Application of Image Analysis for the Identification of Prehistoric Ceramic Production Technologies in the North Caucasus (Russia, Bronze/Iron Age)

The recent advances in microscopy and scanning techniques enabled the image analysis of archaeological objects in a high resolution. From the direct measurements in images, shapes and related parameters of the structural elements of interest can be derived. In this study, image analysis in 2D/3D is applied to archaeological ceramics, in order to obtain clues about the ceramic pastes, firing and shaping techniques. Images were acquired by the polarized light microscope, scanning electron microscopy (SEM) and 3D micro X-ray computed tomography (µ-CT) and segmented using Matlab. 70 ceramic sherds excavated at Ransyrt 1 (Middle-Late Bronze Age) and Kabardinka 2 (late Bronze–early Iron Age), located in in the North Caucasian mountains, Russia, were investigated. The size distribution, circularity and sphericity of sand grains in the ceramics show site specific difference as well as variations within a site. The sphericity, surface area, volume and Euler characteristic of pores show the existence of various pyrometamorphic states between the ceramics and within a ceramic. Using alignments of pores and grains, similar pottery shaping techniques are identified for both sites. These results show that the image analysis of archaeological ceramics can provide detailed information about the prehistoric ceramic production technologies with fast data availability

Surface topography quantification of super hard abrasive tools by laser scanning microscopy

Non-conventional super hard abrasive tools are made of composite materials containing super hard grains, e.g., diamond or cubic boron nitride (CBN) grains, bound by a metallic constitutive phase. These tools are usually produced by means of sintering, and are widely applied in the abrasive machining processes of modern manufacturing, especially in precision machining. The abrasive grains, which induce the material removal processes, are embedded in the metallic binder. They emerge as a consequence of self-dressing, resulting in a self-sharping effect. Therefore, the cutting surface of the tool displays an irregular topography. Quantification of surface topography scenario may supply valuable information to evaluate and understand its correlation to wear mechanisms. In this study, an experimental protocol consisting of five steps: specimen preparation, surface scanning, image assembly, image digital processing and surface quantification, was proposed and validated by characterizing two CBN honing tools used for precision machining: B151/L2/2010/50 (B151) and B91/128/x44/35 (B91) CBN honing stones. It involved the use of laser scanning microscopy and digital imaging processing for assessing significant dimensional, geometrical, and positional properties of CBN grains at the surface of super hard abrasive tools. It was shown that surface topography quantification is an effective method to evaluate and obtain the defined parameters. However, smaller grains may require images with higher resolution; thus, scanning must be refined. Finally, a critical comparative analysis of the experimental results attained for the studied tools pointed out honing stone B91 as more appropriated than B151 one for achieving a higher machining quality of the workpiece.Peer ReviewedPostprint (author's final draft

