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The objectives of this study were to examine the effect of strain and path change on the microstructural evolution of ultrafine grained interstitial free (IF) steel during equal channel angular extrusion (ECAE); to determine the mechanical properties; to observe the resulting texture; and to perform optical and electron microscopy of the resulting material. The effects of different routes of extrusion (A, B, C, C' and E), heat treatment and plastic strains from 1.15 to 18.4 were examined. Monotonous tensile testing was used to determine mechanical behavior of processed materials. X-ray diffraction and TEM analyses were performed to evaluate the effect of processing on texture and grain morphology. Hardness measurements were performed to determine recrystallization behavior of the processed material. Optical microscopy was conducted on heat treated samples to determine their grain size and refinement. Monotonous tensile testing of processed materials showed that there was significant strengthening after the first extrusion. Further processing resulted in increasing values of yield strength and ultimate tensile strength, with ductility at failure varying depending upon which processing route was used. The best tensile strength results were obtained after processing Routes 8C' and 16E, due to the significant grain refinement these routes produced. X-ray diffraction revealed increases in strength of preferred texture along the directions [111] and [001], perpendicular to the transverse plane, for all specimens that were processed using ECAE. TEM observations showed a consistent refinement of grain size as the amount of processing increased, especially within Routes C' and E. Hardness measurements of heat treated specimens showed that the onset of recrystallization occurred at approximately the same temperature of recrystallization as that of pure iron, 450°C. The recrystallization curves for all samples showed that grain growth begins at a temperature of around 700°C. The low carbon content of IF steel made optical microscopy challenging. The grain size of annealed materials becomes finer and more uniform, ranging between 60 and 90 μm2, at high strain levels under Routes C' and E, due to the many potential nucleation sites developed in highly worked material.

Aufgabe des Projektes war die Entwicklung einer neuen Technologie zur Probenpräparation für die Transmissions-Elektronenmikroskopie (TEM) auf der Basis der Ionenfeinstrahlbearbei-tung. Dazu wurden Prozesse der ionenstrahlgestützten Abtragung (Sputtern), der Abschei-dung, des Probenhandling sowie systemeigener Komponenten untersucht. Als Alternative zur Ga- Quelle wurde eine Flüssigmetall-Ionenquelle auf der Basis einer AuGeSi Legierung entwi-ckelt, charakterisiert und in der FIB 4400 eingesetzt. Um eine automatische Bearbeitung bei der Herstellung von TEM-Lamellen zu ermöglichen, erfolgte eine Modifikation der FIB-4400 Software. Das LabView Programm wurde entsprechend modifi-ziert und zusätzlich um nützliche Komponenten ergänzt. Abtragsraten auf der Basis der Volumenverlustmethode wurden experimentell bestimmt. Diese Werte dienen als Ausgangspunkt für eine weiter ausbaubare Datensammlung, die die entwi-ckelte Prozessautomatisierung verfeinert. Für den Tranfer von TEM -Lamellen, die aus dem Volumen präpariert werden, wurde ein spe-zieller lift-off Manipulator entwickelt, gebaut und getestet. Es wurde ein Angebotskatalog erarbeitet, der anhand von Applikationsbeispielen mit verschie-denen Anforderungen (raue Oberflächen, Hochauflösung, poröse Materialien, Materialien mit verminderter Leitfähigkeit) die Kooperationsmöglichkeiten im Dresdener Raum im Rahmen des Materialforschungsverbundes aufzeigt.

No description available.

Zugl.: Aachen, Techn. Hochsch., Diss., 2008

Inaug. - Diss. : Philosophie : Frankfurt am Main ; 1982. - Graphie fautive dans le titre : " traditionnelle " pour " traditionnelle ". - Bibliogr. p.331-334. -

abstract: Semiconductor nanowires (NWs) are one dimensional materials and have size quantization effect when the diameter is sufficiently small. They can serve as optical wave guides along the length direction and contain optically active gain at the same time. Due to these unique properties, NWs are now very promising and extensively studied for nanoscale optoelectronic applications. A systematic and comprehensive optical and microstructural study of several important infrared semiconductor NWs is presented in this thesis, which includes InAs, PbS, InGaAs, erbium chloride silicate and erbium silicate. Micro-photoluminescence (PL) and transmission electron microscope (TEM) were utilized in conjunction to characterize the optical and microstructure of these wires. The focus of this thesis is on optical study of semiconductor NWs in the mid-infrared wavelengths. First, differently structured InAs NWs grown using various methods were characterized and compared. Three main PL peaks which are below, near and above InAs bandgap, respectively, were observed. The octadecylthiol self-assembled monolayer was employed to passivate the surface of InAs NWs to eliminate or reduce the effects of the surface states. The band-edge emission from wurtzite-structured NWs was completely recovered after passivatoin. The passivated NWs showed very good stability in air and under heat. In the second part, mid-infrared optical study was conducted on PbS wires of subwavelength diameter and lasing was demonstrated under optical pumping. The PbS wires were grown on Si substrate using chemical vapor deposition and have a rock-salt cubic structure. Single-mode lasing at the wavelength of ~3000-4000 nm was obtained from single as-grown PbS wire up to the temperature of 115 K. PL characterization was also utilized to demonstrate the highest crystallinity of the vertical arrays of InP and InGaAs/InP composition-graded heterostructure NWs made by a top-down fabrication method. TEM-related measurements were performed to study the crystal structures and elemental compositions of the Er-compound core-shell NWs. The core-shell NWs consist of an orthorhombic-structured erbium chloride silicate shell and a cubic-structured silicon core. These NWs provide unique Si-compatible materials with emission at 1530 nm for optical communications and solid state lasers. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

