Characteristics of Machining Damage and Their Influence on Strength in Alumina Ceramics System

2006 ◽  
Vol 317-318 ◽  
pp. 285-288 ◽  
Author(s):  
Satoshi Tanaka ◽  
Kazuyoshi Sato ◽  
S. Yonetani ◽  
Tsuyoshi Nakamura ◽  
Keizo Uematsu
Keyword(s):  
Grain Size ◽  
Laser Fluorescence ◽  
Machining Process ◽  
Stored Energy ◽  
Alumina Ceramics ◽  
Pressing Method ◽  
Grain Sizes ◽  
Dry Pressing ◽  
Confocal Scanning Laser ◽  
Machining Damage

Machining damage and its influence on strength was examined for alumina ceramics with various grain sizes, which were prepared by dry-pressing method with spray-dried granules, followed by sintering at 1350-1550°C for 2-27 hours. Grain sizes of the sintered bodies were 1-6μm. After machining at the same grinding force, specimens were placed in an alcohol solution of fluorescent dye and dried. The fracture strength was measured by 4 point bending. The machining flaws in the specimens were observed with a confocal scanning laser fluorescence microscope. Machining flaws appeared continuous, wide and deep in the specimen with small grain size, and discontinuous with large size. On ground surfaces, intra-grain fracture appeared on the surface, whereas inter-grain fracture dominates. The continuous, wide and deep flaws were attributed to the dissipation of stored energy associated with the cracks propagation. The result suggested that the stored energy on the machining process increased with decreasing grain size. The strength of the specimen with 1 μm grain size reduced from 500MPa to 250 MPa with machining damage. The strength depended remarkably on the depth of the machining damage.

Retention of the ‹001› Fiber Texture for Fe-Si Electric Motor Steels

2007 ◽  
Vol 550 ◽  
pp. 497-502 ◽  
Author(s):  
Roger D. Doherty ◽  
D. Stojakovic ◽  
Fernando José Gomes Landgraf ◽  
Surya R. Kalidindi
Keyword(s):  
Grain Size ◽  
Finite Element ◽  
Electric Motor ◽  
Rolling Plane ◽  
Fiber Texture ◽  
Taylor Factor ◽  
Stored Energy ◽  
Grain Sizes ◽  
Recrystallized Grain Size ◽  
The Ideal

The ideal sheet texture for electric motor steels, the λ fiber, with 〈001〉 normal to the rolling plane, that can be produced by directional solidification, is largely lost by the required heavy rolling reduction and recrystallization needed to produce thin motor laminations. However by two successive light rolling reductions, followed in each case by recrystallization, the desired texture was largely recovered. Taylor and finite element modeling supported the hypothesis for this successful processing: the low Taylor factor of the λ fiber grains. Although starting from similar grain sizes, the second light deformation produced a much larger recrystallized grain size than did the first light deformation. This result suggests that a lower average Taylor factor in the structure before deformation, resulting in lower stored energy, can increase the recrystallized grain size.

scholarly journals Investigation of Movement of Nourishment Sand of Different Grain Sizes Using Model for Predicting Bathymetric and Grain Size Changes

2009 ◽  
Vol 65 (1) ◽  
pp. 691-695
Author(s):  
Yasuhito NOSHI ◽  
Akio KOBAYASHI ◽  
Takaaki UDA ◽  
Masumi SERIZAWA ◽  
Takayuki KUMADA
Keyword(s):  
Grain Size ◽  
Grain Sizes

The Method of Eliminating Banded Structure and the Effects of Banded Structure on the Transverse Properties in 20G Steel

2013 ◽  
Vol 347-350 ◽  
pp. 1171-1175 ◽  
Author(s):  
Bin Wang ◽  
Hong Mei Hu ◽  
Cui Zhou
Keyword(s):  
Heat Treatment ◽  
Grain Size ◽  
Stress Concentration ◽  
Base Metal ◽  
Metallic Inclusion ◽  
Banded Structure ◽  
Grain Sizes ◽  
Fine Grain ◽  
Treatment Processes ◽  
Metallic Inclusions

The transverse properties were inferior to the longitudinal properties for the existence of banded structure in 20G steel. In order to eliminate the banded structure and improve the transverse performance of 20G steel, different heat treatment processes were adopted. The results showed that conventional normalizing could reduce the banded structure and refine the grain sizes. When 20G was heated with 10°C/min heating rated and then held at 920°C for 2h, the banded structure in the steel was almost eliminated and the microstructure was homogeneous with fine grain size, the strength increased by 14%. The non-metallic inclusion and carbide in the microstructure leaded to stress concentration and separation with the base metal. To some extent, heat treatment can improve the distribution and form of non-metallic inclusions.

