bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Interference Metallurgy – using interference as a tool for micro/nano structuring
Authors: Mücklich Frank , Lasagni Andrés , Daniel Claus
Published: December 2013

Interfering laser beams of a high-power pulsed laser provide the opportunity of applying a direct lateral interaction with the surface microstructure of metals in micro/nano-scale based on photo-thermal nature mechanisms. This “Laser interference metallurgy” allows the creation of periodic patterns of features with a well defined long-range order on metallic surfaces at the scale of typical microstructures (from the sub micrometer level up to micrometers). This technique is an approach to initiate metallurgical processes such as melting, recrystallization, recovery, and defect and phase formation in the lateral scale of the microstructure itself and with an additional long range order given by the interference periodicity. In this work, the laser interference theory is described and used to calculate multi-beam interference patterns. A method to calculate the numbers of laser beams as well as the geometrical arrangement of the beams to obtain a desired periodical pattern prior to experiments is presented. The formation of long-range-ordered intermetallic compounds as well as macroscopic and microscopic variations of mechanical properties on structured metallic thin films are presented as examples.
On dynamic and static strain ageing in Cu-2at.% Mn polycrystals
Authors: Dierke H. , Klose F. B. , Nortmann A. , Neuhäuser H.
Published: December 2013

Measurements of the yield points ΔσA on reloading after ageing at various stress levels (obtained by partial unloading of the tensile specimen) have been performed with Cu-2at.% Mn polycrystals at 313K (strain rate 310−5s−1). At these temperatures solute atoms are supposed to increase the effective obstacle strength (intersections of mobile with forest dislocations) by pipe diffusion from the forest to the mobile dislocations during the waiting time for thermal activation. The stress dependence ΔσA ∝ (σ*)1/3, (with the effective stress σ*) expected according to Friedel's equation is observed. This supports the intersection strengthening model and, hence, the pipe diffusion mechanism for static and dynamic strain ageing in the temperature and strain rate regime of this study.
Microcracks in superalloys: From local in-situ measurements to lifetime prediction
Authors: Marx Michael , Vehoff Horst
Published: December 2013

The establishedK-concept with the Paris law as the central equation often used for life-time prediction and dimensioning does not fit with the micromechanical crack tip opening displacement (CTOD) concept. While theK-concept is based on continuum mechanics, the CTOD is influenced by the local microstructure. Consequently, the CTOD-concept is checked in situ in the scanning electron microscope and is found to be the appropriate micromechanical description of the crack propagation mechanism. However, it is shown that during low cycle fatigue of turbine materials, even under extreme conditions short cracks behave less harmfully than expected. Additionally a new technique of artificial crack initiation by operating with a focused ion beam is used to investigate special crack problems such as the interaction of cracks with microstructural barriers in detail, which was not previously possible in this systematic way.
Residual stress development due to thermal cycling of the particle-reinforced alloy EN AW-6061– experiment and simulation
Authors: Heimann Sebastian , Pohl Michael , Klaska Arne M. , Beck Tilmann
Published: December 2013

The development of residual stresses and strains in the matrix material of the extruded aluminium alloy EN AW-6061-T6 both with no reinforcement and also reinforced with 15vol.% and 22vol.% α-alumina particles was investigated in thermal cycling tests and additionally by finite-element-simulation for the non-reinforced material. For this purpose cylindrical specimens were heated by a 3kW diode laser and cooled by a water quench. Residual stresses in the surface area of the laser beam and temperature distribution inside the specimen were measured. The results were used to validate the finite-element model for calculating stress and strain distributions inside the specimens.
Investigation and modelling of theplasticity-induced martensite formation in metastable austenites
Authors: Smaga Marek , Walther Frank , Eifler Dietmar
Published: December 2013

Mechanical stress–strain hysteresis, temperature and magnetic measurements were performed for the detailed characterisation of the cyclic deformation behaviour of metastable austenitic steels with particular attention to plasticity-induced martensite formation. Specimens of AISI 304, AISI 321 and AISI 348 stainless steels were investigated under plastic strain control at ambient temperature. On the basis of comprehensive experimental data, a model was developed for the description of the plasticity-induced martensite formation in metastable austenites under cyclic loading. The process of martensite formation was described as a function of the cumulative plastic strain and the cumulative strain energy density.
Strengthening of silicon nitride ceramics by shot peening
Authors: Pfeiffer Wulf , Gumbsch Peter
Published: December 2013

Shot peening is a common procedure for improving the static and cyclic strength of metal components by a combination of work hardening and the introduction of compressive stresses into the surface region. Recent investigations showed that high compressive stresses of more than 1 GPa can also be introduced in brittle ceramics such as alumina and silicon nitride under specific shot peening conditions. These stresses dramatically increase the near-surface strength. This paper compiles the current state of the art of shot peening for silicon nitride ceramics. Detailed information about the influence of shot peening on the residual stress state, dislocation density and damage are given. The effect of the residual stresses on the static and cyclic nearsurface strength is quantified.
Assessment of creep behaviour of the die-cast cylinder-head alloy AlSi6Cu4-T6
Authors: Dehler Anja , Knirsch Stefan , Srivastava Vivek , Saage Holger , Heilmaier Martin
Published: December 2013

