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In this work, melt-spun ribbons of AlSi10Mg added with modifiers (Er, Sr, or nano-TiB2) were produced to investigate the combined effect of modification and rapid solidification on eutectic Si. The resulting eutectic microstructures are more isotropic in comparison to that of the base alloy affecting the mechanical properties of the alloys. The modification of Si morphology and supersaturation caused by the modifiers were investigated by microscopy, X-ray diffraction, and differential scanning calorimetry. Compared to melt-spun AlSi10Mg, the eutectic Si network is finer and less continuous when Er or Sr is added, and disrupted with rounded crystals dispersed in the matrix when adding nano-TiB2. The level of supersaturation decreases in the order Er–nano-TiB2–Sr. A transition from columnar Al grains at the wheel side to finer equiaxed grains at the air side was found in the unmodified ribbon and in the one containing nano-TiB2 by means of electron backscattered diffraction. The Er- and Sr-modified ribbons display equiaxed Al grains of constant size throughout their thickness. The average hardness obtained by nano-indentation tests was lower than that of AlSi10Mg. The less continuous Si network causes the hardness drop but provides more isotropic mechanical properties.

Gas atomization is the most used powder production technique since it provides good control on particles shape, surface oxidation and dimension. It is a rapid solidification technique involving fast cooling rates, which are strictly correlated to particle size. This relationship is typically described with a power law function that can be determined experimentally by measuring the microstructural length-scale or through the application of a heat transfer model. Both paths were exploited in the present work focusing on a gas-atomized Al-4.5Cu alloy. Atomized powders were characterized by means of X-ray diffraction, differential scanning calorimetry, light and scanning electron microscopy to investigate the relationship between cooling rate and microstructure length-scale. A recently proposed semi-empirical model was validated and discussed in terms of a physically based heat transfer approach. The change in gas-to-melt mass flow ratio (GMR) was also investigated showing that it does not affect appreciably the relationship between solidification rate and particle size, but does increase the Cu supersaturation in the powders of finer size.

Metal parts produced by Additive Manufacturing, and in particular Laser Powder Bed Fusion (LPBF), suffer from residual stresses due to high thermal gradients causing cyclic expansion and contraction of the alloy. This work deals with the determination of residual stress in rapidly solidified AlSi10Mg samples using two non-destructive techniques: Raman spectroscopy, rapid, unconventional but applicable to Al Si alloys, and XRD (ω-method), used as benchmark, being a classical method for determining residual stresses. Al stress level was studied by XRD both on the surface of LPBF samples and in the interior, after in-depth sectioning. Raman was employed to assess the stress on Si. The effect of particle size and stress on the Raman was separated determining the size distribution of Si particles, making Raman suitable to study residual stresses in alloys containing free Si. Al and Si stresses were evaluated also by means of the Williamson-Hall method: stresses are of tensile type with agreement among all methods. Considering the alloy as a composite, stress on Si was estimated using the Eshelby's model, showing that larger eutectic particles undergo lower stress with respect to nanometric precipitates.

Nanoporous gold thin films have been fabricated through chemical de-alloying of Au-based nanoglass with a nanocolumnar structure, with composition Au40Cu28Ag7Pd5Si20 (at.%), that had previously been deposited by magnetron sputtering. By varying the de-alloying conditions, gold ligaments ranging from 20 to 100 nm were obtained. The microstructure and chemical composition of the as-prepared films were characterised by various techniques. Surface-enhanced Raman scattering (SERS) of thin films was investigated using rhodamine 6G. The results indicate that the main microstructural features with interconnected ligaments and defects of nanoporous gold result in significant SERS enhancement.

In Selective Laser Melting (SLM) layers of atomized powder are spread sequentially on a building platform and melted locally by a laser beam. The melt pool is quenched by the underlying material. SLM of AlSi10Mg alloys results in the development of microstructures consisting of supersaturated primary Al-rich phase surrounded by varied amounts of Al-Si eutectic. The origin of such microstructure is not fully understood. For insight into this issue, this work compares the results of processing AlS10Mgi alloys by SLM and by single-step rapid solidification techniques: Melt Spinning (MS) and Copper Mould Casting (CMC) achieving a range of cooling rates and microstructures which are analysed by means of microscopy, XRD and DSC. The results obtained in these experiments together with the literature available on rapidly solidified Al-Si alloys suggest a correlation among microstructures of the products made with the three techniques. Data on lattice parameter and enthalpy of Si precipitation from primary Al concur in indicating that Si supersaturation scales in the order SLM > CMC > MS. The type and size of microstructural features, i.e. cells, columns, fibrous and lamellar eutectic, reveal the role of solidification conditions (undercooling, recalescence) and precipitation in the solid state for all techniques. Dendrite growth modelling validates the solidification results.

