Multicomponent Metallic Glasses Research Articles

Internal friction of hydrogen-doped metallic glasses

Abstract The hydrogen internal friction (HIF) has been measured for six multi-component metallic glasses. The HIF peak is quite broad with the peak temperature T p decreasing with increasing peak height, Q p −1 . Q p −1 versus T p relation is quite different among the alloys, suggesting a variety of hydrogen site energy distribution depending on the alloy composition. Considering the fact that two-level systems in metallic glasses for hydrogen jump are far from ideal, the observed relaxation strength is impossible to be interpreted in terms of a Snoek-type relaxation mechanism. A new hydrogen relaxation mechanism of a microscopic Gorsky effect has been proposed, where a large heterogeneity of elastic modulus in amorphous structure causes stress-induced hydrogen redistribution in a microscopic scale.

Internal friction of hydrogen-doped metallic glasses of high glass forming ability

Abstract Seven multi-component metallic glasses of high glass forming ability (four Zr-based, a Mg-based, a Pd-based and a La-based glasses) have been hydrogenized electrolytically and internal friction has been measured at temperatures between 80 and 400 K. Hydrogen damping has been observed in every alloy; the internal friction peak is quite broad, where the peak value increases and then decreases and the peak temperature decreases with increasing hydrogen content. Compared with the results of the hydrogen damping in binary metallic glasses so far reported, the peak height versus peak temperature relation is generally shifted to higher temperature side in multi-component glasses, the origin of which has been discussed.

Evaluation of the optimum solute concentration for good glass forming ability in multicomponent metallic glasses

Previous work suggests that the size factor may be the most crucial one on the glass forming ability (GFA). But the alloys in a system have significant deference for GFA. A criterion λ n is defined in the present work to comprehensively evaluate concentration dependence of GFA of alloys in a system. It is found that the values of λ n of bulk glass formers with greatest GFA in Zr-, Pd-, Mg-, Nd- and Fe-based systems are nearly constant of 0.18. Based on the mathematical description of regular polytopes and the dense random packing of hard sphere (DRPHS) model, a cluster model is suggested. This model provides the physical meaningful origin of the λ n from the view of free volume. The glass structure of bulk glass formers with λ n ≈0.18 has optimum defect concentration within the framework of the cluster model. In the term of λ n criterion, an alloy with λ n of about 0.18 will be one of bulk glass former candidates, which is verified by the experimental result of ZrAlNi system.

Mechanical response of Zr-based metallic glass

The new family of Zr-based multicomponent metallic glasses shows a beneficial combination of yield strength value as high as 2 GPa and microplasticity of up to 1% at room temperature and excellent glass-forming ability in a wide supercooled liquid region. Partial devitrification of glassy alloys upon heating or hot working above the glass transition temperature can lead to formation of nanocrystalline precipitates in the glassy matrix. In this case, the mechanical properties depend on the amount of crystalline precipitates. The nature of the brittle crystalline intermetallic phases is likely to dominate the mechanical behavior, leading to the observed decrease in ductility for the annealed samples since the deformation is no longer governed by the deformation mechanism of the amorphous phase. A fully crystallized alloy upon heating has revealed increasing ductility with temperature, exhibiting superplastic-like deformation with high elongation.

Synthesis and Characterization of Amorphous Metallic Alloy Thin Films for MEMS Applications

ABSTRACTMicrostructures of multi-component amorphous metallic glass alloys are becoming increasingly important due to their excellent mechanical properties and low coefficient of friction. In this work, thin films of Zr-Ti-Cu-Ni-Be have been deposited by DC magnetron sputtering in view of exploring their potential technological applications in fields such as Micro Electro Mechanical Systems (MEMS). Their structure, composition, surface morphology, mechanical properties viz., hardness and Young's modulus were analyzed using X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Nanoindentation. Influence of the deposition parameters of sputtering pressure and power upon the composition and surface morphology of these films has been evidenced by SEM, and AFM analysis, showing that such a process yields very smooth films with target composition at low sputtering pressures. These studies are useful in understanding the multicomponent sputtering process.

