bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic analysis of structural transformations induced by annealing of amorphous Si–C–N ceramics derived from polymer precursors
Authors: Golczewski Jerzy Andrzej
Published: December 2013

Thermodynamic modeling has been used to explain structural transformations induced by heat treatment of amorphous Si–C–N ceramics derived from polymers. Nanocrystalline silicon carbide and nanocrystalline silicon nitride identified in the ceramic microstructure have been regarded as metastable NASIC and NASIN phases in the Si–C–N system. The Gibbs energies G(NASIC) and G(NASIN) have been derived and used together with the previously modeled Gibbs energy of the amorphous am-SICN to compute metastable phase diagrams. Computational results allow explanation of the crystallization process of amorphous Si–C–N ceramics. According to this model, the temperature of invariant reaction between carbon and silicon nitride changes with the growth of nanocrystallites, which explains the dependence of the thermal stability on the ceramic microstructure.
Thermodynamic modelling of the Ce–Ni system
Authors: Pisch Alexander , Wang Jiasong , Jorda Jean-Louis
Published: December 2013

The phase equilibria in the Ni-rich part of the Ce–Ni binary system were re-determined using DTA, metallography and SEM/EDX. CeNi5+x
presents a Ni solubility up to x = 0.53 at 1073K. The melting point of CeNi5 is 1608±5K and the CeNi5+x
–Ni eutectic has been observed at 1477±5K and x(Ni) = 0.91. The enthalpy of formation of stoichiometric CeNi5 has been measured by drop dissolution calorimetry in liquid aluminium and a value of ΔfH = −29.1±2.2kJ/moles of atoms was derived. Based on this new experimental data and literature values, a complete thermodynamic modelling of the Ce–Ni diagram was performed.
Thermodynamic properties of B2-AlFeNi alloys: modelling of the B2-AlFe and B2-AlNi phases
Authors: Oates W. A. , Bencze L. , Markus T. , Hilpert K.
Published: December 2013

Results from our recent simultaneous measurement of all three component activities by Knudsen effusion mass spectrometry, together with results available in the literature from vacancy concentration and calorimetric measurements, have been used in a thermodynamic modelling study. The results of this modelling for the binary B2-AlFe and B2-AlNi phases are presented in this communication. A four-sublattice cluster energy model in the point approximation has been used for the configurational contributions to the Gibbs energy. Excitational free energies are incorporated into the configurational energy and non-configurational contributions are considered to be decoupled from the configurational. The modelling has been found to lead to good agreement between calculated and experimental results for both the thermodynamic properties and the vacancy concentrations. It is clear that B2-AlFe is an antisite defect compound at both the lowest and highest temperatures with vacancy defects only predominating, and to only a small degree, at stoichiometry in an intermediate temperature range. In the case of B2-AlNi, however, vacancy defects predominate at stoichiometry over the whole temperature range so that it can be correctly described as a near-triple defect compound.
The Na–H system: from first-principles calculations to thermodynamic modeling
Authors: Qiu Caian , Opalka Susanne M. , Olson Gregory B. , Anton Donald L.
Published: December 2013

The Na–H system thermodynamic properties were assessed using Gibbs free energy model parameters obtained from best fit optimizations to combined experimental and first-principles predicted data. The first-principles finite temperature thermodynamic property predictions, based upon density functional theory ground state minimizations and direct method lattice dynamics, were used to supplement the Na–H dataset wherever experimental information was unavailable or unattainable. The predictions proved to be important for extending the evaluation of the heat capacity of the stable NaH phase to cover the complete 0–2000K temperature range. The predicted thermodynamic properties of the hypothetical NaH3 end-member representing complete interstitial H substitution in solid body-centered cubic Na, provided a physical basis for modeling H dissolution in the Na lattice. The modeling also showed satisfactory agreement with experimental measurements of NaH enthalpies of formation, NaH decomposition pressures, and H solubility in liquid Na.
Investigation of Cu-graphite composites prepared by electroforming
Authors: Zhao Haijun , Liu Lei , Tang Yiping , Shen Bin , Hu Wenbin
Published: December 2013

In this work, Cu-graphite composites were prepared by electroforming technology in an acidic copper sulfate bath with graphite particles in suspension. The factors affecting the codeposition of graphite particles with copper were studied. At a particle concentration of 20gl−1, a current density of 3Adm−2 and a stirring rate of 100min−1 graphite content in the composites was 21.7vol.%. Microhardness and friction coefficient of the composites decreased with increasing graphite content. However, wear mass-loss decreased, but increased with graphite content above 21.7vol.%. The wear mechanisms of pure Cu and Cu-graphite composites were adhesive wear and delaminating wear, respectively.
Effect of tin added to the zinc bath on the formation and the microstructure of hot-dip galvanized coatings
Authors: Avettand-Fènoël Marie-Noëlle , Reumont Guy , Goodwin Frank , Perrot Pierre , Foct Jacques
Published: December 2013

The present study aims to analyze the effect of tin, added to zinc bath containing aluminium, on the microstructure and on the development of spangles of continuous hot-dip galvanized coatings. Different experimental conditions have been explored and the mechanism of nucleation and growth taking place during the solidification of the coating are discussed with the support of a thermodynamics approach.
Nanoindentation creep and stress relaxation tests of polycarbonate: Analysis of viscoelastic properties by different rheological models
Authors: Schiffmann Kirsten Ingolf
Published: December 2013

