Copper coatings produced by additive manufacturing techniques often present complex microstructural heterogeneity. Reducing microstructural heterogeneity is critical for promoting uniform mechanical and corrosion behavior. The current study examines copper coatings at the closure weld zone of a prototype steel container designed to store used nuclear fuel. In this region, the copper coating is produced by two additive manufacturing processes: electrodeposition and cold spray. Microscopy analysis revealed a highly non-uniform microstructure in the as-processed state. After heat treatment at 350 degrees C for 1 h under inert conditions, this heterogeneity was significantly reduced resulting in favourable microstructural characteristics for the current application.

A novel electroformed nanocrystalline nickel cobalt alloy (n-NiCo) developed for sheet metal applications was investigated in terms of microstructure, as well as mechanical, thermal stability, and corrosion properties. The as-received material with a grain size of 18 ± 5 nm exhibited enhanced hardness compared with conventional polycrystalline NiCo mainly due to the Hall–Petch strengthening effect. Differential scanning calorimetry and annealing treatment results revealed that the n-NiCo was stable up to 200 °C for at least 1 h, and the onset of abnormal grain growth was observed when the material was annealed to 250 °C. While low-temperature annealing treatment was shown to increase the hardness of the material slightly, annealing at temperatures of 300 °C and above resulted in a reduction in hardness due to rapid normal grain growth. The n-NiCo sheet exhibited mixed Ni/Co anodic polarization behavior in environments of varying pH.

Electrodeposited nanocrystalline NiFe alloys are compared to their polycrystalline, coarse-grained counterparts to understand the effects of grain size reduction on the passivation kinetics and the chemical structure of the passive film. The passive film formed in acidic sulfate environment was characterized using parallel angle-resolved XPS (PARXPS) to obtain non-destructive compositional depth profiles. The composition (Ni:Fe) of the passive film was insensitive to grain size; however, grain size reduction resulted in increased anodic activity producing thicker films that contained increased concentrations of higher oxide species.

In the design of used nuclear fuel containers for deep geological repositories, copper is considered to be a suitable and long-lived barrier for corrosion resistance. The microstructures of state-of-the-art copper materials used in this application produced through extrusion, a grain boundary engineered electrodeposition technique and cold spraying were studied via electron backscattered diffraction. Desirable microstructural characteristics for localized corrosion resistance of pure copper were compiled from the literature considering grain size, grain boundary character distribution, and crystallographic texture. The subject copper materials were found to have favourable microstructures for localized corrosion resistance, in particular, a high fraction of special grain boundaries, especially Sigma 3 twins, rendering them suitable for the given application. Crown Copyright (C) 2020 Published by Elsevier B.V. All rights reserved.

Intergranular degradation processes, (e.g., corrosion, stress corrosion, cracking, creep cracking) are a frequent cause of premature and unpredictable service failure of engineering components. Recent advances in (1) understanding structure-property relationships for grain boundaries, and (2) characterization techniques for grain boundaries in polycrystalline materials, have provided the means for improved component lifetime prediction, and the opportunity to engineer intergranular-degradation resistant microstructures. In this work, we present our previously developed geometric models for grain boundary structure and grain size effects on intergranular degradation susceptibility. Specific examples are presented of the successful application of the ‘grain boundary engineering’ approach to the prediction and mitigation of intergranular corrosion, stress corrosion cracking, and creep cracking in Ni-based materials.

The correlation between the crystal/defect and the magnetic domain structure of nanocrystalline (nc) bulk nickel produced by electrodeposition was investigated. By means of conventional and high resolution transmission electron microscopy, an average grain size of 23 nm was determined; nano-grains surrounded by low angle and high angle boundaries and the presence of nanotwins and stacking faults were observed. The nc nickel exhibited soft magnetic properties. Lorentz TEM (LTEM) in the Fresnel mode revealed magnetic domains of various sizes in the micrometer range extending over many grains, with a few random pinning sites, exhibiting a magnetic ripple structure and vortices. The LTEM was used to investigate the motion of domain walls driven by an external in situ magnetic field and to determine the domain wall width. Domain wall movement was observed at very small magnetic fields along the hysteresis loop. The correlation of the grain size and magnetic properties shows good agreement with the Herzer random anisotropy model for nanocrystalline materials, although the nc nickel studied here has no traces of an amorphous phase.

Electrodeposited nanocrystalline and conventional polycrystalline NiFe alloys of similar iron content were investigated to understand the effect of grain size on the corrosion behaviour of these materials. Potentiodynamic polarization testing in 1 N H2SO4 revealed similar active-passive-transpassive behaviour with negligible differences in the Tafel and transpassive regions regardless of grain size. It is shown that differences in the region of active dissolution are the result of strong contributions of sulfur impurities in the nanocrystalline electrodeposits rather than being due to grain size alone.

