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This study reports on the ultralubricity of a high-temperature resilient nanocomposite WS2/a-C tribocoating. The coefficient of friction of this coating remains at around 0.02 independently of a thermal treatment up to ∼500 °C, as confirmed by high-temperature tribotests. Moreover, the coating annealed at 450 °C keeps exhibiting a similar ultralubricity when cooled back down to room temperature and tested there, implying a tribological self-adaptation over a broad temperature range. High-resolution TEM observations of the tribofilms on the wear track unveil that WS2 nanoplatelets form dynamically via atomic rearrangement and extend via unfaulting geometrical defects (bound by partial climb dislocations). The (002) basal planes of the WS2 nanoplatelets, reoriented parallel to the tribo-sliding direction, contribute to a sustainable ultralubricity. The declining triboperformance beyond 500 °C is associated with sulfur loss rather than the transformation of WS2 into inferior WO3 via oxidation as suggested earlier. This self-adaptive WS2/a-C tribocoating holds promise for a constant ultralubrication with excellent thermal performance.

High entropy alloys (HEAs), offering a multi-dimensional compositional space, provide almost limitless design opportunities surpassing the frontiers of structural materials development. However, an in-depth appraisal of the fundamental materials physics behind strengthening in HEAs is essential in order to leverage them to achieve greater flexibility in application oriented materials design. This viewpoint paper concentrates on issues regarding inherent compositional fluctuations in HEAs and corresponding impact on strengthening is highlighted. In particular, metal physics based design criteria in multi-phase HEAs are discussed and comparisons between multi-phase and single-phase HEAs are drawn., Scripta Materialia, 187, ISSN:1359-6462, ISSN:1872-8456

The authors regret that in Fig. 1b some data points of s/w ratio were not correctly aligned with the x-axis of target-to-substrate distance. The corrected Fig. 1b is shown below. [Figure presented] The authors would like to apologise for any inconvenience caused.

Surfaces of polycrystalline ferritic Fe–Cr steel with grain sizes of about 13 µm in diameter were investigated with surface sensitive techniques. Thin oxide layers, with a maximum thickness of about 100 nm, were grown by oxidation in air at temperatures up to 450°C and were subsequently characterized using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and atomic force microscopy. Correlative microscopy was applied, which allows for element-specific depth profiles on selected grains with a particular crystal orientation. A strong correlation between the grain orientation and the thickness of the oxide layer was found. The sequence in the oxidation growth rate of ferritic Fe–Cr steel crystal planes is found to be {011} > {111} > {001}, which is unexpectedly opposed to known Fe-based systems. Moreover, for the first time, the Cr/Fe ratio throughout the oxide layer has been determined per grain orientation. A clear order from high to low of {001} > {111} > {011} was detected.

In this research, in situ high-temperature electron backscattered diffraction (EBSD) mapping is applied to record and analyze the migration of the α/γ interfaces during cyclic austenite–ferrite phase transformations in a medium manganese steel. The experimental study is supplemented with related 3D phase field (PF) simulations to better understand the 2D EBSD observations in the context of the 3D transformation events taking place below the surface. The in situ EBSD observations and PF simulations show an overall transformation behavior qualitatively similar to that measured in dilatometry. The behavior and kinetics of individual austenite–ferrite interfaces during the transformation is found to have a wide scatter around the average interface behavior deduced on the basis of the dilatometric measurements. The trajectories of selected characteristic interfaces are analyzed in detail and yield insight into the effect of local conditions in the vicinity of interfaces on their motion, as well as the misguiding effects of 2D observations of processes taking place in 3D.

WSxC(H) coatings were deposited on single crystal silicon(100) wafers by magnetron co-sputtering and reactive sputtering at various target-substrate distances. Upon increasing the distance, the stoichiometric S/W ratio increases from 0.51 to 1.89. Also, the porosity of coatings gradually augments and a columnar microstructure tends to form. Preferential sulfur resputtering rather than contaminations primarily accounts for the low S/W ratio. TEM reveals randomly oriented WS2(002) platelets in the WSxC coatings when deposited at a large distance, which is supported by XRD. The composite coatings exhibit a decreasing hardness and elastic modulus with increasing target-substrate distance. The triboperformance is strongly affected by the coating composition, the target-substrate distance and the testing environment. Cross-sectional TEM of formed tribofilms reveals an obvious reorientation of WS2(002) basal planes parallel to the plane of sliding, leading to an ultralow friction.

