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  • 1
    Electronic Resource
    Electronic Resource
    Calorimetric evaluation of the effects of SiC concentration on precipitation processes in SiC particulate-reinforced 7091 aluminium (1989)
    Springer
    Journal of materials science 24 (1989), S. 1439-1446 
    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 A comprehensive differential scanning calorimetric (DSC) investigation has been conducted on the precipitation and dissolution behaviour of SiC particulate-reinforced 7091 aluminium. DSC is shown to be a particularly attractive experimental technique for developing new thermal and thermomechanical processes for aluminium-based metal matrix composites. These new processes are necessitated due to the deleterious effects that the SiC reinforcement causes on the aluminium matrix precipitation behaviour and the resultant ductility and fracture toughness properties. In this study the effects of SiC concentration and ageing temperatures, times, and sequences were evaluated. In addition to the unreinforced 7091 alloy, composites containing 10, 20 and 30 vol% particulate SiC were characterized. Identifications of specific phases involved in reactions detected with DSC were achieved by making direct correlations to previously published transmission electron microscopy studies. It was found that the presence of SiC in the aluminium significantly affects the solid state transformation kinetics of the 7091 aluminium matrix. Specifically, increasing the SiC concentration was found to decrease the temperatures at which GPI and GPII zones precipitate at their maximum rates and to increase the temperature at which GPI zones revert at maximum rate. The transition phase,η, and equilibrium phase,η, formation kinetics were observed to be insensitive to SiC concentration. Also, increasing the SiC concentration was seen to decrease the temperature at which the equilibrium phase dissolution occurred at its maximum rate. Transformation mechanics have been proposed which are consistent with these observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02397084
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Calorimetric evaluation of the effects of SiC concentration on precipitation processes in SiC particulate-reinforced 7091 aluminium (1989)
    Springer
    Journal of materials science 24 (1989), S. 1439-1446 
    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 A comprehensive differential scanning calorimetric (DSC) investigation has been conducted on the precipitation and dissolution behaviour of SiC particulate-reinforced 7091 aluminium. DSC is shown to be a particularly attractive experimental technique for developing new thermal and thermomechanical processes for aluminium-based metal matrix composites. These new processes are necessitated due to the deleterious effects that the SiC reinforcement causes on the aluminium matrix precipitation behaviour and the resultant ductility and fracture toughness properties. In this study the effects of SiC concentration and ageing temperatures, times, and sequences were evaluated. In addition to the unreinforced 7091 alloy, composites containing 10, 20 and 30 vol% particulate SiC were characterized. Identifications of specific phases involved in reactions detected with DSC were achieved by making direct correlations to previously published transmission electron microscopy studies. It was found that the presence of SiC in the aluminium significantly affects the solid state transformation kinetics of the 7091 aluminium matrix. Specifically, increasing the SiC concentration was found to decrease the temperatures at which GPI and GPII zones precipitate at their maximum rates and to increase the temperature at which GPI zones revert at maximum rate. The transition phase,η, and equilibrium phase,η, formation kinetics were observed to be insensitive to SiC concentration. Also, increasing the SiC concentration was seen to decrease the temperature at which the equilibrium phase dissolution occurred at its maximum rate. Transformation mechanics have been proposed which are consistent with these observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00553179
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Microstructural stability and mechanisms of fatigue and creep crack growth in Ti–24Al–11Nb (1997)
    Springer
    Journal of materials science 32 (1997), S. 2191-2206 
    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 Titanium intermetallics are being developed for long term applications at elevated temperatures, particularly those alloys based on the alloys Ti3Al and TiAl. Typical approaches include the design of appropriate microstructures for room and elevated temperature fatigue and creep resistance. However, a little explored area is the stability of these microstructures at elevated temperature and its effect on fatigue crack growth. The present investigation documented the microstructural stability, fatigue crack behaviour, and stress rupture of Ti–24Al–11Nb, a Nb modified Ti3Al alloy. A coarse two phase α2+β Widmanstatten microstructure was found to exhibit the best resistance to fatigue crack growth. Microstructural stability and elemental segregation were studied as a function of exposure time for up to 500 h at 800°C using transmission electron microscopy (TEM). Results indicate that the Widmanstatten microstructure is metastable and the β phase breaks up into particles. The absence of a continuous β phase surrounding the α2 phase reduces the resistance of the microstructure to fatigue crack growth at room temperature. At elevated temperature the microstructure stability does not play a role in determining the fatigue resistance. A fine Widmanstatten microstructure has the best resistance to creep deformation. Stress rupture tests were conducted in vacuum and air at 649°C and 760°C. Two types of failure mechanisms were seen in stress rupture; these include transgranular and intergranular failure within prior β grains. When tested in air at 760°C a combination of transgranular and intergranular failure occurred. Specimens that exhibited a higher proportion of transgranular failure had longer lives. When tested in vacuum at 760°C the predominant failure mode was intergranular. At 760°C extensive microstructural changes like breakup and spherodization of the β phase occurred under stress while the rate of coarsening without any stress was much slower. At 649°C the specimens tested in vacuum consistently exhibited longer lives. The creep crack growth when tested in air at 649°C was always a brittle transgranular mode while the specimens tested in vacuum always failed by an intergranular mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018551611904
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Notch sensitivity and fractography of polyolefins (1983)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 23 (1983), S. 117-124 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The notch sensitivity of high-density polyethylene (HDPE), polypropylene (PP), and polybutylene (PB) was evaluated using uniaxial tensile deformation and fractographic analysis. Each polyolefin was tested at relatively low and high molecular weights (MW). Only the lower MW HDPE was found to be clearly notch-sensitive. The lower MW PP exhibited some tendency toward notch sensitivity. The lower and higher MW PB, the higher MW HDPE, and the higher MW PP displayed notch strengthening. Whereas PB showed similar notched tensile performance regardless of molecular weight, both HDPE and PP showed higher susceptibility to notch sensitivity at lower molecular weights (and concomitant higher crystallinity). Tendencies toward notch sensitivity or notch stengthening were evidenced in the failure modes of these materials.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760230303
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Microhardness measurements of renal calculi: Regional differences and effects of microstructure (1992)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 26 (1992), S. 1117-1130 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Microhardnesses of five types of renal calculi: calcium apatite (82.5%)/magnesium ammonium phosphate hydrogen (lo%)/ calcium oxalate monohydrate (7.5%); calcium apatite (95%)/calcium oxalate monohydrate (5%); magnesium ammonium phosphate hydrogen (90%)/calcium apatite (10%); calcium oxalate monohydrate (85%)/calcium apatite (15%); and cystine (100%) were measured. Using Knoop and Vickers indenters the effects of chemical composition and microstructure on the microhardness measurement were assessed. Calcium oxalate monohydrate, magnesium ammonium phosphate hydrogen, and cystine stones, without apparent structure pattern, showed neither regional nor directional differences in their microhardness. In contrast, calcium apatite stones, with distinctly concentric laminae structure, showed regional variations which were correlated with the chemical composition of stone constituents. Scanning electron microscopy of the indenter impressions were taken to help in interpreting the directional dependence in Knoop hardness measurements with respect to the microstructure of the calculi. Vickers measurements showed the crystalline stones were isotropic within a layer. Combined results of Knoop and Vickers measurements indicate that the anisotropic Knoop hardness readings seen in the laminated regions were structural but not material-based. Implications of the results for the fragmentation of renal calculi in extracorporeal shock wave lithotripsy are discussed. © 1992 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820260902
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    Paper (German National Licenses)
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