bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ electrochemical nanoindentation of a nickel (111) single crystal: hydrogen effect on pop-in behaviour
Authors: Barnoush Afrooz , Vehoff Horst
Published: December 2013

The hydrogen effect on dislocation nucleation in Ni single crystals with (111) surface orientation has been examined with the aid of a specifically designed nanoindentation set-up for in situ electrochemical experiments. The effect of the electrochemical potential on the indent load–displacement curve, especially the unstable elastic-plastic transition (pop-in), was studied in detail. The experiments allowed the exclusion of the surface from hydrogen effects. The observations showed a pop-in load drop from an average value of 250 to 100N due to in situ hydrogen charging, which is reproducibly observed within sequential hydrogen charging and discharging. Clear evidence is provided that hydrogen atoms facilitate homogeneous dislocation nucleation.
Residual stresses in random-planar aluminium/Saffil® short-fibre composites deformed in different loading modes
Authors: Garces Gerardo , Bruno Giovanni , Wanner Alexander
Published: December 2013

The evolution of residual stress with plastic pre-strain was studied on a squeeze-cast, 2D-random short-fibre-reinforced metal matrix composite (aluminium/Saffil®). The plastic pre-strain was applied in three different modes: (1) uniaxial compression parallel to the fibre plane, (2) uniaxial tension parallel to the fibre plane, and (3) uniaxial compression normal to the fibre plane. The mean deviatoric residual stresses in the aluminium matrix were analysed using neutron diffraction. A major outcome is that the residual matrix stress is controlled by the load transfer to the fibres during deformation of the composite and reverse matrix plastic flow during unloading. The interplay between matrix and fibres depends strongly on the loading mode, and so does the evolution of the residual stresses as a function of pre-strain. This could be rationalised in a unified way using an Eshelby model.
Microstructure and mechanical properties of the extruded Mg-alloys AZ31, AZ61, AZ80
Authors: Mueller S. , Mueller K. , Tao H. , Reimers W.
Published: December 2013

In order to obtain optimum lightweight constructions in the automobile and aircraft industry, it is important to consider the use of extruded magnesium sections. A lot of the recent research has dealt with the extrusion of AZ31. These extrudates often miss the requirements of the automobile or aircraft industry for mechanical properties. A possible solution might be an increase in the aluminum content. Therefore, this paper deals with the extrusion of AZ31, AZ61 and AZ80 and the effect of the aluminum on the extrusion process as well as on microstructure and the mechanical properties of the extrudates. Whereas the aluminum content does not have a significant influence on the texture of the extrudates, the grain size and structure and, thereby, the mechanical properties can be improved by adding more aluminum to the Mg wrought alloys.
High thermal stability of mechanically-alloyed nanocrystalline Cu–Nb alloys
Authors: Botcharova E. , Freudenberger J. , Schultz L.
Published: December 2013

The high thermal stability of a nanocrystalline mechanically-alloyed Cu–Nb alloy was studied by means of isothermal annealing at high temperatures. The structure of the Cu matrix remains nanocrystalline with a grain size of about 50nm even after annealing at 1000°C for 10h. The copper grain growth is described with the help of kinetic analyses. The activation energy of the copper grain growth in Cu-10at.% Nb is about 0.98eV and the grain growth exponent is 4. The enhanced stability of the nanocrystalline Cu microstructure is attributed to the diffusion of Nb atoms along the Cu grain boundaries, “Zener drag” of NbO, Cu2O or Fe7Nb6 particles, and a non-equilibrium state of Cu grain boundaries.
Residual-stress-induced subsurface crack nucleation in titanium alloys
Authors: Ludian Tomasz , Kocan Marcin , Rack Henry J. , Wagner Lothar
Published: December 2013

This investigation has considered the influence of heat treatment, environment and residual stress level on the response of titanium alloys to mechanical surface treatment. It has been shown that the high cycle fatigue benefits to be gained by mechanical surface treatment will depend upon all of these variables. For example, shot peening of Ti–6Al–7Nb a/b solution treated, water quenched and aged condition results in a substantial increase in the high cycle fatigue performance in laboratory air. In contrast, shot peening of Ti–6Al–7Nb a/b solution treated, air cooled and aged condition has only a relatively small impact on the high cycle fatigue performance. This study also shows that high cycle fatigue crack nucleation of mechanically surface treated titanium alloys within the low stress, high cycle regime is associated with subsurface fatigue crack nucleation. Further, that this phenomenon may be related to the presence of a process-induced residual tensile stress necessarily present below the mechanically treated surface and required to balance the outer process-induced residual compressive stresses.
Thermal relaxation of residual stresses in TiN films deposited by arc ion plating
Authors: Matsue Tatsuya , Hanabusa Takao , Ikeuchi Yasukazu
Published: December 2013

The present study investigates crystal orientations and residual stresses in TiN films deposited by arc ion plating. TiN films approximately 2.0 μm thick were deposited on a steel substrate. With a bias voltage of 0 V, the TiN film exhibited strong {110} texture, whereas the dominant orientation of the film deposited at −100V was {111}. TiN films had very high compressive residual stresses: −8.6 GPa in the {110} textured film and −10.0 GPa in the {111} textured film. These residual stresses decreased with increasing annealing temperature and the reduction rate was greater for the {111} than for the {100} film. The behavior of residual stresses in the {111} and {110} textured layers of {111}/{110} textured double-layer film was identical to that for single-layer films.
Anwendung des lokalen Dauerfestigkeitskonzepts zur Bewertung der Wirksamkeit von Schweißnahtnachbehandlungsmaßnahmen
Authors: Nitschke-Pagel Thomas , Wohlfahrt Helmut
Published: December 2013

