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The chemical composition and structural state of advanced alloys are the decisive factors in optimum biomedical performance. This contribution presents unique Ti-Zr-Ge metallic glass thin-film compositions fabricated by magnetron sputter deposition targeted for nanocoatings for biofouling prevention. The amorphous nanofilms with nanoscale roughness exhibit a large relaxation and supercooled liquid regions as revealed by flash differential scanning calorimetry. Ti\textsubscript{68}Zr\textsubscript{8}Ge\textsubscript{24} shows the lowest corrosion (0.17 \textmu A cm\textsuperscript{\textminus2}) and passivation (1.22 \textmu A cm\textsuperscript{\textminus2}) current densities, with the lowest corrosion potential of \textminus0.648 V and long-range stability against pitting, corroborating its excellent performance in phosphate buffer solution at 37 {\textdegree}C. The oxide layer is comprised of TiO\textsubscript{2}, TiO\textsubscript{\emph{x}} and ZrO\textsubscript{\emph{x}}, as determined using X-ray photoelectron spectroscopy by short-term ion-etching of the surface layer. The two orders of magnitude increase in the oxide and interface resistance (from 14 to 1257 {\textOmega} cm\textsuperscript{2}) along with an order of magnitude decrease in the capacitance parameter of the oxide interface (from 1.402 x 10\textsuperscript{\textminus5} to 1.677 x 10\textsuperscript{\textminus6} S s\textsuperscript{n} cm\textsuperscript{\textminus2}) of the same composition is linked to the formation of carbonyl groups and reduction of the native oxide layer during linear sweep voltammetry., 34 Pages, 5 Figures, 4 Tables, 13 Supplementary Figures

A composite of two different medium entropy alloys (MEAs, i.e., CoCrFeNi and AlCoCrFe) was synthesized using ball milling and spark plasma sintering. The composite microstructure contains a homogenous distribution of fcc and bcc phases with submicron-sized grains and exhibits excellent microstructural and phase stability even after 100 h heat treatment at 800 °C. The composite provides a combination of high compressive strength, adequate plastic strain, and multiple strain-hardening stages at room temperature. This first exploratory study on a MEA composite can be used as a template to other systems and illustrates the feasibility of combining two or more MEAs.

The viscoelastic behavior of four different bulk metallic glass (BMG) systems, i.e., Cu46Zr46Al8, Cu44Zr44Al8Co4, Cu44Zr44Al8Hf4, and Cu44Zr44Al8Co2Hf2, is investigated concerning its deformation-mode dependence via dynamic mechanical analysis (DMA) in 3-point bending (TPB), tension, and torsion modes. At temperatures below the glass transition, the considered BMGs deform primarily elastic, and the mechanical response is independent of the testing frequency, whereas, in the glass transition region, the viscoelastic component dominates. Crystallization decreases the viscoelastic contribution, whereas plastic deformation leads to an increase in atomic mobility for all three deformation modes. Compared to tension and torsion, TPB is found to be more sensitive to dynamic mechanical stress. TPB generates a complex stress state in the matrix and can thus introduce substantial variations in loss modulus. Structural analyses carried out by transmission electron microscopy and X-ray diffraction confirmed the amorphous nature of the base composition and structural changes when heated to the intermediate peak temperature observed at 743 K for the TPB mode. Compared to Cu46Zr46Al8, 4 at. pct Co addition in the Cu46−x\2Zr46−x\2Al8Cox amorphous alloy leads to a glass showing relatively higher thermomechanical stability around its glass transition. This study provides evidence for the enhancement of the mechanical properties of CuZr-based BMGs at elevated temperatures by microalloying.

The influence of the crystallization temperature and the pressure on the crystallization kinetics, structure and compression strength of γ-polypropylene was investigated. Samples were produced in a custom-made high-pressure crystallization cell and characterized by differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). It could be shown that the strength is mainly affected by the mean lamellar thickness. The strength of γ-PP is at least 40% higher than α-PP at the same mean lamellar thickness. This confirms the hypothesis that the arrangement of non-parallel chains restricts the number of possible slip systems so that almost no mobile dislocations are generated. The mode of nucleation is only slightly affected by the crystallization pressure. The Avrami coefficient is n = 2.5 ± 0.1 at the beginning of crystallization and largely independent of pressure.

