INTL. SYMP. ON SCIENCE OF INTELLIGENT AND SUSTAINABLE ADVANCED MATERIALS (SISAM)

High level ab initio interaction energy calculations based on coupled cluster methods with singles and doubles and non-iterative singles (CCSD(T)) and scaled opposite-spin (SOS) Møller-Plesset perturbation theory (MP2) were performed on several sandwich (S) and the slipped parallel (SP) dimers of selected polyaromatic hydrocarbons (PAHs) up to coronene encircled by three sets of benzene rings (coronene circum-3 dimer, 300 carbon atoms) in an attempt to reliably compute the π-π stacking interactions of extended aromatic systems [1,2]. Results are compared with density functional theory (DFT) using the B3LYP functional and the D3 dispersion correction. Comparison of coupled cluster with SOS-MP2 results show good agreement for smaller linear polyacenes (benzene to anthracene dimer), whereas the unscaled MP2 results demonstrate a well-known overshooting of interaction energies. The SOS-MP2 method reproduces interring distances quite well in comparison to higher level results. Thus, investigations on the stacking properties of larger systems have been continued at this computational level.
It was found that the coronene circum-2 dimer complex has a sandwich biconcave structure with a stronger interaction (smaller distances) in the center. The distance of 3.33 Ao is significantly smaller than the van der Waals distance of ~3.60 Ao. Slipped parallel structures have been investigated as well. They are in all cases more stable than the sandwich structures. Comparison in terms of inter-sheet bond distances and interaction energies with sandwich structures will be discussed in the presentation

A new continuous severe plastic deformation (SPD) process for metal sheets called single-roll angular-rolling (SRAR) is introduced. The SRAR process achieves maximized deformation homogeneity of metal sheets by combining circumferential shear deformation with channel-angular shear deformation. The grain refinement and mechanical properties were investigated experimentally in relation to the number of repetitive SRAR passes. The finite element method was used to demonstrate that the SRAR process provides highly uniform SPD by strengthening the less deformed region that inevitably occurs near the lower part of the workpiece during the channel-angular deformation processes.

Magnesium alloys as ZK60 are interesting materials for hydrogen storage in the solid state, due to the high volumetric and gravimetric capacities that can be attained, and to the relatively low relative cost of these materials. The development of simpler and more cost effective processing routes of Mg alloys for H2 storage is an important challenge of applied research, in order to make possible the replacement of the intensive time and energy consuming processes based on high-energy ball milling, HEBM. We have explored different alternatives of advanced processing to ZK60 or ZK60 modified with Mm (mischmetal) [1-3], aiming to produce refined microstructures and enhanced H2 storage properties, especially faster activation (first hydrogenation) kinetics. Due to the Mm addition, a network of intermetallic particles is formed at the grain boundaries of the modified ZK60 alloy. Equal-channel angular pressing (ECAP) or rapid solidification by melt-spinning (MS) were combined with a subsequent step of extensive cold rolling (CR). The additional processing by CR caused further grain refinement and breakage of intermetallic particles, as well as favoring crystallographic texture in the (002) direction. All these features promoted a significant improvement in the hydrogen storage capacity. Another approach applied for the ZK60 alloy consisted in the combination of friction stir processing (FSP) with filing. The pulverization of the ZK60 alloy, already grain refined by FSP, has shown to be also an interesting strategy to produce materials with better H-absorption/desorption kinetics.

Among the various families of thermoelectric materials, half-Heusler and full-Heusler systems are appreciated for their excellent mechanical properties and an outstanding thermal stability. While half-Heusler materials are also known for their superior thermoelectric performance as characterized by the so-called figure of merit, ZT, reaching ZT values above 1, the thermoelectric efficiency of full-Heusler systems is still moderate and does not exceed ZT ~ 0.1 - 0.2. The latter finding is based on the unfavorable fact that the total thermal conductivity of such Heusler phases is pretty large, exceeding that of well-behaving thermoelectric materials by more than one order of magnitude. Nevertheless, the power factor of Heusler systems like those based on Fe₂VA1, is comparable, or even exceeds that of well behaving and excellently performing materials based on Bi-Te.
In this contribution, the influence of substitution on different lattice sites (e.g., V/W or Fe/Ni) on the thermoelectric performance is studied, both from experiments as well as from first principles DFT calculations. In addition, we show that thin film preparation of Heusler systems results in an significant enhancement of the power factor pf substantial drop of the lattice thermal conductivity and thus in an dramatic increase of the figure of merit ZT. A number of microscopic observations are accounted for to explain this boost.

Bulk ultrafine-grained, nanocrystalline, and even amorphous materials can be processed using methods of severe plastic deformation (SPD). [1,2] The small grain size as well as the high density of defects can significantly impact the phase stability and thus the physical properties of various materials. Control of phase stability by methods of SPD is of special interest in the case of functional materials such as shape memory alloys. [3] Their unique thermomechanical properties are based on a martensitic phase transformation that can be strongly affected by lattice defects, chemical disordering, and a grain size at the nanoscale. In the present work, examples of SPD processed shape memory alloys include Ni-Ti, low-hysteresis Ti-Ni-Pd, high temperature Ti-Pd and Ti-Pt, as well as ferromagnetic Ni-Mn-Ga. Their phase stability and the martensitic morphology in the small grains were systematically investigated using methods of transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction, including in-situ heating, cooling, and straining experiments carried out in the synchrotron. With decreasing grain size, the martensitic transformation is hindered and metastable adaptive martensitic phases might occur. However, the thermally and stress induced transformations might be suppressed completely in grains smaller than a corresponding critical value. Considering a size dependent energy barrier opposing the transformation and the mechanisms of self-triggered autocatalytic interactions of the transformation in neighbouring grains, the results were modelled using the general thermodynamic framework of martensite formation. [4]

Recently, CoFe₂O₄ is of more physical and technological interest, because among the ferrites, it exhibits the highest magnetocrystalline anisotropy as well as a high magnetostriction (100=590 ppm), high strain sensitivity (one order larger than that of polycrystalline terfenol (λ_s = 1000 ppm)), and low raw material costs, whose properties are appropriated for non-contact sensor and sonar detection field. Additionally, CoFe₂O₄ is an insulator that is one of the few materials which can be used for bulk magnetoelectric composites. The grain size, magnetic properties, and cations distributions in octahedral and tetrahedral sites depend strongly on the production method. With forced hydrolysis method, a grain size of 3 nm could be achieved [1], which is very important for biomedical applications. Pressing ball milled cobalt ferrites under high pressure and sintering in a high external field can obtain a magnetostriction up to 400 ppm [2].
Low temperature magnetization measurements on single crystalline Co_0.8Fe_2.2O₄ gave evidence of a first order magnetic process (FOMP) transition, which occurs when applying the external field in the [111] direction [3]. This transition is also well visible in the magnetostriction data. Such transition gives evidence of two competing anisotropy directions or two no equivalent magnetization sites, which may be due to different valent states at 3d atoms.
Due to the complex preparation methods of single crystal cobalt ferrite, more attention has been given on polycrystalline cobalt ferrites to obtain high magnetostriction. In this work, special emphasis will be given on the temperature dependence of enhanced magnetostriction of CoFe₂O₄ by annealing the sample (produced by ball milling and sintered at 1000°C for 12 h) with strong magnetic field of 10 T, at 300 °C for 3 h and cooling down to room temperature with the presence of field. These results will be compared with those data obtained for the sample before the magnetic field annealing.

