Microstructure

A new mechanism of fracture toughness enhancement in nanocrystalline metals and ceramics is suggested. The mechanism represents the cooperative grain boundary (GB) sliding and stress-driven GB migration process near the tips of growing cracks. It is shown that this mechanism can increase the critical stress intensity factor for crack growth in nanocrystalline materials by a factor of three or more and thus considerably enhances the fracture toughness of such materials.

Field and microstructural analyses of faults with millimeters to hundreds of meters of displacement within welded tuffs at Yucca Mountain, Nevada, has led us to identify four different fault zone architectures. We designate these fault zones as Classes A-D. We conclude that Classes A, C, and D are genetically related and that observed differences in their morphology and deformation mechanisms are related to differences in displacement magnitude and changes in the rheology of faulted rocks. We show that Class A, C, and D fault zones were formed by progressive cataclasis, leading to the development of a foliated gouge core and wide damage zone at the highest displacement magnitudes. By inference, displacement variations across individual high displacement faults are expected to produce significant lateral changes in fault zone architecture. The broad range of fault rock textures and architectures found on the Class A, C, and D continuum may produce important corresponding variability in hydrologic properties in ignimbrites.

Direct foaming of colloidal suspensions is a simple and versatile approach for the fabrication of macroporous ceramic materials. Wet foams produced by this method can be stabilized by longchain surfactants or by colloidal particles. In this work, we investigate the processing of particle-stabilized wet foams into crack-free macroporous ceramics. The processing steps are discussed with particular emphasis on the consolidation and drying process of wet foams. Macroporous alumina ceramics prepared using different consolidation and drying methods are compared in terms of their final microstructure, porosity, and compressive strength. Consolidation of the wet foam by particle coagulation before drying resulted in porous alumina with a closed-cell structure, a porosity of 86.5%, an average cell size of 35 lm, and a remarkable compressive strength of 16.3 MPa. On the other hand, wet foams consolidated via gelation of the liquid within the foam lamella led to porous structures with interconnected cells in the size range from 100 to 150 lm. The tailored microstructure and high mechanical strength of the macroporous ceramics can be of interest for the manufacture of bio-scaffolds, thermal insulators, impact absorbers, separation membranes, and light weight ceramics.

Although there have been numerous studies on metal sulphide precipitation, the research field as a whole is not well integrated. This paper reviews the disparate areas of study into metal sulphide precipitation in an attempt to summarise the current work, as well as to suggest potential for future consolidation in the field. The review encompasses (1) fundamental studies into metal sulphide precipitation, which usually focus on mechanisms and are carried out at very low (micromolar) concentrations; (2) applied studies focussing on metal removal and reaction kinetics (mostly via the aqueous phase); (3) studies that focus on the solid phase and address the crystallization kinetics of the formed particles; (4) studies into precipitation of metal sulphide nanocrystals and lastly, (5) applications of metal sulphide precipitation to effluent treatment processes such as Acid Mine Drainage (AMD) treatment as well as industrial hydrometallurgical processes. The review found that, besides lack of integration between the fundamental and applied areas of study, the applied studies have often used flawed methods to evaluate the efficiency of the metal sulphide precipitation process. Applying classical crystallization theory has also not been entirely successful because of the sparingly soluble nature of the systems. The studies that investigate nanocrystal formation tend to focus mostly on recipes and characterization of the formed particles. The industrial and effluent treatment studies form another area of research that stands relatively isolated from its more scientific counterparts. One of the key insights obtained from the summary of these disparate areas of work is that the level of scientific understanding in each of the fields is vastly different. The fundamental studies into mechanistic aspects of metal sulphide precipitation are far advanced of the other areas. However, they are restricted to very low concentrations, which are of limited value in most process-based hydrometallurgical applications. Most of the applied studies are still at a relatively empirical level, with the findings being highly systemdependent. Truly generic findings are still to be realised in these areas. Developing robust measurement techniques to be able to collect consistent data and thus model the simultaneous nucleation, growth, aggregation and attrition of the nano to micro scale particles is one of the challenges in the field. Understanding and characterising the complex aqueous chemistry, taking into account multiple sulphide and metal species interactions, is another. It is proposed that, by integrating the different priorities of the various study areas (chemistry, reaction mechanisms, crystallization mechanisms, particle characterization and industrial applications) the research field as a whole would benefit.

