High Strength (high + strength)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Terms modified by High Strength

  • high strength concrete

  • Selected Abstracts

    High Strength (Ti58Ni28Cu8Si4Sn2)100,xMox Nanoeutectic Matrix,, -Ti Dendrite, BMG-Derived Composites with Enhanced Plasticity and Corrosion Resistance

    Hesham E. Khalifa
    Semi-solidly processed(Ti58Ni28Cu8Si4Sn2)100,xMox nanoeutectic matrix composites utilize a ductile dendritic , -Ti phase to achieve enhanced plasticity up to 15% total strain while maintaining fracture strengths up to 2300 MPa. The choice of Mo as the , -Ti stabilizer plays an important role in enhancing the work hardening exponent as well as the corrosion resistance in these alloys. [source]

    The Optimal Grain Sized Nanocrystalline Ni with High Strength and Good Ductility Fabricated by a Direct Current Electrodeposition,

    X. Shen
    In this work, six pure Ni specimen which mean grain sizes spans a broad range from ultra-fine to nanometer were fabricated by direct current electrodeposition and a coarse grain Ni was obtained by annealing. A gradual transition of the crystallographic preferred orientation of the deposited Ni from (200) texture to isotropic or random orientation with decreasing the mean grain size was revealed by XRD. [source]

    Sintered Reaction-Bonded Silicon Nitride with High Thermal Conductivity and High Strength

    You Zhou
    Sintered reaction-bonded silicon nitride (SRBSN) materials were prepared from a high-purity Si powder doped with Y2O3 and MgO as sintering additives by nitriding at 1400C for 8 h and subsequently postsintering at 1900C for various times ranging from 3 to 24 h. Microstructures and phase compositions of the nitrided and the sintered compacts were characterized. The SRBSN materials sintered for 3, 6, 12, and 24 h had thermal conductivities of 100, 105, 117, and 133 W/m/K, and four-point bending strengths of 843, 736, 612, and 516 MPa, respectively. Simultaneously attaining thermal conductivity and bending strength at such a high level made the SRBSN materials superior over the high-thermal conductivity silicon nitride ceramics that were prepared by sintering of Si3N4 powder in our previous works. This study indicates that the SRBSN route is a promising way of fabricating silicon nitride materials with both high thermal conductivity and high strength. [source]

    A Novel Concept for Highly Oriented Carbon Nanotube Composite Tapes or Fibres with High Strength and Electrical Conductivity

    Hua Deng
    Abstract A new concept is described for the creation of multifunctional polymer nanocomposite tapes (or fibres) that combines high stiffness and strength with good electrical properties and a low percolation threshold of carbon nanotubes (CNTs). The concept is based on a bicomponent tape (or fibre) construction consisting of a highly oriented polymer core and a conductive polymer composite (CPC) skin based on a polymer with a lower melting temperature than the core, enabling thermal annealing of these skins to improve conductivity through a dynamic percolation process while retaining the properties of the core and hence those of the tape (or fibre). The percolation threshold in the CPC skins of the highly drawn conductive bicomponent tapes could be decreased from 5.3 to 1.1,wt.-% after annealing. [source]

    Snoek-Type High-Damping Alloys Realized in ,-Ti Alloys with High Oxygen Solid Solution

    ADVANCED MATERIALS, Issue 12 2006
    F. Yin
    High strength and a huge Snoek damping peak,properties required for high-damping alloys, which find applications in mechanical structures in attempts to eliminate noise and vibration,are reported to have been realized in ,-type Ti alloys with an oxygen solid solution above 1.0,at,%. The properties of some Ti,25,Nb,x,O (at,%) alloys (see figure) are superior to those of most previously developed high-damping alloys. [source]

