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Vickers Hardness (Vicker + hardness)
Selected AbstractsInfluence of Wet Mechanical Mixing on Microstructure and Vickers Hardness of Nanocrystalline Ceramic,Metal CompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008Tatsuo Kumagai Nanocrystalline (nc) ceramic,metal composite bulk samples have been fabricated by consolidation of mixture of attrition-milled (AM) amorphous base ceramic ((ZrO2,3 mol% Y2O3),20 mol% Al2O3) and AM amorphous base metallic (Ti,48 mol% Al) powders using a pulse-current pressure sintering system. Microstructural observations revealed that the ceramic and metallic colonies appear blocky in morphology in the composite bulk samples, and both the ceramic and the metallic colonies consist of a large number of equiaxed fine grains with the sizes of 78,82 and 81,86 nm, respectively. Mechanical mixing treatments by wet ball milling in ethanol before consolidation process are effective for refinement of the ceramic and metallic colonies. In all the obtained composite bulk samples, the ceramic colonies consist of the dominant phase of tetragonal (t) ZrO2 solid solution (ss) together with the minor phases of monoclinic (m) ZrO2ss and ,-Al2O3. On the other hand, the dominant phase in the metallic colonies changes from Ti3Al (,2) to Tiss (,) with an increase in the t -ZrO2ss volume fraction by abrasion of 3 mol% yttria-stabilized tetragonal polycrystalline zirconia balls during wet mechanical mixing treatments. Such a phase transformation from ,2 to , is considered to be due to the decrease in the aluminum content in the metallic colonies by combination of aluminum with oxygen (i.e., the formation of ,-Al2O3), which is probably taken from ethanol (C2H5OH) into the powders during wet mechanical mixing treatments. The obtained nc composite bulk samples show good Vickers hardness values, which are considerably higher than those estimated from the rule of mixture. [source] Three-Dimensional Printing of Complex-Shaped Alumina/Glass Composites,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Wei Zhang Abstract Alumina/glass composites were fabricated by three-dimensional printing (3DPÔ) and pressureless infiltration of lanthanum-alumino-silicate glass into sintered porous alumina preforms. The preforms were printed using an alumina/dextrin powder blend as a precursor material. They were sintered at 1600,°C for 2,h prior to glass infiltration at 1100,°C for 2,h. The influence of layer thickness and sample orientation within the building chamber of the 3D-printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated. The increase of the layer thickness from 90 to 150,µm resulted in an increase of the total porosity from ,19 to ,39,vol% and thus, in a decrease of the mechanical properties of the sintered preforms. Bending strength and elastic modulus of sintered preforms were found to attain significantly higher values for samples orientated along the Y -axis of the 3D-printer compared to those orientated along the X - or the Z -axis, respectively. Fabricated Al2O3/glass composites exhibit improved fracture toughness, bending strength, Young's modulus, and Vickers hardness up to 3.6,MPa m1/2, 175,MPa, 228,GPa, and 12,GPa, respectively. Prototypes were fabricated on the basis of computer tomography data and computer aided design data to show geometric capability of the process. [source] Fabrication of Structural Leucite Glass,Ceramics from Potassium-Based Geopolymer PrecursorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Ning Xie Leucite glass,ceramics were fabricated by cold isostatically pressing K2O·Al2O3·4SiO2·11H2O geopolymer powders into pellets followed by firing at 950°,1200°C, every 50°C in air. Leucite formation was observed in specimens heat treated to ,1000°C. The relative density, Vickers hardness, fracture toughness, and biaxial flexural strength of sintered samples ranged approximately 96%,98%, 767,865 kg/mm2, 0.94,2.36 MPa·m1/2, and 90,140 MPa, respectively. The toughness and biaxial flexure strength increased with the firing temperature, while the density and hardness were relatively constant. Scanning electron microscopic and transmission electron microscopic analysis revealed that the sintered geopolymer formed leucite crystals and a compositionally variable glassy phase. Samples heated to 1200°C attained the highest biaxial flexure strength and toughness. This higher strength is believed to arise from an optimum in density, leucite content, and crystal size distribution. [source] Fabrication of an Al2O3/YAG/ZrO2 Ternary Eutectic by Combustion Synthesis Melt Casting Under Ultra-High GravityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009Rui Liang This work presents a novel method for preparing an Al2O3/YAG/ZrO2 ternary eutectic whereby combustion synthesis melt casting has been combined with the ultra-high gravity (UHG) technique. The fabricated product had a relative density of 99.3% of the theoretical one. Phase composition and microstructure analyses indicated that the application of UHG resulted in a metal-free ceramic microstructure with no porosity or microcracks. The microstructure comprises ZrO2 rods dispersed in Al2O3. The product had 17.82 GPa Vickers hardness and 5.51 MPa·m1/2 