High-entropy composites (HECs) were subjected to severe straining by high-pressure torsion (HPT) to evaluate their influence on the evolution of microstructure and deformation behavior. Severe straining leads to a homogeneously strained microstructure and inhomogeneous micro-shear bands in these HECs. Nb addition in HECs varies the microstructure from single phase to eutectic, and the Vickers microhardness in HPT HECs increases to 7.45 GPa. Nb addition up to x = 0.80 in as-cast HECs improves the strength of these materials at the expense of its plasticity. Nevertheless, severe straining provides a better combination of strength and ductility without sacrificing its plasticity. Such improvement in properties is attributed to the evolved microstructural features, formation of “transformation-shear bands (T-SBs)” and “deformation-shear bands (D-SBs)” at severe straining. This assures the homogeneous deformation by shear banding and suggests that shear banding is the dominant deformation mechanism when the lamellar spacing becomes saturated upon severe straining.

Recent nanoindentation experiments have shown that in semi-crystalline polymers, strain bursts emerge during creep experiments. A shortcome of nanoindentation is that due to the inhomogeneous stress field, a critical stress for the onset of strain bursts cannot be determined, and the resolution of the method seems to be limited. Since the strain bursts in polymers are in the nm range, an extremely high resolution in deformation measurement is necessary. Such a resolution is provided by modern solid state rheometers having a resolution

Polyetheretherketone (PEEK) is a high-performance semi-crystalline thermoplastic polymer with outstanding mechanical properties, high thermal stability, resistance to most common solvents, and good biocompatibility. A high temperature thermally induced phase separation technique was used to produce PEEK foams with controlled foam density from PEEK in 4-phenylphenol (4PPH) solutions. Physical and mechanical properties, foam and bulk density, surface area, and pore morphology of foamed PEEK were characterized and the role of PEEK concentration and cooling rate was investigated. Porous PEEK with densities ranging from 110 to 360 kg/m

The structure of matter at the nanoscale, in particular that of amorphous metallic alloys, is of vital importance for functionalization. With the availability of synchrotron radiation, it is now possible to visualize the internal features of metallic samples without physically destroying them. Methods based on computed tomography have recently been employed to explore the local features. Tomographic reconstruction, while it is relatively uncomplicated for crystalline materials, may generate undesired artifacts when applied to featureless amorphous or nanostructured metallic alloys. In this study we show that X-ray diffraction computed nanotomography can provide accurate details of the internal structure of a metallic glass. We demonstrate the power of the method by applying it to a hierarchically phase-separated amorphous sample with a small volume fraction of crystalline inclusions, focusing the X-ray beam to 500 nm and ensuring a sub-micrometer 2D resolution

This contribution reveals ultra-high corrosion resistance of high entropy alloys (HEAs), i.e. Ti$_{20}$Zr$_{20}$Nb$_{15}$V$_{15}$Hf$_{15}$Ta$_{15}$ of 1.85 µm yr$^{–1}$ in alkaline environment, adverting their use for battery/fuel cell components. Formation of several nanometers passive oxide layer confirmed by scanning transmission electron microscopy accounts for corrosion resistance which increases with TiOx content. Cathodic Tafel slope of 67 mV dec$^{–1}$ and large transfer coefficient of 0.82 obtained for Ti$_{20}$Zr$_{20}$Nb$_{20}$V$_{20}$Ta$_{20}$ suggest its use for hydrogen electrocatalysis. High amounts of hydrogen storage, 1.7 wt% in Ti$_{25}$Zr$_{20}$Nb$_{15}$V$_{15}$Ta$_{20}$, were confirmed by gas-solid reactions. This HEA also has high corrosion resistance in acidic and saline environments ideal for coatings and surgical tools/implants.