Relative density is a major factor governing the mechanical properties of (nano-)porous materials. In nanoporous gold, a correlation between relative density and the ligaments aspect ratio was recently reported as the result of a meta-study that measured hundreds of published images. The effects of ion-irradiation on nanoporous structures however are not yet well explored. We irradiated samples of nanoporous gold of two different initial characteristic lengths with 30 keV Ga+ ions. The degree of densification was found to be higher for the samples with finer ligaments and to proceed by thickening of ligaments besides the reduction in length also observed in the coarser samples. The proportionality between relative density and aspect ratio in the ion irradiated samples was found to agree well with the previously reported results from specimens of various processing and coarsening routes. The present study points at ion irradiation as a tool to tune these parameters in nanoporous structures and suggests that the correlation between relative density and aspect ratio may be involved in the volume contraction observed during the formation of nanoporous samples by dealloying. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

This paper reports a three-dimensional (3D) stochastic bicontinuous micron-porous graphene foam (3D-MPGF) developed as lightweight binder-free current collectors for sulfur cathodes of lithium-sulfur batteries. 3D-MPGF is synthesized by a facile process that originally combines the synthesis of porous metals by the reduction of metallic salts and chemical vapor deposition (CVD) growth of graphene in a continuous route. 3D-MPGF presents micron-porous structure with both interconnected tubular pores and nontubular pores of sizes from hundreds nanometers to several microns. By adjusting CVD time, the thickness of graphene wall is tunable from few atomic layers to ten layers. Raman results prove a high crystalline of 3D-MPGF. Attributed to the low density and high quality, 3D-MPGF can be used as promising lightweight binder-free current collectors. The 3D-MPGF loaded with S of 2.5 mg cm−2 exhibited an ultrahigh initial capacity of 844 mAh g−1 (of electrode), and maintain at 400 mAh g−1 after 50 cycles at 0.1C (167 mA g−1). With increasing the loading of S, the electrodes present higher areal capacities. When the loading of S is 13 mg cm−2, the areal capacity of 3D-MPGF/S reaches 5.9 mAh cm−2 after 50 cycles at 0.1C. The use of 3D micron-porous graphene foam proves considerably enhanced gravimetric capacity densities (of overall electrode), which can be a direction not only for batteries but also for other energy storage devices.

Self-healing tribocoatings are being developed for aerospace applications to improve the lifetime andreduce the surface maintenance of components in motion. Here the tribo-induced self-healing behaviourof a WS 2 /a-C tribocoating has been evaluated for the first time by in-situ scanning electron microscopy(SEM) to evaluate the mechanisms of damage and self-recovery. In-situ SEM imaging reveals that scratchdamage results in coating brittle fracture and spalling, and that Hertzian pressure affects healing rateat early stages of sliding. WS 2 nanocrystallites, formed via atomic rearrangement at flexural interfaces,enable the healing of irregular damages and congruently offer superlubrication in vacuum. Such damagecontrol in tribo-service may make flawless coatings an unnecessary prerequisite in tribo-applications.

This study reports on the ultralubricity of a high-temperature resilient nanocomposite WS2/a-C tribocoating. The coefficient of friction of this coating remains at around 0.02 independently of a thermal treatment up to ∼500 °C, as confirmed by high-temperature tribotests. Moreover, the coating annealed at 450 °C keeps exhibiting a similar ultralubricity when cooled back down to room temperature and tested there, implying a tribological self-adaptation over a broad temperature range. High-resolution TEM observations of the tribofilms on the wear track unveil that WS2 nanoplatelets form dynamically via atomic rearrangement and extend via unfaulting geometrical defects (bound by partial climb dislocations). The (002) basal planes of the WS2 nanoplatelets, reoriented parallel to the tribo-sliding direction, contribute to a sustainable ultralubricity. The declining triboperformance beyond 500 °C is associated with sulfur loss rather than the transformation of WS2 into inferior WO3 via oxidation as suggested earlier. This self-adaptive WS2/a-C tribocoating holds promise for a constant ultralubrication with excellent thermal performance.

The development of three-dimensional aperiodic energy storage devices is in part impeded by the lack of appropriate aperiodic templates that can withstand the thermal conditions required to deposit energy storage materials within their void space. Herein, the feasibility of an aperiodic three-dimensional architecture for energy storage is demonstrated for the first time by constructing a tricontinuous conductor-insulator-conductor (CIC) nanocapacitor on an aperiodic nanoporous gold scaffold. To accomplish this, the scaffold was characterized using in situ small-angle X-ray scattering (SAXS) during exposure to a thermal environment, revealing that its microstructure eventually stabilizes after undergoing a phase of rapid coarsening, indicating a departure from the 1/4 time-dependent power-law coarsening behavior usually observed at the early stage of the coarsening process. Using this stability regime, we created the CIC by intentionally precoarsening and stabilizing the scaffold before depositing two dissimilar metal oxide films in its void space by atomic layer deposition. Current-voltage characteristics and electrochemical impedance spectroscopy measurements revealed that the un-optimized 3D CIC outperformed its 2D counterpart by μ4× in terms of capacitance. This proof-of-concept device will pave the way to the development of aperiodic three-dimensional energy storage systems with enhanced energy and power densities.

Al0.7CoCrFeNi high entropy alloy (HEA) with a microstructure comprising strain free face-centered cubic (FCC) grains and strongly deformed sub-structured body centered cubic (BCC) grains was subjected to correlative nanoindentation testing, orientation imaging microscopy and local residual stress analysis. Depending on the geometry of BCC-FCC interface, certain boundaries indicated appearance of additional yield excursions apart from the typically observed elastic to plastic displacement burst. The role of interfacial strengthening mechanisms is quantified for small scale deformation across BCC-FCC interphase boundaries. An overall interfacial strengthening of the order of 4 G P a was estimated for BCC-FCC interfaces in HEAs. The influence of image forces due to the presence of a BCC-FCC interface is quantified and correlated to the observed local stress and hardness gradients in both the BCC and FCC grains.