A Au 20 Cu 48 Ag 7 Pd 5 Si 20 metallic glass precursor has been used to synthesize nanoporous gold by chemical de-alloying in a mixture of HNO 3 and HF. Gold ligaments of size ranging from 45 to 100 nm were obtained as a function of HNO 3 concentration, electrolyte temperature and de-alloying time. The as-prepared nanoporous gold exhibited strong surface enhanced Raman scattering (SERS) effect using 4,4′-bi-pyridine as probe molecule. For application in melamine sensing, the detection limit of 10 −6 M was achieved, which indicated that this biocompatible material has great potential as SERS active substrate.

In this work, the chemical de-alloying behavior of Au30Cu38Ag7Pd5Si20(at.%) amorphous alloy which was rapidly solidified from the melt in the form of ribbons were investigated. First a comparison between samples de-alloyed in nitric acid with and without HF was conducted to achieve homogeneous de-alloying process. Then the morphology and structure of nanoporous gold (NPG) were adjusted by tuning the de-alloying parameters, such as HNO3 concentration, electrolyte temperature and de-alloying time. Finally the surface enhanced Raman scattering(SERS) capability of the as-prepared NPG was evaluated using 4,4′-bi-pyridine as probe molecule.

Banded and discontinuous eutectic microstructures were found in melt quenched ribbons and laser melted single tracks of an Al-3%wt Er alloy, respectively. The bands occurring in ribbons are made of alternate primary α-Al phase and eutectic. Their formation is well described by the Han-Trivedi model for banding in alloy solidification. Microstructure fluctuations between fibrous and discontinuous eutectic are seen in laser melted single tracks on the same length scale of bands due to change in local temperature gradient. Overall, various transitions in phase morphology are found in thin zones of material constituting a valuable guideline for interpretation of the solidification mechanism. Nano-indentation tests show that the fine microstructures induce substantial hardening.

For metallic glass synthesis and processing the possible formation of crystals should be described by CCT curves. Motivated by results of the synthesis of wires of the Fe67Mo4.5Cr2.3Al2Si3C7P8.7B5.5 alloy by melt extraction, a methodology is proposed to compute TTT and CCT curves based on the classical nucleation and growth theory. The thermophysical parameters needed for the calculation are entirely derived from DSC experiments, including those expressing the Vogel-Fulcher-Tammann equation for viscosity. The critical cooling rate for amorphous wires is estimated and matched with the CCT curve. Then, the corresponding computed TTT curve is shown to reproduce well the experimental results of isothermal crystallization of the ribbons.

A new high entropy alloy (HEA) has been synthesized using a predictive method recently developed. The alloy performance is compared to that of a benchmark commercial alloys (Stellite®6) as wear resistance material for coating automotive engine valves.Using step by step predictive parameters the occurrence of an fcc solid solution with entropy of mixing higher than the conventional limit of 1.5 R (with R the gas constant) was singled out and verified in the FeCoCrNiW0.3 composition. The as-cast ingot displays W segregation within the fcc grains as revealed by Scanning Electron Microscopy and X-ray Diffraction (XRD) patterns which were fitted by assuming the arc melted alloy contains two solid solutions. The segregation is eliminated by annealing at 1200 °C for 3 h. In these sample a (Co-Fe)7W6-type phase is found embedded in the solid solution matrix. Slip bands around indentation marks suggest low stacking fault energy of FeCoCrNiW0.3. The high entropy alloy (HEA) has been hardened by adding 5 at.% C to form carbides inside the fcc matrix. Conventional hardness, scratch and oxidation resistance tests show that the alloy compares well with Co-based Stellite®6 being the content of the expensive and strategical elements halved with respect to it. Keywords: High entropy alloy, XRD, Scratch, Hardness, Dispersion strengthening

Three dimensional nanoporous gold, with an average ligament size of 50 nm, was fabricated by chemical de-alloying from a new Au based metallic glass precursor. The resultant nanoporous gold gives rise to superior surface enhanced Raman scattering (SERS) capability using 4,4′-bi-pyridine as probe molecules. The SERS intensity mapping images confirm the presence of hot spots. A low detection limit down to 10 − 14 M for bipyridine was achieved, which is attributed to the localized enhanced electromagnetic fields around nano-sized ligaments, the electromagnetic coupling between ligaments, and the trapped SERS sensitive atoms.