    Wood storage in a wide mountain river: case study of the Czarny Dunajec, Polish Carpathians

    omiej Wy
    Abstract Storage of large woody debris in the wide, mountain, Czarny Dunajec River, southern Poland, was investigated following two floods of June and July 2001 with a seven-year frequency. Within a reach, to which wood was delivered only by bank erosion and transport from upstream, wood quantities were estimated for eighty-nine, 100 m long, channel segments grouped into nine sections of similar morphology. Results from regression analysis indicated the quantity of stored wood to be directly related to the length of eroded, wooded banks and river width, and inversely related to unit stream power at the flood peak. The largest quantities of wood (up to 33 t ha,1) were stored in wide, multi-thread river sections. Here, the relatively low transporting ability of the river facilitated deposition of transported wood while a considerable length of eroded channel and island banks resulted in a large number of trees delivered from the local riparian forest. In these sections, a few morphological and ecological situations led to the accumulation of especially large quantities of wood within a small river area. Very low amounts of wood were stored in narrow, single-thread sections of regulated or bedrock channel. High stream power facilitated transport of wood through these sections while the high strength of the banks and low channel sinuosity prevented bank retreat and delivery of trees to the channel. Considerable differences in the character of deposited wood existed between wide, multi-thread channel sections located at different distances below a narrow, 7 km long, channellized reach of the river. Wood deposited close to the downstream end of the channellized reach was highly disintegrated and structured into jams, whereas further downstream well preserved shrubs and trees prevailed. This apparently reflects differences in the distance of wood transport and shows that in a mountain river wider than the height of trees growing on its banks, wood can be transported long distances along relatively narrow, single-thread reaches but is preferentially deposited in wide, multi-thread reaches. Copyright 2005 John Wiley & Sons, Ltd. [source]

    Fabrication of Load-Bearing NiTi Scaffolds for Bone Ingrowth by Ni Foam Conversion,

    Irena Gotman
    Highly porous NiTi scaffolds for bone ingrowth were fabricated by reactive conversion (PIRAC) of commercially available Ni foams. These open cell ,trabecular NiTi' scaffolds possess high strength and ductility and exhibit low Ni ion release. PIRAC deposition of a thin titanium nitride (TiN) layer further improves the corrosion characteristics of "trabecular NiTi" and allows for material bioactivation by alkali treatment or biomimetic Ca phosphate deposition. [source]

    Enhanced Ductility of Dendrite-Ultrafine Eutectic Composite Fe3B Alloy Prepared by a Self-Propagating High-Temperature Synthesis,

    Licai Fu
    The bulk dendrite-ultrafine eutectic composite Fe3B alloy was prepared by a self-propagating high-temperature synthesis. This technique is convenient, low cost, and capable of being scaled up for processing bulk nano/ultrafine-structured materials. The Fe3B alloy is composed of a micrometer-sized dendrite dispersed in an ultrafine laminar eutectic matrix and exhibits both high strength and large ductility in compressive tests. [source]

    High-Strength Porous Copper by Cold-Extrusion,

    H. Utsunomiya
    The authors propose a method to fabricate porous metals with high strength in this paper. Pieces of matrix metal and space-holder metal are deformed together by bulk forming for solid-phase bonding. From the bonded composite, only the space-holder metal is removed. If the deformation and the removal are conducted at cold or warm region, ,wrought' high-strength porous metal can be obtained. In this study, using aluminum as space holder, two types of porous copper with one-dimensional pores, i.e., lotus-type and honeycomb-type rods, have been successfully fabricated by cold extrusion followed by chemical leaching. Both the porous coppers fabricated show higher specific yield strength than a conventional porous metal. [source]

    Martensite Formation in a Ductile Cu47.5Zr47.5Al5 Bulk Metallic Glass Composite,

    S. Pauly
    A Cu47.5Zr47.5Al5 alloy was solidified into rods of 2, 3 and 5 mm diameter and the microstructures as well as the elastic and plastic properties were investigated along the length of each rod. It was found that neither the microstructure nor the mechanical properties vary significantly along the length of the specimens, except for the 5 mm diameter rod where the top part was proved to be fully crystalline containing cubic B2 CuZr (austenite) and monoclinic CuZr (martensite) phases. The differently solidified alloys show high strength and a distinct deformability under uniaxial compression and a work hardening-like behavior. [source]

    The influence of porosity on the fatigue strength of high-pressure die cast aluminium

