bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Cavitation on Absorption and Transport of Hydrogen in Iron
Authors: Chmiel Jarosław , Lunarska Ellina
Published: January 2012

Using the specially designed ultrasonic cavitation facility enabling to measure the hydrogen permeation, the experimental evidence have been provided for hydrogen to ingress in the metal subjected to cavitation in the 3% NaCl solution under the open circuit conditions. Increase in the vibration amplitude resulted in the increase in amplitude of the electrochemical voltage and current pulses and in the hydrogen permeation rate, as well. The cavitation induced modification of hydrogen transport through the membrane has been stated on the base of different appearance of the hydrogen permeation transients at cavitation in comparison with those recorded for the unstressed membrane. The hydrogen behavior has been affected by the cavitation induced dynamic stresses, metal hardening and stress relaxation due to microcracking of the metal.
Iodine-Induced Stress Corrosion Cracking of Zircaloy-4: Identification of Critical Parameters Involved in Intergranular to Transgranular Crack Propagation
Authors: Francon Virginie , Fregonese Marion , Abe Hiroshi , Watanabe Yutaka
Published: January 2012

During power transient conditions in nuclear reactors, uranium oxide pellets expand and crack due to the increase in temperature and their poor thermal conductivity. Moreover, the cladding undergoes creep because of the external pressure, and its diameter shortens. These antagonistic phenomena lead to the establishment of a contact between the pellet and the cladding, called the pellet-cladding interaction. The synergistic effect of the hoop tensile stress and strain imposed on the cladding by fuel thermal expansion and corrosion by iodine released from the UO2 fuel as a fission product at the same time can lead to Iodine-induced Stress Corrosion Cracking (I-SCC) of the Zircaloy-4 cladding. I-SCC failures of zirconium alloys are usually described in three steps: initiation of cracks, intergranular subcritical propagation, and critical propagation with a brittle transgranular propagation mode [1]. Transgranular propagation occurs as soon as the stress intensity factor overshoots a threshold value KI,SCC. It is the critical step and leads to the final ductile failure of the cladding. Transgranular cracks propagate by cleavage-like fracture on basal planes of the hexagonal lattice and fluting; it is the result of a competition between a plastic accommodation of the applied strain and the brittle fracture of basal planes by iodine assisted cleavage.
Perovskites in Solid Oxide Fuel Cells
Authors: Gazda M. , Jasinski P. , Kusz B. , Bochentyn B. , Gdula-Kasica K. , Lendze T. , Lewandowska-Iwaniak W. , Mielewczyk-Gryn A. , Molin S.
Published: January 2012

Perovskite oxides comprise large families among the structures of oxide compounds, and several perovskite-related structures are also known. Because of their diversity in chemical composition, properties and high chemical stability, perovskite oxides are widely used for preparing solid oxide fuel cell (SOFC) components. In this work a few examples of perovskite cathode and anode materials and their necessary modifications were shortly reviewed. In particular, nickel-substituted lanthanum ferrite and iron-substituted strontium titanate as cathode materials as well as niobium-doped strontium titanate, as anode material, are described. Electrodes based on the modified perovskite oxides are very promising SOFC components.
The Effect of Low-Temperature Glow Discharge Nitriding of Duplex Stainless Steel on Absorption and Desorption of Hydrogen
Authors: Gołębiowski Bartosz , Zakroczymski Tadeusz , Świątnicki Wiesław
Published: January 2012

The effect of the nitrided layers produced on ferritic-austenitic stainless steel to hydrogen absorption and desorption was studied. The layers were formed during low-temperature glow discharge nitriding process. The microstructure of steel after nitriding and cathodic hydrogen charging was investigated by means of X-ray diffraction and by scanning electron microscopy (SEM). One of the objectives was to determine the quantity of hydrogen absorbed by the steel samples with and without the nitrided layer. To determine the quantity of the diffusible and trapped hydrogen, the electrochemical permeation and desorption methods were used. The influence of the nitrided layer on the entry, absorption and desorption of hydrogen was determined. The results revealed that the nitrided layer hinders absorption of hydrogen into and desorption of hydrogen from the membrane.
Preparation and Characterization of TiO2 Nanostructures for Catalytic CO2 Photoconversion
Authors: Iwulska Anna , Sliwinski G.
Published: January 2012

The titanium dioxide target (99.7%) of 1 cm in dia was ablated in vacuum by laser pulses (6 ns) at 266 nm and at repetition rate of 10 Hz. During deposition the laser fluence between 1 and 3.5 J/cm2 and the O2 pressure from the range of 10-2 – 1 Pa were applied. The thin TiO2 films were deposited on glass substrate (1 × 1 cm2) heated up to 500 °C. The chemical composition of the film and samples produced by annealing were investigated by spectroscopic techniques (μ-Raman, EDX) and the structure, porosity and surface morphology were analysed by means of SEM and x-ray diffraction (XRD). The SEM inspection of the TiO2 thin film samples indicates that the obtained material is mostly crystalline. After annealing in O2 at 500 °C the structure characterized by the presence of both anatase and rutile phases is observed in the Raman spectra and confirmed by the XRD data. The phase content ratio depends on the O2 pressure applied. Results confirm that nanostructures produced in this way represent densely packed columns and promote deep penetration of guest particles such as CO2.The resulting large active surface is advantageous from the point of view of photocatalytic applications.
Study of Iron-Based Alloys in Solid Oxide Fuel Cell Temperature and Atmosphere Conditions, Effect of a Silver-Coating
Authors: Aubert I. , Jumel J. , Tarek-Lamazouade M. , Vulliet Julien
Published: January 2012

