scholarly journals The Effect of the Addition of Y2O3 on the Microstructure of Polycrystalline Alumina Ceramics

Proceedings ◽  
2018 ◽  
Vol 2 (23) ◽  
pp. 1407
Author(s):  
Serkan Abalı ◽  
Cem Uğur Karaçam
Keyword(s):  
Bending Strength ◽  
Xrd Analysis ◽  
Milling Process ◽  
Alumina Ceramics ◽  
Mechanical Behaviors ◽  
Cold Isostatic Press ◽  
Powder Mixtures ◽  
Polycrystalline Alumina ◽  
Microscope Images ◽  
Pure Al2o3

In the scope of this study, a powder mixture was prepared that contained 3 Al2O3-Y2O3 consisting of 99.99% pure Al2O3 and aluminum oxide of 65–67% and 70% by weight of 99.999% pure Y2O3 powders. After the powders were weighed on a precision scale, the milling process was carried out in a vibratory disc mill. For the granulation, 3 powder mixtures that were subject to sintering were sieved to a size of less than 106 µm in a powder sieve shaker. The powders were shaped with a cold isostatic press after this step and the 3 acquired samples were sintered for 12 h under a temperature of 1923 K. Selected physical and mechanical behaviors were taken by evaluating microhardness measurements, bending strength XRD analysis and electron microscope images of the 3 sintered samples. The changes in the Y2O3 additive and phase composition, microstructure, and mechanic properties were examined.

scholarly journals Sintering of alumina ceramics reinforced with a bioactive glass of 3CaO.P2O5-SiO2-MgO system

Cerâmica ◽  
2015 ◽  
Vol 61 (358) ◽  
pp. 160-167 ◽  
Author(s):  
A. W. Huang ◽  
C. Santos ◽  
R. O. Magnago ◽  
R. F. F. Silva ◽  
K. Strecker ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Relative Density ◽  
Transient Liquid Phase ◽  
Xrd Analysis ◽  
Alumina Ceramics ◽  
Crystalline Phases ◽  
Powder Mixtures ◽  
Solid State Sintering ◽  
Sintering Condition

<p>Alumina-based ceramics, Al<sub>2</sub>O<sub>3</sub>, exhibit a combination of properties which favor its use as biomaterial, specifically as structural dental prosthesis. Its most important properties as biomaterial are its elevated hardness, chemical stability and biocompatibility. Usually, Al<sub>2</sub>O<sub>3</sub> is processed by solid-state sintering at a temperature of about 1600 <sup>o</sup>C, but it is very difficult to eliminate the porosity due to its diffusional characteristics. The objective of this work was the development and characterization of sintered Al<sub>2</sub>O<sub>3</sub> ceramics, densified with a transient liquid phase formed by a bioactive 3CaO.P<sub>2</sub>O<sub>5</sub>-SiO<sub>2</sub>-MgO glass. Powder mixtures of 90 wt.% Al<sub>2</sub>O<sub>3</sub> and 10 wt.% bioglass were milled, compacted and sintered at 1200 <sup>o</sup>C to 1450 <sup>o</sup>C. Comparatively, monolithic Al<sub>2</sub>O<sub>3</sub> samples were sintered at 1600 <sup>o</sup>C/120 min. The sintered specimens were characterized by relative density, crystalline phases, microstructure and mechanical properties. The results indicate that the specimen sintered at 1450 <sup>o</sup>C/120 min present the best properties. Under this sintering condition, a relative density of 95% was reached, besides hardness higher than 9 GPa and fracture toughness of 6.2 MPa.m<sup>1/2</sup>. XRD analysis indicate alumina (αAl<sub>2</sub>O<sub>3</sub>), whitlockite (3CaO.P<sub>2</sub>O<sub>5</sub>) and diopsite [3(Ca,Mg)O.P<sub>2</sub>O<sub>5</sub>], as crystalline phases. Comparatively, monolithic sintered Al<sub>2</sub>O<sub>3</sub> samples presented 92% of relative density with 17.4 GPa and 3.8 MPa.m<sup>1/2</sup> of hardness and fracture toughness respectively.</p>

Pressureless Sintering of MoSi2 Materials

1994 ◽  
Vol 364 ◽  
Author(s):  
Roland Scholl ◽  
Thomas JÜngling ◽  
Bernd Kieback
Keyword(s):  
Phase Formation ◽  
Single Phase ◽  
Bending Strength ◽  
Milling Process ◽  
Full Density ◽  
Pressureless Sintering ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Powder Mixtures ◽  
Molybdenum Silicides

AbstractVarious powder mixtures were prepared by a modified mechanical alloying technique. Starting from elemental Mo-, Si- and C-powders the influence of milling conditions on phase formation during the milling process and the subsequent heat treatment was investigated. Phase formation during sintering and sintering kinetics of activated starting mixtures were studied by differential scanning calorimetry (DSC), thermal graphimetry (TG), X-ray diffraction (XRD) and dilatometry. The results show that phase formation during milling or sintering strongly depends on milling conditions. Optimized powder mixtures of single phase and reinforced molybdenum silicides show high densities up to 98,5 % TD by pressureless sintering in various atmospheres. Full density is possible by post-HIP because the samples show only closed porosity. The microstructure was studied in dependence of sintering parameters. The level of impurities, i.e. C, O2 was determined. Hardness, fracture toughness and bending strength were measured for single phase and particle reinforced materials.