Machining and Wear of High-Alumina Ceramics for Structural Applications

2009 ◽  
Vol 409 ◽  
pp. 137-144 ◽  
Author(s):  
Stojana Veskovic-Bukudur ◽  
Tanja Leban ◽  
Milan Ambrozic ◽  
Tomaž Kosmač
Keyword(s):  
Grain Size ◽  
Wear Rate ◽  
Abrasive Wear ◽  
Direct Relationship ◽  
Bending Strength ◽  
High Alumina ◽  
Alumina Ceramics ◽  
Large Area ◽  
Structural Applications ◽  
Worn Surfaces

The wear resistances of four standard-grade high-alumina ceramics were evaluated and related to their machining ability. Three of the material grades contained 96% of alumina and 4% of either calcium silicate, or magnesium silicate, or manganese titanate in the starting-powder composition. The nominal alumina content in the fourth material was 99.7%. The specimens were fabricated using a low-pressure injection-molding forming technique, followed by thermal de-binding and sintering. After sintering the four materials differ significantly in their grain size, bending strength and Vickers hardness. No direct relationship between the microstructural parameters and the mechanical properties was found, but there was a grain-size dependence of the surface finish after grinding under industrial conditions. The two silicate-containing ceramics exhibited considerably higher wear resistances than the two silicate-free ceramics, but no direct relationship between the abrasive wear rate during grinding and the cutting time was observed. The cutting ability represents a valuable material characteristic for industrial practice, but it should not be directly used for predicting the wear rate during grinding. Quantitative differences in the cutting time and abrasive wear rate were manifested in the different topographies of the worn surfaces. Cutting resulted in relatively large area fractions of plastically deformed surfaces, whereas pullouts dominated the worn surfaces after grinding.

Reactive Milling and Mechanical Alloying in Electroceramics

2010 ◽  
Vol 63 ◽  
pp. 420-424
Author(s):  
Riva Rivas-Marquez ◽  
Carlos Gomez-Yanez ◽  
Ivan Velasco-Davalos ◽  
Jesus Cruz-Rivera
Keyword(s):  
Grain Size ◽  
Mechanical Activation ◽  
Raw Materials ◽  
Planetary Mill ◽  
Fabrication Technique ◽  
Nonlinearity Coefficient ◽  
Grain Sizes ◽  
Zno Varistor ◽  
Reactive Milling ◽  
Good Homogeneity

Using Mechanical Activation it is possible to obtain small grain size and good homogeneity in a ceramic piece. For ZnO varistor devices Mechanical Activation appears to be a good fabrication technique, since good homogeneity and small grain sizes are advantageous microstructural features. The typical formulation is composed by ZnO, Bi2O3, Sb2O3, CoO, MnO2 and Cr2O3 as raw materials, and during sintering, several dissolutions and reactions to form pyrochlore and spinel phases occur. When Mechanical Activation is applied to the entire formulation, it is difficult to know what processes are being mechanically activated due to the complexity of the system. The aim of the present work was to clarify how the mechanical activation is taking place in a typical ZnO varistor formulation. The methodology consisted in the formation of all possible combinations of two out of the five oxides above mentioned and to apply mechanical activation on the mixture of each pair of powders. The results showed that systems containing Bi2O3 are prone to react during mechanical activation. Also, reduction reactions were observed in MnO2. In addition, the powder mixture corresponding to the whole formulation was milled in a planetary mill, pressed and sintered, and varistor devices were fabricated. Improvement in the nonlinearity coefficient and breakdown voltage was observed.

The Processing of Ultrafine-Grained Materials Using High-Pressure Torsion

2007 ◽  
Vol 558-559 ◽  
pp. 1283-1294 ◽  
Author(s):  
Cheng Xu ◽  
Z. Horita ◽  
Terence G. Langdon
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
High Pressure ◽  
High Pressure Torsion ◽  
Metallic Materials ◽  
Grain Sizes ◽  
Ultrafine Grained ◽  
Wide Range ◽  
Ultrafine Grained Materials ◽  
Thin Disks

It is now well-established that processing through the application of severe plastic deformation (SPD) leads to a significant reduction in the grain size of a wide range of metallic materials. This paper examines the fabrication of ultrafine-grained materials using high-pressure torsion (HPT) where this process is attractive because it leads to exceptional grain refinement with grain sizes that often lie in the nanometer or submicrometer ranges. Two aspects of HPT are examined. First, processing by HPT is usually confined to samples in the form of very thin disks but recent experiments demonstrate the potential for extending HPT also to bulk samples. Second, since the strains imposed in HPT vary with the distance from the center of the disk, it is important to examine the development of inhomogeneities in disk samples processed by HPT.