The French Atomic Energy Commission has developed a High Temperature Electrolyzer having an original coaxial architecture. Important elements are spring-like interconnects which allow to cope with thermal dilatation. Specifications of these components are low-cost, long term electrical conductivity achieved by chemical and mechanical stability. Potential candidates are iron-based alloys on which thin silver-coating may be deposited. In this paper we study the interaction of such systems with a mixture of hot vapour and hydrogen that is representative of the electrolyzer environment. Oxidation kinetic is measured by thermogravimetry. The oxide layer composition and morphology of tested samples are then investigated using Energy Dispersive Spectroscopy (EDS) and Auger Electron Spectroscopy (AES). These analyses demonstrate that hydrogen content strongly impacts the oxidation mechanism.
Influence of Type of Material on Performance of Hydraulic Components in Thermal Shock Conditions
Authors: Jasiński Ryszard
Published: January 2012

During the start-up of a hydraulic system in low ambient temperatures an incorrect operation may occur. The principles and conditions of safely operating hydraulic driven machines and devices are essential to designers and operators. For this reason the author of this article has conducted a series of tests on hydraulic components and systems in thermal shock conditions (cooled-down components were supplied with hot working medium). In such conditions, the initial parameters of the hydraulic components and systems determine their correct operation. During the start-up of a hydraulic system in thermal shock conditions, elements of hydraulic components warm up in a non-uniform way, due to various material properties and shapes of parts. Differences in clearances between elements and may lead to the faulty performance of hydraulic components and machine break-down. The selection of appropriate materials for various hydraulic component parts should increase machine safety during start-up in thermal shock conditions.
Internal Friction Study of the Rare Earth Ion Substituted Fast Oxide-Ion Conductors (La1-ΧreΧ)2Mo2O9 (Re=Nd, Gd)
Authors: Wang X.P. , Hu J. , Zhuang Zhong , Zhang Tao , Fang Qian Feng
Published: January 2012

The relaxation and phase transition behaviors of rare-earth ion substituted fast oxide-ion conductors (La1-xRex)2Mo2O9 (Re=Nd, Gd) were investigated by internal friction (IF) measurement in the temperature range 300 K - 950 K. Three different IF peaks (labeled as PL, PH, and PG, respectively) were observed in the rare-earth ion doped La2Mo2O9 samples. Peak PL corresponds to short diffusion processes of oxygen ions among different oxygen vacancy sites. Peak PH is associated with the static/dynamic disorder transition in oxygen ion distribution. Peak PG is a newly discovered peak embodying phase transition-like characteristics and is suggested to be related to order-disorder transition associated with the rearrangement of La/ Re sub-lattice.
Hydrogen-Induced Mechanical Losses in Oxygen-Free Copper
Authors: Ivanchenko Mykola , Yagodzinskyy Yuriy , Hänninen H.
Published: January 2012

Two oxygen-free copper grades with purity of 99.99 % were studied by means of free decay inverted torsion pendulum at the temperature range of 90 – 300 K and frequencies of 0.5 – 2 Hz. One copper grade was oxygen free electrolytically refined copper with oxygen content of 1.2 wt. ppm. The other one was oxygen-free phosphorous-alloyed grade with oxygen content less than 5 wt. ppm and phosphorous content of 30 – 70 wt. ppm. Electrochemical hydrogen charging induces a complex internal friction peak in the studied copper grades. The observed internal friction peak has a relaxation origin with apparent activation enthalpy and pre-exponential factor for the oxygen-free grade of 0.276 ± 0.002 eV and 10-11.59 ± 0.08 s, respectively. The internal friction peak can be fitted by three broadened Debye peaks (P1, P2 and P3) with activation enthalpies and pre-exponential factors of 0.248 ± 0.003 eV and 10-11.4 ± 0.4 s; 0.297 ± 0.004 eV and 10-11.8 ± 0.2 s; 0.36 ± 0.04 eV and 10-12.7 ± 1.4 s, respectively. Phosphorous doping markedly reduces the height of the observed peak. It was also shown that prior deformation by tension suppresses high-temperature components of the complex internal friction peak. Mechanism of relaxation is presumably caused by interaction of H – H pairs (low-temperature component, peak P1), interaction of hydrogen atoms with dislocations (P2) and interaction of hydrogen with impurities (high-temperature component, peak P3). Absorption of hydrogen in the studied copper grades during electrochemical hydrogen charging was confirmed by the thermal desorption method.
Influence of Strain Hardening 1% by Torsion on the Behavior of a Single Crystal Alloy (Cu–at.9% Al) in Internal Friction at High Temperature
Authors: Belamri C. , Belhas S. , Derdour S. , Rivière Andre
Published: January 2012