Inspired by the lotus leaf, nonwetting surfaces have drawn widespread attention in the field of surface engineering due to their remarkable water repelling characteristics. There are many applications for these surfaces, for instance, self-cleaning walls and windows, anti-icing surfaces, or low drag microfluidic channels. However, the adoption of nonwetting surfaces in large scale industrial applications has been hampered by synthesis techniques that are not easily scalable and the limited long term stability and wear robustness of these surfaces in service. This study demonstrates a simple, low cost, and scalable electrochemical technique to produce robust composite coatings with tunable nonwetting properties. The composite coatings are composed of an ultrafine grain nickel matrix with embedded hydrophobic cerium oxide ceramic particles. A comprehensive characterization is performed, including wetting property measurements, electron microscopy, focused ion beam analysis, hardness measurements, and abrasive wear testing to establish the structure-property relationships for these materials. The ultrafine grain structure of the nickel matrix contributes to the high hardness of the composites. As a result of the bimodal CeO2 particle size, hierarchical roughness is present on the surface of the composite, leading to remarkable nonwetting properties, even after 720 m of abrasive wear.

Room temperature thermoelectrical transport was investigated on a series of thick (300 gm), fully-dense electrodeposited nanocrystalline Ni materials with grain sizes below 50 nm. Strong grain size effects were observed on both electrical resistivity and thermal conductivity. As grain size decreased from 47 to 28 nm, the nanocrystalline Ni exhibited an increase in electrical resistivity from 9.42 to 10.2 mu Omega cm, and a reduction of thermal conductivity from 74.7 to 67.3 W/m-K, respectively. Analysis shows that for the nanocrystalline Ni, the change in the values of thermal conductivity and electrical resistivity is mainly due to grain boundary contributions with limited impurity effects. Furthermore, the thermoelectrical transport behavior agrees well with the Wiedemann-Franz law. The corresponding Lorenz numbers varied only in a narrow range from 2.30 x 10(-8) to 2.37 x 10(-8) W Omega/K-2 for the nanocrystalline Ni and were well within the experimentally measured value range of 2.12-2.44 x 10(-8) W Omega/K-2(2 for coarse grained Ni reported in the literature. (C) 2016 Elsevier Ltd. All rights reserved.

In this review, we present an extensive summary of research on superhydrophobic electrodeposits reported in the literature over the past decade. As a synthesis technique, electrodeposition is a simple and scalable process to produce non-wetting metal surfaces. There are three main categories of superhydrophobic surfaces made by electrodeposition: (i) electrodeposits that are inherently non-wetting due to hierarchical roughness generated from the process; (ii) electrodeposits with plated surface roughness that are further modified with low surface energy material; (iii) composite electrodeposits with co-deposited inert and hydrophobic particles. A recently developed strategy to improve the durability during the application of superhydrophobic electrodeposits by controlling the microstructure of the metal matrix and the co-deposition of hydrophobic ceramic particles will also be addressed.

The mechanisms of biological evolution have always been, and still are, the subject of intense debate and modeling. One of the main problems is how the genetic variability is produced and maintained in order to make the organisms adaptable to environmental changes and therefore capable of evolving. In recent years, it has been reported that, in flies and plants, mutations in Hsp90 gene are capable to induce, with a low frequency, many different developmental abnormalities depending on the genetic backgrounds. This has suggested that the reduction of Hsp90 amount makes different development pathways more sensitive to hidden genetic variability. This suggestion revitalized a classical debate around the original Waddington hypothesis of canalization and genetic assimilation making Hsp90 the prototype of morphological capacitor. Other data have also suggested a different mechanism that revitalizes another classic debate about the response of genome to physiological and environmental stress put forward by Barbara McClintock. That data demonstrated that Hsp90 is involved in repression of transposon activity by playing a significant role in piwi-interacting RNA (piRNAs)-dependent RNA interference (RNAi) silencing. The important implication is that the fixed phenotypic abnormalities observed in Hsp90 mutants are probably related to de novo induced mutations by transposon activation. In this case, Hsp90 could be considered as a mutator. In the present theoretical paper, we discuss several possible implications about environmental stress, transposon, and evolution offering also a support to the concept of evolvability.

Room temperature tensile testing was performed on a coarse-grained polycrystalline Ni (32 μm), a nanocrystalline Ni (23 nm) and two nanocrystalline Ni–Fe (16 nm) electrodeposits at two strain rates of 10−1 and 10−2/s. Strain localizations and local temperature increases were simultaneously recorded during tensile testing. For all materials, higher loads or higher strain rate generally resulted in higher peak temperature with the highest temperatures recorded in the fracture regions. The maximum temperature for the nanocrystalline materials was just over 80 °C, which is significantly below the reported temperatures for the onset of thermally activated grain growth. Therefore, the previously reported grain growth observed on similar materials after tensile deformation is likely not thermally activated but a stress-induced phenomenon. Despite the wide grain range from 16 nm to 32 μm, all samples exhibited similar strain localization behavior. Local strain variations initiated in the early stage of macroscopic uniform deformation, subsequent necking and fracture took place in the region of initial strain localization. While the coarse-grained polycrystalline Ni exhibited little strain rate sensitivity, gradually increased strain rate sensitivity was observed for the 23 nm Ni and the two 16 nm Ni–Fe samples, suggesting that both dislocation-mediated and grain-boundary-controlled mechanisms were operative in the deformation of the nanocrystalline Ni and Ni–Fe samples.