Submicrometer Grain Research Articles

Study of 4.5%mol Y<sub>2</sub>O<sub>3</sub>-Doped ZrO<sub>2</sub> with Submicrometer Grain Size

The aim of this study was to obtain 4.5%mol Y2O3-doped ZrO2dense with submicrometer grain size and studying the effects of using oxygen flow during calcination in the electrical properties of bodies sintered. The powders were synthesized by the Pechini method. After synthesis, the resins were dried and the calcinations were performed in air and in oxygen flow at 600°C for 2 h. The powders were pressed with 1600 MPa and sintered by Two Step Sintering (TSS) at 1500°C / 5 min and 1200°C, 1300oC, 1400°C, remaining at these temperatures for 2 and 10 hours. The sinterized samples were characterized by X-ray diffraction, apparent density, scanning electron microscopy and impedance spectroscopy. The apparent densities were greater than 94% for all conditions of calcination and sintering. The value of the activation energy was 0.7eV for the grain and 0.9 eV for the grain boundaries.

Microwave sintering of Ge-doped In2O3 thermoelectric ceramics prepared by slip casting process

Abstract Ge doped In 2 O 3 bulks were prepared by dry uniaxial compaction or slip casting shaping methods followed by a conventional or microwave sintering. Density of slip casted Ge doped In 2 O 3 samples after conventional sintering reaches bulk density close to the theoretical one thanks to an optimized particles arrangement in the slip casted green bulks. Combined with a fast microwave sintering, slip casted bulks possess submicrometer grain size due to limited grain growth. A significant decrease of the electrical resistivity has been measured in slip casted samples sintered by conventional heat treatment. In bulk specimens sintered by microwave heating, a simultaneous increase of electrical resistivity and decrease of the thermal conductivity is observed. From room temperature to 1000 K in air, slip casted samples sintered by conventional or microwave sintering exhibit similar thermoelectric figure of merit ( ZT ) values.

Fault structure and slip localization in carbonate-bearing normal faults: An example from the Northern Apennines of Italy

Carbonate-bearing normal faults are important structures for controlling fluid flow and seismogenesis within the brittle upper crust. Numerous studies have tried to characterize fault zone structure and earthquake slip processes along carbonate-bearing faults. However, due to the different scales of investigation, these studies are not often integrated to provide a comprehensive fault image. Here we present a multi-scale investigation of a normal fault exhumed from seismogenic depths. The fault extends for a length of 10 km with a maximum width of about 1.5 km and consists of 5 sub-parallel and interacting segments. The maximum displacement (370–650 m) of each fault segment is partitioned along sub-parallel slipping zones extending for a total width of about 50 m. Each slipping zone is characterized by slipping surfaces exhibiting different slip plane phenomena. Fault rock development is controlled by the protolith lithology. In massive limestone, moving away from the slip surface, we observe a thin layer (<2 cm) of ultracataclasite, cataclasite (2–10 cm) and fault breccia. In marly limestone, the fault rock consists of a cataclasite with hydrofractures and smectite-rich pressure solution seams. At the micro-nanoscale, the slip surface consists of a continuous and thin (<300 μm) layer composed of coarse calcite grains (∼5–20 μm in size) associated with sub-micrometer grains showing fading grain boundaries, voids and/or vesicles, and suggesting thermal decomposition processes. Micrometer-sized calcite crystals show nanoscale polysynthetic twinning affected by the occurrence of subgrain boundaries and polygonalized nanostructures. Investigations at the kilometres-tens of meter scale provide fault images that can be directly compared with high-resolution seismological data and when combined can be used to develop a comprehensive characterization of seismically active fault structures in carbonate lithologies. Micro and nanoscale investigations along the principal slipping zone suggest that different deformation processes, including plastic deformation and thermal decomposition, were active during seismic slip.

