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Journal of Materials Science: Full Set - Includes `Journal of Materials Science Letters' (v.33, #20)


Effect of Pigmentation on the Microstructure and Properties of Rotationally Molded Polyethylene by M. C. Cramez; M. J. Oliveira; R. J. Crawford (pp. 4869-4877).
Rotational molding of plastics has experienced growth rates of about 12% per annum over the past decade. As a result, ever more demands are being placed on the quality of the moldings in terms of dimensional control and mechanical properties. With most molding methods for plastics, the use of pigments can have a significant effect on the quality of the product. This is particularly true for rotational molding because there are no stresses to assist with dispersion of the pigment, and the slow cooling rates encourage classic spherulite formation. This paper investigates the use of nucleating and non-nucleating pigments in a rotational molding grade of polyethylene. We demonstrate that the amount of work done on the plastic prior to molding affects the microstructure and the mechanical properties of the end product, often in a positive manner. Turbo-blending of pigments is shown to be problematic, particularly if the pigment is of the nucleating type. The amount of pigment used has little effect on strength but reduces toughness dramatically.

Transient Creep Associated with Grain Boundary Sliding in Fine-Grained Single-Phase Al2O3 by H. Yoshida; T. Sakuma (pp. 4879-4885).
Transient creep data for high-purity polycrystalline alumina are examined at the testing temperature of 1150–1250 °C. The data are analysed in terms of the effect of stress and temperature on the extent of transient time and strain.In order to explain the observed transient creep, a time function of creep strain is proposed from a two-dimensional model based on grain boundary sliding. The grain boundary sliding is assumed to take place by the glide of grain boundary dislocations accommodated by dislocation climb in the neighboring grain boundaries. The time function for a creep strain ∈ obtained from the model is given in a form $$ in = a_1 t + a_2 (1 - exp( - a_3 t))$$ which is similar to the previous empirical formula describing the experimental creep curves in metallic alloys. The model predicts that the transient creep strain ∈T is approximately proportional to and the extent of transient creep time tT is inversely proportional to flow stress. The prediction is consistent with the experimental data in high-purity, fine-grained alumina at temperatures between 1150 and 1250°C.

Development of Glass Frit Free Metallization Systems for AIN by A. Adlaßnig; J. C. Schuster; R. Reicher; W. Smetana (pp. 4887-4892).
Currently only glass bonding thick film conductor systems are commercially available for metallizing AlN-ceramic. The glass phase formed between metallization and ceramic impairs the high thermal conductivity of AlN. A new glass frit free metallization system has been developed utilizing the bonding mechanism of active brazing to provide the adhesion of metallization onto the ceramic. Aspects of paste preparation range from the derivation of the metallic powder to the selection of an appropriate printing vehicle which must decompose completely during the firing process under an inert atmosphere. The adhesion strength of the new paste system with the alternative bonding mechanism has been evaluated and contrasted with that of standard thick film pastes.

Processing and Creep Resistance of Nickel/Yttria Composites by Lian-Chao Sun; L. L. Shaw (pp. 4893-4903).
In this study, pure nickel and yttria (Y2O3) were selected as a model system to investigate the feasibility of processing metal matrix composites (MMCs) through a powder metallurgy approach for the in-situ formation of a continuous three-dimensional reinforcement network or the in-situ formation of discrete reinforcements with certain degrees of interconnected clusters. Composites with a volume fraction of Y2O3 ranging from 20 to 50 % were prepared through hot pressing. The density, microstructure and creep resistance of these composites were evaluated as a function of the yttria volume fraction. It was found that a continuous Y2O3 network was formed in composites with 40 and 50 vol % Y2O3, while yttria was discrete with some degrees of interconnected clusters in composites with 20 and 30 vol % Y2O3. The creep rate was reduced by two to three orders of magnitude with the addition of 20 to 30 vol % Y2O3, and it continued to decrease with increasing the volume fraction of yttria to 50%. The analysis indicated that the load transfer to isolated yttria particles could not account for the improved creep resistance of composites with 20 and 30 vol % Y2O3, while the load transfer to a continuous yttria network in composites with 40 and 50 vol % Y2O3 could not be approximated by the model of the load transfer to continuous fibres. The discrepancies are believed to be related to the presence of interconnected yttria clusters, the low relative density of the yttria phase in the composite, and the low load-carrying capability through a three-dimensional network in comparison with the load-carrying capability through continuous fibres. It is suggested that the density of the yttria phase and hence the creep resistance of the composite can be further improved over what have been obtained in this study by densifying the composite at high temperatures and pressures.

