Konventionelles Laserstrahlschweißen von Halbzeugen aus höherfesten Stahlfeinblechen führt zum drastischen Verlust an Umformbarkeit im Schweißnahtbereich. Durch integrierte induktive Erwärmung können der Temperaturverlauf beim Schweißen modifiziert, die Verbindungseigenschaften beeinflusst und die Umformbarkeit verbessert werden. Die Zusammenhänge zwischen Prozessparametern und mechanischen Verbindungseigenschaften werden beschrieben und Anwendungspotenziale aufgezeigt.

Made available in DSpace on 2014-10-09T12:34:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:21Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:34:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:03:21Z (GMT). No. of bitstreams: 0 / Dentre as principais propriedades que devem ter os implantes ortopédicos, tem-se a resistência à corrosão. Os implantes passam por um processo de marcação antes de serem esterilizados, cuja função é prover a identificação e rastreabilidade do produto. Este trabalho teve o objetivo de avaliar o efeito de duas técnicas de marcação, mecânica e a laser, na resistência à corrosão do aço inoxidável austenítico ABNT NBR ISO 5832-1, um dos mais utilizados no Brasil na fabricação de próteses. Os ensaios eletroquímicos realizados constaram de monitoramento do potencial de corrosão em circuito aberto, espectroscopia de impedância eletroquímica, determinação das propriedades eletrônicas do filme passivo via abordagem de Mott-Schottky, medidas de polarização potenciodinâmica cíclica e a técnica eletroquímica de varredura com eletrodo vibrante (SVET), à temperatura de 37°C. O eletrólito utilizado foi uma solução salina de fosfato tamponada de pH 7,4. Foram realizadas análises por microscopia óptica, microscopia eletrônica de varredura, SEM-FEG e, microscopia eletrônica de transmissão. Constatou-se que a marcação a laser diminui a resistência à corrosão por pite ao alterar significativamente as características do filme passivo, quando comparada à marcação mecânica e ao material sem marcações. Foram observadas inclusões de óxidos que foram colocadas em relevo pela dupla incidência do feixe de laser. O ataque da matriz de aço no entorno das inclusões de óxidos promove a formação de micro-frestas entre esta e as inclusões favorecendo o crescimento e a propagação do pite. Este foi o mecanismo proposto para explicar a maior susceptibilidade à corrosão localizada nas áreas afetadas pela marcação a laser. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

O desenvolvimento dos veículos atuais vem sendo impulsionado pela necessidade de redução de massa associada com o aumento da segurança para os passageiros. Na procura de novos materiais e processos para atender estas exigências, os aços bifásicos ferrítico-martensíticos ou DP vêm se destacando entre os aços avançados de alta resistência (AHSS), por apresentar elevada resistência mecânica e boa ductilidade. Da mesma forma, a soldagem a laser vem se mostrando promissora para junção desta classe de materiais. Este processo permite unir os aços DP com boa qualidade metalúrgica sem significativas distorções dimensionais. Embora os aços DP apresentem boa soldabilidade, um amolecimento localizado na zona afetada pelo calor (ZAC) também é observado, especialmente no aço DP1000, que apresenta elevada fração de martensita. Desta forma, esta Tese propõe a soldagem a laser do aço DP1000 de espessura 1,80 mm, seguida de uma sistemática caracterização microestrutural, visando a produção de juntas soldadas suficientemente resistentes. Para isto, foram produzidos cordões numa chapa de aço DP1000, variando a potência nominal de soldagem entre 0,4 e 2,0 kW e a velocidade de soldagem entre 20 e 150 mm/s. A caracterização microestrutural foi conduzida com o auxílio das técnicas de microscopia óptica (MO), microscopia eletrônica de varredura (MEV), difração de raios X (DRX) e difração de elétrons retroespalhados (EBSD). As juntas soldadas mais representativas foram submetidas a ensaios de dureza Vickers e tração uniaxial. Os resultados mostram que é possível produzir juntas soldadas resistentes no aço DP1000. Todavia, é fundamental que a combinação de parâmetros gere soldas com penetração total e mínima largura de ZAC, limitando a quantidade de amolecimento da martensita prévia e a fração volumétrica de austenita retida. Na presente Tese, os melhores resultados foram obtidos para uma potência de 2,0 kW e velocidade de 150 mm/s. / The development of modern vehicles has been driven by the need of mass reduction associated with the increase of the safety of passengers. In the search for new materials and processes to meet these requirements, ferritic-martensitic dual-phase (DP) steels are potential candidates among advanced high-strength steels (AHSS), because of their high mechanical strength and good ductility. In that sense, laser beam welding has been shown promising for joining this class of materials. This process allows joining DP steels with good metallurgical quality without large dimensional distortions. Although DP steels show good weldability, a localized softening in the heat affected zone (HAZ) is also observed, especially in DP1000 steel which contains large amounts of martensite. Thus, laser beam welding has been performed in DP1000 steel with thickness of 1.80 mm, followed by a systematic microstructural characterization, aiming at the production of resistant welded joints. For this, bead-on-plate welds were carried out in DP1000 steel, varying the welding power between 0.4 and 2.0 kW and the welding speed between 20 and 150 mm/s. The microstructural characterization was conducted with the aid of light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD). The most representative welded joints were tested for Vickers hardness and uniaxial tensile test. Results show that it is possible to produce sound and resistant welded joints in DP1000 steel. However, it is critical that the combination of parameters allows the obtainment of welds with full penetration and minimum HAZ width, limiting the amount of softening of prior martensite and the volume fraction of retained austenite. In the present Thesis, this was achieved using a power of 2.0 kW and a welding speed of 150 mm/s.

