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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.

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.

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 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

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.

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.

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.

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, 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.

Definition of the main process parameters, laser power (P), scanning speed (v), hatching distance (hd) and scanning strategy useful for producing dense samples, is fundamental to develop novel alloy compositions for Laser Powder Bed Fusion (LPBF). The present work has two aims: on one side, to verify the processability of a new AlSi10Mg + 4Cu alloy of mixed powders by LBPF; on the other side, on the basis of the experimental analysis, to define a method for processing new alloys. Producing Single Scan Tracks (SSTs), samples with unidirectional scanning strategy and samples with 67° rotated scanning strategy, the proper P-v-hd combinations were identified reaching a final porosity lower than 1.5%. A scenario of hardness and build-up rate vs. energy density is given, to adopt the main process parameters suitable to maximize mechanical properties or productivity. According to the novel method, P-v-hd combinations can be defined through the production and characterization of SSTs and samples with 67° rotated scanning strategy. Through two production steps dense samples can be then obtained, allowing the development of new compositions saving time and reducing costs related to the powder usage. Keywords: Laser Powder Bed Fusion (LPBF), Single scan tracks (SSTs), Hatching distance (hd), Overlap, Process parameters, Hardness, Build-up rate

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.

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.

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.

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.

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.

International audience; In the present work, we discuss the glass-forming ability of various binary alloys in which the glassy phase was not formed even by melt spinning technique with high cooling rate of the melt up to 1 MK/s (some consisted of partly glassy phase), though by commonly accepted guidelines, these alloys could be as good glass-formers as many other binary glasses. The alloys studied belong to binary systems with multiple eutectics; the constituent elements have a negative enthalpy of mixing, and a significant variability of atomic size differences is observed from system to system. The results indicate the necessity of taking into account simultaneously various factors influencing the glass-forming ability including melt fragility.

A novel iron powder obtained by ball milling ribbons of a rapidly solidified cast iron was tested for azo dye degradation in aqueous solution versus commercial Fe and a Fe-based metallic glass powders. The cast iron powders were at least as efficient in promoting the degradation reaction of ethyl-orange and direct blue-6 as the ball-milled metallic glass: dyes decomposition was complete in about an hour. The efficiency of alloy samples increases as a function of the decrease of particles size and does not appear to be strongly due to the structure of the phase containing Fe. The main reason for catalytic efficiency is the presence of metastable phases in the material. The zero valent iron that they contain is more prone to provide electrons for the degradation of N–N double bonds. The starting material is cheap and the sample preparation is straightforward. Therefore, it is believed these samples are suitable for fast degradation at room temperature of azo dyes compared with metallic glasses recently proposed in the literature.

Starting from the Fe 52 Co 23 Nb 4 Si 5 B 16 alloy having good soft magnetic properties and tendency to amorphization, the addition of P, a glass former in Fe-based alloys, is explored up to 4 at.%. The alloys were rapidly solidified by means of planar flow casting and have been characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high temperature differential thermal analysis (HT DSC). The crystallization mechanism has been studied as a function of temperature: it involves primary formation of a bcc phase at low P content and becomes eutectic at 4% P. A remarkable achievement are Time–Temperature–Transformation (TTT) diagrams for primary crystallization obtained by DSC. Magnetisation measurements as a function of temperature in parallel with thermal analysis revealed details of the crystallization sequence. The magnetic softness of alloys has been shown with hysteresis cycles. The use of P appears favourable to amorphization, thermal and magnetic properties up to 2 at.%.

The formation of nanoporous metals by de-alloying is not fully disclosed especially in the case of complex alloys such as amorphous ones. Here a crystalline porous scaffold made of ligaments and pores must originate from a matrix of diverse structure. In this paper a contribution to the field is achieved by pointing out differences that have been noticed comparing ligaments in de-alloyed materials obtained from either amorphous or crystalline precursors. Two multicomponent Au-based alloys in the form of ribbons, an amorphous Au40Cu28Ag7Pd5Si20 and a polycrystalline Au31Cu41Zn12.8Mn15.2, have been chemically de-alloyed in same conditions. The resulting nanoporous materials have been characterized by microscopy and diffraction and the kinetics of the process have been determined. The morphology of ligaments is definitely diverse as well as the size of crystals. This is proven by the ratio, r, between the ligament size and the size of scattering domains obtained by Rietveld analysis: the ligaments formed from the amorphous precursor are constituted by several crystals (r∼5) whereas ligaments from crystalline alloys contain a single domain (r∼1). The results are discussed in terms of surface diffusion and mechanism of growth of ligaments.