Probing of Micromechanical Properties of Compliant Polymeric Materials by V. V. Tsukruk; Z. Huang; S. A. Chizhik; V. V. Gorbunov (pp. 4905-4909).
Scanning force microscopy (SFM) was used for probing nanomechanical properties of compliant polymeric materials with lateral resolution from 20 to 140 nm and indentation depths from 2 to 200 nm. Sneddon's, Hertzian, and Johnson–Kendall–Roberts theories of elastic contacts were tested for a variety of polymeric materials with Young's modulus ranging from 1 MPa to 5 GPa. Results of these calculations were compared with a Sneddon's slope analysis widely used for hard materials. It was demonstrated that the Sneddon's slope analysis was ambiguous for polymeric materials. On the other hand, all models of elastic contact allowed probing depth profile of elastic properties with nanometre scale resolutions. The models gave consistent values of elastic moduli for indentation depth up to 200 nm with lateral resolution better 100 nm for most polymeric materials.

The Chemical and Morphological Properties of Boron–Carbon Alloys Grown by Plasma-Enhanced Chemical Vapour Deposition by D. Zhang; D. N. Mcilroy; W. L. O'Brien; G. De Stasio (pp. 4911-4915).
The stoichiometry and morphology of boron–carbon alloy thin films grown by plasma-enhanced chemical vapour deposition can be significantly modified by varying the deposition rate. Films grown at a rate of 5.5 nm min−1 are characterized by an amorphous-like matrix with carbon-rich and dome-like inclusions. Films grown at a deposition rate of 33 nm min−1 are found to be much more homogeneous and free of carbon-rich and dome-like inclusions. An excitation at 191.7 eV in the B 1s absorption spectrum has been associated with amorphous growth. The relative intensities of the π* and σ* excitations across the C 1s absorption edge of these boron-carbon alloys indicate that carbon bonding is predominantly through sp3 hybridization, while boron bonding is a mix of sp2 and sp3 hybridization.

Time-Dependent Hardness of Particulate-Filled Composites by J. Suwanprateeb (pp. 4917-4921).
Time-dependent hardness of calcium carbonate-polyethylene composites prepared by co-rotating twin screw extrusion has been determined. Hardness of composites were shown to be a power increasing function of the amount of calcium carbonate particles, but decreased as the time under load increased. The degree of time-dependent hardness was observed to be unaffected by filler concentration. All compositions showed similar percentage of hardness decrease with increasing dwell time. A graphical method was devised and able to apply to map the hardness of various filler volume fraction composites at any defined dwell times.

Electrical Conductivity of Ferric Chloride-Doped Poly(Acrylic Acid-Divinylbenzene) by S. M. Yousaf; S. Raza; Z. Ahmad; F. A. Khwaja (pp. 4923-4928).
Polyacrylic acid divinylbenzene was doped with ferric chloride in non-aqueous medium and the effect of concentration of dopant salt on the electrical conductivity of polyacrylic acid divinylbenzene was investigated. The electrical conductivity of pure and doped polymer containing various percentages of iron was measured as a function of temperature (298–383 K) and applied voltage. A linear relationship of current for the entire range of applied voltage (50–500 V) at ambient temperatures suggest ohmic conduction of charge carriers. The electrical conductivity of 1.04, 1.46 and 2.85% ferric-polyacrylatedivinylbenzene at 333 K is 1.2 × 10−12, 4.7 × 10−12 and 4.1 × 10−10 mho/cm, respectively. The increase in conductivity is facilitated by complex formation between carboxylic pendent groups of polymer matrix and ferric ions. Activation energies (−0.527 to −0.436 eV) are lower in the temperature range 298 ≤ T ≤ 353 K but in the higher temperature region 353 ≤ T ≤ 383 K the values tend to increase (0.842 to 1.585 eV).