Structures in textured Cu–Al–Ni shape memory thin films grown by sputtering

The structure and texture formation in Cu–Al–Ni thin films of different thicknesses (1μm to 5μm) grown by DC magnetron sputtering without any intentional heating of the substrate are reported. The as-grown films present grains with an average size of 20nm. The films with thickness of 1μm have a single metastable phase with a hexagonal structure and are textured with planes (0002) parallel to the plane of the films. It was observed that thicker films present phase coexistence between metastable hexagonal and body centered cubic structures with a gradual increment of the body centered cubic phase fraction. The films with thickness of 5μm are textured with planes (0002) and 101¯0 in the hexagonal structure, whereas in the body centered cubic structure the films are textured with {110} planes parallel to the plane of the films. This fact can be associated with self-heating of the substrate during the growth of the films and with the relative stability of the metastable phases. Free standing films annealed in a second step (1123K for 1h) present austenitic phase with L21 structure and sub-micrometric grains textured with {220}L21 planes parallel to the plane of the films. The martensitic transformation temperature was determined from the analysis of resistance against temperature measurements.

In situ elevated temperature transmission electron microscopy of sensitized aluminum–magnesium alloy treated by ultrasonic impact treatment

Abstract

Hardness and flexural strength of single-walled carbon nanotube/alumina composites

This work adds new experimental facts on room temperature hardness and flexural strength of alumina and composites with 1, 2, 5 and 10 vol% single-walled carbon nanotubes (SWNT) with similar grain size. Monolithic Al2O3 and composites were spark plasma sintered (SPS) in identical conditions at 1300 °C, achieving high density, submicrometric grain size and a reasonably homogeneous distribution of SWNT along grain boundaries for all compositions with residual agglomerates. Vickers hardness values comparable to monolithic alumina were obtained for composites with low (1 vol%) SWNT content, though they decreased for higher concentrations, attributed to the fact that SWNT constitute a softer phase. Three-point bending flexural strength also decreased with increasing SWNT content. Correlation between experimental results and microstructural analysis by electron microscopy indicates that although SWNT agglomerates have often been blamed for detrimental effects on the mechanical properties of these composites, they are not the main cause for the reported decay in flexural strength.

Nonlinear Absorption of Submicrometer Grain‐Size Cobalt‐Doped Magnesium Aluminate Transparent Ceramics

Transparent cobalt‐doped magnesium aluminate spinel (Co:MgAl2O4) ceramics with a submicrometer grain size were prepared by spark plasma sintering. For the first time, the nonlinear absorption of Co:MgAl2O4 transparent ceramics was experimentally demonstrated. Both ground state absorption (σGSA) and excited state absorption (σESA) were estimated using the solid‐state slow saturable absorber model based on absorption saturation measurements performed at 1.535 μm. σGSA and σESA for 0.03 at.% Co:MgAl2O4 were found to be 4.1 × 10−19 cm2 and 4.0 × 10−20 cm2, respectively. In the case of 0.06 at.% Co:MgAl2O4 ceramics, σGSA = 2.6 × 10−19 cm2 and σESA= 5.3 × 10−20 cm2 were determined.

Recrystallization Process in Fe-Cr-Al Oxide Dispersion-Strengthened Alloy: Microstructural Evolution and Recrystallization Mechanism

Mechanically alloyed iron-base oxide dispersion-strengthened (ODS) alloys are the class of advanced materials for application in heat exchangers tubing in which creep and oxidation resistance are paramount. The yttria dispersion in such alloys improves the high-temperature creep and stress rupture life. The strength is further enhanced by the development of a coarse-grained microstructure during recrystallization. Factors controlling the evolution of this desirable microstructure are explored in this work, focusing specifically on PM 2000. The results presented in terms of orientation imaging, transmission electron microscopy, and scanning electron microscopy indicate that the recrystallization process consists of two different stages. Before the coarse grain takes place, the alloy undergoes an extended recovery process followed by abnormal grain growth. The initial microstructure consisted of subgrains (submicrometer sizes) with a strong 〈110〉∥RD fiber texture (α fiber), which are transformed into coarse grains (mm sizes) with orientations 〈112〉∥RD. The aim of this study is to describe the mechanisms involved in the intermediate stages of recrystallization process from the submicrometer grain size to the abnormal grain size.