Feedback-controlled nanoindentation with a Berkovich diamond tip has been used to perform creep and stress relaxation tests on polycarbonate at room temperature for a wide range of loads (10–30000μN) and indentation depths (30–3000nm). The creep compliance J(t) and relaxation modulus G(t) have been calculated from experimental data as a function of time in the range t = 0.1–100 (1000)s. The data are analysed by different rheological models which are compared: (1) the Burgers model, (2) the generalised Maxwell/generalised Kelvin model, and two empirical approaches: (3) a logarithmic model, and (4) a power law model. The Burgers model gives a poor description of the material behaviour since it assumes a steady-state flow of material which is not observed in the experimental time range. The generalised models yield a set of discrete relaxation- and retardation time constants. It is shown that these time constants do not correlate with specific molecular moving processes in the polymer, but are only one of several possible parameterisations of the creep and relaxation curves. Numerical differentiation of G(t) and J(t) shows that polycarbonate has continuous relaxation- and retardation time spectra, respectively, and the dynamic viscosity (t) of the material increases linearly with time. The behaviour of polycarbonate is best represented by the empirical power law model, which allows optimum fit of creep/relaxation curves, relaxation and retardation time spectra and time-dependent viscosity.
Thermodynamics of high-temperature cuprous sulfide
Authors: Arita Minoru
Published: December 2013

Published measurements of the diatomic sulfur fugacity were used to make a thermodynamic analysis of high-temperature cuprous sulfide between 789K and 1321K. Gibbs–Duhem integration of the fugacity data was used to determine the enthalpy of formation of stoichiometric Cu2S as −123.8kJmol−1. Statistical thermodynamics was applied to find partition functions, interaction energies, and free energies to characterize the configurational aspects of the phase. Theoretical calculations indicated that Cu vacancies might be localized in one half of the Cu lattice sites under quasi-chemical equilibrium.
Effect of LiYO2 addition on sintering behavior and indentation properties of silicon nitride ceramics
Authors: Matovic B. , Rixecker G. , Boskovic S. , Aldinger F.
Published: December 2013

The influence of the sintering additive LiYO2 (5–15wt.%) on sintering behavior, microstructure and mechanical properties of Si3N4 ceramics was investigated. Since LiYO2 enables densification of Si3N4 at extraordinarily low temperatures, sintering was carried out in the range from 1200–1700°C. Densification was found to be enhanced with increasing additive content due to an increasing volume fraction of the liquid. The phase transformation and grain growth occurred through a solution-reprecipitation mechanism, where the precipitation took place preferentially on pre-existing -Si3N4 nuclei (of which the starting powder already contained 20wt.%). The indentation fracture toughness increased with both sintering time and additive content as a result of the growth of elongated grains.
Modelling of metal–mould interface resistance in the Al-11.5 wt.% Si alloy casting process
Authors: Mirbagheri S. M. H.
Published: December 2013

A computational model is developed to include heat transfer, effects of resistance of the metal–mould interface, and pressure in the simulation of the solidification process. The simulation of the interface resistance is based on the Zero Thickness Element, utilizing the Finite Element Method. The solid boundary conditions, including contact resistances, have been modified by a pressure gradient in each of the Zero Thickness Elements. The pressure gradient has been modelled on experimental data. In order to verify the computational results, an Al-11.5wt.% Si alloy has been poured into a permanent mould and the temperature of the interface measured. Then we modelled the effect of metallostatic pressure on the overall heat transfer coefficient in the metal–mould interface. The comparison between the experimental and the simulation results during the solidification process shows a good consistency that confirms the accuracy of the model for the effect of the interface resistance on solidification time.
Thermal residual stress analysis in continuous Al2O3 fiber reinforced NiAl composites
Authors: Chen H. , Hu W. , Atiser A. , Zhong Y. , Gottstein G.
Published: December 2013

Thermal residual stresses (TRSs) in continuous Al2O3 fiber reinforced NiAl composites with and without a BN interlayer were studied by using the finite element method (FEM). The FEM model includes the effect of neighboring fibers of the composite. A minimum sample thickness and a minimum size of the surrounding composite have to be exceeded in order to obtain the correct TRS distribution in simulation. It is shown that the TRS, caused by different thermal expansion of fiber and matrix in the NiAl composite, is sufficiently large to cause fiber damage owing to twinning on different rhombohedral planes in the sapphire fiber. The introduction of a BN interlayer or a higher fiber volume fraction (40–60%) essentially reduces the TRS level in the NiAl composite and lessens the fiber damage. The residual stress in the NiAl composites was experimentally measured by nanoindentation. A good agreement between measurements and finite element analysis was achieved.
Influence of tension–compression loading history on plastic deformation of Mg wrought alloy AZ31
Authors: Götting Martin , Scholtes Berthold
Published: December 2013

The plastic deformation behavior of the Mg wrought alloy AZ31 is investigated in tension–compression tests at room temperature. It strongly depends on the loading direction and is characterized by dislocation slip as well as by the formation of deformation twins. The latter is reversible in the case of a change of the deformation direction. Because of the pronounced crystallographic texture of the material investigated, a macroscopic deformation anisotropy exists with lower flow stresses in compression than in tension. Hysteresis loops with characteristic shapes are observed when the material is cyclically plastically deformed, depending on the tension–compression loading history.
Analysis of defect configurations with positron lifetime measurements by pulsed low energy beams
Authors: Egger W. , Kögel G. , Sperr P. , Gudladt H.-J.
Published: December 2013