Many investigations have revealed the beneficial effect of mechanical surface hardening in combination with induced compressive residual stresses leading to improved fatigue strength. The benefit will be higher, the higher the quality of the weld is. On the other hand, methods like shot peening are useless if the weld toe profile is poor and the connected notch effect strong. Increased fatigue strength is then only possible after a post weld treatment which produces a smoother shape of the weld toe. Experiments reveal that methods which aim to increase the intensity of the penetration depth do not necessarily produce the best fatigue performance. High intensities of the mechanical surface treatments, especially in ductile aluminium alloys, may produce new geometrical defects which may work against the benefit of the deeper penetration depth of cold hardening and compressive residual stresses. A systematic evaluation of the results of improvement methods is possible with the help of the local fatigue strength concept, which compares the local strength properties and the local load stresses.
Investigation of the thermoelastic response of long-fibre reinforced thermoplasticsby comparison with different non-contactstrain measurement techniques
Authors: Stelzer G. , Klavzar A. , Bos M. , Renz R.
Published: December 2013

Processing of long-fibre reinforced thermoplastics with a discontinuous reinforcement of long glass fibres, especially by direct-processing, leads to inhomogeneous and anisotropic properties. Because of this, locally resolved characterisation of the material properties is necessary. Non-contact testing methods are required to derive these material properties. Locally resolving hysteresis measurement, full-field strain measurement techniques and thermoelastic stress analysis (TSA) are applied to an incremental step test and to a fatigue test. It is shown that there is good correspondence between the local TSA-signals and the locally measured values of the major strain. This correlation is valid not only for lower linear elastic load levels, but also up to nonlinear-viscoelastic levels. A model is presented to describe the correlation between the TSA-signal and the measured major strain.
Experimental observations on thecorrelation between microstructure andfracture of multiphase steels
Authors: Papaefthymiou Spyros , Prahl Ulrich , Bleck Wolfgang , van der Zwaag Sybrand , Sietsma Jilt
Published: December 2013

The aim of this study is to clarify the role of the microstructure in damage evolution. The influence of the transformation induced plasticity effect on the crack initiation and the impact of the different phases in development of cracks are important factors that control the fracture mechanisms. The fracture mechanisms of multiphase steels have been investigated on the basis of extensive light optical microscopy and scanning electron microscopy investigations. On the micro-scale, two failure modes appear: cleavage and ductile fracture, depending on the stress–strain conditions, the internal cleanness, the volume fraction of the retained austenite and the position of the austenite and the martensite grains. If a martensite or an austenite grain fails inside a bainitic island, the crack develops rapidly leading to cleavage fracture. If the failure starts inside the ferritic matrix due to void initiation at hard phases, the emerged void causes ductile damage to the surrounding ferrite.
Thermodynamic assessment of the systems La2O3–Al2O3 and La2O3–Y2O3
Authors: Fabrichnaya O. , Zinkevich M. , Aldinger F.
Published: December 2013

The thermodynamic parameters of the systems La2O3–Al2O3 and La2O3–Y2O3 are assessed using the Calphad technique. The available phase equilibrium data and calorimetric measurements for the LaAlO3, perovskite phase have been used. The calculated phase diagrams are in reasonable agreement with experimental results. However, experimental data for the La2O3–Y2O3 system demonstrated large uncertainty and new experimental study of solid state reactions would be useful to verify the calculated diagram. Experimental investigations of thermodynamic properties are necessary for both systems to verify the calculated phase diagrams and thermodynamic properties.
Thermodynamic investigation of Co–Cr alloys, III: Thermo-analytical measurements using DSC and DTA techniques
Authors: Sterneland Thérèse
Published: December 2013

Several Co–Cr alloys have been investigated by Differential Scanning Calorimetry (DSC) as well as by Differential Thermal Analysis (DTA) in the temperature range 298–1823K. The compositional range investigated was from 0 to 87wt.% Cr with special attention given to alloys with low Cr contents, i.e. 0 to 10wt.% Cr. From the DSC measurements molar heat capacity values, phase transformation temperatures, enthalpies of transformation and Curie transition temperatures were derived. From the DTA measurements, the melting temperatures and melting enthalpies were evaluated. The trends obtained were compared with the results for pure Co as well as the proposed phase diagram reported in literature.
Processing and mechanical behaviour of a dual scale particle strengthened copper composite
Authors: Tiziani C. , Götting M. , Rösler J.
Published: December 2013

Oxide dispersion strengthened (ODS) and dual scale particle strengthened (DSPS) copper composites were successfully manufactured by a powder metallurgical processing route, containing Al2O3 particles with a mean diameter of 17nm as dispersoids and, in the case of the DSPS material, 15% tungsten fibres about 3mm long. Their mechanical behaviour was investigated at ambient and elevated temperatures. The ODS material displayed mechanical properties comparable to those of commercial GlidCop® alloys. Addition of tungsten fibres in case of the DSPS material increased the elevated temperature flow strength relative to the ODS counterpart by about 12%. This result is rationalised by finite element calculations, taking fibre orientation, plastic deformation of the fibres as well as the role of the fibre coating into account.
Electrochemical characterisation of magnesium and wrought magnesium alloys
Authors: Nascimento Maria Lúcia , Fleck Claudia , Müller Wolf-Dieter , Löhe Detlef
Published: December 2013

The electrochemical behaviour of magnesium and different wrought alloys, AZ31, AE42, LAE442, and ZEK100, with and without heat treatment, was examined with the Mini-cell System by linear sweep voltammetry in 0.5wt.% and 3.5wt.% NaCl solution. The corrosion damage was characterised by scanning electron microscopy. Magnesium and the different alloys exhibited strong differences in their electrochemical behaviour. Alloying with aluminium increases the corrosion resistance. However, the magnitude of this improvement depends on uniform sizes and distributions of the Al-rich phases. Similarly, the influence of the heat treatment on the corrosion resistance depends on the produced distribution of precipitates. Magnesium and its alloys corrode quite rapidly in comparison with other metals, and there is pronounced hydrogen development. The latter increased with increasing NaCl concentration, although no great differences in the corrosion in both concentrations were observed, except on pure magnesium and ZEK100.
Low-cycle fatigue and damage of an uncoated and coated single crystal nickel-base superalloy SCB
Authors: Stekovic Svjetlana , Ericsson Torsten
Published: December 2013