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.

Synthesis of Al2O3/AlB12/Al Composite Ceramic Powders by Pulsed Nd:YAG Laser Igniting Method and a Study of their Mechanical Properties

2010 ◽  
Vol 26-28 ◽  
pp. 919-924
Author(s):  
Kai Jin Huang
Keyword(s):  
Fracture Toughness ◽  
Reaction Mechanism ◽  
Nd:Yag Laser ◽  
Bending Strength ◽  
Composite Ceramic ◽  
Composite Ceramics ◽  
Ceramic Powders ◽  
Pulsed Nd:Yag Laser ◽  
Al Composite ◽  
Pure Al2o3

Based on the combined toughening principle, pure Al2O3/AlB12/Al composite ceramic powders have been synthesized using pulsed Nd:YAG laser igniting method. This method starts from Al and B2O3 powder mixtures, after which Al2O3/AlB12/AlN composite ceramics were fabricated by hot-press sintering at 1600°C for 2h under the protection of a N2 atmosphere. XRD and SEM techniques were used to characterize the phases and morphologies of the powders and the ceramics. The bending strength and the fracture toughness of the ceramics were measured by the three-point bending method and the indentation fracture method, respectively. The results show that the pure Al2O3/AlB12/Al composite ceramic powders can be successfully synthesized by pulsed Nd:YAG laser igniting method because the adiabatic temperature of Al-B2O3 system is more than 1800K. Al2O3 and AlB12 phases were formed by the liquid-liquid reaction mechanism and the liquid-solid reaction mechanism, respectively. The bending strength and the fracture toughness of the Al2O3/AlB12/AlN composite ceramics were 525.86MPa and 5.68MPa.m1/2, respectively. These values are 50.25% and 42% greater than those of the pure Al2O3 ceramic (350MPa and 4MPa.m1/2) due to the reinforcing and toughening in-situ formation of small AlN particles.

scholarly journals Effects of Mechanical Ball Milling Time on the Microstructure and Mechanical Properties of Mo2NiB2-Ni Cermets

Materials ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 1926 ◽  
Author(s):  
Lei Zhang ◽  
Zhifu Huang ◽  
Yangzhen Liu ◽  
Yupeng Shen ◽  
Kemin Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Ball Milling ◽  
Milling Time ◽  
Bending Strength ◽  
Volume Fraction ◽  
Milling Process ◽  
Microstructure And Mechanical Properties ◽  
Mechanical Ball Milling ◽  
Ball Milling Time ◽  
Milled Powders

Mo2NiB2-Ni cermets have been extensively investigated due to their outstanding properties. However, studies have not systematically examined the effect of the powder milling process on the cermets. In this study, Mo, Ni, and B raw powders were subjected to mechanical ball milling from 1 h to 15 h. XRD patterns of the milled powders confirmed that a new phase was not observed at milling times of 1 h to 15 h. With the increase in the mechanical ball milling time from 1 h to 11 h, raw powders were crushed to small fragments, in addition to a more uniform distribution, and with the increase in the mechanical ball milling time to greater than 11 h, milled powders changed slightly. Mo2NiB2-Ni cermets were fabricated by reaction boronizing sintering using the milled powders at different ball milling times. The milling time significantly affected the microstructure and mechanical properties of Mo2NiB2-Ni cermets. Moreover, the Mo2NiB2 cermet powder subjected to a milling time of 11 h exhibited the finest crystal size and the maximum volume fraction of the Mo2NiB2 hard phase. Furthermore, the cermets with a milling time of 11 h exhibited a maximum hardness and bending strength of 87.6 HRA and 1367.3 MPa, respectively.

Scanning acoustic microscopy of partly embedded cracks in polycrystalline alumina

1986 ◽  
Vol 320 (1554) ◽  
pp. 237-241 ◽  
Keyword(s):  
Optical Microscope ◽  
Acoustic Microscopy ◽  
Polished Surface ◽  
Scanning Acoustic Microscopy ◽  
Optimum Conditions ◽  
Frame Size ◽  
Polycrystalline Alumina ◽  
Microscope Images ◽  
Optical Micrographs ◽  
Scanning Electron

Reflection scanning acoustic microscopy (SAM) at 1 GHz has been used to examine artificially induced cracks in alumina samples. The results are compared with the corresponding optical micrographs and scanning electron microscope images. For a sample with a 0.08 μm centre-line average (CLA) surface finish, the SAM working with a 400 μm frame size, showed that a crack that appeared to be about 150 μm in length in the corresponding optical image was, in fact, at least 200 μm in length. For a sample with a good engineering finish of 0.15 μm CLA, the SAM was able to reveal crack detail to a degree comparable with that revealed by an optical microscope working under optimum conditions. On a sample with a highly polished surface it was possible to distinguish between cracks and grain boundaries by using the V (z) response of the SAM, in agreement with theory.