In this study, Cu-Al-B4C metal matrix composite (MMC) material was produced by using hot pressing at powder metallurgy (PM) process. Powder samples were prepared in proportion as 5%, 10% and 20% B4C was added in to Cu-%5 Al powder mixture. Prepared powder samples subject to hot pressing at 600 oC, 4 minutes under argon inert gas atmosphere, 30 MPa/cm2 pressure. Pressed specimens were investigated hardness and microstructure. At the result of the experiments, it's fastened down; B4C affected the hardness and microstructure of the materials, which added at the different rates in matrix.

An Al-6.3Li-0.07Sc-0.02Yb (at.%) alloy is subjected to a double-aging treatment to create nanoscale precipitates, which are studied by atom-probe tomography and transmission electron microscopy. After homogenization and quenching, Yb atoms form clusters exhibiting L1 2-like order. A first aging step at 325°C leads to a doubling of microhardness as a result of the formation of coherent precipitates with an Al 3 Yb-rich core and an Al 3 Sc-rich shell. The core and shell both exhibit the L1 2 structure and both contain a large concentration of Li, which substitutes for up to 50% of the Sc or Yb atoms at their sublattice positions. These core/single-shell precipitates provide excellent resistance to overaging at 325°C. Subsequent aging at 170°C increases the microhardness by an additional 30%, through precipitation of a metastable d 0-Al 3 Li second shell on the core/single-shell precipitates, thereby forming a chemically and structurally complex core/double-shell structure. The metastable d 0-Al 3 Li phase is observed to form exclusively on pre-existing core/shell precipitates.

ZrO 2 hollow microspheres with the average diameter of about 500 nm and the shell thickness of about 50 nm were synthesized by a facile technique using carbon spheres as templates. The corresponding ZrO 2 hollow microspheres were obtained by calcining the precursors of C-Zr(OH) 4 core-shell heterostructures, which were synthesized with the precipitation of ZrCl 4 solution with aqueous ammonia on the surface of colloid carbons. SEM, XRD, TGA and BET were used to characterize the composition, morphology, size and crystal structure of synthesized products. The effects of ultrasonic dispersion and separation process on the hollow spheres were studied, and the surfactant PEG-1000 was added to tune the shell structure of synthesized ZrO 2 hollow spheres.

This paper examines the magnitude and determinants of transactions costs for a sample of institutional traders with different investment styles. Using order-level data for recent equity transactions totaling $83 billion, we find that trading costs are economically significant and increase with trade difficulty. In addition, costs vary with traderspecific factors such as investment style and order submission strategy, as well as stock-specific factors such as exchange listing. We find evidence that institutional trades in exchange-listed stocks have lower costs than in comparable Nasdaq stocks.

Alumina bicrystals with low-angle and near-⌺3 <0001> tilt grain boundaries were fabricated using diffusion bonding to study the dislocation structures in alumina grain boundaries. The resulting grain-boundary structures were investigated using high-resolution transmission electron microscopy, and the grain-boundary energies were analyzed using theoretical calculations. It was found that partial dislocations with Burgers vectors of the type 1 3 <101 0> were periodically located in the boundaries and that a stacking fault between pairs of partials was formed in such boundaries. The length of the stacking fault decreased with increased misorientation angles, which was reasonably predicted by the theoretical calculation. In the case of a near-⌺3 grain boundary, an array of displacement shift complete dislocations with the Burgers vector of 1 3 <11 00> was periodically formed along the boundaries. These boundaries did not have stacking faults. The spacing between the dislocations decreased with increased deviation angle from the exact-⌺3 boundary with the tilt angle of 60°. I. Introduction M. Rühle-contributing editor Manuscript No. 186773.