Laser surface treatment of engineering ceramics offers various advantages in comparison with conventional processing techniques and much research has been conducted to develop applications. Even so, there still remains a considerable gap in knowledge that needs to be filled to establish the process. By employing a fibre laser for the first time to process silicon nitride (Si3N4) and zirconia (ZrO2) engineering ceramics, a comparison with the CO2 and a Nd:YAG lasers was conducted to provide fundamental understanding of various aspects of the laser beam-material interaction. Changes in the morphology, microstructure, surface finish, fracture toughness parameter (K1c) were investigated, followed by thermal finite element modelling (FEM) of the laser surface treatment and the phase transformation of the two ceramics, as well as the effects of the fibre laser beam parameter - brightness (radiance). Fibre and CO2 laser surface treatment of both Si3N4 and ZrO2 engineering ceramics was performed by using various processing gases. Changes in the surface roughness, material removal, surface morphology and microstructure were observed. But the effect was particularly more remarkable when applying the reactive gases with both lasers and less significant when using the inert gases. Microcracking was also observed when the reactive gases were applied. This was due to an exothermic reaction produced during the laser-ceramic interaction which would have resulted to an increased surface temperature leading to thermal shocks. Moreover, the composition of the ceramics was modified with both laser irradiated surfaces as the ZrO2 transformed to zirconia carbides (ZrC) and Si3N4 to silicon dioxide (SiO2) respectively. The most appropriate equation identified for the determination of the fracture toughness parameter K1c of the as-received, CO2 and the fibre laser surface treated Si3N4 and ZrO2 was K1c=0.016 (E/Hv) 1/2 (P/c3/2). Surfaces of both ceramics treated with CO2 and the fibre laser irradiation produced an increased K1c under the measured conditions, but with different effects. The CO2 laser surface treatment produced a thicker and softer layer whereas the fibre laser surface treatment increased the hardness by only 4%. This is inconsiderable but a reduction in the crack lengths increased the K1c value under the applied conditions. This was through a possible transformation hardening which occurred within both engineering ceramics. Experimental findings validated the generated thermal FEM of the CO2 and the fibre laser surface treatment and showed good agreement. However, a temperature difference was found between the CO2 and fibre laser surface treatment due to the difference in absorption of the near infra-red (NIR) wavelength of the fibre laser being higher than the mid infra-red (MIR) wavelength of the CO2 laser. This in turn, generated a larger interaction zone on the surface that was not induced further into the bulk, as was the case with the fibre laser irradiation. The MIR wavelength is therefore suitable for Viability and Characterization of the Laser Surface Treatment of Engineering Ceramics 3 the surface processing of mainly oxide ceramics and surface treatments which do not require deep penetration. Phase transformation of the two ceramics occurred at various stages during the fibre laser surface treatment. The ZrO2 was transformed from the monoclinic (M) state to a mixture of tetragonal + cubic (T+C) during fibre laser irradiation and from T+C to T and then a partially liquid (L) phase followed by a possible reverse transformation to the M state during solidification. The Si3N4 transformed to a mixture of α-phase and β-phase (α→ α+β) followed by α+β and fully transforms from α+β → β-phase. What is more, is a comparison of the fibre laser-beam brightness parameter with that of the Nd:YAG laser. In particular, physical and microstructural changes due to the difference in the laser-beam brightness were observed. This research has identified the broader effects of various laser processing conditions, as well as characterization techniques, assessment and identification of a method to determine the K1c and the thermal FEM of laser surface treated engineering ceramics. Also, the contributions of laser-beam brightness as a parameter of laser processing and the influence thereof on the engineering ceramics have been identified from a fundamental viewpoint. The findings of this research can now be adopted to develop ceramic fuel cell joining techniques and applications where laser beam surface modification and characterization of engineering ceramics are necessary.