Mechanical properties of a T6-AlSi6Cu4 cylinder-head alloy are investigated at 4 stress levels up to 545 K through tensile and compressive test to assess creep damage. The effect of over-ageing for 200 h at comparable temperatures was studied through RT hardness tests. Creep behaviour was characterised by a minimum creep rate and an extended steady state was not observed. No threshold stresses were apparent from minimum creep rate vs. stress plots at any of the temperatures studied here. Apparent stress exponents were both temperature and stress dependent and the apparent creep activation energy was 2–3 times the lattice selfdiffusion activation energy for aluminium. The Norton plot was best described by an exponential relation. The total strain to failure exhibited a maximum for a particular applied stress and decreases for both higher and lower applied stress. Creep life is well described by the Monkman– Grant relation at the highest temperature, but exhibits deviations from the idealised behaviour at the lower test temperatures.
New aspects of bending rotation fatigue in ultra-fine-grained pseudo-elastic NiTi wires
Authors: Wagner Martin Franz-Xaver , Eggeler Gunther
Published: December 2013

Bending rotation fatigue experiments are a standard evaluation procedure for pseudo-elastic NiTi wires used in the medical device industry. However, the non-linear mechanical behavior and the possible occurrence of localized deformation during bending complicate the physical interpretation of fatigue life data. In the present study, some related experimental and theoretical aspects are addressed: Optical measurements are used to characterize the local deformation of the wire specimens in a typical experimental setup, and a simple mechanical model of stresses and strains associated with bending rotation is employed to rationalize the impact of several experimental parameters on fatigue life data. Dissipated energies per cycle and unit length are calculated. How dissipation leads to an increase of both specimen temperature and maximum stresses and, therefore, considerably decreases fatigue lives is demonstrated.
Pressure solidification – a novel moulding technique for plastic parts with superior dimensional stability
Authors: Ehrenstein Gottfried W.
Published: December 2013

Sophisticated serial products require precise plastic parts that can be effectively manufactured employing the injection moulding process. However, the cooling of solid and molten material at the same time leads to high shrinkage, warpage and residual stresses. These processing characteristics determine the limits of dimensional stability that can be achieved with conventional injection moulding. A novel processing approach, in which the solidification is accomplished by pressure loading only, makes sure that these difficulties can be overcome. With this approach solidification takes place over the entire moulding at the same time. Investigations have been carried out into the viscosity, compressibility and thermal expansion of amorphous thermoplastics, which allowed evaluation of the physical pre-conditions for the novel moulding technique.
Stability of residual stresses in longitudinally and transversely deep rolled sintered iron under quasistatic and cyclic loading
Authors: Merkel Jens , Schulze Volker , Wanner Alexander , Löhe Detlef , Vöhringer Otmar
Published: December 2013

The residual stresses in flat coupons of sintered iron (ASC100.29) deep rolled on both surfaces were studied in the as-rolled condition and upon quasistatic or cyclic bending.

In the as-rolled condition, the stresses are compressive and exhibit a clear orientation dependence with respect to the rolling direction. Also, a significant difference between the primarily and finally deep rolled surfaces is observed, which can be attributed to the effects of specimen bending occurring during the deep rolling process.

The evolution of the residual stresses during fatigue is partly counter-intuitive: in transversely deep rolled specimens, an increase in compressive residual stresses in the transverse direction is observed within the very first loading cycle. Possible reasons for this unexpected effect are discussed.
Re-evaluation of phase equilibria in the Al–Mo system
Authors: Eumann Markus , Sauthoff Gerhard , Palm Martin
Published: December 2013

Phase equilibria and homogeneity ranges of the intermetallic phases in the Al–Mo system have been determined. The microstructures of samples of fixed composition and of diffusion couples were investigated by light-optical and scanning electron microscopy, the crystallographic structures and lattice constants were established by X-ray diffraction and the compositions of the phases were determined by electron probe microanalysis. In addition, transition temperatures were determined by differential thermal analysis. The homogeneity ranges of the Al-rich intermetallic phases are narrow, with about 0.1 to 0.4at.% widths. The phases and phase equilibria as established in previous studies have been confirmed with the exception of the phase Al3+x
Mo1–x
, which has not been detected. The congruent melting point of Al8Mo3 was found at 1546±3°C and the Al-rich phase boundary for AlMo3 has been determined between 800 and 1200°C.
EBSD and EDX analysis at the cladding–substrate interface of a laser clad railway wheel
Authors: Farooq Muhammad Umar , Klement Uta , Nolze Gert
Published: December 2013

Electron backscatter diffraction and energy-dispersive X-ray spectrometry were used to investigate the intermixed interface produced during laser cladding of a Co–Cr–Mo alloy on a steel substrate. A multi-component system and rapid solidification conditions together lead to a complex microstructure at the interface. The solidification of the cladding starts with the formation of an interface layer, which is about 75lm in thickness and consists of randomly oriented equiaxed grains of Co–Cr–Fe solid solution and martensite. Orientation analysis of the grains in the interface layer revealed that some grains have a special orientation relationship with the former austenite grains in the heat affected zone but the cladding is not formed by epitaxial growth on the substrate. Intermixing of the materials at the interface is providing a strong bond between the substrate and the cladding. For a grain from the interface layer to emerge as columnar grain in the cladding, it was determined that its <001> crystallographic direction is not supposed to deviate more than 25° from the sample normal direction.
Thermodynamic properties of liquid silver–indium–antimony alloys determined from e.m.f. measurements
Authors: Jendrzejczyk Dominika , Gierlotka Wojciech , Fitzner Krzysztof
Published: December 2013