Thermodynamic Calculation of Phase Equilibria in the Ti–Co and Ni–Sn Systems by P. Nash; H. Choo; R. B. Schwarz (pp. 4929-4936).
A thermodynamic model for the titanium-cobalt system has been developed utilizing measured enthalpies of mixing of the liquid and evaluated phase-diagram data. The free energies of the liquid, bcc, fcc, and hcp solid solutions, and TiCo, Ti2Co, TiCo2, and TiCo3 compounds were calculated for a temperature of 400 K. The model and measured heats of crystallization have been used to predict the free energy of the metastable amorphous phase at 400 K, needed for comparison with experimental results on the mechanical alloying of Ti and Co. The predicted glass-forming range for alloys prepared by mechanical alloying is from 10 to 81.5 at. % Co. We adopted a similar approach for modeling the Ni–Sn system to calculate the free energies of Ni3Sn, and Ni3Sn2, and the liquid (amorphous) and fcc solid solutions in the nickel-rich region at 240 K. In this system the inclusion of the magnetic contribution to the free energy of the Ni-rich fcc solid solution is important in interpreting the results of mechanical alloying. We propose a simple transformation of the free-energy curves, which assists in the graphical identification of the glass-forming ranges.

Hollow Alumina Microspheres From Boehmite Sols by M. Chatterjee; D. Enkhtuvshin; B. Siladitya; D. Ganguli (pp. 4937-4942).
Hollow alumina microspheres were obtained from emulsified boehmite sols by an ion extraction method. The viscosity and the equivalent alumina content of the sols were found to affect the characteristics of the derived microspheres. High-viscosity sols produced broken microspheres. A temperature of about 400–500 °C for boehmite to γ-Al2O3 transformation in the gel microspheres was observed by differential thermal analysis and X-ray diffraction. Complete crystallization of the gel microspheres to α-Al2O3 occurred at 1200 °C. A tentative mechanism for the formation of the hollow microspheres is presented.

The Creep and Thermal Stability Characteristics of a Unidirectionally Solidified Al2O3/YAG Eutectic Composite by Yoshiharu Waku; Narihito Nakagawa; Takumi Wakamoto; Hideki Ohtsubo; Kazutoshi Shimizu; Yasuhiko Kohtoku (pp. 4943-4951).
Compressive creep characteristics at 1773, 1873, and 1973 K, oxidation resistance over 1000 h at a temperature of 1973 K in ambient air, and the thermal stability characteristics at 1973 K in ambient air of a unidirectionally solidified Al2O3/YAG eutectic composite were evaluated. At a test temperature of 1873 K and a strain rate of 10−4/s, the compressive creep strength of a eutectic composite manufactured by the unidirectional solidification method is approximately 13 times higher than that of a sintered composite with the same chemical composition. The insite eutectic composite also showed greater thermal stability, with no change in mass after an exposure of 1000 hours at 1973 K in ambient air. The superior high-temperature characteristics are closely related to such factors as (1) the in-situ eutectic composite having a microstructure, in which single crystal Al2O3 and single crystal YAG are three-dimensionally and continuously connected and finely entangled without grain boundaries and (2) no amorphous phase is formed at the interface between the Al2O3 and the YAG phases.