The current review outlines the size-dependent plastic behavior of high-entropy alloys (HEAs) and the underlying deformation mechanisms. Particular focus is laid upon the influence of microstructural design on the small-scale deformation characteristics. The role of defect types as carriers of plasticity is appraised and correlated with the frequently observed mechanical behavior peculiar to the breed of HEAs. Deformation response is classified on the basis of mechanical testing techniques probing intrinsic (nanoindentation techniques) as well as extrinsic size (micro/nanopillar compression) effects. The mechanisms of incipient plasticity and serrated flow behavior in HEAs are discussed. Furthermore, the role of interfaces between crystallographically dissimilar lattices on small-scale deformation behavior in these alloys is assessed. The article provides a clear overview of the existing HEA research in this avenue as well as the critical knowledge gaps that need to be addressed.

Residual stress measurements of thin films are common practice in device technology and are extremely important in particular for the characterization of thin film coatings. A largely ignored stress contribution is the difference in coefficient of hygroscopic expansion between the coating and substrate. This paper presents a rather novel approach to accurately evaluate the residual stress and coefficient of hygroscopic expansion of strongly curved specimens. Silicon-containing plasma polymer coatings with different carbon contents were deposited using hollow cathode arc discharge based PECVD. Samples of different layer composition were produced comprising silicon-containing plasma-polymer layers with a high carbon concentration and more ""inorganic"" SiO2 like layers with lower carbon concentration. All coatings show a compressive stress state. The highest stress was measured in the coating with the highest carbon content (239 ± 6 MPa) and decreases to 94 ± 31 MPa at lower carbon contents. Variation of the humidity showed that all coatings expand under influence of increasing relative humidity. The most inorganic coatings exhibits the highest expansion coefficient of 29.2 ± 2·10−6 (% r.h.)−1. The results obtained were compared with the results from contact angle measurements. An increase in the hygroscopic expansion corresponds with an increasing hydrophilicity of the coatings.

Ion-induced bending phenomena were studied in free-standing nano-sized Al cantilevers with thicknesses in the range of 89-200 nm. The objective is to present a predictive and useful model for the fabrication of micro- and nano-sized specimens. Samples were irradiated in a Tescan Lyra dual beam system with 30 kV Ga+ ions normal to the sample surface up to a maximum fluence of similar to 2 x 10(21) m(-2). Irrespective of thickness, all samples bent initially away from the Ga+ beam; as irradiation proceeded, the bending direction was reversed. The Al cantilever bending behavior is discussed in terms of depth-dependent volume change due to implanted Ga atoms, radiation-induced point defects and interstitial clusters. A kinetic model is designed which is based on a set of rate equations for concentrations of vacancies, interstitial atoms, Ga atoms and clusters of interstitial atoms. The bending crossover is explained by the formation of sessile interstitial clusters in a zone beyond the Ga+ penetration range. Model predictions agree with our experimental findings.

In this work, large-area graphene-based carbon films were synthesized through a fast and low-temperature method. The processing route is illustrated on a free surface of Ni catalyst film by vacuum thermal processing of amorphous carbon. Key in the novel approach is that the synthesis is done at low temperatures, i.e. below 350 °C, and within a time as short as 1 min. The nucleation and growth of graphene on the free surface of nickel and along the interface between Ni film and SiO2 substrate are investigated by using a thin film Ni-C-Ni sandwiched structure on a SiO2/Si substrate. Raman spectroscopy demonstrates that the graphene-based carbon films consist of graphitic carbon rich of defects. HR-TEM observations reveal that the graphene-based carbon film grown on the top free surface is composed of thin multilayer graphene segments (3–6 atomic layers) and thick multilayer graphene segments (more than atomic 10 layers), covering the entire surface of Ni film over a large area. Growth parameters such as growth time, growth temperature and carbon/Ni ratio are reported in detail for a control of graphene growth kinetics. The results point at several attractive strategies for the facile synthesis of graphene-based carbon films for industrial applications. Keywords: Graphene film, Growth behavior, Low temperature, Nickel, Microscopy

Au(I) complexes are studied as precursors for focused electron beam induced processing (FEBIP). FEBIP is an advanced direct-write technique for nanometer-scale chemical synthesis. The stability and volatility of the complexes are characterized to design an improved precursor for pure Au deposition. Aurophilic interactions are found to play a key role. The short lifetime of ClAuCO in vacuum is explained by strong, destabilizing Au–Au interactions in the solid phase. While aurophilic interactions do not affect the stability of ClAuPMe3, they leave the complex non-volatile. Comparison of crystal structures of ClAuPMe3 and MeAuPMe3 shows that Au–Au interactions are much weaker or partially even absent for the latter structure. This explains its high volatility. However, MeAuPMe3 dissociates unfavorably during FEBIP, making it an unsuitable precursor. The study shows that Me groups reduce aurophilic interactions, compared to Cl groups, which we attribute to electronic rather than steric effects. Therefore we propose MeAuCO as a potential FEBIP precursor. It is expected to have weak Au–Au interactions, making it volatile. It is stable enough to act as a volatile source for Au deposition, being stabilized by 6.5 kcal/mol. Finally, MeAuCO is likely to dissociate in a single step to pure Au.

