The Experts below are selected from a list of 723 Experts worldwide ranked by ideXlab platform
Peter Schaaf - One of the best experts on this subject based on the ideXlab platform.
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Laser Nitriding and carburization of materials
Laser Surface Engineering#R##N#Processes and Applications, 2015Co-Authors: Daniel Hoche, J Kaspar, Peter SchaafAbstract:Nitriding and carburizing by Laser irradiation in combination with a process gas is a common method to enhance the surface properties of various materials. This chapter discusses the different aspects of the process starting from fundamental mechanism up to engineering applicability. It will introduce and classify the method followed by a brief but detailed summary on the basic physical and chemical mechanisms involved. Further, the most common materials, their suitability and upcoming opportunities will be discussed. A major goal is to offer an insight into the issues at the model system titanium (Ti-alloys) comprising Laser radiation and time aspects. Carburizing will be the central focus in another section. Surface treatments of steel and nonferrous materials will be explained and examined from different sides. As well, nitrocarburizing as a kind of hybrid process will be introduced. The chapter closes with referring to future developments and trends.
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Laser gas assisted Nitriding of ti alloys
Reference Module in Materials Science and Materials Engineering#R##N#Comprehensive Materials Processing, 2014Co-Authors: Peter Schaaf, J Kaspar, Daniel HocheAbstract:In general, titanium alloys are well known for their good mechanical and biocompatibility properties, but poor tribological behavior. Among other processes, Laser Nitriding has proven to be a promising way to improve the poor tribological behavior of titanium alloys. The current chapter will review the Laser-Nitriding technique with respect to enhancing the wear performance of titanium alloys. The chapter will explain why Laser gas–assisted Nitriding is a promising way to improve the wear resistance of titanium alloys. It will discuss different technological approaches to Laser Nitriding with respect to Laser equipment and the required nitrogen atmosphere, and how plasma may aid Nitriding efficiency. Further, specific characteristics of the solidification process during Laser Nitriding will be presented. Comprehensive results on the hardness and cavitation erosion resistance of Laser-nitrided titanium alloys will be mentioned, and the fatigue behavior of the Laser-nitrided alloy Ti–6Al–4V with derived correlations between the structure and mechanical properties as well as wear resistance will be shown. Finally, conclusions on the applicability and the benefit of the Laser-Nitriding process and directions for future developments in this field are given.
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Laser Nitriding: investigations on the model system TiN. A review
Heat and Mass Transfer, 2011Co-Authors: Daniel Hoche, Peter SchaafAbstract:Nitriding is a well known technique to improve properties of materials. The process utilizing Laser contains many different processes like heat transport and melting effects, diffusion and convection, which partially determine the synthesized coatings. This review concludes the research on titanium nitride synthesis in reactive ambient and draws conclusions for the general handling of the method. Afterwards, it becomes clear which and why, transport processes limit the coating properties.
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Marangoni Convection during Free Electron Laser Nitriding of Titanium
Metallurgical and Materials Transactions B, 2009Co-Authors: Daniel Hoche, Gerd Rapin, Sven Müller, Michelle Shinn, Elvira Remdt, Maik Gubisch, Peter SchaafAbstract:Pure titanium was treated by free electron Laser (FEL) radiation in a nitrogen atmosphere. As a result, nitrogen diffusion occurs and a TiN coating was synthesized. Local gradients of interfacial tension due to the local heating lead to a Marangoni convection, which determines the track properties. Because of the experimental inaccessibility of time-dependent occurrences, finite element calculations were performed, to determine the physical processes such as heat transfer, melt flow, and mass transport. In order to calculate the surface deformation of the gas-liquid interface, the level set approach was used. The equations were modified and coupled with heat-transfer and diffusion equations. The process was characterized by dimensionless numbers such as the Reynolds, Peclet, and capillary numbers, to obtain more information about the acting forces and the coating development. Moreover, the nitrogen distribution was calculated using the corresponding transport equation. The simulations were compared with cross-sectional micrographs of the treated titanium sheets and checked for their validity. Finally, the process presented is discussed and compared with similar Laser treatments.
