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This work systematically investigates the microstructure-property relationship in Mg alloys. Emphasis is placed on understanding, through high resolution crystal plasticity modeling, how grain size and texture collectively impact material strengthening and hardening, net plastic anisotropy, and tension-compression asymmetry. To achieve this, 528 fully three-dimensional finite element calculations are performed, which comprise eleven textures, four grain sizes, six loading orientations, and two uniaxial loading states (tension and compression). The grain size effect follows Hall-Petch relation that depends on both, loading orientation and initial texture. The reduction in extension twinning with grain size refinement is influenced by texture as well. Below a threshold textural strength, grain size refinement leads to an appreciable reduction in the net plastic anisotropy at yield, quantified using Hill anisotropy, and reduced tension-compression asymmetry. Using a micromechanical basis, the effect of grain size and texture on material ductility is predicted to be non-monotonic. The computational predictions serve as synthetic data sets for experimental validation and reduced-order modeling.

• Presents a fully resolved, three-dimensional computational characterization of the interaction effects between grain size and initial texture strength on the orientation-dependent macroscopic mechanical responses of magnesium alloy. • Offers insights into microstructure-property linkages. • Makes projections of the grain size and texture dependent net plastic anisotropy on the possible ductile failure by porosity evolution. This work systematically investigates the microstructure-property relationship in Mg alloys. Emphasis is placed on understanding, through high resolution crystal plasticity modeling, how grain size and texture collectively impact material strengthening and hardening, net plastic anisotropy, and tension-compression asymmetry. To achieve this, 528 fully three-dimensional finite element calculations are performed, which comprise eleven textures, four grain sizes, six loading orientations, and two uniaxial loading states (tension and compression). The grain size effect follows Hall-Petch relation that depends on both, loading orientation and initial texture. The reduction in extension twinning with grain size refinement is influenced by texture as well. Below a threshold textural strength, grain size refinement leads to an appreciable reduction in the net plastic anisotropy at yield, quantified using Hill anisotropy, and reduced tension-compression asymmetry. Using a micromechanical basis, the effect of grain size and texture on material ductility is predicted to be non-monotonic. The computational predictions serve as synthetic data sets for experimental validation and reduced-order modeling. [ABSTRACT FROM AUTHOR]

In the present paper we report proof of consistent non monotonic lattice variation (NMLV) as a function of grain size in nanocrystalline CeO2. By analyzing more than 30 powder samples of CeO2 with grain size ranging from 5 to 200 nm which were synthesized by three different methods, it was found that in the nanocrystalline powders the unit cell parameters are smoothly varying along the decreasing of grain size with moderate contraction between 100 to 30 nm and severe expansion when the grain size become smaller than 20 nm. As a result of these two opposite trends a minimum value of unit cell parameter was detected in grain size between 25 to 50 nm. The lattice parameter change can be modeled as two global effects acting simultaneously. The first one is a contraction due to surface tension and the second one is a lattice expansion caused by ionic bonds weakening as the grain size decreases. This model can be applied to most ionic nanocrystalline materials. Consequently, it is recommended to add a new category “ambient-nano” in the crystallographic and diffraction data bases for nanomaterials with structures controlled by grain size.

0.70BiFeO3‐0.30BaTiO3 (0.70BF‐0.30BT) ceramics have been widely concerned because of their potential applications for high‐temperature piezoelectric devices. In this work, a series of dense 0.70BF‐0.30BT ceramics with average grain size variation from 0.55 to 6.0 μm were prepared. XRD results indicate that 0.70BF‐0.30BT ceramics show the coexistence of rhombohedral and pseudo‐cubic phases and the volume fraction of the rhombohedral phase increase with the grain size. The dielectric, ferroelectric and piezoelectric properties increase with the grain size initially from 0.55 to 5.0 μm and then decrease slightly. Values of d33, Pr, and εr, of 0.70BF‐0.30BT ceramics with the grain size of 5.0 μm are 185 pC/N, 21.2 μC/cm2, and 638, respectively, about five times higher than those ceramics with fine‐grain of 0.55 μm. Of particular importance is that 0.70BF‐0.30BT ceramics with large grain sizes possess better piezoelectric thermal stability due to the much stabler poled domain state with the rising temperature. The detailed structural studies indicate that the enhanced electric properties are owing to the significantly improved domain motion and the increased lattice distortion. This clarifying the relationship between electrical properties and grain size offers a novel way of improving the performances of piezoceramics. [ABSTRACT FROM AUTHOR]

Mechanical size effects at small characteristic dimensions are of intense current interest. In addition to the relevance for microfabrication, microscale compression molding provides a rich laboratory in which mechanical size effects manifest in interesting ways, especially as the characteristic molding dimension approaches the average grain size of the material being deformed. We investigate the effects of punch geometry and grain size on the mechanical response and gap filling behavior in micron scale compression molding. Micron scale long rectangular single-, double-, and triple- punch molding was conducted on polycrystalline Cu with varying grain sizes. Mechanical size effects were observed regarding the compression pressure and the material flow to fill the gaps between neighboring punches. The nominal compression pressure depended significantly on the punch width in single-punch molding and on the spacing between neighboring punches in double-punch molding. Analysis of double- and triple- punch molding data showed that both the punch geometry and the grain size of the molded Cu influence the Cu gap filling behavior in significant ways. Detailed microstructural examinations of molded Cu features were carried out to elucidate the underlying mechanisms. Our findings offer new data on micron scale plasticity and test cases for validating micron scale plasticity models.

