Search

Different weight ratios of cerium (0.5, 1 and 2 wt.%) were produced in a controlled atmosphere by High Pressure Die Cast method to Mg-6Al-0.3Mn-1Sn alloy. The influence of cerium on microstructure and high-temperature mechanical properties was investigated. The microstructure study revealed that the main alloy contains intermetallic phases such as alpha-Mg, beta- Mg17Al12, Mg2Sn and Al11Ce3. The hardness values of the alloys were increased with the addition of 0.5%, 1 and 2 cerium. With the addition of 0.5 wt.% Ce, the yield strength increased to 145 MPa. With the addition of 2 wt.% of Ce, it was found to be 160 MPa with an increase of 14%. Tensile strength was obtained as 190 MPa. Elevated temperature tensile test was carried out at 120 degrees C, 180 degrees C and 240 degrees C, to all the alloys. It was found that increased Ce ratio increased the high-temperature mechanical strength. At 120 degrees C, the highest tensile and yield strength values were obtained with 159 MPa and 147 MPa, respectively, in the alloy with 2% wt. cerium added. In the tensile test performed at 180 degrees C, the highest tensile and yield strength were measured as 91 MPa and 77 MPa, respectively. The operating temperature of Mg alloys produced industrially by HPDC has a significant effect on mechanical properties. High operating temperatures reduce mechanical properties. However, the mechanical properties at high test temperatures were increased by the addition of Ce metal to the AM60-1Sn-XCe alloy produced with HPDC.

We examined the effect of 3p- and 5d-electron doping on the Kondo semiconductor CeFe2Al10 by means of the electrical resistivity (ρ), magnetic susceptibility (χ), and specific heat (C) measurements. The results show that in the 3p-electron-doped system CeFe2Al10−y Si y , the semiconducting behavior is suppressed for y = 0.05, and the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The Si substitution leads to a large decrease in the paramagnetic Weiss temperature θP indicating a reduction in c-f hybridization strength, however the Si does not induce magnetic order up to y = 0.3 down to 2K. The systematic changes in ρ(T), χ(T), and C(T) are similar to those for 5d-electron doped system CeFe2−x Ir x Al10, although, Ir substitution induces a bulk antiferromagnetic transition below 3.1 K in CeFe1.7Ir0.3Al10. These changes can be explained by the collapse of the hybridization gap due to the suppression of the c-f hybridization effect. Our results further confirm that the collapse of the spin/charge gap by an excess electron doping is one of the universal features of the Kondo semiconductors CeT 2Al10 (T = Fe, Ru, and Os).

cited By 4; International audience; Dynamic relaxation processes are fundamental to understand the mechanical and physical properties of metallic glasses. In the current work, mechanical relaxations in a La 30 Ce 30 Al 15 Co 25 bulk metallic glass were probed by dynamic mechanical analysis. In contrast to many metallic glasses, La 30 Ce 30 Al 15 Co 25 metallic glass shows a pronounced slow β relaxation peak. Physical aging below the glass transition temperature T g leads to an increase of the apparent activation energy and a decrease of the slow β relaxation magnitude. The correlation between the slow β relaxation and the main α relaxation is discussed. © 2019

Nanoindentation is used to measure Young's modulus, the hardness, the plasticity, and the yield strength of the phases in Al-50 wt % Sn alloy samples prepared by a traditional method and using liquid-state homogenization. The effect of an increase in the cooling rate by an order of magnitude and alloying with 0.06 wt % Ti or 1 wt % Zr on the mechanical properties of the phases in the Al-50 wt % Sn alloy is studied. The most substantial effect on Young's modulus of the phases in the Al-50 wt % Sn alloy is found to be exerted by the homogenization of the metallic liquid and the introduction of zirconium in the alloy melt: the metal forming of an ingot is improved substantially. © 2013 Pleiades Publishing, Ltd.

Results are presented for a study of the structural and phase transformations that occur in the titanium-nickelide shape-memory alloy Ti 49.5Ni50.5 subjected to heat treatment after deformation-induced amorphization by megaplastic high-pressure torsion (HPT) using five or ten revolutions of Bridgman anvils. The investigations were performed using transmission and scanning electron microscopy, X-ray diffraction, and measurements of the temperature dependences of electrical resistivity and magnetic susceptibility. It has been established that the crystallization of the alloy already occurs upon low-temperature treatment, beginning with ∼500 K. The evolution of the structure and the stage character of the development of crystallization and recrystallization processes depending on temperature have been determined. It has been shown that the annealing of the amorphized alloy makes it possible to obtain highly homogeneous nanostructured, submicrocrystalline, or bimodal states in the B2 austenite. A complete diagram of thermoelastic martensitic transformations of the B2 austenite has been constructed in the region from a nanostructured to a conventional polycrystalline state (with a grain size of 20-50 μm). The effect of size on the stabilization of austenite has been revealed and its specific features have been studied for the B2 → R and B2(R) → B19′ martensitic transformations depending on the structural state of the alloy. © 2013 Pleiades Publishing, Ltd.

Activity and activity coefficients of lanthanum were determined for the first time in gallium–indium eutectic based alloys in a wide temperature range employing electromotive force method. Activity of β-La and super cooled liquid lanthanum in Ga–In eutectic based alloys between 573 and 1073 K linearly depends on the reciprocal temperature: lg a β -La ( Ga – In ) = 5.660 - 15 , 352 T ± 0.093 lg a La ( Ga – In ) = 6.074 - 15 , 839 T ± 0.093 Activity coefficients of β-La and super cooled liquid lanthanum in this system at 617–1073 K are described by the following equations: lg γ β -La ( Ga – In ) = 3.786 - 12 , 216 T ± 0.171 lg γ La ( Ga – In ) = 4.199 - 12 , 703 T ± 0.171 In addition activity of lanthanum in alloys with In was also determined in the same temperature range.

