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An Al-12Si/Al-3.5Cu-1.5Mg-1Si bimetal with a good interface was successfully produced by selective laser melting (SLM). The SLM bimetal exhibits four successive zones along the building direction: an Al-12Si zone, an interfacial zone, a texture-strengthening zone and an Al-Cu-Mg-Si zone. The interfacial zone ( fiber texture. Electron backscatter diffraction analysis shows that the grains grow gradually from the interfacial zone to the Al-Cu-Mg-Si zone along the building direction. Additionally, a strong fiber texture develops at the Al-Cu-Mg-Si side of the interfacial zone and disappears gradually along the building direction. The bimetal exhibits a room temperature yield strength of 267 ± 10 MPa and an ultimate tensile strength of 369 ± 15 MPa with elongation of 2.6% ± 0.1%, revealing the potential of selective laser melting in manufacturing dissimilar materials.

Bulk Metallic Glasses (BMG) show extraordinarily high values of strength and elastic strain. Despite the, in most cases, macroscopically brittle behaviour (especially in tension and bending), extremely high fracture toughness values are reported. Even though it is sometimes stated that huge plastic zones and strain softening make K-based approaches (ASTM E399) or J-integral based approaches (ASTM E1820) difficult for BMG, changes in material behaviour or intrinsic metallic glass materials properties are still inferred by many authors in order to explain the results. In addition, the limited dimensions of fully glassy bulk ingots mean that the available specimen sizes differ from those required by the common standards of fracture toughness testing. In this context, reported results from fracture toughness of prominent Pd-, Pt- and Zr-based BMG are analysed. An in-depth discussion of the size dependent effects on the mechanical loading conditions during fracture toughness testing is provided. As a result, it is shown that the differences and peculiarities of characterized BMG toughness mainly relate to geometrical/mechanical effects of small scale sample testing. They are not due to an intrinsic material property or to a size dependent ramification of intrinsic material behaviour.

The present paper addresses the phenomena of hot cracking of nickel-based superalloys in the perspective of hybrid Laser Metal Deposition (combined application of induction and laser). This includes an extract of relevant theoretical considerations and the deduction of the tailored approach which interlinks material–scientific aspects with state-of-the-art manufacturing engineering. The experimental part reflects the entire process chain covering the manufacturing strategy, important process parameters, the profound analysis of the used materials, the gradual process development, and the corresponding hybrid manufacture of parts. Furthermore, hot isostatic pressing and thermal treatment are addressed as well as tensile testing at elevated temperatures. Further investigations include X-ray CT measurements, electron backscattered diffraction (EBSD), and scanning electron microscopy (SEM) as well as light optical microscope evaluation. The fundamental results prove the reliable processibility of the high-performance alloys Mar-M-247 and Alloy 247 LC and describe in detail the process inherent microstructure. This includes the grain size and orientation as well as the investigation of size, shape, and distribution of the γ′ precipitates and carbides. Based on these findings, the manufacturing of more complex demonstrator parts with representative dimensions is addressed as well. This includes the selection of a typical application, the transfer of the strategy, as well as the proof of concept.

Austenitic Fe-Mn-C-based alloys are considered as promising candidates for biodegradable vascular implants due to their high strength, ductility and mechanical integrity during degradation.The present study demonstrates that microalloying with S and B is an effective method to further enhance the degradation rate and the mechanical properties of a Fe-30Mn-1C twinning-induced plasticity (TWIP) alloy without deteriorating the biocompatibility. For studying the microstructural changes due to S or B addition, the alloys were analysed by X-ray diffraction (XRD) as well as scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDX), wavelength dispersive X-ray analysis (WDX) and electron backscatter diffraction (EBSD). Thereby precipitates of (Fe0.3Mn0.7)S and (Fe,Mn)23(C3B3) types were detected in the austenitic matrix. These precipitates have a distinct influence not only on the mechanical properties under tensile load but also on the occurring corrosion mechanism. This was displayed by potentiodynamic polarization measurements and immersion tests in simulated body fluid (SBF) and associated SEM as well as X-ray photoelectron spectroscopy (XPS) investigations. In vitro cytotoxicity analyses with L929 fibroblast cells indicated that microalloying with S and B does not affect the cytocompatibility.Thus, the novel alloy modifications show a high potential for future application as biodegradable implant material. Keywords: Fe-based alloy, Biodegradable, Microstructure, Mechanical properties, Corrosion behaviour, Cytocompatibility

Ti and Ti-TiB composite materials were produced by selective laser melting (SLM). Ti showed an α΄ microstructure, whereas the Ti-TiB composite revealed a distribution of needle-like TiB particles across an α-Ti matrix. Hardness (H) and reduced elastic modulus (Er) were investigated by nanoindentation using loads of 2, 5 and 10 mN. The results showed higher H and Er values for the Ti-TiB than Ti due to the hardening and stiffening effects of the TiB reinforcements. On increasing the nanoindentation load, H and Er were decreased. Comparison of the nanoindentation results with those derived from conventional hardness and compression tests indicated that 5 mN is the most suitable nanoindentation load to assess the elastic modulus and hardness properties. The wear resistance of the samples was related to their corresponding H/Er and H3/Er2 ratios obtained by nanoindentation. These investigations showed that there is a high degree of consistency between the characterization using nanoindentation and the wear evaluation from conventional wear tests. © 2017 Elsevier B.V.