High field ZnO varistors prepared by spark plasma sintering

ZnO varistors with submicrometre and nanoscaled microstructures and enhanced electrical properties were prepared by spark plasma sintering (SPS). The densification, grain size and switch field of the varistors were compared with those of hot pressed material. The switching field increased with decreasing grain size, and very rapidly below 500 nm. Switching fields up to 180 kV cm−1 were obtained for ceramics with submicrometre grain sizes (380 nm). This is nearly two orders of magnitude higher than those currently reported for commercial ZnO varistors. A nano powder, prepared by high energy milling, was sintered to a high density at much lower temperatures compared with the submicron powders and had a nanoscale grain size (45 nm). The nanoceramic broke down dielectrically under very high fields (>260 kV cm−1) before a varistive response was apparent.

Evolution of morphology and structure of Pb thin films grown by pulsed laser deposition at different substrate temperatures

Pb thin films were prepared by pulsed laser deposition on a Si (100) substrate at different growth temperatures to investigate their morphology and structure. The morphological analysis of the thin metal films showed the formation of spherical submicrometer grains whose average size decreased with temperature. X-ray diffraction measurements confirmed that growth temperature influences the Pb polycrystalline film structure. A preferred orientation of Pb (111) normal to the substrate was achieved at 30 °C and became increasingly pronounced along the Pb (200) plane as the substrate temperature increased. These thin films could be used to synthesize innovative materials, such as metallic photocathodes, with improved photoemission performances.

Development of Nanostructured AA3103 by Equal Channel Angular Pressing and Thermal Treatments

This work presents a study related to the achievement of a nanometric structure in AA3103, employing severe plastic deformation processes (SPD), in this case equal channel angular pressing (ECAP). The changes in the mechanical properties and in the microstructure of AA3103 were studied after being processed by ECAP. Subsequently, scanning electron microscopy was used to determine the evolution of the microstructure after different thermal treatments on the material processed by this severe plastic deformation process. Furthermore, a more profound knowledge of the changes in the mechanical properties of this aluminium alloy was obtained. It was demonstrated that with different appropriate combinations of thermal treatments and ECAP processing, it is possible to significantly improve the mechanical properties through obtaining submicrometric grain size structures.

The flow characteristics of superplasticity

1Division of Materials Science and Engineering, Hanyang University, 133–791, Seoul, South Korea 2Departments of Aerospace & Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453, USA CA 90089–1453, Los Angeles, USA 3Department of Materials Engineering and Civil Construction, Universidade Federal de Minas Gerais, Belo Horizonte 31270–901, MG, Brazil 4Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, SO17 1BJ, Southampton, U.K Attaining superplastic elongations is an important prerequisite for using metals in commercial superplastic forming applications. This review briefly summarizes the principles of superplasticity in conventional materials and then demonstrates that similar behavior, for both the flow properties and the cavitation characteristics, may be attained in ultrafine-grained materials with submicrometer grain sizes produced through the application of severe plastic deformation (SPD). An advantage of using SPD processing is that the regime of superplastic flow is displaced to faster strain rates and often occurs within the region of high strain rate superplasticity.

From core–shell BaTiO3@MgO to nanostructured low dielectric loss ceramics by spark plasma sintering

We report a quite general way to design materials with tailored properties by combining thermolysis and fast sintering approaches. Submicrometric-sized BaTiO3 particles have been directly coated in a continuous nanocrystalline MgO shell through a thermal decomposition process. The electron microscopy study has evidenced a shell composed of randomly oriented MgO nanocrystallites. The final nanostructured composite, made of sub-micrometric MgO and BaTiO3 grains uniformly distributed, is obtained in situ during the SPS process. Such a rearrangement can be explained by the initial core–shell architecture, the weak cohesion of the MgO nanocrystallites and their soft plastic behavior under SPS conditions. The composite effect leads to significant modifications in both the dielectric properties and Curie–Weiss parameters compared to uncoated BaTiO3, especially a decrease and thermal stabilization of both the permittivity and the dielectric losses. We ascribe such changes to the stress generated during SPS through the extended interfaces between the two components.

