Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
W. Pabst
Ceramics-Silikáty , 2004,
Abstract: In this fourth paper of a series on the effective elastic properties of alumina-zirconia composite ceramics the influence of porosity on the effective tensile modulus of alumina and zirconia ceramics is discussed. The examples investigated are alumina and zirconia ceramics prepared from submicron powders by starch consolidation casting using two different types of starch, potato starch (median size D50 =47.2 μm) and corn starch (median size D50 =13.7 μm). The dependence of effective tensile moduli E, on the porosity f, measured for porosities in the ranges of approx. 19-55 vol.% and 10-42 vol.% for alumina and zirconia, respectively, using a resonant frequency technique, was evaluated by fitting with various model relations, including newly developed ones. A detailed comparison of the fitting results suggests the superiority of the new relation E/E0 = (1 - f)·(1 - f/fC), developed by the authors (with the tensile modulus of the dense ceramic material E0 and the critical porosity fC), over most other existing fit models. Only for special purposes and well-behaved data sets the recently proposed exponential relation E/E0 = exp [-Bf/(1 - f)] and the well-known Phani-Niyogi relation E/E0 = (1 - f/fC)N might be preferable.
Optimized Slurries for Spray Drying: Different Approaches to Obtain Homogeneous and Deformable Alumina-Zirconia Granules  [PDF]
Valentina Naglieri,Dan Gutknecht,Vincent Garnier,Paola Palmero,Jér?me Chevalier,Laura Montanaro
Materials , 2013, DOI: 10.3390/ma6115382
Abstract: Spray drying is widely used for producing granulated feed materials for compaction process, which is the current industrial method for manufacturing alumina-zirconia femoral heads. The optimization of the granules compaction behavior requires the control of the slurry rheology. Moreover, for a dual-phase ceramic suspension, the even phase distribution has to be kept through the atomization step. Here we present two approaches addressing the key issues involved in the atomization of a composite system. Alumina-10 vol % zirconia powders were prepared by either a powder mixing route, or by the surface modification of a commercial α-alumina powder with a zirconium salt. Slurries from both powders were spray dried. The correlation between slurry rheology and pH, granules morphology and sintered microstructures was here investigated and discussed on the ground of the two feed materials characteristics. The processing conditions were optimized to obtain dense and homogeneous alumina-zirconia micro-nano composites by both processing routes.
Fracture simulation for zirconia toughened alumina microstructure  [PDF]
Kyungmok Kim,Jean Geringer,Bernard Forest
Physics , 2013, DOI: 10.1108/EC-08-2013-0163
Abstract: Purpose - The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures. Design/methodology/approach - A two-dimensional finite element model is developed with an actual $Al{_2}O{_3}$ - 10 vol% $ZrO{_2}$ microstructure. A bilinear, time-independent cohesive zone law is implemented for describing fracture behaviour of grain boundaries. Simulation conditions are similar to those found at contact between a head and a cup of hip prosthesis. Residual stresses arisen from the mismatch of thermal coefficient between grains are determined. Then, effects of a micro-void and contact stress magnitude are investigated with models containing residual stresses. For the purpose of simulating fatigue behaviour, cyclic loadings are applied to the models. Findings - Results show that crack density is gradually increased with increasing magnitude of contact stress or number of fatigue cycles. It is also identified that a micro-void brings about the increase of crack density rate. Social implications - This paper is the first step for predicting the lifetime of ceramic implants. The social implications would appear in the next few years about health issues. Originality/value - This proposed finite element method allows describing fracture and fatigue behaviours of alumina-zirconia microstructures for hip prosthesis, provided that a microstructure image is available.
Wear behaviour of composite materials based on 2024 Al-alloy reinforced with δ alumina fibres  [PDF]
J.W. Kaczmar,K. Naplocha
Journal of Achievements in Materials and Manufacturing Engineering , 2010,
Abstract: Purpose: Wear improvement of aluminum matrix composite materials reinforced with alumina fibres, was investigated. The effects of the applied pressure and T6 heat treatment on wear resistance were determined.Design/methodology/approach: Wear tests were carried out on pin-on disc device at constant sliding velocity and under three pressures, which in relation to diameter of specimens corresponds to pressures of 0.8 MPa, 1.2 MPa and 1.5 MPa. To produce composite materials porous performs were prepared. They are characterized by the suitable permeability and good strength required to resist stresses arising during squeeze casting process. Performs exhibited semi-oriented arrangement of fibres and open porosity enabled producing of composite materials 10% (in vol.%) of Al2O3 fibres (Saffil).Findings: In comparison with T6 heat treated monolithic 2024 aluminium alloy composites revealed slightly better resistance under lower pressure. Probably, during wear process produced hard debris containing fragments of alumina fibres are transferred between surfaces and strongly abrade specimens. Under smaller pressures wear process proceeded slowly and mechanically mixed layer MML was formed.Research limitations/implications: Reinforcing of 2024 aluminium alloy could be inefficient for wear purposes. Remelting and casting of wrought alloy could deteriorate its properties. Interdendrite porosities and coarsening of grains even after squeeze casting process were observed.Practical implications: Aluminum casting alloys can be locally reinforced to improve hardness and wear resistance under small pressures.Originality/value: Investigations are valuable for persons, what are interested in aluminum cast composite materials reinforced with ceramic fibre performs.