    ABSTRACT Aluminium is a lightweight material with high strength and good corrosion resistance among other beneficial properties. Thanks to these properties, aluminium is more extensively used in the vehicle industry. High-pressure die casting of aluminium is a manufacturing process that makes it possible to attain complex, multi-functional components with near-net shape. However, there is one disadvantage of such castings, that is, the presence of various defects such as porosity and its effect on mechanical properties. The aim of this work was to investigate the influence of porosity on the fatigue strength of high-pressure die cast aluminium. The objective was to derive the influence of defect size with respect to the fatigue load, and to generate a model for fatigue life in terms of a Kitagawa diagram. The aluminium alloy used in this study is comparable to AlSi9Cu3. Specimens were examined in X-ray prior to fatigue loading and classified with respect to porosity level and eventually fatigue tested in bending at the load ratio, R, equal to ,1. Two different specimen types with a stress concentration factor of 1.05 and 2.25 have been tested. It has been shown that the fatigue strength decreases by up to 25% as the amount of porosity of the specimen is increased. The results further showed that the influence of defects was less for the specimen type with the higher stress concentration. This is believed to be an effect of a smaller volume being exposed to the maximum stress for this specimen type. A Kitagawa diagram was constructed on the basis of the test results and fracture mechanics calculations. A value of 1.4 Mpa m1/2 was used for the so-called stress intensity threshold range. This analysis predicts that defects larger than 0.06 mm2 will reduce the fatigue strength at 5 106 cycles for the aluminium AlSi9Cu3 material tested. [source]

    Crack-healing and mechanical behaviour of Al2O3/SiC composites at elevated temperature

    K. ANDO
    ABSTRACT Alumina/silicon carbide (Al2O3/SiC) composite ceramics with large self-crack-healing ability, high strength and high heat-resistance limit temperature for strength were developed and subjected to three-point bending. A semicircular surface crack 100 ,m in diameter was made on each sample. Crack-healing behaviour was systematically studied, as functions of crack-healing temperature and healing time, and the fatigue strengths of the crack-healed sample at room temperature and 1373 K were investigated. Four main conclusions were drawn from the present study. (1) Al2O3/SiC composite ceramics have the ability to heal after cracking from 1273to 1673 K in air. (2) The heat-resistance limit temperature for strength of the crack-healed sample is ,1573 K, and ,68% of the samples fractured from outside the crack-healed zone in the testing-temperature range 873,1573 K. (3) The crack-healed sample exhibited very high fatigue limit at room temperature and also 1373 K. (4) The large self-crack-healing ability is a desirable technique for the high structural integrity of ceramic component. [source]

    Plastic Dissipation Mechanisms in Periodic Microframe-Structured Polymers

    Lifeng Wang
    Abstract Novel lightweight micro- and nanostructured materials are being used as constituents in hierarchically structured composites for providing high stiffness, high strength, and energy absorbing capability at low weight. Three dimensional SU-8 periodic microframe materials with submicrometer elements exhibit unusual large plastic deformations. Here, the plastic dissipation and mechanical response of polymeric microframe structures is investigated using micromechanical modeling of large deformations. Finite element analysis shows that multiple deformation domains initiate, stabilize, and then spread plasticity through the structure; simulated deformation mechanisms and deformation progression are found to be in excellent agreement with experimental observation. Furthermore, the geometry can be used to tailor aspects of 3D behavior such as effective lateral contraction ratios (elastic and plastic) during tensile loading as well as negative normal stress during simple shear deformation. The effects of structural geometry on mechanical response are also studied to tailor and optimize mechanical performance at a given density. These quantitative investigations enable simulation-based design of optimal lightweight material microstructures for dissipating energy. [source]

    Depth distribution of earthquakes in the Baikal rift system and its implications for the rheology of the lithosphere

