Articoli di riviste: "Gradients de microstructure"

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McNelley, Terry R., Keiichiro Oh-ishi e Alexandre P. Zhilyaev. "Microstructure Evolution and Microstructure-Property Relationships in Friction Stir Processing of NiAl Bronze". Materials Science Forum 539-543 (marzo 2007): 3745–50. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.3745.

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Friction stir processing (FSP) has been employed for localized modification and control of microstructures in NiAl bronze materials, which are widely utilized for marine components. The thermomechanical cycle of FSP results in homogenization and refinement and the conversion of microstructures from a cast to a wrought condition within stir zones in the material. However, the direct measurement of stir zone temperatures, strains, strain rates and cooling rates is difficult due to steep gradients and transients in these quantities, and this is an impediment in the assessment of FSP-induced microstructures and properties. Quantitative microstructure analyses following FSP of cast NiAl bronze materials have been used to develop estimates of stir zone thermomechanical cycles. The estimation procedures will be reviewed and the microstructure-based estimates will be compared to results from computational models and embedded thermocouples measurements. Stir zone microstructures comprise a mixture of primary α grains and transformation products of the β that formed during processing. Recrystallization in the primary α occurred due to particle-stimulated nucleation in this low stacking fault energy material. Factors that influence the distribution of strength and ductility in the stir zone appear to include the mixture of microstructure constituents and gradients in microstructure due to gradients in processing conditions.

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Schmidt, Christopher David, Hans-Jürgen Christ e Axel Von Hehl. "Hydrogen as a Temporary Alloying Element for Establishing Specific Microstructural Gradients in Ti-6Al-4V". Metals 12, n. 8 (28 luglio 2022): 1267. http://dx.doi.org/10.3390/met12081267.

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Parts of vehicles, such as landing gear components of aircrafts, are subject to growing demands in terms of sustainability via lightweight design and durability. To fulfill these requirements, the development of thermochemical processes is auspicious. Titanium alloys allow a heat treatment in hydrogen-containing atmosphere for temporary hydrogen alloying, often called thermohydrogen treatment (THT). The investigation presented intends to realize a local microstructure modification of Ti-6Al-4V by means of THT. The study aims to use hydrogen (H) as a promoter for changing the local distribution and morphology of strengthening precipitates during THT as well as the local grain size (microstructural gradient). Both shall improve the fatigue properties of the material after hydrogen degassing. To derive suitable thermohydrogen treatment process parameters, the resulting fatigue crack propagation resistance and fracture toughness after different solution heat treatments are determined experimentally and compared to each other. Moreover, various graded microstructures are evaluated after hydrogen uptake (hydrogenation) and hydrogen degassing (dehydrogenation) using numerically simulated hydrogen concentration profiles, observed hardness curves, metallographically determined microstructure gradients and the corresponding results of the phase analysis by means of X-ray diffraction. The study shows that hydrogenation at 500 °C and dehydrogenation at 750 °C enables the generation of a promising microstructural gradient.

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Jalme, Margaux Saint, Christophe Desrayaud, Julien Favre, Damien Fabrègue, Sylvain Dancette, Christophe Schuman, Jean Sébastien Lecomte, Etienne Archaud e Christian Dumont. "Microstructure Evolution during Multiaxial Processing of TA6V". Materials Science Forum 1016 (gennaio 2021): 1211–17. http://dx.doi.org/10.4028/www.scientific.net/msf.1016.1211.

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Subtransus multiaxial hot forging of α+β Ti-6Al-4V (TA6V) titanium alloy with a β-transformed microstructure aims at obtaining an equiaxed microstructure through α phase globularization. The activation of mechanisms involved in microstructural evolution, such as globularization, depends on parameters such as time, temperature, strain and strain rate. It is also sensitive to the crystallographic orientation of α-lamellae. As a result, multiaxial processing of titanium alloys leads to significant microstructural gradients depending on thermomechanical conditions and initial microstructure. In this study, we focused on the effect of complex thermomechanical paths on microstructural evolutions. Thanks to the MaxStrain Gleeble device, we were able to reproduce such thermomechanical treatments to β-transformed TA6V samples. Stress strain fields obtained with finite element modelling of the MaxStrain test were compared to experimental microstructure gradients. This experimental method offers the opportunity to get closer to industrial open die forging conditions.

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Bruder, Enrico, Tilman Bohn e Clemens Müller. "Properties of UFG HSLA Steel Profiles Produced by Linear Flow Splitting". Materials Science Forum 584-586 (giugno 2008): 661–66. http://dx.doi.org/10.4028/www.scientific.net/msf.584-586.661.

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Linear flow splitting is a new cold forming process for the production of branched sheet metal structures. It induces severe plastic strain in the processing zone which results in the formation of an UFG microstructure and an increase in hardness and strength in the flanges. Inbuilt deformation gradients in the processing zone lead to steep gradients in the microstructure and mechanical properties. In the present paper the gradients in the UFG microstructure and the mechanical properties of a HSLA steel (ZStE 500) processed by linear flow splitting are presented, as well as a calculation of local strength from hardness measurements on the basis of the Ludwikequation. In order to investigate the thermal stability of the UFG microstructure heat treatments below the recrystallization temperature were chosen. The coarsening process and the development of the low angle to high angle grain boundary ratio in the gradient UFG microstructure were monitored by EBSD measurements. It is shown that heat treatment can lead to a grain refinement due to a strong fragmentation of elongated grains while only little coarsening in the transverse direction occurs. A smoothing of the gradients in the UFG microstructure as well as in the mechanical properties is observed.

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Büyük, U., S. Engin e N. Maraşlı. "Directional solidification of Zn-Al-Cu eutectic alloy by the vertical Bridgman method". Journal of Mining and Metallurgy, Section B: Metallurgy 51, n. 1 (2015): 67–72. http://dx.doi.org/10.2298/jmmb140304007b.

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In the present work, the effect of growth rate and temperature gradient on microstructure and mechanical properties of Zn-7wt.%Al-4wt.%Cu eutectic alloy has been investigated. Alloys prepared under steady-state conditions by vacuumed hot filing furnace. Then, the alloys were directionally solidified upward with different growth rates (V=11.62-230.77 mm/s) at a constant temperature gradient (G=7.17 K/mm) and with different temperature gradients (G=7.17-11.04 K/mm) at a constant growth rate (V=11.62 mm/s) by a Bridgman furnace. The microstructures were observed to be lamellae of Zn, Al and broken lamellae CuZn4 phases from quenched samples. The values of eutectic spacing, microhardness and ultimate tensile strength of alloys were measured. The dependency of the microstructure and mechanical properties on growth rate and temperature gradient were investigated using regression analysis.

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Larivière, Sara, Reinder Vos de Wael, Seok-Jun Hong, Casey Paquola, Shahin Tavakol, Alexander J. Lowe, Dewi V. Schrader e Boris C. Bernhardt. "Multiscale Structure–Function Gradients in the Neonatal Connectome". Cerebral Cortex 30, n. 1 (10 aprile 2019): 47–58. http://dx.doi.org/10.1093/cercor/bhz069.