The effect of prior austenite grain size on martensitic transformation has been studied in a high‑carbon steel with the composition of 1.0C-1.5Cr-0.3Mn-0.3Si-Fe (wt%). Powder metallurgy was used to obtain different grain-sized samples given its high performance to resist grain growth during austenitization. It is found that transformation twin is suppressed and replaced by dislocation martensite when the prior austenite grain size (PAGS) is reduced to about 3 μm. Furthermore, besides film-like retained austenite, blocky retained austenite is also observed with a total volume fraction of more than 30% when PAGS reaches 0.54 μm. Unlabelled Image • Powder metallurgy is very effective in the manufacture of ultrafine grain steels. • The martensitic substructure transition exhibits a strong grain-size dependence. • Twin martensite is rare in high carbon martensitic steel with 3 μm grain size. • The stability of austenite with 0.89wt%C is enhanced as grain size reaches 0.53 μm. [ABSTRACT FROM AUTHOR]

We conducted Vickers indentation tests on Fe-free (Mg2SiO4) and Fe-bearing (Mg1.8Fe0.2SiO4) olivine single crystals and high-density polycrystalline material with average grain sizes ranging from 170 to 890 nm. The Vickers microhardness ( H v ) of the Fe-free polycrystalline material with the finest grain size is ~ 17 GPa at a load of 0.1 N, while that of the Fe-bearing single crystal is ~ 8 GPa at the largest load applied. Overall, H v decreases with increasing grain size, load (indentation depth), and the presence of Fe. For each grain size, H v is well characterized by a power law of the form H v / H v 0 ∝ l - x , where H v 0 is the depth-independent value of H v , l represents either grain size or indentation depth, and x is 0.09. Despite the small exponent value for each size effect, the nonlinear interaction of the two size effects results in large variations of H v in our samples. We show that our semi-empirically derived relationship as a function of grain size and indentation depth explains the H v of both polycrystalline and single-crystal olivine at any indentation conditions. Indentation fracture toughness of the finest-grained material is 0.8 MPa m 1 / 2 , which increases slightly to 1.1 MPa m 1 / 2 with increasing grain size, while the toughness of the single crystals varies from 0.5 to 0.8 MPa m 1 / 2 depending on the crystallographic orientation of the fracture planes. [ABSTRACT FROM AUTHOR]

Due to the differences in mineral processing techniques, the grain-size of tailings used in the construction of a tailings pond is not commensurate. It has been determined that the hydrodynamic characteristics of mudflow resulting from the failure of tailings dams are directly influenced by grain-size, solids concentration, and the surface roughness of gully and impoundment geometry. However, the behavior and influence of the grain size of mudflow resulting from a tailings dam failure have not been sufficiently examined. To investigate the effect of grain size on the hydrodynamic characteristics of mudflow surging from tailings dam failure, the law of mudflow evolution, the change of dynamics pressure, and the velocity distributions of mudflow have been obtained via a series of flume experiments utilizing three types of grain size tailings (d50 = 0.72 mm; d50 = 0.26 mm; d50 = 0.08 mm, respectively). This study proves conclusively that with an increase in grain size, the peak value of mudflow depth notably decreases in the same section. Furthermore, it has been noted that both the velocity and the dynamic pressure raise significantly, wherein the velocity displays two distinct primary stages; namely a rapid reduction stage and a slow reduction stage. This research provides a framework for the exploration of the effect of grain size on the hydrodynamics of slurry surging from a tailings dam failure, and all presented results provide an indispensable tool in terms of the accurate assessment of potential damage in the case of a prospective impoundment failure. [ABSTRACT FROM AUTHOR]

A series of molecular dynamics simulations has been carried out to study the mechanical properties of nanocrystalline platinum. The effects of average grain size and temperature on mechanical behaviors are discussed. The simulated uniaxial tensile results indicate the presence of a critical average grain size about 14.1 nm, for which there is an inversion of the conventional Hall-Petch relation at temperature of 300 K. The transition can be explained by a change of dominant deformation mechanism from dislocation motion for average grain size above 14.1 nm to grain boundary sliding for smaller grain size. The Young's modulus shows a linear relationship with the reciprocal of grain size, and the modulus of the grain boundary is about 42% of that of the grain core at 300 K. The parameters of mechanical properties, including Young's modulus, ultimate strength, yield stress and flow stress, decrease with the increase of temperature. It is noteworthy that the critical average grain size for the inversion of the Hall-Petch relation is sensitive to temperature and the Young's modulus has an approximate linear relation with the temperature. The results will accelerate its functional applications of nanocrystalline materials. • MD simulations have been carried out to explore mechanical behaviors of nanocrystalline platinum. • Effects of grain size and temperature on the mechanical properties have been investigated. • The inverse Hall-Petch relation below grain size of 14.1 nm is observed. • The modulus of grain boundary is about 42% of that of grain core. [ABSTRACT FROM AUTHOR]