Definierte strukturierte Hartmetallwerkzeuge für abrasive Prozesse

The challenge of this dissertation concerns the surface structuration of the WC-CoNi hardmetal with defined geometry, despite the fact that the embedded WC grains have irregular geometrical properties and distribution. An advanced method should be found and applied to structure the WC-CoNi hardmetal tool surface. The structured surfaces should be favorable and beneficial to reduce friction or to remove material in abrasive machining processes. Based upon the surface topography characterization of existing abrasive tools, e.g., CBN honing stone, geometrical properties of abrasives can be measured and quantified. The obtained geometrical information can contribute to the reproduction of the abrasive tool surface on WC-CoNi hardmetal. Laser surface texturing is an advanced machining method with high precision and it can effectively avoid some common thermal damage. Therefore, this method is implemented to machine WC-CoNi hardmetal surfaces. It is found that the structured WC-CoNi hardmetal tool can effectively remove material and improve surface quality of the counterpart (workpiece). These surface patterned hardmetal tools emerge then as potential alternative to conventional abrasive tools. Meanwhile, other patterns have also been produced on the hardmetals, and they can be used in the tribological system to reduce friction and improve wear resistance. It is a methodological and technical innovation to fabricate abrasive machining tools using laser to produce defined structures on a hardmetal surface, because it not only expands the utilization of hardmetal as an abrasive tool material but also enables the control and design of abrasive tool surface topography with high precision.Die Herausforderung dieser Arbeit besteht in der geometrischen Strukturierung von WC-CoNi-Hartmetall-Oberflächen, wobei die eingebetteten WC-Körner geometrische unbestimmte Eigenschaften sowie zufällige Verteilungen aufweisen. Es sollen neue Methoden gefunden und angewendet werden, um WC-CoNi Hartmetallwerkzeugoberflächen zu strukturieren. Mit Hilfe dieser Strukturen soll die Reibung reduziert oder Material durch abrasive Bearbeitung gezielt abgetragen werden. Durch eine geeignete Charakterisierung der Oberflächentopographie vorhandener Abrasivwerkzeuge können die geometrischen Eigenschaften von abrasiven Körnern ermittelt und quantifiziert werden. Die erworbenen geometrischen Informationen können zur Reproduktion der Oberflächen von Abrasivwerkzeugen auf Hartmetalloberflächen genutzt werden. Die Laseroberflächenstrukturierung ist ein innovatives Bearbeitungsverfahren mit hoher Präzision und Effizienz. Diese Methode kann wirksam die üblichen thermischen Schäden vermeiden. Daher ist dieses Verfahren zur Bearbeitung von WC-CoNi Hartmetall vorteilhaft. Es konnte bestätigt werden, dass die neuartigen strukturierten WC-CoNi Hartmetallwerkzeuge die Materialien der Werkstücke abtragen und die Oberflächenqualität dieser verbessern. Diese oberflächenstrukturierten Hartmetallwerkzeuge können als potentielle Alternative zu konventionellen abrasiven Werkzeugen dienen. Parallel hierzu wurden weitere Strukturmuster auf Hartmetalloberflächen erzeugt. Die Strukturen können in einem tribologischen System angewendet werden, um Reibung zu reduzieren und Verschleißbeständigkeit zu verbessern. Die definiert erzeugten Strukturen können nicht nur bei Hartmetallen als Schleifwerkzeugmaterial eingesetzt werden, sondern ermöglichen auch eine gezielte Einstellung der Werkzeugoberflächentopographie

Ensuring the in vitro degradation reproducibility of powder metallurgy processed Mg 0.6Ca system

Magnesium degradation is a complex phenomenon that is too difficult to be described by a single influential parameter. Magnesium degradation is often influenced by either overtaking or overlapping factors like the cell culture medium composition, physiological conditions, impurities, and material’s internal microstructure, etc. This poses a challenge in obtaining the reproducible degradation results. Hence, in the present work, microstructural features like porosity and grain size distributions in powder metallurgy (PM) Mg-0.6Ca system were discretely evaluated for their roles in altering the specimen in vitro degradation rates. Importance was also given to the specimen impurity and mechanical properties. Based on the results, the limitations in PM processing conditions towards obtaining robust degradation results or, in other words, the material parameter thresholds to be realized for obtaining reproducible degradation profiles in PM Mg-0.6Ca specimens were put forth. Additionally, using literature evidence, the mechanisms governing pore closure and grain growth during liquid phase sintering of Mg-0.6Ca specimens from the PM processing perspective were determined. PM Mg-0.6Ca specimens were fabricated via powder blending of pure magnesium and master alloy Mg-10Ca powders. Specimens of seven different porosities, from 3% to 21%, were produced by varying sintering temperatures. Specimens with heterogeneous grain size distributions were obtained by surface modification of pure magnesium powders by means of a mechanical sieving treatment. Degradation profiles were analyzed in vitro using a semi static immersion test for 16 days under physiological conditions of 37 °C, 20% O2, 5% CO2, 95% relative humidity. Dulbecco’s modified Eagle’s medium was used as cell culture medium with Glutamax and 10% fetal bovine serum as supplements. Mechanical properties were determined using micro tensile specimens. The results indicate that low mean degradation rates (MDR 95% to ≤ 45% when falling below this value. Similarly, the pore interconnectivity sharply drops from > 95% to < 10% at this porosity, thereby enhancing the degradation reproducibility. From PM processing perspective, the sintering temperature of 570 °C is proven as beneficial to promote liquid fractions high enough to enhance specimen sinter density. The present work also showed that heterogeneous grain growth is prompted by the reduced oxide pinning effect at the grain boundaries during sintering of PM Mg-0.6Ca specimens. The heterogeneous grain growth additionally induced the formation of eutectic lamellar structure α-Mg + Mg2Ca at certain grain boundaries throughout the microstructure, which is otherwise not evident in specimens with a homogeneous grain size. Based on the literature and results of the present work, it is postulated that this eutectic structure is the major reason for a non-reproducible degradation in PM Mg-0.6Ca specimens possessing a heterogeneous grain structure. Though mechanical properties are not majorly affected, it is recommended that heterogeneous grain growth is to be avoided in PM Mg-0.6Ca specimens. The presented results also implicitly conveyed the flexibility of PM as a viable technique to design Mg-Ca materials with tailor made degradation and mechanical strengths

