Binary Amorphous Alloys Research Articles

Ordre local et proprietes physiques des verres metalliques riches en fer

A structural study of the binary amorphous alloys M l− x X x , in which M is a transition metal and X a metalloid shows that a satisfactory description of their structure may be proposed based on a structural unit similar to that found in the crystalline form of the same composition as the glasses. This article describes the results of this study. These results are then used to interpret the influence of other metalloids such as Si and C on the physical properties of Fe-B glasses. Depending on the role of these diverse elements, a distinction between metalloids is proposed which simplifies the choice of alloy compositions with respect to the desired properties.

Amorphous binary alloys obtained by electrolytical and chemical methods

Amorphous alloys, generally obtained by splat cooling condensation on a cold support or sputtering, were prepared in our laboratory at ambient temperature by two other methods. The first one, the oxidoreduction in liquid phase, gives films, the thickness of which is 500 to 2000 A, deposited on an isolating support — glas, plastic or ceramic. The second one, electrolysis of adapted solutions, allows us to obtain some thick layers the thickness of which is in this case, 1 to 100 microns. The support is a conductor, for example, a copper leaf. Experiments reveal a local order characterized by the absence of diffraction peaks in the experimental interference function which is chiefly formed by diffuse rings. We can obtain amorphous materials at ambient temperature if the bath composition leads to an alloy which contains at least 15% of atoms of the metalloid in the case of phosphorous, and 20% of atoms with boron. The upper limits are, respectively, 25 and 35%. It does not seem possible to obtain a bigger quantity of metalloid with these two methods. The local order can be represented by an assembly of clusters in which chemical bonds exist between the metal and metalloid atoms. Every cluster is surrounded by a domain where atomic position is distributed following a Gaussian function. Beyond that the material is completely amorphous.

Effect of irradiation particle mass on crystallization of amorphous alloys

The crystallization temperature of amorphous alloys was found to be significantly lowered by heavy ion or electron irradiation during annealing. However, only heavy ion irradiation altered the mode of crystallization. Both a binary and multi-element amorphous alloy showed this type of response to irradiation. Radiation-enhanced diffusion processes in the amorphous state can explain the increased crystallization kinetics during irradiation. Heavy ion irradiation alters the crystallization mode by causing direct transformation to the final equilibrium phase as opposed to intermediate metastable phase formation during thermal annealing or electron irradiation. The equilibrium phase is believed to nucleate directly in the displacement cascades, which only form during heavy ion bombardment.

Amorphization of Hf-Ni films by solid-state reaction

We report on a detailed study of a new process to produce amorphous binary alloys by solid-state reaction of the elemental constituents from an initially thin-layer configuration. The Ni-Hf system was selected on the basis of the criteria that a fast diffuser (Ni) and a large binary heat of mixing drives the solid-state reaction at temperatures so low (∼ 300 °C) that nucleation and growth of the crystalline phases are suppressed and the amorphous phase becomes the lowest accessible state of free energy. Backscattering spectrometry, x-ray diffraction, and transmission electron microscopy are used to monitor the atomic composition profile and the microstructure of the samples. The kinetics of the amorphous phase formation is consistent with the diffusion-limited growth of a laterally uniform amorphous layer. The substantial and approximately linear composition gradient of the amorphous layer reflects the low atomic mobility of the atoms in the amorphous phase and the broad existence range of the amorphous phase in the binary Ni-Hf system. The latter is consistent with predictions based on the calculated equilibrium free-energy diagram of the system.

EXAFS study of electrodeposited NiP binary alloys

EXAFS measurement was made for the region above the nickel K-absorption edge of NiP binary amorphous alloys, prepared by electrodeposition and rapidly quenched techniques. Experimental data were Fourier transformed. The peak positions of electrodeposited alloys and fcc nickel are similar to each other, while their EXAFS patterns are quite different from that of rapidly quenched NiP amorphous alloys. Increased phosphorous content in electrodeposited NiP alloys was found to shift the 1st peak to the lower side and increase the intensity of the 2nd peak. These results suggest that the atomic arrangements in the alloys are varied by method of preparation and the contents of additives.

Properties of amorphous binary alloys of copper with magnesium and zirconium

Properties of amorphous binary alloys of copper with magnesium and zirconium

Application of Miedema's coordinates to the formation of binary amorphous alloys

It is demonstrated that Miedema's coordinates can described the formation of binary amorphous alloys quite well. With |▵ψ∗| and |▵(1/ n 1 3 ws| representing the ordinate and the abscissa, respectively, it is found that the formed and non-formed areas of binary amorphous alloys can be separated by a straight line, which is given by 10|Δφ|−39 Δ 1 n WS 1 3 −1=0 The results compare well with those obtained from a bond-parametric diagram, wether the alloys under considerations are formed by only melt-quenching techniques, or by melt-quenching and other than melt-quenching techniques, but are not as good as those obtained from bond-parametric diagram including the size factor.