The thermodynamic properties of liquid Ag–Sb–In alloys were determined using solid oxide galvanic cells with zirconia electrolyte. The following galvanic cells were employed:

(I)

Re
+
kanthal,

Ag
x

−

Sb

(

1
−
x
−
y

)

,

In
2

O
3

/
/

ZrO
2

+

(

Y
2

O
3

)

/
/
Ni
O
,
Ni
,

Pt

in the temperature range from 973 to 1200K.

Thermodynamic properties of the liquid phase were described by the Redlich–Kister–Muggianu formula and the phase relations in the ternary system were calculated. The results of the calculations were compared with experimental data available from different literature sources.
Microstructure of the “white layer” formed on nitrided Fe-7wt.% Cr alloys
Authors: Hosmani Santosh S. , Schacherl Ralf E. , Mittemeijer Eric J.
Published: December 2013

The formation of a compound, “white” layer on the surface of Fe-7wt.% Cr alloy, by exposure to a gas mixture of ammonia and hydrogen at 580°C, was investigated. The microstructure of the surface layer was analysed employing light and scanning electron microscopy, X-ray diffraction and electron probe microanalysis. For the first time a quantitative (phase) analysis of such a white layer was carried out, demonstrating the presence of a dispersed CrN phase within a γ| iron-nitride matrix.
The effect of ageing on tensile behaviour, mode I and mixed mode I/III fracture toughness of 7010 aluminium alloy
Authors: Eswar Raju K. S. S. , Mukhopadhyay Ashim K. , Kamat Samir V.
Published: December 2013

The effect of ageing on the tensile behaviour, mode I fracture toughness and mixed mode I/III fracture toughness of 7010 aluminium alloy plate was investigated. It was found that the 0.2% proof stress in this alloy increased from the under-aged temper to the peak-aged (T6) temper and then subsequently decreased in the over-aged (T73) temper. On the other hand, the ductility exhibited a monotonic decrease from the under-aged temper to the over-aged temper. The Ludwigson equation was found to best describe the flow behaviour in all the three ageing tempers. Under mode I as well as mixed mode I/III loading, the highest fracture toughness was seen in the under-aged temper, whereas the fracture toughness values in the peak-aged and over-aged tempers were comparable.
Plane bending fatigue behavior of interstitial-free steel at room temperature
Authors: Islam Mohammed Aminul , Tomota Yo
Published: December 2013

Interstitial-free steels are widely used as thin sheet for automobile external panels. For this type of application, essential properties of the steel are deep-drawability and stretch-formability. However, low-strength interstitial-free steel is nearly pure iron and work on fatigue fracture behavior of this steel might be adopted as a basic study to understand the behavior of high-strength steels used for structural components. In this study, the fatigue fracture behavior of low-strength interstitial-free steel has been studied at room temperature in air and in an argon atmosphere. Fractographic observations on fatigue fracture surfaces reveal a mixed type of fracture mode (intergranular and transgranular cracking) for all specimens. The major portion of intergranular fracture has been found at the regions of low and medium crack lengths. Further increase in the crack length causes a decrease in the proportion of intergranular cracking and, finally, the fracture mode becomes completely transgranular. At the same test temperature, the proportion of intergranular fracture drastically decreased when the test was carried out in the argon atmosphere.
Influence of process parameters on particle characteristics using a combined pressure-swirl-gas atomizer
Authors: Achelis Lydia , Uhlenwinkel Volker , Bauckhage Klaus
Published: December 2013

This paper summarizes the latest results in the development of a combined pressure-swirl-gas atomizer. The main goals of this investigation are to characterize the generated metal powders in terms of spray pattern and particle size distribution. With the combined pressure-swirl-gas atomizer it is possible to create 150kgh−1 of tin powder with mass medians between 30 and 110lm (tin alloys) and geometric standard deviations below 1.9 with a nitrogen consumption of 100kgh−1. Gas flow and melt mass flow can be varied independently of each other, while their characteristic ratio of mass flows can be held below 0.7, which opens new potential for low gas consumption in gas atomization. The experiments were conducted with water and tin melts as model fluids. The comparison of the dimensionless numbers shows that the model experiments are comparable and basically extendable to other melts as long as the material characteristics allow this.
Synthesis and oxidation of Zr3Al3C5 powders
Authors: He L. F. , Zhou Y. C. , Bao Y. W. , Wang J. Y. , Li M. S.
Published: December 2013