To understand the damage behavior of mechanically deformed metallic materials in more detail, the kind of defect and its concentration have to be known. In addition, the kinetics of decomposition and of precipitation hardening are influenced by the presence of defects and the corresponding concentration. Consequently, an analysis of dominating defects would be helpful. Compared with well known techniques, positron annihilation spectroscopy offers the opportunity for lifetime measurements that are characteristic for special kinds of defects, e.g. dislocations, small vacancy clusters and micro-voids. To detect the spatial distribution and to determine the concentration of defects, the low energy pulsed positron beam technique can be used. This technique, in combination with the scanning positron microscope, opens a broad field of applications for defect analysis in metallic and ceramic materials.
The nature of the TRIP-effect in metastable austenitic steels
Authors: Oettel Heinrich , Martin Ulrich
Published: December 2013

The TRIP-effect in metastable austenitic steels is caused by a moderate local martensitic transformation, influencing both the strain hardening and the damage behaviour. The main conditions of a marked TRIP-effect are a low flow stress in the undeformed state, a high strain hardening exponent, a continuous martensitic transformation up to about 20% and a high resistance to damage (e.g. crack formation and propagation). The martensite transformation starts in glide or shear bands and their intersections even at temperatures clearly above the conventionalMd-temperatures, reducing the local stress concentrations and so preventing the onset of damage. Furthermore, high martensite content can be detected along the fracture path impeding the crack propagation by the transformation. To demonstrate the influence of damage on the TRIP-effect the deviations from the so-called Considere-criterion for maximum uniform elongation can be used.
Diffusion of 65Zn in the Mg17Al12 intermetallic compound and in the Mg-33.4wt.% Al eutectic
Authors: Čermák Jiří , Stloukal Ivo
Published: December 2013

The coefficient of 65Zn heterodiffusion in the Mg17Al12 intermetallic compound (-phase) and the eutectic alloy Mg-33.4wt.% Al was measured in the temperature region 598–698K using serial sectioning and residual activity methods. The diffusion coefficient of65Zn in the intermetallic can be written as DI=1.5×10−2m2s−1× exp(–154.3kJmol−1/RT). At temperatures T648K, where the mean diffusion path is greater than the mean interlamellar distance in the eutectic, the effective diffusion coefficient Deff=2.710−2m2s−1exp(–155.1kJmol−1/RT) was evaluated. At two lower temperatures, the diffusion coefficients 65Zn in interphase boundaries were estimated: Db (623K)=1.610−12m2s−1 and Db (598K)=4.4 10−13m2s−1. The specific (Mg)/ interfacial energy =140mJm−2 was assessed from measurement of the time dependence of interlamellar distance during isothermal anneal.
Thermodynamic modeling of the sodium alanates and the Na–Al–H system
Authors: Qiu Caian , Opalka Susanne M. , Olson Gregory B. , Anton Donald L.
Published: December 2013

The thermodynamic properties of the Al–Na and Na–Al–H systems have been assessed by combining the “calculation of phase diagram” approach with first-principles predictions. The Gibbs energies of the individual phases were thermodynamically modeled, where the model parameters were obtained from best fit optimizations to combined experimental and first-principles predicted finite temperature data. The first-principles thermodynamic predictions were based upon density functional theory ground state minimizations and direct method lattice dynamics. The predictions proved to be important adjuncts to the assessments whenever experimental measurements were lacking or not feasible. It was shown that the phase stability conditions of sodium alanates, NaAlH4 and Na3AlH6, were well described with the present models.
Density and excess volumes of liquid copper, cobalt, iron and their binary and ternary alloys
Authors: Brillo Jürgen , Egry Ivan , Matsushita Taishi
Published: December 2013

The densities of liquid copper, cobalt, and iron, their binary and ternary alloys have been measured over a temperature range including the undercooled regime. A non-contact technique was used, consisting of electromagnetic levitation combined with optical dilatometry.

For all samples, the density was a linear function of temperature. The concentration dependence was studied by means of the excess volume which was negligible for Co–Fe and positive for Cu–Fe, Cu–Co, and Cu–Co–Fe.

The density of the ternary alloy could be predicted from the excess volumes of the binary phases without the need to introduce any ternary interactions.
Fracture behaviour of ultrafine-grained materials under static and cyclic loading
Authors: Hübner Peter , Kiessling Rene , Biermann Horst , Vinogradov Alexei
Published: December 2013

Fracture-mechanics experiments were carried out on ultrafine-grained (UFG) samples of copper, titanium and an Al alloy to obtain the fracture behaviour under static and cyclic loading. The UFG-materials investigated show crack resistance behaviour under static loading, which was confirmed by ductile fracture surfaces. Under cyclic load the crack growth rate was described well by the ESACRACK model.
Neutron diffraction residual stress analysis of steel engineering components: a study of the elastic and plastic anisotropy
Authors: Bruno Giovanni
Published: December 2013

The effect of the elastic and plastic anisotropy has been investigated in a welded pipe for nuclear applications (AISI 347) and in a welded plate for conventional power plants (Uni-Fe510D). The analysis has been performed exploiting neutron conventional and reverse time-of-flight spectra and comparing the single peak fit of some set of lattice planes with the Rietveld average. The results show that only some crystallographic directions (namely the 〈311〉 and the 〈111〉 for γ-Fe and 〈211〉 and the 〈110〉 for α-Fe) are in agreement with the average inherent in the Rietveld refinement. Those peaks are therefore recommended for residual stress analysis at steady state sources. The other peaks yield more scattered data (with higher statistical error), but allow spotting the influence of plastic anisotropy. The latter has a greater influence on all single peak data if the macroscopic stress exceeds the bulk yield strength.
Fluidity of Mg–Al–Ca alloys in the high-pressure die casting process
Authors: Zhao Peng , Wang Qudong , Liu Liufa , Wei Zhongshan , Zhai Chunquan
Published: December 2013