A transition band between two deformation bands retains for the most part the orientation (110)[001] and shrinks to a thin interlayer or boundary with increasing degree of deformation. At a certain stage of deformation, the microvolumes that are arranged along the interface of the bands become adjusted to special misorientations. During primary recrystallization, cube-on-edge (Goss) grains, which grow from the transition band, have portions of special boundaries common with the deformed matrix; these boundaries were found earlier between the deformation bands. This indicates that the local domains with special misorientations formed at the stage of cold deformation transform during annealing into the corresponding primary-recrystallization nuclei. © 2013 Pleiades Publishing, Ltd.

The present work deals with the effects of pre- and post-weld heat treatments on microstructure and mechanical properties of alloy 718 friction weld joints. Prior to friction welding, alloy 718 rods were subjected to two types of heat treatments - solution treatment (ST) and solution treatment followed by aging (STA). In the as-welded condition, samples welded with prior ST condition exhibited higher hardness in the weld zone compared to the base material in ST condition and this is attributed to grain refinement due to dynamic recrystallization. Samples welded with prior STA condition exhibited decreased hardness in the weld zone and room temperature tensile properties in relation to the base material in STA condition. It is due to dissolution of ?? (Ni 3Nb) phase as the temperature measured at weld zone was found to be 1118�C. In order to retrieve the hardness and room temperature tensile properties, friction weld joints were subjected to direct aging (DA) treatment. A significant increase in hardness was observed in the weld zone after direct aging for both samples welded in ST and STA conditions. This is attributed to the grain refinement due to dynamic recrystallization and formation of precipitates by the DA treatment. � 2012 Elsevier B.V.

An attempt has been made to predict phase formation using a CALPHAD-based approach for a large number of compositions that are known to form FCC, BCC and a mixture of FCC and BCC phases. The stable phase is assumed to be the first phase that is formed upon cooling from liquid state with the highest driving force. The driving force for other phases at the transition for various compositions is also presented. A comparison between the parametric approach of phase prediction by study of thermodynamic and topological parameters on one hand and the CALPHAD approach on the other is also presented. CALPHAD approach appears to predict BCC phase formation much more accurately than the FCC phase formation. The results indicate that solid solution formation in multicomponent alloys is favored when the ratio of ?S config/?S fusion is greater than 1 and 1.2 for equiatomic and non-equiatomic alloys, respectively. The results also point out that BCC phase is favored when the atomic size difference is larger, which is reflected by a higher value of ?S ?/k. Formation of FCC phase appears to be governed mainly by ?H mix, while BCC phase governed by ?S ?/k, which is representative of strain in the structure. � 2012 Elsevier B.V. All rights reserved.

CuNi bimetallic alloy particles supported on CeO2 are prepared by coprecipitation of the corresponding salt precursors followed by calcination and hydrogen reduction. The supported alloy particles are characterized by PXRD, H2-TPR, XPS, XANES and EXAFS techniques. The PXRD study shows that copper rich oxide phases supported on CeO2 are reduced at 200 �C. However, complete reduction of CuO-NiO phases occurs at 450 �C forming CuNi alloy particles on CeO2. The H2-TPR results show that mixed oxides are reduced at higher temperatures than pure components indicating strong wetting between oxide components and CeO2. The Ni 2p XPS shows stronger interaction between Ni2+ and CeO2 support. XANES and EXAFS studies show the formation of CuNi alloy particles with small surface segregation of Cu. The catalytic activity of the supported CuNi alloy particles is studied by non-oxidative dehydrogenation of cyclohexanol to cyclohexanone reaction. The effect of temperature, contact time and time on stream are examined to gain insights into the catalytic activity of the CeO2 supported CuNi alloy catalysts. Among all the CuNi alloy compositions, CuNi(1:1)/CeO2 catalyst shows higher catalytic activity and selectivity to cyclohexanone. Formation of stable CuNi alloy particles on CeO2 by alloy-redox support interaction and segregation of Cu are crucial factors for catalytic activity. � 2012 Elsevier B.V.

Microstructural features developed along with mechanical properties in furnace brazing of Ti-6Al-4V alloy using STEMET 1228 (Ti-26.8Zr-13Ni-13.9Cu, wt.%) and STEMET 1406 (Zr-9.7Ti-12.4Ni-11.2Cu, wt.%) amorphous filler alloys. Brazing temperatures employed were 900-950 Degree-Sign C for the titanium-based filler and 900-990 Degree-Sign C for the zirconium-based filler alloys, respectively. The brazing time durations were 600, 1200 and 1800 s. The brazed joints were evaluated by ultrasonic test, and their microstructures and phase constitutions analyzed by metallography, scanning electron microscopy and X-ray diffraction analysis. Since microstructural evolution across the furnace brazed joints primarily depends on their alloying elements such as Cu, Ni and Zr along the joint. Accordingly, existence of Zr{sub 2}Cu, Ti{sub 2}Cu and (Ti,Zr){sub 2}Ni intermetallic compounds was identified in the brazed joints. The chemical composition of segregation region in the center of brazed joints was identical to virgin filler alloy content which greatly deteriorated the shear strength of the joints. Adequate brazing time (1800 s) and/or temperature (950 Degree-Sign C for Ti-based and 990 Degree-Sign C for Zr-based) resulted in an acicular Widmanstaetten microstructure throughout the entire joint section due to eutectoid reaction. This microstructure increased the shear strength of the brazed joints up to the Ti-6Al-4V tensile strength level.more » Consequently, Ti-6Al-4V can be furnace brazed by Ti and Zr base foils produced excellent joint strengths. - Highlights: Black-Right-Pointing-Pointer Temperature or time was the main factors of controlling braze joint strength. Black-Right-Pointing-Pointer Developing a Widmanstaetten microstructure generates equal strength to base metal. Black-Right-Pointing-Pointer Brittle intermetallic compounds like (Ti,Zr){sub 2}Ni/Cu deteriorate shear strength. Black-Right-Pointing-Pointer Ti and Zr base filler alloys were the best choice for brazing Ti-6Al-4V.« less

Hall-Petch (HP) relation and the superposition of different strengthening mechanisms in different aluminum alloys with grain sizes in the range of 50 nm-70 ?m were analyzed. HP parameters as high as ? 0 ? 200 MPa and k HP ? 0.14 MPa m 1/2 were observed when the HP relation was fitted directly using the experimentally measured yield strength values. In contrast, considering only the grain size strengthening (by subtracting other strengthening contributions), HP constants of ? 0 ? 10 MPa and k HP ? 0.06 MPa m 1/2 were obtained over wide range of grain sizes for the case of a linear superposition of the various strengthening mechanisms present. This is in excellent accord with the values obtained for pure Al justifying the chosen superposition exponent of n equal unity for the different alloys investigated. Copyright � 2012 WILEY-VCH Verlag GmbH &amp, Co. KGaA, Weinheim.

