Wire-arc additive manufactured (WAAM-ed) Al 4047 alloys under different heat inputs were produced to investigate the effect of heat input on the nanomechanical properties by nanoindentation. The WAAM-ed Al alloys showed hypoeutectic microstructure that consisted of primary Al (α-Al) dendrite and ultrafine Al-Si eutectic. Interestingly, it is found that the hardness of α-Al dendrite and Al-Si eutectic decreased with the increasing heat input, in accordance with the trend of yield strength and microhardness in the previous studies. Different from the microscale mechanism explained by the grain growth model and Hall-Petch relationship, this work reveals the nanoscale mechanism regarding the effect of heat input on hardness, which is the enhanced solid solution strengthening produced by low heat input. However, the heat input had little effect on the SRS and activation volume. This work leads to new insights into the understanding of the heat input effect, and further benefits to improve the targeted mechanical properties and engineering applications of the AM-ed materials.

On achieving low hydrate adhesion force, a precise knowledge of the interactions between hydrate and solid surfaces is a prerequisite. By utilizing molecular dynamics simulations, gas hydrate with an intermediate layer (IML) containing varied gas content is brought to contact with several kinds of solid surfaces. The results show that the presence of gas layers or bubbles on the solid interface can fatally weaken hydrate adhesion strength, which indicates for the first time the possibility of surface chemical design and engineering in fabricating anti-hydrate surfaces. Based on this, a novel passive anti-hydrate surface design approach is proposed by means of an interface gas enrichment strategy to weaken hydrate adhesion strength on solid surfaces.

Without hydrogen, vacancy generation at grain boundary is limited and transgranular fracture mode dominates. When charged, hydrogen as a booster can enhance strain-induced vacancy generation by up to ten times. This leads to the superabundant vacancy stockpiling at the grain boundary, which agglomerates and nucleates intergranular nanovoids eventually causing intergranular fracture.
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The nanoscale creep behavior and creep size effect of a selective laser melted (SLM-ed) Zr-based metallic glass (MG) were investigated by aid of nanoindentation. The creep compliance and creep retardation spectra were extracted from the fitted parameters of the generalized Kelvin model. The creep stress exponent (n) and shear transformation zone (STZ) volume, as the indicators of creep mechanism, were estimated, demonstrating the creep mechanism is the non-Newtonian flow and the creep resistance decreased with the increscent peak loads. A potential mechanism for this creep size effect was revealed in this work: the smaller of the STZ volume, as well as the greater ratio of plastic flow under the higher maximum load, are responsible for the decreasing tendency of creep resistance. The significance of this work lies in the fact that it filled the blank of an in-depth understanding of the atomistic mechanisms in the AM-ed MG during the nanoscale creep deformation process.

Mitigating gas hydrate formation and the subsequent pipeline plugging is of critical importance for ensuring safety in exploring and transporting deep-water resources. Until now active methods that use chemicals and thermal energy are mainly applied in tackling the unwanted hydrate accumulation problems. However, these methods not only are costly and but also can result in unavoidable environmental concerns. The rapid developments in surface modification technology and advanced surfaces design offer alternative solutions to mitigate the challenges raised by gas hydrate. In this review, three current research priorities are pinpointed. Firstly, the intrinsic interactions between solid surface-gas hydrate should be scrutinized, which can shed light in solving the complex role of surface properties in hydrate nucleation. Secondly, hydrate deposition mechanisms and surfaces that could suppress hydrate deposition need to be well addressed. Gas hydrate deposition is more than a sequential process of hydrate agglomeration and should be highly related to chemistry/physics of surfaces. Thirdly, hydrate adhesion from nanoscale to continuum scale need to be corelated, which can facilitate the design of surfaces with low hydrate adhesion. After a thorough review on the fundamental relationships between surfaces and hydrate nucleation, deposition and adhesion, anti-gas hydrate surfaces with potentials of suppressing hydrate nucleation, inhibiting hydrate deposition and lowering hydrate adhesion are discussed, aiming to provide a knowledge base for the design and creation of next generation multifunctional hydrate-phobic surfaces.

The first 3Ω thermal characterization of a silver coated polymer-sphere based isotropic conductive adhesive (AgPS-ICA). This material has a large potential for use in electronics. Thus, we show a new way of characterizing a material group which is of high significance to many technological applications. This would be of interest to both academic and industry researchers looking for a way of thermally characterizing their samples, as well as those interested in thermal transport on the micro- and nanoscale in general.

Gas hydrate is both a valuable future energy source and a threat to the gas transport. Developing anti-gas hydrate surface is a new strategy to mitigate the hydrate agglomeration challenge.

One question has been asked frequently: Is there any corelation between the ice adhesion and gas hydrate adhesion on a solid surface.

Our recent research shows, yes, there is a simple correlation: 

Ice adhesion strength ≈ 5 * Gas hydrate adhesion strength !