The fluidity of Mg – Al – Ca alloys under high-pressure die casting conditions was studied using fluidity tests with spiral specimens. The flow behavior analyses suggest that flow with zero superheat plays a more important role under high-pressure die casting conditions than gravity casting. This can be attributed to the difference between the two kinds of casting process. Fluidity results with a degree of superheat were interpreted on the basis of the effects of calcium on (1) latent heat, (2) viscosity and (3) solidification characteristics. The latent heat and phase accumulation formed by high pressure are the important factors influencing the fluidity of magnesium alloys in the high-pressure die casting process.
Influence of interfaces on the mechanical properties of ultrahigh carbon steel multilayer laminates
Authors: Pozuelo Marta , Carreño Fernando , Carsí Manuel , Ruano Oscar A.
Published: December 2013

To improve impact and flexure properties of ultrahigh carbon steel (UHCS-1.3 wt.% C), a multilayer laminate consisting of 20 layers of the same UHCS has been processed by hot rolling. Two different rolling conditions gave rise to “soft” and “severe” laminates. The toughness of the “soft” laminate, measured by impact test absorbed energy, was more than forty times higher than that of the monolithic UHCS and three times higher than that of mild steels. In contrast, the “severe” laminate showed no increase in toughness with respect to the monolithic UHCS. This large difference in behaviour was studied by means of shear and bend tests, which gave valuable information on bond quality and delamination.
Standard Gibbs energy of formation of Zn17Y2 and Zn12Y determined by solution calorimetry and measurement of heat capacity from near zero Kelvin
Authors: Morishita Masao , Yamamoto Hiroaki , Tsuboki Kohei , Horike Tomohiro
Published: December 2013

The thermodynamic properties of Zn17Y2 and Zn12Y were investigated by calorimetry. The standard entropies of formation at 298 K, were determined from measuring the heat capacities, Cp, from near absolute zero (2 K) to 300 K by the relaxation method. The standard enthalpies of formation at 298 K, were determined by solution calorimetry in hydrochloric acid solution. The standard Gibbs energies of formation at 298 K, were determined from these data. The results obtained are: (Zn17Y2) = – 23.53 ± 1.4 kJ · (mol of atoms)−1; (Zn17Y2) = – 3.05 ± 0.39 J · K−1 · (mol of atoms)−1; (Zn17Y2) = – 22.62 ± 1.4 kJ · (mol of atoms)−1; (Zn12Y) = – 23.89 ± 1.8 kJ · (mol of atoms)−1; (Zn12Y) = – 0.78 ± 0.41 J · K−1 · (mol of atoms)−1; (Zn12Y) = – 23.66 ± 1.8 kJ · (mol of atoms)−1. The electronic contribution to the heat capacity of Zn17Y2 and Zn12Y is found to be similar to pure zinc, indicating that the valence electrons of yttrium in the compound are trapped by the density of states for zinc.
Phase equilibria in the Zn–Fe–S system at 450°C
Authors: Tan Zheng , Su Xuping , Li Zhi , Liu Ya , Wang Jianhua
Published: December 2013

The 450 °C isothermal section of the Zn – Fe – S phase diagram has been constructed using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. In addition to the ternary extensions of the binary Zn – Fe intermediate compounds of ς, δ, Γ1, and Γ, the extensions of the ZnS, FeS and FeS2 compounds were also determined. The solubility of Fe in ZnS is about 20.2 at.%. The solubility of sulfur in all Fe – Zn intermetallic compounds is negligible. The zinc contents of Fe sulfides were not detectable.
Effect of tempering on the microstructure and hardness of ledeburitic chromium steel X155CrVMo12.1
Authors: Markoli Boštjan , Spaić Savo
Published: December 2013

Ledeburitic chromium steel X155CrVMo12.1 for cold-work tools was investigated in the quenched and tempered condition. Using appropriate investigative methods the evolution of the microstructure in all conditions was characterized. The change in state of a multicomponent matrix during tempering is crucial for attaining the required properties of this steel. In the material investigated, shape, size, fraction and distribution of eutectic (primary) carbides played a secondary role. The evolution of tempered martensite and precipitation of secondary hardening carbides of M23C6-type and MC-type from the supersaturated matrix during tempering led to secondary hardening and a secondary hardness peak at about 530 °C. The results show that steel X155CrVMo12.1 also exhibits performance ability at moderately elevated temperatures.
Design of carbide-free low-temperature ultra high strength bainitic steels
Authors: Garcia-Mateo Carlos , Caballero Francisca Garcia
Published: December 2013

There are severe limitations to attaining submicrostructured steels by means of continuous cooling, the achievement of fine grain sizes is limited by the need to dissipate enthalpy during rapid transformation, so that the actual grain size obtained is more than an order of magnitude greater than can be obtained theoretically. Bainitic microstructures obtained by isothermal heat treatment at low temperatures, can overcome the recalescence limitations and at the same time provide a very fine microstructure (nanostructure) that leads to extraordinary mechanical properties. Steel grades for this purpose have been designed by means of phase transformation theory alone and their mechanical properties tested. The results obtained reveal that the microstructure is indeed extremely fine and exhibits high levels of strength accompanied by reasonable ductility and toughness, mainly due to the fine scale of the bainitic ferrite plates achieved. The influence that retained austenite has on the mechanical properties through the TRIP effect is also discussed.
Texture and microstructure evolution of ECAP processed AlMg1Mn0.14 alloy
Authors: Molodova X. , Berghammer R. , Gottstein G. , Hellmig R. J.
Published: December 2013

