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In the aim of evidencing the relationship between Mg2FeH6 synthesis and the size of Fe particles, several specimens have been prepared by applying various milling energies (milling time) on a 2.1 Mg and 1Fe powder mixture doped with a small fraction of Unsaturated Fatty Amine (UFA). The resulting nano-crystalline composite structures display a broad Fe particle size distribution as a function of milling time. The hydrogenation of those complex powders has been conducted at temperatures lower than 400 °C under 60 bar of hydrogen pressure. As expected, the Fe particle size significantly influenced the hydrogenation kinetics. Also, the inevitable distribution of a minor fraction of oxides occurring during the milling process affected greatly the hydrogen storage capacity. Under the low pressure and temperature conditions selected in the frame of this study, lower than 100 bar and 500 °C conventionally used for synthesis of high purity Mg2FeH6, the hydrogenation reaction was demonstrated to be almost completed within 6 h, confirming the fast hydrogen absorption capability of the prepared materials. Plus, nearly 84 wt% of Mg2FeH6 was achieved under the afore mentioned moderate conditions and a minor fraction of unreacted Fe still remained due to diffusion constraints existing at low temperatures.

Different Cu-Zr alloys were hydrogenated under 100 bars of hydrogen pressure at different temperatures. The hydrogenation induced transformation of the initially amorphous phase into a polycrystalline structure characterized by its nanoscale ( 2 . Calorimetry measurements after hydrogenation showed a low temperature exothermic transformation occurring in the alloys hydrogenated at temperatures below 473 K, followed by multiple endothermic peaks at higher temperature attributed to dehydrogenation of different hydride phases. Activation barrier energies of the phase transformation were derived from Kissinger's method, and further characterization involving transmission electron microscopy revealed the existence of delta ZrH 2 with cubic structure contrasting with the typical epsilon ZrH 2 with tetragonal structure. This study evidences the effect of hydrogen pressure, temperature, and the alloy chemistry on the nature of the hydride formation in Cu-Zr binary amorphous alloys during the hydrogenation procedure.

International audience; The hydrogen-induced phase separation of Cu–Zr binary amorphous alloys during hydrogen gas charging at elevated temperature was demonstrated; the homogeneous binary alloy was decomposed into pure Cu and Zr-hydride by absorbing hydrogen into the structure. The decomposition, which is attributed to the opposed affinity to hydrogen of Cu and Zr, took place in nanometer scale. The hydrogen absorption kinetics was compared for the alloys with different compositions. The structure after hydrogen absorption was analyzed using x-ray diffraction, ultra-small and small angle neutron scattering, and electron microscopy.

We report on the formation mechanism of neck during electro-discharge sintering (EDS) upon various electrical input energy using Cu-based metallic glass and W powders. Microstructural investigation reveals that crystalline phases are observed preferentially on the surface of the Cu-based metallic glassy powder indicating energy concentration occurs at the powder surface. Moreover, it is clearly observed that needle-like morphology on the W powder surface suggesting that both surface melting and evaporation take place, followed by rapid freezing the substance. Therefore, these results strongly support that formation of neck during EDS is closely connected to the energy convergence on the thin layer of the powder surface inducing melting or evaporation.

Ni 90 Al 10 amorphous membranes were prepared by means of molecular dynamics (MD) simulation technique with the aim of investigating the structural evolution induced by hydrogen with respect to hydrogen concentration. The short-range ordered (SRO) structures of the as-cast model sample and the structural change by hydrogen charging were analyzed using Voronoi tessellation method. This study indicates that prism and prism-like structures with low coordination number are generated, while intrinsically stable SRO structures in the amorphous membrane annihilate upon hydrogen charging. We discussed the relationship between these local atomic changes and the structural stability which was evaluated from the potential energy change point of view.

The influence of partial substitution of Fe by Cu or Al in Fe 75− x Si 15 Ti 10 (Cu, Al) x ( x = 0 and 4) ultrafine composites on the microstructure and mechanical properties has been investigated. The Fe 71 Si 15 Ti 10 Cu 4 ultrafine composite exhibits a favorable microstructural evolution and improved mechanical properties, i.e., large plastic strain of ∼5% and pronounced work hardening characteristics. The mechanical properties of the ultrafine eutectic composite are strongly linked to the length scale heterogeneity and the distribution of the constituent phases.

A single pulse of 0.57–1.1 kJ/0.45 g-atomized spherical Ti 52 Zr 28 Ni 20 powders in size range of 10–30 and 30–50 μm consisting of a mixture of β-(Ti, Zr) and icosahedral phases was applied to understand the structural evolution of icosahedral phase during electro-discharge sintering (EDS). The structural analysis revealed that high electrical input energies leaded to complete decomposition of icosahedral phase into C14 Laves and β-(Ti, Zr) phases. Furthermore, the critical input energy inducing decomposition of icosahedral phase during EDS is dependent on the size of the powder.