De-alloying, i.e. selective dissolution of alloys, is currently studied to produce nanoporous gold items suited for use in catalysis, electrochemical applications, sensors and actuators. Both crystalline and amorphous alloys can be selectively etched. In the former, less noble atoms are removed from surface terraces of grains layer by layer, while noble ones form mounds. These evolve by undercutting and electrolyte percolation to form a ligament network. The mechanism of ligament development by de-alloying amorphous alloys is unknown. Here we show that for de-alloying a Au-based glass, in this case Au40Cu28Ag7Pd5Si20, percolation of the electrolyte through cracks of the native surface oxide initiates the formation of protuberances which are soon undercut. An interlayer develops, where Au crystals germinate, grow to nanometer size by diffusion and impinge. This is how ligaments start to coarsen. The interlayer is found at all stages between coarsened ligaments and amorphous phase. The ligaments are defective polycrystals, as opposed to single crystals obtained from crystalline alloys.

The development of a new generation of ultra-sensitive sensors for analytical and bio-diagnostic devices requires a strong signal in front of very small quantity of analyte, often present in complex and interfering matrix. Taking advantage of peculiar plasmonic properties of nanoporous gold (NPG), a promising sensor for selective detection of Human Serum Albumin (HSA), a proof-of-concept bioanalyte, was prepared and tested in a conventional micro-Raman spectrometer using Surface Enhanced Raman Spectroscopy (SERS). NPG was synthesized by chemical de-alloying of an amorphous precursor, Au20Cu48Ag7Pd5Si20, starting from melt spun ribbons. A fully de-alloyed ribbon with ligaments of about 60 nm was obtained after 4 h of de-alloying at 70 °C and 10 M HNO3 + 0.5 M HF. This material is self-standing, mechanically resistant, and suitable for wide range of applications. At this stage, NPG is SERS-active toward several molecules, including pyridine, bi-pyridine, and rhodamine at very low concentration. In order to obtain the selective binding properties required to detect molecules in bio-diagnostic applications, immuno-functionalization of NPG was carried out by using an anti-HSA antibody (Ab-anti-HSA) covalently grafted on gold ligaments via the 4-aminothiophenol (4ATP) Raman probe, yielding the SERS-active nanohybrid NPG-4ATP-Ab. SERS signal recorded at increasing HSA concentrations was used for the acquisition of SERS maps and a chemometric regression model allowed to calibrate the sensor. In the best experimental conditions, we were able to get quantitative analysis of HSA at ultra-low concentrations (0.1 ng/l) with SERS. The methodology proposed in this paper has to be considered a major step toward a calibrated device for ultra-sensitive detection of biomolecules by SERS detection.

A novel banded microstructure consisting of regular/anomalous eutectic has been found in hypoeutectic Co-61.8at%Si rapidly solidified by either copper mould casting and melt spinning. The bands originate because of varied undercooling and growth rate in the direction of heat flow towards the copper sinks. Diffusional effects (i. e. rejection of solute) in the presence of limited convection cause fluctuations in growth rates for which the role of recalescence is highlighted. Occasional primary phase/eutectic transitions were also found. The microstructures are contrasted with those seen in furnace cooled samples where diffusion fully occurred in a quiescent melt.

In this work, Pt nanoparticles were electrodeposited through cyclic voltammetry technique on three dimensional nanoporous gold prepared from Au-based metallic glass precursor by chemical de-alloying. The electro-catalytic properties of the as-prepared samples were tested through potential cycling towards methanol oxidation in alkaline solution. Current density plots vs scan numbers indicate that the electrodes are active for the electro-oxidation of methanol and the Pt nanoparticles electrodeposited on gold ligaments contribute to increasing catalytic properties. In particular, results indicate that nanoporous gold with 30 cycles of Pt electrodeposition exhibits competitive higher activity and longer durability towards methanol electro-oxidation.