This paper presents low-cycle fatigue (LCF) behaviour and damage mechanisms of uncoated and coated specimens of a single crystal nickel-base superalloy SCB tested at 500 °C and 900 °C. Four coatings were deposited on the base material, an overlay coating AMDRY997, a platinum-modified aluminide diffusion coating RT22 and two innovative coatings called IC1 and IC3 with a NiW diffusion barrier in the interface. AMDRY997 and RT22 were used as reference coatings. The LCF tests were performed at three strain amplitudes, 1.0, 1.2 and 1.4 %, with, in laboratory air and without any dwell time. The LCF life of the specimens is determined by crack initiation and propagation. Crack data are presented for different classes of crack size in the form of crack density, that is, the number of cracks normalised to the investigated interface length. Micrographs of damage of the coatings are also shown.

The effect of the coatings on the LCF life of the superalloy was dependent on the test temperature and deposited coating. At 500 °C all coatings had a detrimental effect on the LCF life of the superalloy. At 900 °C both AMDRY997 and IC1 prolonged the fatigue life of the superalloy by factors ranging between 1.5 and 4 while RT22 and IC3 shortened the life of the coating – substrate system. Specimens coated with RT22 exhibited generally more damage than other tested coatings at 900 °C. Most of the cracks observed initiated at the coating surface and a majority were arrested in the interdiffusion zone between the base material and the coating. No topologically close-packed phases were found. Delamination was only found in AMDRY997 at higher strains. Surface roughness or rumpling was found in the overlay coating AMDRY997 with some cracks initiating from the rumples. The failure morphology at 900 °C reflected the role of oxidation in the fatigue life, the crack initiation and propagation of the coated specimens. The wake of the cracks grown into the substrate was severely oxidised leading to the loss of Al and Ti to the oxide and resulting in the formation of a γ′ depleted zone. The cracks grew more or less perpendicular to the load axis in a Stage II manner.
Liquid–solid phase equilibria in metal-rich Hf–Ti–Si alloys
Authors: Bewlay Bernard P. , Jackson Melvin R. , Yang Ying , Chang Y. Austin
Published: December 2013

A range of metal-rich Hf – Ti – Si alloys with Si concentrations up to 35.0 at.% was directionally solidified. Liquid – solid phase equilibria in these alloys have been investigated using scanning electron microscopy, X-ray diffraction, and electron beam microprobe analysis. Four phases were identified: (Hf, Ti)5Si3, Hf(Ti)2Si, β(Hf, Ti, Si), and α(Hf, Ti, Si). Microstructural and microchemical evidence provided a clear definition of the Hf – Ti – Si liquidus surface at the metal-rich end and indicated the existence of the invariant reaction:

Liquid + Hf(Ti)2Si → (Hf, Ti)5Si3 + β(Hf, Ti, Si)

This invariant reaction occurs at a composition of approximately Ti-50Hf-9.5Si, and at a temperature of ∼1420 °C.
A comparison of different distributions of azimuth angles in the sin2 ψ-method
Authors: Ortner Balder
Published: December 2013

X-ray stress measurement in a specimen with a biaxial stress state is usually done with the -method, where measurements are carried out at different and. For the values the most usual choice is 0°, 45°, 90°. A better choice would be. The reason why is explained in detail by comparing the error calculus for these two cases.
Deformation twins in ultrafine grained commercial aluminum
Authors: Liu Manping , Roven Hans J. , Yu Yingda
Published: December 2013

Deformation twins in an ultrafine grained commercial Al – Mg – Si alloy with nonequilibrium grain boundaries processed by equal channel angular pressing at room temperature have been observed by means of a transmission electron microscope and a high-resolution transmission electron microscope. It was found that deformation twins formed frequently at the intersections of several grain bands where the critical stress level is reached locally and a change in the dominant slip system may occur due to the significant plastic deformation. Deformation twinning was also observed to occur via partial dislocations emission from grain boundaries and grain boundary junctions in the ultrafine grained alloy. Twins and stacking faults formed by Shockley partial dislocations dissociated from 0° screw dislocations were characterized and analyzed. Three twinning mechanisms suggested by molecular dynamic simulations were identified and their relevance was discussed.
Time-dependent directional solidification of binary Al–Cu alloys in the initial transient
Authors: Zimmermann Gerhard , Drevermann Anne , Sturz Laszlo , Warnken Nils
Published: December 2013

At the start of directional solidification a complex interaction between the movement of the solidification front, the concentration pile-up ahead of the front and the temperature gradient at the solid – liquid interface takes place. Experiments with binary Al-Cu1.3 wt.% were performed in this regime in a Bridgman – Stockbarger type gradient furnace allowing solidification with a planar solid – liquid interface. The time-dependent velocity and temperature profiles were measured during the experiments, whereas the concentration profiles were analysed from the processed samples. The experimental results were compared to predictions from numerical simulations based on the model of Coriell et al. Good agreement is obtained in the description of time-dependent diffusive, planar growth in the initial transient.
Preparation of NiO–LiFeO2 solid solutions: the role of mechanical and thermal treatments
Authors: Berbenni Vittorio , Milanese Chiara , Bruni Gianna , Cofrancesco Pacifico , Marini Amedeo , Chiodelli Gaetano
Published: December 2013