Predominantly single phase Zr3Al3C5 powders were synthesized in an Ar atmosphere using Zr – Al intermetallics and graphite as starting materials. The reaction path of Zr3Al3C5 synthesis was discussed based on differential scanning calorimetry and X-ray diffraction results. Lattice parameters of Zr3Al3C5 determined using the Rietveld method are a = 3.347 Å and c = 27.642 Å. In addition, the oxidation of Zr3Al3C5 powders was tested by using thermogravimetry – differential scanning calorimetry. The starting and complete oxidation temperatures are 400 °C and 1200 °C, respectively. These temperatures are much higher than those for ZrC, suggesting that Zr3Al3C5 has better oxidation resistance than ZrC. On the other hand, the oxidation degree of Zr3Al3C5, defined for the complete carbide – oxide transformation, overshot 100 % during oxidation. This overshooting is attributed to the formation of amorphous carbon. The phase evolution during the oxidation of Zr3Al3C5 was also investigated.
Infrared spectroscopy and X-ray diffraction data of In – Se compounds
Authors: Vassilev Gueorgui P.
Published: December 2013

The aim of the present work is to contribute to the identification of indium – selenium phases. Infrared absorption spectra were obtained from some indium – selenium compounds (In4Se3, InSe, In6Se7, α-In2Se3). X-ray diffractograms of the recently found phase In9Se11 and of InSe are also reported. Both kinds of data can be used for identification of the respective compounds.

It is confirmed that α-In2Se3 is stable at room temperature. The stability of the hexagonal InSe modification is also proved and its lattice parameters are recalculated.
Formation of δ-Al2O3 hollow nanoparticles via a chemical vapor condensation process
Authors: Lee Chang-Woo , Lee Jai-Sung
Published: December 2013

Aluminium oxide nanoparticles were synthesized by a chemical vapor condensation process using aluminium acetylacetonate as a precursor in the temperature range of 700 – 1000 °C. From X-ray diffraction results, it was found that the δ-Al2O3 phase was obtained at 900 °C and 1000 °C. Transmission electron microscopy observation revealed that δ-Al2O3 nanoparticles 10 – 15 nm in diameter consisted of a hollow structure with shells 2 – 3 nm in thickness. The sequential decomposition of acetylacetonate groups observed in thermogravimetry analysis showed that the formation of a hollow structure depends on the characteristics of the metal – organic precursor. Also, a decrease in the transmittance of δ-Al2O3 nanoparticles was found in the wavelength range of 300 – 900 nm by UV-Visible spectrophotometry, which is expected to occur by scattering and absorption of light depending on particle size and hollow structure.
Thermomechanical processing of AA6061 billets for semi-solid forming
Authors: Birol Yucel
Published: December 2013

Extruded bars of AA6061 alloy were heat treated above the solidus temperature to produce wrought aluminium feedstock for thixoforming. The extruded material recrystallized during heating to the semi-solid state, producing nearly equiaxed polygonal grains with high-angle boundaries. Melting started at triple junctions during subsequent isothermal heating and progressed along grain boundaries. The low melting point eutectic phase and the high-angle grain boundaries introduced by recrystallization both promoted the grain boundary melting process. The desired feedstock characteristics, comprising complete grain boundary wetting, a perfectly cylindrical slug shape and an average grain size below 100 microns were obtained after 5 min at 640 °C and 635 °C for extrusion ratios of 14: 1 and 5: 1, respectively.
Cyclic deformation behaviour and lifetime calculation of the magnesium die-cast alloys AZ91D, MRI 153M and MRI 230D
Authors: Ebel-Wolf Barbara , Walther Frank , Eifler Dietmar
Published: December 2013

The magnesium alloys AZ91D, MRI 153M and MRI 230D were investigated in the form of die-cast specimens with a cast-skin. The fine-grained microstructure consists of a dendritic magnesium solid solution and interdentritic precipitates. The cyclic deformation behaviour was characterised in stress-controlled load increase and single step tests by means of mechanical stress – strain hysteresis and temperature measurements. Load increase tests allow a reliable short-time estimation of the endurance limit. With the physically based lifetime calculation method “PHYBAL”, the lifetime of the magnesium alloys can be precisely calculated on the basis of the plastic strain amplitude and the change of the specimen temperature due to cyclic plastic deformation with three experiments. Lifetimes calculated according to “PHYBAL” agree excellently with experimentally determined data.
Identification of liquid/solid transformations in eutectic Pb–Sn alloy
Authors: Brunčko M. , Kneissl A. C. , Kosec B. , Lojen G. , Anžel I.
Published: December 2013

In this paper the applicability and the efficiency of in-situ electrical resistance measurements with a four-probe method for monitoring the solidification process are presented. For this purpose a special measurement cell was developed. It enables simultaneous in-situ electrical resistance and temperature measurements during solidification to characterize the L → S phase transformation of metals and alloys. The method was experimentally demonstrated with a eutectic Pb – Sn (i. e. Pb-61.9 wt.% Sn) alloy. Additionally, the L → S phase transformation was monitored and compared with conventional differential thermoanalysis. The results of our investigation show that the simultaneous in-situ electrical resistance and temperature measurement method is able to determine the exact position of the start and end points of the L → S phase transformations from the resistance curves R(t) and the corresponding temperatures.
Comparison of the plastic strain distribution during equal-channel angular pressing (ECAP) using 2D and 3D FEM modeling
Authors: Zhernakov V. S. , Budilov I. N. , Alexandrov I. V. , Beyerlein I. J.
Published: December 2013