A New Model for the Transverse Modulus of Unidirectional Fiber Composites by Shao-Yun Fu; Xiao Hu; Chee-Yoon Yue (pp. 4953-4960).
In this paper a new micromechanical model for predicting the transverse modulus of unidirectional continuous and discontinuous fiber composites is proposed. This model is based on modeling a composite with a regular array of volume elements and constructing a stress pattern based on simple averaging procedures in the direction transverse to the fiber axis for a representative volume element. The effects of fiber aspect ratio, interfiber spacing and fiber end gap on the transverse modulus of discontinuous fiber composites are discussed in detail. The predictions of the model are compared with existing experimental results for various fiber/matrix systems and very good agreement is found. The present model has advantages over other existing models not only because the effects of fiber aspect ratio, interfiber spacing and fiber end gap are taken into account and the expression for the transverse modulus of composites is simple in form but also because the present model gives precise predictions of the transverse composite modulus.

Microstructure Development in Laser-Processed Al–Ti–Ni Alloys with 25 At. % Ti by A. E. GunnÆs; A. Olsen; J. Taftφ (pp. 4961-4969).
The microstructure of laser-processed (Al1−xNix)3 Ti with Ni content ranging from 5 to 15 at. % has been studied by scanning-and transmission-electron microscopy (SEM and TEM). All samples contain Al-rich dendrites with Ni-rich interdendritic phases. The dendrites in the 5 at. % Ni alloy consist of the Al3Ti phase with the DO22 type structure, whereas the alloys containing 8 to 15 at. % Ni consist of the Al67Ni8Ti25 phase with the L12-type structure. The lattice parameter of the L12 type structure of Al67Ni8Ti25 was determined by comparing the Higher Order Laue Zone (HOLZ) line patterns in experimental and calculated convergent beam electron diffraction disks. The lattice parameter was found to be a = 0.3935 ± 0.0003 nm. Within the L12 type regions of the alloy with 8 at. % Ni, precipitates with a new primitive tetragonal structure was found. The cell dimensions are a = 0.39 nm and c = 1.18 nm. AlNTi2 with Ti: Al ratio equal to 2.0 ± 0.2 was found as needles in interdendritic regions. The cell dimensions are consistent with a = 0.299 nm and c = 1.361 nm and space group P63/mmc.

Polypyrrole Based Microwave Absorbers by V.-T. Truong; S. Z. Riddell; R. F. Muscat (pp. 4971-4976).
Reflection of microwave radiations from single layer and two-layer materials is calculated. Microwave absorbing materials are formulated by mixing a commercially available paint or rubber with the conducting polypyrrole (PPy) powder. The reflection loss strongly depends on thickness and complex permittivity of the material. For a single layer material, optimum values of the real part, ɛ′, and imaginary part, ɛ′′, of the complex permittivity are found by calculations which lead to a minimum reflectivity at a given sample thickness. The ability to readily tailor the conductivity of the PPy powder enables the design of microwave absorbers according to theoretical desired values of ɛ′ and ɛ′′. A paint panel containing 2 wt% of PPy powder with a thickness of 2.5 mm exhibits a reflectivity < − 10 dB (i.e. at least 90% absorption of the incident radiation) over 12 to 18 GHz. Blending and milling during the manufacturing process can destroy the original fibrous shape of PPy aggregates leading to low radiation absorption. In an attempt to achieve a broadband absorber, a two-layer system consisting of a first layer containing PPy powder and a second layer containing carbonyl iron has been fabricated.

Superplasticity of Fine-Grained Fe–C Alloys Prepared by Ingot-And Powder-Processing Routes by W. J. Kim; E. M. Taleff; O. D. Sherby (pp. 4977-4985).
Tensile elongation behavior of fine-grained Fe–C alloys has been investigated as a function of cementite volume fraction, degree of microstructural refinement, and the Zener-Hollomon parameter. The strain rate–stress relationships and creep strengths of Fe–C alloys with carbon contents from 1.3 to 5.25 wt. % C are found to be similar when grain size is similar. Superplastic ductility of ingot-processed alloys initially increases with carbon content but starts to decrease after 2.1% C. The increase of tensile ductility with carbon content below 2.1% C is attributed to a reduction in the case of dynamic grain growth associated with an increase in the number of fine cementite particles, whereas the decrease of tensile ductility above 2.1% C is due to an increase in the number of coarse cementite particles and an increase in the area of cementite/cementite grain boundaries. Superplastic ductility of Fe–C alloys with carbon contents higher than 2.1% C can be significantly enhanced when powder-processing routes are utilized instead of ingot-processing routes. Tensile elongation behavior of cementite-based alloys is revealed to be different from that of iron-based alloys when compared as a function of the Zener-Hollomon parameter.