Abstract: A series of ferroelectric ceramic models with grain and grain‐boundary structures of different sizes are established via Voronoi tessellations. A phase‐field model is introduced to study the dielectric breakdown strength of these ferroelectric ceramics. Afterward, the relation between the electric displacement and electric field and the hysteresis loop are calculated using a finite element method based on a classical and modified hyperbolic tangent model. The results indicate that as the grain size decreases, the dielectric strength is enhanced, but the dielectric permittivity is reduced. The discharge energy density and energy storage efficiency of these ferroelectric ceramics extracted from the as‐calculated hysteresis both increase along with a decrease in their grain size at their breakdown points. However, under the same applied electric field, the ferroelectric ceramic with a smaller grain size possesses a lower discharge energy density but a higher energy storage efficiency. The results suggest that ferroelectric ceramics with smaller grain sizes possess advantages for applications in energy storage devices. [ABSTRACT FROM AUTHOR]

Grain-size effect on functional properties of piezoceramics is nowadays an important topic due to the potential applications of these materials at the submicron scale. In this context, we explore the effect of the grain size reduction on the functional properties stability of piezoceramics. Submicron- and micro-structured Pb(Zr,Ti)O 3 -based materials are taken as model samples to carry out this study. Rayleigh analysis is used to quantitatively evaluate the domain wall contribution. The results show that the stability of properties depends strongly on grain size. Specifically, the nonlinear response decreases significantly when the grain size is reduced to the submicron scale. This behavior can be explained by taking into account that a grain size reduction involves a grain boundary increment, which may clamp domain walls. The results suggest that grain size engineering may be an effective alternative to the widely used compositional engineering in order to control the undesirable nonlinear behavior in piezoceramics. [ABSTRACT FROM AUTHOR]

Manganese-doped Ba0.925Ca0.075TiO3 lead-free piezoelectric ceramics (abbreviated as BCT) with high mechanical quality factor were synthesized by conventional solid-state reaction method. The effects of excess Ba on the crystal structure, microstructure, and electrical properties of the ceramics were systematically investigated. X-ray diffraction and Raman spectra revealed that Ca2+ ions were pushed from Ba sites to Ti sites of BCT when 1.5 mol% extra Ba2+ ions were added after sintering. The grain size of the ceramics was decreased by adding extra Ba2+ ions. The mechanical quality factor and resistivity of the ceramics decreased dramatically when the excess Ba was more than 1.5 mol%. High piezoelectric coefficients ( d33 = 150-190 pC/N ) and high mechanical quality factors ( Qm = 1 000-1 200 ) were obtained in the ceramics when the excess of Ba was between 0.5 mol% and 1 mol%. These results indicated that the properties of BCT ceramics could be tailored by adjusting the content of Ba. [ABSTRACT FROM AUTHOR]

A series of large-scale molecular dynamics (MD) simulations has been performed to study the effects of grain size and ligament diameter on the mechanical properties of nanocrystalline nanoporous gold. Such simulations indicate that the principal deformation mechanism is a combination of grain boundary sliding, grain rotation and dislocation movement. The results of uniaxial tensile tests reveal the presence of a reverse Hall-Petch relation between strength and nominal grain size, rather than the conventional Hall-Petch relationship in the present range of nominal grain size (7.9-52.7 nm). An increase of flow stress may possibly attribute to the lower total proportion of grain boundary sliding and grain rotation in the deformation of samples with larger grain size. The Young’s modulus shows a linear relation with the reciprocal of nominal grain size, which depends largely on the volume fraction of grain boundaries and thus decreasing grain size leads to relatively lower Young’s modulus. MD simulations on samples with ligament diameter ranging from 4.07 to 8.10 nm are also carried out and results show that the increasing ligament diameter resulted in decreased flow stress and increased Young’s modulus. [ABSTRACT FROM AUTHOR]

Due to the differences in mineral processing techniques, the grain-size of tailings used in the construction of a tailings pond is not commensurate. It has been determined that the hydrodynamic characteristics of mudflow resulting from the failure of tailings dams are directly influenced by grain-size, solids concentration, and the surface roughness of gully and impoundment geometry. However, the behavior and influence of the grain size of mudflow resulting from a tailings dam failure have not been sufficiently examined. To investigate the effect of grain size on the hydrodynamic characteristics of mudflow surging from tailings dam failure, the law of mudflow evolution, the change of dynamics pressure, and the velocity distributions of mudflow have been obtained via a series of flume experiments utilizing three types of grain size tailings (d50 = 0.72 mm; d50 = 0.26 mm; d50 = 0.08 mm, respectively). This study proves conclusively that with an increase in grain size, the peak value of mudflow depth notably decreases in the same section. Furthermore, it has been noted that both the velocity and the dynamic pressure raise significantly, wherein the velocity displays two distinct primary stages; namely a rapid reduction stage and a slow reduction stage. This research provides a framework for the exploration of the effect of grain size on the hydrodynamics of slurry surging from a tailings dam failure, and all presented results provide an indispensable tool in terms of the accurate assessment of potential damage in the case of a prospective impoundment failure.

