<p>    </p> <p>Electrical steels are one type of soft magnetic material. They are based on Fe-Si alloys and are widely used for magnetic cores in transformers and electric motors. It is well known that Fe- 6.5Si wt% is the most efficient composition; however, at such a high silicon concentration (6.5wt.% = 12.1 at.% Si in Fe), the poor workability of the alloy makes it unacceptable for industrial production via conventional sheet steel rolling processes. This problem was approached in two different ways. First, a machining-based approach that suppresses the mechanisms that lead to cracking during conventional rolling was implemented for processing of thin metal strips. Two related machining-based sheet production technologies called free machining (FM), and hybrid cutting extrusion (HCE) were used to produce strips of high resistivity electrical steel. The maximum strip width achieved was 50 mm, and it was produced with a combination of FM and light rolling with a surface roughness comparable to cold-rolled sheet surfaces. Second, a new experimental alloy Fe-4Si-4Cr wt% was developed with improved magnetic properties compared to ~ Fe-3.2Si wt% and outstanding workability. Results report that the new experimental alloy has an electrical resistivity of 85 ± 3 𝜇Ω ∙ 𝑐𝑚 which is higher than Fe-6.5%Si. Also, the results on the Fe-4Si-4Cr workability show that this new alloy can withstand 75% cold-rolled reduction. The magnetic properties characterization was done via standard stacked toroid testing, and results show that Fe-4Si-4Cr experimental alloy exhibits excellent magnetic performance with a reduction in core losses of 33% at 400 Hz compared to commercial alloys with ~ Fe-3.2Si wt%. Recrystallization kinetics and texture evolution in the experimental alloy were evaluated for traditionally rolled and machining-based samples. Results were used to construct annealing maps. These maps represent the stages of the annealing process for a range of temperature versus time conditions, i.e., the annealing maps are a graphical summary showing the different stages of the annealing process for the Fe-4Si-4Cr experimental alloy in the two conditions. Despite the significant differences in the deformation texture of the two conditions, the recrystallization kinetics were similar. Finally, the two conditions retained the as-deformed texture in the intermediate annealing but to a lesser degree after completing a full anneal. In the case of the rolled sample, it is possible to trace the original texture fibers (γ-fiber, the partial α-fiber, and the θ -fiber) in the fully annealed data, but the texture intensity is just 2.5 mrd. On the other hand, the texture of the fully annealed HCE sample changes as compared to the as-deformed condition, located close to (110)[112] with a surprisingly strong peak of ~ 25 mrd. </p>

Le domaine du refroidissement est en constante expansion, le système actuel est basé sur la compression/décompression des fluides. Face aux problèmes environnementaux et économiques que ce système présente (natures des fluides frigorigènes et leurs recyclages, nuisances sonores et vibratoires, réglementations contraignantes), de nouvelles solutions techniques alternatives émergent. Ainsi ce travail de thèse porte sur de nouveaux systèmes de refroidissement basés sur les effets électrocalorique et magnétocalorique, respectivement présents dans des films minces de polymère fluoré et dans des composites à matrice polymère et à charges magnétocaloriques. A travers des caractérisations physico-chimiques, électriques, électrocaloriques et magnétocaloriques ces travaux se proposent d’identifier l’origine de l’effet électrocalorique dans des films minces de terpolymère P(VDF-TrFE-CTFE) ferroélectrique relaxeur, mais également d’étudier l’influence de la dispersion des particules magnétocaloriques La(Fe,Si)H dans une matrice polymère de poly(propylène) sur le phénomène magnétocalorique. De plus, dans le cadre de cette thèse, un appareil de mesure directe de l’effet électrocalorique a été développé avec le Dr. Basso de l’INRIM de Turin. La comparaison avec la méthode de mesure indirecte permet d’aborder ce phénomène d’un point de vue thermodynamique afin de faire le point sur la validité des hypothèses thermodynamiques utilisées dans le cas d’un polymère ferroélectrique relaxeur. / The cooling sector is in constant expansion, the current system is based on the compression/decompression of fluids. In front of environmental and economic problems of this system (nature of frigorigen fluids and their recycling, noise and vibration issues, restrictive regulations), new alternative technological solutions emerge. Thus this thesis provides new cooling systems based on the magnetocaloric and electrocaloric effects respectively present in thin films of fluoropolymer and composites with polymer matrix and magnetocaloric loads. Through physicochemical, electrical, electrocaloric and magnetocaloric characterizations, this work intends to identify the origin of electrocaloric effect in thin terpolymer films P(VDF-TrFE-CTFE) which is a ferroelectric relaxor, but also to study the influence of the magnetocaloric particles La(Fe,Si)H dispersion in a polymer matrix of poly(propylene) on the magnetocaloric phenomenon. In addition, as part of this thesis, a direct measurement device of the electrocaloric effect was developed with Dr. Basso from the INRIM of Turin. The comparison with the indirect measurement method comes up with this phenomenon from a thermodynamic point of view to take stock of the validity of thermodynamic assumptions used in the case of a ferroelectric polymer relaxor.