La turbulence atmosphérique générée par une différence de température entre le sol et l'atmosphère, provoque des effets sur les ondes optiques et présente un grand intérêt scientifique depuis de nombreuses années. Les distorsions du front d'onde optique induites par le résultat de la turbulence atmosphérique génèrent un étalement du faisceau au-delà de celles dues à la diffraction pure, à des variations aléatoires de la position du centre de gravité du faisceau, et à une répartition aléatoire de l'énergie du faisceau qui conduit à des fluctuations de l’irradiance.Ces effets ont des conséquences sur les communications optiques en espace libre (OFS), la désignation de cible, le LiDAR hyper spectral, et d'autres applications qui nécessitent la transmission d'ondes optiques dans l'atmosphère sur une grande portée.Tout au long de cette thèse, nous introduisons le concept général de la turbulence, en se concentrant sur la turbulence atmosphérique. Diverses expériences ont été réalisées, par exemple, la propagation de deux faisceaux parallèles dans les conditions de l'optique géométrique pour l'étude des paramètres de turbulence optiques. La même configuration optique a été utilisé pour étudier la meilleure fréquence d'échantillonnage pour la turbulence optique. En outre, nous avons indirectement mesuré l'évapotranspiration de couverts végétaux, pour laquelle nous tenons compte des fluctuations de l'indice de réfraction de la turbulence à travers les variations d’intensités du faisceau laser. Enfin, certaines expériences qui considèrent de nouvelles formes spatiale ou spectrale du faisceau ont également été développées, telles que le saut de mode et un super continuum spectral respectivement, montrant une réduction expérimentale des fluctuations de l'irradiance induite par la turbulence. Ces faisceaux ont une meilleure performance comme émetteur d'informations pour la communication optique en espace libre. / Atmospheric turbulence, generated by a differential temperature between the Earth's surface and the atmosphere, causes effects on optical waves that have been of great interest to scientists for many years. Wave front distortions in the optical wave induced by atmospheric turbulence result in a spreading of the beam beyond that due to pure diffraction, random variations of the position of the beam centroid, and a random redistribution of the beam energy within a cross section of the beam leading to irradiance fluctuations. Those effects have far-reaching consequences on astronomical imaging, free space optics (FSO) communications, remote sensing, laser satellite communication, astronomical imaging, adaptive optics, target designation, hyperspectral LiDAR, and other applications that require the transmission of optical waves through the atmosphere. Throughout this thesis, we introduce a globally concept of turbulence, focusing in atmospheric turbulence.Diverse experiments have been carried out, for instance, the propagation of two parallel thin beams under geometrical optics condition for studying the parameters of optical turbulence, and besides, the same optical configuration was used to investigate the best sampling rate for optical turbulence. Furthermore, we have measured evapotranspiration by remote sensing, in which we have heeded the fluctuations of the refractive index through the intensities of the turbulence. Finally, experiments which involve a new beam are also developed, such as phase-flipped Gaussian beam. This beam shows an experimental reduction on its irradiance fluctuations induced by the turbulence, which means that it has a high performance in optical communications. The experimental reduction aforementioned is proved through the comparison with the theory developed.

The intention of this master‘s thesis is the measurment of relative variance of optical intensity. In the first place, I have been studied Kolmogorov cascade theory of turbulence and relative variance of optical intensity . In addition, I have been deal with turbulent cells, Gaussian beam, Top Hat beam and influence of the atmospheric turbulences on the intensity profile of the laser beam. Lastly I have been measured determine influence of the atmospheric turbulences on the intensity profile of the laser beam and I have been calculated relative variance of optical intensity. I have suggested the optimum beam profile in the turbulent atmosphere from acquired data.

Diploma thesis deal with design of laser beam shaping system. The theoretical part presents basic information about the light spread lika the optical beams. There are also properties of optical and optoelectronic components that are used for shaping the laser beam. The next section provides basic molding methods, their principles and qualities. In the last, experimental, part is first introduced designed computer algorithm, which is then used to calculate the quality parameters shaped laser beams. Following, there are presented the results of measurements and calculations for some of these methods.

This thesis deals with the possibilities of cutting strong steel metal sheets by means of laser and problems rising from the incision, their technological investigation. The basic philosophy consists on the research of the interaction between laser bunch and material, depending on the position of focal poin and sequential results in spec. heat. It determines the main parametres of the incision (from the total quantities and matematical description) which have the biggest effect on the occurence of wide cut and perhaps even on the quality of products and consequential optimalization of these quantities.

Analysis of a laser beam possibilities. Technology of components‘ structure. Design of disposition of a laser’s workplace. Design of a folding brake workplace. Concept of stock holding. Operating expenses of a laser technology. The technical – economic summary.