A detailed microstructural evaluation was executed on the crystallographic texture as well as the mechanisms for nucleation, phase transformation, and grain growth in a Al0.7CoCrFeNi high-entropy alloy. The microstructure and crystallographic orientations were characterized by electron backscatter diffraction, and the chemical composition variations by energy-dispersive X-ray spectroscopy. The cast Al0.7CoCrFeNi alloy started in the BCC phase and partially transformed into the FCC phase. It was found that the Pitsch orientation relationship (OR) dominates the nucleation mechanism of the FCC phase; however, deviations with respect to the Pitsch OR are observed and are attributed to the differently sized atoms forming an ordered B2 phase in the alloy causing lattice distortions. The dual phase BCC–FCC microstructure contains FCC Widmanstätten plates oriented parallel to the {110}BCC planes of the parent grain. It was found that the crystal orientation distribution after the BCC–FCC phase transformation is confined and is explained as a product of the governing mechanisms.

Amorphous metallic glass Cu47Ti35Zr11Ni6Si1 was investigated by load-control nanoindentation experiments using the cube corner indenter tip over a wide range of loading rates. The indentation hardness was calculated using different methods either from the loading curves or indent area. Pop-in events were observed on the loading part of the indentation curves mainly at lower rates of loading. Instantaneous plastic deformation decreases with increasing loading rate according to a power law. At high loading rate the instantaneous deformation is suppressed by continuous plastic deformation and no well-developed pop-ins are observed. The morphology of shear bands in the pile-up area of indents showed no correlation with the pop-in event population of the nanoindentation curves and the loading rate.

The adhesion between carbon fiber-reinforced polymer (CFRP) and titanium parts can be improved by laser surface texturing before gluing them together. Here, a pulsed Nd:YAG laser was employed before bonding of the textured surfaces using an epoxy paste adhesive. To investigate the influence of the laser parameters, the roughness of the surfaces were characterized and correlated to the wettability, by measuring the contact angles of water droplets. Scanning electron microscope (SEM) characterization was also performed showing that under careful conditions, the fiber structure could be maintained. Tensile tests were performed to evaluate the influence of the laser treatment parameters on the joining efficiency. The lap-joint tensile strength tests presented the best results when the titanium surfaces were treated using 5.03 x 10(-3) J pulses and the CFRP sample treated with 5.03 x 10(-4) or 5.03 x 10(-3) J or even using a virginal CFRP surface. Using a virginal CFRP surface, the critical load of fiber delamination was increased and as a consequence the tensile strength attains the highest level of 8.2 MPa.

A correlative method based on electron back scattered diffraction and focused ion-beam-digital image correlation slit milling technique was used to quantitatively determine spatially resolved stress profiles in the vicinity of grain boundaries in pure titanium. Measured local stress gradients were in good agreement with local average misorientation and experimentally calculated geometrically necessary dislocation densities. Stress profiles within few hundred to thousand nanometers near the grain boundary display a local minimum, followed by a typical Hall-Petch type variation of "one over square root of distance". The observed trends allude to local stress relaxation mechanisms active near grain boundaries. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The effects of magnesium aluminum silicate (MAS) glass on the thermal shock resistance and the oxidation behavior of h-BN matrix composites were systematically investigated at temperature differences from 600 degrees C up to 1400 degrees C. The retained strength rate of the composites rose with the increasing content of MAS showing a maximum value at the 60 wt% MAS. Compared with the original strength, the retained strength of the specimen after thermal shock increased to 77% (T=1000 degrees C). The strengthening effect of MAS and the surface microstructural evolution of composites are responsible for the improved thermal shock resistance. Surface oxidation of the composites during the thermal shock process plays a positive role in enhancing the retained strength by self-healing cracks and the appearance of the compressive stress. The oxide layer also acted as a thermal barrier to decelerate the actual thermal stress. Furthermore, this dense layer also improved the oxidation resistance of h-BN matrix composites by prevent diffusion of oxygen. These results indicated that short-term surface oxidation during thermal shock process is favorable to the enhancement of the thermal shock resistance of BN-MAS composite ceramics.

