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A method has been developed to produce grain sizes as low as 5µm in β-CuAlNi alloys and the effect of grain size on mechanical and strain-memory properties was studied. The thermomechanical treatment procedure involved two. sequential warm working and recrystallization steps at 600° C and 800° C respectively on eutectoid alloys. Three different eutectoid alloys, two with Ms temperature of around 0°C and one with Ms = 220° C were used for the present studies. Even at fine grain sizes, the specimens produced were of single β- phase type without any second phases. Two-stage characteristic stress-strain curves were obtained for most of the specimens in both the strain memory and pseudoelastic states. It was found that the ultimate tensile strength and strain to failure increased with decreasing grain size according to a Hall-Petch relationship down to a grain size of 5µm with the exception of one alloy. Fracture strengths of 1,200 MPa and fracture strains of 10% could be obtained. It was found that the major recovery mode, whether pseudoelastic or strain memory, did not have any significant effect on the total recovery obtained. Recovery properties were not affected significantly by decreasing grain size. Approximately 86% recovery could be obtained for an initial applied strain of 5% at a grain size of around 10µm. Grain refinement increased the fatigue life considerably, possibly due to high ultimate fracture strength and ductile fracture mode. Fatigue life of 275,000 cycles could be obtained for an applied stress of 330 MPa and a steady state strain of 0.6%. Most of the fractures are due to intergranular-type brittle fracture. At fine grain sizes, transgranular-type brittle fracture and microvoid coalescence-type ductile fracture dominated the fracture mode. Oxygen segregation at grain boundaries is the possible explanation for the different mechanical properties shown by different alloys in the present work by being a major factor in causing intergranular-type fracture. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

En milieu extérieur les objets en cuivre et alliages cuivreux subissent des altérations qui entraînent des modifications physiques et esthétiques de l’œuvre. Pour limiter ces dégradations il convient de réduire les interactions entre la couche de corrosion et son environnement d’exposition en appliquant un traitement de protection. Ce travail de thèse propose d’étudier deux types de traitements de protection : une cire microcristalline (cire Cosmolloïd) et des solutions de décanoate (NaC10 et HC10). Pour cette étude des échantillons « modèles » en cuivre naturellement corrodés ont été utilisés afin de développer une méthodologie analytique visant à étudier le mode d’action et la pénétration des deux types de traitement de protection appliqués sur des couches de corrosion. Grâce à cette méthodologie il a été observé que bien que l’action en surface varie en fonction de la nature du traitement, la pénétration quant à elle semble dépendre essentiellement de son mode d’application.Un travail de remise en corrosion des échantillons traités a également été mené en conditions d’immersion et en corrosion atmosphérique sous cyclage d’humidité relative, à l’aide de traceurs isotopiques (D2O et 18O), afin d’évaluer qualitativement et de comparer l’efficacité des différents traitements de protection. Des dégradations sous UVB et lixiviation des traitements ont également permis d’étudier la tenue des traitements dans des conditions d’exposition extérieure. La détection des traceurs isotopiques dans les couches de corrosion par ToF-SIMS et analyses NRA, bien que n’ayant pas permis de conclure à une meilleur efficacité d’un type de traitement par rapport à l’autre, ont tout de même révélé des différences de tenues. Tandis que la cire microcristalline se dégrade rapidement sous rayonnement UVB par rapport au traitement HC10, le phénomène de lixiviation semble en revanche dégrader plus rapidement un traitement demeuré en surface de la couche de corrosion. / In outdoor environment copper and copper alloys objects undergo degradations that lead to physical and aesthetic modifications of the artwork. To limit these changes interactions between the corrosion layer and its exposure environment should be reduced by applying protective treatment. This project proposes to study two types of protective treatments: microcrystalline wax (Cosmolloïd wax) and decanoate solutions (NaC10 and HC10). For this study, naturally corroded copper "model" samples were used to develop an analytical methodology to study the action and penetration of the two types of protective treatment applied to corrosion layers. This methodology allowed to observe that although the surface action changes according to the nature of the treatment, the penetration seems to depend essentially on its application.Re-corrosion experiments of treated samples was also carried out under immersion conditions and atmospheric corrosion with relative humidity cycling, both using isotopic tracers (D2O and 18O) in order to qualitatively evaluate and compare the effectiveness of the protective treatments. Degradations under UVB and leaching off treatments also lead to a study of their behavior under conditions of external exposure. The detection of isotopic tracers in the corrosion layers by ToF-SIMS and NRA analysis, even though it wasn’t allow to conclude to a better effectiveness of one treatment over the other, nevertheless revealed holding differences. While microcrystalline wax degrades rapidly under UVB radiation compared to HC10 treatment, the leaching phenomenon seems to degrade more rapidly a treatment remaining on the surface of the corrosion layer.