The reversible ingress of gas phase H₂ into the interior of hydrogen (H)-absorbing metals is widely utilized in metal hydride storage and H₂ purification. On reactive hydride-forming metals, thin palladium (Pd) surface layers promote barrier-free H₂ dissociation and protection from oxidation. The kinetics of H₂ absorption are of particular interest to industrial Pd-catalyzed olefin hydrogenation (fuel reforming and organic synthesis), for which Pd-dissolved H has been identified as the essential reactive ingredient that drives the H₂ addition to the olefinic C=C double bond [1].
The H₂ transportation mechanism between the gas phase and the metal interior, however, has not been understood very well at the atomic level until recently. It is therefore explained here how we revealed the microscopic H₂ absorption process at structurally well-defined Pd single crystal surfaces through our unique combination of H depth profiling with ¹⁵N nuclear reaction analysis [2] and thermal desorption spectroscopy with isotope-labeled (H, D) surface hydrogen. We thereby demonstrate that the H₂ transfer into the Pd is highly sensitive to the surface atomic structure [3]. Based on this insight into the H₂ absorption mechanism, it is shown how the structure-sensitivity can be exploited by means of deliberate surface structural modifications to control, e.g., the desorption dynamics of Pd-dissolved hydrogen in a wide range of temperatures (160-375 K) [4]. Photoelectron spectroscopy and density functional calculations will further demonstrate that a modification of the surface electronic properties by surface-alloying with gold can even accelerate the H₂ absorption 30-fold compared to pure Pd [5].

The structure of glasses is generally taken to be isoconfigurational, although it is well-known that the details of structure arrangement strongly depend on the temperature-time history experienced when establishing the glassy state.
Recent studies of glass-forming metallic systems have revealed intriguing complexity, e.g. unusual shifts in radial distribution functions with temperature change or upon mechanical loading in the elastic or plastic regime. Nearest neighbour distances and medium-range order structural arrangements appear to change, e.g. shorten upon heating or become larger with decreasing temperature. Concomitantly, temperature changes as well as static or dynamic mechanical loading within the nominally elastic regime can trigger significant changes in glass properties, which are directly correlated with local non-reversible configurational changes due to non-affine elastic or anelastic displacements. All these findings strongly suggest that the characteristics of the atomic structure decisively determine the properties of the glass.
Recent findings and developments along these lines will be summarized, and results from high-energy synchrotron x-ray radiation investigations at different temperatures, and after mechanical loading, will be related to the atomic structure of the material and its dependence on temperature, mechanical load, as well as intrinsic heterogeneities and length-scale modulation, such as to elucidate the correlation between atomic arrangement and mechanical properties.

The influence of high pressure torsion (HPT) on the diffusive and displacive phase transformations in sustainable advanced materials has been studied. In diluted Cu-based binary alloys the HPT drives the competition between deformation-driven precipitation and dissolution of precipitates. The dynamic equilibrium between these two processes is reached already after 1.5-2 anvil rotations. The composition of Cu-matrix in this equifinal state is equal to that which can be reached in equilibrium after long annealing at a certain temperature T_eff. T_eff in diluted Cu-based binary alloys increases with increasing activation enthalpy of diffusion of a second component and its melting temperature Tm [1, 2].
In Cu-Al-Ni shape memory alloys, HPT leads to the combination of displacive (austenite-martensite) and diffusive (decomposition of supersaturated solid solution) phase transitions. On the one hand, the HPT of these alloys led to the precipitation of α1-phase in the Al-pure alloy and to the precipitation of γ1-phase in the Al-rich one (as if they were annealed at an effective temperature T_eff = 620-20°C). As a result of this precipitation, the matrix in the first alloy was enriched and in the second one depleted in Al. The resultant composition change in the Cu-rich matrix changed also the route for the martensitic transformations. After HPT, both alloys contained mainly β'3 martensite with a certain amount of γ'3 martensite. Thus, the HPT-driven diffusive transformations (precipitation of α1- and γ1-phase) influence the followed displacive (martensitic) transformation [3].
The combination of displacive and diffusive phase transitions has been observed also under HPT of Ti-Fe and Ti-Co alloys [4].

Although semicrystalline polymers have become increasingly important for technological applications in the past decades, the micromechanical processes on an atomistic scale occurring during plastic deformation are still a matter of dispute [1]. As an example, this concerns the question whether dislocations in the crystalline phase play a role for the macroscopic strength or not [2]. Based on dedicated experimental methods such Multiple X-ray Line Profile Analysis (MXPA), which allows the verification of the presence of dislocations and their quantification [3-6], and nano-creep experiments, as a mechanical probe for dislocation mediated plasticity with sub-nanometer resolution [7], we discuss recent findings on the molecular processes governing the plasticity of semicrystalline polymers. Special emphasis is given to the generation, mobility, and thermal activation of dislocations in particular, and crystallographic defects and transformations in general for several semicrystalline polymer materials.

Magnesium is a promising material for medical applications [1-2], owing to its good biocompatibility. Its high corrosion rate makes it suitable for bioresorbable implants, but it needs to be reduced to match the rate of healing. Addition of Rare Earth (RE) elements promotes the corrosion resistance and strength of Mg, but is usually insufficient. Therefore, the treatment of magnesium alloys by severe plastic deformation, which raises strength and sometimes also the corrosion resistance, seems promising. In this work, a magnesium alloy containing RE elements was processed by equal channel angular pressing (ECAP) in two regimes. Route Bc ECAP was carried with a step-wise decrease in temperature. In the first regime, the temperature was dropped to 350°C after 6 passes at 400°C and further 6 passes were conducted. In the second regime, the temperature was decreased from 425 to 300°C in 25°C decrements, 2 passes being carried out at each temperature. Investigation of the microstructure of the alloy showed that after the ECAP an ultrafine-grained structure with an average grain size of 1.00-0.14 μm and 0.69-0.13 μm for the first and second regimes, respectively. This is to be compared with the average grain size of 70 μm in the initial state. In addition, particles of Mg₄₁Nd₅ phase with an average size of 0.41-0.18 μm and 0.45-0.18 μm were observed for these regimes. The grain refinement achieved was shown to lead to an improvement of mechanical properties. The values of the yield strength, YS=150MPa, the ultimate tensile strength, UTS=220MPa, and the tensile elongation, EL=10.5%, rose to YS=180MPa, UTS=250MPa, and EL=7% and YS=260MPa, UTS=300MPa, and EL=13.2% for the first and the second regimes, respectively. The best combination of properties for the second ECAP regime can be explained by the formation of a sharp prismatic texture, on top of a smaller grain size, as distinct from an inclined basal texture formed after the ECAP by the first regime.

Palladium-hydrogen system is widely used as a model system for investigating behaviors of hydrogen in metals. In this work, we applied different ways of loading on palladium-hydrogen alloys to investigate the effect of hydrogen on generation of lattice defects in palladium subjected to plastic deformation. In cold-rolled palladium-hydrogen alloys, it is shown that hydrogen solute significantly enhances the multiplication of dislocations during deformation, which will give rise to dislocation densities in the cold-rolled metals and results in hardening of the metals. Under the severely plastic deformation condition, the hydrogen solute is found to increase both the densities of deformation induced vacancy agglomerates and of dislocations, while the former also contribute significantly to hardening of the metals. When the alloys are subjected to ultra-fast loading (strain rate up to 10³ s^-1) exerted by a Split-Hopkinson apparatus, the addition of hydrogen leads to the increase in vacancy concentration and dislocation density, too. In this case, the increase in dislocation density is believed to play a major role in hardening palladium.

Samples taken from a room temperature (RT) extruded aluminium alloy 6060 were deformed by equal-channel angular pressing (ECAP, one pass, RT) [1]. Texture measurements by X-ray diffraction reveal a strong predominant <111> fibre texture in the extruded bar. Depending on the alignment of the fibre axis with respect to the ECAP die, strain localization phenomena in form of shear bands are observed. Local texture measurements by electron backscatter diffraction after ECAP reveal a clear shear texture with certain components dominating. The shear texture is related to the starting texture, which determines the slip system activity. Thus, there is a clear correlation between starting texture and shear banding during ECAP. Texture simulations reproducing the experimental texture show that the Taylor factor is constantly decreasing when shear banding takes place while in the case of homogeneous shear it goes over a maximum. This clearly indicates that geometrical softening leads to the mechanical instabilities.