Submitted by Bruna Rodrigues (bruna92rodrigues@yahoo.com.br) on 2016-09-21T14:11:42Z No. of bitstreams: 1 DissRDC.pdf: 7324446 bytes, checksum: 5e04b539c5f14da2f1e2fb0184498eb9 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-21T18:26:41Z (GMT) No. of bitstreams: 1 DissRDC.pdf: 7324446 bytes, checksum: 5e04b539c5f14da2f1e2fb0184498eb9 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-21T18:26:47Z (GMT) No. of bitstreams: 1 DissRDC.pdf: 7324446 bytes, checksum: 5e04b539c5f14da2f1e2fb0184498eb9 (MD5) / Made available in DSpace on 2016-09-21T18:26:54Z (GMT). No. of bitstreams: 1 DissRDC.pdf: 7324446 bytes, checksum: 5e04b539c5f14da2f1e2fb0184498eb9 (MD5) Previous issue date: 2014-07-28 / Não recebi financiamento / The homogenizing heat treatment of aluminium billets has direct influence on extrusion process productivity, surface quality and mechanical properties of extruded shapes. The homogenizing process parameters that impacts on metallurgical properties of 6063 alloys are: temperature, time and cooling rate. The maximum recommended homogenizing temperature for 6063 alloy is 590ºC. The minimum homogenizing time is 2,25h. The minimum cooling rate recommended is 400ºC/h. As for extrusion logs homogenizing process of 6063 6” diameter at Sapa Aluminium Brasil the furnace is a process bottleneck for logs production, this work has investigated about the possibility of time reducing without negative impacts on billet metallurgical properties and without detrimental impacts on productivity of extrusion process and quality of its products. This investigation was done by billet metallographic analysis, cold and hot mechanical tests and extrusion/anodizing trials for different homogenizing time conditions. The results have shown that the time reducing did not cause negative impacts for metallurgical neither for mechanical properties and because of that no detrimental effects for extrusion performance and surface finish and anodized quality was observed. Hence, was possible to decrease 20 minutes on homogenizing time and gain 14,5% of productivity on heat treatment process. / O tratamento térmico de homogeneização de tarugos de alumínio tem influência direta na produtividade do processo de extrusão, na qualidade superficial e nas propriedades mecânicas dos perfis extrudados. As variáveis do tratamento térmico da liga 6063 que influem na qualidade metalúrgica são: temperatura, tempo e taxa de resfriamento. Para liga 6063, a máxima temperatura recomendada de homogeneização é de 590ºC. O tempo mínimo para a homogeneização é de 2,25h. A taxa de resfriamento mínima recomendada é 400ºC/h. Como para o tratamento térmico de tarugos de 6” há um gargalo no forno de homogeneização da Sapa Aluminium Brasil, investigouse neste trabalho possibilidades de redução de tempo no processo de homogeneização evitando impactos negativos na qualidade metalúrgica dos tarugos e/ou na performance dos tarugos no processo de extrusão. Tal investigação foi feita através de análises metalográficas, ensaios mecânicos a frio (dureza e tração) e a quente (torção) e testes práticos no processo de extrusão/anodização para amostras retiradas de tarugos homogeneizados em diferentes condições de tempo de homogeneização. Os resultados obtidos mostraram que a redução no tempo de homogeneização não impactou negativamente na qualidade metalúrgica dos tarugos e nem em suas propriedades mecânicas a frio e que as pequenas variações ocorridas mantiveram-se dentro dos limites de especificação e não reduziram a performance do processo de extrusão bem como as propriedades mecânicas e qualidade superficial dos perfis extrudados. Com isso, foi possível reduzir 20 minutos no tempo de tratamento térmico de homogeneização e gerar um ganho de produtividade de 14,5% no processo.

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