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L0102 - Increasing elastic modulus, strength and CTE of AZ91 by reinforcing pure magnesium with elemental copper
Heat-treatable AZ91 and 3.9 vol.% copper particulate reinforced magnesium composite was synthesized using an innovative disintegrated melt deposition (DMD) technique followed by hot extrusion. Microstructural characterization of the composite material revealed retention and uniform distribution of reinforcement with defect free interface with the matrix. Physical properties characterization revealed improved dimensional stability of composite when compared to AZ91. Mechanical properties characterization revealed an increase in average values of modulus, 0.2% yield strength and ultimate tensile strength of un-heat-treated composite when compared to T6 heat-treated AZ91 while the ductility was adversely affected. An attempt is made in the present study to compare the microstructural, physical and mechanical properties of Mg/Cup composite with that of the commercially used AZ91 alloy.
S.F. Hassan, K.F. Ho, M. Gupta, Materials Letters 58 (2004) 2143-2146
L0101 - Mullite phase formation in oxide mixtures in the presence of Y2O3, La2O3 and CeO2
The effect of oxides (Y2O3, La2O3, and CeO2), on phase formation of mullite, reaction sequence and microstructure evolution, in the mixtures of Al2O3 and SiO2, has been investigated. All three dopants showed a positive effect on the mullitization behavior, lowering the mullite formation temperature by about 100°C. The improved mullitization behavior was attributed to the formation of the low-viscosity liquid phase due to the addition of dopants. The reaction sequence was different in the three doping cases. Two types of yttrium silicate were found in the samples doped with Y2O3, with one being favored at low temperature and another at high temperature. No reaction was observed between CeO2 and Al2O3 or SiO2, while La2O3 was not detected by the X-ray diffraction (XRD) measurement for all doping levels. The samples with La2O3 had the best densification behavior among the three doping cases, while the effect of CeO2 on densification was slightly better than that of Y2O3. The difference in the effects of the three oxides on the mullitization and densification behavior of the doped samples implied the difference in the characteristics of the low-viscosity glass phases formed at high temperatures.
L.B. Kong, T.S. Zhang, J. Ma, F. Boey, R.F. Zhang, Journal of Alloys and Compounds 372 (2004) 290-299
L0100 - Structure, nonstoichiometry and magnetic properties of the perovskites Sr(1-x)CaxMnO(3-d)
The structural, thermal and magnetic properties of the perovskite-type alkaline-earth manganites of the series Sr(1-x)CaxMnO(3-d) (0 < x < 1) were investigated. SrMnO(3-d) forms a hexagonal perovskite lattice and shows a first-order transformation to a highly defective cubic high-temperature modification. By substituting Ca for Sr (x > 0.25) the hexagonal perovskite is suppressed and a cubic (or orthorhombic) lattice becomes stabilized for all temperatures. For x = 0.5 and 0.75 cubic perovskites with a large nonstoichiometry (e.g., d = 0.25 for x = 0.5) are obtained at 1400°C. The defective perovskites are prepared by either quenching from high temperature or by cooling in an inert atmosphere. The oxygen vacancies are easily filled by subsequent reoxidation at low temperature (400-600°C) and stoichiometric samples are obtained. Orthorhombic perovskites are formed at T < 1200°C with the nonstoichiometry d increasing with increasing temperature (e.g., d = 0.06 at 1000°C and d = 0.14 at 1200°C for x = 0.5). Slow cooling in air results in almost complete reoxidation (d = 0). CaMnO(3-d) is an orthorhombic perovskite with a large range of nonstoichiometry (0 < d < 0.30). The cubic to hexagonal phase transformation of the Sr-rich samples is accompanied by a large expansion of the lattice that is reduced by Ca substitution. The Ca/Sr-manganites are antiferromagnets with TN of 170 K for x = 0.5 and d = 0.02 and 120 K for x = 1 and d = 0.05.
J. Töpfer, U. Pippardt, I. Voigt, R. Kriegel, Solid State Sciences 6 (2004) 647-654
L0099 - Ductility improvement of Ni-added molybdenum compacts through the addition of Cu and Fe powders
The sintered density of molybdenum can be significantly improved through the addition of a small amount of nickel. However, such addition impairs the ductility due to the formation of a NiMo intermetallic compound at the grain boundaries. This makes the plastic deformation process, such as rolling, drawing, and forging, impossible. This study shows that when copper is added, the sintered density can be further increased, but, not the ductility. This ductility problem of the Mo-Ni-Cu system can be improved when a small amount of iron is added and when the total amount of the alloying Ni, Cu, and Fe is over 6wt%, such as in the Mo-4Ni- 1Cu-1Fe system. Such improvement is attributed to the elimination of the brittle NiMo compounds in the matrix.
