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Showing papers on "Grain size published in 2010"


Journal ArticleDOI
TL;DR: A survey of previous work related to the relationship between grain size and corrosion resistance for a number of light metamodel classes can be found in this article, with a focus on the effect of grain size on corrosion.
Abstract: Grain refinement is known to lead to improvements in strength and wear resistance. Inherent processing involved in grain refinement alter both the bulk and the surface of a material, leading to changes in grain boundary density, orientation, and residual stress. Ultimately, these surface changes can have an impact on electrochemical behavior and, consequently, corrosion susceptibility as evidenced by the large number of studies on the effect of grain size on corrosion, which span a range of materials and test environments. However, there has been limited work on developing a fundamental understanding of how grain refinement and more generally how grain size affects the corrosion resistance of an alloy. Existing literature is often contradictory, even within the same alloy class, and a coherent understanding of how grain size influences corrosion response is largely lacking. A survey of previous work related to the relationship between grain size and corrosion resistance for a number of light meta...

873 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that yttrium-stabilized zirconia can be sintered in a few seconds at ∼850°C to full density, starting from a green density of 0.5, by the application of a dc electrical field.
Abstract: We show that yttrium-stabilized zirconia can be sintered in a few seconds at ∼850°C to full density, starting from a green density of 0.5, by the application of a dc electrical field (nominally, several hours at 1450°C are needed to complete the sintering process). This finding is explained by the local Joule heating at grain boundaries, which, on the one hand, promotes grain-boundary diffusion (a kinetic effect), while at the same time restricts grain growth (a thermodynamic effect). The smaller grain size and the higher temperature at grain boundaries can then act synergistically to enhance the rate of sintering. These results have a bearing in explaining the widespread spark plasma and microwave-assisted techniques for enhanced sintering.

751 citations


Journal ArticleDOI
TL;DR: In this paper, a review of the pertinent literature combined with the authors' works reveals that a relationship exists between corrosion rate and grain size and reveals an important fundamental relationship that can be exploited for material durability and design.

707 citations


Journal ArticleDOI
TL;DR: In this article, the peak dimensionless thermoelectric figure-of-merit (ZT) of Bi2Te3-based n-type single crystals is about 085 in the ab plane at room temperature.
Abstract: The peak dimensionless thermoelectric figure-of-merit (ZT) of Bi2Te3-based n-type single crystals is about 085 in the ab plane at room temperature, which has not been improved over the last 50 years due to the high thermal conductivity of 165 W m−1 K−1 even though the power factor is 47 × 10−4 W m−1 K−2 In samples with random grain orientations, we found that the thermal conductivity can be decreased by making grain size smaller through ball milling and hot pressing, but the power factor decreased with a similar percentage, resulting in no gain in ZT Reorienting the ab planes of the small crystals by repressing the as-pressed samples enhanced the peak ZT from 085 to 104 at about 125 °C, a 22% improvement, mainly due to the more increase on power factor than on thermal conductivity Further improvement is expected when the ab plane of most of the small crystals is reoriented to the direction perpendicular to the press direction and grains are made even smaller

602 citations


Journal ArticleDOI
TL;DR: In this article, the effect of grain size and grain orientation on deformation twinning in a Fe-22-wt.% Mn-0.6-c TWIP steel was investigated.
Abstract: We investigate the effect of grain size and grain orientation on deformation twinning in a Fe–22 wt.% Mn–0.6 wt.% C TWIP steel using microstructure observations by electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). Samples with average grain sizes of 3 μm and 50 μm were deformed in tension at room temperature to different strains. The onset of twinning concurs in both materials with yielding which leads us to propose a Hall–Petch-type relation for the twinning stress using the same Hall–Petch constant for twinning as that for glide. The influence of grain orientation on the twinning stress is more complicated. At low strain, a strong influence of grain orientation on deformation twinning is observed which fully complies with Schmid's law under the assumption that slip and twinning have equal critical resolved shear stresses. Deformation twinning occurs in grains oriented close to 〈1 1 1〉//tensile axis directions where the twinning stress is larger than the slip stress. At high strains (0.3 logarithmic strain), a strong deviation from Schmid's law is observed. Deformation twins are now also observed in grains unfavourably oriented for twinning according to Schmid's law. We explain this deviation in terms of local grain-scale stress variations. The local stress state controlling deformation twinning is modified by local stress concentrations at grain boundaries originating, for instance, from incoming bundles of deformation twins in neighboring grains.