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This dissertation seeks to establish the possible provenance of copper and copper alloys used at Great Zimbabwe (1000-1700CE) to infer local and regional circulation circuits. It employs archaeological, archival, and geochemical methods to characterize samples of 26 wound wire bracelets, bangles, anklets, necklaces, and other forms of expressive and decorative wear excavated from the southern terrace, (Hill Complex) at Great Zimbabwe. The samples were macroscopically, microscopically, chemically and isotopically characterized to understand the technique of manufacture, chemical composition, lead isotopic ratios and the starting composition of uranium and thorium in relation the model ages. The Pb isotopic data calculated 238U/204Pb (μ), 232Th/ 238U(κ) ratios and estimated model ages (T) were compared with published lead isotopic ratios from various ore samples from central and southern Africa. Within opportunities afforded by the historical record and limitations imposed by small sample sizes especially of the comparative geology, indications are that the studied objects were produced using ores matching the Cu-Ni mineralization at Empress Mine (in Zimbabwe), Cu Ag and Cu Pb Zn Ag mineralization associated with the Kundelungu Plateau (bordering Zambia and Democratic Republic of Congo). This suggests that Great Zimbabwe participated directly and indirectly in the vibrant micro, regional and interregional circulation of copper and other resources. Future work, must however, add more trace element data from the objects and increase the number of samples from ancient mines and other sites to develop a fuller picture of the movement of copper in Iron Age southern Africa through space and time.

When slow wear mechanisms are studied it is important to examine slower processes, such as diffusion. Such processes can have a significant impact over time and can cause other phases to form, which can have a large effect on the wear. This thesis has investigated the diffusion that is believed to take place between brass and cemented carbide tools. This was done to further the understanding of the slow atomic wear which if properly understood, could lead to solutions that would increase the lifetime of the tools. The diffusion pairs were made from a tribological contact and then heat treated to speed up the diffusion process. Different temperatures and times were tested, from 400 °C for 3 h to 700 °C for 24 h. The samples were analysed with SEM and EDS both before and after the heat treatment, to see if diffusion had taken place. However, because of many unexpected processes and reactions the analysis could not confirm that diffusion had taken place. The transportation of Cu at the higher temperatures was much faster than expected, and in some samples, Cu could not be detected after the heating. Since the surface was so mobile, the slower diffusion process did not have time to take place. Many improvements for future experiments are suggested to be able to observe the diffusion, such as depositing a thin film or adding more work material.

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O objetivo desse trabalho foi o de obter-se fios de cobre em três composições químicas distintas da liga Cu-Mg a partir de cobre eletrolítico e de magnésio. Foram avaliadas as etapas envolvidas, começando com a fusão de botões em forno a arco na composição do eutético Cu-Mg, diluição destes botões em forno resistivo, vazamento em lingoteira de cobre, seguido de tratamento térmico de homogeneização em forno resistivo a 910 ºC por 2 h. Os tarugos foram posteriormente trabalhados mecanicamente por forjamento rotativo seguido de um passe final de acabamento por trefilação, para obtenção do fio. As análises químicas realizadas nos lingotes indicaram que a rota de preparação dos fios mostrou-se adequada aos estudos em escala de laboratório, suficiente para a confecção de fios com área de seção transversal de 4 mm2 por 10 m de comprimento, para cada composição de liga. Os fios foram caracterizados mecanicamente por ensaio de tração e de dureza após tratamento térmico de recristalização a 510 ºC por 1 h. Os fios também tiveram as condutividades elétricas medidas na condição recristalizada e os resultados foram comparados com dados experimentais da literatura. Os materiais obtidos mostraram-se adequados à utilização como fio condutor de energia elétrica. Os limites de escoamento e de resistência a tração tiveram seus valores melhorados com o aumento do teor de magnésio na liga, 11 % e 24 %, respectivamente, enquanto houve queda nos valores de condutividade elétrica para cerca de 60 % IACS (International Annealed Copper Standard). / The aim of this work was to obtain copper wires in three different chemical compositions starting from electrolytic copper and magnesium. The mains steps were evaluated, starting from the melting of small eutectic cooper-magnesium specimens in an electric arc furnace, followed by further dilution of this buttons in a resistive furnace and casting it in a copper mould. The as cast billets were homogenized in a resistive furnace at 910 ºC for 2 h. The billets were mechanically cold worked by swaging and a final drawing step to attain a round shape and a reasonable surface quality. The cast ingots chemical analysis indicated that the processing route showed to be adequate, in laboratory scale, to obtain wires with cross sectional area of 4 mm2 and 10 m in length. The wires in both conditions as cold worked and after a recovering heat treatment at 510 ºC for 1 h, were mechanically characterized by tensile testing and hardness. The wires had also the electric conductivity assessed in the recovered heat-treated state and the results were compared to the literature data. The obtained material showed to be adequate to be used as electric conductor. The yield strain and ultimate tensile strength were improved with the increasing amount of Mg in the alloy, 11 % and 24 %, respectively, while the electric conductivity decreased to 60 % IACS (International Annealed Copper Standard).