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co2 Laser Nitriding of titanium
Journal of Physics D, 2008Co-Authors: Daniel Hoche, J Kaspar, M Raaif, F M Elhossary, N Z Negm, S M Khalil, A Kolitsch, S Mandl, Peter SchaafAbstract:Samples of pure titanium were Laser nitrided by continuous wave CO2 Laser irradiation in mixtures of nitrogen and argon gas with different ratios. In all cases, TiN formed in the surface. The properties and the characteristics of the processed samples were evaluated using a nanoindentation technique, optical microscopy, surface roughness measurements, x-ray diffraction and wear resistance measurements. It was found that the nitrogen content in the gas atmosphere has a massive effect on the microstructure and the mechanical properties of the Laser nitrided samples. For all treated samples, the mechanical properties improve with the nitrogen content in the gas atmosphere. Moreover, the thickest TiN layers with high values of the microhardness and good wear resistance were obtained for the titanium sample that was treated in 80% N2 and 20% Ar. In addition, the strain and the grain size of the coatings formed at the surface of the Laser nitrided titanium samples were determined from x-ray data.
T N Baker - One of the best experts on this subject based on the ideXlab platform.
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study of the surface layer formed by the Laser processing of ti 6al 4v alloy in a dilute nitrogen environment
Journal of Materials Processing Technology, 2001Co-Authors: Mohmad Soib Selamat, T N Baker, L M WatsonAbstract:Abstract Optical microscopy, scanning electron microscopy (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and a hardness tester were used to understand the microstructure and to characterise the phases formed in a Ti–6Al–4V alloy at different tracks and depths, produced by Laser Nitriding under a dilute nitrogen environment with a spinning beam. The results show that the solidified melt consists of α′-Ti and TiNx. Using XRD, x was determined to be 0.75 while from XPS, x lay in a range of 0.5–0.8. The melt zone showed a range of hardness of between 500 and 800 HV.
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the importance of preheat before Laser Nitriding a ti 6al 4v alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1999Co-Authors: T N BakerAbstract:Abstract Laser Nitriding of Ti–6Al–4V alloys has been developed to improve the surface properties. It is very important to control the processing conditions to produce a uniformly thick and crack-free surface layer. It has been found that the tendency to cracking is related to the volume fraction of titanium nitrides formed in the melt, and that preheating the material could avoid cracking. The present work, on a Ti–6Al–4V alloy, used a continuous 5 kW CO2 Laser with a spinning beam to investigate the effect of preheating by Laser glazing with overlapping tracks under argon prior to Nitriding. The change in the specimen temperature was estimated using the temperature recorded at the bottom of the specimen and the tendency to cracking examined for each individual track to determine the number of preheated tracks necessary to give a crack-free surface. When preheating by Laser glazing under argon was conducted prior to Nitriding, not only was the tendency to cracking reduced, but also a more uniform depth of the nitrided layer was produced.
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analysis of the phases developed by Laser Nitriding ti6al4v alloys
Acta Materialia, 1997Co-Authors: H Xin, L M Watson, T N BakerAbstract:Laser Nitriding Ti-6Al-4V (Ti64) alloys produces complex microstructures in the solidified melt pool developed during the processing. The microstructures contain mainly titanium nitrides and the {alpha} (or {alpha}{prime}) titanium phase in the matrix. Difficulties have been encountered in identifying the phases and examining the level of residual stress induced by the processing, because of the rapid cooling rate and the nitrogen concentration introduced during the Laser gas alloying which have a combined influence in determining the lattice parameters of the phases. The present work has investigated the microstructures formed mainly in a Ti64 alloy under pure argon and various nitrogen concentration environments during the processing, and also to a lesser extent commercial purity titanium (under 20 vol.% N only) studied for comparison purposes, using metallography, X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). A 5 kW continuous CO{sub 2} Laser with a spinning beam was used for the processing. As a result of this analysis, the identification of the TiN{sub 0.3} phase formed in a Ti64 alloy was confirmed, and the influence of the nitrogen concentration was elucidated. This is considered to be helpful for a better understanding of the Laser processing process.