Preparation of barium titanate ceramics from amorphous fine particles of the Ba–Ti–O system and its dielectric properties

1995 ◽  
Vol 10 (2) ◽  
pp. 306-311 ◽  
Author(s):  
S. Wada ◽  
T. Suzuki ◽  
T. Noma
Keyword(s):  
Dielectric Properties ◽  
Barium Titanate ◽  
Curie Temperature ◽  
Decomposition Method ◽  
Fine Particles ◽  
Nitrate Solution ◽  
Pressing Method ◽  
Calcination Temperatures ◽  
Grain Sizes ◽  
Titanate Ceramics

Using titanium nitrate solution stabilized by chelation, amorphous fine particles of the Ba-Ti-O system were prepared by the mist decomposition method in air. After calcination of these particles, barium titanate ceramics were prepared using the hot uniaxial pressing method, and various properties were investigated. As a result, the grain sizes could be controlled over the range from 58 nm to 187 nm by the sintering temperatures and/or the calcination temperatures, keeping the density almost constant. Moreover, the dielectric properties of the samples showed that the relative permittivity decreased with decreasing grain size, and Curie temperature also shifted to lower temperatures in the same way. In this study, we first found that Curie temperature existed in the barium titanate ceramics with grain sizes from 58 to 147 nm.

Ionic conductivity in nanocrystalline Gd doped ceria

2008 ◽  
Vol 1122 ◽  
Author(s):  
Gianguido Baldinozzi ◽  
David Simeone ◽  
Dominique Gosset ◽  
Mickael Dollé ◽  
Georgette Petot-Ervas
Keyword(s):  
Grain Size ◽  
Ionic Conductivity ◽  
Sol Gel ◽  
Doped Ceria ◽  
Narrow Size Distribution ◽  
Conductivity Measurements ◽  
X Ray Diffraction ◽  
X Ray ◽  
Grain Sizes ◽  
The Impact

AbstractWe have synthesized Gd-doped ceria polycrystalline samples (5, 10, 15 %mol), having relative densities exceeding 95% and grain sizes between 30 and 160 nm after axial hot pressing (750 °C, 250 MPa). The samples were prepared by sintering nanopowders obtained by sol-gel chemistry methods having a very narrow size distribution centered at about 16 nm. SEM and X-ray diffraction were performed to characterize the sample microstructures and to assess their structures. We report ionic conductivity measurements using impedance spectroscopy. It is important to investigate the properties of these systems with sub-micrometric grains and as a function of their composition. Therefore, samples having micrometric and nanometric grain sizes (and different Gd content) were studied. Evidence of Gd segregation near the grain boundaries is given and the impact on the ionic conductivity, as a function of the grain size and Gd composition, is discussed and compared to microcrystalline samples.

scholarly journals Nautilus multi-grain model: Importance of cosmic-ray-induced desorption in determining the chemical abundances in the ISM

2018 ◽  
Vol 615 ◽  
pp. A20 ◽  
Author(s):  
Wasim Iqbal ◽  
Valentine Wakelam
Keyword(s):  
Grain Size ◽  
Surface Temperature ◽  
Gas Phase ◽  
Numerical Models ◽  
Cosmic Ray ◽  
Grain Sizes ◽  
Small Grains ◽  
Grain Model ◽  
Grain Surface ◽  
The Impact

Context. Species abundances in the interstellar medium (ISM) strongly depend on the chemistry occurring at the surfaces of the dust grains. To describe the complexity of the chemistry, various numerical models have been constructed. In most of these models, the grains are described by a single size of 0.1 μm. Aims. We study the impact on the abundances of many species observed in the cold cores by considering several grain sizes in the Nautilus multi-grain model. Methods. We used grain sizes with radii in the range of 0.005 μm to 0.25 μm. We sampled this range in many bins. We used the previously published, MRN and WD grain size distributions to calculate the number density of grains in each bin. Other parameters such as the grain surface temperature or the cosmic-ray-induced desorption rates also vary with grain sizes. Results. We present the abundances of various molecules in the gas phase and also on the dust surface at different time intervals during the simulation. We present a comparative study of results obtained using the single grain and the multi-grain models. We also compare our results with the observed abundances in TMC-1 and L134N clouds. Conclusions. We show that the grain size, the grain size dependent surface temperature and the peak surface temperature induced by cosmic ray collisions, play key roles in determining the ice and the gas phase abundances of various molecules. We also show that the differences between the MRN and the WD models are crucial for better fitting the observed abundances in different regions in the ISM. We show that the small grains play a very important role in the enrichment of the gas phase with the species which are mainly formed on the grain surface, as non-thermal desorption induced by collisions of cosmic ray particles is very efficient on the small grains.

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