First-principles calculations of the variation of the total energy of a ferromagnetic Fe-31.2% Ni alloy upon bainitic transformation are presented. The problem of the loss of stability of the fcc lattice of iron alloys is discussed to show that the fcc lattice is mechanically stable in this alloy. © Pleiades Publishing, Ltd., 2012.

The corrosion behavior of the fusion zone of gas tungsten arc (GTA) welds of AA6061 alloy was studied. The role of GTA welding techniques such as continuous current and pulsed current (PC) with reference filler (AA4043) was studied. The role of the addition of different grain refiners such as scandium (Sc), zirconium, and Tibor to the reference filler was studied. Dynamic polarization testing was used to determine the pitting corrosion resistance of the fusion zone. Optical microscopy and scanning electron microscopy studies were carried out to find the mechanism of corrosion. Out of all the grain refiners studied, better corrosion resistance was observed with 0.5 % Sc addition to fusion zone through reference filler and PC technique. � 2012 Springer-Verlag London Limited.

We present a detailed magnetic critical behavior study of Fe 2CrAl Heusler alloy, for the first time, with rigorous analysis of high precision magnetization data obtained over the critical temperature region. Our studies confirm that B2 type site-disordered in Fe 2CrAl alloy exhibits long-range ferromagnetic order below a well defined Curie temperature (T=208 K). Though the nature of this transition is found to be of second order, the estimated critical exponents ?=0.42, ?=1.356 and ?=4.25, are in between the theoretically predicted values for three-dimensional Heisenberg and mean-field interaction models. However, it is noteworthy that the scaling relations are obeyed indicating renormalization of interactions around the Curie temperature (T C), where magnetization data collapse into two separate branches, above and below T C. This conclusively shows that calculated critical exponents as well as critical temperature are unambiguous and intrinsic to the system. However, magnetization vs temperature data shows another magnetic transition (at T=313 K) above the Curie temperature. It is shown that the short range magnetic correlation exist even beyond T C with cluster moment ?10 2 ? B. This is attributed to a site disorder which results in formation of Cr clusters with short range ferromagnetic order. � 2011 Elsevier B.V. All rights reserved.

cited By 3; International audience; Following aging under stress, Ni-rich TiNi shape memory alloys are subject to a two-way shape memory effect known as the "All Round Memory Effect" (ARME). The latter causes a sample to return to its high temperature shape during heating after being spontaneously deformed on cooling during martensitic and R-phase transformations. This effect has been thoroughly studied for stresses in bending. In this work, we were able to generate ARME with tensile stresses, making it possible to make more quantitative measurements of the effect. Application of a static stress opposite spontaneous deformation during cooling also allowed quantifying the magnitude of internal stresses caused by Ti 3Ni 4 coherent precipitates during aging. © 2011 Elsevier B.V. All rights reserved.

IMI834 (Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si) is a high-tech near-α titanium alloy with improved creep resistance and mechanical property retention at temperatures up to 600°C [1]. It is used in the aerospace industry for compressor disks and blades due to its excellent balance between creep resistance and fatigue strength [2]. The linear friction welding (LFW) behaviour of IMI834 displaying an initial bimodal α+β microstructure was investigated using varying axial pressures during welding. Electron backscatter diffraction (EBSD) was used to characterize the texture and phase fraction of the welded IMI834 samples in the weld zone (WZ) and thermomechanically affected zones (TMAZ) in relation to the base material. Based on microhardness evaluation of the weldments, the WZ was determined to be slightly harder than the base material. © 2012 Trans Tech Publications, Switzerland., 7th International Conference on Processing and Manufacturing of Advanced Materials, THERMEC'2011, 1 August 2011 through 5 August 2011, Quebec City, QC

cited By 17; International audience; The acoustic emission technique was applied to standard tests devoted to evaluate sulfide stress cracking susceptibility of steels for oil and gas industry. The mapping of the density of AE signals vs. their location on the specimen gauge length as a function of time allowed early detection of cracking, and gave meaningful information on incubation times and propagation rates. Sulfide stress cracking initiation was correlated with the presence of critical surface defects. A mechanism involving plastic strain and/or metal dissolution was proposed to account for crack propagation. © 2011 Elsevier Ltd.

In this study, the global and local tensile behaviours of laser welded 5.1-mm thick Ti-6Al-4V alloy were obtained at various welding speeds and defocusing distances using a digital image correlation (DIC) technique with a full field three-dimensional deformation measurement system. The local tensile properties including elastic modulus, yield stress, and maximum plastic strain were determined at various locations by assuming an iso-stress condition. It was found that the elastic modulus and yield stress were maximum in the fusion zone (FZ) and minimum in the heat-affected zone (HAZ). Porosity and underfill defects were the main reasons for the failures in the FZ and/or the HAZ. Maximum plastic strain at fracture was observed at the failure location in most cases., 7th International Conference on Processing and Manufacturing of Advanced Materials, THERMEC'2011, August 1-5, 2011, Quebec City, QC, Canada