Ternary mixtures of Ni – Li2CO3 – Fe2O3 have been used as starting materials in order to prepare binary NiO – LiFeO2 solid solutions to be used as cathodic materal for molten carbonate fuel cells. By a combination of thermoanalytical techniques (Thermogravimetry and differential scanning calorimetry) and diffractometric techniques (X-ray powder diffraction) the present work deals with the study of the role played by thermal and mechanical treatment of the starting mixtures on the preparation of the final solid solutions.
Retained coarse grains in bulk nanocrystalline Ni3Al
Authors: Rentenberger Christian , Karnthaler Hans-Peter
Published: December 2013

Transmission electron microscopy methods were used to study the nanocrystalline structure achieved by severe plastic deformation of L12 long-range ordered Ni3Al. The deformation by high-pressure torsion (up to 40 000 %) leads to a duplex structure consisting of a disordered nanocrystalline and an ordered coarse-grained structure carrying different shear strains. The volume fraction of the nanocrystalline structure increases with strain but varies locally. During the deformation micrometer sized coarse-grained volumes embedded in the nanocrystalline structure are retained; they show a predominance of orientations of high symmetry. This leads to the conclusion that the stability of the coarse grains results from their homogeneous slip caused by a homogeneous activation of the slip systems.
The influence of post-ECAP annealing on the properties of ultrafine-grained 5005 aluminum alloy sheet
Authors: Lapovok R. , McKenzie P. W. J. , Thomson P. F. , Semiatin S. L.
Published: December 2013

Equal Channel Angular Pressing is a well-known method of severe plastic deformation used to obtain ultrafine grained materials with significantly improved mechanical properties. To the present, Equal Channel Angular Pressing has essentially been restricted to the treatment of bulk billets of square or circular cross-section of limited size. A machine developed at Monash University allows the Equal Channel Angular Pressing of sheet material. In the present work, improvement in biaxial formability, associated textures and mechanical properties after one Equal Channel Angular Pressing pass followed by annealing for aluminium alloy 5005 were investigated. An optimal annealing treatment to obtain a good balance of properties was defined.
New trends in superplasticity in SPD-processed nanostructured materials
Authors: Valiev Ruslan , Islamgaliev Rinat , Semenova Irina , Yunusova Nina
Published: December 2013

Recent studies have revealed that bulk nanostructured metals and alloys produced by severe plastic deformation can demonstrate extraordinary superplasticity at low temperatures and/or high strain rates. This work presents new results on superplasticity in several nanostructured Al and Ti alloys focusing on microstructural evolution and strain hardening, as well as the challenges of their application. Grain refinement in these alloys was accomplished using severe plastic deformation techniques. Subsequent superplastic deformation allowed not only to attain their efficient forming, but also to improve the ultrafine-grained structure and to obtain enhanced mechanical properties in the articles produced. The results demonstrate the possibilities of new applications of superplastic forming using bulk nanostructured materials.
Non-microscopical methods for characterization of microstructures and properties of UFG metals
Authors: Zehetbauer Michael J. , Schafler Erhard , Ungár Tamas
Published: December 2013

The paper reports on non-microscopical methods which allow for close investigation of ultrafine-grained metals especially of those processed by different techniques of Severe Plastic Deformation. These are as follows: (i) X-ray Bragg profile analysis, (ii) electrical residual resistivity, (iii) annealing calorimetry, and (iv) positron annihilation spectroscopy. The advantage of these methods lies in their integration/averaging over a certain sample volume so that they are often much closer to macroscopic physical properties than methods of microscopy; furthermore, the values of quantities obtained are more reliable because of strictly objective rules of determination. Typical quantities being relevant for ultra-fine grained materials are (a) grain size and grain size distribution, (b) long range internal stresses, (c) dislocation densities, and (d) concentration of vacancies and/or vacancy agglomerates. While quantities (a) and (b) are important for all classes of ultra-fine grained materials, those of (c) and (d) particularly occur with nanomaterials processed by severe plastic deformation also being responsible for their specific features such as ductility and the presence of non-equilibrium phases.
Indentation-induced densification of soda-lime silicate glass
Authors: Yoshida Satoshi , Sanglebœuf Jean-Christophe , Rouxel Tanguy
Published: December 2013

Glass is densified under a sharp diamond indenter. The densification is not a volume conservative process, and does not contribute to the volume strain around the indentation. This means that densification affects residual stresses around the indentation impression. In order to estimate the densification volume, three-dimensional images of Vickers indentations on soda-lime silicate glasses were obtained before and after annealing. Only the densified volume can be recovered by annealing. After annealing at around glass transition temperature, large volume recovery (55 – 80 %) of Vickers indentation was observed for soda-lime silicate glass. The volume recovery is much larger than the recoveries of indentation diagonal and depth. It is found that the densification of glass under the sharp indenter cannot be ignored for evaluating crack initiation and brittleness of glass. In addition, the residual stresses around the indentation impression were also estimated from the plastically deformed volume and the size of plastic zone around the indentation.
Nanomechanical studies of MEMS structures
Authors: Pustan Marius , Ekwinski Grzegorz , Rymuza Zygmunt
Published: December 2013

The stiffness is a fundamental qualifier of elastically deformable mechanical microcomponents and micromechanisms whose static, modal or dynamic responses need to be evaluated. This paper presents the results of theoretical studies of microcantilevers and microbridges and also a method for experimental stiffness testing using atomic force microscopy. Castigliano's displacement theorem is used herein to derive the stiffness equations. The results of the theoretical and experimental studies are compared and discussed.
Mechanical properties of nanostructured polymer particles for anisotropic conductive adhesives
Authors: He J. Y. , Zhang Z. L. , Kristiansen H.
Published: December 2013