567 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the corrosion resistance of AZ31B alloy with different grain sizes in 3.5% NaCl solution using immersion testing, evolved hydrogen gas measurement and potentiodynamic polarisation measurement.

477 citations


Journal ArticleDOI
TL;DR: In this paper, the saturation microstructure of a single-phase material was studied and it was shown that the saturation grain size decreases with decreasing deformation temperature, although the dependency is stronger at medium homologous temperatures and less in the low temperature regime.
Abstract: In this review, we focus on the saturation microstructure that evolves during severe plastic deformation (SPD). These nanocrystalline or ultrafinegrained microstructures consist predominantly of high-angle boundaries, although low-angle boundaries are also present. Deformation temperature, alloying, and strain path are the dominant factors controlling the saturation grain size in single-phase materials. The saturation grain size decreases significantly with decreasing deformation temperature, although the dependency is stronger at medium homologous temperatures and less in the lowtemperature regime. The saturation microstructure is sensitive to strain rate at medium temperatures and less so at low temperatures. The addition of alloying elements to pure metals also reduces the saturation grain size. The results indicate that grain boundary migration is the dominant process responsible for the limitation in refinement by SPD. Therefore, second-phase particles of the nanometer scale can stabilize even finer microstructures. This mechanism of stabilization of the microstructure is an effective tool for overcoming the limit in refinement of single-phase materials by SPD. The improved thermal stability of the obtained nanostructures is another benefit of the introduction of second-phase particles.

451 citations


Journal ArticleDOI
TL;DR: This paper conducted a statistical analysis on large data sets generated by electron backscattering diffraction (EBSD) to extract quantitative and meaningful relationships between material microstructure and deformation twinning in magnesium.
Abstract: To extract quantitative and meaningful relationships between material microstructure and deformation twinning in magnesium, we conduct a statistical analysis on large data sets generated by electron backscattering diffraction (EBSD). The analyses show that not all grains of similar orientation and grain size form twins, and twinning does not occur exclusively in grains with high twin Schmid factors or in the relatively large grains of the sample. The number of twins per twinned grain increases with grain area, but twin thickness and the fraction of grains with at least one visible twin are independent of grain area. On the other hand, an analysis of twin pairs joined at a boundary indicates that grain boundary misorientation angle strongly influences twin nucleation and growth. These results question the use of deterministic rules for twin nucleation and Hall–Petch laws for size effects on twinning. Instead, they encourage an examination of the defect structures of grain boundaries and their role in twin ...

444 citations


Journal ArticleDOI
TL;DR: A review and overview of a series of works generated in our laboratory over the last 5 years can be found in this paper, where the authors described the development and evolution of a new paradigm for exchange bias in polycrystalline thin films with grain sizes in the range 5-15nm.

389 citations


Journal ArticleDOI
TL;DR: In this article, a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO2 fibers was presented, where the Pd-loaded sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H2 and lower sensitivity to NO2 compared to their unloaded counterparts.
Abstract: This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO2 fibers. Unloaded and Pd-loaded SnO2 nanofiber mats are synthesized by electrospinning followed by hot-pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd-loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO2 crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO2 crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd-loaded specimen, indicating that Pd-loading could effectively suppress the SnO2 grain growth during the calcination step. The Pd-loaded SnO2 sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H2 and lower sensitivity to NO2 compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO-decorated SnO2 crystallites and catalytic effect of PdO in promoting the oxidation of H2 into H2O. These phenomena appear to have a much larger effect on the sensitivity of the Pd-loaded sensors than the reduction in grain size.