Streszczenie W pracy przedstawiono sposób otrzymywania i wyniki pomiarów wáaĞciwoĞci fizycznych ceramiki (Pb1-xLax)(Zr1-yTiy) O3, gdzie x= 0, 03 lub 0, 06, y= 0, 9 (PLZT) oraz (Pb1-xLax)[(Zr1-yTiy) 1-zSnz] O3, gdzie x= 0, 04, y= 0, 9, z= 0, 02, 0, 04, 0, 06, 0, 08 (PLZTS). Materiaáy te naleĪą do roztworów staáych tlenowooktaedrycznych o strukturze typu perowskitu. Badane materiaáy zostaáy wykonane przy uĪyciu klasycznej technologii ceramicznej z wykorzystaniem tlenków. Przedstawione zostaáy wyniki badaĔ ...

Adaptive thin-film nanocomposite coatings comprised of crystalline ductile phases of gold and molybdenum disulfide, and brittle phases of diamond like carbon (DLC) and ytrria stabilized zirconia (YSZ) have been investigated by specialized microstructurally based finite-element techniques. One of the major objectives is to determine optimal crystalline and amorphous compositions and behavior related to wear and durability over a wide range of thermo-mechanical conditions. The interrelated effects of microstructural characteristics such as grain shapes and sizes, local material behavior due to interfacial stresses and strains, varying amorphous and crystalline compositions, and transfer film adhesion on coating behavior have been studied. The computational predictions, consistent with experimental observations, indicate specific interfacial regions between DLC and ductile metal inclusions are critical regions of stress and strain accumulation that can be precursors to material failure and wear. It is shown by varying the composition, resulting in tradeoffs between lubrication, toughness, and strength, the effects of these critical stresses and strains can be controlled for desired behavior. A mechanistic model to account for experimentally observed transfer film adhesion modes was also developed, and based on these results, it was shown that transfer film bonding has a significant impact on stress and wear behavior.

Three types of shot peening treatments were applied to S30432 stainless steel. The effect of shot peening intensity and shot peening method on the residual stress and microstructure has been investigated. The domain size and micro-strain evolutions in near surface layer were characterized systematically via Voigt method. The results reveal that shot peening could induce compressive residual stress in the deformed layer for all shot peening conditions. As the shot peening step and intensity increase, the compressive residual stresses increase in near surface layer, and decease faster in deeper deformed layer. In the deformed layer, the domain size increases, while the micro-strain decreases with the depth increasing. Comparing with the micro-hardness after shot peening, it is concluded that increasing the shot peening step is a considerable way to improve the shot peening effect.

Remnant strain has been measured as a function of temperature in ͑Ba 0.8 Sr 0.2 ͒TiO 3 ͑BST͒ ceramic by mechanical poling in three point bending configuration. BST ceramic exhibits recoverable macroscopic strain with shape memory effect and three jumps in the temperature-dependent strain during thermal cycling under applied force. The jumps are associated with the three structural phase transitions of BST, as confirmed by the simultaneous measurements of dynamic modulus and internal friction. In addition, the orthorhombic phase of BST exhibits a significantly higher strain comparing to that in the tetragonal and rhombohedral phases. X-ray diffraction confirms that the macroscopic strain is due to ferroelastic domain switching and particularly the dominant contribution to the higher macroscopic strain at orthorhombic phase is the higher probability of non-180°domain switching rather than the variation of domain switching strain at different phases.

Ionic chlorination of polystyrene with sulphuryl chloride has been investigated. The reaction proceeds via replacement of ring protons with chlorine; after substituting all aromatic protons, the main chain is partially chlorinated. Chloropolystyrenes containing up to 65 wt% of chlorine have been obtained. The extent of side reactions, mainly crosslinking, depends on the concentration of polymer in the reaction mixture and on the degree of chlorination.