K.S. Hwang, H.S. Huang, International Journal of Refractory Metals & Hard Materials 22 (2004) 185-191
L0098 - Correlation between densification rate and microstructural evolution for pure alpha alumina
Correlation between microstructural evolution and macroscopic measurements has been investigated on pure alpha alumina under non-isothermal conditions. The densification of different as-received and milled powders of alumina has been monitored during sintering. Densification rate curves as a function of relative density are sensitive to microstructure, such as initial parameters of microstructure (agglomeration, pore size, heterogeneities), and heating schedule (thermal pre-treatment, heating rate). Densifi- cation rate curves can be correlated with microstructural evolution during overall sintering and are expected to be a good help to choose raw materials.
D. Lance, F. Valdivieso, P. Goeuriot, Journal of the European Ceramic Society 24 (2004) 2749-2761
L0097 - Synthesis of fine La0.8Sr0.2MnO3 powder by different ways
La0.8Sr0.2MnO3 (LSMO) powders were successfully synthesized by three routes (sol-gel, spray dryer and conventional solid state method). The precursors were characterized by particle size analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The sintering stage of all powders was also investigated by dilatometer. Finally, the sintered LSMO ceramics have been investigated magnetically and electrically in view to study the ferromagnetic-paramagnetic and/or metal-insulator transition. The magnetoresistance MR up to 42% above room temperature has been observed.
D. Grossin, J.G. Noudem, Solid State Sciences 6 (2004) 939-944
L0096 - Preparation of spherical zirconia powder in microemulsion system and its densification behavior
The water droplets in the microemulsion system of cyclohexane/water/TritonX-100/hexyl alcohol can act as the nano-reactors which solubilize zirconium oxychloride and ammonia separately. The precipitation reactions will take place in the confined spaces determined by the droplets size. The minute original reactors help us obtain nano-size spherical zirconia amorphous powder with uniform diameter distribution and weak aggregate. Such powder begins to crystallize at the temperature about 475°C, and its shrinkage of densification will be elementarily finished from 1080 to 1280°C. The powder is formed by dry pressing process. The 99% relative density and 100% tetragonal phase can be obtained when the green body is sintered at 1400°C for 2 h.
T. Ma, Y. Huang, J. Yang, J. He, L. Zhao, Materials and Design 25 (2004) 515-519
L0095 - Effect of ZrO2 additions on sintering of SnO2-based ceramics
The effect of zirconia additions on sintering of CoO doped tin dioxide has been investigated in the temperature range 1100- 1250°C. A first study showed that the substitution of tin by zirconium reduces significantly the volatilisation rate of SnO2 for temperatures greater than 1400°C. It appeared that the zirconium content increase inhibits the densification kinetics of SnO2-based ceramics. Indeed, the relative density did not exceed 93% for a Zr content lower than 6 mol% in the Sn(1-x)ZrxO2 solid solution. This negative effect can be imputed to the elastic distortions caused by the introduction of Zr in the tin dioxide lattice. So, the diffusion rate of point defects such as oxygen or cobalt ions is lowered.
A. Maître, D. Beyssen, R. Podor, Journal of the European Ceramic Society 24 (2004) 3111--3118
L0094 - Microstructural evolution of Y2O3 and MgAl2O4 ODS EUROFER steels during their elaboration by mechanical milling and hot isostatic pressing
Different ODS EUROFER steels reinforced with Y2O3 and MgAl2O4 were elaborated by mechanical milling and hot isostatic pressing. Good compromise between strength and ductility could be obtained but the impact properties remain low (especially for the Y2O3 ODS steel). The materials were structurally characterized at each step of the elaboration. During milling, the martensite laths of the steel are transformed into nano-metric ferritic grains and the Y2O3 oxides dissolve (but not the MgAl2O4 spinels). After the HIP, all the ODS steels remain ferritic with micrometric grains, surrounded by nano-metric grains for the Y2O3 ODS steels. The mechanisms in the Y2O3 ODS steels are complex: the Y2O3 oxides re-precipitate as nano-Y2O3 particles that impede a complete austenitization during the HIP. The quenchability of the ODS steels is modified by the milling process, the oxide nature and the oxide content. Eventually, the advantages and drawbacks of each oxide type are discussed.
