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The formation of the icosahedral (i) quasicrystalline phase has been studied in the cast Al87Mn4Si2Be7 alloy. Under low cooling rates, i-phase particles of about 5 to 15 µm formed in the αAl matrix. A thorough examination of the microstructure revealed the existence of cubic crystalline phases embedded in the i-particles. Microstructural and thermal analyses indicated that the i-particles nucleated heterogeneously from the cubic AlMn(Si)Be4 phases by a peritectic reaction, however with a slight misorientation.

This study examined the parameter governing the plasticity observed in various Cu–Zr containing monolithic amorphous alloys. All the alloys were fully amorphous in their as-cast condition but exhibited different plastic strains. Microscopic observations of the quasistatically compressed alloys showed abundant nanocrystallites in the amorphous matrices in the alloys that exhibited pronounced plasticity. On the other hand, insignificant changes in the microstructure were observed in the alloy that did not show plasticity. The mechanism for the formation of these deformation-induced nanocrystallites was examined from the viewpoints of thermodynamics and kinetics. The role of the deformation-induced nanocrystallites on the plasticity of the amorphous alloy was examined using high-resolution transmission electron microscopy. The results demonstrate that compressive loading facilitates nanocrystallization in monolithic Cu–Zr containing amorphous alloys, resulting in plasticity. The parameter governing the plasticity in these monolithic Cu–Zr containing amorphous alloys lies in the activation energy for the overall crystallization process. 2005 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

W-rich particle-reinforced Ti-based bulk metallic glass (BMG) matrix composites with a compressive strength approaching 3 GPa and a fracture strain of approximately 12% were developed. In contrast to most existing BMG matrix composites, in which the improved ductility was obtained only at the expense of the strength, the composites developed in this study exhibited a significant enhancement in their strength, as well as an improvement in the plasticity. This improvement in the plasticity was attributed to the blocking and circumscription of the shear band propagation, leading to the formation of a large number of shear bands. Using a classical elasticity theory of inclusions, the improvement of the strength was interpreted as resulting from the generation of tensile residual stresses in the matrix due to the difference in the coefficient of thermal expansion between the W-rich particles and the BMG matrix.

The mechanical properties of Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 (Vitreloy 1, (Vit. 1)) have been examined after cold rolling. For the cold rolled Vit. 1 up to 18% in thickness reduction, both ultimate compressive strength and ductility exhibited up to 1.95 GPa with 20% of elongation. It appears that the increase of strength and elongation was due to the high density of shear bands together with in situ nano-crystallization by cold rolling. The in situ nano crystallization was confirmed by Differential scanning calorimetry (DSC) and high resolution transmission electron microscope (HR-TEM). The enhancement of mechanical properties was discussed in terms of in situ nano-crystallization and structural stability of Vit. 1.

The chemical inhomogeneity in Cu 43 Zr 43 Al 7 Ag 7 bulk metallic glass has been investigated using a three-dimensional atom probe to understand the enhanced plasticity under compressive mode observed in an injection-cast alloy. Nanoscale phase separation from the melt into Cu-enriched and Ag-enriched amorphous phases was observed, while no evidence for crystallization was found in the as-cast alloy.

Semisolid slurries of Al-15Cu alloy were produced for rheoforming by a low temperature pouring technique. To investigate the morphological change of the slurry in terms of the particle mean diameter and the roundness factor, samples were extracted during the continuous cooling and the isothermal holding stage of the slurry by a simple technique of interrupt quenching. Results demonstrated that the fine-grained equiaxed dendritic structure, which formed during low temperature pouring, is changed to a globular structure when held at a semisolid temperature for sufficiently long holding time. With regard to the globulization mechanism of the primary α-phase, local melting is considered to take place at the neck of equiaxed dendrites, leading to the separation of small new particles during continuous cooling. These newly formed particles eventually grow during isothermal holding in the semisolid temperature by obeying theD 3=Kt kinetic law, which suggests coarsening by Ostwald ripening.

Zr50Ni27Nb18Co5 amorphous ribbons were hydrogenated using an electrochemical method. Under a current density of 30 mA/cm2, the thermal stability of the amorphous phase was found to increase with the charging time. Hardness and fracture strength were found to be independent of charging time, indicating that the Zr-Ni-Nb-Co amorphous alloys preserved its mechanical integrity.