The material palette available for Laser Powder Bed Fusion (LPBF) process is still limited. The mixing of different powders, here AlSi10Mg + Cu, and alloy synthesis by Single Scan Tracks (SSTs) and Melt Spinning (MS) were performed in this work for fast testing the new composition and reducing the building time and amount of powder employed. Then LPBF massive samples were manufactured to verify the outcome of the procedure. In all three cases an AlSi10Mg + Cu alloy was obtained, some residual inhomogeneity in Cu distribution being found in the SST sample. Microstructural features of the LPBF sample are intermediate with respect to SST and MS ones in terms of cell size of primary Al, while the eutectic morphology of Si is close to that of the ribbons. Nanoindentation tests showed an increase in hardness of the Cu-added samples with respect to that of the base AlSi10Mg alloy. XRD results indicated the occurrence of supersaturation of both Si and Cu in the as quenched samples and DSC analyses provided information on temperature and enthalpy of exothermal signals due to precipitation.

X-NbTaTiZr, with X = Al,V,Cr and Sn , potential High Entropy Alloys obtained by arc melting were annealed to reveal the equilibrium constitution. AlNbTaTiZr and VNbTaTiZr alloys, made of two bcc solid solutions in the as-cast state, are composed of a bcc solid solution plus a minority phase, a Al–Zr intermetallic compound and a Zr–Ti hcp phase, respectively, while Cr and Sn containing alloys always present an intermetallic phase together with a bcc solid solution. Isochronal annealing on V - and Al- alloys revealed the mechanism of formation of the equilibrium microstructure. It is shown with an example in the AlNbTaTiZr system that stable high entropy phases (configurational entropy higher than 1.5 R ) can be identified in equimolar alloys and synthesized. The inspection of the equilibrium microstructures in equimolar compositions together with the data available in literature on single phase HEAs confirm the usefulness of the selection criterion to design equilibrium HEAs previously developed, provided the relevant parameters are employed within the suggested limiting values.

A novel catalyst for water splitting has been prepared by cyclic voltammetry (CV) deposition of amorphous MoS2 on nanoporous gold (NPG) obtained by electrochemical de-alloying a metallic glass precursor, Au40Cu28Ag7Pd5Si20 (at.%). As a function of number of CV cycles, Au ligaments are progressively encapsulated by a thin layer of amorphous MoS2 catalyst for hydrogen evolution. NPG provides a good substrate for deposition having excellent properties of handability and mechanical resistance in addition to catalytic activity, high conductivity and high surface area. Low onset potential, low Tafel slope and interesting values of exchange current density were obtained in linear sweep voltammetry of deposited samples. The synergistic behaviour of the multi-component material provides a highly efficient catalyst for hydrogen making of these samples a good candidate in some instances comparable to the conventional Pt catalyst for hydrogen evolution in acidic environment.

In this study, chemical de-alloying method was used to prepare nanoporous gold (NPG) from the Au containing amorphous alloy, with chemical composition of Au20Cu48Ag7Pd5Si20. Gold nanostructures were electrodeposited on the nanoporous gold by adjusting the applied potentials and deposition times. Using Rhodamine 6G (R6G) as probe molecule, the surface enhanced Raman scattering (SERS) activity of various Au nanostructures on nanoporous gold were compared. The dendritic nanostructures electrodeposited for 3000 s on NPG exhibited strongest SERS effect and high reproducibility. Using this best SERS active substrate for melamine sensing, the detection limit of 10−7 M was achieved.

In this study, Au-based nanoglasses in the form of thin films deposited by magnetron sputtering are comparatively dealloyed. The films have either nanograined or nanocolumnar microstructure, depending on the working pressure of Ar in the sputtering chamber. Nanocolumnar thin films exhibit much higher dealloying rate reducing effectively the dealloying time with respect to nanograined and homogenous thin films. Electrocatalysis experiments indicate that the resulting nanoporous films are active for the methanol electrooxidation, with promising results in term of stability especially for the dealloyed nanocolumnar film.

Corrosion studies in an acidic environment have been performed for the good Au40Cu28Pd5Ag7Si20 glass former with emphasis on the selective dissolution (de-alloying) process. The final porous microstructures obtained from fully amorphous ribbons and ribbons containing crystals as well as composition inhomogeneity in their amorphous matrix. The results are compared by using the same etching conditions. As reference, ribbons containing different crystalline fractions produced by isothermal annealing at temperatures in the glass transition region and then de-alloyed. The results show that a different mechanism of de-alloying operates for amorphous and crystallized materials. The finer homogenous nanoporous structure occurs after de-alloying a fully crystallized ribbon.