Microstructure-Property Relationships in Sintered Alumina Ceramics

2006 ◽  
Vol 45 ◽  
pp. 564-571
Author(s):  
Dušan Galusek
Keyword(s):  
Grain Size ◽  
Stress State ◽  
Liquid Phase ◽  
Processing Conditions ◽  
Microstructure Development ◽  
Alumina Ceramics ◽  
Polycrystalline Alumina ◽  
Glass Forming ◽  
Ultrafine Grained ◽  
Ultrafine Grained Materials

The paper gives a brief overview of polycrystalline alumina ceramics, including the solid-state sintered and ultrafine grained materials, and the liquid phase sintered aluminas. The influence of glass-forming sintering additives of commercial interest (MgO, CaO, SiO2) and processing conditions on microstructure development of polycrystalline alumina ceramics are discussed in more detail. The influence of grain size, the presence and composition of grain boundary glass, and of secondary crystalline phases in partially crystallized triple pockets on stress state in alumina is discussed.

Valorization of Mill Scale Waste by its Incorporation in Fired Clay Bricks

2014 ◽  
Vol 608 ◽  
pp. 8-13 ◽  
Author(s):  
X. Spiliotis ◽  
K. Ntampegliotis ◽  
D. Kasiteropoulou ◽  
S. Lamprakopoulos ◽  
K. Lolos ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Steel Industry ◽  
Bending Strength ◽  
Mechanical Performance ◽  
Milling Process ◽  
Mineral Admixture ◽  
Mill Scale ◽  
Clay Bricks ◽  
Different Temperatures ◽  
Sintering Processes

The mill scale (MS) waste is produced in steel industry during the milling process from the rapid oxidization of the hot iron products, and is mainly consisted of iron oxides (>95%). The aim of this work is to evaluate the utilization of MS (known in Greece as “kalamina”) as an admixture in clay bricks manufacturing by applying extrusion and sintering processes. For that purpose, specimens were formed from various clay/MS mixtures (up to 9 wt% MS) and then fired at different temperatures (up to 1100°C). Shrinkage and weight loss upon firing as well as density, porosity, bending strength and thermal conductivity of sintered specimens were determined and studied as a function of the % MS content and the firing temperature for optimization. The experimental results show that the incorporation of MS in clay bricks production is feasible, as an efficient secondary resource, thus turning waste from one industry into useful feedstock for another one. Specifically, the mechanical performance and thermal conductivity are not significantly affected with increasing the mineral admixture percentage and the sintering temperature.

Quantitative XRD analysis of zirconia-toughened alumina ceramics

1987 ◽  
Vol 22 (10) ◽  
pp. 3566-3570 ◽  
Author(s):  
R. Fillit ◽  
R. P. Homerin ◽  
R. J. Schafer ◽  
R. H. Bruyas ◽  
R. F. Thevenot
Keyword(s):  
Xrd Analysis ◽  
Alumina Ceramics ◽  
Zirconia Toughened Alumina

Fabrication of Electrically Conductive Si3N4 Ceramics by Dispersion of Carbon Nanotubes

2008 ◽  
Vol 403 ◽  
pp. 19-22 ◽  
Author(s):  
Sara Yoshio ◽  
Junichi Tatami ◽  
Toru Wakihara ◽  
Katsutoshi Komeya ◽  
Takeshi Meguro
Keyword(s):  
Carbon Nanotubes ◽  
Electrical Conductivity ◽  
Aspect Ratio ◽  
Xrd Analysis ◽  
Milling Process ◽  
Electrically Conductive ◽  
Sintering Aid ◽  
Lower Temperature ◽  
Different Characteristics ◽  
Si3n4 Ceramics

Electrically conductive Si3N4 ceramics were fabricated by dispersion of different characteristics of carbon nanotubes (CNTs). When the sintering aid of Y2O3-Al2O3-TiO2-AlN was used for lower temperature densification, it was confirmed that CNTs existed in Si3N4 ceramics from SEM observation and SiC was not identified in XRD analysis, which means that CNTs did not react with Si3N4. Relative density and electrical conductivity of the CNT dispersed Si3N4 ceramics depended on the characteristics of CNTs. Aggregation of CNTs, which is outstanding in much thinner CNTs, should limit densification of Si3N4. CNTs were well-dispersed by beads milling in ethanol. As a result, beads milling process was confirmed to be effective in unraveling and dispersing CNTs. It was shown that better dispersion of CNTs with higher aspect ratio resulted in higher density and electrical conductivity.

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