Advanced engineering materials 23(11), 2100159 (2021). doi:10.1002/adem.202100159 special issue: "Neutrons and Synchrotron Radiation - Unique Tools for the Characterization of Materials", A down-sized high-pressure torsion device is developed to be used in an INSTRON deformation machine available at the High Energy Materials Science beamline at PETRA III. This setup allows to obtain synchrotron diffraction patterns in situ during severe plastic straining. Two different materials are studied: in pure Ni, the dislocation density and coherently scattering domain size are analyzed; in NiTi shape memory alloy, amorphization and a reverse martensitic phase transformation are investigated. The in situ experiments facilitate the characterization of the microstructural evolution of these materials depending on uniaxial loading, hydrostatic pressure, and torsional strain., Published by Deutsche Gesellschaft fu��r Materialkunde, Frankfurt, M.

The effects of severe plastic deformation (SPD) by means of high pressure torsion (HPT) on the soft magnetic properties of the iron-based metallic glass Fe$_{73.9}$Cu$_{1}$Nb$_{3}$Si$_{15.5}$B$_{6.6}$ are investigated. With this procedure, it has been possible for the first time to consolidate and deform this high-strength material with a minimum of cracks. X-ray diffraction, differential mechanical and differential scanning analyses, as well as optical and scanning electron microscopy were carried out for characterization of crystallization phenomena and crack formation. For magnetic properties, minor loop hysteresis measurements were done because of their high sensitivity for magnetic structures. Significant influences of HPT-processing on the coercivity as well as on magnetic anisotropy are found and discussed in detail.

This study investigates differences in the deformation mechanisms between room temperature (296 K) and cryogenic temperatures (77 K) and their advantages for low temperature formability in alloys EN AW 1085, EN AW 5182 and EN AW 6016. Compared to room temperature behaviour, tensile tests showed an overall increase in yield strength, ultimate tensile strength and uniform elongation with differences among the principal alloy types. In general, the improved mechanical properties result from higher strain hardening rates at lower temperatures. The application of an extended Kocks-Mecking approach showed a significant reduction of the dynamic recovery and suggested higher dislocation densities upon cryogenic deformation. This was confirmed via in-situ synchrotron experiments, which also reveal a higher proportion of screw dislocations. Moreover, kernel average misorientation maps from electron backscattered diffraction and in-situ cryogenic deformation in a transmission electron microscope displayed a more uniform dislocation arrangement with a reduction of slip lines and less highly misaligned areas after deformation at lower temperatures. Supported by a detailed characterization of the microstructure and its dislocation structure, the associated fundamental mechanisms we reveal, which are at the origin of the exceptional improvement in mechanical properties, are extensively discussed., Materials Science and Engineering: A, 795, ISSN:0921-5093, ISSN:1873-4936

With the discovery of bulk metallic glasses (BMGs), there has been considerable interest in understanding their mechanical behavior. In spite of these previous observations on the relation between plastic deformation of metallic glasses and their diffusion behavior, a detailed understanding on the diffusion of BMGs is still unexplored. We evaluated the contribution of deformation-induced structural transformations (elastic, anelastic, viscoplastic or viscoelastic responsive and plastic strain) on the diffusion of Zr-based bulk metallic glasses in as-cast, elastostatically stressed and plastically deformed states. Experimental investigations of the diffusion process and the elemental distributions in the glassy alloy were performed following plastic deformation by multiple cold rolling and elastostatic cyclic compression, respectively. We compared the vacancy model and the transition state model to verify the diffusion mechanism in the deformed bulk metallic glass. The diffusion of tracer atoms, i.e., Fe, in the bulk metallic glass is affected by viscoelastic responsive strain governing the transition-state model. In contrast, the diffusion of constituent atoms, i.e., Ti, Zr, in the bulk metallic glass is dominantly affected by plastic strain governing the vacancy model. The results reveal that the diffusion behavior of bulk glassy alloys can be changed by variation of the constituent elements and applying different strain modes upon deformation.