The exoskeleton of the lobster Homarus americanus is a multiphase biological composite material which consists of an organic matrix (crystalline α-chitin fibers and various types of non-crystalline proteins) and minerals (mainly calcite). In this study we discuss experimental data about the mesoscopic structure and the crystallographic texture (orientation distribution) of the α-chitin–protein fiber network in this material. The synchrotron measurements reveal very strong crystallographic textures of the α-chitin. According to these data, a large fraction of the α-chitin lattice cells is arranged with their longest axis parallel to the normal of the surface of the exoskeleton. Additionally, a smaller fraction of the α-chitin cells is oriented with their longest axis perpendicular to the cuticle surface. These structural investigations reveal the pronounced role of crystallographic orientation distributions in mineralized biological composite materials which may be of relevance for an improved understanding of biological and bio-inspired nano-composites.

Conditions during the formation of breccias in the Curnamona Province (eastern South Australia) have been investigated through a detailed fractal, microstructural, structural and fluid inclusion study of the breccias, syn-tectonic quartz veins and surrounding rocks. Fractal analysis of clast shapes and clast size distributions were able to distinguish two styles of breccia and indicate that fluid pressure fluctuations played a significant role, though to differing degrees, in the initiation of the brecciation process. Approximate palaeostress orientations prevalent during brecciation and their relationship to the deformational history of the terrane have been reconstructed by combining the orientations of microfractures (sealed microfractures and fluid inclusion planes) with structural field data. Fluid pressure fluctuations of w80 MPa during the brecciation process have been quantified by structurally constrained microthermometric analysis of syn-tectonic fluid inclusions coupled with an analysis of the metamorphic history of the area. Results from this study allow brecciation within the Curnamona Province to be placed within a structural framework and relate the process of brecciation to the interaction between regional hydrothermal alteration/fluid flow systems, shear zone formation and lithological contrasts within the upper crust during the Palaeoproterozoic Olarian Orogeny. These methods and findings provide a template for the study of brecciation processes in other terranes where fluid-induced brittle deformation is a controlling factor in the localisation of major ore deposits. q

a b s t r a c t 22 Artificial neural network analysis was performed to establish a relationship between microstructural 23 characteristics and compressive strength values of cement mortar in this study. Pore properties such 24 as pore area ratio, total pore length, total dendrite length and average roundness, and paste properties 25 such as hydrated part area and unhydrated part area ratios were approached as microstructural charac-26 teristics obtained by digital image analysis. These microstructural quantities were correlated with com-27 pressive strength values of cement mortar incorporating with the chemical admixtures by different 28 dosages, which resulted as several microstructural characteristics. Artificial neural network (ANN) anal-29 ysis indicated that by using ANN as non-linear statistical data modeling tool, a strong correlation between 30 the microstructural properties of cement mortar and compressive strengths can be established.

Flexural strength, crack-density evolution, work of fracture, and critical strain energy release rates were measured for wet and dry specimens of the Strombus gigas conch shell. This shell has a crossed-lamellar microarchitecture, which is layered at five distinct length scales and canbe considered a form of ceramic "plywood". The shell has a particularly high ceramic (mineral) content (99.9 wt%), yet achieves unusually good mechanical performance. Even though the strengths are modest (of the order 100 MPa), the laminated structure has a large strain to fracture, and a correspondingly large work of fracture, up to 13 kJ m-2. The large fracture resistance is correlated to the extensive microcracking that occurs along the numerous interfaces within the shell microstructure. Implications of this impressive work of fracture for design of brittle laminates are considered.

In the present study, blue corn flour films were developed. The cereal grain's total composition (excluding the pericarp) is used to obtain the films. The plasticizing effects of two different polyols such as glycerol and sorbitol on the mechanical, thermal, and microstructural properties of flour films were researched. The results showed that films plasticized with sorbitol had better mechanical properties and less affinity for water than those plasticized with glycerol. The sorbitol-plasticized films were more rigid and did not lose their integrity when immersed in water. The ATR-FTIR spectra of blue corn flour plasticizer with sorbitol showed the presence of the additional band at 1745 cm À1 characteristic of the vibrational carbonyl peak, which confirms the chemical linkages between sorbitol and a polymeric matrix. The effect of the plasticizer on the glass transition temperature (T g) was characterized using differential scanning calorimetry (DSC). T g decreased as the plasticizer content increased. Plasticized glycerol films showed lower T g values than those with sorbitol. SEM observations showed that it was necessary to add plasticizer to maintain film integrity. The sorbitol-plasticized flour films revealed better adhesion between phases, and these films showed a compact structure.