Four potential High Entropy Alloys, CrMoNbTiVWZr, Cr0.3NbMoTiZr0.3, Cr0.3NbMoTiV0.6Zr0.3 and Al0.6Cr0.3NbMoTiV0.6Zr0.3 have been designed using the indications provided by atomic radius and electronegativity mismatch parameters. Alloys were synthesized by arc melting and characterized in the as-cast state and after heat-treatment by X-ray Diffraction and Scanning Electron Microscope experiments. In the as-cast state all alloys have dendritic microstructure, although with varied shapes of dendrites, accompanied by a cubic Laves phase and an hcp phase in the region between the dendrites. After annealing at 1350 °C for 3 h it is shown that only non-equimolar compositions are constituted of bcc high entropy phase complying with the requirements for defining them as HEAs, with a small amount of secondary phases which help in providing high hardness.

High entropy alloys, i.e. solid solution phases, are sought in the X-NbTaTiZr equiatomic system where the X element was chosen as Al, Cr, V and Sn by applying recent criteria based on size and electronegativity mismatch of alloy components, number of itinerant and total valence electrons, and the temperature at which the free energy of mixing changes at the alloy composition. The alloys containing V and Al are mostly constituted by solid solutions in good agreement with prediction.

The existing correlation between the extensive properties, Δ H and Δ S , the enthalpy and entropy difference between liquid and crystal phases has been checked to relate metallic glasses to other classes of amorphous materials. Expressing the specific heat difference, Δ C p , of molten and crystalline metallic glass-formers as a function of temperature with different functional trends, parametric expressions of fragility are derived using relevant temperatures for alloys. It is shown that relationships between the Δ S g /Δ C p,g ratio and such temperatures are useful to estimate unknown quantities when the experimental determination of the specific heat is possible. Thermodynamic indicators of fragility are compared to the kinetic fragility obtained from viscosity data accounting for the estimated errors on parameters which are derived from extrapolations. The outcome of the analysis indicates that a relationship between thermodynamic and kinetic parameters exists. Moreover a systematic scatter for some alloys indicates a diverse behavior which can be ascribed to structure modification either in the liquid or in the solid reference state.

Nanoporous gold has been produced by the electrochemical dealloying of a Au 40 Cu 28 Ag 7 Pd 5 Si 20 metallic glass. Suitable conditions of potential and temperature of dealloying have been established from polarization curves and dealloying has been conducted at the critical potential of 1.05 V in three different electrolytes: 1 M HNO 3 , 1 M HClO 4 and 1 M H 2 SO 4 . The resulting material after 6 h of dealloying was constituted by ligaments made of pure Au and pores. The morphology was determined by SEM: ligaments of about 100 nm was observed and their size appears slightly larger (130 nm) when HNO 3 is used. In the first stages of dealloying (30–300 s), nanopores and nanocrystals, randomly oriented, were found by HRTEM. From these observations a diffusivity value for crystal growth was estimated. A change in growth mechanism was suggested when impingement occurs for long dealloying times. It is suggested that the ligament and pore morphology can be tailored in order to obtain materials with different chemical and physical properties.

Cold rolling of Al87Ni7La6 amorphous ribbons was performed on ribbons embedded in pure Al foils and ribbons alone, in order to study their deformation under constraint. A change in behaviour was observed for the two series of samples due to a different load distribution, so that ribbons alone was deformed up to ɛ = 0.029 without formation of cracks while, for composite samples, small fragments were always formed. In ribbons rolled alone, along with a macroscopic strain, a plastic deformation was observed at a finer scale, in the cavities present on the ribbon surface. The locally induced strain was quantified by taking into account the size change of cavities in samples rolled to different extents. The formation of shear bands and fracture occurring during cold rolling was studied for composite samples: the shear offset, interband spacing and distribution of fracture angles were determined. A Zr55Al20Ni12Cu8Ti5 amorphous ribbon was rolled with Al foils and the toughness value was estimated from the shear band offsets finding good agreement with literature data. Therefore, the toughness was estimated also for the Al-based samples obtaining the value of Kc = 28 MPa m1/2.

The process of de-alloying, i.e. removal of a less noble metal from an alloy, is applied here by electrochemical means to a Au-based metallic glass, Au 40 Cu 28 Ag 7 Pd 5 Si 20 , as a function of potential, temperature, and time. Very fine crystals nucleate with random orientation at the solid–electrolyte interface forming ligaments. The resulting material is constituted by ligaments made of pure Au and pores of smaller size whose dimensions coarsen up as a function of time to slightly above two hundred and below one hundred nanometers, respectively. The microstructure is uniform on both surfaces and across the ribbon. The extent of de-alloying is measured by monitoring the heat of crystallisation of the remaining amorphous phase giving linear trend vs time suggesting the reactions occur on continuously renewed surfaces.