Over the past decade, high entropy alloys (HEAs) have transcended the frontiers of material development in terms of their unprecedented structural and functional properties compared to their counterpart conventional alloys. The possibility to explore a vast compositional space further renders this area of research extremely promising in the near future for discovering society-changing materials. The introduction of HEAs has also brought forth a paradigm shift in the existing knowledge about material design and development. It is in this regard that a fundamental understanding of the metal physics of these alloys is critical in propelling mechanism-based HEA design. The current paper highlights some of the critical viewpoints that need greater attention in the future with respect to designing mechanically and functionally advanced materials. In particular, the interplay of large compositional gradients and defect topologies in these alloys and their corresponding impact on overall mechanical response are highlighted. From the point of view of functional response, such chemistry vis-à-vis topology correlations are extended to novel class of nano-porous HEAs that beat thermal coarsening effects despite a high surface to volume ratio owing to retarded diffusion kinetics. Recommendations on material design with regards to their potential use in diverse applications such as energy storage, actuators, and as piezoelectrics are additionally considered., Metals, 10 (2), ISSN:2075-4701

This study investigates the self-healing capacity of a WS2/amorphous carbon (a-C) tribocoating. It is found that prenotches up to 45 µm wide in the WS2/a-C coating surface can be completely healed under the stimulus of sliding operations. The in situ tribotest of 100, 500, 2000, and 6000 laps confirms a dynamic filling of tribofilms that patch the voids and prenotched damages. The stabilized coefficient of friction (CoF) remains at an ultralow value down to 0.02, independent of the prenotched damage at the top of coating. The sites of notched damage in fact act as lubricant reservoirs to accumulate the otherwise “wasted” debris, which are restored as a superlubricant by the sliding operation. High resolution transmission electron microscopy reveals that WS2 (002) nanoplatelets in the healed notch are parallel to the top coating surface but conformal to the coating/notch interface. The patchy tribofilm holds excellent promise for the self-repair of damages in the field of tribology.

In general, fundamental understanding of radiation resistance of high surface density nanoporous materials and nanoporous coatings is severely lacking. In this contribution ion-induced bending phenomena are studied in free-standing nanoporous Au cantilevers with thickness in the range of 100 to 200 nm. Experiments were performed in a Tescan Lyra dual beam system with Ga+ ion irradiation normal to the sample surface up to a maximum fluence of ~3 × 1019 m−2. Cantilevers bend towards the incident ion beam. It was found that the sensitivity of nanoporous Au samples to radiation-induced bending is substantially higher in comparison to the solid bulk counterparts. The process is described in terms of ion-induced coarsening of the structure top layers, which generates a volume contraction responsible for the bending moment. Therefore it is concluded that radiation-induced coarsening/sintering leads to negative swelling. Radiation-modified effective Young's modulus of the top layers was shown to influence essentially the fluence dependence of bending curvature. Model predictions agree well with our experimental findings showing that inhomogeneous radiation-induced coarsening of nanoporous structure results in bending and that nanoporous materials are less suitable for coatings in nuclear applications under the test conditions.

This paper shows a study on the variation of the flow ratio between oxygen and Hexamethyldisiloxane (HMDSO) in a hollow cathode arc PECVD process. Dynamic deposition rates were measured between 300 and 500 nm * m/ min. The deposited plasma polymer films were analyzed using visible light spectroscopy, X-ray photo -electron spectroscopy (XPS), X-ray reflectivity (XRR), Fourier -transformed infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and water vapor transmission rate (WVTR) measurements. The deposited samples were compared to a reactively sputtered SiO2 thin film. By increasing the oxygen to HMDSO flow ratio, the chemical, density and optical properties of the coating approached the sputtered Si02 film. However the permeation barrier of the SiO2 film only shows a slight improvement over that of the bare PET substrate. The organic coating with high power and low oxygen flow, which was deposited with a deposition rate of 450 nm * m/min, approached the barrier of the sputtered SiO2 thin film with a WVTR of 0.16 g/(m' day). 2016 Elsevier B.V. All rights reserved.

Plastic deformation after indentation of the metallic glass Cu47Ti35Zr11Ni6Si1 at different loading conditions was examined. Discontinuities on the loading curves were observed, the magnitude of which depends on the loading rate. The presence of these discontinuities is influenced by the precise shape of the indentation tip. At lower loading rates and using a cube corner indenter tip the discontinuities on the loading curves are more pronounced. An increase of the loading rate tends to diminish instantaneous plastic deformation as appear by pop-ins. Using a Berkovich type indenter tip the plastic deformation is more steady. It is concluded that the final morphology of the pile-up area strongly depends on the geometry of the indenter tip, whereas no correlation between discontinuities in the loading part of the indentation curve and the formation of shear band patterns was observed.

An amorphous metallic ribbon of Fe40Ni40B20 was used for in-situ observation of the crack propagation and shear band formation during tensile tests. Prior to the tensile tests, two holes (with different positions with respect to the tensile axis) were made by laser ablation as stress concentrators. The nucleation and propagation of shear bands on the ribbon surface during tensile tests were analysed with scanning electron microscopy (SEM). At room temperature inhomogeneous plastic deformation of amorphous alloy occurs via the development of primary and secondary shear bands. The influence of the different loading geometry on the topology of shear bands and crack propagation was studied.