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Abstract The adult functional connectome is well characterized by a macroscale spatial gradient of connectivity traversing from unimodal toward higher-order transmodal cortices that recapitulates known principles of hierarchical organization and myelination patterns. Despite an emerging literature assessing connectome properties in neonates, the presence of connectome gradients and particularly their correspondence to microstructure remains largely unknown. We derived connectome gradients using unsupervised techniques applied to functional connectivity data from 40 term-born neonates. A series of cortex-wide analysis examined associations to magnetic resonance imaging-derived morphological parameters (cortical thickness, sulcal depth, curvature), measures of tissue microstructure (intracortical T1w/T2w intensity, superficial white matter diffusion parameters), and subcortico-cortical functional connectivity. Our findings indicate that the primary neonatal connectome gradient runs between sensorimotor and visual anchors and captures specific associations to cortical and superficial white matter microstructure as well as thalamo-cortical connectivity. A second gradient indicated an anterior-to-posterior asymmetry in macroscale connectivity alongside an immature differentiation between unimodal and transmodal areas, indicating a connectome-level circuitry en route to an adult-like organization. Our findings reveal an important coordination of structural and functional interactions in the neonatal connectome across spatial scales. Observed associations were replicable across individual neonates, suggesting consistency and generalizability.

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Lomte, Amulya, e Bhisham Sharma. "Modeling the acoustic behavior of stepwise gradient porous structures". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 264, n. 1 (24 giugno 2022): 500–508. http://dx.doi.org/10.3397/nc-2022-764.

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Spatial property gradients can significantly enhance the noise reduction potential of porous structures. However, predicting the acoustic behavior of structures with gradient microstructures continues to remain a challenge. For porous structures with controlled periodic microstructures, researchers have recently demonstrated the use of a multiscale asymptotic method to extract the acoustic transport properties necessary for use in semi-empirical predictive models. Here, we propose the adaptation of this method to enable the modeling of porous absorbers with stepwise property gradients. The unit cell of the chosen microstructure is modeled in COMSOL Multiphysics and the acoustic transport properties are extracted using the multiscale method. The extracted properties are then used to formulate the transfer matrix of each unit cell. The global sound absorption and transmission loss behavior of the stepwise gradient structures are further predicted by combining the appropriate local transfer matrices. Our results show that the integration of the unit cell and transfer matrix methods provides a robust way of predicting the acoustic behavior of stepwise gradient porous structures with various combinations of layer thicknesses and geometries. The method provides a computationally efficient method to model such structures and can further the development of porous structures with application-specific acoustical properties.

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Fischer, K., e H. Oettel. "Microstructure Gradients in PVD-TiN Coatings". Materials Science Forum 273-275 (febbraio 1998): 567–72. http://dx.doi.org/10.4028/www.scientific.net/msf.273-275.567.

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9

Georgiadis, H. G. "The Mode III Crack Problem in Microstructured Solids Governed by Dipolar Gradient Elasticity: Static and Dynamic Analysis". Journal of Applied Mechanics 70, n. 4 (1 luglio 2003): 517–30. http://dx.doi.org/10.1115/1.1574061.

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This study aims at determining the elastic stress and displacement fields around a crack in a microstructured body under a remotely applied loading of the antiplane shear (mode III) type. The material microstructure is modeled through the Mindlin-Green-Rivlin dipolar gradient theory (or strain-gradient theory of grade two). A simple but yet rigorous version of this generalized continuum theory is taken here by considering an isotropic linear expression of the elastic strain-energy density in antiplane shearing that involves only two material constants (the shear modulus and the so-called gradient coefficient). In particular, the strain-energy density function, besides its dependence upon the standard strain terms, depends also on strain gradients. This expression derives from form II of Mindlin’s theory, a form that is appropriate for a gradient formulation with no couple-stress effects (in this case the strain-energy density function does not contain any rotation gradients). Here, both the formulation of the problem and the solution method are exact and lead to results for the near-tip field showing significant departure from the predictions of the classical fracture mechanics. In view of these results, it seems that the conventional fracture mechanics is inadequate to analyze crack problems in microstructured materials. Indeed, the present results suggest that the stress distribution ahead of the tip exhibits a local maximum that is bounded. Therefore, this maximum value may serve as a measure of the critical stress level at which further advancement of the crack may occur. Also, in the vicinity of the crack tip, the crack-face displacement closes more smoothly as compared to the classical results. The latter can be explained physically since materials with microstructure behave in a more rigid way (having increased stiffness) as compared to materials without microstructure (i.e., materials governed by classical continuum mechanics). The new formulation of the crack problem required also new extended definitions for the J-integral and the energy release rate. It is shown that these quantities can be determined through the use of distribution (generalized function) theory. The boundary value problem was attacked by both the asymptotic Williams technique and the exact Wiener-Hopf technique. Both static and time-harmonic dynamic analyses are provided.

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Schmidt, Christopher David, Vitali Macin, Peter Schmidt e Hans-Jürgen Christ. "Generation of Microstructural Gradients for Improved Mechanical Properties via Thermo-Hydrogen Treatment of the Metastable Beta Titanium Alloys Beta CTM and Ti 10V-2Fe-3Al". MATEC Web of Conferences 321 (2020): 12017. http://dx.doi.org/10.1051/matecconf/202032112017.

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Structural components must be lightweight and produced resource-saving while still fulfil the increasing durability and reliability requirements. One approach to fulfil these requests is a temporary hydrogen charging of Ti-alloys, which generates lattice distortion and hydrides. The volume difference between hydride precipitates and the alloy matrix results in localized plastic deformation. This triggers recrystallization and enables a finer microstructure as attainable by a conventional heat treatment. The study aims at an elaboration of a thermo-hydrogen treatment that establishes a change in grain size and/or an alteration in distribution and morphology of strengthening secondary α precipitates as a function of the distance to surface (microstructural gradient). The gradient is based on a gradient of the hydride volume fraction. Generally, THT design requires kinetic (temperature dependency of the hydrogen diffusion coefficient DH) in addition to thermodynamic (H/β-Ti-alloy interaction) data, which has been obtained for Ti 3Al-8V-6Cr-4Mo-4Zr and Ti 10V-2Fe-3Al. Subsequent to a solution treatment the variation of hydrogenation time and temperature is operated to establish comparably slight microstructural gradients on these materials. For further investigations it is concluded that materials with less alloying elements ((α+β)-Ti-alloys (e.g.,Ti 6Al-4V)) than these β-Ti-alloys can satisfy the requirements to generate steeper microstructural gradients even better.

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11

Seo, Seongji, e Jiyong Park. "Annealing Heat Treatment for Homogenizing the Microstructure and Mechanical Properties of Electron-Beam-Welded Thick Plate of Ti-6Al-4V Alloy". Materials 16, n. 23 (29 novembre 2023): 7423. http://dx.doi.org/10.3390/ma16237423.

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In the application of Ti-6Al-4V to aerospace structural components, when welding thick plates similar of the thickness of the components, microstructure and hardness gradients emerge between the base material (BM) and the joint. This leads to the issue of significant stress concentration in the BM under tensile stress. To address this problem through post-welding heat treatment, this study conducted heat treatments at temperatures both below (mill annealing, MA) and above the beta-transus temperature (beta annealing, BA) on electron-beam weldments of 18 mm thickness Ti-6Al-4V plates. Subsequently, microstructures and hardness were analyzed at different depths from the upper surface and areas (fusion zone (FZ), heat-affected zone (HAZ), and BM), and tensile properties were measured at various depths. The results indicated that α′ observed in FZ and HAZ was resolved through both MA and BA. Particularly after BA, the microstructural gradient that persisted even after MA completely disappeared, resulting in the homogenization of widmanstätten α + β. Consequently, after BA, the hardness gradient in each zone also disappeared, and the tensile strength was higher than in just-welded and MA heat-treated plates.