376 citations


Journal ArticleDOI
TL;DR: In this paper, the surface conductivity of porous rocks has two contributions: the first is associated with the diffuse layer coating the grains and is frequency-independent as long as the diffuse layers is above a percolation threshold.
Abstract: SUMMARY The surface conductivity of porous rocks has two contributions: the first is associated with the diffuse layer coating the grains and is frequency-independent as long as the diffuse layer is above a percolation threshold. The second contribution is associated with the Stern layer of weakly sorbed counterions on the mineral surface and is frequency-dependent if the Stern layer is discontinuous at the scale of the representative elementary volume. In the frequency range 1 mHz–100 Hz, this second contribution is also associated with the main polarization mechanism observed by the spectral induced polarization method in granular media (neglecting the contribution of other polarization processes like those associated with redox processes and membrane polarization). At the macroscale, we connect the Stern layer contribution to the complex conductivity and to the expectation of the probability distribution of the inverse of the grain size. This is done by performing a convolution between the probability distribution of the inverse of the grain size and the surface conductivity response obtained when all the grains have the same size. Surface conductivity at the macroscopic scale is also connected to an effective pore size used to characterize permeability. From these relationships, a new equation is derived connecting this effective pore size, the electrical formation factor, and the expected value of the probability distribution for the inverse of the grain size, which is in turn related to the distribution of the relaxation times. These new relationships are consistent with various formula derived in the literature in the limit where the grain size distribution is given by the delta function or a log normal distribution and agree fairly well with various experimental data showing also some limitations of the induced polarization method to infer permeability. One of these limitations is the difficulty to detect the relaxation, in the phase, associated with the smaller grains, as this polarization may be hidden by the Maxwell–Wagner polarization at relatively high frequencies (>100 Hz). Also, cemented aggregates of grains can behave as coarser grains.

Journal ArticleDOI
TL;DR: In this article, the micro-structural evolution and grain refinement in ANSI 304 stainless steel subjected to multiple laser shock processing (LSP) impacts were investigated by means of cross-sectional optical microscopy and transmission electron microscopy observations.

Journal ArticleDOI
TL;DR: In this article, the plastic deformation behavior and the effects of the impact time on the LY2 aluminum (Al) alloy during multiple laser shock processing (LSP) impacts were investigated.

Journal ArticleDOI
TL;DR: In this article, the effect of thermal damage on the physical properties of carbonate rocks has been investigated, including microstructure, bulk density, effective porosity and P-wave velocity.

Journal ArticleDOI
TL;DR: In this article, a large strain warm deformation at different temperatures and subsequent intercritical annealing has been applied to obtain fine grained (2.4m) and ultrafine-grained (1.2m) ferrite/martensite dual-phase (DP) steels.
Abstract: Large strain warm deformation at different temperatures and subsequent intercritical annealing has been applied to obtain fine grained (2.4m) and ultrafine grained (1.2m) ferrite/martensite dual-phase (DP) steels. Their mechanical properties were tested under tensile and impact conditions and compared to a hot deformed coarse grained (12.4m) reference material. Both yield strength and tensile strength follow a Hall–Petch type linear relationship, whereas uniform elongation and total elongation are hardly affected by grain refinement. The initial strain hardening rate as well as the post-uniform elongation increase with decreasing grain size. Ductile fracture mechanisms are considerably promoted due to grain refinement. Grain refinement further lowers the ductile-to-brittle transition temperature and leads to higher absorbed impact energies. Besides the common correlations with the ferrite grain size, these phenomena are explained in terms of the martensite particle size, shape and distribution and the more homogeneous dislocation distribution in ultrafine ferrite grains.

Journal ArticleDOI
TL;DR: In this paper, the effect of industrial pre-treatment on the corrosion performance of Mg alloy AZ31 sheet was investigated, and it was found that tempering accelerates the corrosion of AZ31.

