Development of a digital manufacturing process chain for ceramic composites

The development of ceramic matrix composites, with their increasing use in high temperature and corrosive environment applications, is still restricted to ‘trial and error’ approach in comparison to other conventional materials like metals. The main reason behind that is the lack of experimental data due to high manufacturing costs of CMCs which generally includes a chain of several complex processes. This adds to the complexity of this material class and thus, makes it a difficult task to establish a relationship between a component with desired properties and the manufacturing parameters required to realise it. In the current work, the digital aspects are investigated from two point of views to use numerical methods to support the material design process: ‘material’ and ‘manufacturing process’. The case ‘material’ is the focus of this work where, ‘process-structure-property-performance’ (PSPP) relationship is established to study the entire life cycle of a CMC component, starting from the intermediate products, such as fibre preforms or green bodies prior to siliconization process, used in the processing to the mechanical performance of the final machined component under operating conditions. Each aspect of the PSPP relationship is discussed in detail and its implementation is demonstrated with the help of a numerical example. Cohesive zone elements at micro-level and homogenous damage development at macro-level were used to define the non-linear behaviour of the material under mechanical loading. Experimental results obtained for different CMCs such as C/C-SiC, C/SiCN, SiC/SiCN and Al2O3/ Al2O3 were used to validate the results obtained for the finite element models at different scales ranging from micro to macro. With the help of data analysis techniques like image segmentation and machine learning algorithm, computationally inexpensive data-based surrogate models were generated from accurate but computationally expensive physics-based models. A detailed review of the available numerical methods to model the manufacturing process and the process monitoring techniques is given. Based on the data and information obtained from the modelling of the material and the manufacturing process, a concept is proposed for optimized development of a CMC part. The concept combines the generated data with quantified expertise in the fields of material science to realise a manufacturing process chain to facilitate the material design process for CMCs. With the implementation of such an approach, the production cost of CMCs can be reduced by knowledge-based selection of the CMC constituents and manufacturing parameters. This will open the door for new applications of CMCs which would enable the material community to extend their use to other cost-efficient high temperature applications.Die Entwicklung von Verbundwerkstoffen mit keramischer Matrix, die zunehmend bei hohen Temperaturen und in korrosiven Umgebungen zum Einsatz kommen, ist im Vergleich zu anderen herkömmlichen Werkstoffen wie Metallen noch immer auf ein "Versuch-und-Irrtum"-Konzept beschränkt. Der Hauptgrund dafür ist der Mangel an experimentellen Daten aufgrund der hohen Herstellungskosten von CMCs, die im Allgemeinen eine Prozesskette aus mehreren komplexen Verfahrensschritten umfassen. Dies trägt zur Komplexität dieser Werkstoffklasse bei und macht es somit schwierig, eine Beziehung zwischen einem Bauteil mit gewünschten Eigenschaften und den Herstellungsparametern herzustellen. In der vorliegenden Arbeit werden die digitalen Aspekte aus zwei unterschiedlichen Blickwinkeln untersucht, um numerische Methoden zur Unterstützung der Werkstoffauslegung einzusetzen: 'Werkstoff' und 'Herstellungsprozess'. Im Mittelpunkt dieser Arbeit steht der "Werkstoff", bei dem die "Process-Structure-Property-Performance"-Beziehung (PSPP) hergestellt wird, um den gesamten Lebenszyklus eines CMC-Bauteils zu untersuchen. Angefangen bei den Zwischenprodukten, wie z. B. den Faser-Vorkörpern (Preform)vor dem Silizierverfahren, die die Basis der Verarbeitung bilden, bis hin zur mechanischen Belastungsgrenze des fertig bearbeiteten Bauteils unter Betriebsbedingungen. Jeder Aspekt der PSPP-Beziehung wird im Detail untersucht und ihre Umsetzung anhand eines numerischen Beispiels demonstriert. Kohäsive Zonenelemente auf der Mikroebene und homogene Schädigungsentwicklung auf der Makroebene wurden verwendet, um das nichtlineare Verhalten des Werkstoffs unter mechanischer Belastung zu definieren. Experimentelle Ergebnisse, die für verschiedene CMCs wie C/C-SiC, C/SiCN, SiC/SiCN und Al2O3/ Al2O3 erzielt wurden, dienten zur Validierung der Ergebnisse der Finite-Elemente-Modelle auf verschiedenen Skalen von Mikro bis Makro. Mit Hilfe von Datenanalysemethoden wie Bildsegmentierung und ‚Machine-Learning-Algorithmen‘ wurden aus genauen, aber rechenintensiven physikalischen Modellen zeiteffiziente datenbasierte Ersatzmodelle erstellt. Es wird ein detaillierter Überblick über die verfügbaren numerischen Methoden zur Modellierung des Fertigungsprozesses und der Prozessüberwachungstechniken gegeben. Auf der Grundlage der Daten und Informationen, die aus der Modellierung des Materials und der Herstellungsprozesse gewonnen wurden, wird ein Konzept für die optimierte Entwicklung eines CMC-Bauteils vorgeschlagen. Das Konzept kombiniert die generierten Daten mit quantifiziertem Fachwissen in den Bereichen der Materialwissenschaft, um eine Fertigungsprozesskette zu realisieren, die die Werkstoffauslegung für CMCs erleichtert. Mit der Umsetzung eines solchen Ansatzes können die Produktionskosten von CMCs durch eine wissensbasierte Auswahl der CMC-Bestandteile und Herstellungsparameter gesenkt werden. Dies wird die Tür für neue Anwendungen von CMCs öffnen, die es der Materialgemeinschaft ermöglichen wird, ihre Verwendung auf andere kosteneffiziente Hochtemperaturanwendungen auszuweiten