Rolled-up nanotechnology has received significant attention to self-assemble planar nanomembranes into 3D micro and nanotubular architectures. These tubular structures have been well recognized as novel building blocks in a variety of applications ranging from microelectronics and nanophotonics to microbatteries and microrobotics. However, fabrication of multiwinding microtubes with precise control over the winding interfaces, which is crucial for many complex applications, is not easy to achieve by existing materials and technologies. Here, a dry rolling approach is introduced to tackle this challenge and create tight windings in compact and highly symmetric cylindrical microstructures. This technique exploits hydrophobicity of fluorocarbon polymers and the thermal expansion mismatch of polymers and inorganic films upon thermal treatment. Quality parameters for rolled-up microtubes, against which different fabrication technologies can be benchmarked are defined. The technique offers to fabricate long freestanding multiwinding microtubes as well as hierarchical architectures incorporating rolled-up wrinkled nanomembranes. This work presents an important step forward toward the fabrication of more complex but well-controlled microtubes for advanced high-quality device architectures. �� 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Deformation mechanism of a new Ti-16.6Nb-6Co-5.1Cu-6.5Al (at%) alloy is studied using scanning and transmission electron microscopy. The alloy consists of micrometer-sized β-Ti dendrites and an ultrafine-eutectic composed of β-Ti and TiCo phases. The yield strength of the alloy (1.1 GPa) is comparable to that of the metallic glass composites and is coupled with large tensile ductility of about 11%. Transmission electron microscopy analysis reveals that slip lines formed during deformation in the dendrites penetrates the eutectic resulting in formation of a stepped interface and an extra area serving to accommodate shear strains. The β-Ti eutectic component can deform plastically to a high degree supporting deformation of TiCo. The results suggest that microstructural design of the eutectic is important for controlling tensile ductility of dendritic-ultrafine eutectic alloys.

Due to their broad range of properties and excellent processability, Fe-based alloys are considered as potential biodegradable implant materials. In this study, Fe-30Mn-1C and novel microalloyed Fe-30Mn-1C-0.025S were prepared under fast solidification conditions leading to a fine grained austenitic matrix phase. Microalloying with S results in the formation of fine MnS precipitates, which was proven by electron backscatter diffraction. These precipitates cause a significantly increased yield and ultimate strength, also compared to clinical applied 316L, and a change in the initial corrosion mechanisms leading to an enhanced corrosion rate in simulated body fluid (SBF), which was assessed by electrochemical polarization tests.

This paper presents results about the influence of the selective laser melting (SLM) process parameters on a FeCr4Mo1V1W8C1 (wt%) alloy regarding microstructure and mechanical behavior. Tailored parameter variation studies were performed to obtain crack-free and highly dense SLM parts. The microstructure was studied using scanning electron microscopy, X-ray diffraction, Auger electron spectroscopy, and scanning transmission electron microscopy. Additionally, the mechanical properties were investigated by compression and tensile tests. The obtained microstructure is composed of complex nanoscale carbides, retained austenite, and martensite. Caused by the fast directional cooling during SLM, a completely dendritic solidification aligned in building direction occurs. Non-equilibrium segregation leads to an orderly phase arrangement of complex carbides at the boundary of the dendrites surrounded by retained austenite and martensite in the center of the dendrites. A strong work hardening behavior was observed, based on an austenite-to-martensite phase transformation (TRIP effect). This effect accounts for the outstanding mechanical properties such as compression strength of 6000 MPa, a 0.2% tensile yield strength of 560 MPa, and an ultimate tensile strength of over 1000 MPa. These findings reveal that SLM is advantageous for the processing of ultra-high-strength FeCrMoVWC tool steel.

This work presents an investigation on the influence of rare earth additions (Ce) on the microstructure and mechanical properties of a cast Fe85Cr4Mo8V2C1 (element contents in wt%) tool steel. The applied relatively high solidification rate during the casting process promotes the formation of non-equilibrium phases such as martensite, retained austenite as well as a fine network-like structure of complex carbides. This combination of phases and their morphology results in excellent mechanical properties already in the as-cast state. Cerium additions induce a change in phase formation and resulting mechanical properties. Besides morphological and quantitative changes of the main constituent phases, novel carbo-oxide and carbide phases are formed. To investigate this microstructural phenomenon, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDX) were applied. Altogether, the addition of small amounts of the rare earth element cerium together with a tailored casting process results in enhanced mechanical properties compared to the Fe85Cr4Mo8V2C1 alloy and offers new possibilities to obtain high-strength and simultaneously adequate ductile cast steels for advanced tool design.