    Jacques Dverchre
    Summary The correspondence between the predicted brittle,plastic transition within the crust and the maximum depth of earthquakes is examined in the case of the Baikal rift, Siberia. Although little accurate information on depths is available through large- and moderate-size earthquakes, there are frequent indications of foci at 20 km depth and more. We have relocated 632 events recorded at nearby stations that occurred between 1971 and 1997, with depth and epicentral uncertainties less than 5 km, over the eastern and southern parts of the Baikal rift. We have compared these results with other depth distributions obtained in previous studies from background seismicity in the NE rift (1365 events in the Kalar-Chara zone and 704 events in the Muya region). The relative abundance of earthquakes is generally low at depths between 0 and 10 km (7,15 per cent) and high between 15 and 25 km (,50 per cent). Earthquake activity is still significant between 25 and 30 km (9,15 per cent) and persists between 30 and 40 km (7,13 per cent). Very few earthquakes are below the Moho. We use empirical constitutive laws to obtain the yield-stress limits of several layers made of dominant lithologies and to examine whether the observed distribution of earthquakes at depth (519 events controlled by a close station and located within the extensional domain of the Baikal rift system) can match the predicted crustal strength proportion with depth and the deeper brittle,ductile transition in the crust. A good fit is obtained by using a quartz rheology at 0,10 km depth and a diabase rheology at 10,45 km depth with a moderate temperature field which corresponds to a ,100 Myr thermal lithosphere. No dioritic composition of the crust is found necessary. In any case, earthquakes occur at deep crustal levels, where the crust is supposed to be ductile, in a way very similar to what is found in the East African Rift System. From these results we conclude that the seismogenic thickness is ,35,40 km in the Baikal rift system and that the depth distribution of earthquakes is at first order proportional to the strength profile found in a rheologically layered crust dominated by a mafic composition in the ,10,45 km depth range. An upper mantle core with high strength, however, generally prevents it from reaching stress failure at greater depth. [source]

    Transparent Photo-Stable Complementary Inverter with an Organic/Inorganic Nanohybrid Dielectric Layer

    Min Suk Oh
    Abstract Transparent electronics has been one of the key terminologies forecasting the ubiquitous technology era. Several researchers have thus extensively developed transparent oxide-based thin-film transistors (TFTs) on glass and plastic substrates. However, work in transparent electronics has been limited mostly to high-voltage devices operating at more than a few tens of volts, and has mainly focused on transparent display drivers. Low-voltage logic devices, such as transparent complementary inverters, operating in an electrically stable and photo-stable manner, are now very necessary to practically realize transparent electronics. Electrically stable dielectrics with high strength and high capacitance must also be proposed to support this mission, and simultaneously these dielectrics must be compatible with both n- and p-channel TFTs in device fabrication. Here, a nanohybrid dielectric layer that is composed of multiple units of inorganic oxide and organic self-assembled monolayer is proposel to support a transparent complementary TFT inverter operating at 3,V. [source]

    Bulk Metallic Glasses with Functional Physical Properties

    ADVANCED MATERIALS, Issue 45 2009
    W. H. Wang
    Abstract In this review, we report on the formation of a variety of novel, metallic, glassy materials that might well have applications as functional materials. The metallic glasses, with excellent glass-forming ability, display many fascinating properties and features such as excellent wave-absorption ability, exceptionally low glass-transition temperatures (,35,60,C) approaching room temperature, ultralow elastic moduli comparable to that of human bone, high elasticity and high strength, superplasticity and polymer-like thermoplastic formability near room temperature, an excellent magnetocaloric effect, hard magnetism and tunable magnetic properties, heavy-fermion behavior, superhydrophobicity and superoleophobicity, and polyamorphism, all of which are of interest not only for basic research but also for technological applications. A strategy based on elastic-moduli correlations for fabrication of bulk metallic glasses (BMGs) with controllable properties is presented. The work has implications in the search for novel metallic glasses with unique functional properties, for advancing our understanding of the nature and formation of glasses, and for extending the applications of the materials. [source]

    Optically Transparent Nanofiber Paper

    ADVANCED MATERIALS, Issue 16 2009
    Masaya Nogi
    Optically transparent paper of densely packed cellulose nanofibers is prepared without any additives. This material has the same chemical constituents as conventional paper, the only difference being the fiber width and the size of the interstitial cavities. This optically transparent paper exhibits high Young's modulus, high strength, ultralow CTE, and high foldability. [source]

    Silk as a Biomimetic Ideal for Structural Polymers

    ADVANCED MATERIALS, Issue 4 2009
    David Porter
    Two factors are critical for understanding silks: the nanoscale semicrystalline folding structure, which gives high strength and toughness, and the degree of hydration of the disordered fraction, which modifies these material properties. The combination of these two factors allows for a massive range of mechanical properties. Understanding and controlling these two factors are the key to the functionality of protein elastomers. [source]

    Sintered Reaction-Bonded Silicon Nitride with High Thermal Conductivity and High Strength