Microstructure and texture evolution of an AlMg1Mn0.14 alloy after Equal-Channel Angular Pressing (ECAP) and subsequent heat treatment were investigated. Initially the material was subjected to up to 8 passes with a 90° die angle using routes A and Bc. The deformed and annealed states were characterised by crystallographic texture analysis, Electron Back Scatter Diffraction, Transmission Electron Microscopy, optical microscopy and microhardness tests. The recorded texture and microstructure changes were compared to the behaviour of specimens produced by conventional cold rolling. It was shown that the observed discontinuous change in texture, microstructure and microhardness has to be attributed to discontinuous recrystallisation, which proceeded faster for route Bc samples. Furthermore, it was found that ECAP deformed material is more stable against recrystallisation than cold rolled material.
Modelling grain refinement in fcc metals during equal-channel angular pressing by route “C”
Authors: Enikeev Nariman A. , Abdullin Marat F. , Nazarov Ayrat A. , Beyerlein Irene J.
Published: December 2013

Grain refinement and texture evolution during equal channel angular pressing (ECAP) by route “C” are modelled by the visco-plastic self-consistent (VPSC) model incorporating a disclination-based grain subdivision criterion. Simple shear and analytical fan models are used to describe the deformation history during ECAP. Textures calculated after the first four passes of ECAP by both the standard VPSC and the VPSC/disclination models are compared to available experimental data that show a better predictive capacity of the model incorporating the disclination subdivision criterion.
Compressive behaviour of ultrafine-grained AA6063T6 over a wide range of strains and strain rates
Authors: Meyer Lothar W. , Hockauf Matthias , Krüger Lutz , Schneider Ines
Published: December 2013

The flow stress behaviour of commercially available AA6063-AlMg0.5Si0.4 with ultrafine-grain size is investigated over a wide range of strain and strain rates under uniaxial compression. The ultrafine-grained microstructure is achieved by equal channel angular extrusion and characterised by grain sizes well below 1 μm. Results of quasi-static loading show that the ultrafine-grained states behave in an elastic – nearly perfect plastic manner with significantly reduced strain hardening capacity. When compared to the coarse grained counterpart, no change in strain rate sensitivity was measured for the material after two extrusions. In contrast to that, after eight extrusions the material shows significantly increased strain rate sensitivity especially in the range of highest rates above 102 s−1.
Effect of Nb–V addition on the mechanical behaviour and structural stability of ultrafine grained steels
Authors: Vedani M. , Arnaboldi S. , Vimercati G. , Bassani P. , Tuissi A.
Published: December 2013

A study is presented on the microstructural evolution and mechanical behaviour of three ultrafine grained steels produced by severe plastic deformation. Two Nb – V microalloyed steel grades differing only in their Nb content and a C – Mn steel were extensively refined at 773 K by caliber rolling to a reduction of section of the order of 98 %. Grain stability and evolution of mechanical properties during annealing at 873 K were then investigated.

It was demonstrated that tailored annealing treatments lead to a modification of the tensile behaviour of the ultrafine steels, with a more satisfactory combination of strength and uniform elongation. Nb – V microalloying contributed to increasing the stability of the grain structure and allowed achieving slightly improved properties with respect to the C – Mn grade.
Shear deformation of submicron-structured materials
Authors: Hafok Martin , Pippan Reinhard
Published: December 2013

Shear samples with special geometry were produced from high purity nickel and copper in order to study the deformation mechanism in the saturation region of severely plastically deformed metals. The shear samples, pre-deformed by high pressure torsion, were tested in situ at room temperature. Electron back scatter diffraction and back scatter images were used to characterise the change in micro-texture and microstructure after the shear deformation. The experiment revealed that almost all grains were sheared simultaneously, while at higher shear strains the formation of micro shear bands were observed.
Mechanical behavior of nanostructured metals and alloys in the 300–4.2 K temperature interval
Authors: Tabachnikova Elena , Bengus Vladimir
Published: December 2013

Original data of the authors and literature data are presented describing the mechanical behavior of nanostructured metals and alloys at cryogenic temperatures. Bulk ultrafine grained metals and alloys processed by severe plastic deformation through equal channel angular pressing are considered. The mechanical behavior of a number of nanostructured metals and alloys (Cu, Ni, Ti, VT6 and others) were investigated under uniaxial compression and tension at cryogenic temperatures in a wide range of strain-rates. The most important low temperature peculiarities of the nanostructured materials mechanical behavior have been indicated.
Nanoindentation behavior and mechanical properties measurement of polymeric materials
Authors: Cook Robert F. , Oyen Michelle L.
Published: December 2013

During sharp contacts, polymeric materials can exhibit elastic (reversible), plastic (instantaneous irreversible), and viscous (time-dependent irreversible) deformation. Due to viscous effects commonly observed in experiments conducted on polymeric materials, the analytical methods developed for instrumented indentation testing (“nanoindentation”) of elastic-plastic materials cannot be used to determine polymer mechanical properties. Here, a viscous-elastic-plastic sharp indentation model is reframed into normalized coordinates. The updated scheme allows the mechanical properties of polymeric materials to be determined simply from single- or multiple-cycle nanoindentation tests; output parameters are the relative resistance to plastic vs elastic deformation during indentation and the relative time scales for viscous flow during the contact event. The scheme allows the indentation behavior of all materials to be placed on a single map.
Testing the viscoelastic properties of SU8 photo resist thin films at different stages of processing by nanoindentation creep and stress relaxation
Authors: Schiffmann Kirsten Ingolf , Brill Carsten
Published: December 2013