The 18-karat Au43.3Cu31.8Al24.9 alloy displays shape memory effect. The parent phase has L21 structure which transforms to B2 at high temperature. The B2 phase is retained in metastable state by quenching from the B2 field. It then transforms irreversibly with an endothermic peak in Differential Scanning Calorimetry (DSC) to the stable L21 structure in the temperature range between 407 K and 435 K as a function of heating rate. The transformation is, therefore, entropy-driven. Details are reported on the enthalpy of transformation and its temperature dependence. The transformation is discussed with reference to the entropy content of phases as a function of temperature which counteracts austenite stability. The role of vacancy motion is outlined. A comparison is made with analogous transitions occurring in molecular substances and metallic materials.

Results of a thermophysical characterization of a Fe-Cr-Mo alloy in the solid and liquid phases are reported. Methods applied include calorimetry, dilatometry; the laser flash technique for thermal diffusivity measurement and ultrasound pulse echo for the measurement of the room temperature sound velocities and elastic constants. Density in the liquid phase and surface tension were measured by optical dilatometry and by the oscillating drop method on electromagnetic levitated specimen. In addition, surface tension and viscosity were measured by the oscillating drop method on board parabolic flights under reduced gravity conditions. The methods applied and results obtained are presented. This work represents a collaborative effort, including round robin measurements in different laboratories for a characterization of the basic thermophysical properties needed for process simulation.

The dealloying behaviour of Au 42 Cu 29 Ti 8 Si 21 and Au 44 Cu 31 Ti 4 Si 21 amorphous (wheel-side) and partially crystalline (air-side) ribbons was investigated using potentiostatic and galvanostatic etching. The resulting microstructures are: i) on the wheel-side homogeneous porosity with size from tens of nanometers to less than 1 μm in between Au crystals is largely found, ii) on the air-side the porosity occurs on two length-scales, submicrometer as on the opposite size and micrometer where crystals are removed. The importance of surface morphology in the formation of the microstructure is outlined. The role of diffusion and nucleation in the mechanism of surface gold enrichment is established.

Alloys displaying positive enthalpy of mixing demix below a critical temperature. In Co-Cu and related ternaries the miscibility gap is metastable, i.e. it occurs at temperatures lower than the liquidus. In order to study the liquid phase separation high melt undercooling is necessary. This was obtained via rapid solidification techniques using melt spinning and casting in moulding devices, as well as high temperature DSC experiments with samples embedded in a flux. Results are given for Co-Cu, Co-Cu-Fe and Co-Cu-Ni systems. Phase diagrams were optimised using the DSC data. The mechanism of phase separation was investigated by comparing samples produced under different cooling conditions. The hierarchy of microstructures obtained was interpreted accounting for the processing technique and the phase diagram. They constitute a database useful for the interpretation of the thermal history of samples processed in microgravity.

Properties related to the glass transition of metallic melts are reviewed both on empirical ground and using the statistics of local minima in the potential energy landscape of the material. For metallic alloys some correlations have been disputed (e.g., the one between the Kauzmann and VFT temperatures). In the first part of this report these issues are considered and the possible reasons for either good or poor correlation are outlined. Then the relationship of the glass transition to mechanical properties (e.g., strength, moduli) is described with special attention to the failure mechanism of amorphous alloys via shear band propagation. The relationships are discussed for glass-forming alloys in comparison also with properties of other families of glass-formers.

New multinary amorphous materials, based on gold, that can be produced in bulk form due to their high glass-forming tendency, were discovered recently. However little is known about their corrosion properties. In the present study, the characterization of Au 49 Cu 26 . 9 Ag 5.5 Pd 2.3 Si 16.3 amorphous ribbons produced by melt spinning is reported. Their corrosion properties were tested by incubating the samples in artificial sweat and by monitoring the changes in surface structure by SEM and XRD. Before incubation, the surface of the samples was amorphous and flat, characterized only by microfeatures due to the liquid contact with the wheel during quenching. After treatment with artificial sweat, the formation of nanosized crystallites of Au on the sample surface was observed. The surface chemical composition of both sides of the ribbon samples was investigated by XPS. Atomic concentration and chemical states of constituent elements before and after the incubation in artificial sweat were determined. The depth profiling of both sides ofthe samples was carried out by using Ar ion sputtering combined with cyclic XPS measurements. The segregation of Si on one side of the samples and the changes of chemical composition, caused by the treatment in artificial sweat, were revealed.