C. Cayron, E. Rath, I. Chu, S. Launois, Journal of Nuclear Materials 335 (2004) 83-102
L0093 - Thermal stability and mechanical properties of a Zr-based bulk amorphous alloy
The thermal and mechanical properties of a Zr-Al-Cu-Ti-Ni bulk metallic glass were investigated. The glass transition and the crystallization were studied by calorimetry and X-ray diffraction. It was found that the crystallization occurred in two steps. The precipitating phases, and the activation energies were determined. It was established that the crystallization was controlled by the diffusion of the alloying Cu and Ni atoms. The creep behavior was investigated by indentation tests. The viscosity and the activation energy of the deformation process determined from indentation were in reasonable agreement with those obtained by compression tests.
D. Fatay, J. Gubicza, P. Szommer, J. Lendvai, M. Blétry, P. Guyot, Materials Science and Engineering A 387-389 (2004) 1001-1004
L0092 - Improvements in sintered density and dimensional stability of powder injection-molded 316L compacts by adjusting the alloying compositions
Powder injection molding is a process that provides advantages when making small parts with high density and complicated shapes. However, dimensional control of powder injection-molded stainless steel parts is difficult due to the presence of the liquid phase and the large amount of shrinkage that occurs during sintering. This study examines whether such a problem can be overcome through adjustments in the alloy composition and by making use of Thermo-Calc analysis. The results show that, with an increase in the molybdenum content up to the maximum limit according to existing specifications, a compact can be sintered to high densities without the presence of the liquid phase, while maintaining it in the dual-phase region of gamma + delta. In addition, dimensional control is improved. A slower heating rate is also found to be beneficial. These results are explained through dilatometric analysis and phase diagrams that are calculated using the Thermo-Calc program.
G.J. Shu, K.S. Hwang, Y.T. Pan, Acta Materialia 54 (2006) 1335-1342
L0091 - Studies of Fe-Co based perovskite cathodes with different A-site cations
Iron-cobalt based perovskite cathodes with different A-site cations ((Ln0.6Sr0.4)0.99Fe0.8Co0.2O(3-d), where Ln is La, Pr, Sm or Gd) have been synthesised, characterised by a powder XRD, dilatometry, 4-point DC conductivity measurements, and electrochemical impedance spectroscopy (EIS) on cone shaped electrodes. In addition to this scanning electron microscopy (SEM) was used to characterise the bars. XRD revealed that only the La-containing perovskite was hexagonal. The Pr and Sm perovskites were orthorhombic. The gadolinium-based perovskite was a two phase system consisting of an orthorhombic and a cubic perovskite phase. The thermal expansion coefficient (TEC) increased systematically with a decrease in the size of the A-site cation until the gadolinium-containing perovskite where the TEC decreases abruptly. The total electric conductivity was the highest for the La-based perovskite and the lowest for the Gd-based perovskite as determined by 4-point DC conductivity measurements on bars. A clear correlation between the size of the A-site cation and the electrochemical performance was revealed, as the area specific resistance (ASR) was the lowest for the compounds with the smallest A-site cation. This might be explained on the background of the creation of a two-phase structure with a unique microstructure when the size of the A-site cation is lowered, or that one of the phases has a high electro-catalytic activity towards the electrochemical reduction of oxygen.