Industrial scale nanostructuring via Severe Plastic Deformation (SPD) can alter the properties of metals and alloys to increase their performance, extend their useful life cycles, and thereby diminish their environmental impact. Higher performance and longer lasting metals reduce the amount of natural and other resources needed for multiple applications. Thus, nanostructuring effectively increases the sustainability of using alloys to serve societal needs.
We will examine the key advances in SPD-processing that have enabled industrial applications of high performance metals and alloys in various industrial sectors, including energy production and transmission, healthcare, transportation, and electronics. The evolution of scaling of speed, efficiency, and size scale of SPD production will be reviewed. We will also see how the emergence of high performance metals and alloys of aluminum, magnesium, copper, titanium, and iron has been influenced by the convergence of advances in measurement science, process control, and understanding of the microstructural effects of intense shear.

Processing through the application of severe plastic deformation (SPD) produces exceptional grain refinement to the submicrometer or even the nanometer level. The paradox of strength and ductility was suggested several years ago [1] and has become a major topic in all studies of SPD metals. This paradox relates to the fact that metals may be strong or ductile, but generally they fail to exhibit both high strength and high ductility. Since SPD metals have very small grain sizes, it follows that the strength is usually high but the ductility is limited. This presentation examines the significance of this paradox and discusses possible procedures for at least partially alleviating the low ductility, which tends to be an inherent feature of these SPD nanomaterials.

The presentation is focused on structure-property relationship for interfaces in severe plastically deformed (SPD) materials. The results are systematized for different types of SPD treatment, imposed strain, and induced defects, and the deformation parameters used (temperature, total strain and strain rate). The kinetic properties of interfaces in a broad spectrum of severe plastically deformed materials ranging pure metals to alloys, including the high-entropy alloys, are measured. A multi-level hierarchy of short-circuit diffusion paths is shown to be formed in ultrafine grained materials produced by SPD Treatment [1,2]. The key properties of deformation-modified grain boundaries, such as interface width, diffusion rate, free volume excess, are measured and analyzed in detail. A model of the deformation-modified grain boundary state is presented.

Strong and tough materials are desired for structural applications such as transportation vehicles for high energy efficiency and good performance. After over a century's research, we have almost reached the limit on how much further we can improve the mechanical properties of metals and alloys. This raises the question if there exists yet-to-be-explored new strategies to make the next generation of strong and tough materials. Recently, heterostructure is found to produce unprecedented strength and ductility that are considered impossible from our textbook knowledge and materials history. Heterostructured (HS) materials consist of domains with dramatic strength differences. A previously not-well-known mechanism, back-stress strengthening and back-stress work hardening, is found responsible for such a dramatic improvement of mechanical properties. This represents a new paradigm for designing strong and tough structural materials. HS materials have recently attracted extensive attention in the academic community as an emerging research field. Moreover, HS materials can be produced by current industrial facilities at large scale and low cost, and has the potential to revolutionize the manufacturing industry. There are many scientific issues with such materials that challenge the communities of experimental materials science and computational material mechanics. In this talk, the authors will present the current advances as well as future challenges and issues in this emerging field.

X-Ray Line Profile Analysis is a powerful method to characterize the microstructure of deformed materials, especially when high energy and brilliant Synchrotron radiation enables investigations with high time and spatial resolution. Parameters like dislocation density, dislocation arrangement, scattering domain size, and its distribution are parameters of a physical model of peak broadening, which can be applied to high quality diffraction measurements. A small sample high-pressure-torsion-machine was designed in order to perform in-situ diffraction experiments during the deformation process at hydrostatic pressures up to 8GPa in order to follow the strain as well as pressure induced microstructural characteristics of any deformed material. This was possible with the ideal design and equipment at the High-Energy-Materials-Science-beamline at PETRA III in Hamburg. Recent and first results of experiments on HPT-deformed Ni, Ti and BMGs are presented [1].

It is shown in this work that the crystallographic texture can be efficiently used for getting insight into the deformation mechanisms that take place during plastic deformation. The technique is based on the modelling of the 4D nature of the orientation distribution function (ODF) of the grains (3D) which evolves with strain (1D plus). The changes in the texture are more enhanced when the deformation is extremely high, which can be imparted to the material using the various recent severe plastic deformation (SPD) processes. The most relevant effect in SPD is the grain fragmentation process, which has a strong effect on the grain size and shape. By SPD of alloyed metals nano-range grain sizes can be reached (down to 30 nm) by enhancing in this way the role of the grain boundaries (SPD is a top --> bottom process). Alternatively, nano-polycrystals can be constructed using bottom --> up techniques with even smaller grain sizes (by electro-deposition or powder metallurgy). When such materials are deformed, unusual textures develop. It is shown in this work by polycrystal modelling of the texture evolution that the effect of the existence of the large grain boundary surfaces is a change in the operating slip systems when grains are ultra fine (below 500 nm) or nano-sized (below 100 nm). The main effects are: partial slip, nano-twin formation, grain boundary sliding and migration. The overall behaviour of the polycrystal is also changing; initially, when grain size is still large, heterogeneous deformation from grain-to-grain is valid - which requires the use of a self consistent polycrystal model - while for nano grain sizes the polycrystal approaches more the uniform Taylor polycrystal behaviour. The consequence of the Taylor behaviour is a large reduction in the density of geometrically necessary dislocations which is confirmed by EBSD measurements.

Small-scaled materials are used in a broad range of applications, from microelectronic systems to medical devices with a continuous trend towards further down-scaling and function integration. The micro-systems are composed of networks of interfaces separating layers of dissimilar materials with a broad range of chemical, physical and mechanical properties. Interfaces have been recognized as potential sites of failure as a result of incompatibility and thermal mismatch in the multilayered materials. Knowledge of fatigue and degradation behavior and understanding the related micro-mechanism of damage with respect to microstructural characteristics of the constituent materials with focus on their interfaces is a prerequisite for design and fabrication of functional and reliable devices. The common practice for reliability assessment and lifetime estimation of electronic devices are accelerated passive and active thermal cycling tests. In the recent years device manufactures are seeking for highly accelerated and realistic reliability assessment methods to respond to the requirements of the rapidly growing technology and keeping up with market demands. In this context, accelerated isothermal fatigue testing has been introduced as an efficient alternative to conventional thermal procedures. A considerable reduction of testing time is achieved by using dedicated high frequency mechanical fatigue testing set-ups in order to replace the thermally induced strains by equivalent mechanical strains. Based on a physics of failure approach, the relevant failure modes in the material interfaces are induced enabling detection of weak sites of the devices in a very short duration of time. Detailed microstructural investigations and failure analysis provide insights into the micro-mechanism of deformation. On the basis of experimental data and numerical methods, the proposed method is used for prediction of lifetime and delamination growth behavior of small scaled multilayered structures. In this talk, exemplary studies on the application of accelerated isothermal mechanical fatigue testing for lifetime assessment of small scaled interconnects and thin multilayered structures are presented and the advantages and limits of the proposed method is briefly discussed.

Nowadays, it is increasingly understood that the mechanical characteristics of living systems play a fundamental role in their function. Their determination is quite difficult and are required in many applications; for instance, the manufacture of dummies used in the surgical simulation procedures (internal training and learning in continuing education) [1, 2], the manufacture of specialized neo-tissue [3], and the numerical investigation of tissue response to external stimuli. The determination of the mechanical properties of soft biological materials is of great interest for imaging, where these material properties can be used to distinguish healthy and pathological tissues [4]. Mechanical tests are carried out to study the mechanical behavior of biological tissues [5]. This work proposes to use spherical depth sensing indentation experiments for the characterization of soft tissue (cardiac tissue). The tissue dries up quickly and therefore a liquid environment is necessary to perform the experiment. The spherical depth sensing indentation has recently been adapted to operate in such an environment [6]. The present work focuses on the results obtained for cardiac tissue samples. The built-up procedure appear to be effective in a wide range of deformations.