Structure and Magnetic Properties of BaCoTiFe10O19 Thin Films with an Easy-Axis In-Plane Orientation by B. X. Gu (pp. 4987-4990).
BaCoTiFe10O19 hexaferrite thin films with an easy-axis in-plane orientation were prepared by crystallization of amorphous films deposited by rf magnetron sputtering. The structure and magnetic properties were investigated. It is shown that CoTi-doping leads to a reduction of spontaneous magnetization and magnetic moment, which is caused by non-collinear magnetic structure and surface spin canting of small particles. The substitution of CoTi for Fe can adjust coercivity and Curie temperature over a very wide range, while still maintaining the room temperature magnetization. It is found that BaCoTiFe10O19 films exhibit a large squareness of hysteresis loop, Sq = 0.68. Thus, this film is desirable for high-density longitudinal recording systems.

Comparison of Surface Treatment Methods for Promoting the Adhesion of Glass on Titanium by P. Van Landuyt; J.-M. Streydio; F. Delannay; E. Munting (pp. 4991-4999).
A glass allowing the wetting of titanium has previously been developed. Two surface treatments promoting glass adhesion on titanium are compared: preoxidation and phosphatation combined with preoxidation. After preoxidation at 700 °C, a 1 μm-thick TiO2 layer covers titanium. The phosphated titanium substrates are oxidized at 600 °C to obtain a 20 μm-thick oxifluoride layer. After firing, glass adhesion is obtained with both surface treatments, but a “critical time of firing” appears with preoxidized titanium. WDS analysis suggests that diffusion of TiO2 into the glass is responsible for adhesion on preoxidized titanium, while a complex oxifluoride layer allows redox phenomena in the case of phosphated titanium. Pull-off tests have measured a maximum strength from 1.5 to 3 MPa whatever the surface treatment. Measurement of transverse crack densities in the vitreous coatings gives a higher value for phosphated than for preoxidized titanium. This confirms that better adhesion is obtained after phosphatation treatment.

Combustion Synthesis, Powder Characteristics and Crystal Structure of Phases in Ce–Pr–O System by M. Rajendran; K. K. Mallick; A. K. Bhattacharya (pp. 5001-5006).
The combustion method has been employed to produce homogeneous, single phased mixed rare-earth oxides in Ce1 − xPrxO2−y system for x ranging from 0 to 0.7. A cubic fluorite structure is formed for the compositions 0 ≤ x ≤ 0.7, while for x > 0.7 mixed phases are obtained. The mixed oxides are formed at the furnace temperature of 500 °C in a short duration of 10 min. In view of the importance of these powders in catalysis, crystallite size, surface area and porosity measurements have been carried out. The crystallite size of the powders increases with x while the surface area decreases. As the temperature is increased to 850 °C, the surface area decreases and the effect is much pronounced in cerium rich oxides. The powders on calcination above 900 °C in air results in the demixing of Ce and Pr to give two fluorite phases.

Joining of Silicon Carbide Using MgO-Al2O3-SiO2 Filler by H. L. Lee; S. W. Nam; B. S. Hahn; B. H. Park; D. Han (pp. 5007-5014).
Pressureless sintered SiC specimens were joined using MgO-Al2O3-SiO2 (MAS) filler. MAS filler showed excellent behaviour of wetting on SiC substrate above 1480 °C, and the wettability was much influenced by the joining atmosphere. The joining was carried out at 1500 and 1600 °C for 30 min in Ar atmosphere. The flexural strength of the joined specimen showed 342–380 MPa up to 800 °C. However, the flexural strength of the joined specimen decreased to about 80 MPa at 900 °C due to softening of the joint interlayer. The results of the XRD and WDS showed that the reaction between SiC and the MAS filler produced the oxycarbide glass.