Jules Verne stated more than 145 years ago that water will be the coal of the future [1]. Indeed, hydrogen, a highly abundant substance on Earth in the form of water, is a promising energy carrier for producing zero-emission electricity upon reaction with oxygen using fuel cell technology. There are still many scientific and engineering challenges that need to be addressed before Jules Verne’s dream can become true, however. Two of these challenges include hydrogen production from water and hydrogen storage. In this talk, I will present our work on direct hydrogen generation by hydrolysis of nanoporous aluminum in pure water to feed a 2.4 kW PEM fuel cell stack, which in turn can be used to power a low speed electric vehicle. The possibility to make nanoporous aluminum from secondary aluminum and the advent of carbon-free primary aluminum from Elysis [2,3] could make hydrogen production by hydrolysis of aluminum with pure water a promising alternative to hydrogen production by electrolysis of water. References: [1] Ryabchuk, V. K., Kuznetsov, V. N., Emeline, A. V., Artem’ev, Y. M., Kataeva, G. V., Horikoshi, S., & Serpone, N. (2016). Waterwill be the coal of the future-the untamed dream of Jules Verne for a solar fuel. Molecules, 21(12), 1–20. https://doi.org/10.3390/molecules21121638 [2] Corsi, J. S., Fu, J., Wang, Z., Lee, T., Ng, A. K., & Detsi, E. (2019). Hierarchical Bulk Nanoporous Aluminum for On-Site Generation of Hydrogen by Hydrolysis in Pure Water and Combustion of Solid Fuels. ACS Sustainable Chemistry and Engineering, 7, 11194–11204. https://doi.org/10.1021/acssuschemeng.9b00481 [3] ELYSIS. Retrieved from https://www.alcoa.com/global/en/what-we-do/elysis/.

Electron back-scatter diffraction (EBSD) technique, commonly used to study the microstructural characteristics of materials, was employed for the investigation of the surface damage induced through ultra-short laser pulses. Single-crystal silicon surface was irradiated with an Ytterbium-doped YAG (Trumpf-TruMicro 5050) laser source generating laser pulses of 6.7 ps duration, a 1030 nm wavelength and linear polarization. The laser fluence level was set to values lower than the single-pulse modification threshold of the material. The laser pulses were delivered on the surface at conditions of lateral displacement, i.e. a train of laser pulses with a partial overlap (laser track). This approach made it possible to investigate the early stages of modification of the surface. Scanning electron microscope equipped with a field emission gun (Philips XL30 SEM FEG) and EDAX-TSL EBSD system was used for inspection of the surface modifications initiated with pulsed laser radiation. Depth of the generation of back-scattered electrons at different acceleration voltages of the primary beam was estimated by the use of Monte-Carlo simulation. Trajectories of primary and back-scattered electrons in a flat Si surface were generated at an angle of 74° from the surface normal, which is the angle used for the EBSD observations. High sensitivity of EBSD signal allows an estimate of the depth and intensity of the laser induced damage to the crystal lattice. It is found that the thickness of amorphous layer increases gradually with a distance from the feature center. The similarity of surface damage profiles observed at different accelerating voltages of the primary beam indicates that the damage is formed via a gradual crystal damage accumulation in subsurface layer and via the formation and growth of an amorphous layer from the surface.

The continuous growth in energy production from non-renewable resources in order to meet the ever-increasing energy demand has given rise to serious environmental issues and moving toward renewable energy resources is necessary. Heterogeneous catalysts play a key role in the conversion of renewable resources into fuels and chemicals. The performance of heterogeneous catalysts is directly linked to their surface area, since the number of catalytic sites as well as the activity of each catalytic site increase with increasing effective footprint area of a catalyst. Therefore, nanoporous heterogeneous catalysts are very attractive, owing to their high internal surface areas and high density of active sites generated by curved internal surfaces. The overall catalytic performance of nanoporous heterogeneous catalysts can reach orders of magnitude higher than that of planar catalysts counterparts. This paper reviews recent progress toward the applicability of three-dimensional bulk nanoporous metals and their composites in (electro-)catalytic conversion of renewable resources into fuels and value-added chemicals. The primary focus is given to metal-based materials fabricated through dealloying. Dealloyed nanoporous metals and their composites can be used either directly as high-performance (electro-)catalysts, or indirectly as three-dimensional bulk current collectors along with poorly conducting electro-catalyst materials. Limitations of these material systems such as cost, scalability, and long-term stability in-service are discussed.

This paper reports a versatile template-free method based on the hydrogen reduction of metallic salts for the synthesis of nanoporous Ni and alloys. The approach involves thermal decomposition and reduction of metallic precursors followed with metal cluster nucleation and ligament growth. Topological disordered porous architectures of metals with a controllable distribution of pore size and ligament size ranging from tens of nanometers to micrometers are synthesized. The reduction processes are scrutinized through X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The formation mechanism of the nanoporous metal is qualitatively explained. The as-prepared nanoporous Ni was tested as binder-free current collectors for nickel oxalate anodes of lithium ion batteries. The nanoporous Ni electrodes deliver enhanced reversible capacities and cyclic performances compared with commercial Ni foam. It is confirmed that this synthesis method has versatility not only because it is suitable for different types of metallic salts precursors but also for various other metals and alloys.