In the present work, the wetting behaviour of the Cu–GaX (X = 10–30 wt.%) liquid alloys on 304L steel was investigated in vacuum at temperatures between 1123 and 1373 K. Contact angle and surface tension measurements were performed using the sessile drop setup. In general, the Cu–GaX (X = 10–30 wt.%) alloys show good or even excellent wetting on 304L steel. However, the wetting mechanism strongly depends on the Ga content. While for Ga-poor alloys secondary wetting occurs, there is a partial dissolution of steel grains combined with an austenite-to-ferrite transformation for larger Ga contents. Cu penetrates along the grain boundaries of the substrate and provides a path for Ga diffusion into the steel. The dissolution of steel grains at the interface is suggested to be responsible for slowing down of the spreading at elevated temperatures. Understanding these interrelations between microscopic and macroscopic effects is important for the development of new Cu-based liquid alloys containing Ga, especially for applications involving steels. Keywords: Brazing, Reactive wetting, Gallium, Copper, Steel, Phase transformation

This work presents the investigation of the solidification and cooling behaviour of a newly developed Fe92.65Cr4.2V2.1B0.05C1 wt% (FeCrVBC) tool steel with special emphasis to phase formations and transformations. JMatPro simulations were compiled to predict the characteristic temperatures of phase crystallizations and transformations under equilibrium conditions. Differential thermal analysis (DTA) was used to cool down samples from 1500 °C to room temperature with various cooling rates (5, 10, 20, 40, and 50 K/min), whereby differences in the number and position of the resulting peaks occurred. To correlate the peaks with specific phase reactions, the microstructure of the variously cooled samples was analysed by means of optical (OM) and scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), wavelength-dispersive X-ray spectroscopy (WDS), electron backscatter diffraction (EBSD) and microhardness tests. The systematic analyses show that the microstructure evolution of the FeCrVBC alloy strongly depends on the cooling rate. For low cooling rates up to 10 K/min, the austenite-ferrite transformation and a marked formation of M7C3 and M23(C,B)6 secondary carbides were observed. At rates of 20 K/min and above, the austenite-martensite transformation takes place, accompanied with a strong increase of the hardness in dendritic areas. By cooling with rates of 40 K/min and higher, the precipitation of M7C3 or M23(C,B)6 secondary carbides cannot be observed anymore, whereas primary M3(C,B) besides MC carbides were detected. Furthermore it was determined, that the very small content of boron (0.05 wt%) strongly influences the (trans-)formation of special carbides, shown by the comparison to its base alloy without boron, the formerly investigated Fe92.7Cr4.2V2.1C1 wt% (FeCrVC). Consequently, strongly depending on the formed carbides the materials hardness and wear resistance can be significantly affected by boron addition. Concluding, the obtained knowledge about the thermal behaviour of the FeCrVBC alloy and the strong impact of a small addition of boron offers the possibility for tailored adjustment of phases and respective properties for a load-adapted tool design.

This paper demonstrates the successful processing of a high-strength Fe85Cr4Mo8V2C1 tool steel by selective laser melting (SLM). Based on tailored parameter variation studies, crack-free and highly dense FeCrMoVC parts (99.99% relative density) are obtained by this processing method. The applied localized high heat inputs during very short interaction times result in a fine, homogeneous microstructure composed of martensite, austenite, and carbides. This combination of phases together with the morphology of the microstructure results in excellent mechanical properties, such as a microhardness of 900 HV 0.1 (ca. 67 HRC) and a compressive strength of about 3800 MPa combined with a fracture strain up to 15%. Therefore, the SLM processing of this alloy enables a further increase of the hardness and compressive strength compared to the as-cast state.Altogether, processing the FeCrMoVC steel by SLM as one key additive manufacturing technology shows high potential for advanced tool design. Keywords: Selective laser melting, Steel, Microstructure, Hardness, Mechanical properties

Thin film metallic glasses (TFMG) can possess a variety of advantages against crystalline thin metal films. High strength and toughness as well as specific corrosion resistivity are features, which can be widely used in MEMS (micro-electromechanical systems), lab-on-a-chip or surface acoustic wave (SAW) device applications. Amongst others, the Cu–Ti binary alloy system is known for having a moderate glass forming ability (GFA) in mid-composition range. In the present study a systematic characterization of sputter deposited Cu–Ti thin films in dependence on the chemical composition is carried out. Intrinsic stress, Young's modulus, surface roughness and electrical resistivity are discussed with respect to the present phases and microstructure. Especially the films within the amorphous range from 25 to 75 at.% Cu exhibit favorable mechanical properties.

In this work a systematic investigation of the influence of the cooling rate on the microstructure and properties of a newly developed Fe92.7Cr4.2V2.1C1 (FeCrVC) tool steel is presented. By applying a tailored casting process and sufficiently high cooling rates excellent mechanical properties are obtained for the presented alloy already in the as-cast state. Since no subsequent heat treatment is required, the cooling parameters applied during the casting process play a key role with respect to the evolving microstructure and resulting properties. In the present publication the effect of the cooling rate on the microstructure and properties of as-solidified FeCrVC was investigated. By using differential scanning calorimetry (DSC), several samples were heated up and cooled with continuous rates of 3–50 K/min. The received DSC data was used to investigate the alloy’s solidification and phase transformation behavior. Subsequently, these samples were studied regarding their properties and microstructure by different analysis methods (EDX/WDX, EBSD, XRD). With increasing cooling rates the liquidus and solidus temperature are lowered, whereas the solidification interval is enlarged. A higher cooling rate is accompanied by a lower solidification time which results in a refinement of the dendritic microstructure. Furthermore, with rising cooling rates the microhardness increased. This provides the opportunity to make predictions from the applied cooling parameters upon the hardness and vice versa and enables one to draw first conclusions on the mechanical properties of the FeCrVC alloy.

