查看更多>>摘要：? 2022 Acta Materialia Inc.Metal nanolaminate coatings are introduced as a new approach in post-weld treatment methods. A Cu/Ni nanolaminate coating is electrodeposited from a single Cu/Ni citrate bath onto a butt-welded tension-tension fatigue specimen. The nanolaminate coating consists of a Ni base layer and 160 alternating Cu and Ni layers. The specimen is tested in tension-tension fatigue with a stress range close to the yield strength of the specimen. This first study reveals surprisingly high lifetime extensions of welded joints. The tested specimens are examined using FIB/SEM and TEM. Local roughness measurements are carried out with AFM. This leads to observations on crack behavior of nanostructured Cu/Ni multilayers. The Cu layers show initial multi-crack formation, while the cracks arrest at the Cu/Ni interfaces. The Ni layers bridge those cracks and each Ni layer tears individually. Hypotheses are formed on the fatigue behaviour of Cu/Ni multilayers.
查看更多>>摘要：? 2022 Acta Materialia Inc.The existence of iron impurity in magnesium (Mg) is conventionally deemed detrimental to the corrosion resistance against the inorganic solutions, especially over its tolerance limit. We deliberately investigated the biodegradation properties of pure Mg with different contents of Fe by immersing in DMEM+10% FBS. Surprisingly, the impurity of Fe, even its content higher than the tolerance limit previously determined by immersion in inorganic solutions such as NaCl, has no negative effect on the degradation of pure Mg. Pure Mg with a high content of Fe impurity even retains good biocompatibility. Detailed microstructural analyses decipher that the severe local micro-galvanic corrosion caused by the Fe impurity meanwhile promotes the formation of compact Ca-rich corrosion product layer on the top surface, protecting the adjacent Mg matrix from being further corroded. The present discovery provides new insights in designing biodegradable Mg alloys, especially pursuing high-level impurity doping without deteriorating the biocompatibility.
查看更多>>摘要：? 2022Compositional partitioning during uranium alloy oxidation was studied via complementary ex situ - in situ atom probe tomography. Nanoscopic volumes of uranium- 22 at. % molybdenum were exposed to air at room temperature/atmospheric pressure for 30–60 minutes (ex situ), and 300 °C - 10?5 mbar O2 gas for 2–5 minutes in a chemical reaction chamber attached to an atom probe system (in situ). For all environmental conditions, a hypostoichiometric uranium oxide is formed. Reaction fronts are observed at oxide/metal, oxide/hydride, and outer oxide/environment interfaces. Results reveal Mo redistributes across the oxide/metal interface, with a tendency for enrichment in the outer oxide. The formation of a hydrogen-rich subsurface layer between the oxide and base alloy accompanies oxidation in both air and oxygen gas environments. Carbon and silicon impurity elements also redistribute to the outer oxide, contributing to oxide film composition.
查看更多>>摘要：? 2022 Acta Materialia Inc.High-purity α-titanium was implanted with helium to observe cavity morphology – size, number density, and form (i.e., bubbles vs. voids) – effects on materials strength. Increasing implantation temperatures lead to an Arrhenius-type (i.e., exponential) increase in cavity size, a transition from spherical bubbles to faceted voids, and a marked increase in strength (～20–50%). Implanted samples deformed uniformly in contrast to nano-compression of unimplanted or alloyed titanium, but pillars with the largest faceted voids developed a type of bulging localized deformation. Affected voids were repeatedly sheared, becoming rough and shrunken. Dislocation-cavity interactions and the role of helium content within cavities are considered.
查看更多>>摘要：? 2022 Acta Materialia Inc.In this work, we present a diffuse-interface model of anisotropic interface thermal conductivity considering the interface thermal resistance and conductance. It allows to perform simulations with interface thermal imperfections while circumventing the technical and numerical difficulties of reconstructing complex sharp-interface microstructure. The model is implemented in a finite element method. Numerical results show good agreement with the theoretical benchmarks for both thermal conduction simulation and thermal homogenization. To further demonstrate the feasibility of the model, complex microstructures from digitized characterizations and phase-field simulations are homogenized, taking Si-Hf-N as the material system. Normalized interface thermal resistance ranging from 1 to 108 show prominent influence to the homogenized thermal conductivity, which converges when the thermal resistance approaches zero or infinity. Increasing thermal resistance is also unveiled to enhance the thermal anisotropy of the microstructure with highly-oriented inclusions.