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 aim of this study was to investigate the effect of temperature on tribological properties of plasma-sprayed Al-Cu-Fe quasicrystal (QC) coating after laser re-melting treatment. The laser treatment resulted in a more uniform, denser and harder microstructure than that of the as-sprayed coatings. Tribological experiments on the coatings were conducted under reciprocating motion at high frequency in the temperature range from 25 to 650 degreesC. Remarkable influence of temperature on the friction behavior of the coating was recorded and analyzed. Microstructural analysis indicated that the wear mechanisms of the re-melted QC coatings changed from abrasive wear at room temperature, to adhesive wear at 400 degreesC and severe adhesive wear at 650 degreesC owing to the material transfer of the counterpart ball. It was also observed that the ratio of the icosahedral (i)-phase to beta-Al-50(Fe,CU)(50) phase in the coating was higher after test at 400 'C than that at 650 'C. The variation of the ratio UP of coating and of the property of the counterpart ball and coating with the temperature are the two main factors influencing the wear mechanisms and value of the friction coefficient.

Metallic amorphous materials have been widely developed thanks to the outstanding properties including high chemical stability, mechanical strength, and magnetic properties. However, with the exception of a few compositions, the limiting factor is the critical cooling rate for the formation of the amorphous phase. For many applications, it is only the contact surface properties that are important, thus the use of coating techniques such as thermal sprayings has several attractive features. In this paper, we present the microstructure of Ni-based amorphous coatings prepared by laser cladding and vacuum plasma spraying. The utilization of plasma spraying to deposit atomized powder enabled the formation of fully amorphous coating, laser cladding resulted in mostly crystallized structures. Glass forming ability and wear properties of the coatings were discussed as a function of the coating microstructure.

National audience; Cet article présente un état de l art des architectures basées sur IP supportant les environnements hétérogènes réunissant un réseau ad hoc et un réseau d accès fixe combinant liens filaires et liens sans fil. Nous avons principalement centré ce travail sur les aspects d architecture et de gestion de la mobilité. Cet article décrit brièvement le protocole Mobile IP et un représentant des protocoles de micromobilité discutés au sein du groupe de travail Mobile IP de l Internet Engineering Task Force (IETF). Les protocoles de micromobilité IP complètent Mobile IP en offrant un contrôle rapide et sans coupure des handoffs. Finalement, différentes propositions pour l intégration des concepts de mobilité réseau et cellulaire dans un environnement ad hoc sont présentées. Leur objectif est d obtenir une solution de support de mobilité globale au niveau d IP, incluant les notions de réseaux ad hoc et de micromobilité afin de supporter des handoffs rapides dans des zones géographiques restreintes.

A cast iron composition has been modified by additions of Al, B, Y and Cu to the Fe–C master alloy in order to achieve glass forming ability as well as good magnetic properties. Amorphous ribbons were synthesized by rapidly quenching at 106 K/s and the devitrification process was controlled by varying the Y and Cu contents so as to achieve a composite structure of bcc Fe nanocrystals in an amorphous matrix. An improvement of saturation magnetization was observed by annealing the as-quenched ribbons. However, coercivity does not necessarily improve upon annealing, and therefore, the annealing should be judiciously scheduled. Effect of minor impurities in cast iron on the coercivity and saturation of these alloys was found to be insignificant.

In this paper, we introduce a novel idea of using metallic amorphous material as a bipolar plate for polymer electrolyte membrane fuel cell (PEMFC). The major requirement of the metallic bipolar plate material is their high corrosion resistance. Owing to its chemical homogeneity, and absence of defects (like grain boundaries, dislocations, etc.), amorphous materials exhibit a combination of attractive properties for bipolar plates such as high corrosion resistance and high strength (∼ about 2 GPa). The corrosion properties of Fe 48 Cr 15 Mo 14 Y 2 C 15 B 6 and of a newly developed Fe 50 Cr 18 Mo 8 Al 2 Y 2 C 14 B 6 bulk metallic amorphous alloys have been investigated under conditions that simulate the fuel cell environment and are compared with those of a stainless steel. Hydrogen gas and pressurized air were bubbled into a 1 M H 2 SO 4 +2 ppm F − solution at 75 °C solution, throughout the experiment to simulate the respective anodic and cathodic PEMFC environment. In comparison to the stainless steel, the Fe 50 Cr 18 Mo 8 Al 2 Y 2 C 14 B 6 amorphous alloy displays significantly higher corrosion resistance.

