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  • 1
    Electronic Resource
    Electronic Resource
    Liquid metal expulsion during laser irradiation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3317-3322 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: During laser assisted materials processing such as welding, cutting, drilling, or surface alloying, the processing conditions are adjusted to either achieve or avoid liquid metal expulsion. Currently, there is no theoretical model to determine, from fundamental principles, the operating conditions for the initiation of liquid metal expulsion during laser irradiation. Processing conditions necessary for the initiation of liquid metal expulsion during pulsed laser irradiation have been investigated experimentally and theoretically. Lead, titanium, and stainless steel samples were irradiated by single and multiple pulses of varying pulse durations to investigate conditions for liquid metal expulsion. It is demonstrated that using theoretically computed transient spatial temperature profiles, and by balancing surface tension and recoil forces, the conditions for the initiation of liquid metal expulsion can be determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351452
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  • 2
    Electronic Resource
    Electronic Resource
    Modeling of the role of atomic hydrogen in heat transfer during hot filament assisted deposition of diamond (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 712-718 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature and atomic hydrogen concentration profiles in a hot filament type diamond deposition reactor were determined experimentally and theoretically to demonstrate that the reaction of atomic hydrogen on the substrate surface plays an important role in the heating of the substrate. For a given filament temperature, the substrate temperature in helium was significantly lower than that in either pure hydrogen or 1% methane-hydrogen atmospheres. The presence of small amounts of methane in hydrogen did not have any significant effect in influencing the shape of the atomic hydrogen concentration profile. In the space between the filament and the substrate, the concentration field is established mainly due to the diffusive mixing of the atomic hydrogen with the molecular hydrogen and other species in the gas phase. Homogeneous chemical reactions in the gas phase do not significantly affect the atomic hydrogen concentration distribution in this region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351857
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  • 3
    Electronic Resource
    Electronic Resource
    Energy absorption by metal-vapor-dominated plasma during carbon dioxide laser welding of steels (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2045-2050 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: During laser welding, the plasma plume affects the amount of energy reaching the weld surface and the composition and properties of the welds. Light emissions during welding were recorded by emission spectroscopy to understand the energy absorption and the nature of the plasma formed during welding of various grades of steels. The flow of gases and the concentrations of the various metal vapors were computed by solving the Navier Stokes equation and the equations of conservation of various species. The variables studied were shielding gas composition and flow rate and the base metal composition. Until now, self-absorption of emissions arising from species present at high concentrations within the plasma has kept researchers limited to either analyzing ideal situations that are unrelated to the welding process or not accounting for the attenuation of the emissions. It is demonstrated that during welding, the peaks in the emission spectra that are affected by the self-absorption process can be eliminated on the basis of the initial and the terminal energy levels for electronic transitions. By selectively eliminating the affected transitions and by using the numerically computed local concentrations of metal vapors, the absorption of the laser beam energy by the plasma can be accurately determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346555
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  • 4
    Electronic Resource
    Electronic Resource
    Probing laser induced metal vaporization by gas dynamics and liquid pool transport phenomena (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 1313-1319 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: During laser beam welding of many important engineering alloys, an appreciable amount of alloying element vaporization takes place from the weld pool surface. As a consequence, the composition of the solidified weld pool is often significantly different from that of the alloy being welded. Currently there is no comprehensive theoretical model to predict, from first principles, laser induced metal vaporization rates and the resulting weld pool composition changes. The weld pool heat transfer and fluid flow phenomena have been coupled with the velocity distribution functions of the gas molecules at various locations above the weld pool to determine the rates of the laser induced element vaporization for pure metals. The procedure allows for calculations of the condensation flux based on the equations of conservation of mass, momentum and energy in both the vapor and the liquid phases. Computed values of the rates of vaporization of pure metals were found to be in good agreement with the corresponding experimentally determined values. The synthesis of the principles of gas dynamics and weld pool transport phenomena can serve as a basis for weld metal composition control.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350358
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  • 5
    Electronic Resource
    Electronic Resource
