The cyclic-compression behavior of a Cu45Zr45Al5Ag5 bulk metallic glass (BMG) was investigated in order to elucidate the damage initiation and growth mechanisms. The present Cu45Zr45Al5Ag5 BMG was found to have the highest fatigue-endurance limit for BMGs reported to date. Fracture under cyclic compression occurred in a pure shear mode. In addition to many shear bands and cracks, areas of “chipping” were commonly found on the outside surfaces of the fatigue specimens. Crack growth rates were found decrease with cycles. The effects of the as-cast specimen size, cooling rate, and the free volume content on the monotonic and cyclic compression behavior of a Zr-based BMG was investigated. The smaller samples experienced a faster cooling rate, resulting in a higher free volume content. The smaller samples displayed superior monotonic compression and cyclic compression properties. This trend was attributed to a higher free volume content. The effect of the sample aspect ratio (height/diameter) on the cyclic compression behavior of a Zr-based BMG was explored. For smaller aspect ratios (0.5), the yield strength and compressive plastic strain significantly increased when compared to that for an aspect ratio of 2. In general, when the aspect ratio was 0.5, the fatigue lives were longer than when the aspect ratio was 2. The dramatic effect of the sample aspect ratio was attributed to the development of a hydrostatic stress state from the interaction of the uniaxial applied load and the friction stress developed at the interface of the top and bottom specimen surfaces and the platens. The stress-life fatigue behavior and fracture morphology of a (Cu60Zr30Ti10)99Sn1 BMG alloy was investigated under both 3-point and 4-point bending conditions. For all stress levels tested, the fatigue lifetimes tended to be higher for the 3-point loading condition. All fracture surfaces were found to be comprised of four main regions: a crack-initiation site, a stable crack-growth region, an unstable fast-fracture region, and a melting region. Finely spaced parallel marks oriented somewhat perpendicular to the direction of crack propagation were observed in the stable crack-growth region. Analyses of these marks found that their spacing increased with increasing stress intensity- factor range.

EfPm-27 is a Protohistoric bison pound and processing site located in Fish Creek Park in Calgary, Alberta. The site exhibited the presence of metal tools and macroscopically deceptive cut marks suggesting the potential for the presence of both metal and stone cut marks. Moulds of selected cut marks from the assemblage were made and examined with the scanning electron microscope (SEM) to verify or negate the use of metal tools for butchery at the site. SEM images of the cut mark moulds reveal micromorphology that is similar to experimental and published stone tool cut mark SEM images. No evidence for the use of metal tools for butchering was identified. Protohistoric sites research could benefit from the use of SEM analysis of cut marks to distinguish between stone and metal tool use. This would provide important secondary evidence for metal trade items in scenarios where such artifacts may be beyond recovery. Conversely, the presence of metal artifacts at a site does not necessarily imply that they were used for butchery and this assertion must be verified by the presence of metal cut marks.

Light reflected from the scarab beetles Cetonia aurata (C. aurata) and Chrysina gloriosa (C. gloriosa) has left-handed polarization. In this work the polarizing properties and structural characteristics of the cuticles of these two beetles are investigated with two different techniques: scanning electron microscopy (SEM) and Mueller-matrix spectroscopic ellipsometry (MMSE). SEM is used to get cross section images of the epicutucle and the endocuticle. Thicknesses around 18 μm were measured for both layers for C. aurata and between 12 and 16 μm for C. gloriosa. A layered structure is observed in both beetles. In addition, a cusp-like structure is also observed in C. gloriosa. MMSE showed left-handed near-circular polarization of light reflected on both beetles. For C. aurata this is observed in a narrow wavelength range (500-600 nm) and for C. gloriosa in a wider wavelength range (400-700 nm) when measured on golden areas of the cuticle. C. gloriosa also has green areas where the reflected light was linearly polarized. The results are used in regression modelling. A good model approximation was found for C. aurata for angles up to 60 whereas a good starting point for future work was reached for C. gloriosa.

