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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 69 (1999), S. S795 
    ISSN: 1432-0630
    Keywords: PACS: 81.65.Lp; 61.80.Ba; 62.50.tp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. Laser nitriding of iron and other metals is governed by the complicated interplay of the laser–plasma–liquid surface interactions which lead to a superposition of several mechanisms. This article reports on the influence of the nitrogen gas pressure on the nitriding process for stainless steel. The effects of the nitrogen gas pressure on the nitrogen depth profiles and the phase formation are revealed by resonant nuclear reaction analysis, Mössbauer spectroscopy, and X-ray diffraction. We found that the surface nitrogen concentration reaches 10 at. % with a mean value of about 7.5 at. % in the first 150 nm. There seems to be a pressure window between 0.1 and 0.7 MPa for the most efficient treatment. In the surface layer, an additional γ-Fe(N) phase can be distinguished from the original γ-phase of the stainless steel.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4619-4624 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser nitriding is a very efficient method to improve the mechanical properties, surface hardness, corrosion, and wear resistance of iron and steel, with the advantages of a high nitrogen concentration, fast treatment, and accurate position control, and without any undesired heating effect on the substrate. However, the stability of laser-produced iron nitrides is still under investigation. This article reports investigations of the thermal stability of these iron nitrides upon annealing treatments, which were conducted both in vacuum and air. The phase and elemental composition of the nitride layers were deduced from conversion electron Mössbauer spectroscopy, resonant nuclear reaction analysis, and grazing incidence x-ray diffraction. The surface hardness was measured by the nanoindentation method. In laser-nitrided iron, two critical temperatures are found: at 523 K the predominant iron-nitride phase changes from the γ/ε to the γ′ phase. When the temperature exceeds 773 K, all of the nitrogen has escaped from the surface layer. For annealing in air the nitrogen escapes completely already at 673 K, where a thick oxide layer has formed. Stainless steel proved to be more stable than iron, and even up to 973 K no new phases or oxides were produced, here, also, only at 973 K the nitrogen content decreased significantly. Therefore, laser-nitrided stainless steel is well suited for applications. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 168-178 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser nitriding of iron and other metals is governed by the complicated interplay of the laser–plasma–solid interactions which lead to a superposition of several mechanisms. This work reports on the drastic influence of the spatial laser intensity distribution on the nitriding process. The effects of the lateral laser intensity on the nitrogen lateral and depth profiles, the phase formation, the surface topology, and the microhardness are revealed by resonant nuclear reaction analysis, Mössbauer spectroscopy, surface profilometry, and nanoindentation. Homogeneous laser beams lead to a strong reduction or almost the absence of the piston mechanism, thus confining the nitriding and the transport processes to the laser spot and avoiding the fallout. The details are discussed in relation to the results obtained for the raw-beam irradiations. Much higher nitrogen saturation concentrations can be achieved with a homogenized beam, but the surface hardness and the hardening depth are lower than in the case of irradiation with the raw beam. The ε nitride is only found for raw-beam irradiation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 153-155 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In spite of its technological importance, the basic mechanisms of laser nitriding of metals and alloys are hardly understood. The nitrogen depth profiles achieved by laser nitriding of pure iron were measured with high accuracy by resonant nuclear reaction analysis and described by two superimposed diffusion profiles. Using simple estimates, together with the results of marker experiments and laser treatments in 15N-isotopically enriched atmospheres, the development of these profiles with the number of pulses can be simulated in excellent agreement with the experimental results. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2412-2414 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this letter we propose a phenomenological model to explain the nitrogen depth profile in iron after laser nitriding. The model is based on the one-dimensional diffusion equation and two sets of functions are use to fit the experimental profiles: complementary error function (erfc) and Gaussian. The different nature of these profiles reflects the presence of two stages in the process: the nitrogen is supplied in the sample as an erfc, while the diffusion to larger depths takes place as Gaussians. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1439-6327
    Keywords: Maximum Oxygen Uptake ; Bicycle Ergometer Training ; Maximale Sauerstoffaufnahme ; Fahrradergometertraining
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung 6 gesunde untrainierte Normalpersonen im Alter von 22–35 Jahren wurden 4 Wochen lang täglich, außer sonntags, mit einer stufenweise bis zum Maximum gesteigerten Belastung trainiert. Täglich wurde die Sauerstoffaufnahme, das Atemminutenvolumen und die Herzfrequenz bei 100 W steady state Belastung und bei maximaler Belastung registriert. Zweimal wöchentlich wurde 3 min nach Belastung das pH und die übrigen Werte des Säure-Basen-Haushaltes bestimmt. Die maximale Sauerstoffaufnahme nahm im Verlauf des Trainings um 14,9% zu, das maximale Atemminutenvolumen um 17,5%. Die maximale Herzfrequenz nahm um 3,2% ab, der pH-Wert 3 min nach Beendigung der Belastung nahm aus metabolischer Ursache um 0,09 ab. Aus den Ergebnissen geht hervor, daß ein tägliches Training mit stufenweise bis zum Maximum gesteigerter Belastungsintensität sowohl die aerobe als auch die anaerobe Kapazität steigert. Sämtliche Trainingseffekte zeigten einen linearen Verlauf.
    Notes: Summary 6 healthy men aged 22 to 35 years were trained daily except sundays by a stepwise increased bicycle ergometer exercise. Oxygen uptake ( $$\dot V_{{\text{O}}_{\text{2}} } $$ , STPD), ventilation ( $$\dot V_{\text{E}} $$ , BTBS) and heart rate during a 6 min period of 100 watts and during maximum exercise were measured daily. Acid base values 3 min after exercise were measured two times the week. $$\dot V_{{\text{O}}_{\text{2}} } $$ max. increased by 14.9% after 4 weeks of training, $$\dot V_{\text{E}} {\text{max}}$$ . by 17.5%. Maximum heart rate decreased by 3.2%, pH measured 3 min after exercise by 0.09 units. The results indicate that a daily training using stepwise increased load up to the maximum increases aerobic and anaerobic capacity. All training effects showed a linear increase during the 4 week training period.
    Type of Medium: Electronic Resource
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