Metal-coated polymer particles are used as a critical component in anisotropic conductive adhesives. The mechanical properties of polymer particles are of crucial importance to both application and design. In this study, a nanoindentation-based flat punch test approach has been developed to determine the mechanical properties of two polymer particles. Particle A failed at an average deformation of 67.2 %, while no failure was observed for particle C when a maximum 10 mN normal load was applied. The contact stress – strain behavior and contact modulus were obtained from the flat punch test.
Visco-elastic properties of thin nylon films using multi-cycling nanoindentation
Authors: Richter Asta , Gojżewski Hubert , Belbruno Joseph J.
Published: December 2013

Time dependent behavior of thin nylon films is investigated by depth sensing nanoindentation. Different loading rates and holding times are applied in single indentation procedures to study the relaxation behavior of nylon resulting in a characteristic nonlinear displacement – time dependence. Several load – time functions of multi-cycling indentation are developed, such as constant load repetition and incremental load increase mode sometimes containing holding segments. Hysteresis loops in multi-cycling nanoindentation quantify the visco-elastic energy of nylon films. The loading rate does not change the loop size if the maximum and minimum load of the cycle are the same. The unloading process has to be sufficiently large to allow the performance of the visco-elastic relaxation of the material.
The microstructure of ball milled nanocrystalline vanadium; variation of the crystal imperfection and the lattice parameter
Authors: Lamparter Peter , Mittemeijer Eric J.
Published: December 2013

Nanocrystalline vanadium powders have been produced by ball milling in a planetary mill. The morphology of the powder particles has been investigated by scanning electron microscopy. Crystallite size (size of coherently diffracting domains) and lattice-strain variation (microstrain) have been determined from the analysis of the X-ray diffraction-line broadening using the established integral breadth Williamson – Hall and Fourier Warren – Averbach methods. Results obtained from transmission electron microscopy analysis have been compared with the X-ray diffraction results. Ball milling causes an increase in the particle size and a decrease in the grain (crystallite) size with increasing milling time, a lattice-strain variation, due to deformation-induced dislocations, that increases with milling time and deformation-induced stacking faults of density increasing with milling time. The lattice parameter of the vanadium powders, as deduced from the diffraction-peak positions, decreases upon milling linearly with the inverse of the grain size, which has been attributed to grain (crystallite)-boundary stress.
Improved mechanical properties of the high pressure die casting alloy AlSi9Cu3(Fe)(Zn) as a result of the combination of natural and artificial ageing
Authors: Pabel Thomas , Geier Georg F. , Rockenschaub Horst , Hopfinger Michael
Published: December 2013

The present study was performed on the alloy AlSi9Cu3(Fe)(Zn) (EN 1706: 1998) to investigate the effect of different heat treatment conditions. High pressure die cast samples were quenched directly after casting and subsequently stored at room temperature or elevated temperatures. Combinations of natural and artificial ageing were also tested. The static mechanical properties of the alloy were measured at all stages. The results show that it is possible to attain improved mechanical properties by an optimised combination of both treatments.
Rapidly solidified Fe-base alloys as electrode materials for water electrolysis
Authors: Schmidt Andreas , Schubert Thomas , Röntzsch Lars , Weißgärber Thomas , Kieback Bernd
Published: December 2013

Amorphous ribbons of the systems Fe60Co20Si10B10 and Fe50Co20V10Si10B10 have been prepared via melt spinning to be used as electrode materials in alkaline water electrolysis. It turned out that the gas atmosphere during melt-spinning has a significant impact on the surface morphology and microstructure of the ribbons. Furthermore, a comprehensive characterization of the microstructure depending on the peripheral speeds of the cooling wheel was conducted. Moreover, the transition from the amorphous to the crystalline state was investigated via differential scanning calorimetry measurements. Preliminary electrochemical investigations suggest a noticeable improvement of the electrocatalytic activity of the melt-spun amorphous ribbons after an anodic–cathodic pretreatment.
Durchstrahlungselektronenmikroskopische Untersuchungen an explantierten Metall-Metall Hüftgelenken
Authors: Büscher R. , Gleising B. , Dudzinski W. , Fischer A.
Published: December 2013

Kurzfassung

In der vorliegenden Untersuchung sollen die Verschleißmechanismen in künstlichen Metall-Metall- Hüftgelenkspaarungen mit Hilfe von durchstrahlungselektronenmikroskopischen Methoden bestimmt werden. So kann gezeigt werden, dass es im Randbereich von Kobaltbasislegierungen durch plastische Deformation zu einer Neuordnung der Gefügestruktur kommt. Unterhalb der Artikulationsflächen bilden sich Stapelfehler und hexagonaler Martensit sowie ein rekristallisiertes, nanokristallines Gefüge. Dabei stabilisieren die Gitterfehler die rekristallisierte Randschicht, in der nach Auswertung der Elektronenbeugung martensitische Körner mit einer mittleren Größe von unter 100 nm dominieren. Zusammen mit parallel zur Oberfläche verlaufenden Rissen durch die nanokristalline Randschicht kann der wirkende Verschleißmechanismus hergeleitet und schließlich die für das tribologische System der künstlichen Hüfte charakteristischen Verschleißpartikel erklärt werden. Demnach versagt der Werkstoff durch Oberflächenzerrüttung in einer dynamisch rekristallisierten und umgewandelten Randzone, was zu der Ablösung von nanoskopischen und martensitischen Partikeln führt.
Metallographische Präparation von Titandioxid-Schichten für Untersuchungen mit der Elektronenstrahlmikrosonde
Authors: Martin Margit , Ohser-Wiedemann Renate , Müller Angelika , Meyer Susann
Published: December 2013