The aim of this study is to investigate the effects of cryogenic and room temperature pre-deformation on subsequent artificial ageing of Al&ndash, Mg&ndash, Si alloys. Naturally aged and pre-aged samples were strained to 5%, 10% and 20% at RT (25 &deg, C) and under liquid nitrogen, and artificially aged at 185 &deg, C. Pre-deformation generally increases ageing kinetics for both the naturally aged and pre-aged alloys, which increase in proportion to the degree of pre-deformation, and which are slightly more pronounced for the cryogenic condition. The peak strength is constant, except for when a low degree of pre-deformation is used, in which case it is slightly reduced. Cryogenically deformed samples show an increased strength and hardness, compared to samples pre-deformed at RT, when subjected to an equal magnitude of strain. This difference is reduced during artificial ageing. Synchrotron measurements reveal that this behaviour can be linked to the greater dislocation density, which is not completely recovered even after prolonged ageing at 185 &deg, C.

A composite of two different medium entropy alloys (MEAs, i.e., CoCrFeNi and AlCoCrFe) was synthesized using ball milling and spark plasma sintering. The composite microstructure contains a homogenous distribution of fcc and bcc phases with submicron-sized grains and exhibits excellent microstructural and phase stability even after 100 h heat treatment at 800 °C. The composite provides a combination of high compressive strength, adequate plastic strain, and multiple strain-hardening stages at room temperature. This first exploratory study on a MEA composite can be used as a template to other systems and illustrates the feasibility of combining two or more MEAs.

Ti-based metallic glass matrix composites (MGMCs) with a composition of Ti50Zr20V10Cu5Be15 (atomic percent, at. %) exhibit excellent tensile ductility and distinct work-hardening capability. A dislocation pile-up model (DPM) has been established to elaborate the dislocation motion near the yield point and to theoretically derive a linear Hall-Petch-like relationship between the yield strength, σ, and the inverse square root of the diameter of dendrite arms, d−1/2. The materials constant, k, in the present Hall-Petch-like relationship can be calculated on the basis of the pile-up model, and is very close to the experimental value. The hardness variation in the dendrites and the strengthening effect from unloading-reloading tests prove the reasonability of the DPM during tension. The Hall-Petch-like relationship is verified for a variety of MGMCs, whose plastic deformation is only dominated by dislocation motion. Mean-field theory (MFT) has been first utilized to build a relationship between the critical diameter of dendrites, dc, and the composition in MGMCs with the similar atomic percentages of low solubility elements. By tuning the composition, one can universally scale the Hall-Petch-like relationship, and accurately predict the yield strength of such in-situ MGMCs.

The multiplication and interaction of self-organised shear bands often transform to a stick-slip behaviour of a major shear band along the primary shear plane, and ultimately the major shear band b...

In this work, the microstructure and mechanical properties of rapidly solidified Ti50−x/2Ni50−x/2Hf x (x = 0, 2, 4, 6, 8, 10, and 12 at.%) and Ti50−y/2Ni50−y/2Si y (y = 1, 2, 3, 5, 7, and 10 at.%) shape memory alloys (SMAs) were investigated. The sequence of the phase formation and transformations in dependence on the chemical composition is established. Rapidly solidified Ti-Ni-Hf or Ti-Ni-Si SMAs are found to show relatively high yield strength and large ductility for specific Hf or Si concentrations, which is due to the gradual disappearance of the phase transformation from austenite to twinned martensite and the predominance of the phase transformation from twinned martensite to detwinned martensite during deformation as well as to the refinement of dendrites and the precipitation of brittle intermetallic compounds.

Transformation-induced plasticity in CuZr-based bulk metallic glass (BMG) composites opens up a new perspective for the design of ductile BMG composites. In this work, rapid and partial crystallization of BMGs is proposed to tailor microstructures of ductile BMG composites. During the early crystallization stage, the precipitation of B2 CuZr crystals in the Cu42Zr42Al10Co6 BMGs is growth-controlled at low or high heating rates after having passed through a nucleation-dominated temperature region. Abundant nucleation is beneficial for the uniform precipitation of B2 crystals in the glassy matrix. Compared with annealing processes at slow heating, the degree of the free volume annihilation could be reduced to some content by employing a high heating rate. The microstructures of CuZr-based BMG composites can be effectively tuned by changing rapid annealing parameters, which enhances the ductility of the resulting BMG composites. This approach proves to be efficient for the development of ductile metastable alloys and composites. Keywords: Metallic glasses, Crystallization, Annealing, Composites, Deformation