Phase selection theory enables a prediction to be made as to which phase forms first when a molten alloy is solidified. Here it is applied to a multicomponent system to provide information about the δ–γ transition that may occur in high nitrogen and high manganese steels. The theoretical predictions are compared with experimental results for microstructures obtained by means of copper mould casting.

This contribution reports the results of calorimetric measurements of the enthalpy of fusion and liquid specific heat carried out in different laboratories as part of the ground campaign of the Thermolab project. Different equipments and calibration methods have been used and critically evaluated. Thermodynamic calculations using the Thermocalc software have been performed and a comparison has been carried out with the experimental results.

The concepts of melt strength or 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 behaviour of the liquid and the thermodynamic fragility by the entropy loss on undercooling. Using the data presently available on viscosity and introducing a new index, the reduced span of the glass transition range, it is shown that kinetic data comply reasonably well to the general trend of the strong-fragile classification. On the other hand, there are discrepancies for the thermodynamic fragility of metallic glass formers with respect to conventional ones. A recent report in Nature (Novikov and Sokolov, October 2004) has suggested a correlation between melt strength/fragility and the elastic moduli of the glassy material (namely the ratio of the bulk to shear modulus). This is checked for metallic glasses which were not discussed by the Authors of the Nature paper, next to inorganic and organic glasses. It is shown that considering a larger material basis and extending the number of property values in the data base, the correlation becomes rather poor. There is, however, the possibility of distinguishing among each class of glasses, e.g. inorganic, organic, metal-metal and metal-metalloid.

This paper describes the crystallisation of Al 87 Ni 7 La 6 and Al 87 Ni 7 Sm 6 metallic glasses. The substitution of Sm for La in the alloy causes a variation in the transformation mode evidenced by the number of differential scanning calorimeter (DSC) peaks: two for the La containing alloy at low heating rates, than three at high heating rates, and three for the one with Sm. The glass transition becomes manifest for each alloys at a typical heating rate below which it is overlapped by the first crystallisation event due to precipitation of fine Al crystals in both materials. The Kissinger plot for Al 87 Ni 7 La 6 is not strictly linear as a possible consequence of overlapping processes. The second and third transformations of both alloys produce a metastable intermediate and the equilibrium phases, respectively. The second crystallisation steps of Al 87 Ni 7 Sm 6 and Al 87 Ni 7 La 6 involve linear Kissinger plots. The crystallisation behaviour of the two alloys is compared with that of Al 87 Ni 7 Ce 6 and Al 87 Ni 7 Nd 6 which were earlier shown to present two and three transformations, respectively.

This paper concerns 14 carats white gold alloys in which Ni, a major component of most such commercial materials but prone to cause skin allergy problems, has been substituted with other whitening elements. The aim is to analyse in detail the evolution of their microstructure and establish a link with their mechanical properties. Hardness and temperature range of precipitation are provided for the following compositions (weight%): 58.5 Au–26.5 Ag–6 Pd–2 Cu–3 Zn–4 Cr; 58.5 Au–26.5 Ag–6 Pd–2 Cu–3 Zn–4 Mn and 58.5 Au-25 Cu–8 Zn–8 Mn. The hardening phases were identified as ordered AuAg(Cu)Zn 2 , tetragonal CrPd like and Au 3 Mn like compounds.

This paper reports on studies of the effect of different rare earth (RE) elements on the devitrification behaviour of alloys of general composition Al 87 Ni 7 RE 6 (here RE = Ce, Nd). We have evidenced two crystallisation mechanisms as a function of the type of rare earth element. When RE = Ce the transformation proceeds in two steps as shown by Differential Scanning Calorimetry (DSC) traces. When RE = Nd the transformation sequence has an additional step. There is also evidence of a calorimetric continuous background for all alloys which is attributed to diffusional homogenisation of the matrix. The glass transition becomes manifest for both alloys when fast enough rates are used in DSC (higher than 10 K/min and 40K/min, respectively for Al 87 Ni 7 Ce 6 and Al 87 Ni 7 Nd 6 ). The first crystallisation step implies the precipitation of nanocrystalline Al. The kinetics of this process is influenced by the simultaneous occurrence of the glass transition. In Al 87 Ni 7 Ce 6 when it takes place above T g (i.e. at high heating rates) it also implies the formation of an intermetallic compound. Kissinger plots for the first transformation display a kink at temperatures corresponding to the glass transition range marking the change in mechanism for the transformation. In Al 87 Ni 7 Nd 6 the glass transition remain visible after partial crystallisation showing that the matrix is readily homogenised. Therefore the molten state of these alloys appears rather fragile.