Kurzfassung

Photokatalytisch aktive Titanoxidschichten werden mittels anodischer Oxidation unter Funkenentladung hergestellt. Dabei entstehen offenporige, stark strukturierte Schichten. Da deren photokatalytische Aktivität auch von eingebauten Fremdelementen beeinflusst wird, war es notwendig die chemische Zusammensetzung in Abhängigkeit vom Randabstand zu untersuchen. Es werden Präparationsschritte vorgestellt, die es ermöglichen, an derartig offenen Randstrukturen mittels Elektronenstrahlmikroanalyse Konzentrations-Tiefen-Profile aufzunehmen.
Dauerbruch als Folge von korrosionsbedingten Kerben
Authors: Winkler Rolf , von Trzebiatowski Oliver , Zgraggen Markus
Published: December 2013

Kurzfassung

Die vorliegende Arbeit berichtet über die Schadensanalyse einer gebrochenen Pumpenwelle aus dem Stahl Z30C13 (entspricht dem Werkstoff X30Cr13, Werkstoffnummer 1.4028, nichtrostender martensitischer Stahl). Anhand der Fraktographie und den metallographischen Untersuchungen konnte nachgewiesen werden, dass ein Dauerbruch, ausgehend von einer Korrosionsnarbe, vorliegt. Die Korrosion wurde durch konstruktiv bedingte Spalten gefördert. Zudem wurde vom Stahlverarbeiter auf eine, für diesen Werkstoff zum Erreichen einer ausreichenden Korrosionsbeständigkeit, zwingend notwendige Wärmebehandlung (Härten/Anlassen) verzichtet. Die Welle wurde im weichgeglühten Zustand belassen, wodurch der Chrom-Gehalt in der Matrix infolge Karbidausscheidungen unterhalb der Resistenzgrenze von 12% abfällt. Eine unzureichende Passivschichtbildung ist die Folge, weshalb ein lokaler Korrosionsangriff stattfand. Derartige Angriffstellen wirken als Kerben, die letztendlich das Bauteilversagen durch lokale Spannungsüberhöhung eingeleitet haben.
Microstructural Analysis of Impact Wear in Perforating Projectiles
Authors: Martínez Miguel Angel , Antón Natividad , Velasco Francisco , Torralba José Manuel
Published: December 2013

This paper examines the macro- and microstructural characteristics of perforating projectiles type Armour Piercing Discarding Sabot (APDS) 20 mm, after being detained by armour plates normally used as defence against projectiles. The effect of impact of these projectiles against high density alumina tiles with several materials of backing plate (steel, alumina and composite) is studied to determine the structural modifications of these projectiles by microhardness and image analysis. The results provide data for studies of simulation of impacts in the design of armour plating.
Microstructure of a Thin Cast Al-Fe-Mn-Si Strip
Authors: Birol Yücel , Karlik Miroslav
Published: December 2013

The recent trend in Twin Roll Casting has been to reduce the casting gauge to less than 3 mm in order to reduce the processing costs, to take advantage of increasing rates of solidification and to increase productivity. Conventional casters typically cast strips 6 to 10 mm thick and operate at essentially constant production rates in this range. The new generation casters, on the other hand, are able to cast strips down to 1mm and offer a notable increase in the casting speed and thus in the caster productivity. It has been reported that the thin strips show some marked differences with respect to conventional strips owing to the temperature gradients and deformation involved in the thin-gauge casting process and may require different down stream processing cycles. The characterization of the thin strip structure is thus essential. This paper describes the microstructure of a thin-cast (3 mm) Al-Fe-Mn-Si (AA8006) strip in comparison with another strip of the same alloy cast at conventional gauge (6 mm).
Dilatationsrisse infolge Aufpufferung mit NiCr20Nb-Schweißgut auf Rohrbogen aus G-Cu L45
Authors: Oehmigen Hans-Günther , Weiß Reinhard
Published: December 2013

Kurzfassung

An schutzgasgeschweißten Mischverbindungen zwischen Rohrbogen G-Cu L45 und Stahlrohr St 35.8 wurden im Rahmen einer Druckprobe Undichtigkeiten festgestellt. Diese Undichtigkeiten lagen ausnahmslos auf der Kupferseite der Rundnaht.

Die Nahtflanken der aus Sandguss hergestellten Rohrbogen aus G-Cu L45 waren mit einer Nickellegierung vom Typ NiCr20Nb mehrlagig aufgepuffert worden. Anschließend erfolgte mit dem gleichen Schweißzusatz die Verbindungsschweißung.

Metallographische Untersuchungen zeigen, dass diese Undichtigkeiten auf feine interkristalline Trennungen im Abstand von ca. zwei Korndurchmessern neben der Schmelzlinie infolge Dilatationsspannungen im Kupferbogen zurückzuführen sind.

Als Schadenursache können Gussfehler, Heißrisse und die bekannte Wasserstoffkrankheit sicher ausgeschlossen werden.
Untersuchungen zur automatischen Klassifikation von Lamellengraphit mit Hilfe des Stützvektorverfahrens
Authors: Roberts Kathrin , Weikum Gerhard , Mücklich Frank
Published: December 2013

Kurzfassung

Die unterschiedliche Graphitausbildung in Gusseisen ist wesentlich für die mechanischen Eigenschaften dieses Werkstoffes. Deshalb wurden in der Norm EN ISO 945:1994 sechs generelle Formen für die Graphitausbildung und darunter für den Lamellengraphit fünf Anordnungsklassen definiert. Die subjektive Klassifikation letzterer kann zu widersprüchlichen Ergebnissen führen und sollte durch ein objektives Klassifizieren mit Hilfe der Bildanalyse möglichst ersetzt werden.