Amorphous film formation by ion mixing in binary metal systems

A structural difference rule is formulated according to which an amorphous binary alloy film is formed by ion mixing of multilayered sample when the two constituent metals are of different structure, apparently independently of their atomic sizes and electronegativities. The rule is supported by the experimental results we have obtained on eight selected binary metal systems, which cover all possible combinations between b.c.c., f.c.c. and h.c.p. structures. The previous data reported in the literature also support this rule. The available experimental data indicate that the validity of the rule may extend to other structures and to production techniques other than ion mixing. The amorphization mechanism is discussed in terms of the competition between two different structures resulting in frustration of the crystallization process.

Evidence for a new Hume-Rothery phase with an amorphous structure

It will be shown that binary amorphous alloys with a noble metal and a polyvalent non-transition element, as constituents, can be described essentially as a Hume-Rothery phase. Some structural as well as transport properties depend on\(\bar Z\), the average number of the conduction electrons per atom. A strong similarity between the amorphous and the corresponding liquid alloys was found. Alloys of the type mentioned can exist in a homogeneous amorphous phase within a concentration range which is limited on the noble-metal rich side by\(\bar Z\)=1.8 and on the other side by about 20 at% noble-metal content. The influence of the conduction electrons, manifested in the Friedel oscillations of the effective pair potentials, is responsible for structural and electronic transport properties. For amorphous and liquid alloys with\(\bar Z\)=1.8 it is interesting to note thatkpe, the wave number at which the maximum in the structure factor occurs, is equal to 2kF, the diameter of the Fermi sphere. As far as we have determined, all amorphous alloys with\(\bar Z\)=1.8 containing the same noble metal have the same crystallization temperature and the same Hall coefficient independent of the polyvalent element. The individual influence of the polyvalent constituents can only be seen with increasing\(\bar Z\).

Temperature dependence of the electrical resistivity of amorphous Pd-Si alloy

The temperature dependence of the electrical resistivity of amorphous binary Pd-Si alloy has been calculated by means of the t-matrix formulation of the extended Ziman theory. Results obtained are compared with experimental data.

Structural difference rule for amorphous alloy formation by ion mixing

We formulate a rule which establishes a sufficient condition that an amorphous binary alloy will be formed by ion mixing of multilayered samples when the two constituent metals are of different crystalline structure, regardless of their atomic sizes and electronegativities. The rule is supported by the experimental results we have obtained on six selected binary metal systems, as well as by the previous data reported in the literature. The amorphization mechanism is discussed in terms of the competition between two different structures resulting in frustration of the crystallization process.

Structural relaxation during annealing and neutron or electron irradiation, in glassy Ti50Be40Zr10

Abstract We have studied the effects of thermal annealing and both electron and neutron irradiation on the state of short-range order in melt-spun Ti50Be40Zr10 (Metglas 2204), using electrical resistivity measurements. A reversible resistivity variation is observed during thermal cycling with no flux, akin to the one we evidenced recently in two binary all-metal amorphous alloys. It is similarly interpreted in terms of thermodynamical variations of the (metastable) equilibrium degree of chemical short-range order. On the other hand, the resistance of specimens exposed to a fast electron flux at 28 K is but little affected. However it is progressively decreased during post-irradiation isochronal anneals at subambient temperatures with a main, broad stage located between 120 K and 220 K. Interestingly the resistivity evolution related to structural relaxation which takes place above room temperature, in the unirradiated condition, is not markedly influenced by the irradiation. In contrast, irradiation with reactor neutrons at 300 K results in a strong resistivity increase, which is suggested to be reflection of chemical short-range ordering, presumably within the atomic displacement cascades.

Superconducting properties of amorphous Zr-Ge binary alloys

A new type of refractory metal-metalloid amorphous alloys exhibiting superconductivity has been found in a binary Zr-Ge system by a modified melt-spinning technique. Specimens are in the form of continuous ribbons 1 to 2 mm wide and 0.02 to 0.03 mm thick. The germanium content in the amorphous alloys is limited to the range of 13 to 21 at%. These amorphous alloys are so ductile that no cracks are observed even after closely contacted bending test. The Vickers hardness and crystallization temperature increase from 435 to 530 DPN and from 628 to 707 K, respectively, with germanium content, and the tensile fracture strength is about 1460 MPa. Furthermore, the amorphous alloys exhibit a superconducting transition which occurs very sharply. The superconducting transition temperature (Tc) increases with decreasing germanium content and reaches a maximum value of 2.88 K for Zr87Ge13. The upper critical magnetic field for Zr87Ge13 alloy was of the order of 21.8 kOe at 2.0 K and the critical current density for Zr85Ge15 alloy was about 175 A cm−2 at 1.70 K in the absence of an applied field. The upper critical field gradient atTc and the electrical resistivity at 4.2 K increase significantly from 24.6 to 31.5 kOe K−1 and from 235 to 310μΩcm, respectively, with the amount of germanium. The Ginzburg-Landau (GL) parameterк and the GL coherence length §GL (0) were estimated to be 72 to 111 and about 7.9 nm, respectively, from these experimental values by using the Ginzburg-Landau-Abrikosov-Gorkov (GLAG) theory and hence it is concluded that the Zr-Ge amorphous alloys are extremely “soft” type-II superconductor with high degree of dirtiness which possesses theTc values higher than zirconium metal, in addition to high strength combined with good ductility.