Molecular dynamics simulations have been performed to study the mechanical properties of a columnar nanocrystalline copper with a mean grain size between 9.0 and 24 nm. A melting-cooling method has been used to generate the initial samples: this method produces realistic samples that contain defects inside the grains such as dislocations and vacancies. The results of uniaxial tensile tests applied to these samples reveal the presence of a critical mean grain size between 16 and 20 nm, for which there is an inversion of the conventional Hall-Petch relation. The principal mechanisms of deformation present in the samples correspond to a combination of dislocations and grain boundary sliding. In addition, this analysis shows the presence of sliding planes generated by the motion of perfect edge dislocations that are absorbed by grain boundaries. It is the initial defects present inside the grains that lead to this mechanism of deformation. An analysis of the atomic configurations further shows that nucleation and propagation of cracks are localised on the grain boundaries especially on the triple grains junctions. [ABSTRACT FROM AUTHOR]

Epitaxial growth of titanium carbide (TiC) layer is vital for single-crystalline diamond (SCD) to ensure wettability when brazed with metals, however, how TiC grain size affects the mechanical behavior of SCD/TiC interfaces remains unclear. Herein, molecular dynamics simulations were performed to investigate the tensile properties of SCD/TiC combinations with different TiC in-plane grain sizes (d). The results show that d influenced both the elastic and plastic deformation, ascribing to the specific grain boundaries (GBs) network. The Young's modulus of the combinations was found to increase with the increase of d. After yielding, TiC{111} partial dislocations emitting from both the GBs and interfaces were observed to cross GBs or pile-up at GBs, among which d had a negligible effect on the planar-slip induced relaxation. Furthermore, it was found the interaction of dislocation-GB and dislocation-dislocation made a great contribution to strain-hardening. For the combinations with d < 8 nm, it was strengthened by piling-up dislocation at GBs, whereas for the larger d , it was dominated by intragranular dislocation entanglement. Overall, strain localization and micro crack took place at the interfaces due to the absence of plastic mechanism to accommodate strain gradient. This work provided an atomistic insight into the mechanical behaviors in SCD/TiC combinations, offering guidance for interfacial design to improve the mechanical performances in diamond devices. [Display omitted] • Mechanical performances in diamond/TiC combinations were studied by MD simulations. • Detailed stress-strain response and defect evolution were presented. • Grain-size-dependent dislocation mechanism was found. [ABSTRACT FROM AUTHOR]

The impact of a nanostructured Ni–yttria-stabilized zirconia (Ni–YSZ) anode on low-temperature solid oxide fuel cell (LT-SOFC) performance is investigated. By modifying processing techniques for the anode support, anode-supported SOFCs based on thin-film (∼1 μm) electrolytes (TF-SOFCs) with and without the nanostructured Ni–YSZ (grain size ∼100 nm) anode are fabricated and a direct comparison of the TF-SOFCs to reveal the role of the nanostructured anode at low temperature is made. The cell performance of the nanostructured Ni–YSZ anode significantly increases as compared to that of the cell without it, especially at low temperatures (500 °C). The electrochemical analyses confirm that increasing the triple-phase boundary (TPB) density near the electrolyte and anode interface by the particle-size reduction of the anode increases the number of sites available for charge transfer. Thus, the nanostructured anode not only secures the structural integrity of the thin-film components over it, it is also essential for lowering the operating temperature of the TF-SOFC. Although it is widely considered that the cathode is the main factor that determines the performance of LT-SOFCs, this study directly proves that anode performance also significantly affects the low-temperature performance. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulation is conducted to study the deformation behavior of nanocrystalline graphene sheets. It is found that the graphene sheets have almost constant fracture stress and strain, but decreased elastic modulus with grain size. The results are different from the size-dependent strength observed in nanocrystalline metals. Structurally, the grain boundaries (GBs) become a principal component in two-dimensional materials with nano-grains and the bond length in GBs tends to be homogeneously distributed. This is almost the same for all the samples. Hence, the fracture stress and strain are almost size independent. As a low-elastic-modulus component, the GBs increase with reducing grain size and the elastic modulus decreases accordingly. A composite model is proposed to elucidate the deformation behavior. [ABSTRACT FROM AUTHOR]

Demand for micromachine parts, including mini gears, has been increasing recently because of the continuously decreasing size of consumer electronic products. Forging is a conventional method of manufacturing mini gears, and it is characterized by a higher production rate, low material cost, and low total cost. Therefore, many researchers have focused on improving the technology used for forging mini gears. The present study investigated the effect of grain size of a material on the die cavity filling rate for the material during the forging of mini gears. Experimental results were compared against those of a simulation software for analyzing the applicability of software to simulations of materials with different grain sizes. The analysis indicated that materials with large grain sizes exhibit poor material flow capacity on the die base plate compared with materials with smaller grain sizes. For materials with large grain sizes, the maximum load required to fill die cavities is lower. The difference in the maximum load between the experimental results and the simulation results increased when the grain size exceeded the addendum thickness. [ABSTRACT FROM AUTHOR]