Calculations of Crystallization Temperature of Multicomponent Metallic Glasses

A model for calculating crystallization temperature (T x ) of multicomponent metallic glasses is proposed by modifying the Miedema's model which is used for calculating T x of binary systems. The calculations were carried out for nearly 900 metallic glasses including 470 binary and 398 ternary alloys. In the present model, the cavity formation energy (ΔH for cavity ) for multicomponent metallic glasses was theoretically derived on the basis of the Miedema's model. The equation for expressing the relation between experimental T x and theoretical ΔH for cavity was statistically analyzed by the least-squares method, yielding T x = 4.16 x ΔH for cavity + 318. The binary and ternary systems tend to show different equations between Tx and ΔH for cavity . The inherent equation in each system was analyzed as simultaneous achievement of the increase in stability of metallic glasses and decrease in ΔH for cavity due to multicomponent alloying. Furthermore, the glass-forming ability was predicted by reduced crystallization temperature instead of reduced glass transition temperature. As a result, it was found that reduced crystallization temperature can be calculated close to reduced glass transition temperature except for Pt-, Pd- and La-based systems. It is of great importance that T x can be calculated for multicomponent metallic glasses by semi-empirical method.

Computer-Aided Development of Multicomponent Metallic Glasses

ABSTRACTAsynthesized calculation model for developing metallic glasses has been created by taking into account criteria for the achievement of high glass-forming ability (GFA) and viscosity. The model deals with amorphous-forming composition region (AFCR), crystallization temperature (Tx) and three GFA factors: critical cooling rate (Rc), reduced glass-transition temperature (Tg/Tm) and supercooled liquid region (ΔTx=Tx-Tg) where Tg and Tm are glass transition and melting temperature, respectively. The principle of the model is based on thermodynamic functions for multicomponent systems, i.e., mismatch entropy and mixing enthalpy which express the criteria in terms of the number of elements, atomic size differences and the heat of mixing. By combining these thermodynamic quantities with the Miedema's semi-empirical model, AFCR was calculated, and was compared with the experimental results. The GFA factors were also analyzed from viscosity. The Rc was derived from transformation diagram of metallic glasses for crystallization while ΔTx was calculated by solving a differential equation expressing the change in free volume with temperature. As a result of these analyses, Rc-Tg/Tm and R-ΔTx diagrams were found to fit with the experimental results qualitatively. Furthermore, crystallization temperature (Tx) was also calculated for multicomponent metallic glasses by the modification of the Miedema's binary model for the calculation of Tx. The reduced crystallization temperature (Tx/Tl), where Tl is liquidus temperature, was calculated for evaluating GFA of metallic glasses instead of Tg/Tm. Some of the calculation methods used in the present study have theadvantage giving results as a function of composition; thus, there exists possibility to lead to the prediction of glassy alloys compositions. In this sense, the present calculation methods are completely different to the current method for the development of new metallic glasses relying on the empirical criteria which suggest only appropriate systems and/or elements of the alloysfor the achievement of high GFA. In near future, this kind of calculation technique can be used for the prediction of optimal compositions of the metallic glasses with high GFA.

Novel Fe70Zr10Ni6Al4Si6B4 thick metallic glass coating produced by laser cladding

A novel multicomponent thick metallic glass coating has been synthesised by laser cladding. The maximum coating thickness was 1 mm. The clad cooling rate restrained the epitaxial growth of dendrites in the metallic glass coating. The metallic glass had high glass forming ability with a wide supercooled liquid region ranging from 59 to 70 K. The metallic glass coating also revealed high hardness and good corrosion resistance.

Bulk Nanostructured Multicomponent Alloys

Bulk nanostructured composite materials can be obtained by partial devitrification of slowly cooled bulk glass-forming multicomponent metallic glasses or by blending a glassy matrix alloy with insoluble second-phase particles by solid state processing. Their properties are discussed with respect to the effect of the second phases on the thermal stability and on the mechanical properties at room temperature as well as at temperatures around the glass-transition temperature, Tg. Microhardness measurements at room temperature reveal a substantial increase in the hardness of the composites because of the uniform distribution of nanoscale particles in the glassy matrix. Also, there is a significant increase in yield strength with increasing volume fraction of particles. At elevated temperatures around Tg volume fractions of up to 40 vol.-% of nanoscaled particles yield no significant change in strength as compared with the particle-free material, but the deformation behavior of the composites is mainly controlled by the Newtonian viscous flow of the glassy matrix phase. This easy-flow behavior opens a promising route for shaping complex parts of bulk nanostructured composites derived from metallic glasses at moderate temperatures and high strain rates.