IntroductionCurrently, nanocrystalline materials are being widelyinvestigated due to their unique properties. This interest hasspawned the development of various techniques to synthe-size materials exhibiting grain sizes (\20 nm) wherephysical properties are the most exotic. Such processesinclude: high-energy ball milling [1, 2], pulsed electrode-position [3], chemical vapour condensation [4], inert gascondensation [5] etc. However, nanocrystalline samplesproduced from these techniques are either in the formof powders or thin films. Successful consolidation to arte-fact free, fully dense material is required if structuralapplications are ever to be adopted. Many methods toconsolidate these materials (i.e., hot compaction [6],explosive consolidation [7], hot isostatic pressing [8], pre-annealing–compaction–sintering [9] etc.) have been repor-ted in the literature with partial success. In general, thesuccess of these techniques for consolidation hinges on theapplication of high temperatures and pressures, which leadto explosive grain growth in nanocrystalline materials.In situ consolidation technique as developed by Youssefet al. [10] seems promising for the synthesis of consolidatednanocrystalline materials as the step of sintering to bulkdensity is no longer a need and can be eliminated. However,this technique has not been reported widely in the literatureand has been limited to nanocrystalline Zn, Al, Al alloys,copper and copper-based alloys [10, 11]. This study showsthat in situ consolidation of a FeCrNi alloy is possible usingcombination of room temperature (RT) milling and liquidnitrogen temperature milling.Nanocrystalline materials produced by high-energy ballmilling have not been well characterized and the micro-structure of these materials is not well understood. Theprimary challenge in characterization is TEM samplepreparation from ball-milled powders. Nanocrystallinepowders as produced by ball milling are too coarse to beexamined under TEM and the sample preparation for TEManalysis on such powders is not a trivial task. In general,two methods are used for the preparation of conventionalmetallic samples for TEM analysis: electro jet polishingand dimpling followed by ion milling. Nanocrystallinematerials produced by consolidation of ball-milled pow-ders can be problematic for these preparation techniques asthe consolidated samples must first be mechanically thin-ned to \100 lm before being chemically thinned to thefinal thickness. If the material exhibits poor inter-particlebonding, the sample may not withstand the final thinning

Process selection for repair of mechanical components due to wear and corrosion, e.g. damage of aluminum casting housings of fuel injection systems, is based on cost and response time factors, provided that the mechanical performance is maintained within acceptable limits. One of the promising and emerging repair technologies is Cold Gas-Dynamic Spray (CGDS) coating, where a high-pressure gas propels fine powder particles to very high velocities to produce surface coating. It is essential to identify the optimum process conditions and powder composition to produce repaired surfaces with tribological properties close to those of the originally manufactured part (without coating). The objective of this work is to compare the dynamic friction and fretting wear properties of the repaired surfaces using various types of coating composition and spraying techniques. Eight types of CGDS coatings, applied to AMS 4260 aluminum specimens, were fretted against 440C stainless steel specimens at low and high nominal loads to assess their fretting wear resistance, dynamic friction properties and damping capacity. The optimum coating composition and process conditions were identified. In comparison to the uncoated specimen, this optimum coating offered tribological characteristics close to the uncoated material and even better dynamic friction properties. © 2010 Elsevier Ltd. All rights reserved.

A new TiAl-2Nb-2Mo beta gamma alloy was synthesized by powder metallurgy process. HIP'ed and vacuum heat treated specimens were isothermally oxidized at 800 °C and 900 °C in air up to 500 h. The TiAl-2Nb-2Mo alloy oxidized parabolically up to 500 h at both 800 °C and 900 °C. The oxides consisted of outer TiO2 layer, intermediate Al2O 3 layer, and inner TiO2 rich mixed layer and the oxidation mechanisms of the alloy were identical at both temperatures. During oxidation, the degradation of lamellar colonies formed a diffusion zone just below the oxide/substrate interface consisting of γ-TiAl matrix and dispersed beta phases which contained high concentration of Nb and Mo. The oxidation rate of the TiAl-2Nb-2Mo alloy is more sensitive to temperature than those of the Ti-48Al-2Nb-2Cr and Ti-48Al-2Nb-2Cr-W alloys. © 2011 Elsevier Ltd. All rights reserved.

In this paper, the tensile, high cycle fatigue (HCF), Impact and fracture behaviour of Aluminium alloy 2618(AA 2618) reinforced with particulates of Silicon Carbide (SiCp) is discussed. AA 2618/SiCp metal matrix composites (MMCs) were fabricated by two-step mixing of stir casting method followed by forging operation. A significant increase of the elastic modulus and tensile strength in the MMCs respect to the unreinforced alloys were evidenced by the tensile tests, while the elongation at fracture decreased. Temperature effects on the tensile properties at 120�C and 200�C were studied. The high cycle fatigue tests showed a marginal increase in fatigue life over the unreinforced alloys. A SEM analysis of the fracture surfaces showed that tensile feature was controlled by micro-void coalescence, interfacial decohesion and fracture of reinforcing particles, whereas fatigue was controlled by interfacial decohesion at the matrix-particle interface. The impact behaviour of the composites was affected by clustering of particles, particle cracking and weak matrix-reinforcement bonding. Agglomeration of the particles reduced the impact strength. The effect of particle size is invariant to the impact strength.

In the present work the structure and morphology of the phases of nanocomposites formed in rapidly solidified Al–Fe alloys were investigated in details using analytical transmission electron microscopy and X-ray diffraction. Nanoquasicrystalline phases, amorphous phase and intermetallics like Al 5 Fe 2 , Al 13 F 4 coexisted with α-Al in nanocomposites of the melt spun alloys. It was seen that the Fe supersaturation in α-Al diminished with the increase in Fe content and wheel speed indicating the dominant role of the thermodynamic driving force in the precipitation of Fe-rich phases. Nanoquasicrystalline phases were observed for the first time in the dilute Al alloys like Al–2.5Fe and Al–5Fe as confirmed by high resolution TEM. High hardness (3.57 GPa) was measured in nanocomposite of Al–10Fe alloy, which was attributed to synergistic effect of solid solution strengthening due to high solute content (9.17 at.% Fe), dispersion strengthening by high volume fraction of nanoquasicrystalline phase; and Hall–Petch strengthening from finer cell size (20–30 nm) of α-Al matrix.

cited By 5; International audience; Fatigue tests are performed on the Cu-2.16Ni-0.72Si alloy, at different stress ratios, R, at room temperature and 473. K. For R= 0.4 the fatigue strength decreases when temperature is increased. The observation of intergranular cracking on fracture surfaces shows that this phenomenon is related to dynamic embrittlement. © 2011 Elsevier B.V.