This work deals with TiO 2 nanopowders, the grain size of which was intentionally changed from about 10 nm to 30 nm by controlling the flow rate of the titanium organic precursor of C 16 H 28 O 6 Ti in flame spray synthesis (FSS). The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) compared with the results of Brunauer–Emmett–Teller (BET) nitrogen adsorption isotherms and X-ray diffraction (XRD) revealed non-agglomerated, spherical grains composed mostly of anatase. Annealing at 700 °C resulted in a partial phase transformation from anatase to rutile, with rutile crystallites as large as 57 nm. The formation of stoichiometric TiO 2 was confirmed by means of X-ray photoelectron spectroscopy. Electrical conductivity determined from dc and ac measurements increased upon reduction in grain size. The dynamic changes in the electrical resistance observed upon interaction with hydrogen over the range of 50–3000 ppm at a constant temperature chosen within the interval of 200 °C–400 °C, were reproducible. Theoretical model, based on the Schottky barriers formation at grain contacts, was applied to the sensor responses obtained in this work. Experimental data of the electrical conductivity in dry air were used to derive the temperature dependence of the band bending energy ( E O = 0.22–0.38 eV over the temperature range of 200–400 °C). The difference between the activation energy of water desorption and hydrogen atom adsorption (Δ E ) – the only fitting parameter of the adopted model – was found to decrease linearly with the specific surface area (SSA) of the TiO 2 nanomaterials. [ABSTRACT FROM AUTHOR]

The present investigation was undertaken to investigate the effect of quenching rate on the microstructure of Ni50Mn50 − xSn x ribbon alloys and its influence on the martensitic starting phase-transition temperature MS. The study was performed on melt-spun ribbons of a ferromagnetic shape memory alloy (FSMA) of composition Ni50Mn37Sn13 produced by varying the speed of the rotating copper wheel between 15 and 50 m s−1. The resulting samples have a chemical composition close to the nominal one and at room temperature crystallize in a cubic single-phase austenite with the highly ordered L21-type crystal structure without a significant variation in the cell parameter. The average grain size varies between 1.4 and 7.3 µm, while MS increased from 212 to 258 K. Our results suggest that in these materials the average grain size of the parent austenite phase limits the size of the martensite variants, giving rise to its stabilization, while a multivariant transformation mode is maintained. [ABSTRACT FROM AUTHOR]

Abstract: Tantalum polycrystals (grain sizes varying from 2.5 to 30nm) generated by Voronoi tessellation were subjected to tension and compression under uniaxial strain loading at strain rates on the order of 108–109 s−1 using molecular dynamics (MD) simulations. In contrast with MD simulations of FCC metals, the response in tension is significantly different from that in compression. In tension, fracture is initiated at grain boundaries perpendicular to the loading direction. It propagates along grain boundaries with limited plastic deformation, at a stress in the range 10–14GPa. This brittle intergranular failure is a consequence of the high strain rate imposed by MD, leading to a stress that exceeds the grain-boundary cohesive strength. Thus, grain-boundary separation is the principal failure mechanism. In compression, on the other hand, there is considerable plastic deformation within the grains. This occurs at stresses higher than failure in tension. The difference between tensile and compressive response for tantalum is attributed to the difficulty in generating dislocations, in contrast with FCC metals, where tensile failure occurs by void nucleation at grain boundaries associated with partial and perfect dislocation emission. In BCC tantalum, both grain-boundary sliding and dislocation emission are much more difficult. The compressive yield stress is found to increase with grain size in the 2.5nm

Abstract: BiFeO3 (BFO) ceramics of different grain size have been synthesized by spark plasma sintering of sol-gel derived nanoparticles. It was found that with decreasing grain size there occurs an enhancement in magnetization and a simultaneous suppression in current leakage. According to systematic materials characterization, the enhanced magnetization is attributed to the enriched grain boundaries where the missing structural order perturbs the spin helix structure of BFO and thus generates uncompensated spins, while the reduced current leakage is ascribed to fewer conduction paths provided by the compacted grain structure. [Copyright &y& Elsevier]

Abstract: Nickel nanocrystalline thin films were produced by electrodeposition using sulfamate solution. Free-standing thin films with various grain sizes ranging from 9 to 67nm were produced under a constant current with changing the content of brightener and temperature of electrodeposition. The grain-size effect on the fracture strength and the yield strength in tension tests can be divided into two regions: region A with the grain size larger than about 15nm and region B with the grain size between 9 to 15nm. In region A, the tensile strength and yield strength increase following Hall-Petch relation, and the tensile elongation decreases with decreasing grain size. In region B, the tensile and yield strength increases following a different relation of Hall-Petch type, and the tensile elongation also increases with decreasing grain size. The fatigue strength also increases with decreasing grain size following different Hall-Petch relations between region A and B. The resistance to fatigue crack propagation decreases for nanocrystalline films. Scanning electron microscopic observation of deformation near cracks shows two different features depending on the grain-size region A or B. In region A, ordinary slip deformation within the grain is predominant, while grain boundary sliding is more important in region B for fatigue damage formation. © 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11 [Copyright &y& Elsevier]

Abstract: The grain-size effect on the yield stress and the flow strength in micro-polycrystals relates closely to the penetrability of grain boundary (GB) to dislocations. To simulate the dislocation transmission across grain boundary, a dislocation–grain boundary penetration model is proposed and then integrated into the two-dimensional discrete dislocation dynamics (DDD) framework by Giessen and Needleman (1995). By this extended DDD technology, the Hall–Petch effect in micro-polycrystals and the strengthening mechanism are computationally studied, with the main focus on the significant influence of the dislocation transmission across grain boundary that is not fully considered formerly. Results indicate that the Hall–Petch type relation is still applicable, but depends strongly on the GB-penetrability to dislocations, especially for the flow strength at large offset strains. The fitting values of Hall–Petch grain-size sensitive exponents n for initial yield stress and flow stress basically agree with experimentally measured data in published literatures. [Copyright &y& Elsevier]