See our new publication for details: Unraveling Adhesion Strength between Gas Hydrate and Solid Surfaces

Based on numerical simulations, we first proposed a so-called S printing pattern which theoretically can result in the lowest residual stress in additive manufacturing.

Together with Dr. Jonas Hensel's group at Technische Universität Braunschweig, Germany and Dr. Sakari Pallaspuro at Oulu University, Finland, we experimentally compared the S printing pattern with two other common printing patterns. It was found that the S pattern does not only induce lower residual stresses, but also produces smaller coarse-grain size and less porosity!

The novel S pattern 

The experimental verification of the S pattern

The new residual stress eveluation method

Based on finite element simulation results, a novel additive manufacturing deposition pattern, called the S pattern was proposed in an early publication. Compared with other existing printing patterns, it was shown numerically that the S pattern produces the lowest residual stresses.

In the new publication appeared in the Materials and Design, an joint experimental verification program led by Dr. Jonas Hensel at Technische Universität Braunschweig, Germany and Dr. Sakari Pallaspuro at Oulu University, Finland has been carried out to compare the performance of three printing patterns.

Experimental results show that the S pattern does not only induce lower residual stresses, but also produces smaller coarse-grain size and less porosity!

Remarkable progress has been made in surface icephobicity in the recent years. The mainstream standpoint of the reported antiicing surfaces yet only considers the ice–substrate interface and its adjacent regions being of static nature. In reality, the local structures and the overall properties of ice–substrate interfaces evolve with time, temperature and various external stimuli. Understanding the dynamic properties of the icing interface is crucial for shedding new light on the design of new anti-icing surfaces to meet challenges of harsh conditions including extremely low temperature and/or long working time. This article surveys the state-of-the-art anti-icing surfaces and dissects their dynamic changes of the chemical/physical states at icing interface. According to the focused critical ice–substrate contacting locations, namely the most important ice–substrate interface and the adjacent regions in the substrate and in the ice, the available anti-icing surfaces are for the first time re-assessed by taking the dynamic evolution into account. Subsequently, the recent works in the preparation of dynamic anti-icing surfaces (DAIS) that consider time-evolving properties, with their potentials in practical applications, and the challenges confronted are summarized and discussed, aiming for providing a thorough review of the promising concept of DAIS for guiding the future icephobic materials designs.

Reference: Zhuo, Y., Xia, Z., Qi, Y., Sumigawa, T., Wu, J., Šesták, P., Lu, Y., Håkonsen, V., Li, T., Wang, F., Chen, W., Xiao, S., Long, R., Kitamura, T., Li, L., He, J., Zhang, Z., Simultaneously Toughening and Stiffening Elastomers with Octuple Hydrogen Bonding. Adv. Mater. 2021, 33, 2008523. https://doi.org/10.1002/adma.202008523

Gel materials have drawn great attention recently in the anti-icing research community due to their remarkable potential for reducing ice adhesion, inhibiting ice nucleation, and restricting ice propagation. Although the current anti-icing gels are in their infancy and far from practical applications due to poor durability, their outstanding prospect of icephobicity has already shed light on a new group of emerging anti-icing materials. There is a need for a timely review to consolidate the new trends and foster the development towards dedicated applications. Starting from the stage of icing, we first survey the relevant anti-icing strategies. The latest anti-icing gels are then categorized by their liquid phases into organogels, hydrogels, and ionogels. At the same time, the current research focuses, anti-icing mechanisms and shortcomings affiliated with each category are carefully analysed. Based upon the reported state-of-the-art anti-icing research and our own experience in polymer-based anti-icing materials, suggestions for the future development of the anti-icing gels are presented, including pathways to enhance durability, the need to build up the missing fundamentals, and the possibility to enable stimuli-responsive properties. The primary aim of this review is to motivate researchers in both the anti-icing and gel research communities to perform a synchronized effort to rapidly advance the understanding and making of gel-based next generation anti-icing materials.

Carbon sulfur nanothreads (CSNTs) mainly composed of two chiral long alkane chains have been recently fabricated from thiophene by a pressure-induced phase transition in low-temperature, but their mechanical properties remain unexplored. Here, the critical roles of morphology and temperature on the tensile characteristics of CSNTs are for the first time examined using molecular dynamic simulations with a first-principles-based ReaxFF forcefield. It is revealed that CSNTs exhibit high tensile Young's modulus, high tensile strength and excellent ductility, and their tensile properties are morphology and temperature dependent. Morphologically, atomic arrangement with various configurations makes every CSNTs possess unique mechanical properties. Thermally, as temperature varies from 1 to 1500 K, CSNTs become mechanically weakened. In comparison with conventional diamond nanothreads (DNTs) and carbon nitride nanothreads (CNNTs), CSNTs show distinct axial elongation mechanisms, with relatively insignificant changes in chemical bond orders and bond length in the skeleton prior to the final rupture. Instead, the stretching of bond angle and dihedral angle mainly contribute to the global axial elongation, while the torsional deformation is limited due to their perfect global symmetry in the configuration. This study provides fundamental insights into the mechanics of ultra-thin CSNT structures.