    You Zhou
    Sintered reaction-bonded silicon nitride (SRBSN) materials were prepared from a high-purity Si powder doped with Y2O3 and MgO as sintering additives by nitriding at 1400C for 8 h and subsequently postsintering at 1900C for various times ranging from 3 to 24 h. Microstructures and phase compositions of the nitrided and the sintered compacts were characterized. The SRBSN materials sintered for 3, 6, 12, and 24 h had thermal conductivities of 100, 105, 117, and 133 W/m/K, and four-point bending strengths of 843, 736, 612, and 516 MPa, respectively. Simultaneously attaining thermal conductivity and bending strength at such a high level made the SRBSN materials superior over the high-thermal conductivity silicon nitride ceramics that were prepared by sintering of Si3N4 powder in our previous works. This study indicates that the SRBSN route is a promising way of fabricating silicon nitride materials with both high thermal conductivity and high strength. [source]

    Preparation and properties of ,-chitin-whisker-reinforced hyaluronan,gelatin nanocomposite scaffolds

    Parintorn Hariraksapitak
    Abstract Tissue scaffolds made of naturally derived polymers present poor mechanical properties, which may limit their actual utilization in certain areas where high strength is a key criterion. This study was aimed at developing tissue scaffolds from a 50 : 50 w/w blend of hyaluronan (HA) and gelatin (Gel) that contained different amounts of acid-hydrolyzed ,-chitin whiskers (CWs) by a freeze-drying method. The weight ratios of the CWs to the blend were 0,30%. These scaffolds were characterized for their physical, physicochemical, mechanical, and biological properties. Regardless of the CW content, the average pore size of the scaffolds ranged between 139 and 166 ,m. The incorporation of 2% CWs in the HA,Gel scaffolds increased their tensile strength by about two times compared to those of the other groups of the scaffolds. Although the addition of 20,30% CWs in the scaffolds improved their thermal stability and resistance to biodegradation, the scaffolds with 10% CWs were the best for supporting the proliferation of cultured human osteosarcoma cells (SaOS-2). 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

    Morphologies and mechanical properties of HDPE induced by small amount of high-molecular-weight polyolefin and shear stress produced by dynamic packing injection molding

    Zhanchun Chen
    Abstract To better understand the effect of a small amount of high-molecular-weight polyethylene (HMWPE) on the mechanical properties and crystal morphology under the shear stress field, the dynamic packing injection molding (DPIM) was used to prepare the oriented pure polyethylene and its blends with 4% HMWPE. The experiment substantiated that the further improvement of tensile strength along the flow direction (MD) of high-density polyethylene (HDPE)/HMWPE samples was achieved, whereas the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional molding. Tensile strength in both flow and TDs were highly enhanced, with improvements from 23 to 76 MPa in MD and from 23 to 31 MPa in TD, besides the toughness was highly improved. So, the samples of HDPE/HMWPE transformed from high strength and brittleness to high strength and toughness. The obtained samples were characterized via SEM and TEM. For HDPE/HMWPE, the lamellae of the one shish-kebab in the oriented region may be stretched into other shish-kebab structures, and one lamella enjoys two shish or even more. This unique crystal morphology could lead to no yielding and necking phenomena in the stress,strain curves of HDPE/HMWPE samples by DPIM. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Porous Ti-6Al-4V alloy fabricated by spark plasma sintering for biomimetic surface modification

    Masayuki Kon
    Abstract Porous compacts with both biological and biomechanical compatibilities and high strength were developed. Spherical powders of Ti-6Al-4V alloy, which were either as received or surface modified with the use of calcium ions by hydrothermal treatment (HTT), were fabricated by a spark plasma sintering process. The porous compacts of pure Ti were used as reference materials. Porosity was approximately 30%, and compressive strengths were 113 and 125 MPa for the as-received Ti alloy powders and those modified by the HTT process, respectively. The bending strength and elastic modulus of as-received Ti alloy powders were 128,178 MPa and 16,18 GPa, respectively. Each of the compacts was immersed in simulated body fluid (SBF). The amount of adsorption/precipitation of calcium phosphate through the compacts was measured by weight change and was observed by SEM. The compacts were covered with calcium phosphate after 2 weeks of immersion in SBF. The compacts of Ti alloy had plenty of precipitated apatite crystals, and modification by HTT accumulated more precipitation. Because calcium phosphate is a mineral component of bone, apatite, which is precipitated on the surface of the compacts, could adsorb proteins and/or drugs such as antibiotics. It is expected that a large amount of proteins and/or drugs could be impregnated when the porous compacts developed are used. 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 68B: 88,93, 2004 [source]