Abstract: In this paper, a multiscale continuum model is proposed to study the effect of grain size on the macroscopic dissipative response of shape memory alloy polycrystals during isothermal thermoelastic phase transition. In the simplest one-dimensional (1D) heterogeneous structural hierarchy, a series of non-local and non-convex double-well continuum elements are employed to model the micro-instability and the macroscopic stress hysteresis of the material under uniaxial quasi-static stretching. Three characteristic length scales (specimen size L, grain size l and intrinsic material length g) of a bulk polycrystal are imbedded in the 1D chain model and their important roles in the macroscopic dissipation are quantified. It is shown that the specific energy dissipation or the width of the stress hysteresis is governed by two non-dimensional ratios, N(=L/l) and . For a given specimen of size L, the hysteresis decreases rapidly at either very large or small values of l. In particular, it vanishes when the grain size is reduced to the nano-scale where the grain size and the interface thickness become comparable. The above results of the 1D model are reproduced in a two-dimensional (2D) non-local numerical experiment on the energy dissipation during multiple domain evolution in heterogeneous strips. The predictions of the two models agree well qualitatively with the recent experimental observations of the stress hysteresis in nano-grained superelastic NiTi polycrystals. [Copyright &y& Elsevier]

The article offers comparative study of two nanocrystalline (50 and 100&ThickSpace;nm averaged grain size) and two coarse-grain (1.2 and 10&ThickSpace;µm averaged grain size) ceramics by means of Fourier transform infrared spectroscopy in a broad temperature range (10–570&ThickSpace;K). Far infrared reflectivity spectra were fitted with the factorized model of the dielectric function and the evaluated dielectric function was compared with the results of low-frequency dielectric measurements. It appears that the stiffening and weakening of the overdamped soft mode is the only reason for the reduced dielectric permittivity of nanocrystalline ceramics in the paraelectric phase, but a strong grain-size dependence of the dielectric constant in the ferroelectric phase is not connected with the changes in lattice dynamics. All single-crystal symmetry changes were detected in all of the samples, but no phase-transition discontinuities was seen in nanocrystalline ceramics. A coexistence of more than one phase is suggested. Strong dependence of the Curie-Weiss temperature on the grain size, earlier revealed by others, is confirmed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Micron scale single-, double-, triple- punch molding conducted on Cu with various grain sizes. • Effect of punch geometry and grain size on mechanical response and gap filling examined in detail. • Full understanding should consider strain compatibility, hardening rate, & strain gradients. Mechanical size effects at small characteristic dimensions are of intense current interest. In addition to the relevance for microfabrication, microscale compression molding provides a rich laboratory in which mechanical size effects manifest in interesting ways, especially as the characteristic molding dimension approaches the average grain size of the material being deformed. We investigate the effects of punch geometry and grain size on the mechanical response and gap filling behavior in micron scale compression molding. Micron scale long rectangular single-, double-, and triple- punch molding was conducted on polycrystalline Cu with varying grain sizes. Mechanical size effects were observed regarding the compression pressure and the material flow to fill the gaps between neighboring punches. The nominal compression pressure depended significantly on the punch width in single-punch molding and on the spacing between neighboring punches in double-punch molding. Analysis of double- and triple- punch molding data showed that both the punch geometry and the grain size of the molded Cu influence the Cu gap filling behavior in significant ways. Detailed microstructural examinations of molded Cu features were carried out to elucidate the underlying mechanisms. Our findings offer new data on micron scale plasticity and test cases for validating micron scale plasticity models. [ABSTRACT FROM AUTHOR]

Oxide-dispersed iron aluminides with Al contentsranging from 10 to 28 at.% were oxidized in air attemperatures between 600 and 1300°C in order todetermine the critical Al content necessary to form a protective, external alumina scale. AY2O3-Al2O3dispersion, performed similarly to anAl2O3 dispersion, indicated littleeffect of Y on the critical Al content. Compared toingot-processed iron aluminides, the addition of an oxide dispersion reduced thecritical Al content at 900°C. This reduction isattributed to the finer grain size in theoxide-dispersed Fe-Al. [ABSTRACT FROM AUTHOR]

Inorganic and organic pollutants (nutrients and toxic pollutants) ,are liable to accumulate in suspended and bottom sediments. The major transport of these pollutants takes place in the suspended load. Sedimentation and resuspension are in dynamic equilibrium along the river influenced mainly by physical processes. International and national surveys on the Danube sediment concluded that the Danube reach between Vienna and Budapest is one of the most polluted ones in addition to the Irongate reservoir and the downstream reach. The main polluting compounds are petroleum hydrocarbons, including PAHs, and heavy metals. Reservoirs are the major traps of sediment-bound pollutants where pollutant "time-bombs" may be developed. Pollutant monitoring of the bottom sediment requires careful selection of the representative sampling sites where the sediment contains at least 10 percent clay and silt which is enriched in pollutants. Mobilization of the sediment-bound pollutants will result in biological uptake by the benthic organisms. The macrozoobenthons monitoring provides valuable evidence for chronic biological stress associated with contaminated sites. Benthic biodiversity decreased along the studied Danube reach downstream of recognized hot spots such as major cities (Vienna, Bratislava, Budapest) mid polluted tributaries (the Vah river, etc.). Harmonization between chemical measurements and biological observations in the sediment could eventually lead to an effective Danube pollution monitoring system. [ABSTRACT FROM AUTHOR]