Although the grain-refinement practice is well established for wrought Al alloys, in the case of foundry alloys such as near eutectic Al-Si alloys, the underlying mechanisms and the use of grain refiners need better understanding. Conventional grain refiners such as Al-5Ti-1B are not effective in grain refining the Al-Si alloys due to the poisoning effect of Si. In this work, we report the results of a newly developed grain refiner, which can effectively grain refine as well as modify eutectic and primary Si in near eutectic Al-Si alloys. Among the material choices, the grain refining response with Al-1Ti-3B master alloy is found to be superior compared to the conventional Al-5Ti-1B master alloy. It was also found that magnesium additions of 0.2 wt pct along with the Al-1Ti-3B master alloy further enhance the near eutectic Al-Si alloy's grain refining efficiency, thus leading to improved bulk mechanical properties. We have found that magnesium essentially scavenges the oxygen present on the surface of nucleant particles, improves wettability, and reduces the agglomeration tendency of boride particles, thereby enhancing grain refining efficiency. It allows the nucleant particles to act as potent and active nucleation sites even at levels as low as 0.2 pct in the Al-1Ti-3B master alloy. � 2011 The Minerals, Metals & Materials Society and ASM International.

The transformation kinetics and the morphology of structures formed in the Cu-24 at % Ga alloy at a cooling rate of 1 to 4 × 105 K/s are studied. A massive transformation shows up in the Cu-24 at % Ga alloy at slow cooling rates, and this transformation can be replaced, upon sharp quenching, by a martensitic reaction. The transformation kinetics and the morphology of structures formed in the Cu-24 at % Ga alloy at cooling rates of up to 400 kK/s are analyzed in the study. © 2011 Pleiades Publishing, Ltd.

Mechanical properties of bulk nanocrystalline Al–4Cu alloys with grain sizes from 47 to 105 nm, synthesized by mechanically alloying followed by vacuum hot pressing at different temperatures, were analysed through Hall–Petch relation. Hall–Petch analysis revealed a high frictional stress (170 MPa) and a high positive slope ( 0.13 MPa m ) as compared to pure Al, which has a frictional stress (15–30 MPa) and a slope ( 0.06 – 0.09 MPa m ). From a detailed evaluation of different strengthening mechanisms it is inferred that the Al 2 Cu precipitates and oxide particles are the likely reason for such high values of frictional stress and slope.

Structure of the Fe-5.5% Cu alloy has been studied after aging at 500°C to show that the lattice of copper precipitates changes with increasing time of holding at a temperature from bcc to 9R to fcc. The free energy of the solid solutions and the phase-separation diagrams of the bcc and fcc phases of copper have been calculated. Barriers for the nucleation of copper particles with the bcc and fcc lattices have been evaluated. Factors that favor the appearance of intermediate structural forms of copper, which precede the formation of the stable fcc phase, are discussed. © 2010 Pleiades Publishing, Ltd.

High strength with high ductility can be achieved in the titanium alloys by using metal precipitated ceramic particle as reinforcement. In this work, ? ? b or ?-Ti alloy composites were prepared with ?-Ti precipitated TiC particles. A series of Ti-Fe-C-N alloys were prepared and a constitutional diagram was constructed as a function of N and Fe contents. Two criteria were identified for the formation of ?-Ti precipitation. One is the existence of Ti 2C phase and the other is the presence of ?-Ti phase in the matrix. The mechanism of ?-Ti formation from the Ti 2C phase is discussed. � Springer Science+Business Media, LLC 2010.

Wide gap brazing (WGB) of X-40 cobalt based superalloy was conducted in this study using BNi-9 braze alloy with X-40 and IN738 additive alloys. A groove was machined into X-40 bars with a nominal width of 6-35 mm before filler application. Following brazing at 1200°C for 15 min, the microstructure of the as brazed joints was examined using SEM, EDS and nanoindentation technique. Both WGB joints with X-40 and IN783 additive alloys contained primary matrix phase in addition to a number of boron containing phases which assumed either eutectic or discrete forms. Nanoindention testing revealed that these boron containing phases exhibited hardness values several times higher than the base alloy and matrix phase contributing to the embrittlement of the braze joint. Porosity was also observed in both types of WGB braze joints, the degree of which was greatest in the braze joints with IN738 additive alloy. Tensile testing at 950uC showed that the yield strength of both WGB joints was higher than that of the baseline specimens while the ultimate tensile strength of the WGB joints was lower than that of the baseline X-40. The ductility of the WGB joints was significantly inferior to that of the baseline X-40, particularly for WGB with IN 738 additive alloy. © 2010 Institute of Materials, Minerals and Mining.

Neutron powder diffraction experiments and magnetization measurements have been carried out on the intermetallic compound Ce4Ge3 (Cubic, Th3P4-type). The neutron diffraction data obtained in zero field at 2 K, reveal commensurate antiferromagnetic ordering with magnetic moments of Ce directed along (0 0 1) axis (MCe = 1.55(4) ?B) whereas the magnetization data depict two magnetic transitions at ?12 K and at ?6 K, respectively. Isothermal magnetization data obtained at 2 K present complex metamagnetic transition with two plateaus corresponding to magnetic moment values of ?0.35?B/Ce3+ in 2 T and ?0.94 ?B/Ce3+ in 9 T field. � 2009 Elsevier B.V. All rights reserved.