The plastic flow of a copper billet calculated using 2D and 3D finite element modeling are compared during a single extrusion of equal-channel angular pressing. Both models predict deformation heterogeneity irrespective of material behavior, die geometry and friction conditions. On the symmetry plane where the numerical approaches can be compared, their strain distributions differ, especially as the processing conditions deviate from the ideal conditions. Overall the three-dimensional finite element model calculates lower plastic strains than the two-dimensional model.
Fabrication of high strength nanostructured aluminium alloys by hydrostatic extrusion
Authors: Lewandowska Małgorzata , Pachla Wacław , Kurzydłowski Krzysztof J.
Published: December 2013

In the present work, the possibility of obtaining high strength nanostructured aluminium alloys by hydrostatic extrusion has been shown. Billets of 2017 aluminium alloy were subjected to hydrostatic extrusion either immediately after water quenching or after subsequent ageing. The results have shown that processing by hydrostatic extrusion offers a possibility of grain refinement down to the nanometre scale in the age-hardenable aluminium alloy. However, the effectiveness of the process depends on its initial microstructure. The most promising results are obtained if the alloy is deformed in the as-quenched condition. The hydrostatically extruded aluminium alloy exhibits very high tensile strength with reasonable ductility. The stability of mechanical properties over a wide range of temperatures (from cryogenic to well above the ambient) is discussed. The results obtained are compared to similar 2XXX aluminium alloys processed by other severe plastic deformation methods.
Effect of V2O5 doping on the microstructure and local composition of textured Sr0.4Ba0.6Nb2O6 ceramics
Authors: Wang Xian-Hao , Gu Hui , Huang Qing-Wei , You Li-Ping
Published: December 2013

A comparison of phases and the microstructures of textured Sr0.4Ba0.6Nb2O6 ceramics without and with V2O5 addition was carried out using transmission and analytical electron microscopy. The dopant was not found in Sr0.4Ba0.6Nb2O6 grains but in the inter-granular regions, including both grain boundary and second phase. Grain boundaries in the sample without V2O5 are clean, but those in the V2O5-doped sample exhibit a variety of structures, with and without an amorphous film of variable thickness. In general the vanadium excess follows the same trend of film width, while the Sr excess is generally negative and the Ba excess is positive, suggesting that the amorphous films at grain boundaries are rich in V and Ba and deficient in Nb and Sr. The second phase was determined as Ba3V4O13 phase containing small amounts of Sr and Nb. Such V- and Ba-rich inter-granular liquids promoted the densification and texturing, and affected the dielectric constant at low frequency but not the Curie temperature.
Development of SMD 32.768 kHz tuning fork type crystals
Authors: Lee Sungkyu , Moon Yangho , Seo Won-Seon , Ahn Jae-Hwan , Chung Hyungsik
Published: December 2013

Taguchi's design of experiment method and statistical F-test were used to further optimize design parameters for as-fabricated resonance frequency of tuning forks for use in Qualcomm® mobile station modem (MSM)-3000TM series central processing unit chips of code division multiple access, personal communication system, and global system for mobile communication systems. After much trial and error, finite element method modeling and Taguchi's design of experiment method enabled selection of essential design parameters to effectively manufacture tuning fork test samples using photolithography with subsequent photoresist spray coating. As-fabricated resonance frequency values of a tuning fork blank thus manufactured remain almost the same prior to final frequency adjustment of the mounted crystals, regardless of pressure change from ambient to the designated packaging pressure of 6 × 10−5 Torr. The tuning fork test samples thus fabricated were characterized and analyzed using Taguchi's design of experiment method and statistical F-test to evaluate the sensitivity of as-fabricated resonance frequency for various design parameters fror ambient to the designated packaging pressure of 6 × 10−5 Torr. As-fabricated resonance frequency is most sensitive to tine width (x) and variance analysis results showed that only x and y (tine length) are significant design parameters and no design parameter significantly affects the as-fabricated resonance frequency change with the vacuum level of the package: the as-fabricated resonance frequency change with vacuum level turned out to be independent of design parameter contributions.
Fatigue strength and fracture behavior of steels with and without interstitial carbon at room temperature in air
Authors: Islam Mohammed Aminul , Tomota Yo
Published: December 2013

In this study, fatigue performance and fracture behavior of interstitial-free, low carbon and phosphorus-added low carbon steels have been investigated by plane bending fatigue tests at room temperature in air. For all steels, fatigue tests were carried out at a frequency of 1000 cycles per minute, however, a limited number of specimens of low carbon steel were also tested at frequencies of 500 and 1500 cycles per minute. After all mechanical tests, fracture surfaces were cut and examined using scanning electron microscopy to identify the fracture features. At any applied stress level, low carbon steel showed better fatigue performance than interstitial-free steel, and phosphorus addition further improved the fatigue life of low carbon steel. Fractographic observations on fatigue fracture surfaces revealed transgranular fracture for low carbon steel and intergranular fracture for interstitial-free steel. Interestingly, addition of 0.12 wt.% of phosphorus in low carbon steel could not change the dominant transgranular fracture behavior of the steel.
Grain refinement response during twist extrusion of an Al-0.13% Mg alloy
Authors: Berta Marco , Orlov Dmitry , Prangnell Philip B.
Published: December 2013

