1,721,240 research outputs found
Laser nitriding of metals
No full textLaser nitriding can be described as the irradiation of metal surfaces by short laser pulses in nitrogen containing atmospheres. This may lead to a strong take-up of nitrogen into the metal and nitride formation which can improve the metal's surface properties, e.g. the hardness or the corrosion and wear resistance. Here, the laser nitriding of iron, carbon steel, stainless steel, and aluminum was investigated employing a combination of complementary methods. [on beam analysis (Rutherford Backscattering Spectroscopy and Resonant Nuclear Reaction Analysis) was employed for element and isotope profiling. Mossbauer spectroscopy and X-ray diffraction were used for phase analysis. Surface profilometry, optical and electron microscopy revealed the surface topography and morphology obtained after laser nitriding. Microhardness measurements by the nanoindentation technique characterized the mechanical surface properties obtained by the treatment. By this combination of methods it became possible to resolve the influence of the treatment parameters (laser fluence, number of pulses, spot size, spatial intensity distribution, and gas pressure) in different materials treated (iron, carbon steels and stainless steel). It is shown that laser nitriding is a complex process, composed of several superimposed effects. Laser heating, melting and evaporation in combination with plasma formation and the generation of laser-supported absorption waves are the essentials of the process. Pressure- and plasma-enhanced dissolution and diffusion of nitrogen in combination with macroscopic material transport (piston effect, convection, fall-out) are further important effects determining the results. Additional marker experiments and laser treatments in isotopically enriched nitrogen atmospheres allowed to analyze these effects and to develop scenarios for the nitriding process and the material transport mechanisms. A simulation of the nitrogen depth profiles for the single spot irradiations was derived, whose results are in good agreement with the experimentally observed profiles. (C) 2002 Elsevier Science Ltd. All rights reserved
Laser nitriding of iron and aluminum
No full textSamples of pure iron and pure aluminum have been irradiated in nitrogen atmosphere with a pulsed nanosecond excimer laser in the UV wavelength range. For iron, almost all the phases predicted by the Fe-N equilibrium phase diagram are observed, while in aluminum the wurtzite AIN phase is formed. The dimension of the laser spot (typically 5 x 5 mm(2)), the number of laser pulses (1-512), the laser beam fluence (1-8 J/cm(2)) and the pressure of the reactive atmosphere (0.01-10 bar) strongly affect the nitrogen depth profiles and the characteristics of the resulting compounds. Therefore, the influence of these experimental parameters has been systematically investigated. A detailed study of the nitrogen incorporation as a function of the number of pulses and the beam fluence allowed us to model the experimental results giving some important hints on the nitriding process. (C) 2002 Elsevier Science B.V. All rights reserved
Formation and characterization of NaCl-type FeC
No full textCubic FeC nanoparticles were observed in amorphous iron carbon matrix produced by pulsed laser deposition directly onto electron microscopy grids. The observed lattice constant is close to a theoretically predicted value. (C) 2009 Elsevier B.V. All rights reserved
Amorphous stainless steel coatings prepared by reactive magnetron-sputtering from austenitic stainless steel targets
No full textStainless steel films were reactively magnetron sputtered in argon/methane gas flow onto oxidized silicon wafers using austenitic stainless-steel targets. The deposited films of about 200 nm thickness were characterized by conversion electron Mossbauer spectroscopy, magneto optical Kerr-effect, X-ray diffraction, scanning electron microscopy, Rutherford backscattering spectrometry, atomic force microscopy, corrosion resistance tests, and Raman spectroscopy. These complementary methods were used for a detailed examination of the carburization effects in the sputtered stainless-steel films. The formation of an amorphous and soft ferromagnetic phase in a wide range of the processing parameters was found. Further, the influence of the substrate temperature and of post vacuum-annealing were examined to achieve a comprehensive understanding of the carburization process and phase formation.Deutsche Forschungsgemeinschaft (DFG) [Scha 632/11
Simulation and deconvolution program WinRNRA for depth profiling of light elements via nuclear resonance reactions