Effect of 3 mol% Yttria Stabilized Zirconia Addition on Structural and Mechanical Properties of Alumina-Zirconia Composites  [PDF]
M. A. Gafur, Md. Saifur Rahman Sarker, Md. Zahangir Alam, M. R. Qadir
Materials Sciences and Applications (MSA) , 2017, DOI: 10.4236/msa.2017.87041
Abstract: Alumina-Zirconia (Al2O3-ZrO2) composites especially Zirconia Toughened Alumina (ZTA) shows better mechanical properties over alumina. Al2O3-ZrO2 composites were prepared by powder compaction method varying 3 mol% yttria stabilized zirconia (3Y-ZrO2) content from 0 to 20 vol% using small amount of MgO as sintering aid. The composites were sintered for two hours in air at 1580°C. At this temperature maximum density was achieved 99.31% of theoretical density for composite containing 20 vol% 3Y-ZrO2. Density measurement of sintered composites was carried out using Archimedes’s method. Hardness and fracture toughness measurement was carried out using Vickers indentation. Phase content and t-ZrO2 retention were detected by means of X-ray diffraction (XRD). Microstructure of the composites and grain size of alumina and zirconia was determined by Scanning Electron Microscopic (SEM) analysis. Maximum microhardness (17.46 GPa) was achieved for composite containing 5 vol% ZrO2 and maximum flexural strength (684.32 MPa) and fracture toughness (10.33 MPam0.5) was achieved for composite containing 20 vol% of 3Y-ZrO2. The aim of the present work is to investigate the optimum 3Y-ZrO2 content for obtaining maximum density, microhardness, flexural strength and fracture toughness of Al2O3-ZrO2 composites.
Tribological Behaviour of Aluminium/Alumina/Graphite Hybrid Metal Matrix Composite Using Taguchi’s Techniques  [PDF]
N. Radhika, R. Subramanian, S. Venkat Prasat
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2011, DOI: 10.4236/jmmce.2011.105032
Abstract: Tribological behaviour of aluminium alloy (Al-Si10Mg) reinforced with alumina (9%) and graphite (3%) fabricated by stir casting process was investigated. The wear and frictional properties of the hybrid metal matrix composites was studied by performing dry sliding wear test using a pin-on-disc wear tester. Experiments were conducted based on the plan of experiments generated through Taguchi’s technique. A L27 Orthogonal array was selected for analysis of the data. Investigation to find the influence of applied load, sliding speed and sliding distance on wear rate, as well as the coefficient of friction during wearing process was carried out using ANOVA and regression equations for each response were developed. Objective of the model was chosen as ‘smaller the better’ characteristics to analyse the dry sliding wear resistance. Results show that sliding distance has the highest influence followed by load and sliding speed. Finally, confirmation tests were carried out to verify the experimental results and Scanning Electron Microscopic studies were done on the wear surfaces.
Mechanical Behaviour Modelling of an Mg-Stabilized Zirconia Reinforced TRIP-Matrix-Composite under Cold Working Conditions  [PDF]
Sergey Guk, Wolfhart Müller, Katja Pranke, Rudolf Kawalla
Materials Sciences and Applications (MSA) , 2014, DOI: 10.4236/msa.2014.511081
Abstract: In the present work, a new method to predict the stress-strain curves for three-phase materials has been developed. It was applied using the example of an Mg-stabilized zirconia reinforced TRIP-matrix-composite. The content of the ceramic phase was varied between 5% and 20%, whereas the particle size of the ceramic was selected to be 30 to 50 μm. The method is a further development of mixture rule for multiphase materials with more than two microstructure components. The prediction results were compared with the original method of mixture rule and with the IsoE-method. It is shown that the new method significantly improves the convergence compared to the standard method for mixture rule, even though it does not reach the accuracy of IsoE-method. Furthermore, there is an improvement of predicted convergence for large values of the total stress. Finally, a working map was designed for a quick graphical definition of the objective functions.