A novel approach for development of high strength and ductile beta titanium alloys was proposed and successfully applied. The microstructure of the designed alloys is fully composed of a bcc β-Ti phase exhibiting dendritic morphology. The new Ti 68.8 Nb 13.6 Cr 5.1 Co 6 Al 6.5 (at%) alloy (BETA tough alloy) exhibits a maximum tensile strength of 1290±50 MPa along with 21±3% of fracture strain. The specific energy absorption value upon mechanical deformation of the BETA tough alloy exceeds that of Ti-based metallic glass composites and commercial high strength Ti-based alloys. The deformation behavior of the new alloys was correlated with their microstructure by means of in-situ studies of the microstructure evolution upon tensile loading in a scanning electron microscope.

Samples of Cu47.5Zr47.5Al5metallic glass were prepared at different cooling rate,R. The dependence of the X-ray diffraction patterns onRwas analysed by comparing them with corresponding patterns of computer-simulated models generated at different cooling rates as well. The observed changes in the experimental diffraction patterns are reproduced by the simulations, showing an increasing fraction of icosahedral clusters with decreasing cooling rate. The difference of the fractions of icosahedrally coordinated atoms in mould-cast and rapidly quenched Cu47.5Zr47.5Al5averages to 3 (1)%. Different frozen-in thermal displacements and different density are ruled out as a possible origin for the experimental observations.

The phase equilibria of the binary Ce–Zr system have been investigated between 900 K and 1800 K by a combining conical nozzle levitation technique with in situ high energy synchrotron X-ray diffraction. From the diffraction data the phase sequences and the liquidus line were determined experimentally. The Ce–Zr system is an eutectic type. The eutectic reaction L ↔ bcc -Ce+ hcp -Zr occurs at T =1113±5 K at the eutectic composition of 1.5±1 at% Zr. Based on the experimental data a self-consistent thermodynamic description of Ce–Zr phase diagram is derived.

Amorphous metallic alloys can possess a variety of superior properties, such as wear and corrosion resistance or high hardness and strength, when fabricated as thin films. This paper presents a systematic study of metallic Ni–Zr based amorphous thin films as a model system deposited by magnetron co-sputtering on silicon substrates. The whole range of possible compositions was investigated; thickness and deposition conditions were maintained constant. X-ray diffraction revealed a predominantly amorphous structure from 16 to 93 at.% Ni. A comprehensive set of experimental data about the microstructure, intrinsic stresses, electrical resistivity, surface roughness and Young's modulus were acquired. Due to the featureless microstructure the roughness can be tuned to extremely low values, even at relatively thick films.

In order to reveal the true microstructure of a sample one must often go through tedious and time-consuming surface preparation steps. The most abundant ones are polishing and etching using hazardous chemicals. Sputtering in the glow discharge (GD) lends itself as a simple preparation tool, which supplies mild but fast removal of the deformation layer and exposure of the microstructure. However, the GD is not well studied in terms of its use for preparation of samples. In the present work the influence of GD sputtering on the sample surface is systematically studied. Some examples of the samples prepared with GD are shown. Polycrystalline Cu needs up to 8 h to be conventionally prepared, while with GD the same surface is reached after 10 s of sputtering. In the case of the Ti40Nb alloy, sputtering in GD is the best method for the preparation of this material only within 5 min. The successful EBSD-measurements of the considered samples approve the good quality of the prepared surfaces. Various artifacts of sputtering are found. On the one hand they disturb the measurement, but on the other hand, they may contain useful information about the sputtered material.

Nd–Fe–B melt spun ribbons have been hot-compacted and subsequently die-upset together with DyF3 in order to increase coercivity in nanocrystalline hot-deformed magnets. Magnetic measurements reveal enhanced coercivities for low and reduced coercivities for high Dy-fractions. This behaviour is due to a superposition of the formation of (Dy,Nd)2Fe14B and non-magnetic Dy and Nd fluoride and oxide phases. Energy dispersive and wavelength dispersive X-ray elemental maps verified this feature. Heat treatments at 600 °C induce a strong F diffusion along the flake boundaries without inducing grain growth. This diffusion is correlated with the changes in magnetic properties.

Ti-based materials are frequently used worldwide for orthopedic implants. New β-type or glassy alloys with nontoxic alloying elements are investigated with expected improved biofunctionality. The surface regions and surface layers formed at the materials are decisive for the integration of the implant in the body. Thus, the investigation of the surfaces with analytical methods such as XPS and AES is an essential task. We investigated such materials with different alloying elements after electrochemical passivation by both XPS and AES depth profiling. We discuss chemical changes due to the ion sputtering and motivate the use of non-differentiated spectra for AES quantification. The behavior of the alloy elements in the investigated depth profiles is discussed. Copyright © 2014 John Wiley & Sons, Ltd.