Long-term hydrogen storage experiments are discussed, which were performed on MgH₂ and on the Mg alloy ZK60 following prior Severe Plastic Deformation (SPD). Although SPD processing leads to significant enhancement of hydrogen absorption and desorption rates in both materials, these are not necessarily stable with respect to repeated loading/unloading cycles. Cold Rolled (CR) MgH₂, e.g., shows a reduction of capacity by 30% after 100 cycles. In contrast, in ZK60 (Mg-5Zn-0.8Zr) processed by High Pressure Torsion (HPT), both kinetics and storage capacity are stable for at least 200 absorption/desorption cycles.
Analysis starting from Johnson-Mehl-Avrami theory clearly suggests that in the case of CR-MgH₂, nucleation is followed by growth of extended MgH₂ domains, leading to a gradual deterioration of hydrogen diffusion and storage/release characteristics. In the case of HPT-ZK60, however, practically no further growth occurs subsequent to nucleation, thus allowing for permanently enhanced hydrogen diffusion and stable storage/release properties. These results can be understood in terms of the different density and stability of SPD-induced lattice defects acting as nucleation sites in both materials studied [1].

All magnetically ordered materials exhibit a quantum-mechanic mediated exchange between the electron spins of neighbouring atoms: this means that the electronic structure plays the dominant role. In the case of metallic systems, most important are the 3d-metals and alloys, where the band structure of the 3d-electrons and the position of the Fermi level with respect to the spin-up and down electrons determine the state and magnitude of magnetic ordering. This phenomenon is also responsible for the large magnetic moment in metallic 3d-systems (about 2.2 μB) [1].
Due to the strong direct exchange between the 3d-electrons, most of these metals or alloys exhibit a magnetic ordering temperature above room temperature, which makes them invaluably important for modern techniques. For practical applications, extrinsic properties such as the microstructure essentially determines the magnetic behaviour, especially the shape of the hysteresis loop, and consequently the losses. Examples here are Fe-Si alloys (transformers, generators etc) or new systems such as amorphous and nanocrystalline alloys. In nanocrystalline alloys, where the exchange coupling acts over the grain boundaries, this way reducing the anisotropy and consequently the coercivity [2].
The other important group of magnetic elements are the rare earths (La,...Gd,...Lu). There, the effect of the crystal electrical field on the 4f levels and the coupling between the 4f moments (orbital moment L) on the crystallographic axis, causes high magnetocrystalline anisotropies and/or high values of magnetostriction [3].
Therefore, nowadays, alloys between 4f-elements and 3d-elements are used for providing not only high-quality permanent magnets (such as Sm-Co or Nd-Fe-B) but also high- magnetostrictive systems (such as (Tb,Dy)-Fe).
Within this presentation, the fundamental aspects of magnetism — which limits also the achievable magnetization density — are summarised and discussed. Some aspects of the future development in different magnetic materials will also be discussed.

This work will address the research in the area of micro and nanomagnetism, showing results in artificial magnetic micro and nanostructures for high-density magnetic recording and magnonics. New technological high-density storage systems investigations over the past decades have followed the study of artificial magnetic nanostructures as single storage elements. The reduction of the memory elements' size has been used to increase the storage density [1,2]. We have studied the magnetic behavior of T-shaped magnetic micro and nanostructures, experimentally and by micromagnetic simulations. T-shaped magnetic nanostructures have stable magnetic states resulting from the configurational anisotropy, in which stable magnetic states have been predicted for one single element, allowing the storage of two bits of information. Depending on the direction of the applied field, T-shapes can be prepared in four magnetic states. Magnonics is an emerging research field in which spin-waves are used for information transmission and processing. The data can be encoded either in the amplitude or phase, and the absence of charge transport eliminates Joule losses. Spin-wave propagation is usually done in patterned structures that require the continuous application of an external magnetic field, which jeopardizes its efficiency [3]. Magnetic domain walls as propagation channels have been proposed [4] as they exist in remnant magnetic states. The domain walls act as potential wells confining the spin-waves. We have simulated the spin-wave along 180° walls in permalloy slabs. We show that, up to 2 GHz, spin-waves are strongly confined within the wall. The dispersion relation for the confined waves resembles a magnetostatic-dominated Damon-Eschbach mode [5]. We have fabricated rectangular permalloy structures by electron-beam lithography and obtain Landau configuration reproducibly, as confirmed by Kerr microscopy images. This study is aimed to evaluate the suitability of these spin-waves for magnonics.

Magnetostriction is an important magnetic property of soft magnetic materials, which provides different kinds of applications. Low- and high-magnetostriction materials are of interest. For reducing noise in transformers and electric machines, low-magnetostriction materials are desired. However, for sensors and actuator applications, high-magnetostriction materials are the target. In conjunction with magnetostriction, other magnetic properties need to be suitable for applications such as high permeability and low coercive force.
A review of the most promising materials will be presented. In order to understand the high magnetostriction in Fe-based alloys, the lecture focuses on its microscopic origin while building on microscopic investigations. Low magnetostrictive material Fe-Si will also be discussed. Results of magnetic properties on a new low magnetostrictive alloy, Fe-Ti, will be presented.

Focusing on metallic systems, we consider developments in understanding and exploiting the glassy state that is formed when a liquid is cooled into a solid state without crystallizing, having in mind that: "The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition" [1]. Metallic glasses are of particular interest for several reasons, not just for their excellent mechanical properties. They not only have a multitude of possible applications, but they also open up the possibility of using mechanical workings to change the structure and properties of glass [2], something hardly explored for conventional oxide glasses. While plastic deformation can be expected to create structural effects, it is more surprising that there can be significant effects even well within the (nominally) elastic regime [3,4]. In this talk, we explore the diversity that can be achieved in the metallic glassy state, from very high energy ("rejuvenated") to very low energy ("relaxed" and even "ultrastable") states [5]. We also explore the extent to which directionality (anisotropy) can be induced in metallic glasses [6]. In each case, we examine the potential applications of the properties (structural and functional) that can be induced.

Metallic glasses, also known as amorphous alloys or liquid metals, are relative newcomers in the field of biomaterials. They have gained increasing attention during the past decades, as they exhibit an excellent combination of properties and processing capabilities desired for versatile biomedical implant applications [1].
In the present study, we developed new Ti-based glassy alloys without any harmful additions, with potential for orthopaedic and dental applications. Ti₇₅Zr₁₀Si₁₅ and Ti₆₀Nb₁₅Zr₁₀Si₁₅ glassy alloys were obtained by melt spinning and their crystallization behavior, corrosion resistance, and apatite-forming ability were investigated [2,3]. These compositions are marginal glass formers and cannot lead to bulk glass formation. Upon devitrification on heating, the Ti-(Nb)-Zr-Si glassy alloys exhibit nanophase composite microstructures, which lead to a remarkable improvement of mechanical properties. The corrosion and passivation behavior of the alloys in their homogenized melt spun states in Ringer solution at 37°C in comparison to their cast multiphase crystalline counterparts and to cp-Ti and beta-type Ti-40Nb was studied. All tested materials showed very low corrosion rates as expressed in corrosion current densities icorr<50 nA/cm². Electrochemical and surface analytical studies revealed a high stability of the new alloys passive states in a wide potential range. The addition of Nb does not only improve the glass-forming ability and the mechanical properties, but also supports a high pitting resistance even at extreme anodic polarization. With regard to the corrosion properties, the Nb-containing glassy alloy can compete with the beta-type Ti-40Nb alloy. Simulated body fluid (SBF) tests confirmed the ability for formation of hydroxyapatite on the melt-spun alloy surfaces. All these properties recommend the new glass-forming alloys for applications as wear- and corrosion-resistant coating materials for implants.