The electron-induced decomposition of cisplatin (cis-Pt(NH3)(2)Cl-2) was investigated to reveal if ammine (NH3) ligands have a favorable effect on the purity of deposits produced from metal-containing precursor molecules by focused electron beam induced deposition (FEBID). Scanning electron microscopy showed that cisplatin particles of different sizes react violently during electron irradiation. In particular, faceted particles of a few mu m in size started to boil, became spherical and subsequently degraded. Energy-dispersive X-ray spectroscopy gave evidence for the formation of nearly pure platinum and a decrease of the chlorine content. Nitrogen, however, was not detected, pointing to an efficient and rapid removal of NH3. In contrast, PtCl2 particles do not degrade under comparable conditions, demonstrating that the ammine ligand plays an important role in the reduction of cisplatin to pure platinum. The fast release of NH3 ligands under electron exposure was confirmed by high resolution electron energy loss spectroscopy, focusing in particular on low-energy electrons as produced in high amounts during the FEBID process. Finally, FEBID experiments using cisplatin adsorbed from the gas phase onto a surface produced amorphous deposits. In contrast to the decomposed cisplatin particles, these deposits had a chlorine content of about 50 at. %. Only after extensive irradiation in a transmission electron microscope was this chlorine content reduced and were crystalline particles obtained. In conclusion, using NH3 as ligand in metal containing FEBID precursors can favor the formation of pure metal deposits, but its effectiveness depends on the precise experimental conditions.

Transmission electron backscatter diffraction (t-EBSD) was used to investigate the effect of dealloying on the microstructure of 140-nm thin gold foils. Statistical and local comparisons of the microstructure between the nonetched and nanoporous gold foils were made. Analyses of crystallographic texture, misorientation distribution, and grain structure clearly prove that during the dealloying manufacturing process of nanoporous materials the crystallographic texture is enhanced significantly with a clear decrease of internal strain, whereas maintaining the grain structure.

Nanoindentation and thermomechanical experiments on three types of metallic glasses with different glass forming ability were carried out. The nanoindentation behaviour at room temperature was associated with the creep at elevated temperatures. Different discontinuity populations and their shape observed on the nanoindentation loading curves were compared with morphology of plastic deformed indent regions. The influence of the differences in thermal stability of studied alloys on the nanoindentation in these alloys were studied as well.

This contribution to the Festschrift for Professor Jing Zhu concentrates on in-situ electron microscopy, a topic which is key in her scientific work. In particular this paper delineates the possibilities of utilizing in-situ transmission electron microscopy to unravel size effects in the structure-property relationship. We have focused on in-situ compression, tension and cyclic fatigue experiments on non-crystalline metallic materials, also called metallic glasses (MG). In-situ quantitative compression tests revealed intrinsic and strong size effects of taper-free metallic glass nanopillars inside a transmission electron microscope (TEM) on different MG compositions. The deformation is defect-nucleation-controlled in larger pillars but becomes propagation-controlled in smaller pillars. A unique increase in strength and strain hardening was observed for smaller sized specimens in tension which is different compared to compression experiments with the same MG compositions. Under cyclic loading a very interesting new phenomenon was observed of increasing deformability depending on the number of cycles and size. The increase in deformability increases with increasing diameter whereas the number of cycles to reach half of the peak stress is decreasing with increasing diameter. The proposed experimental technique of loading and unloading cycles opens a new route to increase the ductility of metallic glasses.

In the present study, the effect of resistance spot welding scheme (i.e. single and double pulse welding) on the mechanical behaviour of resistance spot-welded DP1000-GI steel is investigated. It is shown that double pulse welding at low welding current decreases the maximum cross-tension strength and mechanical energy absorption capability of the welds. The factors that lead to the lower mechanical performance of double pulse welds are scrutinised. Local residual stress mapping reveals that the compressive residual stress perpendicular to the plane of the pre-crack either decreases or is fully released at the weld edge of double pulse welds. Orientation imaging microscopy analyses show that the martensite formed in front of the pre-crack of double pulse weld has a lower fraction of high-angle grain boundaries and a coarser structure of Bain groups as opposed to the corresponding area of single pulse weld. Lower mechanical performance of double pulse welds produced at lower welding current is ascribed to the lower compressive residual stress normal to the plane of crack and the formation of martensitic structure in front of the pre-crack with a lower fraction of high-angle grain boundaries and coarser Bain groups.

The current work implements a correlative microscopy method utilizing electron back scatter diffraction, focused ion beam and digital image correlation to accurately determine spatially resolved stress profiles in the vicinity of grain/twin boundaries and tensile deformation twin tips in commercially pure titanium. Measured local stress gradients were in good agreement with local misorientation values. The role of dislocation-boundary interactions on the buildup of local stress gradients is elucidated. Stress gradients across the twin-parent interface were compressive in nature with a maximum stress magnitude at the twin boundary. Stress profiles near certain grain boundaries initially display a local stress minimum, followed by a typically observed “one over square root of distance” variation, as was first postulated by Eshelby, Frank and Nabarro. The observed trends allude to local stress relaxation mechanisms very close to the grain boundaries. Stress states in front of twin tips showed tensile stress gradients, whereas the stress state inside the twin underwent a sign reversal. The findings highlight the important role of deformation twins and their corresponding interaction with grain boundaries on damage nucleation in metals.