Electrodeposition of Nis3S2/Ni Composites as High-Performance Cathodes for Lithium Batteries

An alternative electrodeposition technology, which provides an efficient way to complete a better interface contact between electroactive materials and metal foil substrates, was used to prepare Ni3S2/Ni composites in aqueous solutions contained thiourea (TU). The deposition parameters, such as time and TU concentration, were optimized. Surface morphology, chemical composition, and crystal structure of Ni3S2/Ni composites were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD), respectively. A Ni3S2/Ni composite, which consisted of submicrometer grains with size in the range of 0.2–2 μm, was obtained. Galavostatic battery testing shows that the submicrometer Ni3S2/Ni4 composites as cathodes for lithium batteries exhibit a high specific capacity of 338 mAh g–1 at a current density of 0.17 A/g (∼0.6 C), extraordinary capacity retention as well as 95.3% after 100 cycles, and outstanding rate performance, for example, still delivering 180...

Evolution of organic matter in Orgueil, Murchison and Renazzo during parent body aqueous alteration: In situ investigations

Chondrites accreted the oldest solid materials in the solar system including dust processed in the protoplanetary disk and diverse organic compounds. After accretion, asteroidal alteration may have impacted organic particles in various ways. To constrain these processes, we conducted a comprehensive study of organics disseminated within the matrices of the three carbonaceous chondrite falls, Renazzo (CR2), Murchison (CM2) and Orgueil (CI). By combining synchrotron-based STXM and TEM analyses on FIB sections of samples previously characterized by NanoSIMS, we investigated the influence of aqueous alteration on the morphology, isotopic signature, molecular structure, spatial distribution, and mineralogical environment of the organic matter within the matrices. Two different populations of materials are distinguishable: sub-micrometric individual grains, likely dominated by insoluble compounds and diffuse organic matter, finely interspersed within phyllosilicates and/or (amorphous) nanocarbonates at the nanometer scale. We suggest that this latter component, which is depleted in aromatics and enriched in carboxylic functional groups, may be dominated by soluble compounds. Organic matter in Renazzo (CR) mainly consists of chemically-homogeneous individual grains surrounded by amorphous and nanocrystalline phyllosilicates. Evidence of connectivity between organic grains and fractures indicates that redistribution has occurred: some areas containing diffuse organic matter can be observed. This diffuse organic component is more abundant in Murchison (CM) and Orgueil (CI). This is interpreted as resulting from fluid transport at the micrometer scale and encapsulation within recrystallized alteration phases. In contrast to Renazzo, organic grains in Murchison and Orgueil display strong chemical heterogeneities, likely related to chemical evolution during aqueous alteration. The observations suggest that the altering fluid was a brine with elevated concentrations of both organic and inorganic soluble components. Ultimately, when water was consumed by aqueous alteration reactions or lost from the system, soluble organic compounds accumulated in the immediate vicinity of the precipitated carbonates and phosphates. Additionally, the nanometer scale organic/phyllosilicate relationships provide a petrological environment where some of the initially accreted organic matter could have been modified through clay-mediated reactions.