fracture toughness. [source] Synthesis, Physical, and Mechanical Properties of Bulk Zr3Al3C5 CeramicJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007Lingfeng He An in situ reactive hot-pressing process using zirconium (zirconium hydride), aluminum, and graphite as staring materials and Si and Y2O3 as additives was used to synthesize bulk Zr3Al3C5 ceramics. This method demonstrates the advantages of easy synthesis, lower sintering temperature, high purity and density, and improved mechanical properties of synthesized Zr3Al3C5. Its electrical and thermal properties were measured. Compared with ZrC, Zr3Al3C5 has a relatively low hardness (Vickers hardness of 12.5 GPa), comparable stiffness (Young's modulus of 374 GPa), but superior strength (flexural strength of 488 GPa) and toughness (fracture toughness of 4.68 MPa·m1/2). In addition, the stiffness decreases slowly with increasing temperature and at 1600°C remains 78% of that at ambient temperature, indicating that Zr3Al3C5 is a potential high-temperature structural ceramic. [source] Processing and Properties of TiB2 with MoSi2 Sinter-additive: A First ReportJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006T. S. R. Ch. The densification of non-oxide ceramics like titanium boride (TiB2) has always been a major challenge. The use of metallic binders to obtain a high density in liquid phase-sintered borides is investigated and reported. However, a non-metallic sintering additive needs to be used to obtain dense borides for high-temperature applications. This contribution, for the first time, reports the sintering, microstructure, and properties of TiB2 materials densified using a MoSi2 sinter-additive. The densification experiments were carried out using a hot-pressing and pressureless sintering route. The binderless densification of monolithic TiB2 to 98% theoretical density with 2,5 ,m grain size was achieved by hot pressing at 1800°C for 1 h in vacuum. The addition of 10,20 wt% MoSi2 enables us to achieve 97%,99%,th in the composites at 1700°C under similar hot-pressing conditions. The densification mechanism is dominated by liquid-phase sintering in the presence of TiSi2. In the pressureless sintering route, a maximum of 90%,th is achieved after sintering at 1900°C for 2 h in an (Ar+H2) atmosphere. The hot-pressed TiB2,10 wt% MoSi2 composites exhibit high Vickers hardness (,26,27 GPa) and modest indentation toughness (,4,5 MPa·m1/2). [source] Spark-Plasma Sintering of Silicon Carbide Whiskers (SiCw) Reinforced Nanocrystalline AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2004Guo-Dong Zhan The combined effect of rapid sintering by spark-plasma-sintering (SPS) technique and mechanical milling of ,-Al2O3 nanopowder via high-energy ball milling (HEBM) on the microstructural development and mechanical properties of nanocrystalline alumina matrix composites toughened by 20 vol% silicon carbide whiskers was investigated. SiCw/,-Al2O3 nanopowders processed by HEBM can be successfully consolidated to full density by SPS at a temperature as low as 1125°C and still retain a near-nanocrystalline matrix grain size (,118 nm). However, to densify the same nanopowder mixture to full density without the benefit of HEBM procedure, the required temperature for sintering was higher than 1200°C, where one encountered excessive grain growth. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that HEBM did not lead to the transformation of ,-Al2O3 to ,-Al2O3 of the starting powder but rather induced possible residual stress that enhances the densification at lower temperatures. The SiCw/HEBM,-Al2O3 nanocomposite with grain size of 118 nm has attractive mechanical properties, i.e., Vickers hardness of 26.1 GPa and fracture toughness of 6.2 MPa·m1/2. [source] Sintering Behavior and Properties of Iron-Rich Glass-CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2004Alexander Karamanov Iron-rich glass-ceramics were obtained by the sintering of two glass powders, labeled G1 and G2, at heating rates of 5° and 20°C/min followed by an isothermal step in the 850°,1050°C temperature interval. The sintering process was evaluated by the linear shrinkage; the closed porosity was estimated by density measurements; the structure and the morphology of the glass ceramics were observed by scanning electron microscopy. The bending strength, the Young modulus, and Vickers hardness of the glass-ceramics materials were evaluated. The results showed that the sintering process and morphology of the glass-ceramics depends on the amount of magnetite and pyroxene formed. With a low percentage of crystal phase formed (25%,30% typical of G1) the structure is characterized by closed porosity; at higher crystallization (45%,50% typical of G2) open porosity is mainly formed. The properties of the glass-ceramics were not influenced by the heating rate but improved with an increase in the degree of crystallization. [source] Properties of Nitrogen-Containing Yttria,Alumina,Silica Melts and GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Noritaka Saito The viscosity and solubility of nitrogen in Y2O3,Al2O3,SiO2 melts have been systematically examined. The effects of nitrogen content on viscosity for Y-Al-Si-O-N melts and on Vickers hardness of oxynitride