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The stability of Al foams during processing is crucial to producing uniform Al foams. Once pores form during processing, no matter which conventional methods are used, the pores grow and/or merge into large ones, which could cause Al foams to “collapse”. Therefore, it has attracted great attention of researchers to enhance the stability of Al foams during processing for improved quality of Al foams. A novel approach to produce Al-alloy foams, “Rheofoaming”, is presented in this paper. A twin-screw rheomixer fitted with a gas inlet near the end cap is used in this work. The mechanism of this approach is firstly to increase the viscosity of semisolid slurry of Al alloy by adding sub-micron Al2O3 particles and then to mix N2 gas with the semisolid slurry using a twin-screw rheomixer, which can offer high shear rate and intensive turbulence. The gas pores in the semisolid slurry are stretched and broken into smaller ones in the rheomixer. Al foams are very stable during the processing due to small pore sizes and high viscosity of semisolid slurry. The microstructure of rheofoamed Al foams and the process of this new approach have been described in this paper. [ABSTRACT FROM AUTHOR]

Preparation of epoxy/SiO2-TiO2 composites is investigated in this paper. The products are characterized by FT-IR spectroscopy. Results of FT-IR spectroscopy and atom force microscope (AFM) demonstrated that epoxy chains have been covalently bonded to the surface of the SiO2-TiO2 particles. The particles sized of SiO2-TiO2 are about 20–50 nm, which characterized by AFM. The properties of composites such as impact strength, flexural strength, tensile strength and ring-on-block wear are also investigated. Dry sliding wear tests showed that the SiO2-TiO2 particles could improve the wear resistance of the epoxy matrix even though the content of the SiO2-TiO2 particles was at a relatively low level (1.95–2.65 wt%). This makes it possible to develop novel type of epoxy-based materials with improved wear resistance for various applications. The worn surface was observed by scanning electron microscopy (SEM), and mechanisms for the improvement are discussed in this paper [ABSTRACT FROM AUTHOR]

The paper reviews the wear behaviour of oxide ceramics. Wear maps are considered and consequently mild and severe wear are defined. Since the use of ceramics in engineering applications require operation in the mild wear regime, the paper concentrates on mild wear mechanisms, but also considers factors which control the transition to severe wear. Within the mild wear regime, the formation of tribofilms are discussed and the manner in which dislocation activity leads to the wear transition is considered. The wear of so-called ceramic nanocomposites, for which no time dependent wear transition has yet been observed, is considered and the reasons for enhanced performance discussed. The role of transformation toughening in zirconia ceramics is considered in detail, and reasons for the generally poor wear response of these materials defined. [ABSTRACT FROM AUTHOR]

The design of periodic microstructural composite materials to achieve specific properties has been a major area of interest in material research. Tailoring different physical properties by modifying the microstructural architecture in unit cells is one of the main concerns in exploring and developing novel multi-functional cellular composites and has led to the development of a large variety of mathematical models, theories and methodologies for improving the performance of such materials. This paper provides a critical review on the state-of-the-art advances in the design of periodic microstructures of multi-functional materials for a range of physical properties, such as elastic stiffness, Poisson's ratio, thermal expansion coefficient, conductivity, fluidic permeability, particle diffusivity, electrical permittivity and magnetic permeability, etc. [ABSTRACT FROM AUTHOR]

Nano-sized as-synthesized MCM-41 particle, whose pore channels and outer surface full of organic CTAB template, was used as compatibilizers for immiscible polypropylene (PP)/polystyrene (PS) blends. In this paper, the solid structure SiO2 was selected to compare with as-synthesized MCM-41 in properties of PP/PS blend. The mechanical results showed that tensile strength of the blend was increased by 32% and the impact strength was increased by 41.1% by addition low content of as-synthesized MCM-41 compared to pure PP/PS. The presence of SiO2 in the blend cannot improve the mechanical properties obviously. SEM indicated that incorporation of as-synthesized MCM-41 into PP/PS blend can act as compatibilizer, which resulted in a decreased particle size of dispersion phase together with morphological evidence of interfacial adhesion. However, with the presence of SiO2, 1%, 3%, in the blend, the interface did not show clear change compared with the PP/PS blend. [ABSTRACT FROM AUTHOR]