No full textIn this paper, a Windows PC-program is described that performs the transformation of measurement spectra obtained by resonant nuclear reaction analysis (RNRA) into concentration depth profiles. For the shape of the resonance a simple Breit-Wigner form is implemented. For the calculation of the straggling both the Bohr and the Lindhard-Scharff models can be used. The program can be used to evaluate depth profiles of an element in an otherwise homogeneous target. A nanometer depth scale is obtained by considering the concentration-dependent densities of the phases. This is exploited for the investigation of nitrogen profiles via the resonance reaction N-15(p, alpha gamma)C-12. For demonstration purposes the program is used to determine nitrogen depth profiles of laser nitrided iron. (C) 2001 Elsevier Science B.V. All rights reserved
Mass transport mechanisms during excimer laser nitriding of aluminum
No full textSurface layers of aluminum nitride were formed by irradiating pure aluminum substrates in nitrogen atmosphere with a pulsed excimer laser. The beam was focused on the sample placed inside a chamber filled with nitrogen gas. The irradiation was carried out at various laser fluences, nitrogen gas pressures, and numbers of pulses in order to investigate the influence of each parameter on the nitrogen incorporation and the mass transport mechanisms. X-ray diffraction showed the formation of polycrystalline AlN phase with the wurtzite structure, and the analysis of the nitrogen depth profiles by means of resonant nuclear reaction Analysis revealed a monotonic increase of the nitrogen concentration with the ambient gas pressure and the number of laser shots. It has been found that the laser fluence directly determines the temperature of the substrate and strongly changes the transport mechanism. The thermal simulations and the experimental evidence show that for fluences higher than 3 J/cm(2) the temperature of the substrate exceeds 2900 K. This value is higher than the dissociation temperature (similar to2400 K) and close to the melting point (similar to3070 K) of AlN, which can therefore dissociate or melt. The atomic nitrogen can rapidly diffuse to greater depths in the liquid Al matrix or it can degas (outgas) through the surface of the sample, leading to the formation of rather homogeneous concentration profiles. For fluences lower than 3 J/cm(2) the temperature of the substrate is not sufficient to destroy the nitride phase and the AlN grains can move inside the molten Al. In this case, the material transport can be attributed to Brownian motion and thermophoretic drift, which in turn are correlated with the chemical and thermal gradient, respectively
Handbuch 2025/2026 für Studentinnen und Studenten der Physik
No full textSoftcover, 17x24Das Handbuch 2025/2026 ist die „Anleitung“ zum Physikpraktikum für Studentinnen und Studenten der Physik an der Georg-August-Universität Göttingen. Das Praktikum für den Bachelor of Science im Fach Physik wird begleitend zu den Vorlesungen Experimentalphysik I...IV durchgeführt und umfasst insgesamt 25 Versuche. Das inhaltlich ähnliche Grundpraktikum für den Zwei-Fächer-Bachelor umfasst insgesamt 15 Versuche. Dieser Band behandelt experimentelle Grundlagen und 17 Versuche zu Themen der Mechanik, Thermodynamik und zum Elektromagnetismus
Handbuch 2020/2021 für Studentinnen und Studenten der Physik.
No full textDas Handbuch 2020/2021 ist die „Anleitung“ zum Physikpraktikum für Studentinnen und Studenten der Physik an der Georg-August-Universität Göttingen. Das Praktikum für den Bachelor of Science im Fach Physik wird begleitend zu den Vorlesungen Experimentalphysik I...IV durchgeführt und umfasst insgesamt 25 Versuche. Das inhaltlich ähnliche Grundpraktikum für den Zwei-Fächer-Bachelor umfasst insgesamt 15 Versuche. Dieser Band behandelt experimentelle Grundlagen und 17 Versuche zu Themen der Mechanik, Thermodynamik und zum Elektromagnetismus
Handbuch 2022/2023 für Studentinnen und Studenten der Physik
No full textDas Handbuch 2022/2023 ist die „Anleitung“ zum Physikpraktikum für Studentinnen und Studenten der Physik an der Georg-August-Universität Göttingen.
Das Praktikum für den Bachelor of Science im Fach Physik wird begleitend zu den Vorlesungen Experimentalphysik I...IV durchgeführt und umfasst insgesamt 25 Versuche. Das inhaltlich ähnliche Grundpraktikum für den Zwei-Fächer-Bachelor umfasst insgesamt 15 Versuche.
Dieser Band behandelt experimentelle Grundlagen und 17 Versuche zu Themen der Mechanik, Thermodynamik und zum Elektromagnetismus
Handbuch 2022/2023 für Studentinnen und Studenten der Physik
No full textDas Handbuch 2022/23 ist die „Anleitung“ zum Physikpraktikum für Studentinnen und Studenten der Physik an der Georg-August-Universität Göttingen.
Das Praktikum für den Bachelor of Science im Fach Physik wird begleitend zu den Vorlesungen Experimentalphysik I…IV durchgeführt und umfasst insgesamt 25 Versuche. Das inhaltlich ähnliche Grundpraktikum für den Zwei-Fächer-Bachelor umfasst insgesamt 15 Versuche.
Dieser Band behandelt 14 Versuche zu den Themen Wellen, Optik und Quantenphysik
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