This talk will address the general issue of energy production and use, while limiting the consumption of critical raw materials and restraining the impact on the environment that are the pillars of sustainability, which is derived from the framework of this summit series.
The magnetic properties of Nd-Fe-B magnets originate in the intrinsic properties of the hard magnetic Nd₂Fe₁₄B phase (exhibiting large magnetocrystalline anisotropy) [1], but the overall performance of the bulk Nd-Fe-B magnets heavily depend on the material's microstructure, which is determined by the manufacturing route and chemical composition of the alloy [1], [2]. The maximum energy product ((BH)max) of anisotropic sintered Nd-Fe-B magnets is often used as a figure of merit, which is much higher than the (BH)max values of other magnetic materials developed in the past (cobalt magnet steel) and other permanent magnets, that are currently on the market (hard ferrites, alnicos and Sm-Co). For the same performance, less magnetic material is needed, which effectively leads to miniaturization of devices [3].
The disadvantage of sintered Nd-Fe-B magnets is the fact that their intrinsic coercivity (Hci), which is a measure of the magnet's capability to withstand the external demagnetizing fields, especially at high temperatures, heavily depends on the use of heavy rare earth (HRE) elements, dysprosium, and terbium. These elements substitute the Nd atoms in the Nd₂Fe₁₄B phase and adds up to 10 wt. % are common in the high-coercivity magnets [4]. As a result, the magnetocrystalline anisotropy, a property of hard magnetic phases, is increased. But at the same time, the saturation magnetization of the system is lowered due to the antiferromagnetic coupling of the magnetic moments of Dy and Tb atoms with the moments of iron, which weakens the field produced by the magnet. The values of remnant magnetization (Br) and maximum energy product are thus reduced [5]. In addition, the HRE elements are far less abundant than Nd (except in China), and therefore much more expensive [4][6]. In some applications, like traction motors of (hybrid) electric vehicles and electric power steering (EPS) motors, magnets suffer from demagnetization due to the large reverse magnetic fields. Although the standard approach is to use HREs throughout the magnet body to increase its Hci value, certain parts of the magnet are more exposed than others [7][8].
Based on the facts shown above, the purpose of this work is to address the issue of the growing need for critical HRE elements. This was achieved in two ways.
Firstly, nanostructured materials that employ less HREs to achieve high intrinsic coercivity, compared to the microcrystalline materials, were considered for the preparation of the bulk magnets.
Secondly, novel Nd-Fe-B magnets were prepared by using a combination of magnetic powders obtained with one or more of the established manufacturing techniques and condense them into a so-called multicomponent bulk magnet in a fast consolidation step by using a special kind of a hot pressing technique called Pulsed Electric Current Sintering (PECS). By minimizing the process time and using low consolidation temperatures, the magnetic properties of the respective hard magnetic materials were preserved and tailored.
During this study, we optimized the PECS process parameters for each type of the Nd-Fe-B magnetic powders in order to avoid the deterioration of the magnetic properties. We found a suitable combination of magnetic powders with different magnetic properties that can be processed together in a single consolidation step, and we prepared a multicomponent magnet by using a HRE-free and HRE-containing powder. We avoided the diffusion of the HRE element from the HRE-containing into the HRE-free part of the magnet during consolidation.
Based on numerical simulations, we have shown that the demagnetizing fields have significant effects only on certain parts of the magnet that are located near their edges. As a consequence, only those parts need to be protected against demagnetization. Therefore, the highly inventive idea was to develop a magnet with a large volume fraction of its body HRE-free and only using HREs in the exposed parts to significantly improve the performance and to address the issue of the resource efficiency at the same time.

Environmentally friendly, biocompatible, and sustainable materials such as Ti-based alloys and Fe-based nanoclusters or coatings are currently under investigation pointing at specific technological demands, thus being promising as non-toxic implants, drug deliverers, and innovative nano-robotic platforms. This lecture presents computational studies on Ti-based and Fe-based metallic and metallic-hybridic materials, aiming to reveal the electronic origin of the structural, magnetic, and mechanical properties, for the design of materials with predefined properties suitable for new technological applications. The calculations cover different scales, from 'first principles' up to large-scale semi-empirical simulations, always comparing with available experimental data.
As a first example, ab-initio results reveal the electronic rules for the Ti bcc instability that are related to the electronic band structure characteristics along the phonon critical directions and the electronic occupation at the Fermi level. In Ti-based alloys, Nb composition, phase coordination number, and sp dopants enrich these electronic rules. The mechanical stability conditions and the elastic constants predict the TiNb bcc stabilization only for Nb-rich compositions while the directional Youngs modulus along [100] turns out to be smaller than that of bone (about 30 GPa) which makes these compositions most suitable for non-toxic orthopedic implants. This work was supported by the BioTiNet ITN (No. 264635) FP7 Marie Curie project.
The Fe-based nanoclusters and thin coatings with non-magnetic (Cu) or magnetic (Co) substitutions, the Fe surface/edge atoms with Cu first neighbors exhibit the highest magnetic moment of 3.6μ_B ( Fe bcc has 2.1μ_B) for the smallest icosahedral. This moment smoothly decays towards thin film and bulk shape as the size of the cluster increases. Although the Fe-Cu clusters show higher local Fe moment, the average is always highest for the Fe and Fe-Co clusters, due to the difference of d Fe spin up-down electron occupation. These results, supported by SELECTA (No. 642642) H2020-MSCA-ITN-2014 project, could be a basis for the design of environmental sustainable smart alloys with superior magnetic properties.

This lecture reports the changes in hardening and corrosion of biodegradable Mg-Zn-Ca alloys caused by HPT-processing and long-term heat treatments, which have been applied in order to strengthen the alloy and to adapt the Younga's modulus of the alloy to that of the human bone, for suitable application as an biodegradable implant material. The structural changes are represented by the evolution of precipitates as well as of deformation induced defects like dislocations and vacancy clusters. The studies aimed to quantify the individual effects of the structural modifications to strength and to corrosion rate, with the final goal to optimize the alloy for the use as biodegradable implants with respect to mechanical properties as well as corrosion rate [1].
The thermomechanical procedure used in this work follows that of Orlov et al. [2] applied to Mg-Zn-Zr alloy ZK60. Both the precipitates as well as the vacancy clusters achieve strength increases; in case of the latter, the Zn atoms act as trapping sites not only for HPT-induced dislocations but also for vacancies. So far, overall increases of strength of up to 250% were reached. Quantitative estimations show that the vacancy clusters contribute far more to the total strength increase than the precipitates. Furthermore, vacancy concentrations of at most 10-5 cause the hardness increase measured [3]; the experimental results, however, exhibited vacancy concentrations till to even 10-3 which means that a significant part of the HPT-induced vacancies stays single and thus does not contribute to hardening.
The corrosion rate as well as the Younga's modulus remained unchanged during the processing history consisting of both HPT deformation as well as heat treatments, thus making these alloys a very attractive biodegradable material.
This work has been supported by projects J2-7157 of the Slovenian Research Agency ARRS, and I2815-N36 of the Austrian Science Fund FWF.