The microstructure of the Al-Mn(-Cu)-Be-Si alloys analyzed by X-ray diffraction and TEM consisted of icosahedral (i) quasicrystal particles embedded in aAl matrix. The conjoint addition of Si and Be elements enabled the i-phase formation in Æ10 mm specimens prepared by conventional casting technique. The size, volume fraction and stability of the i-phase were found to be dependent on the Mn content. The addition of 2 at.% Cu did not affect the formation and stability of the i-phase but contributed significantly to the enhancement of the mechanical properties.

The thermal stability and glass forming ability of Cu50-xZr43Al7Agx (x=0, 1, 3, 5, and 7) bulk metallic glass alloys have been investigated. The glass forming ability in the Cu−Zr−Al−Ag alloys increased proportionally to the Ag content and show good correlations with thermal parameters such as ΔTx(=Tx-Tg), Trg(=Tg/T1) and γ(=Tx/(Tg+T1)). For the Cu43Zr43Al7Ag7 alloy, fully amorphous rods of 8 mm diameter were successfully fabricated by copper mold casting. Mechanical tests on this composition revealed also remarkable properties with compressive strength around 2000 MPa and large ductility.

In order to investigate the mechanical relaxation behavior of the Zr 36 Ti 24 Be 40 amorphous alloy, the dynamic mechanical properties were measured using dynamic mechanical analyzer (DMA). From the data collected during isothermal multi-frequency dynamic mechanical measurements, the master curves for storage and loss moduli over a broad range of temperature were constructed using the time–temperature superposition (TTS) principle. The temperature dependence of the shift factor was found to follow the Arrhenius relationship and the activation energies, calculated from the Arrhenius relationship, were about 93 and 390 kJ/mol for low temperature mechanical relaxation and viscous flow, respectively. According to the temperature dependence of the shift factor above T g , no evidence for phase separation was found. The fragility index was also calculated from the relationship between shift factors and temperature and was found to be m ≈34, suggesting that the Zr 36 Ti 24 Be 40 amorphous alloy can be classified...

The icosahedral phase formation and associated structural evolutions in the Al–Cu–Fe ternary system have been examined through the repeated cold rolling and folding (R&F) process of elemental foils with a target composition of Al 62.5 Cu 25 Fe 12.5 (at.%). Upon early increments of the rolling and folding cycles, the elemental Fe foil was dispersed through the refined Al and Cu layers. When the rolling and folding step reached 40 cycles the Al 2 Cu phase has been observed, however, no ternary phases were identified even upon additional R&F cycles. The stable icosahedral phase (i-phase) could be obtained after isothermal annealing of the R&F processed specimens at 650 and 750 °C. The phase evolution during repeated cold R&F process of the Al–Cu–Fe system and upon heat-treatments are discussed in terms of the formation and dissolution of the Al 2 Cu and Al 7 Cu 2 Fe phases.

The frictional and wear behavior of several bulk metallic glasses (BMGs) were investigated at room temperature under dry sliding condition. The influence of the type of motion on the tribological properties was of particular interest. Under identical sliding condition, the BGMs investigated in this study exhibited rather similar frictional behavior, with values ranging from 0.35 to 0.43. However, the present results indicated a significant difference in the wear performance. Surface modifications in the wear tracks were found to be dependent on the counterpart material and the nature of the sliding motion, and to contribute to the variations of the tribological properties of bulk metallic glasses.

This paper presents the results of the study on the effect of laser melting–solidification processing on the structure and tribological properties of plasma spray Al–Cu–Fe quasicrystalline alloy coatings. Dense and hard coatings were obtained by the laser post-treatment processing and the volume fraction of the icosahedral (i) phase was found to be dependent on the laser power and scanning velocity conditions. Using a parameter δ , defined as the ratio of the laser power P , to the scanning velocity v , i-phase was observed to form for low values of δ as a consequence of the high cooling rates. Furthermore, a correlation was worked out between the microhardness and the parameter δ . Owing to the microstructure modification, the laser post-treatment provided significant improvement to the tribological properties of the plasma sprayed Al–Cu–Fe QC coatings. The frictional behavior was found to be dependent on the constituent phases formed in the laser post-treated coatings. In particular, low values of the friction coefficient were recorded in the early stage of the test for coatings containing a high volume fraction of i-phase. However, owing to the brittleness of the i-phase, the difference of the frictional behavior was reduced after 150 cycles, and the friction coefficient for all laser post-treated coatings stabilized at a value which was approximately half that of the as-received plasma sprayed coatings. After laser post-treatment, the wear rate was significantly improved only for the coatings containing a high content of i-phase.