Starting from the bulk glass-forming composition Mg 59.5 Cu 22.9 Ag 6.6 Gd 11 , the development of a bulk glassy matrix composite alloy with high strength and ductility was attempted by adding a large amount of Sc to induce the formation of the MgSc intermetallic compound. However, copper-mould casting of the modified composition, Mg 54.7 Cu 11.5 Ag 3.3 Gd 5.5 Sc 25 , as rods with 3 and 5 mm diameter, yields besides the expected MgSc, a second (CuSc) and a third (Mg 3 Gd-type) intermetallic. These compounds are surrounded by a Mg-rich matrix, possibly composed of glassy regions and a Mg-based terminal solid solution. Although the obtained microstructure deviates largely from the expected one, the new alloy exhibits very high strength, i.e. 790 MPa, and visible plastic deformation, i.e. 0.9%. Shear dimples were found in MgSc.

This work describes the effect of small boron additions (0.01, 0.05 and 0.1 wt%) on the microstructure and mechanical properties of a high strength Fe92.7Cr4.2V2.1C1 (wt%) alloy prepared by applying relatively high cooling rates and pure preparation conditions. The special manufacturing process promotes the formation of martensite, retained austenite and MC (M=V, Cr) carbides and leads to excellent properties under compressive and abrasive loading already in the as-cast state, so that a time-consuming and expensive heat-treatment is not required. Due to microalloying with boron, these properties can be further improved by microstructural changes. Thereby, an increase of the martensite and a drop of the austenite volume fraction was detected by X-ray diffraction (XRD). Furthermore, boron additions lead to the formation of (Fe,M) 3 (B,C) carbides, which were verified by a combination of electron backscatter diffraction (EBSD) and dispersive X-ray spectroscopy (EDS/WDS) as well as transmission electron microscopy (TEM). With increasing amount of boron, these carbides form an interlocking network-like structure with the MC carbides, which leads in combination with the rising martensite fraction to FeCrMoVBC alloys showing significantly improved abrasive wear resistance and increased hardness compared to the Fe92.7Cr4.2V2.1C1 base alloy. Altogether, microalloying of the FeCrVC alloy with boron combined with a tailored casting process presents a fast and cost-effective method to enhance the performance of the alloy for the application as cutting and forming tool material.

We have introduced a facile strategy to fabricate sandwich-stacked SnO2/Cu hybrid nanosheets as multichannel anodes for lithium-ion batteries applying rolled-up nanotechnology with the use of carbon black as intersheet spacer. By employing a direct self-rolling and compressing approach, a much higher effective volume efficiency is achieved as compared to rolled-up hollow tubes. Benefiting from the nanogaps formed between each neighboring sheet, electron transport and ion diffusion are facilitated and SnO2/Cu nanosheet overlapping is prevented. As a result, the sandwich-stacked SnO2/Cu hybrid nanosheets exhibit a high reversible capacity of 764 mAh g(-1) at 100 mA g(-1) and a stable cycling performance of ~75% capacity retention at 200 mA g(-1) after 150 cycles, as well as a superior rate capability of ~470 mAh g(-1) at 1 A g(-1). This synthesis approach presents a promising route to design multichannel anodes for high performance Li-ion batteries.

Many Heusler compounds are predicted to be half-metallic ferromagnets and thus find extensive interest as materials for spintronic applications, an example of which is the Co2Cr1–xFexAl series. So far, bulk samples of that series, in particular, Cr-rich samples, do not verify those predictions, and various studies have yielded results that are fraught with anomalies. Thin films as well do not meet expectations, neither in magnetoresistance ratio nor in degree of spin polarization and magnetic moments. Polycrystalline samples of Co2CrAl, Co2FeAl, and Co2Cr0.6Fe0.4Al were found to be phase segregated, a hurdle easily tackled by using the optical floating zone (FZ) technique. Hence, in this work, we have carried out crystal growth of Co2Cr1–xFexAl Heusler compounds, as a step toward understanding the intrinsic material properties of this series. Our results demonstrate that, although the phase segregation is eliminated in the FZ grown samples, an unexpected phase transformation via spinodal decomposition tak...

Samples of low modulus beta-type Ti40Nb and cp2-Ti were chemically treated with 98% H2SO4 + 30% H2O2 (vol. ratio 1:1) solution. Surface analytical studies conducted with HR-SEM, AFM, and XPS identified a characteristic nanoroughness of the alloy surface related with a network of nanopits of ∼25 nm diameter. This is very similar to that obtained for cp2-Ti. The treatment enhances the oxide layer growth compared to mechanically ground states and causes a strong enrichment of Nb2O5 relative to TiO2 on the alloy surface. The in vitro analyses clearly indicated that the chemical treatment accelerates the adhesion and spreading of human mesenchymal stromal cells (hMSC), increases the metabolic activity, and the enzyme activity of tissue non-specific alkaline phosphatase (TNAP). Surface structures which were generated mimic the cytoplasmic projections of the cells on the nanoscale. Those effects are more pronounced for the Ti40Nb alloy than for cp2-Ti. The relation between alloy surface topography and chemistry and cell functions is discussed. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 31–41, 2014.

Logarithmic spirals are found on different length scales in nature, e.g., in nautilus shells, cyclones, and galaxies. The underlying formation laws can be related to different growth mechanisms, pressure gradients, and density waves. Here, we report on the self-organized formation of symmetric logarithmic crystallization spirals in a solid material on the micrometer length scale, namely, in an amorphous Ge:Mn layer on a Ge substrate. After exposure to a single light pulse of a flashlamp array, the Ge:Mn layer is crystallized and reveals a partially rippled surface and logarithmic microspirals. Finally, we present a model describing the formation of the crystallization spirals by directional explosive crystallization of the amorphous Ge:Mn layer, which is triggered by the flashlamp light pulse.

