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Hard Materials (hard + material)
Selected AbstractsSynthesis of Hard Materials by Field Activation: The Synthesis of Solid Solutions and Composites in the TiB2,WB2,CrB2 SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2001Hisashi Kaga The synthesis of solid solutions of (Ti,W,Cr)B2 from elemental reactants using the field-activated, pressure-assisted synthesis method and employing the SPS apparatus was investigated. The nature of the products depended on temperature; they were nearly pure solid solutions at 1900°C with minor amounts of ,-WB. The product density and microhardness depended on the temperature of synthesis for the same value of applied pressure (64 MPa). Samples with the highest density (94%) corresponded to a hardness of 22.7 GPa. When annealed at 1500°C, the solid solutions decomposed, precipitating a (W,Ti,Cr)B2 phase in a spinodal form. In addition, ,-WB precipitates in the form of thin (0.4,5.3 nm) layers were observed. They existed in a 60°/120° orientation to the (Ti,W,Cr)B2 matrix, in agreement with previous observations. Highly faceted, small (nanosized) pores associated with the ,-WB precipitates were also observed. [source] Microstructural characterization of laser surface melted AISI M2 tool steelJOURNAL OF MICROSCOPY, Issue 3 2010J. ARIAS Summary We describe the microstructure of Nd:YAG continuous wave laser surface melted high-speed steel, namely AISI M2, treated with different laser scanning speeds and beam diameters on its surface. Microstructural characterization of the remelted surface layer was performed using light optical and scanning electron microscopy and X-ray diffraction. The combination of the three techniques provided new insights into the substantial changes induced by laser surface melting of the steel surface layer. The advantage of the method is that it avoids the difficult and tedious work of preparing samples of this hard material for transmission electron microscopy, which is the technique normally used to study these fine microstructures. A melted zone with a dendritic structure and a partially melted zone with a heterogeneous cellular structure were observed. M2C carbides with different morphologies were identified in the resolidified surface layer after laser melting. [source] Mechanochemical Formation of Metal,Ceramic CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2000Nicholas J. Welham A mechanical activation technique has been used to form composites of alumina with titanium carbide, nitride, or carbonitride, both with and without elemental iron. The composites were formed by reacting elemental aluminum with either ilmenite (FeTiO3) or rutile (TiO2) concentrates in the presence of carbon and/or nitrogen in a ball-mill at ambient temperature. The reaction was complete for the ilmenite samples after milling but was completed only for rutile under hot pressing conditions. Microhardness measurements indicated that the composites had hardnesses in the range 19,30 GPa (1740,2750 VHN), with only a small variation within each sample. Elemental mapping of the pressed pellets indicated that titanium and aluminum were evenly distributed on a submicrometer level whereas iron tended to coalesce into <20 ,m particles in the presence of TiC. The coalescence decreased with the carbon content of the hard material until iron was evenly distributed with TiN. A superstoichiometric amount of aluminum led to the formation of iron,aluminum phases which decreased the iron coalescence. The XRD crystallite size of the alumina was 30,50 nm and was 25,50 nm for the titanium phases, confirming the extremely fine microstructure. [source] Multiscale modeling of hard materials: Challenges and opportunities for chemical engineeringAICHE JOURNAL, Issue 5 2000Dimitrios Maroudas First page of article [source] Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Paolo Colombo Preceramic polymers were proposed over 30 years ago as precursors for the fabrication of mainly Si-based advanced ceramics, generally denoted as polymer-derived ceramics (PDCs). The polymer to ceramic transformation process enabled significant technological breakthroughs in ceramic science and technology, such as the development of ceramic fibers, coatings, or ceramics stable at ultrahigh temperatures (up to 2000°C) with respect to decomposition, crystallization, phase separation, and creep. In recent years, several important advances have been achieved such as the discovery of a variety of functional properties associated with PDCs. Moreover, novel insights into their structure at the nanoscale level have contributed to the fundamental understanding of the various useful and unique features of PDCs related to their high chemical durability or high creep resistance or semiconducting behavior. From the processing point of view, preceramic polymers have been used as reactive binders to produce technical ceramics, they have been manipulated to allow for the formation of ordered pores in the meso-range, they have been tested for joining advanced ceramic components, and have been processed into bulk or macroporous components. Consequently, possible fields of applications of PDCs have been extended significantly by the recent research and development activities. Several key engineering fields suitable for application of PDCs include high-temperature-resistant materials (energy materials, automotive, aerospace, etc.), hard materials, chemical engineering (catalyst support, food- and biotechnology, etc.), or functional materials in electrical engineering as well as in micro/nanoelectronics. The science and technological development of PDCs are highly interdisciplinary, at the forefront of micro- and nanoscience and technology, with expertise provided by chemists, physicists, mineralogists, and materials scientists, and engineers. Moreover, several specialized industries have already commercialized components based on PDCs, and the production and availability of the precursors used has dramatically increased over the past few years. In this feature article, we highlight the following scientific issues related to advanced PDCs research: (1) General synthesis procedures to produce silicon-based preceramic polymers. (2) Special microstructural features of PDCs. (3) Unusual materials properties of PDCs, that are related to their unique nanosized microstructure that makes preceramic polymers of great and topical interest to researchers across a wide spectrum of disciplines. (4) Processing strategies to fabricate ceramic components from preceramic polymers. (5) Discussion and presentation of several examples of possible real-life applications that take advantage of the special characteristics of preceramic polymers. Note: In the past, a wide range of specialized international symposia have been devoted to PDCs, in particular organized by