Short term sub-glass transition annealing controls the structural reordering and nanocrystallization of CuZr − based bulk metallic glasses (BMGs). Using this method, 5 times higher resistance against strain softening as confirmed by three-point bending tests is attained. Homogenously dispersed nanoparticles in sizes of 20–50 nm accounts for the remarkable shifts and peak formations on reciprocal space together with the diffraction spots observed on 2D diffraction pattern. Real-space pair distribution function analysis reveals noticeable changes in peak shapes and positions correlated with the changes in short- to medium-range ordering. The differences in the partial nearest neighbor numbers upon annealing mark the dominant Zr − Zr pair to diminish whereas the Cu − Cu pair becomes prominent, hinting that Cu diffusion is mainly responsible for structural reordering and formation of new phases. The pursued study using hard X-ray synchrotron radiation reveals important aspects of structural changes preceding nanocrystallization, which in turn enhances the mechanical performance in BMGs.

The temperature-dependent atomic structural evolution of a Zr 64.13 Cu 15.75 Ni 10.12 Al 10 metallic glass is studied by in-situ high-energy X-ray diffraction in the temperature range of 79–553 K. The interatomic distance in the first nearest neighbor shell increases with decreasing temperature, while the interatomic distance in other atomic shells decreases. This decrease in the interatomic distances causes volume shrinkage and an increase in the strength of the metallic glass. The volume shrinkage can be quantitatively described by the Varshni function. The structural information is helpful for deeply understanding of the origin of the rejuvenation of metallic glasses at the cryogenic temperatures.

The thermal stability of deformation-induced dislocations was investigated in polypropylene (PP) during annealing by means of in-situ X-ray diffraction using synchrotron radiation. The samples were cold rolled to high strains (e = 1.2) in order to introduce a high number of dislocation lattice defects and immediately stored in liquid nitrogen afterward. Then, stepwise annealing was applied from −180 °C up to above the melting temperature (165 °C) while synchrotron X-ray diffraction patterns were recorded at each step. The resulting low noise, high angular resolution diffraction patterns were evaluated using multireflection X-ray profile analysis (MXPA), revealing parameters such as the dislocation density and the thickness of the crystalline lamellae as a function of the annealing temperature. Two significant decreases of the dislocation density were found at annealing temperatures of about 10 and 85 °C. These distinct changes in the dislocation density could be identified as the mechanisms of β- and α-re...

The formability difference between good and marginal glass-forming systems is investigated by micro-surface patterning of hierarchical features using thermoplastic net-shaping (TPN). For each alloy, a remarkable change in the flow behaviour is observed as the applied force along with the pressing time and temperature are optimized. The flow kinetics of glassy alloys with different glass-forming abilities is best described by the formability parameter S, which is defined by the ratio of the width of the supercooled to undercooled liquid region (Tl − Tg)/(Tx − Tg). Reproducible micro-engineered surfaces with high uniformity can be established by controlled TPN processing.

Flash Joule-heating was applied to the Cu47.5Zr47.5Al5 metallic glass for designing fully crystalline metastable nanocomposites consisting of the metastable B2 CuZr and low-temperature equilibrium Cu10Zr7 phases. The onset of crystallization was in situ controlled by monitoring resistivity changes in the samples. The effect of heating rate and annealing time on the volume fraction of the crystalline phases and mechanical properties of the nanocomposites was studied in detail. Particularly, an increase of the heating rate and a decrease of the annealing time lead to a lower number of equilibrium Cu10Zr7 precipitates and an increase of tensile ductility. Tailoring of these non-equilibrium microstructures and mechanical properties may not be possible unless one starts with a fully glassy material that opens new perspectives for designing metastable nanomaterials with unique physical properties.