Twist extrusion is a recently developed method of severe plastic deformation that principally uses torsion to generate high strains in a repeatedly extruded billet, while maintaining a constant cross-section. The method thus results in a deformation gradient across the billet section. To date, the grain refinement behaviour of alloys deformed by twist extrusion have only been investigated qualitatively. In this study high resolution electron backscattered diffraction has been used to quantify the deformation structures produced by twist extrusion, in a model, single-phase, Al-0.13 % Mg alloy, with the aim of investigating the potential of the technique for producing ultra-fine grained metals, as well as the homogeneity of the microstructure and strain distribution in processed billets.
The effect of grain size on strain rate sensitivity and activation volume – from nano to ufg nickel
Authors: Vehoff Horst , Lemaire Delphine , Schüler Kerstin , Waschkies Thomas , Yang Bo
Published: December 2013

The strain rate sensitivity of nanocrystalline nickel was studied at different temperatures in tensile tests and with a nanoindenter in order to examine the effect of grain size on the different deformation mechanisms of nanocrystalline materials. The experiments yielded, depending on temperature and strain rate, the strain rate sensitivity, the activation volume and the creep exponents as a function of stress and grain size. From the creep experiments the transition between grain boundary sliding and dislocation climb as a function of temperature was obtained. The strain rate jump tests gave extremely small activation volumes, nearly a factor of 100 smaller than in conventional nickel as a function of grain size. To help in understanding this behaviour the strain rate sensitivity of single grains was tested with a nanoindenter. The results clearly showed that the primary interaction of dislocations with grain boundaries is the reason for the strong rate effects and small activation volumes observed.
Deformation behaviour, microstructure and processing of accumulative roll bonded aluminium alloy AA6016
Authors: Topic Irena , Höppel Heinz Werner , Göken Mathias
Published: December 2013

The technologically relevant aluminium alloy AA6016 was successfully processed using accumulative roll bonding to 8 cycles (∊von Mises = 6.4) in order to obtain an ultrafine-grained microstructure with an average grain size of approximately 200 nm. With the aim of optimising the accumulative roll bonding process detailed investigations on the robustness, the type of rolling mill, the influence of temperature, the microstructural evolution and the mechanical properties have been carried out. Processing at 230 °C provided a good compromise between thermal stability and interlamellar bonding. Samples strained up to 6 cycles (∊von Mises = 4.8) showed an increase in the yield strength by a factor of 3 in comparison to the as-received material. The ductility of the roll bonded samples was slightly sacrificed, although an increase in ductility can be achieved by increasing the number of accumulative roll bonding cycles. The mechanical properties depend on the strain rate, as has also been found for many other ultrafine-grained materials. Annealing of ultrafine-grained samples revealed a stability limit of approximately 200 °C.
Ultrafine-grained materials: a personal perspective
Authors: Langdon Terence G.
Published: December 2013

The Chinese philosopher Lao Tzu wrote that “a journey of a thousand li begins with a single step”.† My first step on the road to ultrafine-grained materials occurred on 5 May, 1989, when I boarded a plane in Los Angeles on the way to Ufa via Copenhagen and Moscow. This review provides a very brief summary of the historical development of ultrafine-grained materials and my personal journey through this important area of materials research.
Getting accurate nanoindentation data from time-dependent and microstructural effects of zinc
Authors: Tohid Reza R. , Bull Steve J.
Published: December 2013

The main objective of this study was obtaining accurate data from nanoindentation experiments on zinc. Nanoindentation experiments can be performed under displacement control, load control, or open loop conditions at different loading/unloading rates. All the above control schemes and range of loading rates were used to test pure zinc samples with different surface preparation using a Hysitron Triboindenter fitted with a blunt Berkovich indenter. The results showed that displacement control with a high loading/unloading rate gave the most reliable results. However, because of the anisotropy of zinc and its large grain size the material should be considered as a single crystal on the scale of the impression generated. It has been found that using the feedback control of nanoindentation experiments can give a significant improvement in the results compared to open loop control due to the time-dependent behaviour of zinc. A full factorial design of experiments approach was performed to investigate the optimum combination of the feedback parameters to obtain accurate and reliable data for the hardness and Young's modulus of zinc.
Nanomechanical characterization of relaxation processes in As–S chalcogenide glasses
Authors: Trunov Michael , Nagy Peter M. , Dub Sergey , Kalman Erika
Published: December 2013

Nanoscale mechanical properties of As – S binary chalcogenide glasses for bulk and thin-film samples have been studied, using the nanoindentation technique for a step loading procedure. All components of glass deformation (plastic, elastic. and visco-elastic, or retarded) have been evaluated during the nanoindentation process. An essential redistribution of these components was observed during unloading depending on the composition of the glasses. The same nanoindentation procedure was applied to bulk, as-deposited and annealed thin-film samples of the glasses. Plots of deformation components vs. As concentration (or average covalent coordination number ) show a minimum around the As25S75 – As30S70 composition ( ≈ 2.30), which corresponds to the rigidity percolation composition, i. e., the transition from the floppy phase to the intermediate one.
Nanomechanical studies of ultrathin polymeric resist films
Authors: Koszewski Adam , Gorski Tomasz , Reuther Freimut , Rymuza Zygmunt
Published: December 2013