This contribution reviews the relationships between thermophysical properties of glass-forming alloys: glass transition, specific heat, entropy of fusion, fragility indexes, using recent models for ranking undercooled liquids and glasses. These rely on both empirical correlations and on the description of local minima in potential energy landscapes of the material.Then, the relationships between mechanical properties and some of the above quantities are considered and discussed with the aim of getting insight into the mechanism of shear band propagation during mechanical failure when, following up a shear offset event, a local temperature rise occurs and the shear band matures to give a runaway crack.

The H–La–Ni system has been assessed according to the CALPHAD method. To this purpose, an assessment of the La–Ni binary system has been taken from the literature, while the H–Ni system has been partially reassessed with respect to the liquid phase, in order to be consistent with generally used lattice stability of liquid hydrogen. A first assessment of binary H–La system has been carried out in this work. The binary LaH x phase has been described with the sublattice model, in order to take into account a composition variations for 2 ≤ x ≤ 3 . Calculated p – c – T curves and Van’t Hoff plots agree well with experimental data. In the ternary system, hydrogen absorption data have been considered for the LaNi 5 intermetallic compounds, leading to the LaNi 5 H 7 hydride. Because the compound and the hydride have the same structure, the equilibrium between the two phases has been described as miscibility gap. Also in this case, calculated p – c – T curves and Van’t Hoff plots agree rather well with experimental data. The equilibrium phases have been calculated in the ternary system. The present thermodynamic description can be a useful tool for predicting the hydrogen absorption and desorption behaviour in commercial vessels based on the AB 5 compounds.

Amorphous alloys are metastable phases which have generated considerable interest in recent years because of their promising properties. This review considers thermodynamic and kinetic aspects in the modelling of metallic amorphous phases. The relevant literature on the glass transition and the thermodynamics of amorphous phases is discussed in detail. The CALPHAD approach is used for thermodynamic modelling: it employs collected experimental data to obtain a reliable assessment of properties and metastable phase diagrams. Thermodynamic modelling of Short Range Order (SRO) in the liquid and glass transition is described and critically discussed with regard to rapid solidification experiments. Solid state amorphization and amorphization by means of deposition are also discussed. The extension to kinetics is then described, involving a number of modelling parameters. Predictions can thus be carried out of the Glass Forming Range (GFR), i.e. the composition range where glass formation is expected, according to different levels of approximation and for various processes. The importance of model parameters (thermodynamic driving force, interfacial energy, transport properties) is also assessed and some case studies (Cu–Zr, Fe–B and Cu–Mg–Y) are discussed. Recent results on the simulation of nanocrystals growth in amorphous materials are reported.

In this work, electrochemical de-alloying of an amorphous alloy, Au 40 Cu 28 Ag 7 Pd 5 Si 20 , cast in ribbon form by melt spinning, has been performed, obtaining self standing nanoporous materials suitable for use as electrodes for electrocatalytic applications. The de-alloying encompasses removal of less noble elements and the crystallization of Au, resulting in interconnected ligaments whose size and morphology are described as a function of time. Depending on de-alloying time, the crystals may contain residual amounts of Cu, Ag and Pd, as shown by Auger Electron Spectroscopy (AES), Energy Dispersive Spectroscopy (EDS) and Cyclic Voltammetry (CV) in a basic solution. Current density peaks in the 0.16–0.28 V range (vs Ag/AgCl) indicate that the porous ribbons are active for the electro-oxidation of methanol. The partially de-alloyed samples, which still partially contain the amorphous phase because of the shorter etching times, have finer ligaments and display peaks at lower potential. However, the current density decreases rapidly during repeated potential scans. This is attributed to the obstruction of Au sites, mainly by the Cu oxides formed during the scans. The fully de-alloyed ribbons display current peaks at about 0.20 V and remain active for hundreds of scans at more than 60% of the initial current density. They can be fully re-activated to achieve the same performance levels after a brief immersion in nitric acid. The good activity is due to trapped Ag and Pd atoms in combination with ligament morphology.