It is well known that texture and microstructure play a crucial role in determining properties of metallic materials. The evolution of microstructure and texture during deformation and annealing of copper and some copper base alloys have been investigated to some extent. However, the knowledge about the role of the mode of deformation, particularly different variants of rolling deformation, is still very limited for deformation and annealing texture of two-phase copper alloys. Therefore it appeared important to study the influence of deformation path (in the present case, mode of rolling) on texture and microstructure in two-phase copper alloy Cu-40Zn alloy. Hot rolled bar of Cu-40Zn alloy (as-received material) was subjected to unidirectional and cross rolling ( multi-step cross-rolling) at room temperature with strain per pass (true strain) being constant for each step. In multi-step cross-rolling, the rolling direction was altered (rotated by 90°)after each pass. Strains corresponding to rolling reduction of 50% and 80% were given to as-received material through each of the different mode of rolling. In a second route, the as-received material was solution treated at 800°C for 4 hours first and then subjected to rolling in the same manner as above. A piece was cut from each of the as-rolled materials and was subjected to annealing at 560°C for one hour for recrystallization. The bulk textures were determined by measuring the pole figures at the center of the rolled as well as the annealed specimen using X-ray texture goniometer based on Schultz reflection geometry. Three dimensional texture analyses were carried out using the method of orientation distribution function(ODF). Micro-textures and associated microstructural parameters were determined using a Field Emission Gun Scanning Electron Microscope(FEG-SEM) operated at 20KV, equipped with Electron back scattering detector(EBSD). In the experimental material, texture was examined for both the α (fcc) and the β (ordered cubic) phases. In the present investigation, α phase of unidirectional rolled as-received material had Bs {011}<112> orientation as the strongest component whereas for multi-step cross rolled material P(BND) {011}<111> orientation had the maximum intensity, which could be obtained by rotating the Bs orientation and about ND.The texture development of β phase of as-received unidirectional rolled sample could be understood in terms of relaxed constraints Taylor model. The initial texture had a pronounced effect on texture development of α phase for solution treated alloy during deformation. This material exhibited very strong P(BND) {011}<111> orientation for unidirectional as well as for multi-step cross rolling. For cross rolled alloys, this orientation is promoted by two factors simultaneously, (i) initial texture and (ii) special attributes of cross rolling process. The volume fraction of cube oriented grains was very low for all recrystallized samples because of dominance of Bs orientation in the deformation texture plus formation of shear bands in the microstructure. The texture of β phase for unidirectionally rolled solution treated alloy got sharpened on annealing. However, strength of texture decreased with increasing deformation. Grain boundary (and CSL boundary) analyses were carried out with EBSD data. These analyses indicated that all the recrystallized samples had a high number of Σ3 boundaries. The proportion of Σ3 boundaries was higher in multi-step cross-rolled annealed material. The deformed material had higher number fraction of low angle boundary than any other special boundary. Solution treated material had an average grain size of α phase smaller than the as-received material. Another dimension of the present investigation was to characterize the microstructural features in three dimension(3D) in order to examine the morhphology of constituent phases using serial sectioning. In the present work, 3D studies were carried out on the alloy after post deformation annealing. The alignment of serial section images and generation of 3D image out of the stack of 2D images was carried out through standard software. The same was used to measure the suitable 3D microstructural parameters from the 2D sections. Three dimensional microstructural parameters like mean caliper diameter of β particle, number of β particles per unit volume ‘Nv’, surface to volume ratio for β phase particles (α- β interface) ‘Sv’, were calculated. Number of β particle intercepts per unit area ‘NA’ was determined by measuring number of β phase particle in each section. The volume of a β particle as calculated from the caliper diameter using three-dimensional microstructural analysis, which could not get directly determined with conventional two-dimensional microscopy.