[Display omitted] This work investigates the microstructure-property linkages in magnesium (Mg) with an emphasis on understanding interaction effects between the grain size, texture, and loading orientation. A single crystal plasticity framework endowed with experimentally informed micro Hall-Petch type relations for the activation thresholds for slip and twinning is adopted to resolve polycrystalline microstructures over a broad texture-grain size space. The macroscopic trends from the simulations corroborate with experiments. The synergistic effects of microstructural engineering on the micromechanical characteristics are mapped, which reveal their role in the emergent macroscopic behaviors. The simulations predict reduced extension twinning with grain size refinement even though the micro Hall-Petch coefficient for twinning is smaller than that for the non-basal slip modes. While grain refinement and textural weakening generally reduce the net plastic anisotropy and tension-compression asymmetry, the degree to which these macroscopic behaviors are tempered depends on the loading orientation. The results offer preliminary insight into the roles that texture and grain size may play in the damage behavior of engineered Mg microstructures. [ABSTRACT FROM AUTHOR]

The grain-size effect on phase transition temperatures orthorhombic → tetragonal, Tot, and tetragonal → cubic (ferroelectric → paraelectric), Tc, of barium titanate samples (BaTiO3) was studied by using differential scanning calorimetric technique (DSC). This last temperature was also measured by using impedance spectroscopic technique (IS). The results indicate that the obtained values of Tc (for each grain size sample) when the sample forms and it does not forms part of an external electric circuit, by using IS and DSC techniques, respectively, are equal. On the other hand, it was observed that while the grain size increases the temperatures and enthalpies transitions as well as their thermal hysteresis increases. These results are in agreement with the Arlt et al. [G. Arlt, D. Hennings, and G. of With, J. Appl. Phys. 58, 1619 (1985)] hypothesis that systems with greater grain size exhibit greater internal tensions, thus requiring greater thermal energy to produce the ferroelectric → paraeléctric transformation. This hypothesis could also be applied to the other structural phase transition: the orthorhombic → tetragonal one. [ABSTRACT FROM AUTHOR]

• Extended dislocations dominate the plastic deformation of nanolaminated PAl/Gr composites. • The dislocation-GB interaction transits to a dislocation-Gr interaction with the decreasing of laminate thickness. • The greater ability of storing dislocations at the interface contributes to the strain-hardening capability. • The back-stress strengthening mechanism is induced by GNDs to accommodate the deformation gradient. • A CLS model considering back-stress strengthening can accurately predict the flow stress of PAl/Gr composites. Nanolaminated metal/graphene composites can have many special mechanical properties, thanks to a high density of interfaces. Even though the interface effect is a key mechanism for the propagation of dislocations in nanolaminated metal/graphene composites, it is not well understood. In this paper, simulations of the molecular dynamics of nanolaminated polycrystalline aluminum/graphene (PAl/Gr) composites are performed. The results provide insight into the grain-size effect on plastic flow stress of nanolaminated PAl/Gr composites and the underlying mechanism. Extended dislocations are found to dominate the plastic deformation of the PAl/Gr composites. Both the PAl/Gr interface and the Al grain boundaries (GBs) interact with the dislocations. Three dislocation propagation forms are observed in the PAl/Gr nanolaminated composite based on the Al grain-size. By decreasing the laminate thickness, the dislocation-GB interaction can transition to a dislocation-graphene interaction. When the Al layer thickness is smaller than the in-plane grain size, the strain-hardening capability is increased due to greater ability of the dislocation/graphene-interface to store dislocations than the GBs. Besides, geometrically necessary dislocations are induced because of the deformation gradient between the graphene and Al grains, which lead to back-stress strengthening and thus strain hardening. Accordingly, a confined layer slip mechanism, which considers back-stress, is used to predict the flow stress of the PAl/Gr composites. [ABSTRACT FROM AUTHOR]

In this work, we investigated the processing-microstructure-property relationships for magnetoelectric (ME) particulate composites consisting of hard ferromagnetic CoFe2O4 (CFO) particles dispersed in a Nb-doped PbZrxTi1-xO3 (PZT) soft ferroelectric matrix. Several preparation steps, namely PZT powder calcination, PZT-CFO mixture milling and composite sintering were tailored and a range of microstructures was obtained. These included open and closed porosities up to full densification, PZT matrices with decreasing grain size across the submicron range down to the nanoscale and well dispersed CFO particles with bimodal size distributions consisting of submicron and micron sized components with varying weights. All samples could be poled under a fixed DC electric field of 4 kV/mm and the dielectric, piezoelectric and elastic coefficients were obtained and are discussed in relation to the microstructure. Remarkably, materials with nanostructured PZT matrices and open porosity showed piezoelectric charge coefficients comparable with fully dense composites with coarsened microstructure and larger voltage coefficients. Besides, the piezoelectric response of dense materials increased with the size of the CFO particles. This suggests a role of the conductive magnetic inclusions in promoting poling. Magnetoelectric coefficients were obtained and are discussed in relation to densification, piezoelectric matrix microstructure and particle size of the magnetic component. The largest magnetoelectric coefficient α33 of 1.37 mV cm−1 Oe−1 was obtained for submicron sized CFO particles, when closed porosity was reached, even if PZT grain size remained in the nanoscale. [ABSTRACT FROM AUTHOR]