the American Ceramic Society, the European Materials Society, and the Materials Research Society. Most of the reviews available on PDCs are either not up to date or deal with only a subset of preceramic polymers and ceramics (e.g., silazanes to produce SiCN-based ceramics). Thus, this review is focused on a large number of novel data and developments, and contains materials from the literature but also from sources that are not widely available. [source] Set temperature dependence of fractional thermal loading and effective stimulated emission cross section of a diode double end pumped TEM00 Nd:YAG laser for micromachining applicationLASER PHYSICS LETTERS, Issue 5 2006S. K. Sudheer Abstract We discuss the set temperature dependence of fractional thermal loading and effective stimulated emission cross section of an efficient, diode double end -pumped Nd:YAG laser using two 30 W pump diodes with a CW output power greater than 8 W in polarized TEM00 mode near-diffraction limited beam suitable for micromachining applications of ultra hard materials like diamond. The temperature dependence of effective stimulated emission cross section for 4F3/2 , 4I11/2 transition and fractional thermal loading of Nd:YAG are determined where the pump power induced thermal lensing is used to make the cavity stable and in thermally stabilized solid state lasers the cavity parameters change dynamically with the pump power and hence the overlap integrals become a function of absorbed pump power. It is observed that the fractional thermal loading is increasing with increase in set temperature of laser crystal and effective stimulated emission cross section is increasing almost linearly with the increase in set temperature of laser crystal and pump laser diodes up to 30 °C the rated value of the pump diodes and thereafter the cross section decreases with increase in temperature. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Ultra-incompressible and hard technetium carbide and rhenium carbide: First-principles predictionPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 3 2008Yuan Xu Wang Abstract Using density functional theory, the author predicts that the compounds ReC and TcC with the hexagonal WC-like structure are ultra-incompressible and hard materials. This is concluded from the very large bulk and shear moduli. The phonon dispersion reveals no soft modes indicating the stability of the two materials. The calculated density of states shows that ReC and TcC are metallic. The structural and elastic properties of OsC, IrC, and PtC with hexagonal and cubic structure are also investigated for comparison. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis of ultrafine titanium carbonitride powders,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2001Frederic Monteverde Abstract Titanium-carbonitride-based materials are very hard materials with increasing technical importance. They are mainly used in composites with various metal carbides and/or metallic binders (cermets) for metal cutting operations. These applications call for the synthesis of titanium carbonitride powders with homogeneous chemical composition, as small as possible grain size and narrower grain size distribution. Nowadays on the market, only commercial submicrometric (0.5,2,,m) powders are available. Starting from blends of nanosize commercial TiN or TiO2 powders mixed with different carbon powders (carbon black, active carbon), this study aimed to set up a low-cost process to synthesize fine and pure TiC1,X,NX powders with an X value close to 0.5. The morphology of the as-obtained powders and the progress of the reaction were investigated by scanning electron microscopy and X-ray diffraction. The stoichiometric parameter X was estimated on the basis of a TiC1,X,NX Raoultian solid solution together with Vegard's rule. The results are presented and discussed to assess relations between powder characteristics and processing conditions. The most encouraging results were obtained using a mixture TiN,+,10,wt%C (carbon black) processed at 1430,°C for 3,h under flowing argon. Regularly shaped particles with limited agglomeration ranged from 100 to 300,nm and an X value close to 0.5 Copyright © 2001 John Wiley & Sons, Ltd. [source] Thermally Responsive Supramolecular Nanomeshes for On/Off Switching of the Rotary Motion of F1 -ATPase at the Single-Molecule LevelCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2008Satoshi Yamaguchi Dr. Abstract The artificial regulation of protein functions is essential for the realization of protein-based soft devices, because of their unique functions conducted within a nano-sized molecular space. We report that self-assembled nanomeshes comprising heat-responsive supramolecular hydrogel fibers can control the rotary motion of an enzyme-based biomotor (F1 -ATPase) in an on/off manner at the single-molecule level. Direct observation of the interaction of the supramolecular fibers with a microbead unit tethered to the F1 -ATPase and the clear threshold in the size of the bead required to stop ATPase rotation indicates that the bead was physically blocked so as to stop the rotary motion of ATPase. The temperature-induced formation and collapse of the supramolecular nanomesh can produce or destroy, respectively, the physical obstacle for ATPase so as to control the ATPase motion in an off/on manner. Furthermore, this switching of the F1 -ATPase motion could be spatially restricted by using a microheating device. The integration of biomolecules and hard materials, interfaced with intelligent soft materials such as supramolecular hydrogels, is promising for the development of novel semi-synthetic nano-biodevices. [source] On the Ekberg, Kabo and Andersson calculation of the Dang Van high cycle fatigue limit for rolling contact fatigueFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2004M. CIAVARELLA ABSTRACT Recently, various methods have been proposed to assess the risk of rolling contact fatigue failure by Ekberg, Kabo and Andersson, and in particular, the Dang Van multiaxial fatigue criterion has been suggested in a simple approximate formulation. In this note, it is found that the approximation implied can be very significant; the calculation is improved and corrected, and focused on the study of plane problems but for a complete range of possible friction coefficients. It is found that predicted fatigue limit could be much higher than that under standard uniaxial tension/compression for ,hard materials' than for ,ductile materials.' This is in qualitative agreement, for example, with gears' design standards, but in quantitative terms, particularly for frictionless condition, the predicted limit seems possibly too high, indicating the need for careful comparison with experimental results. Some comments are devoted to the interplay of shakedown and fatigue. [source] | ||||||||||||||||