    The effect of the addition of poly(methyl methacrylate) fibres on some properties of high strength heat-cured acrylic resin denture base material

    D. Jagger
    summary, The self-reinforcement of acrylic resin with butadiene styrene surface treated poly(methyl methacrylate) fibres has been reported to have the potential to substantially improve the transverse bend strength of conventional heat-cured acrylic resin. The aim of this study was to investigate the effect of the addition of butadiene styrene surface treated poly(methyl methacrylate) fibres in cross-ply arrangement to high impact acrylic resin on the transverse and impact strength. Specimens were prepared as specified in the International Standard Organization and British Standards for the Testing of Denture Base Resins (ISO 1567, 1988; BS 2487, 1989) and the British Standard Specification for Orthodontic resins (BS 6747, 1987) for transverse bend and impact testing. The impact strength was measured using a Zwick pendulum impact tester and the transverse bend strength measured using a Lloyds Instruments testing machine. The results showed that the impact strength was not improved with the addition of fibres, high impact acrylic resin with fibres (LF) 111 kJ m,2 and high impact acrylic resin (L) (125 kJ m,2). The modulus of rupture was decreased with the addition of fibres (578 MPa) for (LF) compared with (604 MPa) for (L). The modulus of elasticity was also reduced with the addition of fibres (18349 MPa) (LF) and 20862 MPa (L) as was the peak load (LF) (508 N) and (L) (558 N). It was concluded that the addition of surface treated poly(methyl methacrylate) fibres in cross-ply arrangement to high strength acrylic resin did not produce an improvement in the impact or transverse strength and cannot be recommended as a method of reinforcement. [source]

    The discovery of polymer-clay hybrids

    Masaya Kawasumi
    Abstract The first successful example of a polymer-clay hybrid was nylon-clay hybrid (NCH), which is a nano-meter-sized composite of nylon-6 and 1-nm-thick exfoliated aluminosilicate layers of the clay mineral. NCH was found and developed at Toyota Central Research and Development Laboratories over 17 years ago. The NCH containing a few weight percentages of clay exhibits superior properties such as high modulus, high strength, and good gas-barrier properties. The key for the discovery of NCH was the polymerization of a nylon monomer in the interlayer space of the clay. This highlight presents the development of NCH from its discovery to its commercialization. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 819,824, 2004 [source]

    Fabrication of High-Strength Continuous Zirconia Fibers and Their Formation Mechanism Study

    He-Yi Liu
    Continuous zirconia fibers with a nanometer ceramic structure and a tensile strength up to 2.8 GPa were fabricated by pyrolyzing polyacetylacetonatozirconium precursor fibers through a special atmosphere heat treatment. DSC-TGA, GC-MS, IR, SEM, and TEM were used to study the fiber transformation mechanism during heating. Results showed that special atmosphere heat treatment could make the organics in the fibers come out directly without carbonization and remove them almost entirely under 400C, and the obtained zirconia fibers had few defects, good continuity, and high strength. [source]

    Microstructure Tailoring for High Thermal Conductivity of ,-Si3N4 Ceramics

    Hiroshi Yokota
    ,-Si3N4 ceramics sintered with Yb2O3 and ZrO2 were fabricated by gas-pressure sintering at 1950C for 16 h changing the ratio of "fine" and "coarse" high-purity ,-Si3N4 raw powders, and their microstructures were quantitatively evaluated. It was found that the amount of large grains (greater than a few tens of micrometers) could be drastically reduced by mixing a small amount of "coarse" powder with a "fine" one, while maintaining high thermal conductivity (>140 W(mK),1). Thus, this work demonstrates that it is possible for ,-Si3N4 ceramics to achieve high thermal conductivity and high strength simultaneously by optimizing the particle size distribution of raw powder. [source]