Bulk Nanostructured Multicomponent Alloys

Bulk nanostructured composite materials can be obtained by partial devitrification of slowly cooled bulk glass-forming multicomponent metallic glasses or by blending a glassy matrix alloy with insoluble second-phase particles by solid state processing. Their properties are discussed with respect to the effect of the second phases on the thermal stability and on the mechanical properties at room temperature as well as at temperatures around the glass-transition temperature, Tg. Microhardness measurements at room temperature reveal a substantial increase in the hardness of the composites because of the uniform distribution of nanoscale particles in the glassy matrix. Also, there is a significant increase in yield strength with increasing volume fraction of particles. At elevated temperatures around Tg volume fractions of up to 40 vol.-% of nanoscaled particles yield no significant change in strength as compared with the particle-free material, but the deformation behavior of the composites is mainly controlled by the Newtonian viscous flow of the glassy matrix phase. This easy-flow behavior opens a promising route for shaping complex parts of bulk nanostructured composites derived from metallic glasses at moderate temperatures and high strain rates.

Nucleation and growth of a multicomponent metallic glass

The metallic glass samples of Fe 67Co18B14Si1 (2605CO), prepared by the melt spinning technique were procured from the Allied Corporation. The kinetics of crystallization of this multicomponent glassy alloy is studied using differential scanning calorimetry (DSC). The crystallization data have been examined in terms of modified Kissinger and Matusita equations for the nonisothermal crystallization. The results show enhanced bulk nucleation in general. At high heating rates added to it is surface induced abnormal grain growth resulting in fractal dimensionality.

Metallic glasses

Multicomponent metallic glasses are being made in ever greater dimensions, and subjected to a wider range of shaping processes. Compositions are under active development to improve soft-magnetic, hard-magnetic and mechanical properties. Significant advances have also been made in exploiting metallic glasses as precursors in making ultra-fine grained materials with useful properties.

Some evidence for ‘directional atomic pair ordering’ in a cobalt-based metallic glass

Time-of-flight neutron diffraction has been used to study structural anisotropy in a wide-ribbon sample of the multicomponent metallic glass Fe 4Co 67Cr 7Si 8B 14 prepared by continuous casting. A planar sample held at 45 ° to the incident beam was examined by two stationary counters at 90 ° left and 90 ° right, so that the directional structure factors, S l(Q), S w(Q), S t(Q) corresponding to the three orthogonal directions in the ribbon (length l, width w and thickness t) were determined. It was found that the directional Structure Factor S t(Q) had stronger oscillations than S l(Q) and S w(Q) . Comparison of the directional S(Q) with the total structure factors for FeB and CoB glasses suggest that the result may be tentatively associated with ‘atomic directional pair ordering’ of the Fe-Fe first neighbour pairs in the t direction. The diffraction data have been analysed in the context of the atomic level stress model of metallic glass structures.

Mechanical alloying of highly processable glassy alloys

Glasses are generally produced from the undercooled liquid state by rapid quenching methods or quasi-statically at slow cooling by the effective control of heterogeneous nucleation sites. For metallic systems the latter method recently has led to the development of multicomponent metallic glasses with large glass forming ability and a wide supercooled liquid region before crystallization. Large-scale bulk samples of such alloys can be produced by conventional casting techniques. Alternatively, glass formation can be achieved by solid-state processing without passing through the liquid state. This crystal-to-glass transition is observed when a sufficiently high energy level is reached and kinetic conditions prevent the establishment of equilibrium. Hence, mechanical alloying as a special form of solid-state reaction technique and subsequent consolidation of the resulting powders above the glass transition temperature can be used to prepare bulk metallic glasses via the powder metallurgy route. The glass formation and the thermal stability of mechanically alloyed glassy alloys are compared with data for melt quenched samples showing that basically the same glassy state can be reached approaching it from the liquid or the solid state. Special emphasis is given to the glass forming ranges achievable by the different techniques and to the influence of impurities. Results for consolidated bulk samples are presented and compared with data for cast bulk specimens.

Solidification Analyses for the Fabrication of Bulky Multicomponent Metallic Glasses and their Properties

AbstractThe liquid-crystalline transformation during continuous cooling was examined for a Zr60Al10Ni10Cu15Pd5 alloy which was ejected into a wedge-shape cavity in a copper mold or solidified on a copper hearth by unidirectional arc melting. The structure consists of a glassy phase in the wedge angles smaller than 10 degrees and changes to glassy and crystalline phases in the higher angle range. The start (Cs) and termination (Ct) points for the transformation were determined and the continuous-cooling-transformation (C. C. T. ) curves were constructed. The nose temperature (Tn) and the time (tn) up to the nose point in the C. C. T. curves were 1018 K and 0.93 s. The critical cooling rate for glass formation defined by (Tm-Tn)/tn is 110 K/s. Furthermore, with the aim of clarifying a solidification condition for formation of a bulk glassy alloy by unidirectional arc melting, the relation between the formation of a glassy phase and the solidification parameters of moving velocity of liquid/solid interface (V), temperature gradient (G) and cooling rale (R) was examined. The glassy phase was obtained in the condition of V>3 mm/s, G>4 K/mm and R>40 K/s. The supercooling reaches 385 K at 40 K/s. The large supercooling ability is presumably due to the formation of a highly dense randomly packed structure where the nucleation of a crystalline phase and the atomic rearrangement for growth reaction are difficult.