The purpose of this study is to highlight the influence of the strain hardening on internal friction behaviour of a copper single crystal alloy Cu-Al (9% at.) using Isothermal Mechanical Spectroscopy (IMS) technique. To do this, the sample was cold worked about 1% by torsion and tested at different stabilized levels of temperatures. Thus the specimen have been progressively heated to 1179 K and then cooled down to room temperature. The advantage of IMS experiments is to allow to compare the isothermal internal friction spectra obtained during heating (in this case, the annealing temperature (TA) is equal to the temperature of measurement (TM) with the measurements performed at various temperatures during cooling after annealing at 1179 K (TM< TAin this case). The results obtained in increasing temperature step by step (TA= TM) show the existence of two (02) independent relaxation peaks from 914 K to 1179 K. The first one, called here P1(at about 0.7 TMeltat 1Hz), decreased with increasing the annealing temperature, while a new relaxation peak P2(at about 0.9 TMeltat 1Hz) progressively developed. However for high temperature annealing, IMS tests (TA> TM) does reveal only one peak P2. It appears, therefore, clearly that the strain hardening is responsible for the P1existence. To monitor the evolution of P1and P2with the temperature, a method of peaks decomposition already published was applied. The relaxation parameters, deduced from the Arrhenius plots, were thus accurately determined. The mechanism responsible of the P1and P2peaks appearance has been attributed to the movement of dislocation segments inside the sample microstructure.
Eutectoid Al-51at%Zn Alloy Studied by Isothermal Mechanical Spectroscopy
Authors: Rivière Andre , Pelosin Veronique , Gerland Michel
Published: January 2012

sothermal mechanical spectroscopy measurements were performed in an Al-51 at % Zn alloy at various temperatures below and above the eutectoid transition temperature: during a heating the α-β eutectoid mixture changes into α solid solution at 550 K. Damping experiments were performed in a very large frequency range (10-5– 50 Hz) between room temperature and 673 K. Internal friction spectra performed between 200 K and 540 K, exhibit two thermally activated relaxation peaks (P1 and P2). P1 decreases and disappears with the increase of measurement temperature while P2 appears and increases. P2 totally disappears above the eutectoid transition temperature. Above 550 K, a new peak (P3) is evidenced at very low frequency. The relaxation parameters of P3 (limit relaxation time τ0= 9×10-7and activation energy H = 105 kJ/mole (1.1 eV)) allow to associate this peak with the motion of sub grain boundaries. P1 and P2 (τ0≈ 10-7and H ≈ 70 kJ/mole (0.75 eV) for both peaks) are associated with a thermally induced atom diffusion across the α-β interface.
Studies of Condensed Matter at Low Temperatures by Ultrasonic and other Mechanical Spectroscopies
Authors: Elbaum Charles
Published: January 2012

In the second half of the twentieth century and in the first decade of the twenty first century, many new phenomena came to light in the fields of condensed matter and of materials properties’ at low temperatures. A few examples of these phenomena are: the plasticity and the behavior of dislocations in solid helium-4 (a quantum solid), “high” temperature superconductivity, occurrence of superfluid flow in solid helium (“supersolid”), and, Bose-Einstein condensation of cold atoms. In this presentation descriptions and some discussions are given on the role played in these studies by ultrasonic and other forms of mechanical spectroscopy.
Mechanical Spectroscopic Study of Equal-Channel Angular Pressed Al-Ni Eutectic Alloy
Authors: Watanabe Yoshimi , Zhang Zuo Gui , Sato Hisashi , Inamura Tomonari , Hosoda Hideki
Published: January 2012

In this study, temperature dependence of internal friction, tand, of ECAPed Al-Ni eutectic alloy was measured using a dynamic mechanical analysis (DMA) to discuss the recrystallization behavior of the alloy. The temperature dependence of internal friction of 8 passed samples shows a large peak at around 200 °C on heating, while this peak disappears on the subsequent cooling stage. Moreover, smaller peak was observed for 2 passed samples. Therefore, it can be concluded that the origin of the peak comes from the recrystallization of a-Al.
Fatigue Behavior of Magnesium Alloy AJ91 Studied by Amplitude Dependent Damping Measurements
Authors: Riehemann Werner , Trojanová Zuzanka
Published: January 2012

The amplitude dependent damping of two bending beam samples of magnesium alloy AJ91 (9 wt.% Al, 1 wt.% Sr) was measured at room temperature in as cast condition, after quenching from high temperatures into water of room temperature and after various bending cycles to fatigue. Some measurements were performed successively with about 33 Hz and 100 Hz resonant frequency. The measurements show typical dislocation damping in as cast condition, after heat treatment at temperatures lower than 420°C, and cycle numbers lower then 50.000. For higher quenching temperatures the damping increases over the whole measured strain range with increasing quenching temperature and number of cycles to fatigue. After quenching from temperatures higher than 478°C the crack damping becomes dominant. The effects of damping seem to increase with increasing frequency. In one sample damping of individual cracks could be identified in the amplitude dependent damping curves by their characteristic course very similar to the ones postulated in an earlier publication by a simple rheological model [4]. The extending of crack length leads to a shift of the damping to lower strains.
Ultrasonic Study of Elastic and Anelastic Properties of C/Mg-2wt.%Si Composite
Authors: Golyandin S. , Sapozhnikov K. , Kustov Sergey
Published: January 2012

Microstructural changes induced in a carbon fiber – magnesium matrix composite during thermal cycling in the range of 100 - 360 K are detected by an ultrasonic technique. The composite was comprised of Mg-2wt.%Si alloy matrix reinforced with long unidirectional carbon fibers (volume fraction of about 30%). Temperature variations of the elastic modulus of the composite are largely determined by elasticity of the carbon fibers stressed by the thermally expanded/contracted matrix. Anelastic properties of the composite (internal friction and modulus defect) are caused by dislocation motion in the matrix. Temperature spectra of anelasticity of the composite are controlled by a competition between creation of fresh mobile dislocations under the action of thermal stresses and immobilization of the fresh dislocations by atmospheres of mobile point defects.
Static Strain Aging in Fe-Mn-N Alloys Investigated by Impulse Excitation Internal Friction Analysis
Authors: Jung Jae Hyuk , Kozeschnik Ernst , Han Seong Ho , De Cooman Bruno C.
Published: January 2012