In this paper, we report the formation of the new quaternary icosahedral quasicrystal in the Al–Mn–Si–Be system, which has a primitive icosahedral structure and has a significant lower cooling rate at the time of its formation. The icosahedral quasicrystalline phase was found to form in the Al-rich composition of Al–Mn–Si–Be alloy by conventional casting technique as well as by rapid quenching technique, indicating that the addition of Be to Al–Mn–Si alloys improves the quasicrystal forming ability. The icosahedral phase in conventionally cast Al–Mn–Si–Be alloys forms as a dendritic phase in the under-cooled melt showing five well-developed branches indicating the five-fold symmetry structure. At the later stage of the growth of the icosahedral phase, 1/1 approximant phase forms heterogeneously from the icosahedral phase. The Al–Mn–Si–Be icosahedral phase is metastable, and transforms into the 1/1 cubic approximant phase at high temperature.

The precipitation behaviour of a hexagonal two-dimensional aperiodic phase in Al-rich Al–Mn–Be alloy has been investigated. Upon heat treatment at temperatures above 450°C, the icosahedral phase formed in a conventionally cast Al–2.5 at.% Mn–3 at.% Be alloy transforms into the stable hexagonal H1 phase. The solute partitioning during transformation leads to the precipitation of a hexagonal two-dimensional aperiodic approximant phase (H′ phase). The precipitates have an orientation relationship with the α-Al matrix. The similarity of the diffraction features indicates that the hexagonal two-dimensional aperiodic structure of the H′ phase is an intermediate structure between the true sixfold quasiperiodic structure and the hexagonal structure of the crystalline counterpart H1 phase.

The effect of Be addition on the formation of quasicrystalline phases in Al-rich Al–Mn(–Be) alloys has been investigated. A metastable icosahedral quasicrystalline phase was found to form in a 93.5Al–5Mn–1.5Be (in wt%) alloy prepared by a conventional casting technique, indicating that the addition of Be to Al–Mn alloys improves the quasicrystal forming ability. The icosahedral phase in conventionally cast Al–Mn–Be alloys forms in the undercooled melt with the equilibrium growth morphology of the pentagonal dodecahedron. Heat treatment at 540 °C for 100 h results in the precipitation of small platelets of a two-dimensional quasiperiodic phase in the α-Al matrix. These precipitates have an orientation relationship with the α-Al matrix.

In this paper, we intend to present results on the effect of a soft phase on the tribological properties of Al–Cu–Fe-based composite coatings. Quasicrystalline-based composite powders with a Sn volume fraction varying from 0% to 30% were prepared by gas atomization before deposition onto medium carbon steel substrates by the air plasma spray technique. The friction and wear behavior of the QC composite coatings was investigated in dry air with a ball-on-disk test machine under reciprocating motion. The results of this experimental investigation indicated that the addition of 20 vol.% Sn enabled an improvement of the wear owing to an enhancement of the fracture toughness of the composite coatings.

The effect of replacement of lanthanide by misch metal (Mm) in La-Al-TM (TM; transition metal, Ni, Cu and Co) alloys has been investigated to evaluate the possibility of fabrication of in-situ glass matrix composites withenhanced properties. For the as-cast cylindrical Mm 5 5 Al 2 5 Ni 1 0 Cu 1 0 alloy ingot with 3 mm diameter, the microstructure is consisted of two kinds of a few μm size crystalline phases (volume fraction: 4.6%) uniformly distributed in the metallic glass matrix. The substitution of La by Mm reduces the glass forming ability (GFA), i.e., lower the reduced glass transition temperature, Trg (= T g /T L , where T L is the liquidus temperature) and smaller superliquid temperature region, ΔT x (= T x - T g , where, Tg is the glass transition temperature and T x the onset temperatures of crystallization), enabling the fabrication of in-situ BMG matrix composite. The Mm 5 5 Al 2 5 Ni 1 0 Cu 1 0 metallic glass matrix composite sample exhibits the compressive fracture strength of 931 MPa, and in particular enhanced the compressive plastic strain of 1.2% before failure. The enhanced strength and ductility was explained by the presence of fine crystalline phases embedded in the BMG matrix, which led to a multiple shear band formation.

