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  • 1
    Electronic Resource
    Electronic Resource
    Solute segregation to grain boundaries in MgO-doped alumina (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2795-2797 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spatial distribution of Mg solute in polycrystalline, single-phase Al2O3 has been obtained, using a secondary ion imaging technique. Segregation of Mg to the Al2O3 grain boundaries is clearly observed—strong evidence that the principal role of MgO is to reduce the grain boundary mobility via a solute-drag mechanism. In addition, Mg (dopant) and Ca (impurity) are shown to cosegregate, shedding further light on magnesium's ability to stabilize microstructural evolution in Al2O3. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113478
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  • 2
    Electronic Resource
    Electronic Resource
    Role of second-phase particles in the oxidation of Al-Li alloys (1992)
    Springer
    Oxidation of metals 37 (1992), S. 23-37 
    Details
    ISSN: 1573-4889
    Keywords: aluminum-lithium alloys ; oxidation ; second-phase particles ; secondary ion mass spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Oxidation behavior of Al-Li alloys, containing a high volume fraction of Ferich second-phase particles, was studied at 530°C and 200°C. Morphological studies showed enhanced growth of Li-rich oxides in the vicinity of the insoluble second-phase particles. Microanalytical depth profiling of the oxide layer with a high resolution scanning ion microprobe indicated rapid diffusion and subsequent oxidation of Li at the free surface. Examination of the alloy surface after removal of the oxide layer suggested that the initial oxide growth occurred in the lateral direction. Secondary ion image depth profiling of the alloy surface after oxide removal revealed Li segregation to the alloy/second-phase interface, supplying Li for accelerated oxidation. A microstructural model of the oxidation process in this case is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665629
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  • 3
    Electronic Resource
    Electronic Resource
    Morphological and microchemical phenomena in the high-temperature oxidation of binary Al-Li alloys (1991)
    Springer
    Oxidation of metals 36 (1991), S. 361-378 
    Details
    ISSN: 1573-4889
    Keywords: aluminum-lithium alloys ; oxidation ; oxide nucleation ; lateral oxide growth ; secondary ion mass spectrometry ; scanning ion microprobe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The high-temperature oxidation behavior of binary Al-Li alloys has been characterized by scanning electron microscopy and secondary ion mass spectrometry in order to understand the mechanism of rapid oxidation in these alloys and to correlate the oxide morphology to its microchemistry. The oxide scale developed on polished specimens during short exposures in air at 530°C shows characteristic nodules that usually nucleate at grain boundaries. Examination of the alloy surface after removal of the oxide layer shows that the initial growth of the oxide nodules occurs laterally in addition to thickening normal to the oxide/alloy interface. Microchemical analysis of the oxide film with a scanning ion microprobe reveals a thick Li-oxide layer at the oxide/gas interface indicating preferential oxidation of Li at the free surface; the rest of the oxide film is composed of both Al- and Li-rich oxides, probably Li2O and LiAlO2 The presence of trace impurities (K, Na, F, and Cl) in the oxide scale was also detected. A microstructural model for the development of the oxide film in the Al-Li system is presented on the basis of both morphological and microanalytical data obtained in this study; this new model is compared with existing models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01151586
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  • 4
    Electronic Resource
    Electronic Resource
    Control of calcium hexaluminate grain morphology in in-situ toughened ceramic composites (1996)
    Springer
    Journal of materials science 31 (1996), S. 3223-3229 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of processing conditions on the morphology of calcium hexaluminate (CA6) grains in Al2O3: 30 vol% CaO·6Al2O3 (CA6) ceramic composites was investigated. Specimens were prepared by in-situ reaction sintering using precursor powders of alumina, and either calcium carbonate or calcium oxide. In some samples, 1 vol% anorthite glass was added as a sintering aid. X-ray diffraction was used to study the phase development in the as-calcined and sintered states. The resultant microstructures were characterized using both scanning electron microscopy (SEM), and imaging secondary ion mass spectrometry (SIMS). It was found that the CA6 grains developed a platelike morphology when CaCO3 was used as the starting calcium-rich powder. In contrast, samples prepared using CaO resulted in equiaxed CA6 grains. This result was observed to be independent of the anorthite glass addition. The findings are rationalized in terms of distinct CA6 reaction mechanisms, resulting from differences in the reactivity of the powders during the early stages of calcining.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354672
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  • 5
    Electronic Resource
    Electronic Resource
    Optimization of chemical reactions between alumina/silica fibres and aluminium-magnesium alloys during composite processing (1997)
    Springer