The Fe-Mn-N alloys used in the present study showed an unexpected increase of both the yield strength and the ultimate tensile strength after prestraining and strain aging. In order to understand the mechanism of this phenomenon, which is due to solute N, static strain aging tests were carried out in combination with resonant impulse excitation internal friction analysis. It is shown that the interaction between thermal kinks and solute N atoms plays an essential role in the increase of the tensile strength.
Internal Friction and Magnetic After-Effect Study of Dislocation Dynamics in Thermally Aged Fe-1%Cu-C Alloys
Authors: Minov Boris , Dupré Luc , Konstantinović Milan J.
Published: January 2012

The effect of Cu-precipitation on the dislocation dynamics is studied by internal friction and magnetic after-effect measurements of thermally aged Fe1%CuC. We found that the copper precipitation in these alloys is accompanied by carbon redistribution. The results of both experiments showed that the hardening regime is governed by an increase of the dislocation density due to the growth of copper precipitates, while in the softening regime carbon redistribution plays a major role.
Hydrogen-Dislocation Interaction in Austenitic Stainless Steel Studied with Mechanical Loss Spectroscopy
Authors: Yagodzinskyy Yuriy , Ivanchenko Mykola , Hänninen H.
Published: January 2012

Mechanical loss of pre-strained and hydrogen-charged specimens of 316L austenitic stainless steel has been measured by the free-decay method using an inverted torsion pendulum at frequencies around 1 Hz. It is found that in addition to known hydrogen Snoek-like relaxation process observed at about 240 K a new peak of mechanical loss appears around 270 K. The peak has a relaxation origin with enthalpy close to 0.78 eV and pre-exponential factor of relaxation time is found to be about 10-12.5s. Effects of the pre-strain and parameters of electrochemical hydrogen charging on the hydrogen peak in deformed austenitic stainless steels are measured. The obtained results are discussed in terms of the Snoek-Köster mechanism and specifics of hydrogen atomic distribution in a multi-component substitutional alloy of austenitic stainless steel. Based on the analysis the binding energy of hydrogen to dislocation in 316L steel is evaluated to be about 0.16 eV.
Internal Friction Study of the Influence of Deep Cryogenic Treatment on the Microstructure of a Bainitic Steel
Authors: Min Na , Ji Tian Yu , Zhu Li Juan , Wu Xiao Chun , Wang Hong Bin
Published: January 2012

The influence of deep cryogenic treatment (DCT) on the microstructure of a bainitic steel is investigated by means of internal friction and transmission electron microscopy (TEM). Two relaxation peaks (Pc1and Pc2) are observed during cooling and one relaxation peak (Ph) during heating from 100 to 320K. Peak Pc1may be related to dislocation pinning. Peak Phis attributed to dislocation-carbon atoms interaction. The decreasing of peak Phafter cycles deep cryogenic cooling indicates that soaking time under the deep cryogenic temperature is not contributed to the precipitation of carbides, while the cycles cryogenic treatment lead to more fine carbides precipitation.
Release of Tetrahydrofuran, Structural Phase Transitions and Dynamic Relaxation Processes in Ca (BH4)2
Authors: Paolone Annalisa , Palumbo O. , Rispoli P. , Cantelli Rosario , Rönnebro E. , Luedtke A. , Chandra D.
Published: January 2012

Various calcium borohydride samples were investigated by means of combined measurements of thermogravimetry and mass spectrometry, and anelastic spectroscopy. On heating, the release of 2-5% tetrahydrofuran (THF) is detected in all the samples at temperatures below ~480 K, even in those which were previously thermally treated, according to procedures known from the literature, in order to remove the solvent. Dehydrogenation takes place above 480 K. Above room temperature the temperature dependence of the Young modulus of Ca (BH4)2clearly monitors the release of THF and two irreversible structural phase transitions: from the α to the α’ phase around 460 K and from the α’ to the β phase, nearly completely evolved around 590 K. Moreover, the coefficient of elastic energy dissipation presents two dynamic processes below room temperature; a peak around 120 K characterized by an activation energy of 0.20 eV and a pre-exponential factor typical of atom-cluster relaxations, that we attributed to the dynamics of THF molecules retained in the borohydride lattice, and a peak around 200 K, possibly due to the relaxation of H vacancies.
Isothermal Mechanical Spectroscopy in Equiatomic CuZr Alloy
Authors: Belamri D. , Pelosin Veronique , Belhas S. , Rivière Andre
Published: January 2012

An equiatomic CuZr alloy quenched from 1073 K was studied by isothermal mechanical spectroscopy and X-Ray diffraction. Experiments were performed using a very large frequency range (10-4Hz – 50 Hz) at different temperatures. For each temperature of measurement, experiment started after complete microstructure stabilization of the sample. At room temperature, the X–Ray diffraction spectrum shows that there are two CuZr monoclinic phases as a consequence of a martensitic transformation. These structures are characterized by the existence of twinning defects for the first one and a high dislocation density for the other. Both monoclinic phases disappear at higher temperatures and first transform into the cubic CuZr phase, then this cubic phase transforms into Cu10Zr7and CuZr2phases above 763 K. Internal friction spectra exhibit two relaxation peaks (P1, P2), at low and high temperatures, respectively. After rapid cooling of the sample from 1273 K, the first peak P1appears from room temperature and disappears after annealing above 673 K. The P2peak appears at about 800 K and increases for measurements at higher temperature up to 880 K. This temperature range corresponds with the existence of both Cu10Zr7and CuZr2phases. These two peaks are associated with a relaxation linked to the dislocation microstructure in the two CuZr monoclinic phases for P1 and in the Cu10Zr7and CuZr2phases for P2.
High Temperature Internal Friction in Fine Grain and Nano-Crystalline Zirconia
Authors: Simas P. , Castillo-Rodríguez M. , Nó M.L. , De-Bernardi S. , Gómez D. , Domínguez-Rodríguez A. , San Juan José
Published: January 2012