Refinement of Cast Microstructure of Hypereutectic Al-Si Alloys Through the Addition of Rare Earth Metals by Joonyeon Chang; Inge Moon; Chongsool Choi (pp. 5015-5023).
Microstructural observation and thermal analysis of Al-21 wt % Si alloys with different rare earth metals were performed to examine the effect of rare earth metal on the refinement of primary silicon phase. Simultaneous refinement of both primary and eutectic silicon morphology is achieved with the addition of rare earth and its effect increases with the amount of rare earth addition and cooling rate. Depression of 12–17 °C in primary reaction temperature and 2–7 °C in eutectic temperature is measured with the addition of rare earth. Rare earth bearing compounds were not believed to act as a nucleation agent of primary silicon phase. Some rare earth bearing compounds determined to AlCe were around primary silicon in the matrix. The twin density of eutectic silicon remains same regardless of the addition of rare earth. The refinement of silicon in rare earth treated hypereutectic Al-Si alloys is supposed to be due to the suppression of the nucleation temperature of silicon phase.

Synthesis of HMDS Radical Terminated Perhydropolysilazane by Y. Shimizu; K. Suzuki; O. Funayama (pp. 5025-5028).
The chemical stability of perhydropolysilazane is improved by the introduction of HMDS (1, 1, 1, 3, 3, 3-hexamethyldisilazane) radical. The increase rate of the number average molecular weight of HMDS radical-introduced perhydropolysilazane was ten times slower than that of raw perhydropolysilazane. 1H-NMR analysis revealed that HMDS molecules mainly reacted with terminal Si-H3 groups of perhydropolysilazane.

On the Effects of Surface Treatments on the Mechanical Strength of Carbon Fibres by P. Bertrand; M-H. Vidal-Sétif; R. Valle; R. Mévrel (pp. 5029-5036).
TiB2, pyrolytic carbon (Cpyr) and Cpyr + TiB2 double layer coatings have been envisaged as potential protective coatings to prevent the deleterious interface reactions between the carbon fibre and the aluminium matrix during composite manufacturing. These coatings have been obtained by low pressure chemical vapour deposition on T800H carbon fibre yarns. In spite of a 20 % increase in the coated monofilaments tensile strength observed for very thin Cpyr coatings, a strength decrease as a function of the coating thickness is recorded for single Cpyr or TiB2 layers. For the TiB2 coatings, this decrease fits well with Ochiai's model which simulates the notch effect induced by a cracked brittle layer. Concerning the Cpyr coatings, a lower damaging effect is observed as compared to TiB2, it may be explained by the difference between the Young's moduli of both layers. Although the initial fibre properties are not perfectly maintained in the case of the double layer, the crack deviation role of the Cpyr coating succeeds in preserving the coated fibres from the TiB2 notch effect, thus leading to a noticeable strength increase.

The Measurement of Compressive Creep Deformation and Damage Mechanisms in a Single-Phase Alumina Part I Grain boundary sliding by C. R. Blanchard; R. A. Page (pp. 5037-5047).
Grain boundary sliding (GBS) has been hypothesized to act as the primary driving force for the nucleation and growth of grain boundary cavities in ceramics undergoing creep. In addition, GBS is often a major mode of deformation during high-temperature creep. This paper demonstrates the importance of GBS with mode II GBS measurements performed using a stereoimaging technique on a single-phase alumina tested under constant compressive stresses of 70 and 140 MPa at 1600 °C. Measurements were taken at constant time intervals during creep. The results support previous observations that GBS is stochastic and history independent. GBS displacements at given time intervals are shown to fit a Wiebull distribution. During steady-state creep, GBS displacements increased linearly with time at a constant sliding rate of ≈ 6.0 × 10−5 μm s−1 at 70 MPa and ≈ 1.3 × 10−4 μm s−1 at 140 MPa. Also, an average of 67% of the grain boundaries exhibited measurable sliding throughout the creep life of the 140 MPa test. Results of the GBS measurements are used to modify an existing creep model describing stochastic GBS. In part II of this paper [1], the GBS measurements reported are related to the associated creep cavitation measured in specimens tested under identical conditions.