Alumina–zirconia composites functionalized with laminin-1 and laminin-5 for dentistry: Effect of protein adsorption on cellular response

The present paper describes a study on laminin interaction with the surface of two alumina–zirconia composites with different percentages of ZrO2, both with submicrometric grain size. As major molecules within the basement membrane (BM), laminins are important protein fragments for epithelial cell adhesion and migration. On the other hand, alumina–zirconia composites are very attractive materials for dental applications due to their esthetic and mechanical properties. X-Ray photoelectron spectroscopy and atomic force microscopy were used to study the adsorption of two types of laminin, laminin-1 (Ln-1) and laminin-5 (Ln-5), onto the ceramics surfaces. The in vitro cell response was determined by intracellular phosphorylation of major kinases. Ceramics samples functionalized with laminins showed better cellular activation than untreated specimens; furthermore, cellular activation was found to be greater for the composite with higher percentage in zirconia when functionalized with Ln-5, whereas the adsorption of Ln-1 resulted in a greater activation for the alumina-rich oxide.

Achieving superplasticity in ultrafine-grained metals

Superplasticity refers to the ability of some materials to pull out to exceptionally high elongations prior to failure. It is now well established that superplastic flow requires both a high testing temperature and a small grain size that is typically less than ∼10μm The processing of ultrafine-grained metals with submicrometer grain sizes through the application of severe plastic deformation (SPD) provides an opportunity for achieving excellent superplastic properties in bulk metals provided these small grains are reasonably stable at elevated temperatures. There have been numerous recent developments in the production of superplastic flow in metals processed by SPD and these developments are reviewed in this report. The analysis shows there is an excellent potential for achieving high superplastic elongations in metals processed by SPD, these high elongations often occur at very high strain rates and, in addition, the behaviour of these metals is consistent with the predictions from deformation mechanism maps.

An investigation of hydrogen storage in a magnesium-based alloy processed by equal-channel angular pressing

Equal-Channel Angular Pressing (ECAP) can be successfully used to process Mg and Mg-based hydrides to produce bulk samples with enhanced hydrogen sorption properties. The primary advantages associated with ECAP processing are the shorter processing time, lower cost and the production of safer and more air-resistant bulk material by comparison with powders produced by high-energy ball milling. ECAP can produce special features for hydrogen absorption such as preferential textures, an increased density of defects and submicrometer grain sizes. In this research, ECAP was used to process a commercial AZ31 extruded alloy in order to evaluate its use as a hydrogen storage material. The ECAP was conducted under conditions of temperature and number of passes in order to avoid grain growth. Additional experiments were conducted on commercial coarse-grained magnesium to evaluate the effect of sample thickness on the sorption properties. The ECAP sample was evaluated in two different orientations and it is shown that better hydrogen properties are related to a refined microstructure allied to the (0001) texture.

Transparent sub-micrometre alumina from lanthanum oxide doped common grade alumina powder

Common grade high purity alumina (99.99%) powder doped with lanthanum oxide was slip cast, dried and pressureless sintered to sub-micrometre grain sized alumina at 1380–1410 °C. Samples that attained >96% theoretical density (TD) were subsequently hot isostatically pressed to fully dense alumina having ≥99.95% TD. Sintered sub-micrometre alumina samples, ground to 2 mm thickness and polished to 0.5 μm surface finish, displayed >82% transmission in the 3–5 μm wavelength range. Samples of 0.5 mm thickness also exhibited 40–60% transmission in the visible wavelength region of 400–900 nm. Lanthanum oxide addition within 0.10 wt% was shown to be favourable for improved transparency in the visible region. The alumina samples also exhibited high Vickers hardness values of 2144+45 kg/mm 2 at 5 kg indentation load.

Oxidic Composite for Dental Purposes: Effect of the Laminin 1 Adsorption on Cells Growth

As major molecules of the basement membrane (BM), laminins are important protein fragments for the epithelial cell adhesion and migration. Since oxidic ceramics are potentially suitable for dental applications, the present paper is focused on the study of laminin interaction with the surface of two alumina-zirconia composites with different percentage in ZrO2, both with submicrometric grain size. Laminin 1 (Ln-1) was adsorbed onto the surface and the interaction was studied via XPS. The cells grown on the laminin-functionalized materials showed good vitality and spreading.