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  • 1
    ISSN: 1573-4889
    Keywords: weldment ; weld metal ; heat-affected zone (HAZ) ; delta ferrite ; surface profilometry ; 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 Regions with different microstructures have been identified in the weldments of 9Cr-1 Mo steel. Weldments comprising threthree regions, i.e., weld metal, heat-affected zone (HAZ), and base metal, were oxidized in air at 923 K for different durations up to 500 hr. The crown area of the weld metal was found to form a thicker oxide scale than the other regions of the weldment. When the oxidation kinetics of different regions were compared (by separating out the coupons of the HAZ and the crown and root portions of the weld metal and then oxidizing them), the crown area of the weld was found to oxidize at a much higher rate than the others. Scanning electron microscopy (SEM) was carried out to assess the morphological variations in the different regions of the weldment. The compositional variations in the scales over the different regions have been characterized by the energy-dispersive analyses of X-rays (EDX), and the results thereof have also been corroborated by secondary ion mass spectrometry (SIMS).
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4889
    Keywords: grain size ; acoustic emission ; secondary-ion mass spectrometry ; surface profilometry ; growth stresses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The synergistic influence of prior-austenite grain size and silicon content of 9Cr−1Mo steel on the resistance to scale spallation has been studied in air at 773 K (for 500 hr) and 973 K (12 hr). Two steels, irrespective of their grain size and Si content, did not show spallation during oxidation at 773 K. Spallation occurred at 973 K, and fine-grain steels exhibited less spallation resistance than coarse-grain ones (in low-as well as high-Si steels). Among the four possible combinations of grain size ans Si content, the steel with low Si and fine grains showed least resistance to spallation, while the steel with high Si and coarse grains showed the best resistance. Spallation was found to initiate in the areas adjoining the oxide ridges formed at the alloy grain boundaries. Oxide scales at the ridges and within the grains were analyzed by scanning electron microscopy (SEM/EDX) and secondary-ion mass spectrometry (SIMS). These analyses suggest depletion of silicon from the areas adjoining grain boundaries, resulting in thicker scaling that triggers spallation in such areas. For similar grain-size materials, the necessary thickness for spallation was attained earlier with low-Si steel rather than in high-Si steel.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2019-07-13
    Description: A modal spectrum technique was used to study coherent instability modes triggered by naturally occurring disturbances in a circular jet. This technique was applied to a high Reynolds number jet for both untripped and tripped nozzle exit boundary layers, with both cases having a core turbulence level of 0.15 percent. The region up to the end of the potential core was dominated by the axisymmetric mode, with the azimuthal modes dominating further downstream. The growth of the azimuthal modes was observed closer to the nozzle exit for the jet with a transitional boundary layer. Whether for locally parallel flow or slowly diverging flow, even at low levels of acoustic forcing, the inviscid linear theory is seen to be inadequate for predicting the amplitude of the forced mode. In contrast, the energy integral approach reasonably predicts the evolution of the forced mode.
    Keywords: Acoustics
    Type: E-7882 , Experiments in Fluids (ISSN 0723-4864); 17; 6; 415-426
    Format: text
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