The effect of processing parameters (rotation speed and traverse speed) on the corrosion behaviour of friction stir processed high strength precipitation hardenable AA 2219-T87 alloy was investigated. The results indicate that the rotation speed has a major influence in determining the rate of corrosion, which is attributed to the breaking down and dissolution of the intermetallic particles. Corrosion resistance of friction stir processed alloy was studied by potentiodynamic polarization, electrochemical impedance spectroscopy, salt spray and immersion tests. � 2008 Elsevier Masson SAS. All rights reserved.

The plane strain fracture toughness, KJI c and crack growth toughness in terms of the non-dimensional tearing modulus, TR of Al-Cu alloy were evaluated following the J-integral method. An empirical relation is proposed for estimating the fracture toughness from the tensile properties. The estimated fracture toughness values from the empirical relation are found to be in good agreement with the measured fracture data. The microstructural as well as strength variations in the subject alloy were examined through different aging treatments (viz., under aging (UA), natural aging (NA), peak aging (PA) and over aging (OA)). The microstructural observations in different aging conditions were made through transmission electron microscopy (TEM) to understand the type of phase or intermediate stages of the phase present (GP zones, ??, ?? or ?). Fracture toughness testing has been carried out on 14 mm thick compact tension (CT) specimens and estimated the crack extension by unloading compliance technique. It was noted that the yield strength increases and fracture toughness decreases with the increase in the degree of aging from NA to PA condition. On overaging the alloy to a yield strength level as that of UA, it was not possible to retain the UA level of fracture toughness. The highest crack growth toughness is exhibited by the NA temper. The fractography analysis revealed that the fracture mode was predominantly transgranular dimpled rupture. Fracture initiation occurred by void nucleation at the second phase particles. The differences in the fracture toughness of the alloy in different aging conditions were shown to be dependent on the differences in the matrix deformation behavior and the strength differential. � 2008 Elsevier B.V. All rights reserved.

A system of mean field rate equations is employed for describing the kinetics of solid-solid phase separation within the immiscibility gap of binary alloys. The system allows us to study the time evolution of both supersaturation and diffusion length of the components in the metastable phase. It is shown that in the case of simultaneous nucleation the system of differential equations leads to a simple formula for the characteristic time of the transformation in terms of material parameters and initial supersaturation. The nucleation rate is computed on the basis of the classical nucleation theory and the alloy is assumed to behave as a regular solution. It turns out that for low values of the initial supersaturation the nucleation process can be considered as simultaneous. It is also found that thermally activated nucleation takes place for supersaturation values lower than about 0.21. The assumption of a concentration-independent diffusion coefficient and the effect of nucleus curvature on interface composition have been analyzed and discussed.

Fatigue crack growth rate (FCGR) and dwell-FCGR tests were conducted at 704C° in a vacuum environment and compared with data obtained under lab air conditions for various microstructural conditions of ATI 718Plus Alloy (718Plus) and Waspaloy. The results indicated that environmental damage has a significant impact on the FCGR characteristics of both alloys, particularly in the near-threshold regime. The dwell fatigue crack propagation behaviour under vacuum conditions displayed identical behaviour irrespective of differences in microstructural features. The observed crack growth rates under vacuum decreased dramatically compared to lab air test results, highlighting the crucial impact of environmental damage on the dwell-fatigue crack propagation resistance of both alloys. The fracture mode for 718Plus was observed to be predominately intergranular in both the FCGR and dwell-FCGR test conditions, with the effect of long-term thermal exposure leading to a larger fraction of transgranular failure. Waspaloy fracture surfaces revealed a predominantly transgranular deformation mode. The fracture surfaces of 718Plus and Waspaloy all exhibited transgranular fracture under vacuum test conditions and were nearly indistinguishable in crack topography. Dynamic embrittlement is believed to be the governing mechanism for intergranular failure of 718Plus leading to grain boundary decohesion. Improvement of dwell-fatigue crack propagation resistance of 718Plus may be strongly related to the coarsening of the γ hardening phase, with potential further improvement via implementation of a bimodal γ heat treatment. EDX analysis showed that the 8 phase just at the crack tip becomes oxidized and may be a contributing factor in the susceptibility of the grain boundaries during the dwell-FCGR tests. The presence of Nb-rich carbides along the dwell-fatigue crack path of 718Plus was also identified. Carbides located behind the crack front were heavily oxidized and those carbides observed just ahead of the crack tip showed no oxidation. It is believed that oxidation of these NbC particles near grain boundaries may be linked to the environmental susceptibility of 718Plus during dwell-fatigue crack propagation., 12th International Symposium on Superalloys, Superalloys 2012, September 9-13, 2012, Seven Springs, PA, USA

Ni-Cr-B-Si coatings are used in many industrial applications in order to improve wear and/or corrosion properties. These coatings have traditionally been deposited by thermal spray techniques but the laser cladding process is also being increasingly employed to produce Ni-Cr-B-Si coatings with superior functional properties. In this research, the microstructural evolutions and the phase formations in the laser cladding of a Ni-Cr-B-Si alloy and their effects on the hardness of the clad layer are discussed. Results of this study show various types of boride and carbide phases can form in each track of the clad layer. These changes demonstrate the potential for tuning the properties of these coating by controlling the processing conditions. © 2011 WIT Press.