In this paper, the viscoelastic properties of wood under water-saturated conditions are investigated from 10 to 135 °C using the WAVET apparatus. Experiments were performed via harmonic tests at two frequencies (0.1 and 1 Hz) for several hours. Four species of wood were tested in the radial and tangential material directions: oak ( Quercus sessiliflora), beech ( Fagus sylvatica), spruce ( Picea abies) and fir ( Abies pectinata). When the treatment is applied for several hours, a reduction of the wood rigidity is significant from temperature values as low as 80–90 °C and increases rapidly with the temperature level. The storage modulus of oak wood is divided by a factor two after 3 h of exposure at 135 °C. This marked reduction in rigidity is attributed to the hydrolysis of hemicelluloses. The softening temperature of wood is also noticeably affected by hygro-thermal treatment. After three short successive treatments up to 135 °C, the softening temperature of oak shifted from 79 °C to 103 °C, at a frequency of 1 Hz. This reduction in mobility of wood polymers is consistent with the condensation of lignins observed by many authors at this temperature level. In the same conditions, fir exhibited a softening temperature decrease of about 4 °C. In any case, the internal friction clearly rises. [ABSTRACT FROM AUTHOR]

A study of the structural characteristics of the composites [Pb(Fe0.5Nb0.5)O3(PFN)] x -[Cr0.75Fe1.25O3(CRFO)]100− x ( x = 0 (CRFO100), 10, 50, 90, 100) was performed in this work. The compounds PFN100 and CRFO100 were prepared by conventional solid-state method and investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and 57Fe Mössbauer Spectroscopy techniques. The X-ray analysis shows that PFN100 is tetragonal and the CRFO100 phase has a trigonal symmetry. The refinement of all the composites was also performed and discussed in this paper. The Mössbauer spectrum for the composite samples shows a paramagnetic doublet and a sextet probably assigned to a magnetic phase associated to Fe+3. For the sample PFN100, only a magnetic field of 49.5 T (isomer shift (δ) = 0.21 mm/s) was detected. For the composite sample, the δ and Δ are typical of Fe ions at sites of octahedral coordination. [ABSTRACT FROM AUTHOR]

Auxetic materials are those which exhibit negative Poisson’s ratio, i.e. these solids expand transversely when stretched longitudinally. In recent years the concept of semi-auxetics has been examined for cellular solids based on combination of re-entrant and hexagonal microstructures. In this paper we identify a type of rotating unit that gives positive Poisson’s ratio so that a study can be made on rotating sub-structures that exhibit both positive and negative Poisson’s ratio characteristics. A second type of rotating geometry, whose Poisson’s ratio shifts from negative to positive as stretching increases, has also been identified. Based on kinematical studies we explore the relationship between the on-axis Poisson’s ratios in terms of novel lattice geometry and the magnitude of deformation. [ABSTRACT FROM AUTHOR]

The microstructures and dry sliding wear behavior of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al–7Si–2.5Cu cast alloys have microstructures consisting of uniformly distributed α-Al grains, eutectic Al– silicon and fine CuAl2 particles in the interdendritic region. These alloys exhibited better wear resistance in the cast condition compared with the same alloy subjected to only grain refinement or modification. The improved wear resistances of Al–7Si–2.5Cu cast alloys are related to the refinement of the aluminum grain size, uniform distribution of eutectic Al-silicon and fine CuAl2 particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate the influence of the microstructural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys by grain refinement, modification and combined action of both on the sliding wear behavior. [ABSTRACT FROM AUTHOR]

The link between the electromagnetic properties of steel and its microstructure is a complex one, depending on both phase fractions and morphology. In this paper, both analytical and three-dimensional finite element (3D FEM) modelling techniques were applied to the prediction of permeability for steel with a given ferrite fraction for random ferrite/austenite distributions. Experimental measurements from a multi-frequency electromagnetic sensor on samples generated by hot isostatic pressing (HIPping) of powder mixtures were used to evaluate the analytical and FEM predictions. Theoretical treatment of the relationship between the sensor output and the effective permeability is also given; in particular, it was found that the zero crossing frequency of the real part of the inductance is approximately linearly related to the permeability for high (> 40%) ferrite percentages. The EM sensor can therefore be used to identify the samples across the full range (0–100%) of ferrite percentages using both the zero crossing frequency (> 40%) and trans-impedance (0–40%). The effect of banded (non-random) microstructures on sensor output and the prediction of the upper and lower bounds of permeability are also discussed. [ABSTRACT FROM AUTHOR]