Stability of amorphous alloys

The thermal stability of a number of Ti-base and Zr-base amorphous alloys was studied by means of differential scanning calorimetry. The crystallization temperatures of these amorphous alloys and those reported in the literature for a variety of other amorphous alloys (actinide-base alloys an refractory metal-base alloys) were analysed in terms of the corresponding formation enthalpies. It is shown that there is no correlation between the crystallization temperatures and the formation enthalpies. On the other hand the crystallization temperatures were found to scale more or less linearly to the corresponding formation enthalpies of a hole the size of the smaller type of atom in the binary amorphous alloys.

Experimental and calculated EXAFS spectra of a binary amorphous alloy

The Cu K shell EXAFS spectrum of a binary amorphous alloy of Cu57Zr43 has been calculated using a model structure generated by computer. The results showed a general agreement with the experimental spectrum measured for a melt-spun amorphous alloy with the same composition. Calculation showed that interference between two partial spectra of different pairs and structural disorder inherent in the amorphous structure seriously reduced the magnitude of the spectrum, making it difficult to deduce structural information from the measured EXAFS spectrum. However, the multiple scattering contribution to the EXAFS spectrum is found to be negligibly small, as well as the contribution from the atoms which are not nearest neighbours, compared with the nearest neighbour contributions; the EXAFS measurement can be useful for obtaining structural information on the nearest neighbours shells of binary amorphous alloys, if combined with complementary information.

Magnetic and stress annealing of Fe 80T 3B 17 amorphous alloys

The influence of transition metal additives to eutectic Fe-B on the magnetic and stress induced anisotropy was investigated. The results are compared with the same properties of binary Fe-B amorphous alloys and treated by taking into account the chemical and physical properties of the transition metal in question.

Thermal stability data of amorphous binary alloys

Data on the thermal stability of amorphous (glassy) binary alloys are compiled. Where available, alloy preparation method, crystallization temperature and method of measurement of crystallization temperature are tabulated. Other relevant aspects such as crystallized phases and compositions, glass transition temperature and analytical parameter variations also are given when data are available.

The Curie temperature and magnetization of Fe-base amorphous binary alloys containing transition metal

Several kinds of Fe-base amorphous alloys with transition metals were prepared by means of a co-sputtering technique. The reduction of the magnetic moment of Fe-Ta and Fe-Nb amorphous alloys is much more pronounced than that of Fe-Hf and Fe-Zr amorphous alloys. Fe-Mo, Fe-V and Fe-W amorphous alloys are paramagnetic. The concentration dependence of the Curie temperature also exhibits a similar tendency. Such behavior can be explained by a d-band filling model. The magnetic-carrier ratio is larger than unity, indicating itinerant magnetic behavior. The reduced magnetization curves of the present alloys are flatter than those of crystalline Ni and Fe, and Co-base amorphous alloys.

Bonding in liquid and amorphous binary semiconductor alloys

Abstract Bonding at stoichiometry and away from stoichiometry in binary ordered non-crystalline semiconductors is classified into covalent, ionic and metallic types. The composition dependence of their transport properties is shown to depend principally on the bonding configuration of any excess of a constituent beyond stoichiometry (compensated covalent, dative covalent or ionic) and not on whether the bonding at stoichiometry itself is covalent or ionic. Band models are introduced which explain the composition dependence of transport and optical properties of CsAu, GaAs, MgBi, MgSb, LiPb, CsSb, GaTe, GeTe and PbTe alloys. It is suggested that substitutional doping might be observable in a-GaP or a-GaAs over a small range of off-stoichiometric compositions. The group-IV chalcogenides show examples of both compensated covalent responses (for example, GeTe) and doped, ionic responses (for example, PbTe), depending on ionicity. It is proposed that in non-crystalline phases a critical value of covalent gap separates those systems existing in a 4 : 2 coordinated SiO2-like covalent structure from those with an ionic PbTe-type structure.

Flux flow and critical currents in an amorphous superconductor Zr85Si15

Abstract Studies have been performed on the resistive states in the superconducting mixed state of the amorphous binary alloy Zr85Si15(Tc=2.71K) prepared by the improved liquid quenching technique. Observed critical currents are extremely low so that the flux flow resistivity can be well defined in the whole range of the magnetic field except just below Hc2 where sharp peak effect appears. We obtained the GL parameter κ=130 and GL coherence lengths ξ ★ (0)=70 A that can be estimated from H★c2(0), the extrapolated value using the Kim's law. It is the amorphous state that brings about a high κ and extremely “soft” type II superconductivity.