Pulsed laser irradiation of plasma sprayed alumina-zirconia coatings

Plasma sprayed alumina and zirconia coatings are widely used coatings for many industrial applications. One of the most important applications is the production of thermal barrier coatings (TBCs). As sprayed alumina-zirconia coatings have relatively high degree of porosity and the properties of these coatings, such as high temperature, corrosion resistance, toughness and abrasion resistance may thereby be reduced. Laser surface treatment is one novel method that has potential for eliminating porosity and producing a homogeneous surface layer. In this research work the effect of excimer laser annealing on the surface of alumina-zirconia coatings was investigated. Alumina-40% zirconia (AZ-40) coatings were sprayed with a water-stabilized plasma spray gun. The coated surface was treated by excimer laser having a wavelength of 248 nm and pulse duration of 24 ns. In the first phase of the work an analytical model was developed in COMSOL Multiphysics 4.2 in order to investigate the effect of the defects on the heat distribution at the surface of samples irradiated by KrF beam. The model revealed that much higher temperatures were localized at areas having defects than at continuous surfaces. A detailed parametric study was carried out to investigate the effects of different laser surface treatment parameters including laser energy density (fluence), pulse repetition rate (PRR), and number of pulses on the microstructure, surface morphology, and mechanical properties of the coatings. The surface structure of the treated coating was examined by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). Treating the surface with low laser energy of 200mJ/cm2 etched a very thin layer from the coating, which helped revealing the microstructures initially present but hidden on the surface of as sprayed coatings. High laser energy of 800mJ/cm2 resulted in significant changes in the coat surface morphology where eutectic colonies growing in a pool of zirconia matrix were identified on the surface. The surface of untreated coating was continuously alternating up and down; it had a zigzag nature. After irradiating the surface with high laser fluence of 800mJ/cm2 the zigzag nature of roughness profile of untreated coating disappeared. Also irradiating the surface with high pulse repetition rate exhibited dome-like structures on the surface, which were associated with an increase in surface hardness

Visualization and modeling of evaporation from pore networks by representative 2D micromodels

Evaporation is a key process for the water exchange between soil and atmosphere, it is controlled by the internal water fluxes and surface vapor fluxes. The focus of this thesis is to visualize and quantify the multiphase flow processes during evaporation from porous media. The retained liquid films in surface roughness (thick-film flow) and angular corners (corner flow) have been found to facilitate and dominate evaporation. Using the representative 2D micromodels (artificial pore networks) with different surface roughness and pore structures, this thesis gives visualizations of the corner and thick-film flow during the evaporation process, presents the enhanced hydraulic continuity by corner and thick-film flow, and tests the validity of the SSC-model which assumes corner flow is dominant for the mass transport during evaporation. Surface roughness and wettability are proved both experimentally and theoretically to play a key role for the time and temperature behaviors of the evaporation process, besides, this thesis shows that for a consistent description of the time-dependent mass loss and the geometry of the corner/thick-film flow region, the fractality of the evaporation front must be taken into account

ToScA North America (6 – 8 June 2017, The University of Texas, Austin, TX) Program

ToScA North America will address key areas of science, including Multi-modal Imaging, Geosciences, Forensics, Increasing Contrast, Educational Outreach, Data, Materials Science and Medical and Biological Science.University of Texas High-Resolution X-ray CT Facility (UTCT); Jackson School of Geosciences, The University of Texas at Austin; Natural History Museum (London); Royal Microscopical Society (Oxford, UK)Geological Science

An Interactive Algorithm for Image Smoothing and Segmentation

This work introduces an interactive algorithm for image smoothing and segmentation. A non-linear partial differential equation is employed to smooth the image while preserving contours. The segmentation is a region-growing and merging process initiated around image minima (seeds), which are automatically detected, labeled and eventually merged. The user places one marker per region of interest. Accurate and fast segmentation results can be achieved for gray and color images using this simple method