Engineering ceramics are being developed to improve their high-temperature mechanical properties and in particular creep resistance. Recently the production of fine grain ceramics undergoes another step-forward with the development of new technologies to produce nanocrystalline materials. The question is whether the properties depending on the grain size can be extrapolated at nanoscale or, on the contrary, new microscopic mechanisms could appear to be dominant at this nanometer grain size. In the present work we study, by mechanical spectroscopy, the high temperature behavior up to 1350°C of a fine grain Zirconia and a nanocrystalline Zirconia sintered in a conventional way. A new forced torsion pendulum, recently built, has been used for the mechanical spectroscopy measurements. The high temperature background (HTB) of internal friction has been measured as a function of temperature for different frequencies in both materials. The analysis of the HTB shows that the fine grain Zirconia exhibits a single process of defects mobility, with an apparent activation enthalpy similar to the one measured by creep. On the contrary, the HTB of the nanocrystalline sample becomes more complex, showing a much higher energy loss, which will be discussed at the light of the internal friction spectra analysis.
Anelastic Effects of Phase Decomposition in 14-Carat AuAgCu Alloy
Authors: Tkalcec Iva , Mari Daniele , Schaller Robert
Published: January 2012

A relaxation peak has been observed in the internal friction spectrum of 18-carat AuAgCu yellow gold alloys at about 750K for 0.5Hz. It is related to the presence of grain boundaries, since it is absent in the spectrum of single crystals. For the 14-carat yellow gold alloy (Au38%Ag32%Cu30%), a phase decomposition between silver-rich and copper-rich solid solution occurs in the same temperature range. The effects of the phase decomposition on the internal friction and the dynamic modulus are studied by isochronal and isothermal measurements and correlated with the microstructure evolution. Upon cooling, the phase decomposition starts at grain boundaries at about 840K, producing a fine lamellar structure, and the grain boundary peak amplitude strongly decreases. As the phase decomposition progresses at the interior of the grains upon further cooling, the internal friction background increases. It remains very high in heating until solid solution homogenisation, which occurs above 890K. Such an increase of the internal friction background is observed also in the single crystalline alloy and may be attributed to the interfaces between lamellae of the silver and copper-rich phase.
Grain Boundary Relaxation in 18-Carat Yellow Gold
Authors: Maier Ann Kathrin , Tkalcec Iva , Mari Daniele , Schaller Robert
Published: January 2012

Au60Ag30Cu10(in at%) gold alloy exhibits a mechanical loss spectrum composed of a Zener peak due to Cu atoms in the solid solution and of a second relaxation peak at higher temperature or lower frequency. It is shown that this second peak is related to the presence of grain boundaries as it is absent in the spectrum of a single crystal. This mechanical loss peak, which is stable and reproducible in heating and cooling cycles, is thermally activated with an activation enthalpy of 2.35 eV and an apparent limit relaxation time of 9.6·10-17s. As it is hard to imagine that a whole grain should slip at once along a touching grain, the relaxation peak is interpreted by a dislocation model, which may account not only for the activation parameters but also for the stress amplitude dependency of the peak.
Amplitude Dependent Damping of Aluminum-Matrix-Nanoparticle-Composites
Authors: Kazakewitsch A. , Riehemann Werner
Published: January 2012

Aluminum-matrix-nanoparticle-composites were produced by ball milling of micro scale aluminum powder in air atmosphere with subsequent consolidation by hot extrusion and also additional hot swaging. They were investigated in this condition after step by step isochronal annealing with successive increasing annealing temperature and quenching into water to room temperature. The material was investigated by amplitude dependent damping, hardness and density measurements, all at room temperature. For all measured amplitude dependent internal friction (ADIF) curves the damping increases with increasing strain amplitude. After some annealing treatments a knee occurs in the medium strain amplitude region of these curves. Moreover between annealing temperatures from 360°C to 480°C the strain dependent damping becomes a maximum, i.e. a peak in the ADIF curves occurs. Other ADIF curves of quenched and fatigued material show characteristic peaks that can be attributed to individual single cracks. It is shown that all these effects are due to the formation, opening and compression of cracks present in the sample or created by thermally exerted stresses.
Analysis of Microstructural Changes with Temperature of Thermally Sprayed WC-Co Coatings by Mechanical Spectroscopy
Authors: Mari Daniele , Berger L.M. , Stahr S.
Published: January 2012