AISI 316 austenitic stainless steels have been plasma nitrided using a dc glow discharge unit in order to investigate the influence of gas composition on microstructure and corrosion behavior of treated samples. Corrosion properties of untreated and plasma nitrided 316 steels ...

The characteristics of microstructures at various locations behind the pin tool extraction site were studied in copper after FSP that had been conducted with continuous quenching to enhance cooling rates. The substructures initially formed around the pin tool consist of very small crystallites having sizes of a few tens of nanometers. It is proposed that the processing conditions result in formation of microband structures around pin tool in the presence of severe strain heterogeneity. The microbands appear as nanoscale elongated crystallites surrounded by high-angle boundaries. The elongated crystallites transform to nearly random oriented and equiaxed grain structures by shape adjustment during the initial stages of cooling from the peak temperature. Nanocrystalline structures ∼174 nm in size were produced in OFHC copper by FSP.

Two aspects critical to the fracture behavior of three-wire stainless steel cladding were investigated by the Heavy-Section Steel Technology (HSST) Program: (1) radiation effects on cladding strength and toughness, and (2) the response of mechanically loaded, flawed structures in the presence of cladding (clad plate experiments).

Surface fine structure and structural defects in the open framework material VSB-1 have been investigated by electron microscopy. Crystal growth phenomena are proposed by a building unit model: (i) a unit is formed by two building units; (ii) they are linked to form first channels; and (iii) the whole network is grown via a layer-by-layer growth mechanism. A planar defect was observed in highresolution transmission electron microscope (HRTEM) image taken with the [0001] incidence, and diffuse streaks related to the presence of defects were observed in a series of electron diffraction (ED) patterns. The microstructure model derived from the defect structure gives information on crystal growth. These defects highlight an open site that could be the pillar of a new crystal growth process. The study of defects and crystal growth is important in understanding physical properties such as catalytic or magnetic properties, and in synthesising a new open framework structure. r

The oxygenation process of the top seeded melt-grown (TSMG) single-grain YBa2Cu3O7/Y2BaCuO5 (123/211) bulk superconductors was studied by microstructure observations. It is shown that the c-cracks in these bulks are formed in the oxygenated orthorhombic layer along the a/b-macrocracks. The lattice contraction of the 123 phase in a/b-plane induces tensile stresses in the oxygenated layer, which cannot be relaxed by twin boundary motion. The critical spacing of the c-macrocracks, λcr=14 μm, at oxygenation temperature 380 °C, estimated using Thoules’s model, is in a good agreement with the c-macrocrack spacing measures on standard TSMG 123/211 single-grain samples.

The densification of silicon nitride was carried out by Hot Isostatic Press (HIP) sintering via glass-encapsulation method. The sintering performing techniques were studied in order to obtain high strength properties. a-Si:JN4 raw powder was used as the starting material in addition with a composition of 3 wt% Ah03 and 5 wt% Y203 . That ratio corresponds to the liquid phase compositions at the lowest temperature in the system Ah03 -Y203 -Si0 2 with having high strength at room temperature. Density, microstructure, hardness and fracture surface of specimens were measured. The experimental results showed that silicon nitride could have density nearly to theoretical density. X-ray Diffraction pattern indicated the transformation of a-phase to J3-phase occurred in every sintered specimens and fully transformed to J3 phase after complete soaking for 2 hrs. The development of elongated grains was related to the formation of large nuclei during phase transformation. The SEM micrographs and fractograph also showed the J3 rodlike grain. For the specimens having density over than 95%, the calculated hardness was appoximately between 14-16 GPa.