The floating-zone growth of massive intermetallic single crystals is very often unsuccessful due to unfavorable solid–liquid interface geometry and insufficient mixing of the melt which depends on the flow in the molten zone. A tailored magnetic two-phase stirrer system with radio frequency (RF) heating has been developed which enables the control of the melt flow by a significant change of the flow field. The magnetic system was used for the crystal growth of the Heusler compound Mn3Si due to their interesting properties such an itinerant antiferromagnetic and incommensurate spin-density wave state. The grown crystals were oriented and cut to samples with the crystallographic orientations (100) and (110) normal to a plane. Measurements of the temperature dependence of magnetization and specific heat are discussed in terms of contributions of other thermodynamic phases and phase transitions.

New Ti–Cu–Ni shape memory bulk metallic glass composites were obtained by carefully controlling the cooling rate upon quenching. This allows for the formation of a metastable microstructure consisting mainly of ductile, spherical martensitic Ti(Ni,Cu) precipitates embedded in an amorphous matrix also containing a small volume fraction of TiCu and Ti2Cu precipitates. These composites exhibit large ductility and high strength combined with a strong work-hardening behaviour. A deformation mechanism is proposed with the help of experimental observations and finite-element simulation. The simulation results demonstrate that stress concentrations occur around the precipitates, which promotes a heterogeneous stress distribution and the formation of multiple shear bands. Additionally, different transformation temperatures were observed for martensitic precipitates depending on whether they are completely or partially embedded in the amorphous matrix.

The effect of low-temperature on the active deformation mechanism is studied in pure copper. For this purpose, cryogenic wire drawing at liquid nitrogen temperature (77 K) was performed using molybdenum disulfide lubrication. Microstructural investigation and texture analysis revealed severe twin formation in the cryogenically drawn copper, with a broad twin size distribution. The spacing of the observed deformation twins ranges from below 100 nm, as reported in previous investigations, up to several micrometers. The extent of twin formation, which is significantly higher when compared to other cryo-deformation techniques, is discussed with respect to the state of stress and the texture evolution during wire drawing. � 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The aim of this work is growth and characterisation of Ti55Nb45 (wt%) single crystals by floating-zone single crystal growth of intermetallic compounds using two-phase radio-frequency (RF) electromagnetic heating. Thereby, the process and, in particular, the flow field in the molten zone is influenced by additional magnetic fields. The growth of massive intermetallic single crystals is very often unsuccessful due to an unfavourable solid–liquid interface geometry enclosing concave fringes. It is generally known that the crystallization process stability is enhanced if the crystallization interface is convex. For this, a tailored magnetic two-phase stirrer system has been developed, which enables a controlled influence on the melt ranging from intensive inwards to outwards flows. Since Ti is favourably light, strong and biocompatible, it is one of the few materials that naturally match the requirements for implantation in the human body. Therefore, the magnetic system was applied to crystal growth of Ti alloys. The grown crystals were oriented and cut to cubes with the desired crystallographic orientations [1 0 0] and [1 0 1] normally on a plane. The electron backscatter diffraction (EBSD) technique was applied to clearly determine crystal orientation and to localize grain boundaries. The formation of oxidic nanotubes on Ti surfaces in dependence of the grain orientation was investigated, performed electrochemically by anodic oxidation from fluoride containing electrolyte.

In the present work, the mechanical behaviour at different strain rates of a high strength tool steel with the composition Fe88.9Cr4.3V2.2C4.6 (at.%), manufactured under relatively high cooling rates and highly pure conditions, was studied. The applied preparation conditions promote a microstructure composed of martensite, retained austenite and a fine network of special carbides already in the as-cast state. This special phase combination yields a structural material with superior mechanical properties under quasi-static loading, exhibiting an extremely high engineering compression strength of almost 4000 MPa combined with a large compression strain of about 20% due to deformation-induced martensite formation. However, the knowledge of the performance of this material under dynamic loading conditions is also very important for its possible application as a novel kind of tool steel. For this reason, compression tests in the strain rate range of 10−3–103 s−1 were performed and the transformation-induced plasticity (TRIP effect) was investigated. The analysis of the transformation behaviour of the retained austenite reveals that the rate of martensite formation decreases with increasing strain rate. Furthermore, an increase of the offset yield stress and the compression strength with increasing strain rate together with a remarkable plasticity was detected.

The process of the preparation of graphitic nanoplatelets via chemical intercalation and thermal exfoliation of graphite was considered. The dependence of the properties of the final product on the microstructure of the raw material and on different process parameters was analyzed. It is shown that the microstructure of the raw material has considerable influence on the structural transformations during the different preparation steps. The observed differences can be understood assuming that intercalation is initiated at the edges of graphite crystallites by the formation of intercalate nuclei. Essential differences of the nucleation time appear for unequal types of microstructure and give rise to different intercalation states. It is also shown that the sub-process of washing and drying the samples after intercalation is most critical and has significant influence on the characteristics of the final products. The results suggest that graphite fibres with sub-micron diameter and orientation of the crystallographic c-axis along the fibre axis will be particularly favourable for the preparation of graphitic nanoplatelets.