Methods to determine the fragility index, m , both in thermodynamic and kinetic terms are reviewed and applied to two Fe-based glass formers, Fe 40 Ni 40 P 14 B 6 and Fe 41 Co 7 Cr 15 Mo 14 C 15 B 6 Y 2 . The thermodynamic fragility is obtained from entropy curves based on experimental data of the liquid specific heat and of the enthalpy of transformation from glass or liquid to crystal phases. The thermodynamic fragility appears systematically higher than the kinetic one because of the large scatter of data and their extrapolation to obtain the Kauzmann temperature of vanishing entropy. A practical method to estimate the viscosity of glass formers in the undercooling regime was derived from the fragility index and its correlation with parameters of the VFT equation. It provides reasonable agreement with experimental data.

This work deals with the effect of Ni addition on the liquid–liquid phase separation in the Cu–Co system which displays a liquid metastable miscibility gap. Cu–Co–Ni samples with different compositions have been processed by differential scanning calorimetry using a fluxing technique to precisely determine transformation temperatures. The ternary phase diagram has been evaluated by Calphad, extrapolating the binary systems and optimizing ternary parameters using the experimental results of the present work. Ni additions reduce the demixing temperature, bringing the binodal line below the peritectic. The mechanisms of demixing and formation of microstructures have been clarified for low and high Ni content.

Experimental determinations of the glass transition and related properties in alloys are reviewed. Several recent measurements of viscosity, specific volume and heat capacity in the undercooling regime have become possible after the discovery of bulk glass forming alloys. The data allow verification of models on the kinetics and thermodynamics of such melts. The notion of melt fragility, borrowed from the description of inorganic and molecular glasses, has become popular also for metallic alloys: the kinetic fragility is described by the viscous behavior of the liquid and the thermodynamic fragility by the entropy loss on undercooling. The experimental viscosity data for metallic glass formers presently available can be reasonably framed within the strong–fragile classification. On the other hand, there are major discrepancies for the thermodynamic fragility of metallic glass formers with respect to conventional ones. The reason for such disagreement is twofold: on the experimental ground there are difficulties in obtaining fully reliable thermodynamic data in sufficiently wide temperature ranges; on the conceptual side the definition of the configurational entropy of the liquid with a suitable reference state is controversial. Among fragility indexes, the reduced width of the transition range proves most useful. The trend of the glass transition as a function of composition is also discussed in relation to the progressive ordering of the liquid on undercooling.

Some Cu-based alloys, like Cu–Co, Cu–Fe and Cu–Co–Fe, display a liquid metastable miscibility gap. When the melt is undercooled below a certain temperature depending on the alloy composition, they present a separation in two liquid phases, followed by coagulation before dendritic solidification. In order to predict the phase equilibria and the mechanisms of microstructure formation, a determination of the metastable monotectics in the phase diagrams is essential. This paper focuses on the up-to-date findings on the Cu–Co, Cu–Fe and Cu–Co–Fe metastable miscibility gap in the liquid phase. Furthermore, the knowledge on the phase equilibria in the three systems is extended by presenting new results obtained by differential scanning calorimetry (DSC) and comparing them with the calculated phase diagrams.

In the first part of the paper, the solidification of AISI 304 is simulated by means of the multicomponent phase selection theory to predict which phase forms first when the molten alloy is solidified either δ or γ. In the last part of the paper, multicomponent diffusion theory has been used in order to treat the moving boundary problem in solidification and describe microsegregation phenomena.

The Cu–Co system displays a metastable miscibility gap in the liquid state. A considerable amount of work has been performed to study phase separation and related microstructures showing that demixing of the liquid is followed by coagulation before dendritic solidification. Due to kinetic competition of transformation phenomena, the mechanisms have not been fully disclosed. This contribution reviews such findings with the help of a computer calculation of the phase diagram and extends the present knowledge by presenting new results obtained by rapidly solidifying various Cu–Co compositions using a wide range of cooling rates achieved by forcing the liquid into cylindric and conic moulds and by melt spinning.

This paper deals with Co42Cu58 (at.%) alloy processed to obtain a cooling rate gradient during solidification. The Co–Cu system displays a metastable miscibility gap in the liquid state. Undercooling of the melt beyond a certain limit results in liquid separation and formation of droplets of the minority phase in a matrix of the dominant phase. The material was melted and cast in a wedge shaped copper mould to obtain a gradient of cooling rates. The cooling history of the alloy during the solidification was monitored by insertion of thermocouples at different positions in the mould. During cooling, the melt separated into droplets of Co-rich and Cu-rich phases. The Co-rich droplets are mainly coagulated along the major axis of the samples and an explanation of this segregation mechanism is proposed. The distribution of the size of the Co-rich particles was measured in various areas along the sample and correlated to the cooling rate.