The viscoelastic properties of SU8-25 photo resist coatings have been investigated by means of nanoindentation creep and stress relaxation tests. Different stages of processing of SU8 have been tested: (a) Spin coating and pre-bake only, (b) exposure to ultraviolet light for different durations, (c) different cross-linking times of the resist and finally (d) the completely processed sample (post-bake, develop and hard-bake). At each stage creep and stress relaxation tests have been performed with loads of 2 mN or indentation depth of 500 nm covering creep/relaxation times from 0.1 s to 1000 s. From the raw data the following viscoelastic functions have been computed: the creep compliance J(t) and relaxation modulus G(t), the relaxation and retardation time spectra H() and L(), and the dynamic viscosity (t). It has been found that different pre-bake times influence the viscosity of the film. The cross-linking of the SU8 starts immediately after exposure even without applying a post-bake. A strong increase in viscosity can be observed within the first 4 h after exposure due to the progress of cross-linking at room temperature. After the finish of cross-linking the dynamic viscosity has increased by 50 times. Observation of impression recovery after unloading over 3 days indicated up to 75 % immediate and retarded elastic recovery for the fully processed film, while the simply pre-baked sample only exhibied 25 % recovery and 75 % irreversible viscous flow.
Viscosity measurement of liquid ternary Cu–Ni–Fe alloys by an oscillating cup viscometer and comparison with models
Authors: Brillo Jürgen , Brooks Rob , Egry Ivan , Quested Peter
Published: December 2013

Viscosity data on Cu – Ni – Fe have been obtained using an oscillating cup viscometer. In this method, a liquid sample is suspended in a crucible which performs damped angular oscillations. Viscosities are calculated from the time period and the decay of the amplitude.

The temperature dependence of the measured viscosities can be described by an exponential Arrhenius law, taking into account an activation energy for the viscous flow. The activation energies for the ternary alloys were found to be linear combinations of the corresponding activation energies of the pure elements Cu, Ni, and Fe. At constant temperature, a non ideal mixing behaviour was observed and the data were compared with several quantitative models. Close agreement of the experimental results was found with the predictions of two models by Kaptay and Hirai.
A kinetic study of nickel coating on boron nitride micro-particles
Authors: Li Fan , Zhang Dengjun , Sichen Du
Published: December 2013

In the present work, the mechanism of nickel coating on BN particles by hydrazine reduction was studied. A nickel sulfate – ammonium sulfate – ammonia – hydrazine hydrate plating system was employed. It was found that Pd on the surface of BN particles acted as an active center for nickel deposition at the initial stage of the process. Thereafter, Ni itself would act as an active center to catch Ni from the solution through the reaction: Ni2+ + 2H*ad ß Ni + 2H+. The rate of the process was found to be controlled by the reaction at the interface under the present experimental conditions. A kinetic model was proposed on the basis of the experimental results. The model predictions were found to be in agreement with the experimental data.
Focused Ion Beam Preparation and EFTEM/EELS Studies on Vanadium Nitride Thin Films
Authors: Rogers Michael , Kothleitner Gerald , Berendes Antje , Bock Wolfgang , Kolbesen Bernd O.
Published: December 2013

A two-beam focused ion beam (FIB) instrument was used to prepare transmission electron microscopy (TEM) specimens of vanadium nitride layers produced by rapid thermal processing in a NH3 or N2 atmosphere. For the FIB preparation method an in-situ liftout technique was used, which was found to be highly efficient regarding specimen transfer yield but also very convenient as the final milling steps were carried out with the TEM specimen already fixed to the TEM grid. Electron energy-loss spectroscopy (EELS) and energy-filtering TEM (EFTEM) was applied to characterize the films morphologically and chemically. EFTEM investigations provided chemical information over the whole film thickness and revealed that the vanadium nitride layers consisted partly of two different nitride phases. By interpreting the EELS near edge structure of the nitrogen K-edge and comparing them to high-resolution spectra recorded on a monochromator TEM at an energy resolution of ∼0.25 eV, the nitride layers could be unambiguously identified.
Focused Ion Beam (FIB): Applications in Micro- and Nanoanalysis in Geosciences and Applied Mineralogy
Authors: Wirth Richard
Published: December 2013

Recently the focused ion beam (FIB) tool has been successfully used to prepare site-specific geological specimens for subsequent analysis by TEM, and as a stand-alone instrument for micromachining of materials such as diamond. FIB enables to prepare a TEM foil from the specific location of interest. TEM foils with the dimensions 20 × 10 × 0.150 micrometer can be cut from nearly any sample by means of a Ga-ion beam. The preparation of a TEM-ready foil with similar dimensions takes about 4 hours in a fully automated process, which is significantly faster than conventional argon ion milling. It is this unique possibility of site-specific TEM foil preparation, which enables TEM investigation of submicron-sized mineral inclusions in mantle minerals such as diamond, garnet or olivine, thus providing an insight into the pressure-temperature conditions and chemical composition of the Earth's mantle during formation of the encapsulating minerals. A FEI FIB200 instrument is operated at the GFZ Potsdam since more than two years and TEM foils from many rock-forming minerals such as olivine, garnet, pyroxene, amphibole, quartz, apatite or glass, metals, ceramic materials and even microfossils have been successfully prepared and subsequently investigated by TEM. The first finding of nanometre-sized diamond aggregates in melt inclusions enclosed in a silicate mineral (pyroxene) in mantle xenoliths from Hawaiian lavas illustrates the enormous potential of this technique. Another novel application of FIB in geosciences is micromachining diamonds, which are used for high-pressure diamond anvil cells (DAC).
TEM-Zielpräparation unter REM-Beobachtung mittels Zweistrahl-FIB
Authors: Altmann Frank
Published: December 2013