Development of a digital manufacturing process chain for ceramic composites

Die Entwicklung von Verbundwerkstoffen mit keramischer Matrix, die zunehmend bei hohen Temperaturen und in korrosiven Umgebungen zum Einsatz kommen, ist im Vergleich zu anderen herkömmlichen Werkstoffen wie Metallen noch immer auf ein "Versuch-und-Irrtum"-Konzept beschränkt. Der Hauptgrund dafür ist der Mangel an experimentellen Daten aufgrund der hohen Herstellungskosten von CMCs, die im Allgemeinen eine Prozesskette aus mehreren komplexen Verfahrensschritten umfassen. Dies trägt zur Komplexität dieser Werkstoffklasse bei und macht es somit schwierig, eine Beziehung zwischen einem Bauteil mit gewünschten Eigenschaften und den Herstellungsparametern herzustellen. In der vorliegenden Arbeit werden die digitalen Aspekte aus zwei unterschiedlichen Blickwinkeln untersucht, um numerische Methoden zur Unterstützung der Werkstoffauslegung einzusetzen: 'Werkstoff' und 'Herstellungsprozess'. Im Mittelpunkt dieser Arbeit steht der "Werkstoff", bei dem die "Process-Structure-Property-Performance"-Beziehung (PSPP) hergestellt wird, um den gesamten Lebenszyklus eines CMC-Bauteils zu untersuchen. Angefangen bei den Zwischenprodukten, wie z. B. den Faser-Vorkörpern (Preform)vor dem Silizierverfahren, die die Basis der Verarbeitung bilden, bis hin zur mechanischen Belastungsgrenze des fertig bearbeiteten Bauteils unter Betriebsbedingungen. Jeder Aspekt der PSPP-Beziehung wird im Detail untersucht und ihre Umsetzung anhand eines numerischen Beispiels demonstriert. Kohäsive Zonenelemente auf der Mikroebene und homogene Schädigungsentwicklung auf der Makroebene wurden verwendet, um das nichtlineare Verhalten des Werkstoffs unter mechanischer Belastung zu definieren. Experimentelle Ergebnisse, die für verschiedene CMCs wie C/C-SiC, C/SiCN, SiC/SiCN und Al2O3/ Al2O3 erzielt wurden, dienten zur Validierung der Ergebnisse der Finite-Elemente-Modelle auf verschiedenen Skalen von Mikro bis Makro. Mit Hilfe von Datenanalysemethoden wie Bildsegmentierung und ‚Machine-Learning-Algorithmen‘ wurden aus genauen, aber rechenintensiven physikalischen Modellen zeiteffiziente datenbasierte Ersatzmodelle erstellt. Es wird ein detaillierter Überblick über die verfügbaren numerischen Methoden zur Modellierung des Fertigungsprozesses und der Prozessüberwachungstechniken gegeben. Auf der Grundlage der Daten und Informationen, die aus der Modellierung des Materials und der Herstellungsprozesse gewonnen wurden, wird ein Konzept für die optimierte Entwicklung eines CMC-Bauteils vorgeschlagen. Das Konzept kombiniert die generierten Daten mit quantifiziertem Fachwissen in den Bereichen der Materialwissenschaft, um eine Fertigungsprozesskette zu realisieren, die die Werkstoffauslegung für CMCs erleichtert. Mit der Umsetzung eines solchen Ansatzes können die Produktionskosten von CMCs durch eine wissensbasierte Auswahl der CMC-Bestandteile und Herstellungsparameter gesenkt werden. XIV. Dies wird die Tür für neue Anwendungen von CMCs öffnen, die es der Materialgemeinschaft ermöglichen wird, ihre Verwendung auf andere kosteneffiziente Hochtemperaturanwendungen auszuweite