Vorgestellt wird der Einsatz des Stützvektorverfahrens bei dem durch Berechnung einer separierenden Hyperebene mit maximaler Bandbreite im m-dimensionalen Raum binär klassifiziert wird. Die Lage der Hyperebene wird von Stützvektoren definiert, die durch Messung bildanalytischer Kenngrößen an Trainingsbildern ermittelt werden. In dieser Untersuchung wurden zu jedem Bild sechs stereologische Parameter und 14 Haralick-Parameter errechnet. Die Trainingsbasis waren 350 von Experten klassifizierten Trainingsbilder. Untersucht wurde die Klassifikationsgüte des Stützvektorverfahrens. Außerdem war es möglich die Relevanz der 20 Parameter für die Klassifikation der einzelnen Graphitanordnungen zu bestimmen. Das Stützvektorverfahren erscheint als interessantes Klassifikationsverfahren aus dem Bereich “Maschinelles Lernen”, das zukünftig auch allgemeiner für metallographische Bilder eingesetzt werden kann.
2D Quantitative Characterization of Microstructural Inhomogeneities in the Pressure Die Cast AZ91 Magnesium Alloy
Authors: Prakash D.G. Leo , Regener Doris
Published: December 2013

Inclusions, shrinkage pores and gas pores are the major processing defects of pressure die cast AZ91 magnesium alloy. These inhomogeneities influence the mechanical properties of the material. Hence, quantitative characterization of size and arrangement of inclusions, shrinkage and gas microporosity is expected to be useful to understand the processing-property-microstructure correlation. In the present work an image analysis procedure has been explained to separately quantify the above inhomogeneities. The important parameters of image processing like montage creation, magnification selection and shrinkage pore separation are explained. The inclusions, shrinkage and gas micropores were separated by the above procedure and size, nearest neighbor distance distributions of these inhomogeneities were obtained in order to characterize the material.
Schäden im Zusammenhang mit dem Schmelztauchverzinken
Authors: Zgraggen Markus , Winkler Rolf , Winkler Markus , Germ Harald , Trüllinger Samuel , Faller Markus , Trzebiatowski Oliver von
Published: December 2013

Kurzfassung

Beim Schmelztauchverzinken von Stahlkonstruktionen kommt es immer wieder zu Schadensfällen. Die gesamte Fertigungskette hat auf das Schadensgeschehen letztlich einen Einfluss. Es liegt also häufig ein unglückliches Zusammenspiel verschiedener Einflussgrössen vor. Anhand von Schadensuntersuchungen kann aufgezeigt werden, wo in der Fertigungskette optimiert werden kann, um solche Schäden zu vermeiden.
Mikrostrukturelle Merkmale von martensitischen Chromstählen und deren Einfluss auf die Kriechfestigkeit
Authors: Maile Karl , Zies Gernot , Scheck Rudi , Kuppler Dorothee , Ruoff Herbert , Rauch Markus , Klenk Andreas , Scheu Christina
Published: December 2013

Kurzfassung

Martensitische 9–11% Chromstähle stellen für moderne Hochleistungsdampfkraftwerke wesentliche Strukturwerkstoffe für den Bereich Kessel, Turbine und Rohrleitungen dar. Die Festigkeit und Schädigungsentwicklung unter Kriechbeanspruchung in diesen Stählen wird maßgeblich von den Vorgängen in der Mikrostruktur beeinflusst. Im Vergleich zu niedriglegierten warmfesten ferritischen Stählen wird eine andere Schädigungsentwicklung beobachtet: Die Anzahl der Kriechporen wird zwar in ähnlicher Weise von der Beanspruchung (Grad der Mehrachsigkeit) und dem Werkstoffverhalten (Kriechdehnung) beeinflusst, es zeigt sich jedoch eine deutlich geringere Porenzahl. Die Ausbildung der Poren ist ebenfalls unterschiedlich. Für eine Beschreibung des Schädigungszustandes müssen in den martensitischen 9–11% Chromstählen zudem die Versetzungsdichte, die Subkorngröße und insbesondere die Ausscheidungscharakteristik herangezogen werden. Eine Kombination konventioneller TEM, EFTEM, EDX und Beugungsuntersuchungen ermöglicht die Ermittlung dieser Größen. Der Vergleich von Proben mit unterschiedlichen Zeitstandfestigkeiten zeigt, dass die Kriechfestigkeit von der Stabilität der M23C6 und MX Ausscheidungen abhängig ist. Das Auftreten der Z-Phase kann in einen Zusammenhang mit schlechteren Kriecheigenschaften des Stahls gebracht werden.
Microstructure of Laser Hardened Martensitic High Nitrogen Steel Subsurfaces
Authors: Runiewicz Anna , Dudzinski Wlodzimierz , Fischer Alfons
Published: December 2013

Martensitic high nitrogen steel (MHNS) offers an excellent combination of mechanical, chemical and tribological properties. Nitrogen is an alloying element responsible for higher corrosion resistance [1]. The investigated material X30CrMoN15-1 was in tempered conditions in order to get sufficient toughness. Afterwards the surface was laser hardened thus the material gains increase of hardness and partly dissolution of precipitates. To improve the corrosion and wear resistance the wear test in artificial see water was performed. The surface and subsurface was analysed as to the type of phase changes during the laser heat treatment comparing to the initial state of the material. The investigation was performed using transmission electron microscope (TEM).
Effekte des Laserumschmelzens auf das Gefüge und die Härte von Grauguss mit Lamellen- und mit Kugelgraphit
Authors: Benkißer Gunter , Pohl Michael , Heßing Christian
Published: December 2013