Studies of magnetic nanoparticle systems have attracted much interest in the past few years, owing to their fundamental interest and technological applications [1]. In particular, the correlation of parameters such as size, morphology, crystalline structure, and shape of the particles with the resulting magnetic properties has been thoroughly investigated, but many questions remain to be answered. Besides the effect of grain size distribution— which strongly affects the magnetic response of the system— there are important factors that need to be controlled, such as the surface of the particles (both roughness and composition gradient), the shape, and the phases formed within the nanograins.
Another crucial point is the role played by magnetic interactions among the magnetic entities. This subject has been extensively studied from both experimental and theoretical approaches, but even now it is not clear how the dipole-dipole interactions can affect the macroscopic magnetic response of the system. Many different, often conflicting models have been applied to explain the experimental data on interacting magnetic nanoparticle systems. Consequently, there has been a considerable discussion about the existence of significant collective effects in magnetic nanoparticle systems, and several speculations regarding a spin-glass-like phase at low temperatures on dipole-dipole interacting systems. With the inclusion of dipolar interactions the problem becomes complex, and it is usually solved by means of some approximation. One of the most used methods to investigate the role of interactions has been Monte Carlo simulations. In addition, novel phenomenological approaches have proposed analytical models that explicitly take into account the correlation arising from the dipolar interactions on nearly superparamagnetic systems.
As a matter of fact, the lack of close-to-ideal samples (with controlled grain size, shape, etc.) hindered more systematic experimental studies. In turn, the absence of perfectly reliable experimental data did not allow a consistent comparison with theoretical models and/or computer simulations.
A brief review on the existing models will be given, and new experimental results on sets of sputtered and chemically grown nanocrystalline samples will be shown. Systematic studies as a function of grain size, distance among magnetic entities will be analysed through the different theoretical models, demonstrating the great importance of dipolar interactions on the magnetic properties of granular systems.

Grain boundary migration is an important phenomenon during hot working of materials. It is key to understanding the microstructural evolution during the deformation process, and is an essential mechanism for microstructural design of materials. This phenomenon of grain boundary migration during hot forming has been a central research area in material science in the last century. It was long assumed that grain boundary migration during cold deformation does not occur. The generation of ultrafine grained and nanocrystalline material by low temperature heavy plastic deformation has been introduced during the last two decades. In order to understand the minimum grain size, which can be achieved by these processes, it becomes quite evident that grain boundary migration plays a key role. A central question of this grain boundary movement is: "What are the driving forces and what controls the resistance against the movement of the grain boundaries at these low temperatures?" Further important points resulting from this question are: "What is the role of thermally activated processes and what is the contribution of stress and strain induced transfer of atoms from one grain to the other?" This presentation will focus on these central questions by analyzing grain boundary movement as a function of deformation temperature, strain rates, strain paths, impurities, and alloying elements. It will be shown that grain boundary movement during heavy plastic deformation at low temperature has a similar importance as in the case of dynamic recrystallization during hot working, only the driving forces are different. Finally, it will be shown that these phenomena of deformation induced grain boundary migration at low temperatures are important in order to understand the strength of ultrafine grained and nanocrystalline materials.

Silver is a soft, precious metal widely used in electronics, medicine, and in the jewellery sector, due to its exceptional properties such as low electrical resistance, antibacterial behaviour, shiny appearance, and resistance to tarnishing. However, final products are usually made of silver alloys to achieve reasonable hardness and strength needed for these kinds of applications. However, alloying is not always the desirable practice, especially in jewellery, as it can reduce tarnishing and corrosion resistance. Therefore, Severe Plastic Deformation is a promising way to improve the mechanical properties [1].
The copper-free silver alloy of the composition Ag 97.2 wt%, In 1.5 wt%, Ge 1.0 wt%, others 0.3 wt% was developed, cast, and cold-drawn. In order to further improve mechanical properties, room-temperature Equal Channel Angular Pressing (ECAP) along with two-step forging (open-die and impression-die forging) and rolling — as two diverse methods of conventional post-deformation — were performed. In this manner, the original grain size of 130 μm was refined to an ultrafine-grained microstructure with mean grain size of 420 nm. Consequently, the combination of ECAP, two-step forging and rolling resulted in outstanding mechanical properties: tensile yield strength of 491 MPa (+355% compared to the as cold-drawn strength), ultimate tensile strength of 550 MPa (+196%), and Vickers hardness of 167 HV1 (+234%). Furthermore, a much more homogeneous hardness distribution over the whole cross-section of the bars was achieved by ECAP.
Contrary to some reports on pure silver [2, 3] both, the microstructure and strength remained thermally stable for at least one year at room temperature as well as for at least 100h and 2h at 100°C and 150°C, respectively.
Thus, ECAP is able to effectively increase the mechanical properties of this lean silver alloy which exhibits desirable tarnishing and corrosion resistance.

Metallic glasses belong to the class of advanced materials, which exhibit mechanical properties, corrosion resistance, and magnetic properties far superior to that of crystalline materials of similar compositions. Rare earth (RE) containing metallic glasses, which hold some extraordinary properties (such as a very low glass transition temperature), however, have not been extensively studied in the past. Due to the complex electronic and magnetic structure induced by the RE elements, their alloys are expected to possess some excellent fundamental properties. The subject of this paper addresses Ce- and Gd-based metallic glasses, which differ upon their magnetic moments and electronic configurations. At room temperature (RT), cerium reveals paramagnetic behavior with a low magnetic moment of 0.6 μB, while gadolinium, on the other hand, shows the transition into the ferromagnetic state just below RT and possesses one of the highest magnetic moments among REs, with 7.5 μB. Electronic structure of cerium has an unusual 4f electron configuration, which fluctuates up to 4 outer electrons depending on its neibourhood, thus giving Ce and its alloys some unexpected physical properties, such as significant volume change or the emergence of a Kondo state. The fundamental differences between Ce and Gd based metallic alloys originate in different electronic and magnetic structure and the goals of the proposed doctoral dissertation are focused to the experimental analysis of structure, thermal analysis, microstructure and magnetic properties of the multicomponent alloys.
Coupling of the fundamental physical and magnetic properties of Ce and Gd, with elements of Al, Fe, and Cu (which by the way are respectively immiscible in each other) is to date unknown. The subject of the proposed talk is to provide fundamental answers and to show a connection between the composition and structure of the alloy and corresponding properties. The purpose here is to investigate the influence of Ce and Gd rare earth (RE) with greatly differing magnetic moments, on the structure, thermal properties, microstructure and magnetic properties of multicomponent Al-RE-Fe-Cu alloys.
Formation and stability of glasses can be traced via differential thermal analysis (DTA) and calorimetry (DSC), which also enable the characterization of transformation kinetics. Via pulsed electric current sintering (PECS), powdered samples can be formed into bulk metallic glasses through the process of thermoplastic consolidation in the vicinity of the glass transition temperature (Tg). Magnetic properties of the glasses are analyzed as a function of temperature and time, via controlled crystallization at a temperature 5°C higher than the crystallization temperature (Tx) and time-varying from several minutes to hours. Detailed structural and microstructural characterization is performed via X-ray diffraction (XRD) and electron microscopy, which encompasses scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
The field of RE-based metallic glasses has not yet been thoroughly investigated concerning the influence of low and high magnetization RE elements on the structure and magnetic properties. It is of fundamental significance to connect the observed magnetic behavior of glasses with their structural features. In this view, particularly interesting is the coupling between the crystalline lattice and magnetic properties since the behavior of short-range ordered amorphous materials is different from long-range ordered crystalline matter. Another parameter that plays a role is the interlinking effect of the Gibbs free energy and transformation kinetics, in the metastable region of the highly viscous glass when TgThe hypothesis is based on the fact that the electronic structure and magnetic moments of Ce and Gd are significantly different. It is expected that consequently the difference will also be reflected in the magnetic behaviour of the corresponding alloys. Due to the metastable nature of the glassy materials, heating above Tx will trigger crystallization. However, since some of these alloys possess a well marked Tg that is lower than Tx, we are offered with a temperature gap, which facilitates the study of the transition from viscous glassy state (at Tg) to the crystalline state commencing at Tx. Experimental parameters are varied through the selection of different annealing temperatures and annealing times. Differences in structure, microstructure, and magnetic properties are anticipated with different amounts of crystallites; however, detailed experimental work is essential to provide acute answers.