The oxidation behavior in air of gas atomized Al–Cu–Fe–Be powders was investigated during isothermal exposures at 750, 800, and 830 °C. Oxidation data obtained at 750 °C for Al–Cu–Fe and Al–Cu–Fe–Cr powders are also presented and used as references. Thermogravimetric analyses showed that Be significantly improved the oxidation resistance of the icosahedral phase at 750 °C. At this temperature the i-phase in Al–Cu–Fe–Be powders was found to be stable even after oxidation for 300 h, while oxidation at and beyond 800 °C led to the formation of a cubic β′-phase. Auger analyses suggested that, in addition to its role on the stability of the icosahedral phase, the presence of Be in the oxide layer provided efficient protection against air oxidation at high temperature.

The effect of Be (beryllium) addition and the influence of cooling rate on the solidification path of the icosahedral (i) phase in conventional casting Al 62− x Be x Cu 25.5 Fe 12.5 ( x =0,1,3,5,7 at.%) alloys were investigated by means of X-ray diffraction, differential thermal analysis, SEM and EDX analyses. The addition of Be has been found to modify the i-phase formation mechanism from peritectic reaction to primary solidification. The volume fraction of the i-phase has been observed to increase from 45% for x =0 to 90% for x =7. These results suggested that the substitution of Al by Be is favorable for the increase of the quasicrystal-forming ability (QFA) of the i-phase. Two parameters have been proposed for defining and assessing the QFA for i-phase formed by peritectic reaction. These parameters can be expressed by the reduced quasicrystal transition temperature T rq = T p / T l and the reduced undercooling Δ T r =Δ T lp / T l , respectively, ( T l : liquidus temperature, T p : peritectic peak temperature, and Δ T lp = T l − T p : freezing range of primary phase).

This article presents the results of a study on the microstructure and mechanical properties of Al-Si-Cu-Fe specimens produced by the spark plasma sintering (SPS) technique. The microstructure of the starting powder and bulk specimens was analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The formation of the icosahedral and decagonal quasi-crystalline phases in the as-gas-atomized powders is described for the first time. It is then shown that these metastable phases transformed into the 1/1 cubic-approximant phase upon heating at about 600 °C. Second, the effects of SPS process parameters such as the temperature and time have been investigated. Owing to the generation of a spark discharge between neighboring powder particles, dense cylindrical samples were obtained after a short sintering time of 30 minutes at the temperature of 650 °C. The highest values of the Vickers microhardness, about 8.9 GPa, were obtained when the powders were sintered in the temperature range of 600 °C to 650 °C for a holding time of 30 minutes, while the fracture toughness was found to be inversely proportional to the sintering temperature. However, at the sintering temperature of 650 °C, the fracture toughness increased from about 1.40 to 1.52 MPa √m as the holding time increased from 10 to 60 minutes. As compared to cast specimens, the enhanced mechanical properties are explained by the refined microstructure resulting from the low temperature and short sintering time applied during SPS processing.

The tribological behavior of Al–Ni–Co–Si quasicrystalline (QC) coatings prepared by air plasma spray (APS) and high velocity oxy-fuel (HVOF) techniques was investigated in dry sliding condition against a Cr-coated cast iron disc. Tests were performed for different parameters of the load, sliding velocity, and temperature under a reciprocal motion. Our results demonstrated the influence of the coating microstructure on the frictional and wear behavior. Values of the coefficient of friction measured for HVOF coatings against Cr-coated cast iron disc were found to be about 14% lower than those of APS coatings. Under the standard condition, HVOF coatings exhibited a better wear resistance than APS coatings, however, this difference was reduced for tests performed under the highest values of the load and temperature investigated in this study. The sliding conditions imposed in this study led to significant modifications of the contacting surfaces characterized by the formation of a transfer film on the counterpart material, densification of the coating subsurface, and generation of wear particles. The variations of the coefficient of friction with the testing parameters were explained by the third body concept. It was also shown that the wear performance was dependent on the local surface properties of the QC coatings.

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.