EfPm-27 is a Protohistoric bison pound and processing site located in Fish Creek Park in Calgary, Alberta. The site exhibited the presence of metal tools and macroscopically deceptive cut marks suggesting the potential for the presence of both metal and stone cut marks. Moulds of selected cut marks from the assemblage were made and examined with the scanning electron microscope (SEM) to verify or negate the use of metal tools for butchery at the site. SEM images of the cut mark moulds reveal micromorphology that is similar to experimental and published stone tool cut mark SEM images. No evidence for the use of metal tools for butchering was identified. Protohistoric sites research could benefit from the use of SEM analysis of cut marks to distinguish between stone and metal tool use. This would provide important secondary evidence for metal trade items in scenarios where such artifacts may be beyond recovery. Conversely, the presence of metal artifacts at a site does not necessarily imply that they were used for butchery and this assertion must be verified by the presence of metal cut marks.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 107-109). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 107-109). Also available on the Internet.

In this research, corrosion behaviour of A36 carbon steel under engineered disbonded coating was investigated in sulphuric acid solutions containing sodium chloride and iron (III) sulphate. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) analyses were carried out to study the morphology and phase composition of corrosion products formed on the carbon steel surface. The results of the SEM analysis showed that only general and pitting corrosion occurred on the carbon steel surface with the engineered crevice. The size of the pits increased as the sulphuric acid and sodium chloride concentrations increased. Moreover, the corrosion products had an open, irregular and loose structure at the pits mouth. The loose and open structure of the corrosion products facilitates diffusion of chloride ions, oxygen, water and contaminants into the carbon steel surface. In contrast, the corrosion products had a very compact and continuous structure outside the pits which provided a good protection against further corrosion. The x-ray diffraction analysis showed that the corrosion products layer mainly consisted of lepidocrocite (γ-FeOOH), goethite (α-FeOOH) and iron sulphide (FeS) on the crevice edges. The Pourbaix diagram of iron in sulphuric acid solution at room temperature indicates that iron sulphide is formed on the metal surface at different pH values. The akaganeite (β-FeOOH) diffraction peak was not identified in any spectrum which could be due to the low concentration of chloride ions in the solutions. Furthermore, the number of lepidocrocite peaks decreased as the sulphuric acid concentration increased from 10 g l-1 to 50 g l-1. The lepidocrocite is dissolved in the presence of sulphuric acid, and the dissolved ion acts as an oxidant to the metal and hence lower lepidocrocite peaks are identified. Electrochemical noise measurement (ECN) testing was also performed to investigate the corrosion process occurring on the carbon steel surface with the engineered crevice. The results of the ECN measurements showed that current increased during first few minutes and then decreased slightly. Also, the coupled potential did not change after an initial shift in negative direction. The low current flowing through the carbon steel electrodes and the constant potential showed that the crevice corrosion did not develop. These results imply that the crevice corrosion may not occur on the carbon steel surface in acidic solutions containing chloride ions.

Carbon nanotubes (CNTs) have extraordinary electrical and mechanical properties, and many potential applications have been proposed, ranging from nanoscale devices to reinforcement of macroscopic structures. However, due to their small sizes, characterization of their mechanical properties and deformation behaviours are major challenges. Theoretical modelling of deformation behaviours has shown that multi-walled carbon nanotubes (MWCNTs) can develop ripples in the walls on the contracted side when bent above a critical curvature. The rippling is reversible and accompanied by a reduction in the bending stiffness of the tubes. This behaviour will have implications for future nanoelectromechanical systems (NEMS). Although rippling has been thoroughly modelled there has been a lack of experimental data thus far. In this study, force measurements have been performed on individual MWCNTs and vertically aligned carbon nanofibers (VACNFs). This was accomplished by using a custom-made atomic force microscope (AFM) inside a scanning electron microscope (SEM). The measurements were done by bending free-standing MWCNTs/VACNFs with the AFM sensor in a cantilever-to-cantilever fashion, providing force-displacement curves. From such curves and the MWCNT/VACNF dimensions, measured from SEM-images, the critical strain for the very onset of rippling and the Young’s modulus, E, could be obtained. To enable accurate estimations of the nanotube diameter, we have developed a model of the SEM-image formation, such that intrinsic diameters can be retrieved. We have found an increase in the critical strain for smaller diameter tubes, a behaviour that compares well with previous theoretical modelling. VACNFs behaved very differently, as they did not display any rippling and had low bending stiffnesses due to inter-wall shear. We believe that our findings will have implications for the design of future NEMS devices that employ MWCNTs and VACNFs. / <p>Artikel 2 Image formation mechanisms tidigare som manuskript, nu publicerad: urn:nbn:se:kau:diva-16425 (MÅ 150924)</p>