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12

Hansen, A. C., e W. E. Foslien. "A macroscale mixture theory analysis of deposition and sublimation rates during heat and mass transfer in dry snow". Cryosphere 9, n. 5 (23 settembre 2015): 1857–78. http://dx.doi.org/10.5194/tc-9-1857-2015.

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Abstract. The microstructure of a dry alpine snowpack is a dynamic environment where microstructural evolution is driven by seasonal density profiles and weather conditions. Notably, temperature gradients on the order of 10–20 K m−1, or larger, are known to produce a faceted snow microstructure exhibiting little strength. However, while strong temperature gradients are widely accepted as the primary driver for kinetic growth, they do not fully account for the range of experimental observations. An additional factor influencing snow metamorphism is believed to be the rate of mass transfer at the macroscale. We develop a mixture theory capable of predicting macroscale deposition and/or sublimation in a snow cover under temperature gradient conditions. Temperature gradients and mass exchange are tracked over periods ranging from 1 to 10 days. Interesting heat and mass transfer behavior is observed near the ground, near the surface, as well as immediately above and below dense ice crusts. Information about deposition (condensation) and sublimation rates may help explain snow metamorphism phenomena that cannot be accounted for by temperature gradients alone. The macroscale heat and mass transfer analysis requires accurate representations of the effective thermal conductivity and the effective mass diffusion coefficient for snow. We develop analytical models for these parameters based on first principles at the microscale. The expressions derived contain no empirical adjustments, and further, provide self consistent values for effective thermal conductivity and the effective diffusion coefficient for the limiting cases of air and solid ice. The predicted values for these macroscale material parameters are also in excellent agreement with numerical results based on microscale finite element analyses of representative volume elements generated from X-ray tomography.

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Hansen, A. C., e W. E. Foslien. "A macroscale mixture theory analysis of deposition and sublimation rates during heat and mass transfer in snow". Cryosphere Discussions 9, n. 2 (5 marzo 2015): 1503–54. http://dx.doi.org/10.5194/tcd-9-1503-2015.

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Abstract. The microstructure of a dry alpine snowpack is a dynamic environment where microstructural evolution is driven by seasonal density profiles and weather conditions. Notably, temperature gradients on the order of 10–20 K m−1, or larger, are known to produce a faceted snow microstructure exhibiting little strength. However, while strong temperature gradients are widely accepted as the primary driver for kinetic growth, they do not fully account for the range of experimental observations. An additional factor influencing snow metamorphism is believed to be the rate of mass transfer at the macroscale. We develop a mixture theory capable of predicting macroscale deposition and/or sublimation in a snow cover under temperature gradient conditions. Temperature gradients and mass exchange are tracked over periods ranging from 1 to 10 days. Interesting heat and mass transfer behavior is observed near the ground, near the surface, as well as immediately above and below dense ice crusts. Information about deposition (condensation) and sublimation rates may help explain snow metamorphism phenomena that cannot be accounted for by temperature gradients alone. The macroscale heat and mass transfer analysis requires accurate representations of the thermal conductivity and the effective mass diffusion coefficient for snow. We develop analytical models for these parameters based on first principles at the microscale. The expressions derived contain no empirical adjustments, and further, provide self consistent values for thermal conductivity and the effective diffusion coefficient for the limiting cases of air and solid ice. The predicted values for these macroscale material parameters are also in excellent agreement with numerical results based on microscale finite element analyses of representative volume elements generated from X-ray tomography.

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Liao, Z., L. Zhang, X. Huang e D. Juul Jensen. "Microstructural and textural gradients in SLM-manufactured AlSi10Mg after low-draught cold-rolling and heat treatment". Journal of Physics: Conference Series 2635, n. 1 (1 novembre 2023): 012038. http://dx.doi.org/10.1088/1742-6596/2635/1/012038.

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Abstract Additively manufactured AlSi10Mg is often subject to a two-stage heat treatment, namely solid solution treatment followed by artificial aging, to achieve optimal properties. Before such heat treatments, slight surface plastic deformation may be applied to modify the surface quality and properties. However, gradients in microstructure and texture near the surface introduced by the plastic deformation may cause undesired microstructural and textural evolutions during subsequent heat treatment. In this work, we introduce plastic deformation in the surface layer in an SLM-manufactured AlSi10Mg sample by relatively low-draught cold rolling and we investigate the through-thickness variations in microstructure and texture in the deformed state and after heat treatment. The SLM-manufactured AlSi10Mg sample has a fine-scale microstructure and a weak texture, and is rather thermally stable during subsequent heat treatments. Applying 10% low-draught cold rolling to the SLM-manufactured AlSi10Mg sample is found to introduce a near Goss texture in the surface layer, while little change is observed in the center layer. After subsequent solution treatment and aging, abnormal grain growth occurred in the surface layer resulting in remarkable through thickness gradients in microstructure and texture.

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Zalesak, J., J. Todt, R. Pitonak, A. Köpf, R. Weißenbacher, B. Sartory, M. Burghammer, R. Daniel e J. Keckes. "Combinatorial refinement of thin-film microstructure, properties and process conditions: iterative nanoscale search for self-assembled TiAlN nanolamellae". Journal of Applied Crystallography 49, n. 6 (1 dicembre 2016): 2217–25. http://dx.doi.org/10.1107/s1600576716017258.

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Because of the tremendous variability of crystallite sizes and shapes in nanomaterials, it is challenging to assess the corresponding size–property relationships and to identify microstructures with particular physical properties or even optimized functions. This task is especially difficult for nanomaterials formed by self-organization, where the spontaneous evolution of microstructure and properties is coupled. In this work, two compositionally graded TiAlN films were (i) grown using chemical vapour deposition by applying a varying ratio of reacting gases and (ii) subsequently analysed using cross-sectional synchrotron X-ray nanodiffraction, electron microscopy and nanoindentation in order to evaluate the microstructure and hardness depth gradients. The results indicate the formation of self-organized hexagonal–cubic and cubic–cubic nanolamellae with varying compositions and thicknesses in the range of ∼3–15 nm across the film thicknesses, depending on the actual composition of the reactive gas mixtures. On the basis of the occurrence of the nanolamellae and their correlation with the local film hardness, progressively narrower ranges of the composition and hardness were refined in three steps. The third film was produced using an AlCl3/TiCl4precursor ratio of ∼1.9, resulting in the formation of an optimized lamellar microstructure with ∼1.3 nm thick cubic Ti(Al)N and ∼12 nm thick cubic Al(Ti)N nanolamellae which exhibits a maximal hardness of ∼36 GPa and an indentation modulus of ∼522 GPa. The presented approach of an iterative nanoscale search based on the application of cross-sectional synchrotron X-ray nanodiffraction and cross-sectional nanoindentation allows one to refine the relationship between (i) varying deposition conditions, (ii) gradients of microstructure and (iii) gradients of mechanical properties in nanostructured materials prepared as thin films. This is done in a combinatorial way in order to screen a wide range of deposition conditions, while identifying those that result in the formation of a particular microstructure with optimized functional attributes.

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Castelluccio, Gustavo M., Hojun Lim, John M. Emery e Corbett C. Battaile. "Crack tip microplasticity mediated by microstructure gradients". Fatigue & Fracture of Engineering Materials & Structures 44, n. 9 (14 giugno 2021): 2337–55. http://dx.doi.org/10.1111/ffe.13493.

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17

WINTER, MATTHIAS. "An example of microstructure with multiple scales". European Journal of Applied Mathematics 8, n. 2 (aprile 1997): 185–207. http://dx.doi.org/10.1017/s0956792597003021.