Phase formation and thermal stability for an Al–Mn–Be alloy have been investigated by melt-spinning and conventional casting. Significant differences in the phase formation and the thermal stability of the microstructure were found as a result of the different cooling rates. In the melt-spun ribbons, a large volume fraction of a metastable icosahedral phase was found to coexist with an Al solid solution. In the bulk cast ingots, the primary phase formed in the two-phase microstructure was a hexagonal approximant phase of quasicrystals. This phase that solidified in the form of faceted particles embedded in the Al solid matrix proved to be thermodynamically stable during annealing at 540 °C for 100 h. The effect of Be addition on the formation of the stable approximant phase is discussed in terms of the Hume–Rothery mechanism.

The sliding friction and wear performance of Al–Ni–Co–Si quasicrystalline coatings deposited by the high-velocity oxy-fuel technique were investigated under dry sliding conditions. This study indicated that changes in the imposed sliding test conditions modified the friction and wear behavior of quasicrystalline coatings. Qualitative analysis of the contact interface and wear debris were performed with the aim of understanding the role of the third body on the friction and wear processes. The dependence of the coefficient of friction on the sliding velocity and counterpart material was explained by the stick-slip behavior. It was also shown that test conditions favorable for the formation of thick intermediate layers and the densification of the coating subsurface led to low wear rates. Large cylindrical particles, formed by agglomeration of small wear debris, were suggested as a beneficial factor for the reduction of the coefficient of friction.

A bulk material that consists of the stable icosahedral phases (I-phases) in the Ti–Zr–Ni system has been fabricated in a hot press using mechanically alloyed (MA) powders. Considerable amounts of amorphous phase and nanocrystals are formed after MA for more than 30 h in the mixture of elemental powders (Ti, Zr, Ni) with the overall composition of Ti 41.5 Zr 41.5 Ni 17 . The amorphous phase transforms into the I-phase in the temperature range of 573–673 K during continuous heating in differential scanning calorimetry (DSC) with the heating rate of 40 K/min. The powders MA for 40 h are hot-pressed for 2 h at 873 K under the applied pressure of 900 MPa to form a bulk I-phase material. The evolution of the Vickers microhardness has been examined in the load range of 0.5–10 N. The indentation size effect is accompanied by a modification of the fracture pattern. At a low value of the load, no crack is observed. As the load increases, the first cracks observed around the indenter are lateral cracks, and then radial cracks are found for load larger than 1 N.

International audience; The addition of a low concentration of group 5 elements to the Ti40Zr29Be16Cu8Ni7 BMG alloys resulted in the formation of particles with icosahedral quasiciystalline symmetry of different size and volume fraction embedded in BMG matrices. Since the i-phase is known for its excellent corrosion resistance, the properties of the TM-containing Ti-based BMGs, with 0

International audience; The variation of the hydrogen permeability with time was monitored during the permeation of hydrogen through metallic amorphous membranes of Ni45-XNb30Zr25CoX (X=0, 7.5, and 15 at%) in the temperature range of 350 to 450 A degrees C. For tests performed between 3 and 5 bars, the alloy with the medium content of Co, i.e., 7.5 at%, had the most pronounced degradation while the alloy without Co showed less of a decrease in the hydrogen permeability with time. The change in the hydrogen permeability with the Co content was discussed in connection with the difference in the activation barrier energy for crystallization in the alloys.

International audience; The surface of the AISI 420 martensitic stainless steel was subjected to High Current Pulsed Electron Beam (HCPEB) treatment The microstructure in the melted layer consisted of a three phase mixture: (i) fine delta-Fe grains formed via epitaxial growth from the substrate, (ii) larger gamma-grains nucleated from the top surface of the melt and (iii) some needles-like variants issued from the solid state martenitic transformation. Despite this complex multiphase microstructure, the corrosion performance, tested in a sulfuric acid solution, was significantly enhanced by the HCPEB treatment. The increase in corrosion potential and delayed pitting are essentially attributed to an increase in Cr content, rising from 13.3 wt. % in the bulk to about 14 wt. % at the surface, together with a very limited amount of surface craters. This low density of craters did not give rise to significant deep hardening in the sub-surface but the top surface melted layer hardness was increased by more than 50% because of the triggering of the martensitic transformation.