Kurzfassung

Die Transmissionselektronenmikroskopie (TEM) ist eine wichtige Untersuchungsmethode und wird industriell zunehmend für die Charakterisierung der stetig kleiner werdenden Strukturen mikroelektronischer Bauelemente eingesetzt. Die dafür notwendige Zielpräparation wird im wesentlichen mittels fokussierender Ionenstrahltechnik (focused ion beam, FIB) durchgeführt, wobei die Anforderungen an Präzision und Qualität der hergestellten TEM-Proben ständig wachsen. Insbesondere spezielle TEM-Techniken, wie Elektronenenergieverlustspektroskopie (electron energy loss spectroscopy, EELS) und höchstauflösende TEM aber auch scanning-TEM (STEM) im Rasterelektronenmikroskop (REM) erfordern geringste Probendicken bei minimaler FIB-Strahlschädigung. Mit der Möglichkeit einer REM-Beobachtung der FIB-Bearbeitung in modernen Zweistrahl-FIB-Anlagen können TEM-Proben noch präziser als bisher zielpräpariert werden.
Untersuchung von Bronzeeinlagerungen in einem Krug aus Graupastenkeramik aus der Tartesierzeit (VII Jahrhundert. V. CHR.)
Authors: Bravo Esther , Avalo Raquel , Dietz Christian , Criado Antonio Javier , Martínez Juan Antonio , Criado Antonio José
Published: December 2013

Kurzfassung

Mit Hilfe der Rasterelektronenmikroskopie sowie EDX-Analyse wurden Bronzeeinlagerungen in einem Krug aus Graupastenkeramik untersucht. Dieser stammt von einer Fundstelle in der Nähe von Toledo, Spanien und wird auf das VII. Jahrhundert vor Christus datiert. Sowohl die ermittelte Zusammensetzung der binären Kupfer-Zinn-Bronze als auch die Interpreation der Kristallfeinstruktur erhärten die Hypothese, dass es sich bei dem Krug um ein Artefakt der tartesischen Kultur handelt. Dies deutet seinerseits darauf hin, dass der Einflussbereich dieser frühiberischen Kultur wesentlich ausgedehnter war als bisher angenommen.
Beitrag zur Metallographie von Kupfer und Kupferlegierungen
Authors: Hofmann Uwe , Bögel Andreas , Hölzl Helga , Kuhn Hans-Achim
Published: December 2013

Kurzfassung

Es gibt eine große Menge verschiedener Legierungen auf Kupferbasis. Sie werden als Werkstoffe in unterschiedlichen Anwendungsgebieten eingesetzt. Dementsprechend vielfältig sind Gefüge wie auch die Schadensbilder, die durch eine Überbeanspruchung von Bauteilen aus Kupferwerkstoffen entstehen. In der vorliegenden Arbeit werden exemplarisch die typischen Gefüge von Kupfer, von niedrig und hoch legierten Kupferlegierungen vorgestellt. Wichtige metallphysikalische Zusammenhänge und Besonderheiten werden erläutert. Einige Beispiele technischer Schadensfälle werden besprochen. Sämtliche lichtmikroskopische Untersuchungen werden mit derselben Methode zur Schliffpräparation und Gefügeentwicklung eingeleitet.
Schadensanalyse der gebrochenen Rotorwelle einer Windenergieanlage mit überraschendem Resultat
Authors: Hülmann Gregor
Published: December 2013

Kurzfassung

Während des normalen Betriebes einer Windenergieanlage (WEA) kam es zum Absturz der Rotorblätter und des Rotorkopfes. Der Turm der WEA wurde beschädigt, die Rotorblätter völlig zerstört (Bild1). Die Ergebnisse einer durchgeführten Schadensanalyse ergaben, dass die Rotorwelle gebrochen war. Es konnte ein typischer Schwingbruch (Dauerbruch) festgestellt werden. Ursache des Dauerbruches war eine im Bereich des Hauptlagers der Rotorwelle vorgenommene Auftragsschweißung.
Influence of Alloying Elements on the Surface Morphology of Electroless Deposits for Ni-P Based Alloy Systems
Authors: Bangwei Zhang , Hoawen Xie , Shuzhi Liao , Lindig S. , Taglauer E.
Published: December 2013

We used SEM (scanning electron microscopy) to study the amorphous and crystalline deposits of Ni-P, Ni-Sn-P and Ni-Sn-Cu-P alloy systems with magnifications of 500x, 1000x, 5000x, 10000x and 20000x. We found first that the morphology only can be displayed clearly with magnifications of 5000x for most of these deposits, some of them must be up to 10000x. It is very difficult to see any features with magnifications below 1000x. The features look like cauliflower, some like arranged oranges with nearly uniform size, or like arranged potatoes. Our results also show that the size of these features decreases with increasing contents of P, Sn+P, and Sn+Cu+P in the deposits. A formula relating the size and content could be worked out, which is an inverse proportional relationship. The SEM pictures of these deposits indicate that the deposits are really dense, thus causing them to have superior properties.
Darstellung Verstärkter Kunststoffe mittels RE-Detektor (REM) und Mikroradiografie
Authors: Bürger Colette , Ehrenstein Gottfried W.
Published: December 2013

