallites and patterns calculated from generated models we found that the first observed structures coincide with long range vacancy ordered structures derived from CsCl-type structure, known as τ-structures. The Pd atoms are in the corners and the Si atoms or vacancies are in the centers of basic cubic cell, respectively. It is possible to interpret the formation of these transition structures as consequence of occurrence of small areas with different chemical composition present in original amorphous structure as a result of rapid quenching. After ageing the τ-structures transform by diffusion to the stable Pd₉Si₂ structure.     

Complex primary crystallization kinetics of amorphous Finemet alloy

The complex primary crystallization kinetics of the amorphous Finemet soft magnetic alloys has been analyzed by non-isothermal DSC measurements. The local activation energies E_c(α) were determined by an isoconversional method without assuming the kinetic model function and its average value was about 383 kJ/mol. The nucleation activation energy E_n and growth activation energy E_g were 425 and 333 kJ/mol, respectively. And the apparent local activation energies E_c can be expressed by E_n and E_g as follows: E_c = aE_n + bE_g. The local Avrami exponents lies between 1 and 2 in a wide range of 0.2 < α < 0.9, and it indicates that dominating crystallization mechanism in the non-isothermal primary crystallization of amorphous Finemet alloy is one dimensional growth at a near-zero nucleation rate for surface crystallization. The significant variation of local Avrami exponent and local activation energy for primary crystallization with crystallized volume fraction demonstrates that the primary crystallization kinetics of amorphous Finemet alloy varies at different stages. In addition, the variable local activation energies E_c(α) and local Avrami exponents n(α) are applicable and correct in describing the primary crystallization process of the amorphous Finemet alloy according to the theoretical DSC curve simulation.     

Microstructural evolution of slowly solidified Cu-Ti-Zr-Ni amorphous alloy

The microstructures of slowly solidified Cu-Ti-Zr-Ni bulk amorphous alloy were identified by X-ray diffractometry (XRD) and transmission electron microscope (TEM). XRD and TEM examinations show that the deep eutectic structures of the tested alloy consist of CuTi₂-Cu₁₀Zr₇、Cu₃Ti-CuZr、Cu₃Ti-Cu₁₀Zr₇-CuZr low-order eutectics. Moreover, short-range ordering clusters in the melt with configuration similar to that of Cu₁₀Zr₇ compound may contribute to the glass forming ability of bulk amorphous Cu-Ti-Zr-Ni alloy.     

Indentation-induced microhardness changes in glasses: Possible fictive temperature increase caused by plastic deformation

The microhardness around a large indentation was measured for different types of glasses. In soda-lime silicate glass, a typical normal glass, the region in the immediate vicinity of the indentation was found to exhibit a lower hardness than the region far removed from the indentation. In silica glass, a typical anomalous glass, the region in the immediate vicinity of a large indentation was found to exhibit a higher hardness than the region far removed from the indentation. Asahi less brittle glass, an intermediate glass between normal and anomalous glasses, was found to exhibit little change in hardness in the vicinity of the large indentation. These findings can be explained by a deformation-induced fictive temperature increase leading to a lower hardness for soda-lime silicate glass and a higher hardness for silica glass.