One way of computing the macroscopic behavior of a material sample with complex microstructure is to construct a finite element model based on a micrograph of a representative slice of the material. The quality of the results produced with such a model obviously depends on the quality of the constructed mesh. In this article, we describe a set of routines that modify and improve the quality of a 2D mesh. Most of the routines are guided by an effective element ‘‘energy” functional, which takes into account the shape quality of the elements and the homogeneity of the elements as determined from an underlying segmented image. The interfaces and boundaries in the image arise naturally from the segmentation process. From these routines, we construct a close-to-automatic mesh generator that requires only a few inputs, such as the linear sizes of the largest and smallest features in the micrograph.

This study examined the effect of adding common carp sarcoplasmic proteins (Sp-P) on the gel characteristics of threadfin bream surimi and kamaboko while maintaining constant moisture and myofibrillar levels. Based on the temperature sweep test, which is involved in heating of surimi gel from 10 to 80 • C to monitor the viscoelastic properties, at temperature range of 40 to 50 • C, the decrease level (depth of valley) in storage modulus (G) thermograph was in proportion to the concentration of added Sp-P. Storage modulus (G) showed greater elasticity after adding Sp-P compared with the control without Sp-P. Furthermore, the breaking force and distance and consequently gel strength of the resultant kamaboko were improved significantly (P > 0.05). Thus, added Sp-P did not interfere with myofibrillar proteins during sol-gel transition phase but associated with textural quality enhancement of resultant kamaboko; however, addition of Sp-P from the dark muscle of the carp decreased the whiteness of the resultant surimi. Furthermore, according to the SEM micrographs, the gel strength could not be associated with either the number of polygonal structures/mm 2 or the area of the polygonal structures in the kamaboko gel microstructure.

A new silver-cobalt arsenate, Ag 4 Co 7 (AsO 4) 6 , is synthesized by solid state reaction method and characterized by X-ray diffraction and impedance spectroscopy. The phase crystallizes in the monoclinic space group C2/m with a = 10.755(2) Å, b = 14.937(2) Å, c = 6.731(2) Å, and b = 106.17(3)°. The structure is described as a three-dimensional anionic framework having interconnecting tunnels running along [1 0 0] and [0 1 0]. The former contains the silver cations. Ball milling is used as mechanical means to reduce the particles sizes of the as synthesized powder. At the optimal sintering temperature of 1173 K, dense ceramics (96% of the relative density) are obtained. Their microstructure is characterized by scanning electron microscopy. The conductivity of the ceramics is studied at different relative densities over a temperature interval from 437 to 773 K. The high conductivity at 210°C (3.3 Â 10 À5 S cm À1) and the activation energy (Ea = 0.45 eV) show that Ag 4 Co 7 (AsO 4) 6 is a fast ionic conductor.

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The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique [IEEE Trans. UFFC, 45:30 (1998)] has demonstrated sensitive detection of subwavelength channel defects (38-m diameter reliably and 6-m diameter occasionally) in flexible 220-m-thick food package seals (17.3 MHz, Ϸ 86 m). However, the underlying subwavelength defect detection mechanism is poorly understood. In this contribution, a theoretical modeling study was undertaken to elucidate the mechanism. The subwavelength diameter channel was fused in-between two plastic package films by applying heat from one side of the films. The sample cross-section microstructure was characterized from both optical and acoustic images. The cross-section impedance profiles along sample thickness dimension were determined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. Transient finite-element heat conduction analysis and impedance profiles of multiple-sealed package samples showed that the single-sided heating process caused an asymmetric impedance profile. A generalized impedance model was proposed based on these observations. An efficient two-dimensional simulation tool using a finite-difference time-domain method and the perfectly matched layer numerically evaluated the defect detection behavior of the radio-frequency (rf) echo waveforms. The normalized correlation coefficients between the simulated and the measured rf echo waveforms were greater than 95% for this generalized model, which suggested the validity of the proposed impedance model.