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overlapping Laser tracks to produce a continuous nitrided layer in ti 6al 4v alloy
Journal of Materials Science, 1997Co-Authors: T N BakerAbstract:Continuously overlapping a number of tracks resulted in a significant influence in Laser Nitriding of a Ti–6Al–4V alloy. Not only was the microstructure in the overlapped areas found to be different from that in the non-overlapped areas, but also the microstructures developed by successive tracks could influence each other, especially for the first few Laser tracks. Moreover, the melt-pool depth and profile changed with the sequence number of the overlapped tracks. This resulted in a non-uniform surface layer and therefore non-uniform surface properties. The correlations between the processing parameters and melt-pool depth and hardness were determined, which leads to a method or principle for the design and control of the processing whenever track overlapping is required. A second important consideration is the effect of specimen thickness on the resultant microstructure. A CO2 continuous spinning Laser beam was used in this work.
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The effect of Laser surface Nitriding with a spinning Laser beam on the wear resistance of commercial purity titanium
Journal of Materials Science, 1996Co-Authors: S. Mridha, T N BakerAbstract:Laser Nitriding of commercial purity titanium using various concentrations of helium and nitrogen has been carried out. The surface appearance and microstructure of a treated layer were found to be dependent on the beam power density, interaction time, velocity and concentration of nitrogen. X-ray diffraction analyses have led to the conclusion that the dendrite layer in the resolidified zone of the nitrided specimens consisted mainly of TiN. The surface roughness of specimens after various Laser treatments was investigated by SEM and a surface profilemeter. Using optical microscopy, the dendrite TiN and needle-like structure in the melt zone, and the large grain structure in the heat affected zone, were investigated. The surface wear resistance of Nitriding CPTi was significantly improved compared to the untreated or Laser glazed material, and the wear data were found to correlate with scanning electron microscopy observations. Two layers, having different microstructures, thickness and abrasive wear resistance were identified. Further, 100% overlapping considerably improved the wear resistance of the nitrided specimens.
Seunghwan Lee - One of the best experts on this subject based on the ideXlab platform.
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elastic plastic properties of titanium and its alloys modified by fibre Laser surface Nitriding for orthopaedic implant applications
Journal of The Mechanical Behavior of Biomedical Materials, 2021Co-Authors: Hadi Asgharzadeh Shirazi, Chi Wai Chan, Seunghwan LeeAbstract:Abstract Laser Nitriding is one of the most promising approaches to improve wear resistance of Ti alloy surfaces and may extend the use in orthopaedic implants. In this study, three types of Ti alloys, namely alpha commercially pure Ti (“TiG2”), alpha-beta Ti–6Al–4V (“TiG5”), and beta Ti-35.5Nb-7.3Zr-5.7Ta (“βTi”), were subjected to an open-air Laser Nitriding treatment. Essential elastic-plastic mechanical properties including elastic modulus, hardness, elastic energy, plasticity index, and hardness-to-elasticity ratio of the Laser-treated Ti alloys were characterized using nanoindentation experiment. The results showed that the elastic modulus, hardness and elastic energy values of all Ti samples significantly increased in the nitrided layer compared to respective bare substrates for all three Ti materials. Across different Ti samples, βTi sustained its relatively lower elastic modulus, but presented comparable hardness, elastic energy, plasticity index, as well as hardness-to-elasticity ratio in the nitrided layer compared to the other two Ti alloys. Overall, amongst three medical grade Ti alloys in this study, βTi appeared as the most appealing candidate for joint replacement applications even solely in view of mechanical compatibility when combined with surface Laser Nitriding. Nevertheless, Laser Nitriding treatment in this study tended to cause a residual compressive stress on all Ti alloys as displayed by cracks developed in the nitrided layer and analyzed on βTi by X-ray diffraction (XRD) and further nanoindentation tests.