The development of bio-compatible materials for bone implants bone healing is one of the key research areas in biomaterials. In this paper, composites of polyether-ether-ketone (PEEK) (a bio-compatible polymer) and hydroxyapatite (HA) were synthesized using thermal process, The qualities of the composites were analyzed with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) for characterizing the nature of stress and bonding. The morphological study of the PEEK-HA composites were studied through Scanning electron microscopy. The compressive nature of the composites as well as raw materials was observed based on XRD data with internal lattice-strain analysis. The temperature-modulated differential scanning calorimetry (TM-DSC) and conventional differential scanning calorimetry (DSC) were performed for analyzing the crystallization process. The TM-DSC showed that both reversing and non-reversing processes were active during the crystallization between 160 °C–330 °C. However, a higher residual time of PEEK at elevated temperatures tends to facilitate polymer degradation and spread the crystallization process over a broader temperature range. Addition of HA particles provided heterogeneous nucleation sites for crystallization but also reduced the mobility of polymer chains. The combination of enhanced nucleation rate, reduced chain mobility and polymer degradation processes together lead to a wide range of crystallinity in PEEK-HA composites.

Journal of alloys and compounds 784, 1323 - 1333 (2019). doi:10.1016/j.jallcom.2019.01.063, For bulk metallic glasses (BMGs) structural anisotropy has been studied for many years, but usually for small creep strains, rather than for large strains associated with the viscoplastic flow. In this study, the structural modifications in the short-to-medium range order of $\mathrm{Zr_{55}Cu_{30}Al_{10}Ni_{5}}$ BMG is deliberated for the first time upon simultaneous high-pressure torsion (HPT) and in-situ annealing around the glass transition temperature $(T_{g})$. The changes are evaluated in terms of hardness by microindentation, thermal properties by differential thermal calorimetry, chemistry by energy dispersive X-ray, and structural properties by synchrotron X-ray diffraction and transmission electron microscopy. A remarkable increase of the glass transition temperature and the absence of the shoulder of the crystallization peak along with remarkable softening and shear thinning reveals that even at $T_g$ the material gains flow characteristics because of the extreme pressure applied. A clear shift towards smaller wave vector $Q$ in the peak positions of the partial distribution function $G(r)$ , and reconfiguration of the bonding between $Zr - Zr$ and $Zr - Cu$ atomic pairs extracted from the deconvolution of the radial distribution function $RDF(r)$ are observed with changing the processing temperature. The findings give insight into the atomic and nano-scale modifications in BMGs due to high-pressure torsion at different temperatures which would be essential to tune the intrinsic properties of BMGs to attain the desirable hardness and thermal stability for a specific application., Published by ScienceDirect, Amsterdam [u.a.]

Shear transformation zone (STZ) remains the fundamental unit to explain plastic flow in metallic glasses (MGs). Although STZs have been known and characterized for decades now the morphological and dynamical characteristics of STZs are not fully understood yet. Here, simulating athermal quasistatic shearing processes, the atomic-level mechanisms underlying elastic and plastic deformation in MGs are disclosed. Given the highly heterogeneous nature of glassy materials and the related rugged energy landscape the activation of STZs is observed from an early level of elastic deformation until the final shearing stage. The STZs identified within the elastic and plastic ranges have similar fingerprints but different magnitude and dynamics. Long-range overlapping STZ fields constrain atomic rearrangements and limit quantifying structure-dynamics correlations that explains the difficulty in establishing an ideal structure-property relationships for MGs.

The effect of different degrees of plastic deformation on the frequency dependence of coercive field and losses in NO Fe–(3 wt%)Si was investigated measuring hysteresis loops on a ring-shaped core over a frequency range of 0.5–1000 Hz. The investigation was performed under sinusoidal and triangular external field $H(t)$ . Although $H(t)$ induce a similar quasi-sinusoidal magnetic induction (similar hysteresis loops), the loop area is smaller for that measured by triangular applied field resulting in smaller magnetic losses. The coercive field and the total losses of all samples increase with increasing frequency; however, the influence of frequency becomes gradually smaller with plastic deformation. The total losses that increase due to plastic deformation at low frequencies become at high frequencies smaller in deformed samples than in an undeformed material. A similar behavior was found in the frequency dependence of the coercivity. Due to a periodic quasi-sinusoidal $B(t)$ , the losses were analyzed using the concept of loss separation. While the quasi-static (hysteresis) loss increases, classical and excess losses decrease with increasing deformation.