The potential of application of in-situ neutron diffraction for studies of solidification of Al alloys have been previously reported by the authors for the binary hypereutectic A-Si system. This illustrated the potential of neutron diffraction for high resolution melt analysis at near-liquidus temperatures required for advanced studies of grain refining, eutectic modification, etc. The solid and liquid volume fractions were determined based on the change of intensity of neutron diffraction peaks over the solidification interval. The path of non-equilibrium solidification for the alloy modified with addition of copper and magnesium is very complex. Phase diagrams and FactSage-based computations give only approximate kinetics of solid phase(s) evolution during cooling and solidification. On the other hand, in-situ neutron diffraction, coupled with the results of thermal analysis, provides non-biased experimental data on phase evolution; for example, on formation of FCC Al-Cu-Si and diamond silicon during solidification of hypereutectic Al-Si-Cu alloy., TMS 2011 - 140th Annual Meeting and Exhibition, 27 February 2011 through 3 March 2011, San Diego, CA

3 páginas, The magnetic entropy change (ΔSM), temperature of peak ΔSM (Tpk) and refrigerant capacity (RC) in Fe(RE)80B12Cr8 (RE = La, Ce, or Gd) alloys were studied. Increasing La, Ce, and Gd content led to relatively constant, decrease, and increase in Tpk, respectively. Both the phenomenologically constructed universal curve for ΔSM and field dependence power laws demonstrated that these alloys exhibited similar critical exponents at Curie temperature. With 5% Ce added to Fe80B12Cr8, Tpk could be tuned near room temperature with relatively constant peak ΔSM. Fe79B12Cr8La1 exhibited enhanced RC compared to Gd5Si2Ge1.9Fe0.1. The tunable Tpk and enhanced RC are needed in active magnetic regenerators., This work was supported by the U.S. AOARD Grant No. AOARD-08-4018 , program manager, Dr. R. Ponnappan, by the Spanish Ministry of Science and Innovation and EU FEDER Project No. MAT 2010-20537 , the PAI of the Regional Government of Andalucía Project No. FQM- 6462 , and the United States Office of Naval Research Project No. N00014-11-1-0311 .

Properties and structure of liquid Fe-C alloys with carbon concentration up to 20 at% at temperatures up to 2500 K were calculated using molecular dynamics modelling. Interaction between Fe-Fe and Fe-C atoms was described using the embedded atom potential (EAM). The Morse potential was chosen for Fe-C pair interaction, while C-C pair interaction was presented in the form of the repulsive potential. Parameters of potentials were adjusted using experimental data for density, internal energy, bulk modulus and distance between Fe and C atoms in liquid Fe-C alloys near the liquidus temperature. Calculated density and molar volume of Fe-C alloys at 1873 K decreased with increasing carbon concentration; a temperature coefficient of density of liquid alloys was, practically, independent of the carbon concentration. Carbon content of the alloys had a negligible effect on the distance between Fe-Fe and Fe-C atoms and on a sum of coordination numbers Fe-Fe and Fe-C. Distribution of atoms in the first coordination sphere in the Fe-C alloys was close to statistical. Copyright © 2012 De Gruyter.

The use of powerful analytical methodologies for the evaluation of the performance of commercial oxygen storage materials based on oxygen transient isothermal isotopic exchange experiments is illustrated in this study. Ce x Zr1-x O2-based oxygen storage materials were investigated. The materials were characterized for their dynamic oxygen storage and release properties through the pulse injection technique allowing the measurement of the oxygen storage capacity (OSC), and for their surface and bulk oxygen mobility through transient isothermal 18O isotopic exchange experiments. Very high OSC values were obtained after calcination in air at Tcalc. = 700 or 850 °C. However, after thermal aging at 1000 or 1100 °C of the as prepared samples, a significant deterioration of their OSC was observed. This fact was found to correlate with the significant increase in the activation energy of surface oxygen mobility. On the contrary, smaller increase in the activation energy of bulk oxygen diffusion with increasing Tcalc. was observed. © 2009 Springer Science+Business Media, LLC. 52 13-20 2013 2018 Cited By :12

Effects of Mn addition on the devitrification kinetics, microstructure and hyperfine inter- action parameters of FeCoMnNbB alloys were investigated. As-cast and nanocrystalline samples were studied by different experimental techniques and results were correlated. Mn alloying pro- voked a significant lowering of the Curie temperature of the amorphous phase. No big changes were observed in the microstructure of the nanocrystalline alloys with the Mn additio

Recent experimental results indicate the possible realization of a bulk odd-frequency superconducting state in the compounds CeCu$_2$Si$_2$, and CeRhIn$_5$. Motivated by this, we present a study of the quantum transport properties of a normal metal/odd-frequency superconductor junctions in a search for probes to unveil the odd-frequency symmetry. From the Eliashberg equations, we perform a quasiclassical approximation to account for the transport formalism of an odd-frequency superconductor with the Keldysh formalism. Specifically, we consider the tunneling charge conductance and tunneling thermal conductance. We find qualitatively distinct behaviour in the odd-frequency case as compared to the conventional even-frequency case, in both the electrical and thermal current. This serves as a useful tool to identify the possible existence of a bulk odd-frequency superconducting state., Comment: 7 pages, 3 figures. Accepted for publication in Physical Review B

The aim of this work was to probe the back-spillover of labile O, OH and H species during steam reforming of phenol towards H2 production in the 773-1028 K range over Rh supported on MgO and Mg-Ce-Zr-O mixed-metal oxides. This was made possible through steady state isotopic transient kinetic analysis (SSITKA) and other transient isotopic experiments (use of D2O and 18O2) combined with temperature-programmed desorption ones. The size of the active pool of H-containing intermediate species (H and/or OH) present in the H-path of reaction as a function of reaction T was measured over the 0.1 wt% Rh/50Mg-25Ce-25Zr-O catalyst by SSITKA experiments. It was found that the size of this pool decreases by 18% in the 773-928 K range (θ = 68.9-56.3), whereas a significant decrease (by a factor of 10) was observed between 928 and 1028 K. These results demonstrate that most of the active H and OH species reside on the support and metal-support interface. Two kinds of H-containing intermediate species are likely to participate in the H-path of reaction. An inverse D kinetic isotopic effect was measured for the H2 formation in the phenol steam reforming reaction in the 773-1028 K range. © 2006 Elsevier B.V. All rights reserved. 116 3 341 347 Cited By :34

