Investigation of glass forming ability in Ce–Al–Ni alloys

The compositional dependence of the glass forming ability (GFA), the correlation between their GFA and the GFA related parameters, and the thermal stability of the Ce–Al–Ni alloys were investigated. Rapidly quenched Ce₆₅Al_xNi_35 ? x (x = 2, 5, 10, 17, 20) and Ce₇₀Al_xNi_30 ? x (x = 2, 5, 10, 15, 20) ribbons were prepared by melt spinning, and their phase transformations were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The experimental results indicated that the GFA of Ce₆₅Al_xNi_35 ? x (x = 2, 5, 10, 17, 20) and Ce₇₀Al_xNi_30 ? x (x = 2, 5, 10, 15, 20) alloys increased firstly and then decreased with the increasing of the Al content up to 20 at.%, respectively. It was found that only one parameter, F₁, in evaluated currently available empirical GFA parameters searching for metallic glasses with a good GFA, can reflect the GFA of the Ce–Al–Ni alloys. It was indicated that the thermal stability of alloy with fully amorphous maybe lower than that of alloy with partial amorphous.     

The structure of Al–Cu and Al–Si eutectic melts

The structure of Al₈₃Cu₁₇ and Al₈₈Si₁₂ liquid eutectic alloys has been studied using the X-ray diffraction (XRD) and reverse Monte-Carlo (RMC) methods. The total and partial structure factors and pair correlation functions as well as structure parameters obtained therefrom have been analyzed. Chemically ordered Al–Cu groups significantly effect the structure in Al₈₃Cu₁₇, while a tendency to chemical ordering between atoms of an unlike kind is negligible in Al₈₈Si₁₂.     

Investigation of directional solidified Al–Ti alloy

Al–1 wt% Ti alloy was directionally solidified upwards under argon atmosphere under the two conditions; with different temperature gradients (G = 2.20–5.82 K/mm) at a constant growth rate (V = 8.30 μm/s) and with different growth rates (V = 8.30–498.60 μm/s) at a constant temperature gradient (G = 5.82 K/mm) in a Bridgman furnace. The dependence of characteristic microstructure parameters such as primary dendrite arm spacing (λ₁), secondary dendrite arm spacing (λ₂), dendrite tip radius (R) and mushy zone depth (d) on the velocity of crystal growth and the temperature gradient were determined by using a linear regression analysis. A detailed analysis of microstructure development with models of dendritic solidification and with previous similar experimental works on dendritic growth for binary alloys were also made.     

Thermal conductivity of FeS2 pyrite crystals in the temperature range 50–300 K

The thermal conductivity of two single-crystal samples of pyrite FeS₂ are investigated by the method of stationary longitudinal heat flux in the temperature range 50–300 K. The low electrical conductivity of the crystals with a small impurity content causes an identical value of experimental lattice thermal conductivity. The temperature dependence of the phonon mean free path is established.     

Effect of Al additive on the formation of cubic boron nitride in Li3N–hBN system under HPHT

We have investigated the effect of Al on cBN formation in Li₃N–hBN system at 5.0 GPa and 1300–1650 °C. Regular cBN single crystals of 0.2–0.5 mm in size were obtained. It appears that the presence of Al in hBN powder facilitates the formation of cBN crystals with regular shape, although it does not have any catalytic action for hBN–cBN phase transformation. With increasing Al concentration, the color of cBN changed darker from amber to black and the threshold temperature for cBN formation became higher. X-ray diffraction and Raman spectroscopy indicate that AlN formed by reaction of Li₃N and Al and some B liberated in system.     

Radiation induced color centers in 50PbO–50P2O5 glass

The effect of γ-irradiation in the dose range of 5 kGy up to 25 kGy on the optical absorption spectra of 50PbO–50P₂O₅ glasses is reported. The spectral absorption of these glasses before and after γ-irradiation was measured in the spectral range of 300–900 nm at room temperature. The radiation induced absorption in this spectral range shown to consist of two bands centered approximately at 545 nm and 730 nm. The fundamental absorption edge shifts generally to lower energies with increasing γ-irradiation dose up to 25 kGy in this glass sample. The intensity of the induced absorption bands increases linearly with increasing γ-irradiation dose. The higher energy band (HEB) may be due to a hole in a singly bonded non-bridging oxygen distant from a modifier cation, while the lower energy band (LEB) is also due to a hole in similar oxygen which is interacting with a neighboring cation.     