K. Kammer, Solid State Ionics 177 (2006) 1047-1051
L0090 - Physical properties of BaMg(1/3)Nb(2/3)O3-BaCo(1/3)Nb(2/3)O3 solid solutions
Structural, electric and magnetic properties of Ba3Mg(1-x)CoxNb2O9 based dielectric ceramic compounds have been studied. The samples, prepared by a solid state reaction method, were characterised by X-ray powder diffraction (XRPD), electron microscopy (SEM), dielectric (epsilon(T)) and magnetic measurements (khi-1(T)). The XRPD analyses showed that the crystal structure of these compounds does change by the increase of substitution degree, passing froma superstructure hexagonal-type, P3m1 (no. 164), space group (SG) to a simple structure cubic-type, Pm3m (no. 221), SG. However, the evolution of the elementary unit cell lattice parameter can be followed and it exhibit a linear increasing tendency with increase in the substitution, indicating the existence of a solid solution through out the investigated range of substitution (0-1). Themicrostructure analysis shows a variation inthe grain size and also the porosity of the samples with the degree of substitution. The results are in good agreement with that of dielectricmeasurements, which also showed that the dielectric constant (epsilon) increases with the increase of cobalt content. The magnetic characterization of cobalt substituted samples showed an antiferromagnetic type super-exchange interaction between thesemagnetic ions. At the same time, the values of effective magnetic momentum (µeff) are close to the value that corresponds to Co2+ free ions. The study highlights the possibility of modelling these materials by substitutions, in order to improve properties of negative-positive-zero (NPO) type dielectric applications.
A. Veres, S. Marinel, M. Pollet, Journal of Physics and Chemistry of Solids 67 (2006) 822-827
L0088 - Mechanical and thermal expansion behavior of hipped aluminum-TiB2 composites
Aluminum-TiB2 composites reinforced with 5-20 vol.% ceramic particles were prepared by powder metallurgy (PM) method. Hot isostatic pressing was employed to consolidate the green PM products. The microstructure of metal matrix composites (MMCs) was found to depend greatly on the relative particle size (RPS) ratio between the aluminum and ceramic particles. Microstructural examination revealed that RPS value of 0.56 favors both the densification of MMC compacts and better uniform distribution of ceramic particles. Tensile measurements showed that the Young's modulus and ultimate tensile strength of the Al-TiB2p MMCs tend to increase with increasing TiB2p volume content at the expense of tensile ductility. Thermal expansion property of hipped MMCs was measured in the temperature range from 85 to 600°C. The results showed that the increase in the volume fraction of TiB2 reinforcement reduces the coefficient of thermal expansion (CTE) of the Al-TiB2 composites. Moreover, the CTE versus temperature plots exhibited an apparent peak minimum at ~380°C during the first heating stage for the composites reinforced with TiB2 >15 vol.%. This peak corresponds to the onset of relaxation for the compressive stress, leading to the Al matrix to deform plastically.
S.C. Tjong, K.F. Tam, Materials Chemistry and Physics 97 (2006) 91-97
L0087 - Improving the performance of lead-free solder reinforced with multi-walled carbon nanotubes
In this study, varying weight fractions of multi-walled carbon nanotubes were successfully incorporated into 95.8Sn-3.5Ag-0.7Cu solder, to synthesize novel lead-free composite solders. The composite solders were synthesized via the powder metallurgy route of: blending, compaction, sintering and extrusion. The extruded materials were then characterized for their physical, thermal and mechanical properties. With the addition of increasing weight percentage of carbon nanotubes, the composite solders experienced a corresponding decrease in density values and wetting property improved. The melting temperatures of the composite solders were found to be unchanged with the carbon nanotube additions. Thermomechanical analysis of the composites also showed that the presence of reinforcements decreased the average coefficient of thermal expansion of the solder matrix. An improvement in the mechanical properties was also recorded with the presence of increasing carbon nanotubes. An attempt was made, to correlate the increasing presence of reinforcements with the physical, thermal and mechanical properties obtained.
S.M.L. Nai, J. Wei, M. Gupta, Materials Science and Engineering A 423 (2006) 166-169
L0086 - Evidence of the formation of a new rock-salt type compound Li2MgTiO4 and of its role on the properties of the Li doped MgTiO3
This work deals with the sintering of MgTiO3 in presence of Lithium salt and more precisely with lithium halide. These last sintering agents lead to the formation of a new rock-salt type structure Li2MgTiO4. This new phase was synthesized by a classical solid-state route and their electric and dielectric properties were characterize. The formed material is a type I dielectric material with a permittivity close to 12 with dielectric losses inferiors to 0.3% in the range of -50 to 150°C. X-ray diffraction and investigation by TEM were also performed. The influences of the formation of this new phase on the properties of MgTiO3 are described here.