The Measurement of Compressive Creep Deformation and Damage Mechanisms in a Single-Phase Alumina Part II Correlation of creep cavitation and grain boundary sliding by C. R. Blanchard; R. A. Page; S. Spooner (pp. 5049-5058).
It has been theorized that stochastic grain boundary sliding (GBS) is the primary driving force for the nucleation, growth, and coalescence of cavities located on the grain boundaries of polycrystalline ceramics undergoing creep. This paper reports on the results of co-ordinated measurements of both GBS and creep cavitation during the creep of a single-phase alumina. Constant compressive stress creep experiments were performed at a temperature of 1600 °C, and stress levels of 70, 100, and 140 MPa. Small angle neutron scattering measurements (SANS) show that cavities nucleate continuously due to creep at all three stress levels, and that since negligible cavity growth was measured, creep cavitation appears to be ruled by a nucleation rather than a growth process. Also, at a constant creep temperature, the number and volume of cavities measured was observed to decrease with a decrease in the applied stress. GBS displacements reported in Part 1 of this paper [1] are related to the number of cavities nucleated per unit volume and shown to relate directly, thereby providing experimental evidence that GBS may act as the driving force for creep cavitation.

Capillary Flow Behaviour of Microcrystalline Wax and Silicon Carbide Suspension by H. Suwardie; R. Yazici; D. M. Kalyon; S. Kovenklioglu (pp. 5059-5067).
Suspensions of ceramic particles in low or high molecular weight polymers are shaped into various three-dimensional parts using various moulding and extrusion technologies. Such bodies are subsequently fired-up and sintered to remove the binder. The utilities of such three-dimensional ceramic bodies depend on the restrictions related to the shapeability of the ceramic suspension, hence to the flow and deformation behaviour of the suspension. In this study, factors affecting the flow and deformation behaviour of a 50% by volume of silicon carbide in a wax binder was investigated. Consistent with the previously observed behaviour of other highly filled materials, the ceramic suspension exhibited viscoplasticity, plug flow and wall slip. Furthermore, flow instabilities associated with the axial migration of the low viscosity binder under the imposed pressure gradient were observed. These results pinpoint to the various difficulties associated with the collection of rheological data and emphasize the relevance of various flow mechanisms, including wall slip and mat formation and filtration based flow instabilities, which would also occur in processing/shaping flows of such ceramic suspensions including extrusion and moulding.

Precipitations in an Yttrium-Containing Low-Expansion Superalloy by R. M. Wang; Y. F. Han; C. Z. Li; S. W. Zhang; D. H. Ping; M. G. Yan (pp. 5069-5077).
The resistance to stress-accelerated grain-boundary oxygen embrittlement and notch-bar rupture strength in Fe–Ni–Co–Nb–Ti low-expansion superalloy has been improved significantly by trace yttrium addition. The precipitates in the matrix as well as along the grain boundaries have been studied systematically. The platelet precipitates in the matrix and along the grain boundaries have a hexagonal crystal structure (space group, P6/mmm) with lattice parameters a = 0.498 nm and c = 0.408 nm. The crystallographic orientation relationship between the phase and the matrix is found to be $$(overline 1 { ext{ }}overline 1 1 )_gamma //(0 0 0 1)_H ,[overline 1 1 0]_gamma //[1 1 overline 2 0]_H $$ . The semi-continuous discrete precipitates along the grain boundaries have an orthorhombic crystal structure with lattice parameters a = 0.45 nm, b = 0.80 nm and c = 1.20 nm. High-resolution images show that the interface between the precipitates and the matrix is semicoherent.
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