Journal ArticleDOI
TL;DR: In this paper, the effect of alumina particle size and its amount on the relative density, hardness, microstructure, wear resistance, yield and compressive strength and elongation in Al-Al2O3 composites was investigated.
Abstract: Al matrix composite is well known, in which Al2O3 is the most widely used reinforcement. The aim of this study is to investigate the effect of alumina particle size and its amount on the relative density, hardness, microstructure, wear resistance, yield and compressive strength and elongation in Al–Al2O3 composites. To this end, the amount of 0–20 wt.% alumina with average particle sizes 48, 12 and 3 μm was used along with pure aluminum of average particle size of 30 μm. Powder metallurgy is a method used in the fabrication of this composite in which the powders were mixed using a planetary ball mill. Consolidation was conducted by axial pressing at 440 MPa. Sintering procedure was done at 550 °C for 45 min. The results indicated that as the alumina particle size is reduced, density raises at first, then, declines. Moreover, as the alumina particle size decreases, hardness, yield strength, compressive strength and elongation increase and factors such as wear resistance, microstructure grain size and distribution homogeneity in matrix decreases. For instance, as the alumina particle size gets smaller from 48 to 3 μm at 10 wt.% alumina, hardness rises from 50 to 70 BHN, compressive strength improves from 168 to 307 MPa and wear rate rises from 0.0289 to 0.0341 mm3/m. On the other hand, as the amount of alumina increases, hardness and wear resistance increase and relative density and elongation is decreased. However, compressive and yield strength rise at first, then drop. For example, if the amount of alumina with 12 μm particle size increases from 5 to 10 wt.%, hardness increases from 47 to 62 BHN and compressive strength rises from 190 to 273 MPa. Nevertheless, erosion rate after 300 m decreases from 0.0447 to 0.0311 mm3/m.

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate a way to impart severe plastic deformation to magnesium at room temperature to produce ultrafine grain size of similar to 250 nm through equal channel angular extrusion (ECAE).

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the influence of grain size on the corrosion rate of Mg and found a significant variation in corrosion rate with the number of ECAP passes, and hence grain size, which is of key significance.
Abstract: This study seeks to clarify the influence of grain character on the corrosion rate of Mg. There is a special need to understand the largely unknown corrosion–grain size relationship for Mg, which nominally displays poor corrosion resistance, since any efforts to reduce or control the rate of Mg corrosion are of large technological significance. In this work, the microstructure is modified by equal channel angular pressing (ECAP) with up to eight passes, to achieve a range of refined microstructures ranging in grain size from a few hundred micrometres to a few micrometres. Results reveal a significant variation in corrosion rate with the number of ECAP passes, and hence grain size, which is of key significance. The results are discussed in terms of grain size, misorientation, along with resultant surface state produced and electrochemical/polarisation signatures collected.

Journal ArticleDOI
TL;DR: In this article, the influence of UST parameters and solidification conditions on the final grain structure is analyzed, and it was found that small additions of zirconium and titanium can significantly increase the efficiency of ultrasonic melt treatment under the stipulation that grain refinement is performed in the temperature range of primary solidification of Al3Zr.
Abstract: It is well known that ultrasonic melt treatment (UST) promotes grain refinement in aluminum alloys. Cavitation-aided grain refinement has been studied for many years; however, it is still not being applied commercially. The current article summarizes the results of experimental work performed on various alloying systems at different stages of solidification. The influence of UST parameters and solidification conditions on the final grain structure is analyzed. It was found that small additions of zirconium and titanium can significantly increase the efficiency of UST, under the stipulation that grain refinement is performed in the temperature range of primary solidification of Al3Zr. The possible mechanisms for this effect are discussed.

Journal ArticleDOI
TL;DR: In this article, the tensile deformation behavior and microstructural evolutions of twinning induced plasticity (TWIP) steel with the chemical composition of Fe-31Mn-3Al-3Si and average grain sizes in the range of 21-726μm have been analyzed for each grain size, the Hollomon analysis and also the Crussard-Jaoul analysis as an alternative method to describe the work hardening behavior were investigated.