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a single parameter approach to enhance the microstructural and mechanical properties of beta ti nb alloy via open air fiber Laser Nitriding
Surface & Coatings Technology, 2020Co-Authors: Chi Wai Chan, Graham C Smith, Xianwen Chang, Mohammad Amin Bozorgzadeh, Seunghwan LeeAbstract:Abstract In this study, the idea of applying open-air Laser Nitriding to improve the microstructural and mechanical properties of beta Ti-45 at.% Nb alloy was demonstrated. Surface cracking after Laser Nitriding is one of the main reasons impeding direct translation of the Laser Nitriding technique from the laboratories to industries as cracks can be the weak points to initiate mechanical and corrosion failures in long-term usage. With proper selection of duty cycle (DC) between 40% (modulated mode) and 100% (continuous wave, CW mode) to control the Laser energy input and Laser-material-gas interaction time, the cracking problems of Laser Nitriding can be alleviated and even solved. A crack-free and uniformly gold-coloured nitrided surface was successfully obtained at the DC of 40% in this study. The morphology, microstructure, composition and mechanical properties of the nitrided samples were studied and analysed by optical microscopy (OM), scanning electron microscopy (SEM), SEM-energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Vickers micro-hardness tests. The OM results indicated that minimum overlapping between the Laser tracks would give desirable results to obtain the crack-free surface. The measurements from the SEM micrographs indicated the depth of the Laser-nitrided areas ranged between 22 and 43 μm. The XRD findings showed that a clear conversion of the TiNb surface to a nitride as a result of Laser Nitriding was observed. The maximum hardness, as measured by the Vickers method in cross-sections, lie in the range of 780 to 870 HV after Laser Nitriding. To summarise, control of DC to obtain a crack free and quality surface via fiber Laser Nitriding in open air is a simpler and quicker approach in comparison with the conventional substrate preheating and nitrogen (N) dilution approaches. The single-parameter approach is more efficient than parameter optimisation via design of experiments (DOE) employed in conventional methods.
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Fibre Laser Nitriding of titanium and its alloy in open atmosphere for orthopaedic implant applications: Investigations on surface quality, microstructure and tribological properties
Surface and Coatings Technology, 2017Co-Authors: Chi Wai Chan, Graham C Smith, Seunghwan Lee, Clare DonaghyAbstract:Laser Nitriding is known to be an effective method to improve the surface hardness and wear resistance of titanium and its alloys. However, the process requires a gas chamber and this greatly limits the practicability for treating orthopaedic implants which involve complex-shaped parts or curved surfaces, such as the tapered surface in a femoral stem or the ball-shaped surface in a femoral head. To tackle this problem, a direct Laser Nitriding process in open atmosphere was performed on commercially pure titanium (grade 2, TiG2) and Ti6Al4V alloy (grade 5, TiG5) using a continuous-wave (CW) fibre Laser. The effects of varying process parameters, for instance Laser power and nitrogen pressure on the surface quality, namely discolouration were quantified using ImageJ analysis. The optimised process parameters to produce the gold-coloured nitride surfaces were also identified: 40 W (Laser power), 25 mm/s (scanning speed), 1.5 mm (standoff distance) and 5 bar (N2pressure). Particularly, N2pressure at 5 bar was found to be the threshold above which significant discolouration will occur. The surface morphology, composition, microstructure, micro-hardness, and tribological properties, particularly hydrodynamic size distribution of wear debris, were carefully characterized and compared. The experimental results showed that TiG2 and TiG5 reacted differently with the Laser radiation at 1.06 μm wavelength in Laser Nitriding as evidenced by substantial differences in the microstructure, and surface colour and morphology. Furthermore, both friction and wear properties were strongly affected by the hardness and microstructure of titanium samples and direct Laser Nitriding led to substantial improvements in their wear resistant properties. Between the two types of titanium samples, bare TiG2 showed higher friction forces and wear rates, but this trend was reversed after Laser Nitriding treatments.
Klaus-peter Lieb - One of the best experts on this subject based on the ideXlab platform.
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Laser plume dynamics during excimer Laser Nitriding of iron
Journal of Applied Physics, 2003Co-Authors: M Han, Klaus-peter Lieb, E Carpene, Peter SchaafAbstract:On the time scale of tens to hundreds of nanoseconds, high intensity pulsed excimer Laser irradiation of iron in nitrogen atmosphere produces thin iron nitride layers with high nitrogen concentration. The Laser plasma, or Laser plume, which plays a crucial role in the complicated interactions within the Laser–plasma–metal system, depends strongly on the ambient nitrogen gas pressure. Its influence was investigated in the nitrogen gas pressure range from 0.05 bar to 10 bar. The nitrogen depth profiles were measured via the nuclear resonance reaction 15N(p,αγ)12C, while the phases formed in the surface layer were analyzed by conversion electron Mossbauer spectroscopy and x-ray diffraction. Utilizing sequentially 15N-enriched and natural nitrogen atmospheres, the evolution of the nitrogen depth profiles during the Laser Nitriding process was traced. The experimental results suggest that the one-dimensional Laser-supported combustion wave model reasonably describes the Laser–plume dynamics and the Nitriding e...