The manuscript demonstrates the direct transgranular to intergranular fracture transition process controlled by hydrogen-influenced plasticity, by scrutinizing the tensile responses of Ni Σ5(210)[001] GB with varied hydrogen concentration using atomistic modeling. Compared with the Σ3 coherent twin GB which traps nearly no H atoms, H will form an atmosphere at the Σ5 GB due to the high trapping energy and excess volume and induce a higher initial local stress. In the case without H, less stress is built up at the Σ5 GB region during deformation, which leads to transgranular fracture. In contrast, H suppresses the stress-releasing ability of the Σ5 GB, which causes a local stress concentration and promotes local plasticity on the GB. This further leads to early dislocation emission, severe twinning evolution, increased number of vacancies and thus enhanced nanovoiding on the GB. The growth of nanovoids with H finally completes the transgranular to intergranular-fracture transition. These findings enrich our knowledge of hydrogen-induced intergranular fracture at the microscale.

A new paper published in Materials Science and Engineering A

The microstructure and crystallographic orientation-dependent nanomechanical characteristics of an additively manufactured (AM-ed) high-entropy alloy (HEA) were investigated by aid of nanoindentation and SEM. Furthermore, the effect of heat treatment on AM-ed HEA was explored by comparing with as-printed HEA. Interestingly, it is found that the grain {101} has the highest hardness and elastic modulus, whereas the creep resistance of grain {111} is the greatest, with the indicators of the creep mechanism showing lattice diffusion is the dominant mechanism. Heat treatment in the current study can increase the hardness and elastic modulus but decrease the creep resistance slightly. This work elucidates the grain orientation dependence on nanomechanical properties and the role of heat treatment, and sheds light on the nanoscale creep behavior and the corresponding creep mechanisms in the AM-ed HEA.

The local structure and heat transfer properties (thermal conductivity and interfacial conductance) in model semi-crystalline polyethylene (PE) are studied by non-equilibrium molecular dynamics. Three different force fields with different levels of detail (all-atom, all-atom with constraints, and united-atom) are compared. We find that the structure of the model PE is significantly influenced by the choice of force field. The united-atom force field results in a reduced overall crystallinity and an over-idealized organization of the polymer chains, compared to the all-atom force fields. We find that thermal transport properties are not greatly influenced when structural effects are taken into consideration, and our results suggest that united-atom models can be used to study heat transfer properties of model PE, with decreased computational cost.

The experimental method and setup for determining the heat transfer coefficient under CO2 condensation is developed and validated. Condensation heat transfer coefficient of CO2 on smooth surfaces of Cu, Al and stainless steel as well as hierarchical surfaces of Cu based micro and nanostructures have been investigated. It is found that the heat transfer coefficient increases with increasing the saturation pressure and increased surface area. The best of the structured surfaces resulted in a heat transfer coefficient 66% higher than that of the unstructured surface.

Nanoparticles hold promising potentials in enhanced oil recovery. The mechanics of nanoparticles interacting with different components in confined nanochannels still awaits in-depth clarification. In the current work, atomistic modeling and molecular dynamics simulations were utilized to investigate three different nanoparticle dispersion patterns in nanochannels with trapped oil droplets, namely nanoparticles favoring in water, in oil, and in both phases. The special focus of this study is to detail the local pressure in the nanochannels induced by the injections of nanoparticles. The results reveal the key effects of different nanoparticles on altering the atomistic mechanics in the complex nanofluid system and shed light on the rational design and selection of nanoparticles in practice. Particularly, the local pressure in the three-phase contact area triggered by hydrophilic nanoparticles was found to feature the famous structural disjoining pressure, which supplied supporting evidences to the former continuum medium based analytical study from the atomistic level for the first time. 

Current synthetic elastomers suffer from the well‐known trade‐off between toughness and stiffness. By a combination of multiscale experiments and atomistic simulations, a transparent unfilled elastomer with simultaneously enhanced toughness and stiffness is demonstrated. The designed elastomer comprises homogeneous networks with ultrastrong, reversible, and sacrificial octuple hydrogen bonding (HB), which evenly distribute the stress to each polymer chain during loading, thus enhancing stretchability and delaying fracture. Strong HBs and corresponding nanodomains enhance the stiffness by restricting the network mobility, and at the same time improve the toughness by dissipating energy during the transformation between different configurations. In addition, the stiffness mismatch between the hard HB domain and the soft poly(dimethylsiloxane)‐rich phase promotes crack deflection and branching, which can further dissipate energy and alleviate local stress. These cooperative mechanisms endow the elastomer with both high fracture toughness (17016 J m⁻²) and high Young's modulus (14.7 MPa), circumventing the trade‐off between toughness and stiffness. This work is expected to impact many fields of engineering requiring elastomers with unprecedented mechanical performance.

News: No ice, ice, baby!