Facilitating growth of InAs–InP core–shell nanowires through the introduction of Al

InAs nanowires were grown on GaAs substrates by the Au-assisted vapour–liquid–solid (VLS) method in a gas source molecular beam epitaxy (GSMBE) system. Passivation of the InAs nanowires using InP shells proved difficult due to the tendency for the formation of axial rather than core–shell structures. To circumvent this issue, Al_xIn_1?xAs or Al_xIn_1?xP shells with nominal Al composition fraction of x=0.20, 0.36, or 0.53 were grown by direct vapour–solid deposition on the sidewalls of the InAs nanowires. Characterisation by transmission electron microscopy revealed that the addition of Al in the shell resulted in a remarkable transition from the VLS to the vapour–solid growth mode with uniform shell thickness along the nanowire length. Possible mechanisms for this transition include reduced adatom diffusion, a phase change of the Au seed particle, and surfactant effects. The InAs–AlInP core-shell nanowires exhibited misfit dislocations, while the InAs–AlInAs nanowires with lower strain appeared to be free of dislocations.     

Glass forming ability of the Al–Ce–Ni system

In the present work, the glass forming ability (GFA) and its compositional dependence on Al–Ni–Ce system alloys were investigated as a function of several thermal parameters. Rapidly quenched Al₈₅Ni_15?XCe_X (X = 4,5,6,7,10), Al₉₀Ni₅Ce₅, Al₈₉Ni_2.4Ce_8.6, Al₈₀Ni_15.6Ce_4.4 and Al₇₈Ni_18.5Ce_3.5 amorphous ribbons were produced by melt-spinning and the structural transformation during heating was studied using a combination of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results showed that the GFA and the thermal stability in the Al-rich corner of Al–Ni–Ce system alloys were enhanced by increasing the solute content and specifically the Ce content.     

Nano-crystallization behavior of Zr–Cu–Al bulk glass-forming alloy

The glass-forming ability and devitrification behavior of a Zr₅₅Cu₃₅Al₁₀ bulk glass-forming alloy were examined to elucidate the very high nanocrystallization product density (> 10²³ m^?3). The crystallization kinetics and structural changes in the glassy alloy were studied using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The observed sequential phase formation during isothermal reaction and the high nanocrystal density are consistent with the influence of residual oxygen even at low levels (< 500 ppm) to promote nucleation.     

Possibility of AlN growth using Li–Al–N solvent

The possibility of AlN growth using Li–Al–N solvent was investigated. Based on theoretical prediction, we selected Li₃N as a suitable nitrogen source for AlN growth. First, vapor phase epitaxy using Li₃N and Al as source materials was performed to confirm the following reaction on the growth surface: Li₃N+Al=AlN+3Li. The results suggest that the reaction proceeds to form AlN on the substrate under appropriate conditions. Next, AlN growth using Li–Al–N solvent was carried out. The Li–Al–N solvent was prepared by annealing of mixtures composed of Li₃N and Al. The results imply that AlN was formed under an Al-rich condition. Moreover, it was found that Li was swept out from AlN grains during growth. The results suggest that AlN growth using Li–Al–N solvent might be a key technology to obtain an AlN crystal boule.     

Electroactive complex in thermally treated Ge-Si 〈Cu,Al〉 crystals

It is shown by Hall measurements that quenching complexly doped Ge_{1 − x} Si _x 〈Cu, Al〉 (0 ≤ x ≤ 0.20) crystals from 1050–1080 K leads to the formation of additional electroactive acceptor centers in them. The activation energy of these centers increases linearly with an increase in the silicon content in the crystal and is described by the relation E _k ^x = (52 + 320x) meV. Annealing these crystals at 550–570 K removes the additional acceptor levels. It is established that the most likely model for the additional electroactive centers is a pair composed of substituent copper and aluminum atoms (Cu _s Al _s ) or interstitial copper and substituent aluminum atoms (Cu _i Al _s ). It is shown that the generation of additional deep acceptor levels must be taken into account when using the method of precise doping of Ge_{1 − x} Si _x 〈Al〉 crystals with copper.     

Magnetic behavior,transport properties and nanocrystallization of melt-spun YxCe50 − xCu42Al8 (0 ≤ x ≤ 50) amorphous system