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Laser Nitriding of iron with Laser pulses from femtosecond to nanosecond pulse duration
Applied Physics Letters, 2002Co-Authors: Peter Schaaf, Klaus-peter Lieb, M Han, E CarpeneAbstract:Pulsed-Laser Nitriding is an attractive method to improve metal surface properties, such as hardness, wear, and corrosion resistance, with the advantage of simple experimental setup, rapid treatment, and precise process control. Here, the dependence of the Laser Nitriding process on the Laser pulse duration was investigated over five orders of magnitude in a series of experiments employing pulsed Lasers ranging from nanosecond excimer Laser pulses (55 ns) and Nd-doped yttrium aluminum garnet (Nd:YAG) Laser pulses (8 ns), to ultrashort Ti:sapphire Laser pulses (150 fs). The results revealed that for all Laser pulse durations and different wavelengths a large Nitriding effect was observed. The excimer Laser shows the highest Nitriding efficiency. The basic processes for the femtosecond pulsed Laser are not well understood but seem to result at least partly from processes within the plasma, whereas nanosecond Nitriding is based mainly on processes within the liquid/solid surface.
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Influence of the spatial Laser intensity distribution on Laser Nitriding of iron
Journal of Applied Physics, 1999Co-Authors: F Landry, Klaus-peter Lieb, Peter SchaafAbstract: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, Mossbauer 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 irr...
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origin of nitrogen depth profiles after Laser Nitriding of iron
Applied Physics Letters, 1999Co-Authors: Peter Schaaf, F Landry, Klaus-peter LiebAbstract: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.
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Laser Nitriding of iron influence of the spatial Laser intensity distribution
Applied Surface Science, 1999Co-Authors: F Landry, Peter Schaaf, M Neubauer, Klaus-peter LiebAbstract:Abstract Laser Nitriding of metals and alloys has attracted technological interest. Nevertheless, the basic Nitriding mechanisms are hardly understood. Here, a detailed analysis of the nitrogen profiles, laterally and in depth, the surface profiles and the microhardness is given in their respective dependence on the spatial Laser intensity profile. Irradiation with a homogenised Laser beam results in a more homogeneous lateral nitrogen distribution and a smooth surface as compared to irradiation with the inhomogeneous raw beam. Furthermore, the nitrogen saturation concentrations reach over 10 at.% in the case of the homogenised beam, which is significantly higher than the 3–4 at.% found for the raw beam. On the other hand, the hardness and the hardening depth are considerably larger for the raw beam treatment, which is explained by the high amount of the e-nitride phase formed only in this case.
F Landry - One of the best experts on this subject based on the ideXlab platform.
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modeling of nitrogen depth profiles in iron after Nitriding with a homogenized Laser beam
Applied Physics Letters, 2000Co-Authors: E Carpene, F Landry, Peter SchaafAbstract: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.
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Influence of the spatial Laser intensity distribution on Laser Nitriding of iron
Journal of Applied Physics, 1999Co-Authors: F Landry, Klaus-peter Lieb, Peter SchaafAbstract: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, Mossbauer 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 irr...
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origin of nitrogen depth profiles after Laser Nitriding of iron
Applied Physics Letters, 1999Co-Authors: Peter Schaaf, F Landry, Klaus-peter LiebAbstract: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.
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Laser Nitriding of iron influence of the spatial Laser intensity distribution
Applied Surface Science, 1999Co-Authors: F Landry, Peter Schaaf, M Neubauer, Klaus-peter LiebAbstract:Abstract Laser Nitriding of metals and alloys has attracted technological interest. Nevertheless, the basic Nitriding mechanisms are hardly understood. Here, a detailed analysis of the nitrogen profiles, laterally and in depth, the surface profiles and the microhardness is given in their respective dependence on the spatial Laser intensity profile. Irradiation with a homogenised Laser beam results in a more homogeneous lateral nitrogen distribution and a smooth surface as compared to irradiation with the inhomogeneous raw beam. Furthermore, the nitrogen saturation concentrations reach over 10 at.% in the case of the homogenised beam, which is significantly higher than the 3–4 at.% found for the raw beam. On the other hand, the hardness and the hardening depth are considerably larger for the raw beam treatment, which is explained by the high amount of the e-nitride phase formed only in this case.