The solubility of calcium carbonate (limestone) particles depends on the amount of CO2 dissolved in the water, which is a function of temperature and the pressure of CO2 that is in equilibrium with water. At a constant temperature, increasing CO2 pressure increases the solubility of CaCO3, and decreasing CO2 pressure favours the crystallisation of CaCO3. This dissolution–crystallisation behaviour of CaCO3 can be used in the development of carbonate binders—a process called “cold sintering”—of limestone. This paper examines the effect of a range of parameters on the cold sintering process of limestone powder. The parameters studied are CO2 gas pressure (atmospheric, 10 atm and 35 atm), exposure time (0–90 min), post-compaction pressure (10 and 15 MPa) and compact pressing time (10–60 min). The water/limestone powder ratio was kept constant at 0.2 (by weight). The compressive strength of the limestone compacts was used as a measure of the efficiency of the carbonate binder formation process, and scanning electron microscopy was used to study the microstructural developments. The results show that carbonate binders can be produced by cold sintering of limestone powder. Exposure of limestone compacts to high CO2 pressure followed by post-compaction at high mechanical pressure, enhances the strength of the compact. From the microstructural data, it is evident that newly formed calcium carbonate crystal growths are responsible for the strength improvements observed. The amount of water that is used in the limestone powder mixture is one factor that controls the quantity of the cementing phase. Future work has to be focussed on the application of methods to further increase the solubility of calcium carbonate, as the amount of calcium carbonate available for recrystallisation is important in producing a strong binder. [ABSTRACT FROM AUTHOR]

Gd3+ was chosen as a substitute for Bi3+ in BiNbO4 ceramics, and the substitution effects on the sintering performance and microwave dielectric properties were studied in this paper. The high temperature triclinic phase was observed only in the Bi0.98Gd0.02NbO4 ceramics when sintered at 920 °C. Both bulk densities and dielectric constant (εr) increased with the sintering temperature, while decreased with the Gd content. The quality factor ( Q) exhibited a correlation to the Gd content and the microstructures of Bi1− x Gd x NbO4 ceramics. At the sintering temperature of 900 °C, Bi0.992Gd0.008NbO4 ceramics exhibited microwave dielectric properties of εr ∼ 43.87, Q × f ∼ 16,852 GHz (at 4.3 GHz), and its temperature coefficient of resonant frequency (τf) was found to be near-to-zero. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study on the influence of microstructure on the corrosion behavior of a α–β Ti–5%Ta–1.8%Nb alloy—a candidate material for use in high concentrations of boiling nitric acid. The “as cast” alloy had a lamellar structure and showed a corrosion rate of about 1.5 mpy. Thermo-mechanical processing of the cast alloy resulted in a structure of predominantly of equiaxed α with random distribution of fine β particles. This “reference” structure was further modified employing different heat treatments similar to that for commercial titanium alloys such as mill annealing, solution treatment and aging or over aging treatments. Corrosion rates evaluated in boiling nitric acid in the liquid, vapor and condensate phases, showed low values ∼1 mpy. Of these, the lowest corrosion rate (∼0.03 mpy) was exhibited by the structure with minimum amount of β phase, distributed in an equiaxed α matrix. This structure was obtained by aging of the solution treated “reference” alloy. Hence, solution treatment high in the α + β phase field followed by aging at a temperature low in the α + β phase field has been identified as the optimum treatment to obtain a microstructure with superior corrosion resistance. [ABSTRACT FROM AUTHOR]