On the basis of the Fe84.3C4.6Cr4.3Mo4.6V2.2 high-speed tool steel, manufactured under relatively high cooling rates and highly pure conditions, a further improvement of the mechanical characteristics by slight modification of the alloy composition was attempted. For this, the alloy Fe88.9Cr4.3V2.2C4.6 was generated by elimination of Mo. By applying special preparation conditions, a microstructure composed of martensite, retained austenite, and a fine network of special carbides was obtained already in the as-cast state. This material exhibits extremely high compression strength of over 5000 MPa combined with large compression strain of more than 25% due to deformation-induced martensite formation. With this alloy a new composition of transformation-induced plasticity-assisted steels was found, which shows an extreme mechanical loading capacity.

Dendrites are one of the major microstructural constituents of peritectic alloys. In the present work, the effect of melt convection on the secondary dendritic arm spacing (SDAS) and volume fraction of properitectic α-Fe was investigated during solidification of stoichiometric Nd–Fe–B alloys using the forced crucible rotation technique. The resulting microstructure of the alloy in consideration of melt convection has been investigated using scanning electron microscopy and optical microscopy. The average SDAS was determined for each sample from the whole cross-section of the cylindrical test samples using image analyzing software LEICA QWIN. A detailed statistical analysis of the spacing distribution was performed on the basis of the variation of SDAS values, averaged from about 80 to 120 dendrites in different zones. The α-Fe volume fraction, measured by vibrating sample magnetometer (VSM), reduces with increasing crucible rotation frequency. Similarly, the SDAS values decrease with increasing rotation frequency. These results are explained from the viewpoint of a reduced melt convection state under steady forced crucible rotation leading to a reduced effective mass transfer coefficient.

Deformation and fracture of Saffil fiber (SF) reinforced Mg, Mg-8 wt.% Li and Mg-12 wt.% Li composites was monitored by means of in-situ scanning electron microscopy during 3-point bend tests. Mg and MgLi matrix composites (10 vol.% SF) were prepared by the melt infiltration technique. Poor interfacial bond causes premature failure of the SF/Mg composite that is usually triggered by the debonding of perpendicular fibers at the convex composite surface. Strong interfaces in SF/Mg12Li composite result in multiple cross-breakage of aligned fibers which is indicative of their participation in the composite strengthening. Resultant composite strengthening is frustrated by massive stress relaxation of the Mg12Li matrix. Strong interfaces and fairly high strength of the Mg8Li matrix cause remarkable strengthening of SF/Mg8Li composites. The cleavage of phases in two-phase Mg8Li matrix plays an insignificant role in the composite failure.

We show the impact of lateral structuring on the optical properties of organic thin films in microcavities. The active material tris-(8-hydroxy quinoline) aluminium (Alq3) was deposited using shadow mask evaporation, resulting in various micron sized shapes. A simplified box model is employed to describe the steady state electric field distribution in these mesa cavities. The complex mode structure measured in transmission and photoluminescence is confirmed by a transfer matrix calculation and a Fourier transform of the internal electric field distribution.

The initial microstructure of thin electroplated Cu films was investigated for different layer thicknesses and plating conditions. The initial grain size of electroplated Cu thin films was found to be distributed homogeneously whereas the initial texture was inhomogeneous over film thickness. With increasing film thickness a transition occurs from a basis-oriented into a field-oriented texture. The knowledge about initial Cu microstructure for different plating conditions helped to clarify the factors of influence for Cu room-temperature recrystallization, called self-annealing. Furthermore, beside the microstructure also incorporated impurities were found to be of great importance for Cu self-annealing particularly in the case of a varying additive content in electrolyte.

The deformation behavior of rapidly solidified two-phase amorphous Ni–Nb–Y alloy has been investigated by nanoindentation and high-resolution scanning electron microscopy and correlated with the mechanical properties of the two individual phases composing the system (Ni–Y and Ni–Nb). While the elastic deformation of the two-phase alloy obeys the rule of mixtures for a composite, the plastic deformation is governed by the softer matrix but enhanced, in part, by the deflection of shear bands by the globular harder phase.

An annealed Cu blanket film was investigated in situ at high temperature using electron back-scatter diffraction (EBSD). The primary aim of the experiment was to study the changes in the (111) texture in the Cu film where the microstructure was already stabilized by previous annealing treatment. Two separate investigations were carried out at the same location of the film for better statistical reliability of data. It was found that the (111) planes got increasingly inclined to the specimen surface with increasing temperature. Additionally, a change in the strength of {111} and {111} texture components was observed with increasing temperature. Absence of these phenomena in freestanding Cu film indicates the impact of substrate on the behavior of (111) grains. The effect of substrate on the peculiar behavior of the (111) grains has been explained by a model which describes the contribution of both dislocations and diffusion to the observed phenomenon. The tilting of the (111) grains is discussed with reference to the recently reported Bauschinger effect in the Cu films.