An atomic force microscope with a specially constructed stiff cantilever was used to study the mechanical properties of ultrathin polymeric resist films devoted to use in nanoimprint lithography. The methodology, the equipment used in these studies and the results of the estimation of the Young's modulus versus temperature are presented and discussed.
Area function calibration in nanoindentation using the hardness instead of Young's modulus of fused silica as a reference value
Authors: Schiffmann Kirsten Ingolf
Published: December 2013

For nanoindentation hardness and Young's modulus measurements the area function of the indenter has to be calibrated carefully since direct measurement of the contact area is not possible. Most often this is done by making a series of indentations into a material with known Young's modulus, e. g. fused silica. In this paper it will be shown that this method may lead to significant deviations in hardness values found over the lifetime of the indenter due to successive rounding of the tip. Additionally, depth-dependent hardness values may apparently be found which would falsify all hardness determinations. Using instead the hardness of fused silica as a reference value these problems will be avoided. Additionally, the calibration becomes independent of material constants such as the Young's modulus of the diamond tip and the Poisson ratios of both indenter and sample, which enter into the conventional calibration method.

Finally, this paper discusses whether the indentation modulus determined by nanoindentation and the Young's modulus determined by, for example, tensile testing, are quantitatively equal. This is a precondition for the traceability of the Young's modulus method often mentioned as its main advantage.
Unusual architecture of the exceedingly tough Macadamia “nut”-shell as revealed by atomic force microscopy and nanomechanics
Authors: Naimi-Jamal M. R. , Kaupp G.
Published: December 2013

Unlike previous assumptions, the 3D microscopic construction of the macadamia wooden shell (a model for bionics' design) is far from being “isotropic”. The consequences for the exceedingly high toughness towards cracking are investigated by atomic force microscopy to evaluate the vertical stiffeners in a fullerene-type surface architecture of the only 160 μm thick hardshell that is known to withstand up to 2000 N compressive load. Nanoindentations provide hardness and elasticity modulus at stiffeners and more compliant polygon material, as well as differences of indentation coefficients and work of indentation. Nanoscratching provides scratch coefficients and specific full scratch work values that can be compared with varied other materials using interpolations with linear relations between nanomechanical parameters. A particular lotus-type effect is found for the macadamia hardshell surface.
On the precipitation processes in commercial QE22 magnesium alloy
Authors: Lambri Osvaldo Agustin , Cuello Gabriel Julio , Riehemann Werner , Lucioni Jose´
Published: December 2013

Electrical resistivity measurements, differential thermal analysis, mechanical spectroscopy and small angle neutron scattering studies have been performed on commercial QE22 magnesium alloy. The aim of this work is to resolve the appearance of Guinier – Preston zones and also to survey the small angle neutron scattering technique for various temperatures in this alloy. The coupling of all the employed experimental techniques in this work is crucial for detecting the precipitation of the Guinier – Preston zones. This is due to the strong changes in the microstructure produced by the main precipitation process, which starts at about 440 K and ends at about 640 K. We found that the temperature at which Guinier – Preston zones start to grow is about 473 K and that the dissolution temperature is 537 K.
Thermal diffusivity measurements of some industrially important alloys by a laser flash method
Authors: Abas R. Abdul , Hayashi M. , Seetharaman S.
Published: December 2013

In the present work, thermal diffusivity measurements of three industrially significant alloys, viz. 90Ti.6Al.4V, stainless steel with 25Cr and 6Ni as well as plain carbon steel with 0.7 % carbon have been carried out as a function of temperature. The aim of this work is to study the effect of temperature and microstructure on the thermal diffusivities of these alloys. For the 90Ti.6Al.4V alloy, thermal diffusivity increases with temperature below 1225 K. Above this temperature, the values started decreasing probably due to the dissolution of Ti3Al intermediate phase in the matrix, which would result in an increase in the disorder of the structure. For 25Cr: 6Ni stainless steel, the thermal diffusivity is nearly constant up to about 700 K. Above this, there is an increase in the thermal diffusivities with temperature during the heating cycle, which was reproducible during thermal cycling. On the other hand, the slope of the curve increases above 950 K.

In the case of the 0.7 % carbon steel, the thermal diffusivity shows a decreasing trend with temperature below the Curie point for the alloy, where the alloy consists of bcc + fcc phases. Above this point, only the fcc phase is prevalent and the thermal diffusivity was found to increase with temperature. Heat transfer is carried out by lattice vibration (phonons) as well as electrons. The contribution of electrons varies depending upon the type of alloy. In this study, the highest electron contribution was found in 0.7 % carbon steel, while the lowest was in stainless steel. The thermal conductivity values of these alloys are in good agreement with the calculated values using the model proposed by Mills.
Modelling of the β → α + β transformation in a metastable β Ti alloy based on the growth kinetics and the morphology of the α plates
Authors: van Bohemen Stefan M. C. , Laars Menno van der , Sietsma Jilt , Zwaag Sybrand van der
Published: December 2013