    Role of heat transfer and fluid flow in the chemical vapor deposition of diamond (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2424-2432 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The role of fluid flow and heat transfer in determining the quality of the diamond films and the rate of their deposition in a hot-filament chemical vapor deposition (HFCVD) reactor was investigated both experimentally and theoretically. The equations of conservation of mass, momentum, and enthalpy were solved numerically to calculate the temperature and fluid flow fields. Experiments were conducted with various flow configurations, and the deposition rates and the spatial variations of film thickness were examined in each case. The films were characterized by Raman spectroscopy, x-ray, and scanning electron microscopy. The influences of free and forced convection, and diffusion due to concentration and temperature gradients (Soret effect) were examined. Comparison of the computed results with the experimental data revealed the importance of thermal diffusion in the HFCVD of diamond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346502
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  • 6
    Electronic Resource
    Electronic Resource
    High-pressure phases of SiO2 made in air by Fedoseev–Derjaguin laser process (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1687-1689 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Exposure of a falling stream of 1 μm average size α-quartz particles to a continuous wave or pulsed CO2 laser beam in air resulted in the formation of a complete series of high-pressure phases of silica: coesite, stishovite, and apparently even denser forms with α-PbO2 and Fe2N structures. Since the laser exposure technique works with the carbon black to diamond transition, the technique is confirmed as a simple and generally applicable means to achieve the same effects as exposure to several hundred kilobars pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100469
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  • 7
    Electronic Resource
    Electronic Resource
    Hydrogen assisted heat transfer during diamond growth using carbon and tantalum filaments (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2068-2070 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Much of the previous work on the role of atomic hydrogen in diamond growth has been focused on its formation on various refractory metal filaments, its reaction in the gas phase and its role in the growth mechanism. In contrast, the effect of atomic hydrogen recombination on substrate heating is addressed in this letter. Experiments were conducted in vacuum, helium, and hydrogen environments. Tantalum and carbon filaments were used to vary atomic hydrogen generation rates. Furthermore, methane was added in some experiments to determine its effect on hydrogen assisted "chemical'' heating of the substrate. The results indicate that when substantial amounts of atomic hydrogen are generated at the filament, reactions of atomic hydrogen at the diamond growth surface have a pronounced effect on the substrate temperature. Use of carbon filaments lead to significantly diminished atomic hydrogen generation rates and much lower substrate temperatures. Additions of small amounts of methane to hydrogen also resulted in reduced atomic hydrogen generation rates and, consequently, lower substrate temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107091
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  • 8
    Electronic Resource
    Electronic Resource
    Transport phenomena in the scale-up of hot filament-assisted chemical vapor deposition of diamond
    Amsterdam : Elsevier
    Surface & Coatings Technology 62 (1993), S. 349-355 
    Details
    ISSN: 0257-8972
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0257-8972(93)90266-Q
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  • 9
    Electronic Resource
    Electronic Resource
    TEM characterization of structural changes in graphite plates due to pulsed CO2 laser irradiation (1990)
    Springer
    Journal of materials science 9 (1990), S. 1071-1074 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727879
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  • 10
    Electronic Resource
    Electronic Resource
    Metal distribution in alumina/aluminium composites synthesized by directed metal oxidation (1996)
    Springer
    Journal of materials science 31 (1996), S. 5101-5108 
    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 directed oxidation of molten aluminium alloys by vapour phase oxidants can be used to produce Al2O3/Al ceramic matrix composites. The toughness of these composites is determined by the amount and the nature of metal distribution in the composite. This paper addresses the problem of understanding the metal distribution in Al2O3/Al composites and its dependence on growth temperature. Electrical conductivities and microstructures of Al2O3/Al composites synthesized by directed oxidation of Al-5056 alloy are investigated. The high conductivity of the Al2O3/Al composite compared to sintered Al2O3-4 wt% MgO is shown as a proof of the presence of some continuous metal channels in the composite. The activation energy forthe diffusion of the dominant charge carrier in the oxide matrix is found to be 1.36 eV from the analysis of the conductivity data. Both the amount of metal in the composite and the extent of interconnection of the metal channels decrease with increasing growth temperature. The observed changes in microstructure with temperature can be explained by considering temperature variations of grain boundary energies in alumina and the alumina/aluminium interfacial energy. The metal content of the Al2O3/Al composites, prepared by directed oxidation of Al-5056 alloys, can be tailored by the choice of the growth temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00355911
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