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This paper studies a vectorial problem in the calculus of variations arising in the theory of martensitic microstructure. The functional has an integral representation where the integrand is a non-convex function of the gradient with exactly four minima. We prove that the Young measure corresponding to a minimizing sequence is homogeneous and unique for certain linear boundary conditions. We also consider the singular perturbation of the problem by higher-order gradients. We study an example of microstructure involving infinite sequential lamination and calculate its energy and length scales in the zero limit of the perturbation.

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Rodríguez-Parra, Jesús, Rodrigo Moreno e Isabel Nieto. "Effect of cooling rate on the microstructure and porosity of alumina produced by freeze casting". Journal of the Serbian Chemical Society 77, n. 12 (2012): 1775–85. http://dx.doi.org/10.2298/jsc121018132r.

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Freeze casting is a well-known shaping technique to produce materials with directional porosity. One of the major problems is the difficulty to control the cooling rate thus leading to gradients in pore size and homogeneity. This work deals with the manufacture of alumina ceramics with directional porosity by freeze casting of aqueous suspensions. An experimental set-up was prepared in order to apply different cooling rates. Freeze casting tests were done with an aqueous alumina suspension after optimization of its rheological behavior. The porosity and microstructural features of sintered bodies produced under different experimental conditions were studied and analyzed. It is concluded that the cooling rate influences the microstructure while final temperature has a much lower influence. Also, the microstructural analysis shows that there is a gradient in the directionality of pores, being lower at the bottom and the top and higher in the central region of the specimens.

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Li, Lingxiao, Jiyan Liu, Yuhao Wang, Guozhu Zhang e Fengshan Du. "Study on the Effect of Microstructure Gradients Caused by Heat Gradients on Hydrogen Embrittlement Sensitivity in Heavy Forgings". Metals 12, n. 4 (1 aprile 2022): 610. http://dx.doi.org/10.3390/met12040610.

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The hydrogen embrittlement problem of alloy steel heavy forgings not only has the common properties of general hydrogen embrittlement, but also has the characteristics brought by its scale characteristics. The research of hydrogen embrittlement, combined with its characteristics and commonness, is of vital importance for the service safety of engineering structures. The temperature field and microstructure distribution in the machining process were investigated through the simulation of a finite element. On this basis, the physical simulation experiments were carried out to obtain the microstructure of heavy forgings in radial directions. The hydrogen embrittlement sensitivity was characterized by electrochemical hydrogen charging and slow strain rate tests (SSRT). The microstructure and fracture morphology of the samples were characterized to explore the law and mechanism of hydrogen embrittlement sensitivity gradient distribution along the axial direction. It is helpful to understand the hydrogen embrittlement of heavy forgings in order to guide engineering practice.

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Nastac, Laurentiu. "A 3D Multiscale Model for Prediction of the Microstructure Evolution in Ti6Al4V Components Produced by Laser Powder Bed Fusion". IOP Conference Series: Materials Science and Engineering 1281, n. 1 (1 maggio 2023): 012002. http://dx.doi.org/10.1088/1757-899x/1281/1/012002.

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Abstract A transient 3D multiscale model has been created to simulate the evolution of solidification microstructures rapidly and effectively in Ti6Al4V parts produced through Laser Powder Bed Fusion (LPBF). The microstructure simulation tool has been enhanced to account for rapid solidification conditions in Ti6Al4V alloys during processing of multi-layer multi-track LPBF parts. The simulation tool can evaluate the impact of part geometry, lase power input, laser speed, and laser beam shape on the formation of the microstructure in LPBF-processed Ti6Al4V alloy. The multiscale model considers several factors, including preferential crystallographic growth direction, isomorphism, epitaxy, melt pool motion, and temperature gradients to generate the observed texture and morphology of the microstructure in Ti6Al4V components. The model can evaluate various microstructure characteristics, such as grain size and texture. Consequently, it could aid in controlling the formation of solidification microstructures in Additive Manufacturing (AM) processed parts. The simulation tool has been previously validated by using IN625 laser remelting experiments made by National Institute of Standards and Technology. The 3D simulation tool can also be utilized to predict the microstructure formation in Ti6Al4V components produced by the Electron Beam AM processes.

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Sandhya, S., e G. Phanikumar. "Investigation of Fusion Weldments of Semi-Solid Aluminium A356 Alloy: Pool Geometry and Microstructure". Materials Science Forum 765 (luglio 2013): 751–55. http://dx.doi.org/10.4028/www.scientific.net/msf.765.751.

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A fusion welding technique to join a semi-solid processed A356 cast plate is explored using Gas Tungsten Arc Welding (GTAW). Semi-solid metal (SSM) billets of non-dendritic microstructure produced by rheocasting in a mould placed inside a linear electromagnetic stirrer were used for this study. GTAW experiments were conducted to simulate different thermal gradients near the fusion zone. The geometries of the weld pool as well as the temperature gradient in the fusion boundary were measured to understand the microstructure evolution. Simulation of the welding process was performed to aid in the analysis. Quantitative metallography provided the shape factor as a measure of globularity of the primary a-Al phase. Based on the studies, a model has been proposed to explain the observation of globular microstructure in the fusion zone of the welds. Conclusions show a positive correlation of thermal gradient with globular microstructure formation in this class of alloys.

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Weiland, H., e J. Liu. "Applications of microtexture analysis for materials characterization using SEM and TEM techniques". Proceedings, annual meeting, Electron Microscopy Society of America 52 (1994): 614–15. http://dx.doi.org/10.1017/s0424820100170803.

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Research and development in material science require the understanding of structure and property relationship. In many instances, such a relationship at a local microstructural scale is crucial for a mechanistic insight. Spatially-resolved microtexture analyses based on both scanning and transmission electron microscopy have now become powerful tools for these studies. By these techniques, not only can a linkage be established between morphological and crystallographic components of the microstructure, grain boundary details can be obtained as well. The choice of the SEM- or TEM-based microtexture technique for a study, however, depends on the specific needs. Several industrial examples of applied and basic work will be used for illustration.Industrial deformation processes such as extrusion, rolling and forging are generally inhomogeneous. As a result, strain gradients, and consequently, microstructure gradients, are intrinsic to most industrial products. For example, a laboratory-produced plane strain extrusion of an Al-Zn-Mg-Cu alloy exhibits a range of complex grain structures (Fig. 1a).

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Wang, Qiushuang, Wenyou Zhang, Shujun Li, Mingming Tong, Wentao Hou, Hao Wang, Yulin Hao, Noel M. Harrison e Rui Yang. "Material Characterisation and Computational Thermal Modelling of Electron Beam Powder Bed Fusion Additive Manufacturing of Ti2448 Titanium Alloy". Materials 14, n. 23 (30 novembre 2021): 7359. http://dx.doi.org/10.3390/ma14237359.

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Ti-24Nb-4Zr-8Sn (Ti2448) is a metastable β-type titanium alloy developed for biomedical applications. In this work, cylindrical samples of Ti2448 alloy have been successfully manufactured by using the electron beam powder bed fusion (PBF-EB) technique. The thermal history and microstructure of manufactured samples are characterised using computational and experimental methods. To analyse the influence of thermal history on the microstructure of materials, the thermal process of PBF-EB has been computationally predicted using the layer-by-layer modelling method. The microstructure of the Ti2448 alloy mainly includes β phase and a small amount of α″ phase. By comparing the experimental results of material microstructure with the computational modelling results of material thermal history, it can be seen that aging time and aging temperature lead to the variation of α″ phase content in manufactured samples. The computational modelling proves to be an effective tool that can help experimentalists to understand the influence of macroscopic processes on material microstructural evolution and hence potentially optimise the process parameters of PBF-EB to eliminate or otherwise modify such microstructural gradients.