Thermally sprayed hardmetal coatings can be used to improve the wear or fatigue resistance of mechanical parts. Depending on the deposition conditions, their microstructure and phase composition are out of equilibrium at different levels due to the extreme heating/cooling rates. In the present study, the changes that occur with temperature variation are monitored by mechanical spectroscopy. Requirements to specimen of mechanical spectroscopy created the need to prepare WC-17%Co coatings of 1.2 mm thickness by high velocity oxy-fuel (HVOF) spraying. The coatings, separated from the substrate by spark erosion, were tested in a forced torsion pendulum between room temperature and 1570 K at a temperature scanning rate of 1K/min. The mechanical loss spectrum shows different features. At 800 K, a maximum M1 is observed in coincidence with a sudden increase of the elastic modulus. The change of the elastic modulus is due to a densification of the material possibly related to cobalt recrystallization. A relaxation peak located at about 1100 K is typically found in WC-Co hardmetals. It is attributed to the movement of dislocations in the cobalt phase. A sharp peak is observed at 1510 K on heating and at 1410 K on cooling. Such peak is due to the reversible transition from W3Co3C at high temperature to W6Co6C at low temperature as proven by X-ray diffraction. The reversibility of such transformation was observed for the first time.
Internal Friction and Shear Modulus of Graphene Films
Authors: Liu Xiao , Metcalf Thomas H. , Robinson Jeremy T. , Perkins F. Keith , Houston Brian H.
Published: January 2012

We report internal friction and shear modulus measurements of several types of synthesized graphene films. They include reduced graphene oxide, chemical-vapor deposited (CVD) graphene films on thin nickel films and on copper foils. These films were transferred from their host substrate into a water bath, and re-deposited onto to a high-Q single crystal silicon mechanical double-paddle oscillator. A minimal thickness dependence of both internal friction and shear modulus was found for reduced graphene oxide films varying thickness from 4 to 90 nm and CVD graphene films on nickel from 6 to 8 nm. The shear modulus of these multilayered films averages 53 GPa. Their internal friction exhibits a temperature independent plateau below 10K. The values of the plateaus are similar for both the reduced graphene oxide films and CVD graphene films on nickel, and they are as high as the universal "glassy range" where the tunneling states dominated internal friction of amorphous solids lies. In contrast, CVD graphene films on copper foils are 90~95% single layer. The shear modulus of these single layer graphene films are about five times higher, averaging 280 GPa. Their low temperature internal friction is too small to measure within the uncertainty of our experiments. Our results demonstrate the dramatic difference in the elastic properties of multilayer and single layer graphene films.
Mechanical Spectroscopy of Hyperstabilized Martensites
Authors: Kustov Sergey , Santamarta R. , Cesari E. , Sapozhnikov K. , Nikolaev V. , Fedorov V. , Krymov V. , Van Humbeeck Jan
Published: January 2012

The internal friction of the hyperstabilized martensite demonstrates very low values, both above and below the nominal martensitic transformation temperature, due to a pronounced pinning effect. Over a wide temperature range it is comparable with the level of damping in the parent phase. A study of the temperature dependence of the non-linear ultrasonic internal friction and its strain amplitude hysteresis indicates that the diffusion, assisted by dislocations/interfaces, is quite pronounced and in Ni-Fe-Ga and Cu-Al-Be alloys it operates at temperatures around 20 K. The renucleation of the lamellar parent phase during the reverse martensitic transformation close to 600 K is accompanied by an internal friction peak which demonstrates a substantial transitory contribution. After renucleation of the parent phase the samples recover a conventional martensitic transformation with the internal friction level in the martensite comparable to the one in non-stabilized samples. Observations of a relaxation peak in the parent phase of different alloys for temperatures just below the renucleation stage of the reverse transformation point to the essential role of diffusion in the nucleation of the parent phase in hyperstabilized martensites.
A Strain-Glass Transition Observed in Au7Cu5Al4 Ternary Alloys
Authors: Jin Xue Jun , Jin M. J. , Liu J. Y. , Fan G. L.
Published: January 2012

Strain glass is a new type of glass state discovered recently in Ni-rich Ti-Ni ferroelastic alloys. It is formed by doping sufficient point defects such as solute atoms or alloying elements into a martensitic alloy to destroy the long range strain order generated by the diffusionless martensitic phase transformation. The strain glass was observed in an off-stoichiometric Heusler Au7Cu5Al4 alloy by the mechanical spectrum analysis. The martensitic transformation was experimentally confirmed following the occurrence of strain glass transition during the cooling. It is different from the model developed mainly in Ni-Ti based alloys among which the martensitic transformation was totally suppressed once the strain glass transition takes place. We conclude that newly observed strain glass in an off-stoichiometric Au7Cu5Al4 alloy belongs to one type of precursor phenomena.
Effects of Pinning and Atomic Ordering on Damping Properties and Martensitic Transformation of Copper-Based Shape Memory Alloys
Authors: Kustov S. , Cesari E. , Van Humbeeck Jan
Published: January 2012

The effects of long-range atomic order and pinning of interfaces on anelastic properties of Cu-based martensite have been distinguished by means of studying strain amplitude dependences of internal friction and Young’s modulus defect, assuming that low-and high-amplitude stages of the strain amplitude dependence correspond to the oscillations within and beyond pinning atmospheres.
Magnetomechanical and Structural Internal Friction in Ni-Mn-In-Co Metamagnetic Shape Memory Alloy
Authors: Salas Daniel , Cesari E. , Golovin I. , Kustov S.
Published: January 2012