abstract: The goal of this research was to reduce dislocations and strain in high indium content bulk InGaN to improve quality for optical devices. In an attempt to achieve this goal, InGaN pillars were grown with compositions that matched the composition of the bulk InGaN grown on top. Pillar height and density were optimized to facilitate coalescence on top of the pillars. It was expected that dislocations within the pillars would bend to side facets, thereby reducing the dislocation density in the bulk overgrowth, however this was not observed. It was also expected that pillars would be completely relaxed at the interface with the substrate. It was shown that pillars are mostly relaxed, but not completely. Mechanisms are proposed to explain why threading dislocations did not bend and how complete relaxation may have been achieved by mechanisms outside of interfacial misfit dislocation formation. Phase separation was not observed by TEM but may be related to the limitations of the sample or measurements. High indium observed at facets and stacking faults could be related to the extra photoluminescence peaks measured. This research focused on the InGaN pillars and first stages of coalescence on top of the pillars, saving bulk growth and device optimization for future research. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2011

Dissertação (mestrado profissional) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Métodos e Gestão em Avaliação, Florianópolis, 2015. / Made available in DSpace on 2016-05-24T17:41:13Z (GMT). No. of bitstreams: 1 338285.pdf: 2513554 bytes, checksum: fdded9a350387a19f94cadf3fa640b4d (MD5) Previous issue date: 2015 / No presente estudo utilizou-se uma modelagem multidimensional do Exame Nacional do Ensino Médio (ENEM), por meio da Teoria da Resposta ao Item multidimensional (TRIM) com o objetivo de melhor compreender o aprendizado do avaliado. O ENEM (1998-2008) era um exame interdisciplinar estruturado por cinco competências expressas por 21 habilidades. Assim, por ser uma avaliação em que não podemos, a priori, considerar unidimensional, realizou-se uma análise da dimensionalidade e interpretação de suas dimensões. Inicialmente foi analisado o conjunto de 63 itens da prova amarela do ENEM 2001 em uma amostra de 10.000 respondentes. Nessa fase foi abordada a dimensionalidade da prova e a escolha do modelo que melhor se ajustava aos dados. Em seguida, foi ajustado um modelo multidimensional da TRI, com cinco dimensões, e foi feita uma relação das competências da prova do ENEM com os fatores, por meio da analise dos itens da prova. Nesta relação ficou evidenciada uma relação mais expressiva das cinco competências com somente três dimensões. Por último, foi feita uma comparação dos avaliados que acertaram 40, 50 e 60 itens na prova, através da analise da porcentagem do número de acerto em cada competência e escores, estimados por meio dos modelos multidimensionais da TRI, em cada uma das cinco dimensões, com a finalidade de interpretar o desempenho desses avaliados.<br> / Abstract : In the present study we used a multi-dimensional modeling of the National Examination of Secondary Education (ENEM), through multidimensional item response theory (MIRT) in order to better understand the learning assessed. The ENEM (1998-2008) was an interdisciplinary examination structured for five competencies expressed by 21 skills. So, being an assessment, we can not, a priori, to consider one-dimensional, there was an analysis of dimensionality and interpretation of its dimensions. Initially we analyzed the set of 63 items Yellow proof of ENEM 2001 on a sample of 10,000 respondents. In this phase it addressed the dimensionality of proof and choosing the model that best fit the data. Then a multidimensional model of TRI was adjusted with five dimensions, and was made a list of ENEM proof competencies with the factors through the analysis of the test items. This relationship was evidenced a more significant relationship of the five competencies with only three dimensions. Finally, a comparison of the assessed was made that hit 40, 50 and 60 items in the race through the analysis of the percentage of the hit number in each jurisdiction and scores, estimated by the multidimensional IRT models in each of the five dimensions in order to interpret the performance of these reviews.