J. Bernard, D. Houivet, M. Hervieu, J.M. Haussonne, Solid State Sciences 8 (2006) 598-605
L0085 - Thermal expansion of near stoichiometric (U,Er)O2 solid solutions
Thermal expansions of (U,Er)O2 solid solutions were investigated between room temperature and 1673 K by using a thermo-mechanical analyzer. Lattice parameters of the (U,Er)O2 pellets are lower than that of UO2 and they decrease as the Er contents increase. The linear thermal expansion and average thermal expansion coefficients of (U,Er)O2 are higher than that of UO2. For the temperature range from room temperature to 1673 K, the average thermal expansion coefficient values for UO2 and (U0.8Er0.2)O2 are 10.94x10^(-6) and 11.42x10^(-6) K-1, respectively.
S-H. Kim, H-S. Kim, Y-W. Lee, D-S. Sohn, D-S. Suhr, Materials Letters 60 (2006) 1480-1483
L0084 - Development of a novel hybrid aluminum-based composite with enhanced properties
In the present study, a novel aluminum-based hybrid composite containing titanium particulates (discontinuous/particulates reinforcement) and iron mesh (continuous/interconnected reinforcement)was synthesized using a solidification processing route involving disintegrated melt deposition coupled with hot extrusion. Microstructural characterization studies conducted on hybrid composite revealed reduced grain size (~44%) when compared to monolithic aluminum, uniform distribution of unreacted and reacted titanium in matrix, and absence of reaction products at the iron-wire/aluminum matrix interface. Results of properties characterization revealed that the presence of hybrid reinforcement led to a reduction in coefficient of thermal expansion (~7.6%) and an increase in hardness, elastic modulus (~10%), 0.2% yield strength (20%) and ultimate tensile strength (~27%). The enhancement in properties realized in hybrid composite was found to be much higher when compared to conventional Al/SiC composite formulations containing relatively higher weight percentages of SiC particulates.
M. Gupta, M.O. Lai, C.Y.H. Lim, Journal of Materials Processing Technology 176 (2006) 191-199
L0082 - Fabrication of gapless triangular micro-lens array
This study presents a new process to fabricate gapless triangular micro-lens array (GTMA) optical film. The process includes ultraviolet (UV) lithography, photoresist reflow process, Ni-Co electroplating and hot embossing technique. After photoresist triangular column array is defined by UV lithography, reflow technique is applied to melt photoresist triangular column array into the shape of triangular micro-lens array. With this reflowed triangular micro-lens array, metal Ni-Co is deposited and covered uniformly on the triangular micro-lens array using electroplating process. The growth rate of Ni-Co is controlled at 0.4-0.6 µm/min at electroplating current density of 1 A/dm2 (ampere square decimetre, ASD). After this electroplating process, a mold of GTMA is obtained, which is served as the primary mold. Next, with passivation technique applied on this primary mold's surface, a secondary mold is obtained by applying the electroplating process again. This secondary mold is served as master for the subsequent hot embossing process to replicate the GTMA pattern onto polymeric material of polymethyl methacrylate (PMMA) sheet. The Ni-Co mold with hardness over hardness of vicker (Hv) 650 is obtained. The stiffness and hardness of the mold play important roles in GTMA hot embossing process. In addition, this PMMA-based GTMA film used as optical film offers a 100% fill factor and high optical coupling efficiency to improve luminance. The optical measurement shows that this optical film with GTMA pattern increases 15.1% of luminance for backlight module (BLM) of liquid crystal display (LCD).
C.T. Pan, C.H. Su, Sensors and Actuators A Physical 134 (2007) 631-640
L0081 - The rock salt oxide Li2MgTiO4: Type I dielectric and ionic conductor
The exploration of the Li-Ti-Mg-O system, using both sol-gel technique and solid state reaction method, allowed a new phase, Li2MgTiO4, with disordered rock salt structure (a = 4.159 Å ) to be synthesized. The latter is shown to be a good type I dielectric material, with a relative constant of 15 at high frequency and low dielectric loss (tand < 10^(-3)) over the temperature range - 60 to 160°C. It is also observed that the sintering temperature of this phase is strongly lowered by adopting the sol-gel technique compared to solid state reaction (1150°C instead of 1300°C). Finally we show that this phase exhibits cationic conductivity above 400°C (s600°C = 9 x 10^(-5) S cm-1).
M.V.V.M. Satya Kishore, S. Marinel, V. Pralong, V. Caignaert, S. D'Astorg, B. Raveau, Materials Research Bulletin 41 (2006) 1378-1384
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