    High-Strength Porous Silicon Carbide Ceramics by an Oxidation-Bonding Technique

    Jihong She
    Porous silicon carbide (SiC) ceramics were fabricated by an oxidation-bonding process in which the powder compacts are heated in air so that SiC particles are bonded to each other by oxidation-derived SiO2 glass. Because of the crystallization of amorphous SiO2 glass into cristobalite during sintering, the fracture strength of oxidation-bonded SiC ceramics can be retained to a relatively high level at elevated temperatures. It has been shown that the mechanical strength is strongly affected by particle size. When 0.6 ,m SiC powders were used, a high strength of 185 MPa was achieved at a porosity of ,31%. Moreover, oxidation-bonded SiC ceramics were observed to exhibit an excellent oxidation resistance. [source]

    The use of post-mortem Raman spectroscopy in explaining friction and wear behaviour of sintered polyimide at high temperature

    P. Samyn
    Abstract Due to their thermal stability and high strength, polyimides are an aromatic type of polymer that is used in sliding equipment functioning under high loads and elevated temperature. However, its tribological behaviour under high temperature and atmospheric conditions is not fully understood. It has been reported that a transition from high towards lower friction occurs ,somewhere' in the temperature region between 100C and 200C; however, a correlation with changes in the polyimide molecular structure remains difficult to illustrate and it is not certain whether or not this transition is correlated to lower wear. In the present work sliding experiments under controlled bulk temperatures between 100C and 260C are performed. A transition is observed in both friction and wear at 180C which is further explained by microscopic analysis of the transfer film on the steel counterface and Raman spectroscopy of the worn polymer surfaces. A close examination of the spectra reveals transitions in relative intensity of certain absorption bands, pointing to different orientation effects of the molecular conformation at the polymer sliding surface at 180C. Copyright 2006 John Wiley & Sons, Ltd. [source]

    Novel Thermoplastic Composites from Commodity Polymers and Man-Made Cellulose Fibers

    Hans-Peter Fink
    Abstract Summary: A new class of fibre reinforced commodity thermoplastics suited for injection moulding and direct processing applications has been developed using man-made cellulosic fibres (Rayon tire yarn, Tencel, Viscose, Carbacell) and thermoplastic commodity polymers, such as polypropylene (PP), polyethylene (PE), high impact polystyrene (HIPS), poly(lactic acid) (PLA), and a thermoplastic elastomer (TPE) as the matrix polymer. For compounding, a specially adapted double pultrusion technique has been employed which provides composites with homogeneously distributed fibres. Extensive investigations were performed with Rayon reinforced PP in view of applications in the automotive industry. The Rayon-PP composite is characterized by high strength and an excellent impact behaviour as compared with glass fibre reinforced PP, thus permitting applications in the field of engineering thermoplastics such as polycarbonate/acrylonitrile butadiene styrene blends (PC/ABS). With the PP based composites the influence of material parameters (e.g. fibre type and load, coupling agent) were studied and it has been demonstrated how to tailor the desired composite properties as modulus and heat distortion temperature (HDT) by varying the fibre type or adding inorganic fillers. Man-made cellulose fibers are also suitable for the reinforcement of further thermoplastic commodity polymers with appropriate processing temperatures. In case of PE modulus and strength are tripled compared to the neat resin while Charpy impact strength is increased five-fold. For HIPS mainly strength and stiffness are increased, while for TPE the property profile is changed completely. With Rayon reinforced PLA, a fully biogenic and biodegradable composite with excellent mechanical properties including highly improved impact strength is presented. [source]

    Positron annihilation study of recrystallization behaviour in Zr2.5%Nb alloy

    S. Mulki
    Abstract In CANDU reactors Zr 2.5%Nb alloy is used as pressure tube material due to low neutron absorption cross section, a high resistance to corrosion in water, high strength and good creep resistance. The two phase alloy consists of ,-fcc and ,-bcc. The recrystallization behavior of Zr2.5Nb strongly depends on morphology and distribution of second phase. In this study, the material was deformed to 60% and then was recrystallized in , + , region for different duration (i.e. 2 minutes to 14 days at 700 C). The recrystallized microstructure was characterized by Orientation Imaging Microscopy (OIM). The evolution of microstructure was examined by Positron Lifetime Spectroscopy and Doppler Broadening measurement for each heat treated samples. Results from positron annihilation studies and other microstructural examination have been used to rationalize the recrystallization aspects, defects and ,-phase distribution. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]