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The expansion in application of the selective laser melting (SLM) process for fabrication of new alloy materials continues. However, to date, there has been no investigation of the effect of this process on the final microstructure of 'melt sensitive' powder alloys such as mechanically alloyed oxide dispersion strengthened (ODS) FeCrAl. In this study commercial PM2000 powder, a ferritic ODS alloy strengthened by a fine dispersion of nano-scale yttria particles, was used in a layer based SLM rapid prototyping process to manufacture thin walls. Laser input power and scan speeds were varied between 10-50W and 0.1-0.3ms-1 , respectively. Electron channelling contrast images of the resulting microstructures revealed a columnar grain structure aligned perpendicular to the surface of the build substrate. Measurements of the diameter of yttria particles retained in the walls using transmission electron microscopy indicated that agglomeration and coarsening had taken place for samples processed at the slowest scan speed. By contrast ODS particles retained in a wall made at twice the slowest scan speed showed no evidence of agglomeration and appeared to have coarsened to a lesser extent, exhibiting a smaller mean diameter. This opens the possibility of using these alloys in novel applications processed using rapid prototyping technologies.

The effect of tin content in the equilibrium phases of the Cu-Zn-based alloys, within the range of chemical compositions with interest to brass producers is described. For this purpose, ternary alloys with copper contents between 55.4 and 67.5 wt.% and tin contents up to 5.30 wt.% have been studied. The chemical composition of each alloy has been determined by X-ray fluorescence spectrometry (XRF). Isothermal homogenization, followed by rapid cooling, has been employed to determine the equilibrium phases at different temperatures. The homogenized alloys have been observed by scanning electron microscopy and the respective chemical analysis of the phases determined by electron probe microanalysis (EPMA). The statistical analysis of the obtained results enable to correlate the chemical composition of equilibrium phases with temperature. The chemical composition of the three-phase field, for the studied temperatures, has also been determined.

Porous silicon carbide (SiC) ceramics with different pore size were prepared from SiC powders, an aluminum yttrium garnet (Y3Al5O12, YAG) as a sintering additive, and three different sizes of templates (polymer microbeads) by a sacrificial template technique. Their microstructure and mechanical strengths were evaluated as a function of template size, i.e., pore size. Porosity of these porous SiC ceramics increased with increasing the template content, regardless of template size. Pore size was proportional with the template size. The growth of faceted grains was accelerated with increasing the template size. Both flexural and compressive strengths decreased with increasing the porosity whereas both strengths increased with decreasing the template size, i.e., pore size. Typical flexural and compressive strengths of the porous SiC ceramics fabricated using 8 μm-templates were ~55 MPa and ~240 MPa at ~45% porosity, respectively.

Porous cordierite ceramics with controlled porosity were fabricated via a reaction sintering using expandable microspheres as sacrificial templates and ceramics-filled polysiloxane as a precursor for cordierite ceramics. The influence of the sintering temperature, the template content, and the additive composition on the microstructure, porosity, and compressive strength has been investigated. The results showed that the template content, the sintering temperature, and the sintering additive composition have a significant effect on the porosity. By controlling the template content, the sintering temperature, and the sintering additive composition, it was possible to produce porous cordierite ceramics possessing a wide range of porosities ranging from 11! to 72!. The compressive strength was influenced by both the porosity and the additive composition. The compressive strength of the porous cordierite ceramics containing 6 mass! kaolin as a sintering additive was Ĭ150 MPa at 35! porosity.

In the present study, we investigate a microstructure which shows a three-step martensitic transformation on cooling from the high temperature regime and two DSC peaks on heating. Using in situ neutron diffraction phase analysis based on Rietveld full profile fitting it is shown how the volume fractions of B2, R and B19 phases evolve during the three step transformation on cooling and the reverse transformation on heating. We used TEM as a complementary method to support our neutron diffraction findings. The first DSC peak on cooling is related to a complete transformation of the B2 matrix to R phase and the second and third peak on cooling are associated with the formation of B19 in two stages. On heating also, the B19 → R transformation is accumulating in two stages, with the second stage overlapping with the R → B2 transition.