查看更多>>摘要：? 2022 The Author(s)Dislocation-enhanced electrical conductivity is an emerging topic for ceramic oxides. In contrast to the majority of present studies which focus on large-scale crystal deformation or thin film fabrication to introduce dislocations, we use a nanoindentation “pop-in stop” method to locally generate 〈011〉 edge-type dislocations at room temperature, without crack formation, on the (100) surface of a rutile TiO2 single-crystal. Ion beam assisted deposition of microcontacts allowed for both deformed and non-deformed zones to be locally probed by impedance spectroscopy. Compared to the dislocation-free region, a local enhancement of the electrical conductivity by 50% in the dislocation-rich regions is found. The study paves the way for local “mechanical-doping” of ceramics and oxide materials, allowing for the use of dislocations to tune the local conductivity with high spatial resolution.
查看更多>>摘要：? 2022 Acta Materialia Inc.The chemical short-range order (CSRO) in a face-centered cubic equiatomic NiCoFeCrMn high-entropy alloy was revealed directly from advanced transmission electron microscopy in this work. Further, instead of controlling CSRO by conventional heat treatment, we show a new possibility of tailoring CSRO by radiation. The multiple types of atoms in such high-entropy system are more prone to form CSRO under radiation compared to that only under thermodynamic equilibrium conditions, due to the rearrangement of the chemical ordering during the non-equilibrium thermal spike period and the radiation-enhanced diffusion mechanism. Our results show an increase in the fraction of CSRO area by ～45% after high-temperature irradiation with a dose of 50 DPA. Accordingly, we demonstrated that enhanced CSRO can be achieved by controlling the irradiation dose and temperature, which provides a new route to explore the kinetic evolution and effect of CSRO in complex alloy systems.
查看更多>>摘要：? 2022 Acta Materialia Inc.High entropy alloys (HEAs), as a promising metallic material, are comprised of five or more elements in equal or close to equal atomic fractions, which is received more and more attention due to its multi-principal-element effects. Moreover, solid solution phase and severe lattice distortion characteristics of HEAs are particularly beneficial to hydrogen storage. In this study, a new hexanary HEA TiZrFeMnCrV with single C14 Laves phase was prepared by arc melting and mechanical milling. The TiZrFeMnCrV alloy has super-fast hydrogen absorption kinetics and can absorb hydrogen 1.80 wt.% under mild conditions of 30 °C. The TiZrFeMnCrV alloy has excellent absorption/desorption cycling performance, and the capacity still stabilizes at around 1.76 wt.% during the 50 cycles. The design of high entropy alloy can provide guidance for the new type of hydrogen storage materials.
查看更多>>摘要：? 2022 Acta Materialia Inc.We present a new superdense and superhard carbon allotrope with P2221 space group and 8 atoms in the unit cell, naming P2221-C8. The density of P2221-C8 is 3.579 g/cm3, which is denser than diamond and even BC8. The energetical, dynamical and mechanical stabilities of P2221-C8 are confirmed by the calculation of energy, phonon frequencies and elastic constants, respectively. The hardness ranges from 88 GPa to 94 GPa according to different models, which is comparable with that of the diamond. The bandgap is indirect with 4.475 eV, which is smaller than that of the diamond. In addition, the match between simulated X-ray diffraction (XRD) and detonation experiments shows a possible way to synthesis it.
查看更多>>摘要：? 2022Measurements of electrical resistance have been used extensively as a failure criterion in cyclically loaded conductive films. However, not much research has been performed on extracting additional information contained within such resistance data sets. This study shows that an increase in peak width evidences a transition from cracks bridging to through-thickness crack formation. A Au/Cr bilayer system on a polyimide substrate is used for data generation but the method is applicable to any material system where both necking and through-thickness cracks are formed and no immediate formation of electrically insulating oxide layers occurs upon damage initiation. The method is easy to implement, and has the ability to replace time-intensive and destructive inspection methods.
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