The present paper reports results on the Gd-doped Co–Cu granular alloys and metallic glasses prepared by different processing methods. The main aim of this research was to produce a ternary alloy which radically changes its magnetoresistance (MR) properties below critical temperature. A detailed study on the evolution of the structure and phase separation is presented basing on X-ray diffractometry (XRD) analysis and scanning electron microscopy (SEM) observation. MR was measured by means of a two point probe method in magnetic field using a new experimental device which was patented thereafter.

The microstructure of Sn 96.4 Ag 2.8 Cu 0.8 (at.%) solder alloy when rapidly quenched onto an Au surface finish has been found to range from nanometer to micrometer-sized features. This striking microstructure contained a spectrum of phases from the Au–Sn phase diagram, while Ag and Cu did not appear to participate in the solidification process. Within the solder contact, a eutectic with 40 nm interlamellar spacing was observed, along with the presence of layered intermetallics. Observations of these phases and their orientation offer better understanding of the solidification of Pb-free solders onto Au.

The objective of the study described in the following paper is to examine the variations in the structure, thermal and mechanical properties of Zr-based amorphous ribbon of composition Zr50–Ni27–Nb18–Co5, upon electrochemical charging with hydrogen. Structural analysis showed that the amorphous nature of the alloy was retained for low hydrogen concentrations. But beyond a critical concentration, hydrogenation of the glassy alloy played a major role in altering the structural and thermal stability, and mechanical properties. Particularly for relatively high concentrations (>16 at.%), hydrogen induced nanocrystallization and simultaneous reduction in fracture strength were observed. Hydrogen embrittlement occurred at high concentrations and was attributed to the reduction in cohesion between atoms due to the presence of hydrogen. © 2005 Elsevier B.V. All rights reserved.

The effect of substitution of Y for Fe on the glass forming ability (GFA), magnetic and mechanical property has been studied in Fe 77 − x Nb 6 B 17 Y x ( x = 0–4) alloys. Replacement of 1–4 at.% Fe by Y increased the thermal stability of the glass and liquid phase in the Fe–Nb–B–Y alloys. It was found that the Fe 74 Nb 6 B 17 Y 3 alloy exhibited the largest T rg (0.60) and γ (= T x /[ T g + T L ]) (0.396) values enabling the fabrication of bulk metallic glass (BMG) with a diameter of up to 2 mm. The BMG alloy (≥74 at.% Fe) exhibited high compressive fracture strength and hardness of about 3 GPa and 1060 Hv, respectively. The partial replacement of 3 at.% Fe by Y in Fe–Nb–Y–B improved the alloy magnetization saturation by about 10%.

The influence of beryllium (Be) addition on the quasicrystal-forming ability (QFA) in Al–Cu–Fe and Al–Mn systems has been investigated using conventional solidification technique. For a series of as-cast (Al 62− x Be x )Cu 25.5 Fe 12.5 ( x =0,1,3,5,7) alloys, the Be addition modified the icosahedral phase formation mechanism from peritectic reaction to primary solidification and resulted in the increase in the volume fraction of the i-phase from 40% for x =0 to 90% for x =7. Such an enhancement of the QFA with the increase of Be content can be represented by using the reduced quasicrystal transition temperature proposed in the present paper. In Al–Mn alloy system, microstructural changes due to the addition of Be were examined in detail by comparing as-cast Al 90 Mn 2.5 Be 7.5 alloy with Al 97.5 Mn 2.5 bulk ingot. For this alloy system, the substitution of Al by Be was found to reduce substantially the critical Mn-content and cooling rate necessary for the formation of the i-phase.

To investigate the role of tribological reactions on the friction and wear of quasicrystalline materials, coatings with two alloy compositions have been prepared by plasma and HVOF spraying techniques. The tribolayers were characterized by the formation of a transfer film on the counterface and densification of the coating subsurfaces. It was observed that the thickness of the transfer film and pore-free region were dependent on the composition and process used for the deposition of the coatings as well as the sliding velocity. As the sliding velocity increased, the growth rate of the transfer film decreased, resulting in a decrease of the coefficient of friction. On the other hand, the wear rate appeared to be controlled by the thickness of the pore-free region formed within the coating surface zone.

The corrosion properties of the Fe 45-x Cr 18 Mo 14 C 15 B 6 Y 2 M x (with M=Al, Co, Ni, N andx=0, 2) bulk metallic glasses have been investigated in a 1 M H 2 SO 4 + 2 ppm F - solution at 80 °C with H 2 and air bubbling, which simulate environments of the polymer electrolyte membrane fuel cell. The partial replacement of 2 at.% Fe led to significant modification of the corrosion behavior and resulted in corrosion resistances superior to that of stainless steel.