In the present study, the impact of copper substrate grain size on the structure of the succeeding electrodeposited nickel film and its consequent corrosion resistance in 3.5% NaCl medium were evaluated before and after functionalization with stearic acid. Nickel layers were electrodeposited on two different copper sheets with average grain size of 12 and 25 µm, followed by deposition of stearic acid film through self-assembly. X-ray diffraction analysis of the electrodeposited nickel films revealed that the deposition of nickel film on the Cu substrate with small (12 µm) and large (25 µm) grains is predominantly governed by growth in the (220) and (111) planes, respectively. Both electrodeposited films initially exhibited a hydrophilic nature, with water-contact angles of 56° and <10°, respectively. After functionalization with stearic acid, superhydrophobic films with contact angles of ~150° were obtained on both samples. In a 3.5% NaCl medium, the corrosion resistance of the nickel layer electrodeposited on the copper substrate with 25 µm grains was three times greater than that deposited on the copper substrate with 12 µm grains. After functionalization, the corrosion resistance of both films was greatly improved in both short and long immersion times in 3.5% NaCl medium. [ABSTRACT FROM AUTHOR]

This paper is aimed at investigating the mechanical properties and deformation mechanisms of nanocrystalline copper under nanoindentation. The Voronoi tessellation method is adopted to generate nanocrystalline structures with stochastic grain orientations that mimic those in experiments. Grain-size effect is studied and discussed via molecular dynamics simulations. The results reveal the inversion of Hall-Petch relation about hardness at a grain size of 15.1 nm, which agrees well with previous works in tension. Below the critical grain size, grain boundary sliding, grain growth and grain rotation are easily observed. Grain boundary motion is the dominant deformation with smaller grain size below 15.1 nm while dislocation motion dominates above the critical value. It is noteworthy that the elastic recovery in indentation direction, increases with larger grain size and monocrystalline copper behaves with the strongest elastic recovery. The study further reveals the deformation mechanism of nanocrystalline copper under nanoindentation and accelerates the functional applications of nanocrystalline materials. Material science; computational material. • Nanocrystalline structure is generated by Voronoi tessellation method. • Nanoindentation behaviors of nanocrystalline copper are investigated. • The critical grain size for the inversion of Hall-Petch relation is about 15.1 nm. • Grain boundary sliding, grain rotation and grain growth are easily observed. • The depth elastic recovery is sensitive to grain size. [ABSTRACT FROM AUTHOR]

Grain size is an important controlling factor of the chemical composition of sediments. To understand the role of grain size in the content of rare earth elements (REE) in tropical mountainous river sediments and to establish suitable provenance proxies, sediments collected from Pahang River and Kelantan River, Peninsular Malaysia, were determined for REE contents in six size fractions (<2 μm, 2–4 μm, 4–8 μm, 8–16 μm, 16–32 μm, and 32–63 μm). The results indicate that the total REE contents (∑REE) from these two rivers are weakly correlated with grain sizes. The normalized REE patterns of various grain-size fractions to <63 μm fractions revealed a flat pattern for light rare earth elements (LREE), but were gradually enriched in heavy rare earth elements (HREE) with increasing grain size. These results indicate that the grain size constraint on REE is very complex. The relationship between REE contents and mineral compositions of size-fractioned sediments further suggests that clay minerals cause high REE contents in clay components (<2 μm). The dilution effect of quartz and feldspars on REE is another controlling factor, leading to low REE content in medium-fine silt components (2–32 μm). In addition, heavy minerals, zircon, monazite and amphibole, play an important role in enriching REE in coarse silt components (32–63 μm), especially zircon as the major contributor to the enrichment of HREE with increasing grain size. By combining the content of REE, the normalized REE patterns and the REE characteristic parameters for different grain sizes, we find that the 4–8 μm fraction is sensitive to REE variation among the six size fractions investigated. Furthermore, the relationship between upper continental crust-normalized δEu and (Gd/Yb) is reliable for distinguishing the sediment characteristics of Pahang River and Kelantan River and can therefore be used as an effective indicator for identifying Malaysian river-sourced sediments in the southern South China Sea. • REE compositions in different grain-size fractionated sediments from two tropical mountainous rivers are different. • Mineral composition is the main controlling factor of the grain size effect on REE. • The 4–8 μm fraction represents REE variation sensitively among six size fractions investigated in these two rivers. • δEu UCC -(Gd/Yb) UCC discriminant diagram can be used to distinguish Malaysian river-sourced sediments in the southern SCS. [ABSTRACT FROM AUTHOR]