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24

Kamalova, N. S., N. N. Matveev, N. Yu Evsikova e V. I. Lisitsyn. "Dynamics of potential difference changes in a biocomposite microsection for different temperature gradients". Известия Российской академии наук. Серия физическая 87, n. 9 (1 settembre 2023): 1322–26. http://dx.doi.org/10.31857/s0367676523702320.

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Abstract (sommario):

The method of formalized modeling revealed the complex nature of the dependence of the parameters of the process of rearrangement of the biocomposite microstructure on the temperature gradient. Based on the analysis of the dynamics of changes in the potential difference formed along the thickness of the birch wood microcut, the parameters of the biocomposite polarization process for various temperature gradients have determined.

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25

Zöllner, Dana, e Wolfgang Pantleon. "Grain growth in thin film under strong temperature gradients". IOP Conference Series: Materials Science and Engineering 1249, n. 1 (1 luglio 2022): 012010. http://dx.doi.org/10.1088/1757-899x/1249/1/012010.

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Abstract (sommario):

Abstract Grain growth in thin films has attracted lots of attention due to the numerous applications of polycrystalline films, on one hand, and modified properties due to changes in the microstructure caused by thermal effects, on the other hand. While the phenomenon of grain growth is well understood in general, effects of e.g. temperature gradients leave questions open still today. In the present study, we investigate the influence of strong temperature gradients on grain growth in thin films. To that aim, a modified three-dimensional Potts model algorithm is employed, where the annealing temperature depends on the position within the sample leading to spatial heterogeneities in the grain boundary network. As a consequence of different mobilities, a drag effect occurs on the boundary network evolution that has serious consequences for the microstructures evolving during grain growth.

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26

Vuorinen, E., V. Heino, N. Ojala, O. Haiko e A. Hedayati. "Erosive-abrasive wear behavior of carbide-free bainitic and boron steels compared in simulated field conditions". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 232, n. 1 (24 novembre 2017): 3–13. http://dx.doi.org/10.1177/1350650117739125.

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Abstract (sommario):

The wear resistance of carbide-free bainitic microstructures have recently shown to be excellent in sliding, sliding-rolling, and erosive-abrasive wear. Boron steels are often an economically favorable alternative for similar applications. In this study, the erosive-abrasive wear performance of the carbide-free bainitic and boron steels with different heat treatments was studied in mining-related conditions. The aim was to compare these steels and to study the microstructural features affecting wear rates. The mining-related condition was simulated with an application oriented wear test method utilizing dry abrasive bed of 8–10 mm granite particles. Different wear mechanisms were found; in boron steels, micro-cutting and micro-ploughing were dominating mechanisms, while in the carbide-free bainitic steels, also impact craters with thin platelets were observed. Moreover, the carbide-free bainitic steels had better wear performance, which can be explained by the different microstructure. The carbide-free bainitic steels had fine ferritic-austenitic microstructure, whereas in boron steels microstructure was martensitic. The level of retained austenite was quite high in the carbide-free bainitic steels and that was one of the factors improving the wear performance of these steels. The hardness gradients with orientation of the deformation zone on the wear surfaces were one of the main affecting factors as well. Smoother work hardened hardness profiles were considered beneficial in these erosive-abrasive wear conditions.

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27

Reis, Ana Carmen C., e Leo Kestens. "Cross-Sectional Texture Gradients in Interstitial Free Steels Processed by Accumulated Roll Bonding". Solid State Phenomena 105 (luglio 2005): 233–38. http://dx.doi.org/10.4028/www.scientific.net/ssp.105.233.

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Abstract (sommario):

An interstitial-free steel was severely plastically deformed in an accumulative roll bonding (ARB) experiment with 10 consecutive passes applied at 480°C. Nominal reductions of 50% per pass and an intermediate annealing treatment of 5 min. at 520°C were employed. A total true strain of evM = 8.00 was applied, which corresponds to an accumulated reduction of 99.9%. The evolution of texture and microstructure was monitored by means of orientation imaging microscopy. A lamellar microstructure, characteristic of severely rolled sheet materials, was observed even after the highest strains. The average lamellar width was determined as a function of rolling strain. Under the experimental limitations in terms of spatial resolution, no significant difference was observed between the average lamellar width in the mid-section and near the surface of the sheet. Texture analysis revealed a conventional cross-sectional gradient with plane strain rolling components in the mid-layers and shear components in the subsurface regions. Although these different strain modes did not affect the microstructure in terms of the average lamellar spacing, an effect was observed on the average aspect ratio of the grains. This was much higher in the sheared (surface) layers than in the plane strain compressed (centre) areas. The surface structure did not have an effect, though, on the bulk microstructural evolution in spite of the specific nature of the ARB process during which the surface layer of one pass reappears in the mid-section of the next pass.

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28

Wang, Jian-Bao, Guang-Chun Xiao, Wei Zhao, Bing-Rong Zhang e Wei-Feng Rao. "Microstructure and Corrosion Resistance to H2S in the Welded Joints of X80 Pipeline Steel". Metals 9, n. 12 (7 dicembre 2019): 1325. http://dx.doi.org/10.3390/met9121325.

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Abstract (sommario):

The microstructure and corrosion resistance in H2S environments for various zones of X80 pipeline steel submerged arc welded joints were studied. The main microstructures in the base metal (BM), welded metal (WM), coarse-grained heat-affected zone (CGHAZ), and fine-grained heat-affected zone (FGHAZ) were mainly polygonal ferrite and granular bainite; acicular ferrite with fine grains; granular bainite, ferrite, and martensite/austenite constituents, respectively. The corrosion behavior differences resulted from the microstructure gradients. The results of the micro-morphologies of the corrosion product films and the electrochemical corrosion characteristics in H2S environments, including open circuit potential and electrochemical impedance spectroscopy, showed that the order of corrosion resistance was FGHAZ > BM > WM > CGHAZ.

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29

Liu, Yao, e Songlin Cai. "Gradients of Strain to Increase Strength and Ductility of Magnesium Alloys". Metals 9, n. 10 (22 settembre 2019): 1028. http://dx.doi.org/10.3390/met9101028.

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Abstract (sommario):

A strain gradient was produced in an AZ31B magnesium alloy through a plastic deformation of pure torsion at a torsional speed of π/2 per second. Compared with the base material and with the alloy processed by conventional severe plastic deformation, the magnesium alloy provided with a strain gradient possesses high strength preserving its ductility. Microstructural observations show that strain gradient induces the formation of an inhomogeneous microstructure characterized by statistically stored dislocation (SSD) density gradient and geometrically necessary dislocation (GND). GNDs and dislocation density gradient provide extra strain hardening property, which contributes to the improvement of ductility. The combination of SSD density gradient and GND can simultaneously improve the strength and ductility of magnesium alloy.

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30

Ferry, Michael. "Uniformity of Grain Coarsening in Submicron Grained Al-Sc Alloy Containing Local Variations in Texture". Materials Science Forum 495-497 (settembre 2005): 609–14. http://dx.doi.org/10.4028/www.scientific.net/msf.495-497.609.