Kurzfassung

Im vorliegenden Bericht werden die Effekte des Laserstrahlumschmelzens auf das Gefüge und die Härte von Grauguss mit Lamellen- und mit Kugelgraphit dargestellt. Zum Umschmelzen der Randschicht dient ein cw CO2-Laser mit einer nominellen Strahlleistung von 4,5 KW. Die Strahlformung erfolgt mit einem Strahlintegrator, der auf der Probenoberfläche einen quadratischen Brennfleck mit einer Kantenlänge von 9 mm erzeugt. Aus den hergestellten Laserspuren werden für die metallographischen Untersuchungen und Härtemessungen Querproben entnommen. Infolge des Selbstabschreckens der aufgeschmolzenen Randschicht durch den kalten Grundwerkstoff erfolgen die Erstarrung der Schmelze und die Phasenumwandlungen im festen Zustand unter Ungleichgewichtsbedingungen. Folglich bilden sich in der feinkörnigen Umschmelzzone metastabile Phasen mit erhöhter Härte: Zementit, Restaustenit, Martensit. An die Umschmelzzone schließt sich die Wärmeeinflusszone an, deren Gefüge durch die erreichte Spitzentemperatur und die beschleunigte Abkühlung bestimmt ist. Durch das Laserstrahlumschmelzen ergibt sich eine beträchtliche Aufhärtung der Randschicht, die man auf die Kornfeinung des Gefüges und die harten, metastabilen Phasen in der laserbehandelten Randschicht zurückführen kann.
Einfluss der Vorverformung auf die Entwicklung der Rauigkeit bei durch Kavitationserosion beanspruchten Werkstoffen
Authors: Stella J. , Pohl Michael
Published: December 2013

Kurzfassung

Das Verhalten der Rauigkeit bei kavitiertem Cu, Ni, CuZn30 und CuAl7 wurde durch konfokale Laser-Raster-Mikroskopie (Confocal Laser Scanning Microscopy: CLSM) untersucht. Die Werkstoffe wurden in lösungsgeglühten und gewalzten Zuständen vermessen. Die Untersuchung zeigte, dass obwohl die Inkubationsphase durch Walzen verlängert wird, die Entwicklung des Pa-Parameters in der Inkubationsphase eine hohe Ähnlichkeit bei lösungsgeglühten Materialien und gewalzten Proben aufweist. Eine Ausnahme wurde im Fall bei lösungsgeglühtem CuAl7 festgestellt, bei dem die Pa-Werte erheblich höher als die beim gewalzten Material waren, da eine starke Änderung des Gefüges durch die Wärmebehandlung stattfand.
SEM Micrographs from NiTi-based Shape Memory Alloys after Mechanical Polishing and Electropolishing
Authors: Zhang Zhonghua , Pfetzing Janine , Frenzel Jan , Neuking Klaus , Eggeler Gunther
Published: December 2013

In the present study we investigate microstructures of NiTi-based shape memory alloys (SMAs) using scanning electron microscopy (SEM) in combination with mechanical polishing and electropolishing. The results show that electropolishing is quite useful for microstructural characterization of NiTi-based SMAs revealing morphologies of second phases, characteristic features of eutectic regions, growth mechanisms of primary carbides and coarsening of second phases.

Furthermore, three-dimensional morphologies of martensitic variants, twins, and substructures can be identified in electropolished high temperature SMAs like NiTiHf and NiTiZr.
Gefügedarstellung der stranggepressten Aluminiumknetlegierung EN AW-6061 und der MMC-Werkstoffe EN AW-6061 verstärkt mit 15 und 22 Vol.-% Al2O3-Partikeln
Authors: Klaska Arne M. , Ohl Adelheid , Kerscher Eberhard , Beck Tilmann , Löhe Detlef
Published: December 2013

Kurzfassung

Die stranggepressten, unverstärkten und mit 15 und 22 Vol.-% α-Aluminiumoxidpartikeln verstärkten Aluminiumknetlegierungen EN AW-6061 wurden metallographisch untersucht, um die Korngrenzen und die Ausscheidungsstruktur darzustellen. Dazu wurden kontrastierte und nicht kontrastierte Schliffe mit unterschiedlichen Verfahren angefertigt und die Ergebnisse verglichen. Probleme bei der Anfertigung nicht kontrastierter Schliffe zeigten sich vor allem bei der Erzeugung einer planen Oberfläche bei den MMC-Werkstoffen. Bei der Darstellung der Kornstruktur wurden die Ergebnisse durch die unterschiedlichen Reaktionen von Korngrenzen und Subkorngrenzen auf das jeweilige Ätzmittel beeinflusst. In dieser Arbeit wird ein Verfahren beschrieben, mit dem nicht kontrastierte Schliffe der untersuchten MMC-Werkstoffe in gleichbleibender Qualität erzeugt wurden. Außerdem stellte sich heraus, dass die besten Ergebnisse in Bezug auf die Darstellung der Korn- und Subkorngrenzen sowie der Ausscheidungen beim unverstärkten Werkstoff mit einem Ätzverfahren nach Weck zu erreichen sind. Diese Ätzung führte in Verbindung mit dem ebenfalls entwickelten Schleif- und Polierverfahren auch bei den partikelverstärkten Verbundwerkstoffen zu den besten Ergebnissen. Das Vorätzen mit destilliertem Wasser und Natriumhydroxid brachte bei der unverstärkten Legierung durch eine homogenere Färbung der Körner und einen schwächerern Kontrast eine nochmalige Verbesserung der Ergebnisse.
Mechanical Cross-Sectioning of Au/Cu Wire Ball Bond with Underneath Cu/low-k Interconnect Layers
Authors: Murali Sarangapani , Srikanth Narasimalu
Published: December 2013

Standard metallographic cross-sectioning of copper and gold wire bonds with underneath Cu/low-k interconnect layers are difficult, easily they fracture during polishing. It can be overcome by appropriate liquid molding methodology and polishing using semi-automatic system at very low frictional forces and using finer alumina or diamond lapping films. SEM observation of the polished microstructures up to 5000–8000× magnification does not reveal micro cracks or smearing of copper.