The strain amplitude-independent and strain amplitude-dependent components of the internal friction in a Ni45Mn36.7In13.3Co5 metamagnetic shape memory alloy have been studied as function of temperature, strain amplitude and polarizing magnetic field. For ultrasonic oscillation frequency (91 kHz) and low strain amplitudes (10-7-10-5), the experimental results show that the internal friction in the ferromagnetic austenite is much higher than in non-magnetic martensite. We suggest that this unusual relationship is due to a high contribution of the magnetomechanical component to the internal friction of the ferromagnetic austenite.
Mechanical Spectroscopy, a Tool to Characterize Cement Latex Composites
Authors: Foray G. , Cardinal S. , Malchere A. , Pelletier J.M.
Published: January 2012

Fair dispersion of polymer and control of component grain size are key properties to achieve high performances building material (i.e. ultra high strength concrete, self-levelling floor, or exterior insulation composite system). As microstructure analysis in an organic/inorganic hydrated co-matrix material is time consuming, mechanical spectroscopy temperature analysis could characterise both the polymer and the hydrates in the same run. The temperature dependence of the storage modulusG’and the loss modulus G’’ of some composite building material was therefore measured between 173 and 470 K by mechanical spectroscopy (Dynamic Mechanical Analysis). A model material was then defined to enable DMA latex/cement interaction study. The latex was reinforced by either a microfiller (OMYA limestone) or a microfiller and a nanofiller (hydrated Lafarge cement paste CEM I 52.5 R). The latex evaluated in this study was a 210nm styrene butyl acrylate (SBA). The measurements confirmed that polymer environment was not hindered by micro or nanofiller (i.e. cement). The hydrated cement paste transformation onset was measured at 373K, but occurred at higher temperature as latex content increased. ESEM micrographs performed during heating have proven that within the hydrated cement paste many parallel cracks propagated at once, while within SBA hydrated cement paste no cracks were observed. The hydrated cement microstructure was modified by SBA, and became less sensitive to temperature increase due to SBA latex ability to deform.
Investigation of Local Shear Transformation in a Metallic Glass by Means of High Amplitude Internal Friction Measurements
Authors: Nakamura A. , Kamimura Yasushi , Edagawa Keiichi , Takeuchi Shin
Published: January 2012

In order to investigate flip-flop transitions of shear transformation zones (STZs) which are believed to be the elementary deformation sites in metallic glasses, internal friction measurements have been conducted for a commercial bulk metallic glass of a Zr-based alloy (Johnson alloy). Since the STZ is an asymmetrical two-level system, it is necessary to measure the internal friction at a high amplitude or under a bias stress condition to detect the transitions. Measurements have been made at temperatures between 130 K and 573 K at frequencies between 0.1 Hz to 10 Hz. The results showed that quite a broad peak appears between 200 K and 500 K in high amplitude internal friction measurements. The broad peak, observed for the first time in metallic glass, is interpreted to be due to flip-flop transitions of STZs having a broad spectrum, 0.5∼1.2 eV, of the activation enthalpy.
Mechanical Spectroscopy Investigation of Liquid Pb-Bi Alloys
Authors: Montanari Roberto , Varone Alessandra
Published: January 2012

Liquid Pb–Bi eutectic alloy has been selected as coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system. The alloy has been characterized in liquid state from melting (125 °C) to 650 °C by mechanical spectroscopy. Experiments have been carried out using hollow reeds of austenitic stainless steel filled with the Pb-Bi alloy and sealed at the extremities. From 350 °C to 520 °C modulus shows a remarkable drop accompanied by a broad internal friction maximum. In the same temperature range radial distribution functions, determined from X-ray diffraction patterns, evidenced variations of the mean distance between the 1st nearest neighbour atoms. The anelastic phenomena have been attributed to a structural re-arrangement of liquid metal. For comparison, other alloys of the Pb-Bi system with hypo-eutectic composition have been investigated.
Determination of Residual Stresses by Means of Dynamic Resonant Method
Authors: Gadaud P. , Pautrot S.
Published: January 2012

Young’s modulus and damping coefficient measurements performed on various materials by means of dynamic resonant method in free bending mode, exhibit transient effects during first heating, while there is no obvious structural evolution. It has been more particularly observed on sintered and rolled bulk materials as well as coated materials. It can be indubitably related to the release of internal stresses introduced during elaboration. The measurement of the resonance frequency shift associated to this release and the development of a model of beam vibration integrating the presence of internal stresses allow the estimation of the initial level of internal stresses. The mechanical model comes from the application of Hamilton principle minimizing potential and kinetic energies described by the Lagrangian of the vibrating system. Then, the effect of internal stresses is introduced, based on a model of pre-stressed vibrating beam found in literature. Three experimental illustrations are given: a HIP (high isostatic pressure) sintered MAX phase with compression internal stresses, a 70 % rolled Co base steel with very high elastic limit and anisotropic plane tension stresses and a platinum aluminide coating deposited on AM1 superalloy.
Toward High-Resolution Mechanical Spectroscopy HRMS - Logarithmic Decrement
Authors: Magalas Leszek B. , Majewski M.
Published: January 2012

In this work, we present the comparison between different methods used to compute the logarithmic decrement,δ. The parametric OMI method and interpolated DFT (IpDFT) methods are used to compute theδfrom free decaying oscillations embedded in an experimental noise typical for low-frequency mechanical spectrometers. The results are reported forδ= 5×10-4, = 1.12345 Hz and different sampling frequencies, = 1 kHz and 4 kHz. A new YM algorithm yields the smallest dispersion in experimental points of the logarithmic decrement and the smallest relative errors among all investigated IpDFT methods. In general, however, the IpDFT methods suffer from spectral leakage and frequency resolution. Therefore it is demonstrated that the performance of different methods to compute theδcan be listed in the following order: (1) OMI, (2) YM, (3) YMC, and (4) the Yoshida method, Y. For short free decays the order of the best performers is different: (1) OMI and (2) YMC. It is important to emphasize that IpDFT methods (including the Yoshida method, Y) are discouraged for signals that are too short. In conclusion, the best methods to compute the logarithmic decrement are the OMI and the YM. These methods will pave the way toward high-resolution mechanical spectroscopy HRMS.
Toward High-Resolution Mechanical Spectroscopy HRMS - Resonant Frequency –Young’s Modulus
Authors: Magalas Leszek B. , Majewski M.
Published: January 2012