    Journal of materials science 32 (1997), S. 1953-1961 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An Al–Si–Cu–Mg alloy reinforced with alumina/silica fibres (Fiberfrax®, alumina/silica ratio=45/55) has been extensively characterized in terms of microstructure, interfacial chemical reactions and mechanical properties. The composite was fabricated by squeeze casting. The above characteristics were measured as a function of (a) calcination temperature of the fibre preform before infiltration, and (b) subsequent composite heat treatment. The main reaction that occurs during the processing of aluminium alloy matrix composites is the reduction of silica in the binder and fibres by magnesium from the matrix. When calcined below 1000°C, the fibres remain amorphous with a coating of porous silica binder. In this condition, the reinforcement reacts strongly with the matrix during heat treatment of the composite. In contrast, at high calcination temperatures (1200°C), the fibres transform partially into mullite and the silica binder densifies; these fibres are somewhat less reactive with the matrix. In both cases, the matrix/reinforcement reactions are very strong during high-temperature heat treatment, leading to a complete reduction of silica in some cases. The degradation caused by chemical reactions adversely affects the mechanical properties of these composites. Therefore, in order to optimize the mechanical properties of this composite, the fibre preform first must be calcined at high temperature, then the composite heat treatment limited to low temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018585730134
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  • 6
    Electronic Resource
    Electronic Resource
    Microstructural evolution during transient liquid-phase bonding in a Ni-base superalloy/sapphire fiber composite (1999)
    Springer
    Journal of materials science 34 (1999), S. 5187-5197 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Transient-liquid-phase (TLP) bonding was used to fabricate a Haynes 230 Ni-base superalloy/sapphire fiber composite for high-temperature applications. Boron was used as a melting-point depressant for the Ni, to aid superalloy infiltration of the fibers. Preliminary study of the composite indicated an incomplete TLP bonding cycle. Therefore, microstructural and microchemical analyses were carried out to determine the TLP bonding mechanism. It was found that the TLP process did not occur under local thermodynamic equilibrium conditions at the solid/liquid interfaces, contrary to the primary assumption of conventional models, so a modified model for TLP bonding is proposed. The main differences between the proposed and the conventional models are: (a) the concentration of the melting-point depressant increases with time during isothermal solidification, (b) extensive boride segregation at γ grain boundaries and boride precipitation occurs within γ grains adjacent to the interlayer in the initial composite assembly, (c) because of the relatively high boron concentration in the interlayer, the TLP bonding cycle was incomplete, resulting in residual-liquid borides. To achieve ideal TLP bonding, four modifications are recommended: (i) use less boron, (ii) use finer sapphire fibers, (iii) create smaller initial grain sizes in the γ matrix and (iv) increase the homogenization time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004707812417
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  • 7
    Electronic Resource
    Electronic Resource
    Microstructure, tensile properties and fracture behaviour of an Al-Cu-Mg alloy 2124 (1993)
    Springer
    Journal of materials science 28 (1993), S. 3205-3213 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The microstructure, tensile properties and fracture behaviour of aluminium alloy 2124 were studied. Detailed optical and electron microscopical observations were made to analyse the as-received microstructure of the alloy. It is shown that microstructural characteristics have a profound influence on tensile properties and quasi-static fracture behaviour of the alloy. Tensile test results indicate that the alloy has uniform strength and ductility in the longitudinal and transverse orientations. The elongation and reduction in area are higher in the transverse direction of the extruded plate. No change in fracture mode was observed with direction of testing. Fracture, on a microscopic scale, was ductile, comprising of void nucleation, growth and coalescence. The fracture process is discussed in terms of competing influences of intrinsic microstructural features, deformation characteristics of the matrix and grain-boundary failure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00354237
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  • 8
    Electronic Resource
    Electronic Resource
    Imaging microanalysis of ceramic materials with a scanning ion microprobe (1994)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 21 (1994), S. 117-122 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: This article discusses the application of a scanning ion microprobe coupled with secondary ion mass spectrometry (SIMS) in the microanalytical characterization of ceramic materials. The high spatial resolution afforded by the microprobe mode, in conjunction with the analytical sensitivity of SIMS, make this technique ideally suited to explore the microchemistry of ceramics, which have complex microstructures and contain several trace and light elements. Two case studies of interface analysis are presented: YBa2Cu3O7-x superconductors and sintered silicon carbide. Sodium and chlorine impurities were found to segregate to the grain boundaries of melt-grown YBa2Cu3O7-x, accompanied by oxygen deficiency. In SiC sintered with Al2O3, Al was present along the grain boundaries in elemental from and at triple-grain junctions as Al oxide second phases.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740210209
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