Strengthening of metallic glasses after high pressure working and low temperature annealing

The effects of high pressure working and low temperature annealing on the structure and microhardness of Fe-, FeNi- and Co-based metallic glasses have been investigated. The possibility of strengthening has been found for both binary and multicomponent metallic glasses. The behaviour of the microhardness dependence on the applied pressure, with a microhardness maximum at 3–5 GPa, and the behaviour of the microhardness dependence on the temperature of annealing, with two maxima, are discussed in terms of rearrangements of structural defects in metallic glasses. A certain similarity of high pressure working and low temperature annealing effects on the structure and microhardness of metallic glasses has been found.

Studies on the corrosion of two multicomponent iron base metallic glasses in potassium sulphate solution

Corrosion studies were carried out on two multicomponent iron based metallic glasses, Fe81B13.5Si3.5C2 (METGLAS 2605SC) and Fe87Co18B14Si (METGLAS 2605CO), in a 0.5 M potassium sulphate solution of pH 4.0. Weight loss measurements indicated comparable corrosion rates for the two alloys. Potentiostatic polarization studies showed nearly the same cathodic currents for these alloys during cathodic polarization. During anodic polarization, lower currents were obtained for the 2605CO alloy as compared to the 2605SC alloy. Neither of the alloys exhibited passivity during anodic polarization. Auger Electron Spectroscopy and X-ray Photo-electron Spectroscopy studies showed that FeOOH was the major constituent of the film formed on the 2605SC alloy and that in the case of the 2605CO alloy, a mixture of FeOOH, Co(OH)2 and CoO was present in the corrosion film. An enrichment of C, B, and Si occurred in the film formed on the first alloy while that formed on the latter was enriched in Co. These two amorphous alloys were found to be more resistant to corrosion in potassium sulphate solution as compared to the binary Fe80B20 glass. Enrichment of the surface film in the constituent metalloid species in the case of the 2605SC glass and Co enrichment of this film in the case of the 2605CO glass appears to contribute to this enhanced corrosion resistance.

Mechanism of structural relaxation in a metallic glass

In the present paper, the relaxation phenomena in a multicomponent metallic glass, Ni 45 Fe 5 Co 20 Cr 10 Mo 4 B 16 , has been investigated through electrical resistance, acoustic emission and Mössbauer spectroscopy to understand the mechanism of structural relaxation in the amorphous matrix. Isothermal electrical resistance measurements clearly show that the structural relaxation occurs discontinuously through a number of discrete steps. There exists a good deal of correspondence between the variations of the acoustic emissions and the electrical resistance with time and temperature. It is shown that the stepwise change in the electrical resistance arises due to the viscous flow in the matrix which is associated with the acoustic emissions. Fourier deconvolution analysis of the Mössbauer spectra recorded at room temperature was carried out for the as-received sample as well as those relaxed at various annealing temperatures. The QS-distributions and QS-IS correlation, so obtained, clearly show that the structural relaxation induces a small but definite change in the short-range order. Present results indicate that the viscoelastic flow is the primary unit process responsible for structural relaxations in the matrix.

Characterisation of models of multicomponent amorphous metals: The radical alternative to the Voronoi polyhedron

A generalisation of the Voronoi polyhedron procedure for examining the detailed local structures in multicomponent metallic glass models is described. The resulting radical plane polyhedra depend upon the relative sizes of the model atoms and form an assembly of polyhedra which completely fill space. Application of the method to two slightly different models of amorphous Pd 4Si illustrates the sensitivity of the technique to changes in local structure, and how such changes in polyhedron topology may relate to the changes in real space The method may be particularly useful in examining local changes on structural relaxation.

Calculation of the Crystallization Behaviour of Metallic Glasses

ABSTRACTA method is proposed to calculate the crystallization behaviour of multicomponent metallic glasses with several phases. Various geometric shapes of precipitate can be considered. The model also takes into account changes in concentration which arise during precipitation.