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Abstract (sommario):

The effect of fine particles on the uniformity of grain coarsening in a submicron grained Al-Sc alloy containing significant local variations in texture has been investigated using high resolution EBSD. The alloy was processed by severe plastic deformation and low temperature ageing to generate a fine-grained (0.8 µm diameter) microstructure containing either a dispersion of nanosized Al3Sc particles or a particle-free matrix. The initial processing generated a uniform grain size distribution, but the distribution of grain orientations was inhomogeneous with the microstructure containing colonies of grains consisting predominantly of either HAGBs or LAGBs with the latter possessing orientation gradients of up to 10 o/µm. Despite the marked differences in boundary character between these regions, the alloy undergoes slow and uniform grain coarsening during annealing at temperatures up to 500 oC with no marked change in the grain size distribution, boundary distribution and texture. A model of grain coarsening that takes into account the influence of fine particles on the kinetics of grain growth within an orientation gradient is outlined. The model predicts that a large volume fraction of fine particles (large f/r-value) tends to homogenize the overall rate of grain coarsening despite the presence of orientation gradients in the microstructure.

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31

Lavery, Andone C., Christopher Bassett e Scott Loranger. "How prevalent is acoustic scattering from physical microstructure?" Journal of the Acoustical Society of America 151, n. 4 (aprile 2022): A148—A149. http://dx.doi.org/10.1121/10.0010930.

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Abstract (sommario):

Any oceanic environment with spatial gradients in sound speed and density can result in acoustic scattering hot spots. These acoustic hotspots can be rapidly evolving and vary in their spatial heterogeneity. Here, we present data collected with a variety of split-beam and multi-beam echosounders illustrating the broad array of environments and spatial scales associated with scattering from physical microstructure, including shear instabilities in estuarine environments, non-linear internal waves on the continental shelf, strong interface scattering due to double-diffusion, scattering from strong gradients, or interfaces, and turbulent microstructure at the new England Shelf Break Front. The theoretical acoustic scattering formulations for different types of physical microstructure are applied to these different environments, and recommendations are made for optimal frequency bands to sample the different types of physical microstructure and the optimal measurements for inference of parameters that describe the physical microstructure. The impact of other scattering sources, such as suspended sediments, bubbles, and biological targets, on successful acoustic sampling of physical microstructure is also discussed. [This work was supported by the ONR.]

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32

Lavery, Andone C., Christopher Bassett e Scott Loranger. "How prevalent is acoustic scattering from oceanic microstructure?" Journal of the Acoustical Society of America 152, n. 4 (ottobre 2022): A152. http://dx.doi.org/10.1121/10.0015857.

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Abstract (sommario):

Any oceanic environment with spatial gradients in sound speed and density can result in acoustic scattering hot spots. These acoustic hotspots can be rapidly evolving and vary in their spatial heterogeneity. Here, we review acoustic scattering models for turbulence and present data collected with a variety of split-beam and multi-beam echosounders illustrating the range of environments and spatial scales associated with scattering from physical microstructure, including shear instabilities in estuarine environments, non-linear internal waves on the continental shelf, strong interface scattering due to double-diffusion, scattering from strong gradients or interfaces, and turbulent microstructure at the New England shelf break front. The theoretical acoustic scattering formulations for different types of physical microstructure are applied to these different environments, and recommendations are made for optimal frequency bands to sample the different types of physical microstructure and the optimal measurements for inference of parameters that describe the physical microstructure. Limitations imposed on detection and quantification of scattering from the physical microstructure due to sources including suspended sediment, bubbles, and biological targets, are also discussed. [Work supported by the ONR.]

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33

Bhattacharya, Kaushik, Nikan B. Firoozye, Richard D. James e Robert V. Kohn. "Restrictions on microstructure". Proceedings of the Royal Society of Edinburgh: Section A Mathematics 124, n. 5 (1994): 843–78. http://dx.doi.org/10.1017/s0308210500022381.

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Abstract (sommario):

We consider the following question: given a set of matrices with no rank-one connections, does it support a nontrivial Young measure limit of gradients? Our main results are these: (a) a Young measure can be supported on four incompatible matrices; (b) in two space dimensions, a Young measure cannot be supported on finitely many incompatible elastic wells; (c) in three or more space dimensions, a Young measure can be supported on three incompatible elastic wells; and (d) if supports a nontrivial Young measure with mean value 0, then the linear span of must contain a matrix of rank one.

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34

Kanders, U., e K. Kanders. "Nanoindentation Response analysis of Thin Film Substrates-I: Strain Gradient-Divergence Approach". Latvian Journal of Physics and Technical Sciences 54, n. 1 (1 febbraio 2017): 66–76. http://dx.doi.org/10.1515/lpts-2017-0007.

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Abstract (sommario):

Abstract Nanoindentation is a widely-used method for sensitive exploration of the mechanical properties of micromechanical systems. We derive a simple empirical analysis technique to extract stress-strain field (SSF) gradient and divergence representations from nanoindentation data sets. Using this approach, local SSF gradients and structural heterogeneities can be discovered to obtain more detail about the sample’s microstructure, thus enhancing the analytic capacity of the nanoindentation technique. We demonstrate the application of the SSF gradient-divergence analysis approach to nanoindentation measurements of bulk silicon.

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35

Satyawali, P. K., A. K. Singh, S. K. Dewali, Praveen Kumar e Vinod Kumar. "Time dependence of snow microstructure and associated effective thermal conductivity". Annals of Glaciology 49 (2008): 43–50. http://dx.doi.org/10.3189/172756408787814753.

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Abstract (sommario):

AbstractThis paper presents a sequential evaluation of snow microstructure and its associated thermal conductivity under the influence of a temperature gradient. Temperature gradients from 28 to 45 Km–1 were applied to snow samples having a density range 180–320 kgm–3. The experiments were conducted inside a cold room in a specially designed heat-flux apparatus for a period of 4weeks. A constant heat flux was applied at the base of the heat-flux apparatus to produce a temperature gradient in the snow sample. A steady-state approach was used to estimate the effective thermal conductivity of snow. Horizontal and vertical thick sections were prepared on a weekly basis to obtain snow micrographs. These micrographs were used to obtain snow microstructure using stereological tools. The thermal conductivity was found to increase with increase in grain size, bond size and grain and pore intercept lengths, suggesting a possible correlation of thermal conductivity with snow microstructure. Thermal conductivity increased even though surface area and area fraction of ice were found to decrease. The outcome suggests that changes in snow microstructure have significant control on thermal conductivity even at a constant density.

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36

Qu, Wenying, Min Luo, Zhipeng Guo, Xiaogang Hu, Ang Zhang, Fan Zhang, Daquan Li e Yongzhong Zhang. "Effect of Temperature Gradient on the Grain Size Homogeneity of SEED Produced Semi-Solid Slurries by Phase-Field Simulation". Materials 12, n. 20 (11 ottobre 2019): 3309. http://dx.doi.org/10.3390/ma12203309.

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Abstract (sommario):

The distribution homogeneity of grain size affects the fluidity of the semi-solid slurry, which in turn affects the properties of the casting. One key factor affecting grain size uniformity resides in the nucleation number, which has been studied thoroughly, while the other factor is temperature gradient which has not been investigated yet. In this study, the microstructure evolutions under certain temperature gradients are investigated by experiment and simulation using a two-dimensional quantitative phase-field (PF) model. A parallel and adaptive mesh refinement algorithm is adopted to solve the nonlinear phase-field equations. The results indicate that temperature gradient can affect the size distribution of microstructure in the semi-solid slurry prepared by the SEED process. A higher temperature gradient (in the range of 0.230~0.657 °C/mm) along the radial direction is beneficial to the homogeneity of the grain size in a slurry.