De-alloying of an amorphous precursor is attractive to get a fine microstructure after copious nucleation of crystalline hillocks. However, the noble metal atoms freed on the alloy surface gain high mobility causing coarsening of ligaments. This work describes the de-alloying by free corrosion of a Au-based amorphous alloy in HNO3 at different temperatures and concentrations. Gold ligaments ranging from 47 to 155 nm have been obtained as a function of acid content. Scanning Electron Microscopy, Transmission Electron Microscopy and X-ray Diffraction was used to characterize the nanoporous structure of dealloyed samples. Moreover, an evaluation of the surface diffusion coefficient and of the activation energy and entropy for diffusion of Au adatoms have been performed to study the mechanism of dealloying under free corrosion conditions in comparison with previous studies.

Thin films of nominal composition Fe84.3Si4P3B8Cu0.7 have been prepared by sputtering from ribbons of the same alloy. Their microstructure has been studied by means of X-ray diffraction, differential scanning calorimetry and transmission electron microscopy, and reveals a partly amorphous state in the as-prepared samples. Their magnetic properties are soft and comparable to those measured on rapidly quenched ribbons. After annealing in furnace at temperatures up to 400 °C, their soft magnetic properties are improved thanks to the development of a fully nanocrystalline state. Annealing at higher temperature causes the coarsening of the α -Fe like grains, the development of hard magnetic phases and an increase of the coercive field.

Al–TM–RE (TM: transition metal, RE: rare earth metal) and Al–RE alloys were analysed with the aim of studying phase selection under various processing conditions. The metastable phases formed in binary Al-rich systems (notably Al–Sm) are revised for a unified interpretation of the literature. Two groups of alloys had different behaviour as for phase selection. In Al 88 Fe 9 Nd 3 and Al 87 Ni 10 Ce 3 stable intermetallic compounds form as primary phases during solidification. Nanocrystalline Al is formed at high undercooling. This may occur directly in rapid solidification or when fully amorphous materials are suitably annealed. In Al 90 Sm 8 Ni 2 and Al 90 Sm 8 Fe 2 metastable intermetallics form during rapid solidification together with a fraction of amorphous phase, whereas nanocrystalline Al forms on annealing the amorphous phase.

A series of tellurite glasses containing TeO2, ZnO, and Na2O and doped with 1000 ppmw of Er2O3 has been synthesized. The series displays good thermal stability. Based on thermal analysis results, we chose to investigate the viscosity in the temperature range 310–395°C, using Al as the best material for plates in the rheological measurements. First, the viscosity vs. strain (strain sweep) at fixed temperatures and angular frequencies was investigated. Then, having fixed the strain value, the viscosity curve vs. angular frequency was determined. Finally, the viscosity–temperature curve of all the glasses prepared was determined and fitted by different equations, including the viscosity value at the glass transition temperature, Tg, measured at a heating rate of 2°C/min. The best fit was obtained using the Cohen–Grest equation. The stability of the glasses was determined by comparing ΔT values (ΔT = Tx − Tg, with Tx being the onset crystallization temperature). For a glass containing 10 mol% Na2O, ΔT reached 176°C. The crystalline phases formed on heating were always TeO2, Na6ZnO4, and Zn2Te3O8.

Typical compositions of austempered ductile cast irons in different metallurgical states were studied with the aim of making a detailed assignment of thermal effects seen using differential scanning calorimetry (DSC) to transformations occurring in the alloy phase constitution and microstructure. In austempered specimens the transformation of retained austenite is revealed by an exothermic reaction at temperatures above 450°C which depend on the content of alloying elements. Martensite transformations are seen in a wide temperature range starting at ∼100°C and giving exothermic and endothermic overlapped DSC signals due to relaxation, carbon diffusion, and tempering. It is concluded that DSC is a powerful tool for detecting tiny traces of martensite in austempered materials.

The thermal stability and viscous flow behavior of amorphous Zr 65 Al 8 Ni 27− x Cu x (x= 12, 17 and 22) ribbons were examined by using differential scanning calorimetry and thermomechanical analysis. It was observed that the viscosity decreases with increasing temperature until the first steady-state viscous flow temperature is reached and above this temperature the viscosity depends on both the composition and applied stress.

A reaction between Ni and Al in equiatomic amounts was promoted by cold-rolling. Foils of the elements were repeatedly rolled. After each pass the composite was folded, producing a multilayered structure of elements still unreacted by intimately intermixed to give a crystallite size of a few nanometers. When the composite was heated to around 200 °C, a reaction occured resulting in the formation of NiAl3. Further heating at 450 °C brings about the formation of NiAl. The process was followed by DSC and XRD. The final product consisted of flakes of intermetallic compound with no particles of the elements still detectable.