Resonant laser-induced breakdown spectroscopy (RLIBS) was investigated to improve the limit of detection (LoD) of lead traces in copper alloys. A 5-ns optical parametric oscillator laser pulse was used to ablate the sample (front edge of the pulse) and resonantly excite the lead atoms in the vapor plume (rear edge of the pulse). The laser was tuned to the Pb I 283.31 nm line and the Stokes direct-line fluorescence signal at 405.78 nm was recorded. The experiments were performed in air at atmospheric pressure. The influence of the main experimental parameters, namely the laser wavelength, laser fluence and acquisition delay, on the signal-to-noise ratio (SNR) for the Pb I 405.78 nm line was studied experimentally. We found that the best SNR for the Pb I 405.78 nm line was achieved for a laser fluence of about 1.4 J cm-2, corresponding to the onset of visible damage on the sample, and an acquisition delay of about 5 ns. When the laser was on resonance a Pb I 405.78 nm signal could however be observed for a fluence as low as 0.25 J cm-2. For fluences greater than about 5 J cm-2, similar results were obtained whether the laser wavelength was tuned on resonance or not. Under these optimal conditions, the relative LoD for lead was estimated to be about 8 parts per million, accumulating over 500 laser shots. This amounts to an improvement of about 11-fold when compared to non-resonant LIBS in typical conditions. The corresponding absolute LoD was estimated to be about 0.8 femtograms and was calculated from optical coherence tomography measurements of the crater profiles. The fact that the best performances of RLIBS were obtained near the onset of visible damage on the sample indicates that this approach is particularly suitable for minimally destructive elemental analysis. © 2011 The Royal Society of Chemistry.

We have studied the magnetocaloric effect in a series of Fe88−2xCoxNixZr7B4Cu1Fe88−2xCoxNixZr7B4Cu1alloys. The partial substitution of Fe by Co and Ni leads to a monotonic increase in the Curie temperature(TC)(TC) of the alloys from 287 K for x=0x=0 to 626 K for x=11x=11. The maximum magnetic entropy change (ΔSpkM)(ΔSMpk) at an applied field of 1.5 T, shows a value of 1.98 J K−1 kg−11.98 J K−1 kg−1 for x=8.25x=8.25. The refrigerant capacity (RC) has maximum values near 166 J kg−1166 J kg−1 (for x=0x=0 and 2.75). These values place the present series of alloys among the best magnetic refrigerant materials, with an RC ∼40%∼40% larger than Gd5Si2Ge1.9Fe0.1Gd5Si2Ge1.9Fe0.1 and ∼15%∼15% larger than Fe-based amorphousalloys.

In this study, the corrosion properties of Zn-Co alloys prepared by the electrodeposition method from a sulfate bath under potentiostatic conditions on steel and aluminum substrates have been investigated. The deposit morphology and elemental composition were examined by scanning electron microscopy (SEM)/EDX. The preferred crystallographic orientations of the deposits have been determined by the x-ray diffraction (XRD) technique. The effects of bath composition on the phase structure, morphology and corrosion behaviors have been studied. It has been observed that the cobalt content strongly affects the structure and corrosion stability of Zn-Co alloys. It was found that amorphous alloys were obtained with high Co contents, while crystalline alloys were formed with high Zn contents. © 2009 The Royal Swedish Academy of Sciences.

This experimental study investigates the coupled effect of the force developed by the shape memory alloy (SMA) actuators and the force required for the large deflection of an elastica member in a compliant parallel mechanism. The compliant mechanism developed in house consists of a moving platform mounted on a superelastic pillar and three SMA wire actuators to manipulate the platform. A three-axis MEMS accelerometer has been mounted on the moving platform to measure its tilt angle. Three miniature force sensors have been designed and fabricated out of cantilever beams, each mounted with a pair of strain gauges, to measure the force developed by the respective actuators. The force sensors are highly sensitive and cost effective compared to commercially available miniature force sensors. Calibration of the force sensors has been accomplished with known weights, and for the three-axis MEMS accelerometer a rotary base has been considered which is usually used in optical applications. The calibration curves obtained, with R-squared values between 0.9997 and 1.0, show that both the tilt and force sensors considered are most appropriate for the respective applications. The mechanism fixed with the sensors and the drivers for the SMA actuators is integrated with a National Instrument's data acquisition system. The experimental results have been compared with the analytical results and it was found that the relative error is less than 2%. This is a preliminary study in the development of a mechanism for eye prosthesis and similar applications. � 2008 IOP Publishing Ltd.

Below 1 K the thermal expansion coefficient α of Al3Ce is negative and linearly approaches zero at 0 K. The pressure variation of the specific heat yT deduced from the initial variation of α is very strong : ∂γ/∂P = 0.62 J/K2 mole kbar . These properties cannot be interpreted with a single ion Kondo effect model but can be interpreted in terms of Fermi liquid (F.L.) behaviour. The magnetostriction experiments clearly show the differences between an ordinary F.L. such as 3He and the F.L. built with a lattice of magnetic ions coupled with and by itinerant electrons.

The effect of cooling rate on the solidification characteristics of the iron-rich intermetallics in 206 cast alloys with iron contents up to 0.5 wt% was investigated. The iron-rich intermetallics were analyzed and characterized by using Scanning Electron Microscopy (SEM), Differential Scanning Calorimeter (DSC) and Thermal Analysis (TA). It was found that Chinese script α-Fe and platelet β-Fe phases are the two main iron-rich intermetallics up to 0.3 wt% Fe. With increasing cooling rate, the precipitate temperature increases for α-Fe but decreases for β-Fe and eventually the formation of the β-Fe will be completely suppressed. At 0.5 wt% Fe, two extra iron-rich intermetallics, Chinese script Alm(FeMn) and platelet Al 3(FeMn) are experimentally observed. With increasing cooling rate, the Al3(FeMn) or Al6(FeMn) phases that precipitated at relatively low cooling rate can be replaced by Alm(FeMn) and α-Fe. The critical cooling rate to effectively suppress the formation of the platelet β-Fe and obtain dominant Chinese script α-Fe or Al m(FeMn) decreases with increasing iron level., Light Metals 2012 - TMS 2013 Annual Meeting and Exhibition, 3 March 2013 through 7 March 2013, San Antonio, TX