glasses also have been examined. Although the viscosity of Y2O3,Al2O3,SiO2 melts was decreased, the solubility of nitrogen into the melts was increased with increased Y2O3 content. These results indicated that the yttrium ion behaved as a network modifier. Therefore, the structural units for viscous flow became small, and the amount of nonbridging oxygen increased in the melts when the Y2O3 content increased. The viscosity of Y-Al-Si-O-N melts and Vickers hardness of oxynitride glasses remarkably increased with increased nitrogen content. These results suggested that the substitution of nitrogen for oxygen in the melts may have led to a high average coordination of nonmetal atoms and that the increased cross-linking produced a more rigid glass network. [source] Micromechanical behaviour of gel grown pure and doped potassium hydrogen tartrate single crystalsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2009I. Quasim Abstract Micromechanical characteristics of (001) and (111) planes of gel grown pure, sodium- and lithium-doped potassium hydrogen tartrate single crystals as revealed by indentation induced technique are described. The indentation size effect (ISE) exhibited by the crystals is explained on application of proportional specimen resistance (PSR) model and the analytical law of Hays and Kendall. The load independent values of Vickers hardness of (001) and (111) planes of these crystals as indicated by indentation experiments and computed on the basis of PSR model and the analytical law are shown to be in good agreement. The doping by sodium or lithium results in the increase in hardness of potassium hydrogen tartrate crystals. The crystals exhibit hardness anisotropy. The values of yield strength of each plane of both pure and sodium and lithium doped potassium hydrogen tartrate single crystals are estimated using appropriate equations. [source] Changes in the mechanical properties of tooth-colored direct restorative materials in relation to timePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2003Gülbin Sayg Abstract The objective of this study was to determine the flexural strength, flexural modulus, Vickers hardness of a packable composite (Surefil), and an ormocer (Definite) in comparison with a microhybrid composite (Z-100), a microfil composite (Silux Plus) and a polyacid-modified composite resin (Dyract). Flexural strength and flexural modulus were determined using a three-point bending device. Microhardness was measured with a Vickers indentor. The specimens of each material were prepared according to manufacturer's instructions. The specimens were stored in artificial saliva at pH 6, all at 37°C. The groups were tested at the beginning of the test, at 3 months and at 6 months. Flexural strength values of Surefil and Definite showed a progressive increase. The highest MPa values were determined for Surefil (134.4,MPa) and the lowest MPa values were obtained for Dyract (59.6,MPa). The highest flexural modulus values were revealed for Surefil (10.000 GPa). Z-100, Silux Plus and Definite showed a tendency to decline in relation to time for their flexural modulus. GPa values of Silux Plus were stable at 3 and 6 months. Vickers hardness numbers showed that Surefil was the hardest and Dyract was the weakest material. Copyright © 2003 John Wiley & Sons, Ltd. [source] Comparative mechanical property characterization of three indirect composite resin materials compared with two direct compositesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2003Dr. Figen Demirel Abstract Various new indirect composite materials have been developed with required advantages. In this study three indirect composite material (Artglass, Belleglass HP, Targis) were tested for flexural strength, fracture toughness, wear resistance and hardness against Filtek P60 and Z-100. Five specimens of each material were fabricated according to the manufacturer's directions. The flexural strength and fracture toughness was measured using the bending test. The wear test was performed to accelerated wear in a toothbrushing apparatus. Vickers hardness was measured for each of the tested materials. The statistical tests used for flexural strength, fracture toughness, wear and hardness were One-way ANOVA and Kruskal,Wallis test. The level of statistical significance chosen was p,=,0.05. Results of the study showed that Filtek P60 was superior to the other composites in all tests. Significant differences were found among the materials. The differences in flexural strength, fracture toughnes, wear and hardness may have been due to differences in chemistry or method of polymerization of the composites. Copyright © 2003 John Wiley & Sons, Ltd. [source] Microstructures and Mechanical Properties of Hot-Pressed ZrB2 -Based Ceramics from Synthesized ZrB2 and ZrB2 -ZrC Powders,ADVANCED ENGINEERING MATERIALS, Issue 3 2009Wei-Ming Guo The influence of ZrC on the microstructure and mechanical properties of ZrB2 -SiC ceramics was investigated. SEM observation showed that the presence of ZrC greatly inhibited the grain growth of ZrB2 and SiC phases. With the introduction of ZrC, the Vickers' hardness, fracture toughness, and bending strength of the sintered ceramics increased significantly. [source] | ||||||||||