Amorphous Y_xCe_50 ? xCu₄₂Al₈ (0 ≤ x ≤ 50) ribbons prepared by melt-spinning on the Cu wheel were subjected to X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and to the measurements of magnetization and resistivity in the temperature range from 1.7 to 300 K. Effective activation energies, characteristic crystallization temperatures and enthalpies of as-quenched alloys have been determined. Two stages of crystallization have been observed in most samples (except shallow effects in Ce₅₀Cu₄₂Al₈). The activation energies have been calculated from the Kissinger relation to be 247 ± 18 and 570 ± 56 kJ/mol for Y₂₅Ce₂₅Cu₄₂Al₈ and Y₅₀Cu₄₂Al₈, respectively. The absence of the endothermic effect for x = 50, usually associated with a glass transition, below the primary crystallization event, indicates the presence of dispersed polyamorphous packing with a wide range of local glass transitions. The magnetization versus temperature plot for Y₂₅Ce₂₅Cu₄₂Al₈ points to a magnetic ordering at temperatures considerably below 50 K. This observation has been confirmed by the temperature dependence of resistivity, which exhibits a singularity at the same temperature. Moreover, a negative temperature coefficient of resistivity, characteristic of disordered systems, was observed. The electrical resistivity in the Y₂₅Ce₂₅Cu₄₂Al₈ amorphous alloy is governed by the weak localization of electrons.     

Magnetic and transport studies of σ-phase Fe50V50 alloys with different thermal history

The influence of the formation conditions of the sigma phase in an equiatomic FeV alloy on the magnetic and electric transport properties is studied. It is found that a sigma phase sample with higher resistivity (subject to a previous long annealing) has a much sharper magnetic transition than one formed after a shorter heat treatment and quenching, although both have very similar magnetic moments and ferromagnetic transition temperatures (T_c ～ 15 K from minimum dM/dT).     

Study of the reversible martensitic transformation in Cu?Zn?Al alloy by positron annihilation

The positron lifetime measurement to investigate phase transformations: martensitic phase (MP) ⇔︁ parent phase (PP) in Cu Zn Al alloy has been used. We have observed the generation of new defects by MP → PP transformation; these defects are liquidated by martensitic transformation. This effect is only observed in case of high concentration vacancies in alloy. In order to explain the nature of these defects we take into consideration the supervacancies idea.     

Corrosion behavior and in vitro biocompatibility of Zr–Al–Co–Ag bulk metallic glasses: An experimental case study

Ni- and Cu–free Zr–Al–Co–Ag bulk metallic glasses (BMGs) were synthesized by copper mold casting. The effects of Ag addition for partially replacing Co of Zr₅₃Al₁₆Co₃₁ BMG on the corrosion behavior, surface chemistry and in vitro biocompatibility of BMGs were investigated. The Zr–Al–Co–Ag BMGs are spontaneously passivated with low passive current densities in phosphate buffered saline (PBS) solution. Partial substitution of Co by Ag is effective in improving the corrosion resistance of the Zr–Al–Co BMG. X-ray photoelectron spectroscopy (XPS) measurements reveal that the Ag addition increases the concentration of Zr and decreases the concentration of Al in the surface passive film of BMGs, which is responsible for the enhanced corrosion resistance of Zr–Al–Co–Ag BMGs. Mouse MC3T3-E1 pre-osteoblast cell proliferation results and morphology observations show that the Zr–Al–Co–Ag BMGs exhibit comparable cell viability and proliferation activity with those of Ti–6Al–4V alloy, demonstrating their good biocompatibility. The high corrosion resistance in PBS and low in vitro cytotoxicity of Zr–Al–Co–Ag BMGs suggest an initial biocompatibility for biomedical applications.     

Volume and viscosity of Zr–Cu–Al glass-forming liquid alloys

We examined the volume and viscosity of Zr–Cu–Al glass-forming liquid alloys to clarify the origin of a frozen free volume in glassy alloys. Since an excess free volume imparts toughness and ductility to glassy alloys, we attempted to increase this volume in glass structures so that they could be used as engineering materials. The maximum frozen excess free volume was observed in the ternary eutectic composition of the Zr–Cu–Al alloy system; however, its origin remains unclear. We attempted to reveal the mechanism of the formation of the frozen excess free volume in Zr–Cu–Al glassy alloys.     

The effect of TiO2 on phase separation and crystallization of glass-ceramics in CaO–MgO–Al2O3–SiO2–Na2O system

The experiments were carried out on studying the effect of phase separation on nucleation and crystallization in the glass based on the system of CaO–MgO–Al₂O₃–SiO₂–Na₂O. In the experiments, TiO₂ was chosen as nucleating agent. Three batches of 5, 8 and 10 wt% TiO₂ substitution were investigated by the techniques of DSC, XRD, FTIR and FESEM equipped with EDS. XRD and FTIR analysis indicated that the super cooled glasses were all amorphous, the heat treatment leading to nucleation would cause a disruption of silica network which followed phase separation. The phase separation followed the generation of crystal seeds Mg(Ti, Al)₂O₆. FESEM observation and EDS analysis revealed that the more TiO₂ content of glass, the more droplet separated phase and crystal seeds after nucleation heat treatment. The main crystal phase is clinopyroxene, Ca(Ti, Mg, Al)(Al, Si)O₆, of crystallized glass.