Journal ArticleDOI
TL;DR: Optical spectroscopy and X-ray diffraction show a substantial improvement in plasmon resonance quality for square-particle nanoantennas after annealing due to an enlarged grain size from 22 to 40 nm and improved grain boundaries described by the electron reflection coefficient.
Abstract: The effect of grain boundaries on the electron relaxation rate is significant even for large area noble metal films and more so for plasmonic nanostructures. Optical spectroscopy and X-ray diffraction show a substantial improvement in plasmon resonance quality for square-particle nanoantennas after annealing due to an enlarged grain size from 22 to 40 nm and improved grain boundaries described by the electron reflection coefficient. The electron relaxation rate due to the grains is shown to decrease by a factor of 3.2.

Journal ArticleDOI
TL;DR: In this paper, the effect of reduction in particle size on the temperature dependent magnetization of chemically synthesized BiFeO3 nanocrystals with average grain size of 55 nm was reported.
Abstract: Here, we report the effect of reduction in particle size on the temperature dependent magnetization of chemically synthesized BiFeO3 nanocrystals with average grain size of 55 nm. The X-ray photoelectron spectroscopy results show a significant broadening of binding energy peaks associated to Fe3+ 2p3/2 core levels due to the reduced size. Additionally, due to the nanosize effect, the M-H loops show a significant coercivity starting from 390 K with an anomaly located in the vicinity of 150 K in our Hc vs T as well as Mr/Ms(50 kOe) vs T curves. At this temperature, both Hc and Mr/Ms(50 kOe) undergo minima. Additionally, our results for the first time show the evidence of existence of a low temperature anomaly due to spin-glass transition in the range from 40−44 K in the field cooled magnetization curves. In bulk single crystals, this transition is reported to be situated at around 50 K, however, this transition remained so far undiscovered in the recent studies on BiFeO3 nanoparticles due to the insufficien...

Journal ArticleDOI
TL;DR: In this paper, a new model is proposed that aims to capture within a single modelling frame all the main microstructural features of a severe plastic deformation process, including the evolution of the grain size distribution, misorientation distribution, crystallographic texture and the strain-hardening of the material.

Journal ArticleDOI
TL;DR: In this article, the A-site non-stoichiometry in Ba1−xZr0.8Y0.2O3−δ, a candidate electrolyte material for fuel cell and other electrochemical applications, was investigated.
Abstract: Recent literature indicates that cation non-stoichiometry in proton-conducting perovskite oxides (ABO3) can strongly influence their transport properties. Here we have investigated A-site non-stoichiometry in Ba1−xZr0.8Y0.2O3−δ, a candidate electrolyte material for fuel cell and other electrochemical applications. Synthesis is performed using a chemical solution approach in which the barium deficiency is precisely controlled. The perovskite phase is tolerant to barium deficiency up to x = 0.06 as revealed by X-ray diffraction analysis, but accommodates the non-stoichiometry by incorporation of yttrium on the A-site. The dopant partitioning can explain the decrease in cell constant with increasing x, the decrease in proton conductivity (the latter as measured by a.c. impedance spectroscopy under humidified atmosphere), and the decrease in grain size in the sintered compacts. Within the single-phase region barium deficiency also has a detrimental impact on grain boundary conductivity, as a result both of the decreased grain size, leading to a higher number density of grain boundaries and of an increased per boundary resistivity. At higher values of x, a two phase system is observed, with yttria appearing as the predominant secondary phase and the barium zirconate reverting to an undoped composition. From the relative concentrations of the observed phases and their lattice constants, the ternary phase behavior at 1600 °C (the sintering temperature) is generated. Both the bulk and grain boundary conductivities are sharply lower in the two-phase system than in the single phase compositions. The control over processing conditions demonstrates that it is possible to reproducibly prepare large-grained, stoichiometric BaZr0.8Y0.2O3−δ with a total conductivity of 1 × 10−2 Scm−1 at 450 °C, while revealing the mechanisms by which barium deficiency degrades properties.