The metallic ribbons Fe40Ni40B20, Cu47Ti35Zr11Ni6Si1 and Zr65Cu17.5Ni10Al7.5 with different microhardness and glass forming ability were studied at different loading rates from 0.05 to 100 mN/s. We describe in details the differences in elemental discontinuities on the loading curves for the studied alloys. It was found that the discontinuities began at a certain local deformation independently on the macroscopic mechanical properties of a ribbon. More developed discontinuities at higher deformations are created for the materials with lower microhardness and so lower strength.

This paper presents a statistical method to analyze instabilities that can be introduced during imaging in scanning electron microscopy (SEM). The method is based on the correlation of digital images and it can be used at different length scales. It consists of the evaluation of three different approaches with four parameters in total. The methodology is exemplified with a specific case of internal stress measurements where ion milling and SEM imaging are combined with digital image correlation. It is concluded that before these measurements it is important to test the SEM column to ensure the minimization and randomization of the imaging instabilities. The method has been applied onto three different field emission gun SEMs (Philips XL30, Tescan Lyra, FEI Helios 650) that represent three successive generations of SEMs. Important to note that the imaging instability can be quantified and its source can be identified.

This paper investigates the adhesive interface in a polymer/metal (polyethylene terephthalate/steel) laminate that is subjected to uniaxial strain. Cross-sections perpendicular to such interfaces were created with a focused ion beam and imaged with scanning electron microscopy during straining in the electron microscope. During in situ straining, glide steps formed by the steel caused traction at the interface and initiated crazes in the polyethylene terephthalate (PET). These crazes readily propagated along the free surface of the PET layer. Similar crazing has not been previously encountered in laminates that were pre-strained or in numerical calculations. The impact of focused ion beam treatments on mechanical properties of the polymer/metal laminate system was therefore investigated. It was found that mechanical properties such as toughness of PET are dramatically influenced by focused ion beam etching. It was also found that this change in mechanical properties has a different effect on the pre-strained and in situ strained samples.

The paper concentrates on in situ bending tests and analysis of the failure of materials exhibiting strong anisotropy. As a typical example, Ti2AlC microcantilevers (MCs) were scrutinized. The anisotropic flexural strength of Ti2AlC MCs was measured, and the strength of the strong orientation was found to be two and half times as high as that of the weak orientation. The transition of fracture strength and mechanisms could be evaluated. Our findings have generic implications for future study on the fracture behavior of layered materials. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A versatile method to fabricate taper-free micro-/nanopillars of large aspect ratio was developed with focused ion beam (FIB) cutting. The key features of the fabrication are a FIB with an incident angle of 90° to the long axis of the pillar that enables milling of the pillar sideways avoiding tapering and the FIB current can be reduced step by step so as to reduce possible radiation damage of the milled surface by Ga ions. A procedure to accurately determine the cross-section of each pillar was developed.

In this study experimental and modelling methods are used to examine the microstructural and bending responses of laser-formed commercially pure titanium grade 2. The in situ bending angle response is measured for different processing parameters utilizing 3D digital image correlation. The microstructural changes are observed using electron backscatter diffraction. Finite element modelling is used to analyse the heat transfer and temperature field inside the material. It has been proven that the laser bending process is not only controlled by processing parameters such as laser power and laser beam scanning speed, but also by surface absorption. Grain size appears to have no influence on the final bending angle, however, sandblasted samples showed a considerably higher final bending angle. Experimental and simulation results suggest that the laser power has a larger influence on the final bending angle than that of the laser transverse speed. The microstructure of the laser heat-affected zone consists of small refined grains at the top layer followed by large elongated grains. Deformation mechanisms such as slip and twinning were observed in the heat-affected zone, where their distribution depends on particular processing parameters.

In this study, microstructural evolutions and phase selection phenomena during laser deposition of a hardfacing Ni-Cr-B-Si-C alloy at different processing conditions are experimentally investigated. The results show that even minor variations in the thermal conditions during solidification can modify the type and morphology of the phases. Higher undercoolings obtained at faster cooling rates suppressed the primary borides and encouraged floret-shape mixtures of Ni and Cr5B3 via a metastable reaction. Variations in the boride phases are discussed in terms of nucleation-and growth-controlled phase selection mechanisms. These selection processes also influenced the nature and proportion of the Ni-B-Si eutectics by changing the amount of the boron available for the final eutectic reactions. The results of this work emphasize the importance of controlling the cooling rate during deposition of these industrially important alloys using laser beam or other rapid solidification techniques. (C) The Minerals, Metals & Materials Society and ASM International 2013

Based on a recently published recursive model describing the geometry of laser clad coatings and on experimental track characteristics we propose specific functions to describe the geometry of laser clad coatings formed by overlap of individual tracks depending on the processing parameters. The recursive model provides a very good description ofthe whole geometry of the coating from the Height H and width w of a single laser track for any overlap ratio OR. We have shown in the past that the height and width of a single track are well correlated with the main laser cladding processing parameters for both coaxial and side cladding set-ups. Combining these two approaches leads to prediction of the complete geometry of laser clad coatings from basic processing parameters. These parameters are: Feeding rate F, Laser beam scanning speed S and overlap ratio OR. The character of the functions that describe the height and waviness of the final coating is the same for both coaxial and side cladding set-ups.