The kinetics of the isothermal β → α + β transformation in a metastable β titanium alloy has been studied by dilatometry. Based on thermodynamic aspects, the volume diffusion of Mo in the titanium matrix ahead of the interface, the interface mobility, and the morphology of the primary α plates, a transformation model is developed, which incorporates mixed-mode behaviour of the transformation in the initial stage. Fraction curves are calculated based on the simulated growth of a typical α plate within the β phase having a volume determined from the nucleus density. For comparison, fraction curves are calculated using a three-dimensional model of the β grain in which a number of plates are simulated to grow with purely diffusion-controlled kinetics. It is shown that the calculated growth rate with the mixed-mode transformation model gives a better representation of the growth rate at the start of the transformation than the purely diffusion-controlled model.
Assessment of creep rupture life of weldments of martensitic steels
Authors: Roos Eberhard , Maile Karl , Klenk Andreas , Bauer Mathias
Published: December 2013

Martensitic steels are of major importance for modern high efficient power plants. Their long-term creep rupture characteristics are essential for the economic and reliable design of high temperature components. However, the weldments in such components have to be considered as a potential failure area under long-term creep loading as the heat affected zone of ferritic creep resistant materials (for example new martensitic steels) is exposed to significant microstructural changes due to the heat input during welding. Furthermore, the stress situation and multiaxiality of the stress state in the weld region changes permanently due to creep and relaxation. Evaluation therefore has to be based on experimental investigation that means uniaxial creep tests of crossweld creep specimens. The microstructrural characterisation of the heat affected zone and the comparison with the situation in the optimised base material has also to be taken into account. Heat affected zone simulation of specimens and the relevant experimental investigation deliver an important basis for the modelling of the stress – strain situation. All these aspects have to be combined in the inelastic computation in order to consider all relevant effects: the individual creep strength in the different regions of the heat affected zone as well as the influence of the subsequent state of stress multiaxiality.

The paper highlights recent and on-going research activities in Germany in this domain. It also demonstrates the importance of inelastic calculation for the design of welded pipes.
Characterization of amorphous Nb oxide and its influence on Mg hydrogen sorption
Authors: Brum Mariana C. , da Conceição Monique O. T. , Guimarães Claudinei S. , dos Santos Dilson S. , Dias Marcos L.
Published: December 2013

Amorphous Nb2O5 was synthesized by combining niobium ethoxide with an amine surfactant. The material turned out to have a high surface area, 287 m2 g−1, and a homogeneous structure. The material was shown to be amorphous despite the heat treatment performed within a range of 150 to 550°C. The surface area of Nb2O5 reduced to 105 m2 g−1 after heat treating at 350°C. The activation energy of the Nb2O5 crystallization reaction was found to be 327 kJ mol−1. The surface area of Nb2O5 reduced significantly with heat treatment but it still improved the hydrogen kinetics since the desorption rate was 1.5 wt.% min−1. The addition of a small amount of amorphous Nb2O5 to magnesium hydride, throughout milling, helped overcoming limitations inherent to solid hydrogen storage.
Metallographische Untersuchungen an Verbundstrukturen aus Aluminiumschaum mit thermisch aufgespritzten Schichten
Authors: Maurer Matthias , Koch Dieter , Zhao Lidong , Lugscheider Erich
Published: December 2013

Kurzfassung

Aluminiumschäume stehen an der Schwelle industrieller Anwendungen. Viele neue Einsatzgebiete können für diese neuen Werkstoffe gefunden werden, wenn sich eine definierte, verschleiß- und korrosionsbeständige Oberfläche einstellen lässt. Dies ist sehr gut mit den Verfahren des thermischen Spritzens möglich. Die metallographische Beurteilung dieser Verbunde ist sehr anspruchsvoll, da die teils sehr harten Schichten gänzlich andere Eigenschaften aufweisen als der sehr weiche und großporige Aluminiumschaum. Im folgenden Artikel werden die Aluminiumschäume sowie die zur Veredelung verwendete Spritztechnik kurz vorgestellt; den Schwerpunkt bilden eine angepasste metallographische Präparation sowie Probleme, die hierbei auftreten können.
Einfluss von Lüdersbändern auf die Schwingfestigkeit von Proben unterschiedlicher Geometrie aus einem normalgeglühten Stahl Cm15
Authors: Laue Sascha , Bomas Hubert , Mayr Peter
Published: December 2013

Kurzfassung

Bei der Verformung normalgeglühter Stähle treten bei Überschreitung der Streckgrenze Lüdersbänder auf, deren Ausprägung in starkem Maße von der verwendeten Probengeometrie abhängig ist. Mit der Entstehung und Ausbreitung geht eine starke Veränderung der Oberflächentopografie einher, die eine bei Umformprozessen meist unerwünschte Oberflächenstruktur hervorruft. Auch bei zyklischer Beanspruchung kann es zur Bildung und Ausbreitung von sogenannten Ermüdungslüdersbändern kommen, die eine Veränderung des Oberflächenzustands bewirken und somit die Schwingfestigkeit beeinflussen. Dieser Beitrag zeigt auf, wie sich unterschiedliche Probengeometrien aus einem normalgeglühten Stahl Cm15 bei einsinniger Verformung verhalten und welche Konsequenzen sich aus diesem Materialverhalten für eine zyklische Beanspruchung ergeben.