The microstructure, mechanical properties, and dynamic mechanical properties of the various intermetallic-reinforced in-situ Al–Al3Ni eutectic composites were investigated for different compositions with increasing Cu content. The microstructure changes from a nanofiber-like Al3Ni-reinforced composite structure to a various intermetallic-reinforced composite structure. Moreover, the addition of Cu induces changes in the phases composing the composite, especially the kind of intermetallic compounds, such as Al3Ni, Al3NiCu, Al7Ni4Cu, and Al2Cu. According to these microstructural evolutions, the mechanical strength under compressive loading is drastically enhanced from about 200 to 1200 MPa, and a typical strength-ductility tradeoff, e.g., the plasticity is reduced from more than 70% to less than 2% with the strength increase, is also observed. The precipitation behavior which can lead to improving further strengthening was observed employing in-situ TEM, Vickers hardness, and DSC investigations. The damping properties are also improved with increasing Cu content, especially at high-temperatures; but regrettably, the maximum operating temperature is decreased. We will discuss the origin of the enhanced strength and propose a route to obtain composites with optimized mechanical and damping properties for application in different fields.

Thermal sensitive сoiled artificial muscles with a large muscle stroke (87%) based on oriented ultrahigh molecular weight polyethylene fibers were created. The storage modulus and the recovery stress were used as indicators to determine the optimal conditions for the orientation process of the UHMWPE fibers. The working mechanism of the coiled artificial muscles was discussed in terms of a one-way shape memory effect (SME).

Nanoindentation creep experiments on polyethylene were carried out in order to investigate dislocation-based plastic deformation mechanisms. Similarly to that reported in a recent paper (Li J and Ngan AHW, Scr Mater 62:488–491 (2010)), discrete deformation processes occur during nanoindentation creep tests which again seem to arise from the break-off of dislocation avalanches. That interpretation is supported from systematic studies of the effect of variations of the loading rate and of the applied load on the number and the height of bursts. © 2015 Society of Chemical Industry

In-situ X-ray diffraction was applied to isotactic polypropylene with a high volume fraction of !-phase (!-iPP) while it has been compressed at temperatures below and above its glass transition temperature Tg. The diffraction patterns were evaluated by the Multi-reflection X-ray Profile Analysis (MXPA) method, revealing microstructural parameters such as the density of dislocations and the size of coherently scattering domains (CSD-size). A significant difference in the development of the dislocation density was found compared to compression at temperatures above Tg, pointing at a differ- ent plastic deformation mechanism at these temperatures. Based on the individual evolutions of the dislocation density and CSD-size observed as a function of compressive strain, suggestions for the deformation mechanisms occurring below and above Tg are made.

The aim of the paper was to use recent experimental dislocation data for the development and testing of a dislocation mediated strength model based on that introduced by Scogna and Register for semicrystalline polymers. It is shown that the model can successfully describe measured and evaluated data of high density polyethylene (PE-HD) on the flow stress as function of strain rate and temperature. Similar coincidences of model fit with experimental yield stress data from literature for polypropylene and polyethylene-ethylenemethacrylic acid co-polymers (E/MAA) were found which suggests prevailing of dislocation mediated plasticity mechanisms also in these materials. It also turned out that two parameters of the model – namely the dislocation density and the lamella size – are not determined by the molecular chemistry but by the conditions of processing and/or sample preparation. Therefore the model allows for a reliable estimation of the dependence of the yield stress on these conditions.

Samples of γ -iPP were prepared by crystallization at elevated pressures using a specially designed pressure chamber. The γ -phase was subsequently investigated by dedicated in-situ X-ray diffraction experiments during deformation using synchrotron radiation. Parameters such as the crystallinity, the density of dislocations and the coherently scattering domain size (CSD-size) which in polymers corresponds to the lamella size, have been evaluated as a function of the strain by means of the multi-reflection X-ray line profile analysis (MXPA). Compared to the results for the α -phase, those for the γ -phase reveal an enhanced strength and a strongly reduced evolution of the dislocation density. The latter is explained in terms of a model comprising the formation of misfit dislocations.