This paper deals with the effects of preparation methods on the texture development and densification in textured SrBi4Ti4O15 (SBT) ceramics. The specimens were prepared by the oriented consolidation of anisotropic particles (OCAP), templated grain growth (TGG) and reactive templated grain growth (RTGG) methods. The specimens with extensive texture were obtained by all methods except for TGG with small template and large matrix particles. The origin of extensive texture development was the growth of aligned platelike particles. A characteristic of microstructure was the formation of colonies, in which platelike grains contacted face-to-face. The size of colonies was dependent on the preparation method, and determined the size of pores between colonies, which had a large effect on the sintered density. The OCAP and RTGG methods gave the green compacts composed of only platelike particles and large colonies and pores formed during sintering. The TGG method gave the green compacts composed of platelike and equiaxed particles and prevented the formation of large colonies and pores during sintering. Thus, the dense, highly-textured SBT ceramics were obtained by the TGG method. [ABSTRACT FROM AUTHOR]

This paper reviews recent research upon the application of Raman microscopy to the characterisation of silicon carbide monofilaments produced by CVD (chemical vapour deposition). It is demonstrated that Raman microscopy is an invaluable technique allowing qualitative information about stoichoimetry variation in silicon carbide monofilaments to be obtained, as it readily detects both crystalline and amorphous carbon and silicon. It is shown that it is possible to characterise the morphology of the SiC crystallites in the monofilaments from analysis of the Raman line shapes. It is also demonstrated that Raman spectroscopy can be used to follow deformation of SiC monofilaments and to determine residual stresses in SiC-monofilament-reinforced metal-matrix composites. In addition, it is shown that it is possible to evaluate internal stresses in the carbon coatings of SiC monofilaments. [ABSTRACT FROM AUTHOR]

This review paper is focussed on the characterization of the microstructural development during liquid phase sintering and post-densification crystallisation heat treatment of ceramic materials based on the Si3N4 or SiC structures. Grain shape and size distributions, assessed by quantitative microscopy in combination with stereological methods, and fine scale microstructures, investigated by electron diffraction and high resolution imaging and microanalysis in the TEM, are discussed and related to the fabrication process and the overall composition of the ceramic material. It is demonstrated that combined high resolution analytical and spatial information from chemically and structurally distinct fine scale features, such as grain boundary films of residual glass, is obtained by electron spectroscopic imaging and subsequent computation of elemental distribution images. These images reveal that residual glassy grain boundary films are rich in oxygen and cations originating from the metal oxide/nitride additives, consistent with fine probe EDX analysis in the FEGTEM. Elemental analysis with high spatial resolution has also shown that grain growth into pockets of residual liquid/glass is associated with diffusion profiles in the glass in front of the growing grain. High resolution imaging in the TEM and elemental maps computed from electron energy filtered images show that the intergranular film thickness, in general, varies within a particular silicon nitride or sialon microstructure. Furthermore, grain boundaries, apparently free from residual glass may co-exist with glass-containing grain boundaries in some silicon nitride microstructures. In addition to the choice and weight fraction of sintering additives, factors such as the ionic radius of the cations originating from the additives, the local nano-scale chemistry and the relative grain orientation have an effect on the volume fraction and morphology of the intergranular microstructure. [ABSTRACT FROM AUTHOR]

In this paper, recent progress in magnesium matrix composite technologies is reviewed. The conventional and new processes for the fabrication of magnesium matrix composites are summarized. The composite microstructure is subsequently discussed with respect to grain refinement, reinforcement distribution, and interfacial characteristics. The mechanical properties of the magnesium matrix composites are also reported. [ABSTRACT FROM AUTHOR]

Recently, ultra-hard polycrystalline diamond was synthesized from graphite by direct conversion under static high pressure. This paper describes the microstructure features of thus formed polycrystalline diamond. Transmission electron microscopy and electron diffraction have revealed that the polycrystalline diamond has a mixed texture of a homogeneous fine structure and a lamellar structure. The former structure consists of fine-grained diamond particles of several tens of nanometers across, which are randomly oriented. The latter structure has bending diamond layers, which may reflect deformed shapes of locally layered graphite of starting material. The experimental results suggest that diamond particles in the homogeneous fine structure are transformed from graphite in the diffusion process, while diamond layers in the lamellar structure are formed in the martensitic process from graphite via the hexagonal diamond phase. It is also noted that significant grain growth occurred at a high temperature of ∼2700°C, and the lamellar structure was segmentalized to form new grain boundaries. [ABSTRACT FROM AUTHOR]