Multiple studies in recent years have proven severe plastic deformation (SPD) techniques as a very efficient way to produce nanostructured metals and alloys with significantly improved mechanical and functional properties, with the latter affected by several factors, including ultrafine grains and also the atomic structure of boundaries in resulting nanomaterials [1,2]. This report presents the results of complex studies of the formation of different grain boundaries (low angle and high angle ones, special and random, equilibrium and non-equilibrium with strain-distorted structure, as well as with the presence of grain boundary segregations and precipitations) in nanostructured materials processed using SPD with various regimes and routes. This entails materials with superior multifunctional properties [3,4], i.e. the combination of high mechanical and functional properties (corrosion and radiation resistance, electrical conductivity, etc.) that are induced by grain boundary design. Particular emphasis is placed on the physical nature and the use of multifunctional nanomaterials for their innovative applications in medicine and engineering.

Bulk metallic glasses (BMG’s) combine high strength, hardness and elastic strain limit, they may show good soft-magnetic properties and excellent corrosion resistance as well as high homogeneity and isotropy. The viscous flow workability in the supercooled liquid region makes metallic glasses an excellent candidate for the next generation engineering materials. However, the limited ductility of BMG’s is detrimental for many potential applications. Recent results indicate that structural relaxations on the nanometer scale and their percolation may be involved in the formation of shear transformation zones (STZ) and shear bands that control the ductility of BMG’s. Considerable effects of aging/rejuvenation of BMG’s on their mechanical properties and on structural and dynamic relaxations were reported. Hence, there is fundamental scientific interest in understanding the interplay of structural and dynamic relaxations for equilibrated as well as non-equilibrated BMG’s. In the present study we use in-situ X-ray diffraction to study the structural rearrangements during annealing from 77 K up to the crystallization temperature of CuZr based BMG’s brought out of equilibrium by high pressure torsion performed at cryogenic temperatures. These structural changes are correlated with dynamic mechanical analysis (DMA) and differential scanning calorimetry to determine dynamic relaxations as well as crystallization.

High performance of hydrogen storage requires not only fast absorption/desorption kinetics but also lower operating temperature near ambient pressure. A process of severe plastic deformation through high-pressure torsion (HPT) was applied to two major hydrogen storage metallic materials such as Ti-based and Mg-based systems. Microstructures were well refined by the HPT process, so that nanograins were formed in the materials. For the Ti-based system, an HPT-processed TiFe intermetallic no longer requires pre-activation that limits practical use, as it involves exposure to hydrogen atmosphere under high pressures (>3 MPa) at high temperatures (~700 K). The lack of requirement for pre-activation is because hydrogen diffusion is enhanced through introduction of high densities of lattice defects such as grain boundaries [1]. Furthermore, the HPT-processed TiFe was not deactivated even after storage in air [2]. Application of the HPT process to Mg₂Ni made its hydrogen storage performance improved so that hydrogen absorption is feasible at a reduced temperature of 423 K with faster hydrogen kinetics. This was due to the introduction of high densities of planar lattice defects such as grain boundaries and stacking faults [3].

Thermoelectric materials are able to directly convert thermal energy into electrical energy, and vice versa. The potential of a material for thermoelectric applications is determined by the dimensionless figure of merit, ZT, which is directly proportional to the Seebeck coefficient squared and the temperature, and inversely proportional to the electrical resistivity and thermal conductivity, the latter consisting of an electronic and phonon part. As the Seebeck coefficient, the resistivity and electronic part of the thermal conductivity, are interdependent, one way to enhance ZT is to reduce the phonon part by enhancing the scattering of the heat carrying phonons.
High pressure torsion (HPT) is known as an outstanding technique in the methods of severe plastic deformation (SPD) to produce bulk ultra fine grained and nano crystalline materials, by introducing many grain boundaries as well as defects like dislocations and point defects [1,2,3].
In the first step, HPT-mediated nano crystallization was used to reduce the thermal conductivity of ball milled (BM) and hot pressed (HP) skutterudites. The samples, which were HPT processed after BM and HP, show enhanced ZT values up to a factor of 2 in comparison to BM and HP samples.
In the second step, HPT at elevated temperatures and in argon atmosphere was used to directly consolidate skutterudite powders into a solid. This way, time and energy consuming BM and HP can be avoided [4,5].
In this paper, we compare the grain sizes as well as dislocation densities and structural, physical, and mechanical properties of BM + HP samples with BM + HP + HPT samples, along with HPT produced samples (synchrotron diffraction data, collected from 300 - 800 K, SEM and TEM investigations reveal the modifications).

Global GDP projections for the 21st century have been updated recently. The newly developed shared socio-economic pathways (SSPs) in 2016 represent a set of widely diverging narratives; they show that in 2050, the loss in global GDP between SSP5 will mean Taking the Highway (fossil fuels development) dominated growth path vs. the Taking the Green Road (Sustainability) path, which means a totally renewables originated energy sourcing of 2%. The global GDP is projected to be in the range of $200 to $300 trillion, which could mean a calculated loss of 4 to 6 trillion USD. When considering the total stock market capitalization of fossil fuel companies today is about $5 trillion and the GDP of 2016 was $75.6 trillion USD, the need of a viability analysis on the economic sustainability of fossil-fueled development emerges.
Further, if action is taken to tackle climate change and to keep temperature rise under 2°C, most of the coal, oil, and gas reserves will have stay in the ground. The technological development of renewables-sourced power generation in meeting merchant market requirements is dizzy, backed by ground progress within the latest RES power supply auctions. Lithium and Vanadium Ion batteries, hydrogen storage, and many other storage technologies provide promising progress, whereby settlement of further technological challenges is still needed. This paper addresses how the Renewable Energy Sources stand and perform in the market on merchant basis, and how their future is expected to evolve under free market conditions.

Through severe plastic deformation of metals, defects like vacancies, dislocations, and grain boundaries are generated. These defects are stabilized in metals by segregation of hydrogen and carbon to these defects. Excess vacancies and their clusters are determined by positron annihilation spectroscopy and indirectly by orders of magnitude enhanced diffusion coefficients. Transmission Electron Microscopy (TEM) and Atom-Probe-Tomography (APT) reveal the nanocrystalline microstructure and segregation to grain boundaries. The excess solute reduces defect formation energies and leads to an increased defect density during plastic deformation. This is quantitatively described in the defactant concept [1,2]. According to a theory originating from Gibbs [3], an excess of a different substance at boundaries can reduce their energy, leading to a reduced driving force for their annihilation, the most prominent example of which being the reduction of surface energy by surfactants like foaming agents. This was extended to grain boundaries containing segregated alloying elements, and to general defects like vacancies and dislocations [1,2]. It was proposed that these alloying elements lead to reduced defect formation energies which in turn lead to increased defect densities, the limiting case of which is an amorphization of the structure.

Besides skutterudites and Zintl phases, Half Heusler (HH) alloys are currently the most promising candidates for thermoelectric (TE) devices at elevated temperatures; they can be used in a wide range of temperatures, and their starting materials are abundant and cheap [1]. In particular, the nanostructuring of TiNiSn-based thermoelectric materials - not only by ball-milling but also by preferably system-inherent phase separation - has accomplished multicomponent HH alloys with attractive ZTs for n-type TE materials based on (Ti,Zr)-Ni-Sn. These values could be achieved on the basis of a profound knowledge not only on isothermal phase relations, temperature dependent solubilities, but also on solidification behavior.
The detailed experimental investigation of the constitution of the (Ti,Zr)-Ni-Sn systems, including liquidus projections, Scheil solidification diagrams, as well as CALPHAD modelling, provided the necessary basis for an elaborate synthesis (annealing/hot-pressing) route in order to get a suitable and reproducible microstructure. In addition, exploiting inherent but coherent binodal/spinodal demixing at subsolidus temperatures within the sections TiNiSn-ZrNiSn and TiNiSn-HfNiSn, we were able to achieve for the n-type half Heusler alloy Ti0.5Zr0.25Hf0.25NiSn a ZTmax = 1.5 at 825 K. The demixing is a balanced effect of destabilisation of the solid solution by a positive enthaphy of mixing, compensated by elastic strain energy (coherent binodal) but also by the entropy of mixing. In this respect, the five component thermoelectric material can be considered as a so-called pseudoternary high-entropy alloy system. The experimental data are backed by SEM/TEM analyses as well as by DFT results.