In the present work, we report the inicrostructural and mechanical properties of
failed coupling wit/i an airlock in a flour ini!!. The coupling n’hich was made 01
alumniniuni alloy is used to transmit torque froimi the electric motor to an airlock used
on (1 flour miiill production line. The tracture that occurred at the root of the teeth of
tim e coupling wa in i ‘estigated using i ‘arious tests and ana lys is. The tests includes.
miiacro examination, micro—structural examination, composition analysis, hardness
and tensile test were employed for this ¡11H stigation. From the tests carried out, it was
observed from tue macro examination that the coupling undergoes a brittle failure.
Howe ver, composition analysis revealed a relative/v high weight composition of
aluminium (87.5 wt. %) suggesting that the coupling was made of alumnimiiumn based
alloy. The significant presence of Cu and Zn at 2.77 ii’t. % and 1.03 wi. % respectively
indicates that the alloying elements were mainly of copper and zinc. The tensile test
result revealed that the immaterial lias an ultimate tensile strength of 1 78 N/mm2 ii’h ic/i
is comparatively lower than most aluminium alloys. This might be as a result of the
high Si comilpositiomi of 7.24 wt. % obseri’edtroiii the ciiemiiüil comnpositiomial analvsis.
The hardness result showed the Brine/I hardness of the fractured saliij)leS as 76.53
BHN. The mnicrostructure of time coupling at three different sections gave threeMicrostructural and Mechanical Properties of Failed Coupling with An Airlock In A Flour Mill
http://www.iaeme.com/ IJMET/index.asp 796 editor@iaeme.com
different micrographs, further proving uneven distribution of the aluminium alloy
element. Thus, the presence of Si at relatively high percentage, often intended to
increase the strength, wear resistance and weldability may be detrimental to the
coupling ductility and tensile strength and may have contributed to the early fracture
of the coupling.

A method to estimate the Minkowski dimension using neighborhood operations is described. Its implementation using a software package IMAGER-2 on a square grid with eight connectivity is presented. It is observed that a range of successive pairs of dilations helps in arriving at the best estimate. The methodology is applied to find the Minkowski dimension of the skeleton of a stress corrosion crack.

This article studies the properties of a wide range of friction-stir-welded joints with dissimilar aluminum alloys or thicknesses. Two aluminum alloys, namely, 2024-T3 and 7075-T6, are selected for the study and are welded in ten different combinations of alloys and thicknesses. The ...

The importance of breakfast cereal flakes (BCF) in Western diets deserves an understanding of changes in their mechanical properties and microstructure that occur during soaking in a liquid (that is, milk or water) prior to consumption. The maximum rupture force (RF) of 2 types of breakfast flaked products (BFP)--corn flakes (CF) and quinoa flakes (QF)--were measured directly while immersed in milk with 2% of fat content (milk 2%) or distilled water for different periods of time between 5 and 300 s. Under similar soaking conditions, QF presented higher RF values than CF. Soaked flakes were freeze-dried and their cross section and surface examined by scanning electron microscopy. Three consecutive periods (fast, gradual, and slow reduction of RF) were associated with changes in the microstructure of flakes. These changes were more pronounced in distilled water than in milk 2%, probably because the fat and other solids in milk become deposited on the flakes&#39; surface hindering liqu...

The effect of isothermal exposure on elevated-temperature time-dependent fatigue crack propagation (FCP) in INCONEL Ò alloy 783 is investigated. Commercially produced alloy 783 was annealed and aged following the standard heat treatment procedure. One set of specimens was then isothermally exposed at 500°C for 3000 hours. Both set of specimens were subjected to FCP tests with various hold time periods and sustained loading crack growth tests at 538°C and 650°C in laboratory air environment. Without hold time, as produced and isothermally exposed materials had comparable fatigue crack growth rates (FCGR) at both test temperatures. With hold times of 100s and 300s, as-produced and isothermally exposed specimens had comparable FCPR at 538°C. Hold time testing of as-produced material at 650°C showed abnormal time-dependent FCP and sustained loading crack growth retardation. However, hold time testing of isothermally exposed material at 650°C showed steady sustained loading crack growth and full time-dependent FCP typically observed in many superalloys. Comparison with alloy 718 data from the literature shows that FCP rates of as-produced alloy 718 and isothermally exposed alloy 783 are comparable at 650°C. A full time-dependent FCP model based on the damage zone concept and thermal activation equation is proposed to characterize the fatigue crack growth behaviors.