1,721,486 research outputs found
The effects of alloying elements on microstructures and mechanical properties of γ/γ′-strengthened Co-Ti-based alloys
No full textOxidation behavior of AlN/CrN multilayered hard coatings
Full text linkAbstract We report on the oxidation behavior of AlN/CrN multilayers at 900 °C, deposited by radio frequency magnetron sputtering. It is shown that oxidation in this system is controlled by diffusion of Cr towards the surface and formation of Cr2O3. Cr diffusion is found to mainly occur along grain boundaries. Thus, coherent cubic AlN/CrN multilayer regions with coarse columnar grain structures are found to be oxidation resistant, whereas regions decomposed into hexagonal AlN/cubic CrN are prone to oxidation
The maximum separation cluster analysis algorithm for atom-probe tomography: Parameter determination and accuracy
No full textAtom-probe tomography is a materials characterization method ideally suited for the investigation of clustering and precipitation phenomena. To distinguish the clusters from the surrounding matrix, the maximum separation algorithm is widely employed. However, the results of the cluster analysis strongly depend on the parameters used in the algorithm and hence, a wrong choice of parameters leads to erroneous results, e.g., for the cluster number density, concentration, and size. Here, a new method to determine the optimum value of the parameter d(max) is proposed, which relies only on information contained in the measured atom-probe data set. Atom-probe simulations are employed to verify the method and to determine the sensitivity of the maximum separation algorithm to other input parameters. In addition, simulations are used to assess the accuracy of cluster analysis in the presence of trajectory aberrations caused by the local magnification effect. In the case of Cu-rich precipitates (Cu concentration 40-60 at% and radius 0.25-1.0 nm) in a bcc Fe-Si-Cu matrix, it is shown that the error in concentration is below 10 at% and the error in radius is <0.15 nm for all simulated conditions, provided that the correct value for d(max), as determined with the newly proposed method, is employe
The martensitic transition pathway in steel
No full textThe martensitic transformation (MT) lays the foundation for microstructure and performance tailoring of many engineering materials, especially steels, which are with > 1.8 billion tons produced per year the most important material class. The atomic-scale migration path is a long-term challenge for MT during quenching in high-carbon (nitrogen) steels. Here, we provide direct evidence of (1(1) over bar 2) body-centred tetragonal (BCT) twinned martensite in carbon steels by transmission electron microscopy (TEM) investigation, and the increase in tetragonality with the C content matches X-ray diffraction (XRD) results. The specific {1(1) over bar 2}(BCT) twin planes which are related to the elongated c axis provide essential structural details to revisit the migration path of the atoms in MT. Therefore, the face-centred cubic (FCC) to BCT twin to body-centred cubic (BCC) twin transition pathway and its underlying mechanisms are revealed through direct experimental observation and atomistic simulations. Our findings shed new light on the nature of the martensitic transition, thus providing new opportunities for the nanostructural control of metals and alloys. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology
Modeling the constitutive behavior of polycrystalline metals based on dislocation mechanisms
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Structure property relations of cuticular photonic crystals evolved by different beetle groups (Insecta, Coleoptera)
No full textPhotonic crystals are optically active materials that can inhibit the propagation of light within certain frequency ranges. This type of material has shown many new and exciting optical effects which have led to considerable advances in technology. Investigating the design of the periodic structures of photonic crystals is one of the essential research fields aiming at optimized optical properties for technical applications. In nature, many living organisms have evolved biological photonic crystals which are able to generate vivid iridescent colors. These biological model systems, especially the photonic structures formed by the cuticle of insects, have already been shown to be a rich source of inspiration for the design and development of synthetic optical materials. In this study, I investigated the relations of structure and optical properties of the cuticular photonic crystals of five beetle species from three different systematic groups with the goal to evaluate their design principles. A large variety of methods for microscopic investigations and chemical analysis were applied to characterize the microstructure and composition of these photonic crystals experimentally. Their optical properties were both experimentally measured and theoretically characterized based on models derived from the structural analysis. The results show that the investigated species of Ground beetles and Scarab beetles have evolved multilayer structures and helicoidal structures in different regions of their cuticles: epicuticle and exocuticle, respectively. The weevil species has formed three-dimensional photonic crystals based on a D-surface structure (diamond) in scales which are outgrowths of the cuticle. Through modifications of structure and chemical composition of these basic structures, the investigated beetles obtain optical properties that are optimized to meet the imposed ecophysiological strains. In some cases, unusual and unexpected optical effects were observed. The principles of both the basic structuring of these photonic crystals and the additional modifications provide us inspirations for the design of synthetic composite materials with not only novel optical properties, but also combinations with other physical properties in a balanced equilibrium
Lattice Boltzmann modeling of advection-diffusion-reaction equations in non-equilibrium transport processes
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