We analyse a huge and very precise trace of contact data collected during 6 months on the entire population of a rehabilitation hospital. We investigate the graph structure of the average daily contact network. Our main results are to unveil striking properties of this structure in the considered hospital, and to present a methodology that can be used for analysing any dynamic complex network where nodes are classified into groups.

Aluminum matrix composites reinforced by Al62Cu26Fe12 gas atomized powders were produced by conventional metallurgical processes, such as gravity casting with stirring and hot extrusion. This investigation was mainly focused on the dependency of the yield stress at room temperature as a function of the volume fraction of reinforcement, but other variables such as the matrix, coating layer around the particles, and processing were also investigated. For as-extruded composites, the addition of the Al-Cu-Fe particles improved the yield stress, although not dramatically owing to the large particle size. In contrast, it was found that the yield stress was considerably enhanced for the as-cast composites up to 10%(AlCuFe)p, while an asymptotic value was observed afterward. The dominant parameter appeared to be the strength of the matrix, which was found to be proportional to the volume fraction of the reinforcement. These results are discussed in relation with the possible strengthening mechanisms in order to estimate the role of the icosahedral and related crystalline phases on the increase of yield stress.

The effect of Si addition on the icosahedral forming Al 65 Cu 20 Fe 15 alloy was investigated. Conventional casting and melt spinning were employed with the addition of Si element. As Si was added up to 5 at.% replacing the Al atoms, the volume fraction of the i-phase gradually decreased. However, with increasing Si content further up to 15 at.%, an 1/1 cubic approximant phase formed instead of the i-phase. After heat treatment at 750°C for 3 h, the volume fraction of the β-phase increased in an Al 64 Cu 20 Fe 15 Si 1 alloy, while the volume fraction of the 1/1 approximant phase increased in an Al 50 Cu 20 Fe 15 Si 15 alloy. The Al 50 Cu 20 Fe 15 Si 15 alloy showed a relatively high hardness and fracture toughness compared to the other Si containing Al–Cu–Fe alloys.

An Al 62 Cu 26 Fe 12 alloy was gas-atomised to prepare powders containing icosahedral quasicrystalline phase. For synthesizing composites, pure Al was selected as matrix material, and the Al 62 Cu 26 Fe 12 powders were added to the molten aluminum during the casting. A Ni coating with a thickness of approximately 5 μm deposited onto the Al 62 Cu 26 Fe 12 particles proved to be effective in preserving the original powder structure during casting. The composites showed a relatively good bonding between the Al 62 Cu 26 Fe 12 particles and matrix, despite the partial dissolution of the small satellite particles. Mechanical properties evaluated through compression and indentation tests of the composites indicated a significant increase of the yield stress especially in the range up to 10% volume fraction of reinforcing particles. Strengthening mechanisms were reviewed to estimate the role of the icosahedral and coexisting crystalline phases on the increase of the yield stress.

The focus of this study has been the effect of air plasma spray processing parameters on the characteristics of the Al–Cu–Fe quasicrystalline coatings. Key variables controlling the particle temperature and velocity and substrate temperature, such as the arc current, spraying distance, powder flow rate, and preheating of the substrate surface, were of primary interest. Significant effects of the process parameters on the microstructure and subsequent mechanical properties of the coatings were observed. Process conditions favorable for the formation of coating layers with larger amount of quasicrystalline phase led to the higher values of the microhardness, although it resulted in a relatively large porosity level. The bonding strength was found to be slightly dependent on the spraying distance, powder feeding rate, and preheating of the substrate. However, the predominant variable appeared to be the coating thickness, where a significant reduction of the bonding strength was reported as the coating thickness was increased up to 100 μm .

Room temperature mechanical properties of the Al/(AlCuFe)p and Al96Cu4/(AlCuFe)p cast composites were estimated from uniaxial compressive test and continuous ball indentation technique. Values of the Young’s modulus and yield stress determined from continuous ball indentation tests were slightly overestimated, suggesting a surface effect on the mechanical properties. However, it was shown that the Al-Cu-Fe particles provided a significant increase of the elastic modulus, yield stress, and strain hardening, especially in the range up to 10% volume fraction of reinforcements. Also, determination of the hardness by continuous-ball-indentation tests revealed a strong influence of the matrix strength on the mechanical properties of the conventionally cast composites.