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37

Ma, Xiaotian, Shuangming Xu, Feifan Wang, Yaobang Zhao, Xiangchen Meng, Yuming Xie, Long Wan e Yongxian Huang. "Effect of Temperature and Material Flow Gradients on Mechanical Performances of Friction Stir Welded AA6082-T6 Joints". Materials 15, n. 19 (22 settembre 2022): 6579. http://dx.doi.org/10.3390/ma15196579.

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Abstract (sommario):

The temperature and material flow gradients along the thick section of the weld seriously affect the welding efficiency of friction stir welding in medium-thick plates. Here, the effects of different gradients obtained by the two pins on the weld formation, microstructure, and mechanical properties were compared. The results indicated that the large-tip pin increases heat input and material flow at the bottom, reducing the gradient along the thickness. The large-tip pin increases the welding speed of defect-free joints from 100 mm/min to 500 mm/min compared to the small-tip pin. The ultimate tensile strength and elongation of the joint reached 247 MPa and 8.7%, equal to 80% and 65% of the base metal, respectively. Therefore, reducing the temperature and material flow gradients along the thickness by designing the pin structure is proved to be the key to improving the welding efficiency for thick plates.

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38

ŞAHIN, M., E. ÇADIRLI e H. KAYA. "INFLUENCE OF THE SOLIDIFICATION PARAMETERS ON DENDRITIC MICROSTRUCTURES IN UNSTEADY-STATE DIRECTIONALLY SOLIDIFIED OF LEAD–ANTIMONY ALLOY". Surface Review and Letters 17, n. 05n06 (ottobre 2010): 477–86. http://dx.doi.org/10.1142/s0218625x10014326.

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Abstract (sommario):

Pb-9.3wt.%Sb alloy was directionally solidified upwards under argon atmosphere under the two conditions; with different temperature gradients, (G = 0.93–3.67 K/mm) at a constant growth rate (V = 17.50 μm/s) and with different growth rates (V = 8.30–497.00 μm/s) at a constant (G = 3.67 K/mm) in a Bridgman furnace. The dependence of characteristic microstructure parameters such as primary dendrite arm spacing (λ1), secondary dendrite arm spacing (λ2) and dendrite tip radius (R) on the growth rate (V) and the temperature gradient (G) were determined by using a linear regression analysis. A detailed analysis of microstructure were also made and compared with the theoretical models and similar experimental works on dendritic solidification in the literature.

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39

Rollett, Anthony D., Francis Wagner, Nathalie Allain-Bonasso, David P. Field e Ricardo A. Lebensohn. "Comparison of Gradients in Orientation and Stress between Experiment and Simulation". Materials Science Forum 702-703 (dicembre 2011): 463–68. http://dx.doi.org/10.4028/www.scientific.net/msf.702-703.463.

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Abstract (sommario):

We examine the relationship between local gradients in orientation, which are quantified with the Kernel Average Misorientation, and the grain boundary network in an interstitial-free steel sheet, before and after 12% tensile strain. A portion of the unstrained microstructure is used as input to a full-field spectral viscoplastic code that simulates the same deformation. The orientation gradients are concentrated near grain boundaries in both experiments and simulation. Mapping out stress gradients in the simulation suggests that the development of orientation gradients is strongly correlated with such gradients.

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40

Kotecký, Ondřej, Suzanne Degallaix e Jaroslav Polák. "Growth of Short Fatigue Cracks Emanating from Notches in an Austenitic-Ferritic Stainless Steel". Key Engineering Materials 348-349 (settembre 2007): 117–20. http://dx.doi.org/10.4028/www.scientific.net/kem.348-349.117.

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Abstract (sommario):

The present work studies the effect of the microstructure and of the stress gradient on the early fatigue crack growth in a two-phase austenitic-ferritic stainless steel. Fatigue tests were performed on two geometries of double edge notched specimens. Direct optical observations of the surface are used to measure the surface crack growth rates. The results are presented and the effects of stress and strain gradients on the crack propagation kinetics are discussed.

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41

Panov, Dmitrii, Egor Kudryavtsev, Stanislav Naumov, Denis Klimenko, Ruslan Chernichenko, Vladimir Mirontsov, Nikita Stepanov, Sergey Zherebtsov, Gennady Salishchev e Alexey Pertcev. "Gradient Microstructure and Texture Formation in a Metastable Austenitic Stainless Steel during Cold Rotary Swaging". Materials 16, n. 4 (17 febbraio 2023): 1706. http://dx.doi.org/10.3390/ma16041706.

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Abstract (sommario):

The paper aimed to study the evolution of the microstructure and texture gradient of a 321-type metastable austenitic stainless steel during cold rotary swaging. Cold rotary swaging was carried out with a reduction of up to 90% at ambient temperature. Pronounced gradients of the α’-martensite volume fraction, the axial texture of austenite (⟨111⟩ and ⟨001⟩) and α’-martensite (⟨101⟩), and non-uniform microhardness distribution along the rod diameter were obtained after a reduction of 80–90%. According to the finite element analysis, moderate tensile stresses were attained in the center, whereas high compressive stresses operated at the edge. Due to water cooling of the rod surface and heating of the rod center during processing, a temperature gradient was also derived. Features of strain-induced martensitic transformation, microstructure and texture evolution, and non-uniform hardening during cold rotary swaging were discussed.

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42

Nomoto, Sukeharu, Masahito Segawa e Makoto Watanabe. "Non- and Quasi-Equilibrium Multi-Phase Field Methods Coupled with CALPHAD Database for Rapid-Solidification Microstructural Evolution in Laser Powder Bed Additive Manufacturing Condition". Metals 11, n. 4 (13 aprile 2021): 626. http://dx.doi.org/10.3390/met11040626.

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Abstract (sommario):

A solidification microstructure is formed under high cooling rates and temperature gradients in powder-based additive manufacturing. In this study, a non-equilibrium multi-phase field method (MPFM), based on a finite interface dissipation model, coupled with the Calculation of Phase Diagram (CALPHAD) database, was developed for a multicomponent Ni alloy. A quasi-equilibrium MPFM was also developed for comparison. Two-dimensional equiaxed microstructural evolution for the Ni (Bal.)-Al-Co-Cr-Mo-Ta-Ti-W-C alloy was performed at various cooling rates. The temperature-γ fraction profiles obtained under 105 K/s using non- and quasi-equilibrium MPFMs were in good agreement with each other. Over 106 K/s, the differences between the non- and quasi-equilibrium methods grew as the cooling rate increased. The non-equilibrium solidification was strengthened over a cooling rate of 106 K/s. Columnar-solidification microstructural evolution was performed at cooling rates of 5 × 105 K/s to 1 × 107 K/s at various temperature gradient values under a constant interface velocity (0.1 m/s). The results show that, as the cooling rate increased, the cell space decreased in both methods, and the non-equilibrium MPFM was verified by comparing with the quasi-equilibrium MPFM. Our results show that the non-equilibrium MPFM showed the ability to simulate the solidification microstructure in powder bed fusion additive manufacturing.

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43

Plumeri, J. E., e W. Z. Misiolek. "Design of a novel experimental profile for the development of a numerical model for extrusion processing of a magnesium alloy". IOP Conference Series: Materials Science and Engineering 1270, n. 1 (1 dicembre 2022): 012085. http://dx.doi.org/10.1088/1757-899x/1270/1/012085.