Kurzfassung

Zur Darstellung von Verstärkungsmitteln, deren Verteilung und Orientierung in Kunststoffen, wird sich üblicherweise der Lichtmikroskopie an Anschliffen bzw. Dünnschliffen bedient. Teilweise werden jedoch aufgrund fehlender Tiefeninformationen bzw. geringer Kontraste nur unbefriedigende Ergebnisse erhalten. Eine Alternative stellt deshalb die Darstellung im REM mittels des RE-Detektors dar. Um höhere Tiefeninformationen zur Faserorientierung zu erhalten, steht als weiteres Verfahren die Mikroradiografie zur Verfügung. Die Mikroradiografie nutzt den in der Elektronensäule des REM fokussierten Primärelektronenstrahl, um Röntgenstrahlung zu erzeugen und ausreichend dünne Präparate (bis 150 μm) zu durchstrahlen. Anhand der mikroradiografischen Bilder können z.B. Bindenähte aufgrund der Faserorientierung erkannt werden, die mittels Lichtmikroskopie bzw. REM nicht darstellbar sind.
Anwendung eines stereoskopischen Verfahrens zur fraktografischen Charakterisierung von grobkeramischen Baustoffen
Authors: Manhart C. , Harmuth H.
Published: December 2013

Kurzfassung

Es wurde eine fraktografische Untersuchungsmethode zur Charakterisierung der Bruchflächen von Baustoffen mit einem grobkeramischen Gefüge entwickelt. Diese basiert auf einer stereoskopischen Vermessung, der Erstellung eines digitalen Bruchflächenmodells sowie einer computergestützten Auswertung, die im vorliegenden Fall die Autokorrelationsfunktion und die laterale Korrelationslänge bestimmt. Bei den Untersuchungen von Feuerfestbaustoffen zeigte sich ein Zusammenhang zwischen der lateralen Korrelationslänge und Parametern, die aus der bruchmechanischen Materialcharakterisierung abgeleitet wurden und die Sprödigkeit der Baustoffe widerspiegeln. Die fraktografische Untersuchung wurde an Bruchflächen durchgeführt, die nach einer bruchmechanischen Untersuchungsmethode, dem Keilspalttest, hergestellt wurden.
3D Investigations of Plasma Erosion Craters using FIB/SEM Dual-Beam Techniques
Authors: Jeanvoine Nicolas , Holzapfel Christian , Soldera Flavio , Mücklich Frank
Published: December 2013

Plasma erosion craters caused by electrical discharges on the surface of materials are important features of the erosion processes resulting in the degradation of electrodes. In the present work, electrical discharges were produced on a bi-metallic Ni/Cu multilayered surface. By means of Dual Beam techniques, coupling a focused ion beam (FIB) and a scanning electron microscope (SEM), not only the surface but also the sub-surface structure of the craters were investigated. Using the combination of SEM, FIB and STEM-EDX, a complete three-dimensional investigation of the craters were carried out. The analysis of the microstructure modifications as a function of depth enabled to determine the field of interaction between the plasma and the material.
Metallographische Präparation von dotiertem Tantal für licht- und rasterelektronenmikroskopische Mikrostrukturuntersuchungen
Authors: Mayer Svea , Pölzl Silvia , Hawranek Gerhard , Bischof Michael , Scheu Christina , Clemens Helmut , Knabl Wolfram
Published: December 2013

Kurzfassung

Dünne kornwachstumsresistente Tantaldrähte werden zur Herstellung von elektrischen Tantalkondensatoren verwendet. Um den Herstellungsprozess zu optimieren, ist es wichtig, die Mikrostruktur von dotiertem Tantal nach unterschiedlichen Herstell- bzw. Wärmebehandlungsschritten zu untersuchen. Dies setzt jedoch voraus, dass eine geeignete artefaktfreie Präparationsmethode für dotiertes Tantal vorliegt, beziehungsweise die bestehenden Methoden verbessert werden. In der vorliegenden Arbeit werden optimierte Präparationsmethoden für licht- und rasterelektronenmikroskopische Untersuchungen vorgestellt. Neben der Beschreibung der Probenpräparation wird auch auf die wichtigsten Ergebnisse der anschließenden mikrostrukturellen Untersuchungen eingegangen.
Mechanical Behavior and Deformation Modes of Commercially Pure Titanium under Impact Tensile Load
Authors: Sun Q. Y. , Zhu R. H. , Yu Z. T. , Gu H. C.
Published: December 2013

The impact tensile test was carried out on hot-rolled commercially pure titanium at temperature from 293 K to 77 K. The microstructures after fracture were examined by transmission electron microscope to determine the deformation modes. Strength and ductility increase with decreasing temperature from 293 K to 77 K. The investigation on the microstructure shows that slip cooperates with twinning in the deformation, and twinning becomes more active at lower temperature. At high strain rate titanium exhibits obvious strain hardening and twinning plays an important role in strain hardening. {1012} twin is identified in the microstructure at room temperature and three types of twins were identified at 77 K, which are {1011}, {1012}, {1121} twins.
Kontrastberechnung und Optimierung der optischen Beschichtung in der Interferenzschichten-Metallographie
Authors: Gaudig Wolfgang
Published: December 2013

Kurzfassung

Die Theorie der Interferenzschichten-Metallographie wird von ersten Prinzipien ausgehend unter Verwendung komplexer Berechnungstechniken dargestellt. Sie wird angewendet, um den Kontrast zwischen Restaustenit und Martensit zu berechnen, wobei eine logarithmische Definition des Kontrastes entsprechend photographischer Lichtmessstandards zugrunde gelegt ist. Es wird gezeigt, wie die Theorie zur Auffindung des optimalen Beschichtungsmaterials und der optimalen Schichtdicke zum Erreichen maximalen Kontrastes genutzt werden kann. Es wird auch aufgezeigt, wie die visuelle Kontrolle der Schichtdicke zu verbessern ist.