Oxidation developed from the surfaces into the cores of the microwaved particles. Metallic particles were also formed during microwave exposure. Lihir gold ore, in which gold was finely disseminated in pyrite and marcasite, was an extremely refractory gold ore. Without pretreatment, only 37-39% of the gold could be extracted with sodium cyanide. However, this was improved after the head ores or floatation concentrates were pretreated by microwave radiation. 74.581.2% of the gold was extracted from the microwave treated head ore. The hydrometallurgical pretreatment of pyrite and marcasite in a microwave field and a conventional heating environment was also investigated.I,n a nitric acid solution, pyrite and marcasite can be rapidly leached. Reaction temperature and the concentration of HNO3 had a significant influence on decomposition rate. Marcasite had a substantially higher i decomposition rate than pyrite. Microwave heating could promote the dissociation of marcasite and pyrite, compared with conventional heating. This was caused by special volumetric heating during microwave exposure that may induce local overheating or improve the interactions between the high dielectric loss minerals and the leaching solution. Kinetic investigations show that the decomposition of both the minerals in a nitric acid medium is controlled by chemical reactions on the surfaces of particles. The decomposition is a second order reaction with respect to nitric acid concentration. Less than 5- 7% of the decomposed sulphur was transformed into elemental sulphur during the leaching of both the minerals

Titanium carbide (TiC) and titanium carbonitride (Ti(C,N)) are both common components in hard, wear resistant ceramic-metal composites, or cermets. In this study the intermetallic nickel aluminide (Ni3Al) has been used as a binder for the production of TiC and Ti(C,N) based cermets. These cermets offer several improved characteristics relative to conventional WC-based ‘hardmetals’, such as lower mass and improved oxidation resistance, which are also combined with high fracture resistance, hardness and wear resistance. The cermets were produced using an in-situ, reaction sintering procedure to form the stoichiometric Ni3Al binder, with the binder contents varied from 20 to 40 vol%. However, for high N content Ti(C,N) cermets, the wettability of molten Ni3Al is relatively poor, which leads to materials with residual porosity. Therefore various amounts of Mo2C (1.25, 2.5, 5 and 10 vol%) were incorporated into the Ti(C0.3,N0.7)-Ni3Al cermets, with the aim of improving the densification behaviour. Mo2C was found to improve upon the wettability during sintering, thus enhancing the densification, especially at the lower binder contents. The tribological behaviour of TiC and Ti(C,N) cermets have been evaluated under reciprocating sliding conditions. The wear tests were conducted using a ball-on-flat sliding geometry, with a WC-Co sphere as the counter-face material, for loads from 20 to 60 N. The wear response was characterised using a combination of scanning electron microscopy, energy dispersive X-ray spectroscopy, and focused ion beam microscopy. Initially, two-body abrasive wear was observed to occur, which transitions to three-body abrasion through the generation of debris from the cermet and counter-face materials. Ultimately, this wear debris is incorporated into a thin tribolayer within the wear track, which indicates a further transition to an adhesive wear mechanism. It was found that Mo2C additions had a positive effect on both the hardness and indentation fracture resistance of the samples, but had a detrimental effect on the sliding wear response of the cermets. This behaviour was attributed to increased microstructural inhomogeneity with Mo2C additions.