Changes in texture and microstructure during the thermal treatment of Cu films have been studied in situ using electron back-scatter diffraction (EBSD). A partially recrystallized Cu film which still had its microstructure evolving at room temperature was investigated using orientation imaging microscopy. Two separate investigations were conducted—the first one at different locations of the film and at different temperatures and a second one at the same location of the film and at different temperatures. The orientation of the (111), (110) and (100) grains within the plane of Cu film was investigated from the orientation distribution functions. There was an increased tendency of the (111) and (110) grains to form either {111} or {111} and {110} texture respectively at higher temperature. The impact of elastic strain energies and dislocation glide in formation of these textures at higher temperatures has been analyzed in the light of some recent observations reported in literature. The variation in the area fraction of different fiber texture components, as a function of temperature, has been discussed in correlation with the measured mean grain size, grain boundary misorientation distribution and stress states. Stress state during the entire thermal cycle was monitored by wafer curvature technique and the traces of additive impurities at the surface were measured using X-ray photoelectron spectrometry. The possible role of impurities in affecting the behavior of texture components at high temperature is discussed. Comparison was made between the EBSD and X-ray diffraction texture data.

The correlation between the microstructure of a 340nm thick Al metallizations deposited on a thin Ti adhesive layer and damage due to acoustomigration was investigated. For this reason, the {111} textured metallization was acoustically loaded by gradually increasing rf power up to 3.6W. The hillock and void formation during load experiments was mostly detected at such grain boundary triple junctions, which consist of two grain boundaries with misorientation angles 30^o. The results were achieved by means of scanning electron microscopy, electron back scattered diffraction, and focused ion beam technique.

Limited reliability of interconnect material mainly due to current induced electromigration defects is one of the serious issues of actual and future microelectronic devices. The influence of interfaces and microstructure on electromigration damage in Cu interconnects became an open question again and needs further studies. In order to find correlations between microstructural details and localization of electromigration defects generated in narrow electroplated Cu lines, microstructure of entire line was recorded by electron back scatter diffraction measurements with high lateral resolution, and then electromigration test was performed in high vacuum under direct SEM observation. In the result, a number of hillocks were found to have grown in the vicinity of (100) grains having at least one high angle grain boundary around it. Fatal voids often formed at the cathode end and produced dielectric cracking in some cases. Furthermore, voiding started from the sidewall of interconnect trenches mostly at such places where (111) grains with high angle grain boundaries were located.

A novel phase-separated Ni-based amorphous alloy is prepared in a glass forming system by rapid quenching of a Ni58.5Nb20.25Y21.25 melt. The microstructure consists of two amorphous Nb-enriched and Y-enriched regions with a size distribution from micrometer dimensions down to several nanometers. Decomposition takes place in the melt prior to solidification. The miscibility gap in the solid and liquid state of the binary Nb–Y system extends into the ternary Ni–Nb–Y alloy as a consequence of the positive mixing enthalpy between Nb and Y. The two-phase amorphous Ni58.5Nb20.25Y21.25 alloy crystallizes in a first step by the primary precipitation of the cubic Ni2Y phase from the Y-rich amorphous phase. At much higher temperatures the remaining Nb-rich amorphous phase crystallizes into Ni7Nb6.

The effect of silver in pure nickel on the quality of the primary recrystallization cube texture was investigated after intense cold rolling and annealing. Texture sharpness and thermal stability in the nickel tapes could be improved by micro-alloying with silver in the range of 100–500 at. ppm Ag. The sharpest cube texture was observed for the Ni + 100 at. ppm Ag material after annealing at 550 °C (FWHM(111) = 4.4°). Further, the nickel oxide layer grown thereon had a sharp cube texture rotated by 45° relative to the metallic substrate. Grain boundaries showed a typical zigzag image and the grain form was fractal-like.

Cube textured substrate tapes were prepared by cold forming and annealing from nickel and microalloyed nickel in order to manufacture long flexible superconductors of the YBCO (YBa 2 Cu 3 O 7− δ ) type. It was shown that sulphur as a metallurgical trace impurity can hinder the processes of cube texture formation in nickel based materials. Experiments were performed to overcome this detrimental effect of sulphur by microalloying of different nickel qualities with Mo, W or Ag and by specific heat treatments.

The characteristic domain size of nanostructured Cu is evaluated using X-ray diffraction (XRD) as well as by scanning (SEM) and transmission (TEM) electron microscopy. TEM describes the grain size, whereas XRD provides the size of the sub-grain structures (dislocation cells in the case of heavily deformed Cu). In contrast, SEM gives the size of both grains and substructures, with values in good agreement with the corresponding results from TEM and XRD. Through the proper use of these analytical techniques it is possible to achieve the complete characterization of nanostructured materials.

Two different Cu films were studied in situ in FEG SEM as a function of temperature using electron back scatter diffraction (EBSD). Two different Cu films, one of which was partially recrystallized (film A) and the other annealed (film B) were investigated. Both EBSD and X-ray diffraction data showed that for film A there was a competition between the surface/interface and strain energy minimization with increasing temperature. The decrease in the area fraction of (110) grains with increasing temperature was attributed to segregation of impurities at the grain boundaries surrounding the (110) grains. In case of film B the (111) planes got increasingly inclined to film surface with increasing temperature under the influence of stress induced diffusion. For both the films there was an increasing tendency of the (111) grains to form either {111} or {111} texture at high temperature. The (110) grains showed an increased tendency to form {110} at high temperature. The role of substrate in formation of these textures at has been explained based on in situ high temperature EBSD study of freestanding Cu film.