In this paper, we compare the values of the resonant frequency computed according to the OMI algorithm, DFT, and interpolated DFT methods for a set of 100 free decaying oscillations. It is unequivocally demonstrated that the performance of the different methods can be listed in the following order: (1) OMI, (2) YM, (3) YMC, (4) Agrež, and finally (5) the well known Yoshida method, Y. For very short signals the order of the best methods is different: (1) OMI, (2) YMC. It is pointed out that the DFT methods, including the Yoshida method, are discouraged for analysis of signals that are too short. This effect is explained in terms of spectral leakage. By contrast, short free decaying signals can be successfully analyzed with the OMI and the YMCmethod. We conclude that the use of the OMI and the YM, i.e. the interpolated DFT method, can substantially increase the resolution of low-frequency resonant mechanical spectrometers (the decrease in dispersion of experimental points and the minimization of relative errors can be readily obtained.) For this reason a much more precise estimation of the logarithmic decrement is also simultaneously feasible.
Mechanical Relaxation Studies of Sub-Rouse Modes in Amorphous Polymers
Authors: Wu Xue Bang , Wang Hua Guang , Liu Chang Song , Zhu Zhen Gang
Published: January 2012

Mechanical spectroscopy is a powerful tool for the investigation of molecular dynamics of amorphous polymers over a large temperature range and frequency scale. In this work, by using high precision shear mechanical spectroscopy tool, we have investigated the segmental dynamics from local segmental relaxation to sub-Rouse modes in a series of amorphous polymers. We have demonstrated the existence of sub-Rouse modes slower than the local segmental motion in amorphous polymers. The sub-Rouse modes exhibit a similar change of dynamics at the same temperature TB ~1.2 Tg, as the local segmental relaxation through the temperature dependence of relaxation time and relaxation strength. Furthermore, the crossover relaxation time of the sub-Rouse modes at TB is almost the same for all the polymers investigated, i.e. τα'(TB) = 10-1±0.5 s, which is independent of molecular weight and molecular structure. This remarkable finding indicates that solely the time scale of the relaxation determines the change in dynamics of the sub-Rouse modes. According to the coupling model, the crossover is suggested to be caused by the onset of strong intermolecular cooperativity below TB. Hence the results suggest that the sub-Rouse modes and their properties are generally found in amorphous polymers by mechanical spectroscopy, and reveal the cooperative nature of the sub-Rouse modes.
Ab Initio Based O-O Investigation and the Snoek Relaxation in Nb-O
Authors: Blanter M.S. , Dmitriev V.V. , Ruban Andrei V.
Published: January 2012

t is common knowledge that interstitial-interstitial interaction influence on the Snoek relaxation. We used a computer simulation of this effect in the Nb-O alloy to test the adequacy of various models of the O-O interaction and clarify the mechanism of this effect The energy calculations in the first twelve coordination shells have been performed by the projector augmented-wave (PAW) method as implemented in the Viennaab initiosimulation package (VASP). The energies have been calculated in different ways which vary in the method of determination the energy of non-interacting O-O pairs. The energies calculated on the various variants are similar but in one case there is O-O repulsion in all first twelve coordination shells, whereas in another one can see attraction in four of twelve shells. Internal frictionQ-1was calculated as a sum of the contributions from individual interstitial atoms in different environments, each of which being assumed to be the Debye function. It is assumed that long-range interaction of oxygen atoms affects the distribution of these atoms and the energy of each interstitial atom in the octahedral interstices before a jump and after a jump. The Monte Carlo method is used for simulating short-range order of interstitial atoms and for calculating values of energy changes. Comparison of the calculated temperature and concentration dependence of the Snoek peak with the published data showed that the PAW supercell calculation of the O-O interactions in Nb describes the behavior of the interstitial solid solution adequately. It proves also that the impact of interstitial atom concentration on the Snoek relaxation is connected to the mutual attraction of these atoms.
Application of Density Functional Theory to Point Defect Anelasticity of Carbon-Containing Austenitic Alloys
Authors: Gibala Ronald , Counts W.A. , Wolverton C.
Published: January 2012

We have used density functional theory (DFT) to determine binding energies (BE’s) of carbon-vacancy (C-v) point-defect complexes of probable importance to C-based anelastic relaxation processes in fcc iron alloys. Calculations are presented for three types of stable point defect clusters: C-v pairs, di-C-v triplets, and tri-C-v quadruplets. We demonstrate semi-quantitative consistency of the calculated BE’s with internal friction results on Fe-36%Ni-C alloys. The BE’s, which are in the range-0.37 eV to-0.64 eV, were determined for a hypothetical non-magnetic (NM) fcc Fe. The effect of the magnetic state of fcc Fe on some of these quantities was investigated by DFT and is shown to be significant; the BE’s appear to be reduced in antiferromagnetic (AFM) fcc Fe.