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Abstract (sommario):

Magnesium alloys are an important structural material to many global industries. Their high specific physical properties are useful in the design of lightweight engineering systems. In this study, the development of a numerical model for the prediction of high-temperature extrusion of an Mg-Zn-Ce alloy (ZE20) is presented. A novel design of an I-shaped profile for extrusion processing was created as part of this effort. This design was used to produce extrudates with large strain gradients across a single profile. In parallel, new numerical tools were developed to predict the extrusion behaviour of the ZE20 alloy. Finite element simulation of the indirect extrusion laboratory trials was used to calibrate the numerical model. Microstructural measurements of experimental samples through EBSD analysis were compared with simulation calculations, and insights into the relationship between extrusion temperature, strain, and resulting microstructure were gained. A fully recrystallised, bimodally distributed grain microstructure was observed throughout the samples. Proportions of grain refinement within the bimodal distribution were shown to correspond with localised strain gradients for a profile with nearly uniform temperature. Ultimately, extrusion press load calculations using the numerical model were shown to be within 5% of experimental trial values.

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44

Branagan, D. J., M. J. Kramer, Y. L. Tang e R. W. McCallum. "Maximizing loop squareness by minimizing gradients in the microstructure". Journal of Applied Physics 85, n. 8 (15 aprile 1999): 5923–25. http://dx.doi.org/10.1063/1.369915.

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45

Dalwadi, M. P., I. M. Griffiths e M. Bruna. "Understanding how porosity gradients can make a better filter using homogenization theory". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, n. 2182 (ottobre 2015): 20150464. http://dx.doi.org/10.1098/rspa.2015.0464.

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Abstract (sommario):

Filters whose porosity decreases with depth are often more efficient at removing solute from a fluid than filters with a uniform porosity. We investigate this phenomenon via an extension of homogenization theory that accounts for a macroscale variation in microstructure. In the first stage of the paper, we homogenize the problems of flow through a filter with a near-periodic microstructure and of solute transport owing to advection, diffusion and filter adsorption. In the second stage, we use the computationally efficient homogenized equations to investigate and quantify why porosity gradients can improve filter efficiency. We find that a porosity gradient has a much larger effect on the uniformity of adsorption than it does on the total adsorption. This allows us to understand how a decreasing porosity can lead to a greater filter efficiency, by lowering the risk of localized blocking while maintaining the rate of total contaminant removal.

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46

Veaux, M., S. Denis e P. Archambault. "Modelling and experimental study of the bainitic transformation, residual stresses and deformations in the quenching process of middle alloyed steel parts". Journal de Physique IV 120 (dicembre 2004): 719–26. http://dx.doi.org/10.1051/jp4:2004120083.

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Abstract (sommario):

Big efforts have been made these last twenty years in order to model the behaviour of steel parts in heat treatment processes [1]. Models for microstructural evolutions during continuous cooling, coupled with thermomechanical calculations do exist, but complete experimental validations of these models are still necessary. Here, we mainly present a complete experimental validation procedure from the scale of small homogeneous specimen to the scale of massive pieces with thermal gradients. Comparisons between experimental and calculated results (transformation kinetics and thermomechanical behaviour) are presented first. Then, massive cylinders quenched in air, cold oil and cold water are considered and numerical simulation results in terms of microstructure distributions, residual stresses and deformation are compared to experimental ones. The whole study concerns more specifically the bainitic transformation of a middle alloyed steel and it is shown that the effect of internal stresses on the transformation kinetics is a first order parameter in order to predict correctly microstructural gradients developed in a quenched part.

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47

Chen, J. Z., Liang Zhen, Bao You Zhang, Y. X. Cui e Sheng Long Dai. "Through-Thickness Microstructure, Texture and Strength Gradients in AA 7055 Rolled Plate". Materials Science Forum 546-549 (maggio 2007): 957–60. http://dx.doi.org/10.4028/www.scientific.net/msf.546-549.957.

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Abstract (sommario):

Through-thickness microstructure, texture and mechanical property gradients in the longitudinal section of AA 7055 rolled plate have been investigated using electron back-scattered diffraction (EBSD) technique. Quantitative analysis of the microstructure and texture through the plate thickness was conducted. It was found that the microstructure and texture are obviously non-homogeneous through the plate thickness. From center to surface, more equiaxed grains are observed. As expected, the degree of recrystallization increases with increasing the S value. The grains in the center layer exhibited preferential orientations while the most grains near the surface presented a random one. The strength of each observed layer has also been tested.

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48

Nikas, Dimitrios, Yubin Zhang e Johan Ahlström. "Effect of annealing on microstructure in railway wheel steel". IOP Conference Series: Materials Science and Engineering 1249, n. 1 (1 luglio 2022): 012059. http://dx.doi.org/10.1088/1757-899x/1249/1/012059.

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Abstract (sommario):

Abstract Railway wheels are commonly made from medium carbon steels (~0.55 wt.% C), heat treated to a near pearlitic microstructure with 5–10% pro-eutectoid ferrite. During the operation of freight trains, where block brakes are used, high thermal loads occur together with the high contact stresses, which combined can affect the mechanical properties of the material. In this study, the effects of annealing on local microstructure and mechanical properties in pearlitic railway wheel steel were investigated using electron microscopy and micro-hardness. It is found that after annealing at 650 °C, the room temperature hardness reduces about 25%, accompanied by significant spheroidization of cementite in the pearlitic colonies, though the size and the orientation gradients of the pearlitic colonies have not changed much. The relationship between the microstructural changes and the mechanical properties are discussed.

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49

Lloyd, Isabel K., Yuval Carmel, Otto C. Wilson Jr. e Geng Fu Xu. "Microwave Processing of Ceramics". Advances in Science and Technology 45 (ottobre 2006): 857–62. http://dx.doi.org/10.4028/www.scientific.net/ast.45.857.

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Abstract (sommario):

Microwave (MW) processing is advantageous for processing ceramics with tailored microstructures. Its combination of volumetric heating, a wide range of controlled heating rates, atmosphere control and the ability to reach very high temperatures allows processing of 'difficult' materials like high thermal conductivity AlN and AlN composites and microstructure control in more readily sintered ceramics such as ZnO. MW sintering promotes development of thermal conductivity in AlN (225 W/mK) and its composites (up to 150W/mK inAlN-TiB2 and up to 129 W/mK in AlN-SiC when solid solution is avoided). In ZnO, heating rate controls sintered grain size. Increasing the heating rate from 5°C/min. to 4900°C decreases grain size from ~10 μm (comparable to conventional sintering of the same powder) to nearly the starting particle size (~ 1μm). Microstructural uniformity increases with sintering rate since ultra-rapid MW sintering minimizes the development of thermal gradients due to heat loss.

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Yang, Ping, Yuan Yuan Shao, Ning Zhang, Ling Cheng e Wei Min Mao. "Effects of Grain Boundaries in Columnar Grained Electrical Steels during Deformation and Recrystallization". Materials Science Forum 753 (marzo 2013): 173–76. http://dx.doi.org/10.4028/www.scientific.net/msf.753.173.

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Abstract (sommario):

The crystallographic and topographic anisotropies of columnar grains can exert strong influence on the subsequently hot rolled, cold rolled and annealed microstructures, textures and properties. The single type tilting grain boundaries among columnar grains will behave differently depending on grain orientations, rolling direction and stress state due to hot rolling and thus affect in return the microstructure and texture to some extents. This work aims to reveal the effects of grain boundaries and their neighboring grain orientation gradients in three types of Fe-3Si in differently processed samples using EBSD technique.

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Articoli di riviste sul tema "Gradients de microstructure"

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