The effect of nanometric zirconia particle additives on microstructure and mechanical properties of dense alumina
Lukasz Zych,Radoslaw Lach,Krzysztof Haberko,Pawel Rutkowski
Processing and Application of Ceramics , 2009,
Abstract: Zirconia additives have favourable influence on mechanical properties of dense alumina polycrystals. It results from the martensitic transformation of tetragonal zirconia particles into monoclinic symmetry at the crack tip propagating through a material. Usually applied zirconia particles were of sub-micrometer or micrometer sizes. In the present work nanometric zirconia particles prepared by hydrothermal crystallization technique were introduced into the alumina matrix. Both, zirconia and alumina powders were homogenized in an aqueous suspension of pH selected on the basis of the zeta (ξ) potential measurements. It was found that this factor influences greatly strength of the resulting powder agglomerates and hence mechanical properties of the sintered material.
Fracture toughness of advanced alumina ceramics and alumina matrix composites used for cutting tool edges  [PDF]
M. Szutkowska
Journal of Achievements in Materials and Manufacturing Engineering , 2012,
Abstract: Purpose: Specific characteristics in fracture toughness measurements of advanced alumina ceramics and alumina matrix composites with particular reference to α-Al2O3, Al2O3-ZrO2, Al2O3-ZrO2-TiC and Al2O3-Ti(C,N) has been presented.Design/methodology/approach: The present study reports fracture toughness obtained by means of the conventional method and direct measurements of the Vickers crack length (DCM method) of selected tool ceramics based on alumina: pure alumina, alumina-zirconia composite with unstabilized and stabilized zirconia, alumina–zirconia composite with addition of TiC and alumina–nitride-carbide titanium composite with 2wt% of zirconia. Specimens were prepared from submicro-scale trade powders. Vicker’s hardness (HV1), fracture toughness (KIC) at room temperature, the indentation fracture toughness, Young’s modulus and apparent density were also evaluated. The microstructure was observed by means of scanning electron microscopy (SEM).Findings: The lowest value of KIC is revealed by pure alumina ceramics. The addition of (10 wt%) unstabilized zirconia to alumina or a small amount (5 wt%) of TiC to alumina–zirconia composite improve fracture toughness of these ceramics in comparison to alumina ceramics. Alumina ceramics and alumina-zirconia ceramics reveal the pronounced character of R-curve because of an increasing dependence on crack growth resistance with crack extension as opposed to the titanium carbide-nitride reinforced composite based on alumina. R-curve has not been observed for this composite.Practical implications: The results show the method of fracture toughness improvement of alumina tool ceramics.Originality/value: Taking into account the values of fracture toughness a rational use of existing ceramic tools should be expected.
Processing and Characterization of Yttria-Stabilized Zirconia Foams for High-Temperature Applications  [PDF]
Ana María Herrera,Amir Ant?nio Martins de Oliveira Jr.,Antonio Pedro Novaes de Oliveira,Dachamir Hotza
Journal of Ceramics , 2013, DOI: 10.1155/2013/785210
Abstract: In this work ceramic foams of 3 and 8 mol% yttria-stabilized zirconia (3YSZ and 8YSZ) were manufactured by the replication method using polystyrene-polyurethane foams with pore sizes in the 7–10 ppi range. A second coating was carried out on presintered foams in order to thicken struts and hinder microstructural defects. The produced ceramic foams were structurally and thermomechanically characterized. Samples recoated with 3YSZ presented the highest relative densities ( ) which contributed to a better mechanical and thermal behavior. 1. Introduction Porous radiant burners are devices used in applications benefit from radiant thermal heating. Numerous industries employ this technology for firing and drying, lower pollutant emission, and better product quality reached with these burners [1, 2]. Other functional advantages are a higher flame velocity within the porous structure when compared to a laminar free flame (due to the preheated of reagents), higher turn-down ration, higher efficiency in heat transfer by radiation, and the possibility of burning low calorific value fuels or very lean mixtures [3]. Ceramics foams for porous radiant burners are mainly produced by the replication method from polymeric templates. The method consists in the impregnation of a polymeric sponge with a ceramic slurry followed by a heat treatment which leads to the burning out of the organic body (sponge) and to the sintering of the ceramic skeleton [4]. Along the manufacture process, there are key parameters that must be taken into account to ensure the final product effectiveness. Among them, the most important are the linear expansion coefficient, maximum working temperature and thermal shock resistance of the ceramic material, thixotropy and pseudoplasticity of the ceramic slurry, and, finally, the heating rate of the thermal treatment. According to the above, the most reliable ceramic materials to work with are cordierite, mullite, silicon carbide, alumina, partially stabilized zirconia (YSZ), and some composite systems [5–13]. Cellular ceramics are already commercially available for a wide range of technological applications including filters, membranes, catalytic substrates, thermal insulation, gas burner media, refractory materials, and lightweight structural panels [5–7]. In these cases, reticulated porous ceramics are used because of their functional properties, such as low thermal expansion coefficient and thermal conductivity, high permeability, and chemical inertness [7]. Considering the particularities associated with each specific application, reticulated
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.