A modified two-state-variable unified constitutive model is presented to model the high-temperature stress-strain behavior of a 319 cast aluminum alloy with a T7 heat treatment. A systematic method is outlined, with which one can determine the material parameters used in the experimentally based model. The microstructural processes affecting the material behavior were identified using transmission electron microscopy and were consequently correlated to the model parameters. The stress-strain behavior was found to be dominated by the decomposition of the metastable θ′ precipitates within the dendrites and the subsequent coarsening of the θ phase, which was manifested through remarkable softening with cycling and time. The model was found to accurately simulate experimental stress-strain behavior such as strain-rate sensitivity, cyclic softening, aging effects, transient material behavior, and stress relaxation, in addition to capturing the main deformation mechanisms and microstructural changes as a function of temperature and inelastic strain rate.

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.

The thermal and mechanical properties of 1 mm diameter rod specimens were investigated over a wide composition range of the Cu–Zr binary alloy system. Our results indicated that alloys with composition near Cu–36 at.% Zr have a higher activation energy and a lower plastic deformation during compression test than those of compositions near Cu–50 at.% Zr. A relationship between the activation energy and the plastic deformation could be worked out suggesting that the lower is the activation energy to crystallization, the larger is the plastic deformation.

The hydrogen permeability of a melt-spun Ni 60 Nb 30 Ta 10 (numbers indicate at.%) amorphous alloy has been examined in the temperature range of 573–673 K and pressures up to 0.6 MPa. Pd 60 Cu 40 alloy membranes were also evaluated in the same manner. The permeated hydrogen flux was increased with increasing the temperature and the difference of hydrogen pressure between the feed side and permeate side of the membrane. The maximum hydrogen permeability of the Ni 60 Nb 30 Ta 10 glassy alloy was 4.13 × 10 −8 mol/m s Pa 1/2 at 673 K, which was almost twice the permeability of Pd 60 Cu 40 alloy measured under the same conditions. These permeation characteristics imply the possibility of future practical application of the glassy alloys as the hydrogen separation membrane.

Accurate measurements of the fracture appearance transition temperature and fracture toughness KIC are greatly desired for engineering in steam power plant, especially from the standpoint of life extension. The current toughness of materials at critical locations is a key characteristic necessary for the remaining life analysis. For this purpose, small punch test techniques using miniature-sized specimens have been investigated on header components. Linear relationships, obtained between mechanical characteristics determined from small punch tests and from Charpy tests, have been used to estimate the fracture appearance transition temperature. Energy based and fracture stress formulations have been applied to estimate the fracture toughness in the upper- and lower-shelf regimes on a class of low alloy steels.

Small punch test techniques have been used to evaluate the mechanical properties of components from miniature-sized specimens. Correlations between mechanical characteristics determined from small punch tests and uniaxial tensile tests have been obtained on low alloy steels. Analytical formulations, with an appropriate description of the uniaxial stress–strain behavior, have been used to model the elastic bending, plastic bending and membrane stretching regimes of small punch load–deflection curves. These equations have been applied to austenitic 12Cr–1Mo steel in the temperature range 25–600°C, and have been verified on ferritic 1Cr–0.5Mo steel at ambient temperature. These formulations have also been used to estimate the uniaxial tensile stress–strain behavior of ferritic 2.25Cr–1Mo and AISI 403 steels from experimental small punch load–deflection curves.

We investigated the microstructural evolution of Sn96.4Ag2.8Cu0.8 solder through in situ heating transmission electron microscopy observations. As-soldered bump consisted of seven layers, containing the nanoeutectic lamella structure of AuSn and Au5Sn phases, and the polygonal grains of AuSn2 and AuSn4, on Au-plated Cu bond pads. Here, we found that there are two nanoeutectic lamellar layers with lamella spacing of 40 and 250 nm. By in situ heating above 140°C, the nanoeutectic lamella of AuSn and Au5Sn was decomposed with structural degradation by sphering and coarsening processes of the lamellar interface. At the third layer neighboring to the lamella layer, on the other hand, Au5Sn particles with a zig-zag shape in AuSn matrix became spherical and were finally dissipated in order to minimize the interface energy between two phases. In the other layers except both lamella layers, polycrystal grains of AuSn2 and AuSn4 grew by normal grain growth during in situ heating. The high interface energy of nanoeutectic lamella and polygonal nanograins, which are formed by rapid solidification, acted as a principal driving force on the microstructural change during the in situ heating.