Collagen hydrogels have been expansively used to mimic the extracellular matrix for three dimensional (3-D) tissue engineering applications because of their excellent biocompatibility and biodegradability. But the poor mechanical properties of collagen hydrogel causes substantial shrinkage during 3-D cell culture [1,2]. In this study, we fabricated a collagen hydrogel reinforced with lyophilized polysaccharide nanofibers (Col/NFs) to reduce the shrinkage of collagen hydrogels. The viscoelastic properties of Col/NFs were measured by using a rheometer. Viability and proliferation of human mesenchymal stromal cells (hMSCs) cultured in the hydrogel, were evaluated using Live and Dead assay, and MTT assay, respectively. Shrinkage rates of Col/NFs hydrogel after hMSCs culture were measured for 15 days. The viscose and elastic modulus of Col/NFs hydrogels were increased with increase of NFs concentration. The proliferation of hMSCs in of Col/NFs hydrogel was slower than that of collagen hydrogel. The viability of hMSCs in both hydrogels was more than 95%. Shrinkage of Col/NFs hydrogel during hMSCs culture were significantly reduced by used NFs. Further, osteogenic differentiation of hMSCs was confirmed using von kossa staining. In conclusion, shrinkage controlled Col/NFs hydrogels can be used bone tissue engineering.

The development of new functionalized materials is one of the key goals in science and technology. Since the discovery of fullerenes, carbon nanotubes and graphene, carbon-based material have attracted peak interest because of its versatility and the outstanding electronic and mechanical properties. In addition to these now well-known compounds, other types of carbon material have been found recently in the form of graphene quantum dots and carbon nanodots, which offer new alternatives to the previously mentioned examples. The key to a successful systematic development of new compounds is the possibility of chemical functionalization by means of covalent and non-covalent derivatization.
In the present talk, two aspects in the wide range of applications indicated above are discussed. One is the doping of polycyclic aromatic hydrocarbons (PAHs) by nitrogen with application to the important class of zethrenes [1] as one example. High-level quantum chemical calculations have been performed for the computation of the electronic structure of the different PAHs investigated. The calculations demonstrate clearly how drastic enhancements to the biradicaloid character and reductions of the excitation energy gaps can be achieved by different doping positions.
In the second part of the talk, a first approach to the quantum chemical calculation of luminescence properties of carbon nanodots [2,3] is presented. These properties are of great interest since they can be utilized in bioimaging applications, for dye-sensitized solar cells and supercapacitors. The great advantage of the carbon nanodots for the purpose of bioimaging is their low toxicity and excellent biocompatibility. The current challenge is to move their blue fluorescence to the red, which can be achieved by chemical doping. In our investigations, excimer formation and charge transfer in the nanodots have been modeled by means of stacked dimers of pyrene, coronene and circum-coronene sheets. Doping has been performed by replacing carbon atoms by nitrogen atoms or by substituting hydrogen atoms by halogen at the periphery of the PAHs. The absorption and emission spectra have been calculated, which show a characteristic dependence on the doping positions.

Incremental ECAP, unlike conventional ECAP, works in small steps in which deformation and feeding are divided between two different tools acting asynchronously. Incremental processing reduces forces and allows processing in relatively large billets. The major advantage of this technique is that the specimens are in the form of plates with a rectangular shape, which makes them suitable for further processing, e.g. via deep drawing, which may extend the range of potential applications of UFG materials.
Plates of 1xxx and 3xxx series aluminum were processed by Incremental ECAP and evaluated in terms of microstructure, mechanical properties, anisotropy and formability. It was demonstrated that incremental ECAP is one of the most effective severe plastic deformation methods in terms of grain size refinement and high angle grain boundaries formation. Eight passes brings about grain size reduction to below 500 nm and very high fraction of high angle grain boundaries of about 80%. The plates exhibit in planar and through thickness isotropy which manifest by the independence of YS, UTS and R -values on the testing direction and fairly uniform distribution of microhardness across thickness. Such properties were attributed to randomized texture developed during processing and uniform microstructure with ultrafine equiaxed grains in all three plate's planes. The values of the parameters describing ability for deep drawing are very promising, as r values only slightly decrease with I-ECAP passes while they became independent on testing direction. This indicates that although the processed plates are slightly prone to wall thinning (typical for aluminum alloys), they are resistant to earing formation, which is one of the main technological problem in deep drawing. The combination of isotropic parameters, enhanced mechanical strength, and suitable ability to deep drawing may yield attractive products with a considerable potential for further forming.

Periodic ripple and nanoripple patterns are generated at the surface of amorphous steel after femtosecond pulsed laser irradiation (FSPLI). Formation of such ripples is accompanied by the emergence of a surface ferromagnetic behavior, which is not initially present in the non-irradiated amorphous steel. The occurrence of ferromagnetic properties is due to the FSPLI-induced surface devitrification of the glassy structure to form ferromagnetic (a-Fe and Fe₃C) and ferrimagnetic [(Fe,Mn)₃O₄ and Fe₂CrO₄] phases located in the ripples. The generation of magnetic structures by FSPLI turns out to be one of the fastest ways to induce magnetic patterning without the need of any shadow mask. Furthermore, the adhesion force, wettability and nanomechanical properties of the surface treated by FSPLI are also studied and compared to those of the as-cast amorphous alloy. These effects are of interest for applications (e.g., biological, magnetic recording, etc.).

The high compressive stresses imposed by high pressure torsion allows plastic deformation of machine chips and metallic particles until close contact is reached. The severe torsion straining provides the condition for "self-welding" of these particles, creating a continuous metallic matrix. This technique has been used to produce aluminum matrix composites [1, 2] and has also been used to consolidate magnesium particles [3]. Processing magnesium by high pressure torsion is especially interesting since it has been shown that it leads to exceptional ductility [4]. The present work describes the use of high-pressure torsion to consolidate magnesium with reinforcement phases into metal matrix composites. The microstructure of the composite was evaluated by scanning electron microscopy and the mechanical strength was estimated by microhardness testing. It is shown that a dense microstructure is attained after several turns of torsion, and the hardness of the processed composite is higher than the pure metal base. The present work shows that it is possible to improve magnesium strength by introducing hard phases during high pressure torsion consolidation of particles.

Materials performance depends on the microstructure. Different electron microscopy techniques characterize microstructures almost perfectly and comprehensively, but there are still issues hidden from the scrutiny of electron microscopy: residual and internal stresses [1,2]; load partitioning [1-3]; strain fields [4]; very small lattice defects [5]; bulk average quantitative density numbers [6-8]; and others. Diffraction peak broadening or line profile analysis proves to be a valuable tool complementing electron microscopy for characterizing and quantifying these issues [9]. Modern line profile analysis procedures are based on physically modeled profile functions of different microstructural elements [7,9-11]. In a recent development, the Marquard-Levenberg analytical method has been combined with a special statistical Monte-Carlo procedure, providing global optimization of the physical parameters of microstructure properties [12]. We shall cover the correlation between TEM or X-ray determined dislocation densities in plastically deformed single crystals [1,2,6], in high pressure torsion deformed Ta and Nb [13]; the long range internal stresses in dislocation cell-structures [1,2,6,14], lath martensite steels [3], or the planar defect structure in high temperature sintered SiC [15]. It will be shown how the synergy between electron microscopy and line profile analysis adds to a more comprehensive characterization of substructures. The synergy between the two techniques renders a more complete understanding of both the qualitative and quantitative properties of microstructure elements in terms of dislocation types and densities, dipole character of different dislocation arrangements, internal stresses, or planar defect densities [1-15].