Journal ArticleDOI
TL;DR: In this article, the authors report (FePt)Ag-C granular thin films for potential applications to ultrahigh density perpendicular recording media, that were processed by co-sputtering FePt, Ag, and C targets on MgO underlayer deposited on thermally oxidized Si substrates.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the evolution of microstructure and functional superelastic properties of Ni-Ti wires subjected to a non-conventional heat treatment by controlled electric pulse currents.

Journal ArticleDOI
TL;DR: In this paper, a model for grain refinement in magnesium alloys processed by ECAP based on the principles of dynamic recrystallization where new fine grains are formed along the initial boundaries and along twin boundaries is presented.
Abstract: Equal-channel angular pressing (ECAP) is an effective tool for refining the grain structure of magnesium alloys and improving the ductility at moderate temperatures. However, grain refinement in these alloys differs from other metals because new grains are formed along the boundaries of the initial structure and these newly formed grains slowly spread to consume the interiors of the larger grains in subsequent passes. A model is presented for grain refinement in magnesium alloys processed by ECAP based on the principles of dynamic recrystallization where new fine grains are formed along the initial boundaries and along twin boundaries. This model provides an explanation for a wide range of experimental data and introduces the concept of grain size engineering for achieving selected material properties in magnesium alloys.

Journal ArticleDOI
TL;DR: In this article, the effect of process parameters such as rotational and traverse speeds, tool penetration depth and tilt angle on the formation of defects such as cracks, tunnelling cavity and also on sticking of matrix material to the tool was investigated.
Abstract: Friction stir processing (FSP) was used to fabricate SiC/AZ91 composite layer. Effect of process parameters such as rotational and traverse speeds, tool penetration depth and tilt angle on the formation of defects such as cracks, tunnelling cavity and also on sticking of matrix material to the tool was investigated. Also, effect of these parameters was studied on the mechanical properties and microstructures of specimens. Microstructure studies were carried out by optical and SEM. Results showed that FSP is an effective process to fabricate SiC/AZ91 composite layer with uniform distribution of SiC particles, good interfacial integrity and significant grain refinement. Increasing the rotational speed leads to a decrease in the grain size and an increase in the traverse speed leads to a decrease in the grain size. There are upper and lower limitations for these speeds which were determined. PD is a more effective parameter to produce sound surface layer. PD value was affected by traverse and rotational speeds and the tilt angle values. This study shows that by using 5 μm SiC particles, the stir zone grain size reduces from 150 to 7.17 μm and stir zone hardness increases from 63 to 96 Hv.

Journal ArticleDOI
01 Aug 2010-Geology
TL;DR: In this paper, the authors present the first systematic investigation of the recrystallized grain size distribution, for quartz mylonites deformed over a wide range of conditions, with distinct maxima at 10-20 μm and 70-80 μm, and minima at 35-40 μm.
Abstract: The dynamically recrystallized grain size is a material parameter associated with dislocation creep of crystalline solids that is especially important as a flow stress indicator via piezometer calibrations. Grain sizes have been measured in many studies of deformed rocks as well as metals and ceramics, but global analyses of the frequency distribution of dynamically recrystallized grain sizes are lacking. Here we present the first systematic investigation of the recrystallized grain size distribution, for quartz. The grain diameters, compiled from 555 samples of 31 studies of quartz mylonites deformed over a wide range of conditions, extend from ∼3 μm to 3 mm, with distinct maxima at 10–20 μm and 70–80 μm, and minima at 35–40 μm and ∼120 μm. The frequency maxima correlate with distinct microstructures and the minima with the transitions between these microstructures, which we interpret to result from the dominance of the recrystallization mechanisms of bulging, subgrain rotation, and grain boundary migration recrystallization. These results demonstrate the necessity of distinct piezometer calibrations for different recrystallization mechanisms and highlight the importance of the recrystallized grain size for theoretical models of dynamic recrystallization.