The Effect of Direct Laser Deposition Process Parameters on Microstructure and Mechanical Properties of Ti-6Al-2Sn-4Zr-6Mo

Blown powder Direct Laser Deposition (DLD) is a type of Additive Manufacturing (AM) that is of interest to the aerospace industry as a method of performing high-integrity repairs of critical components. The properties of the deposited material are largely influenced by process parameters such as beam power, velocity, hatch spacing, beam radius and powder feed rate. It is critical for a high-quality repair, that the effect of these process parameters on the solidification microstructure and hence the mechanical properties are fully understood. The work presented here focuses on quantifying the effect of process parameters on DLD of the α+β titanium alloy Ti-6Al-2Sn-4Zr-6Mo (Ti-6246). This alloy demonstrates high strength and good corrosion resistance and is a suitable replacement for Ti-6Al-4V in aerospace applications. This is due to its ability to perform at higher temperatures which is important as gas turbine engines push towards higher efficiencies and hence elevated operating temperatures. A Design of Experiment (DoE) was used to map a potential process window that would be suitable for Ti-6246 DLD repair of compressor bladed disks (Blisks). The aim was to identify combinations of process parameters that resulted in a fully-dense defect-free build that produced repeatable mechanical properties comparable to the parent Ti-6246 blisk material. Ten deposits were built with five different parameter sets using an RPM 557 laser deposition machine. Tensile specimens were machined from the build for uniaxial tensile testing. Small sections of each build were also retained for microstructural analysis, with the aim to correlate process parameters with the size of the resultant α+β lamellar microstructure. The α-lath width was found to generally increase with decreasing line energy density (beam power divided by velocity), although the effects of additional process parameters such as powder feed rate is also important and the influence of this is also explored. The results from this work were used to determine response surfaces relating process inputs such as energy density to process outputs such as 0.2% yield stress. These were then used to provide recommendations for future work with the aim of optimizing the DLD process window for Ti-6246 as a suitable repair method. The experimental work was supported by the development of a thermal model. This helped to inform how process parameters influenced the laser deposition conditions. The thermal model was calibrated against a thin-wall aerofoil-type build and reasonable agreement was found between predicted and measured melt depths for a range of process parameters. The thermal model also can help to provide predictions about the how further optimisation of the process window may affect mechanical properties. Some of the key findings and outcomes of this work are: • Development of an automated process to measure the size of Ti-6246 α+β lamellar microstructure produced by DLD. This automated process was validated using manual measurement techniques and was found to be a robust and trustworthy method that significantly decreases the time to gather microstructural data. • Size of the α-laths were generally found to be <1µm, apart from a dendritic zone at the top of each of the builds which has remained fine due to lack of coarsening from repeated thermal cycles. • Definition of a process window for the DLD of Ti-6246 which can produce dense builds with minimal defects (as revealed by both SEM and XCT analysis). • Testing of Ti-6246 DLD builds showed mechanical properties (tensile strength, 0.2% yield stress and elongation) comparable to parent forged material and within requirements set by Rolls-Royce for repair purposes. • Linear regression and response surface analysis showed that laser beam velocity (v) had the most effect on mechanical properties, particularly the 0.2% yield stress. Hatch spacing had little to no quantifiable effect on the mechanical properties. • Recommendations for process optimisation and productivity gains include increasing the hatch spacing and/or beam velocity to increase productivity. • Development of a Gaussian-based thermal model used to define a new parameter – melt pool saturation level (MPSL), this being the ratio between melting capacity of the laser and the actual amount of material being melted during the DLD process. • The MPSL was used to calculate an upper limit to the PFR and DLD process inputs were used to define a lower limit or “aspirational” PFR. Hence, the model developed in this work is useful in an industrial setting as it can reduce the number of test deposits needed to down-select the best process parameters and therefore define a suitable process window

Non-volatile liquid-film-embedded microfluidic valve for microscopic evaporation control and contactless bio-fluid delivery applications

Quick evaporation speed of microfluids can cause many unexpected problems and failures in various microfluidic devices and systems. In this dissertation, a new evaporation speed controlling method is demonstrated using a thin liquid-film based microfluidic valve. Microfluidic droplet ejectors were designed, fabricated and integrated with the liquid-film based microfluidic valve. The thin liquid film with nonvolatility and immiscibility exhibited excellent microfluidic valve functionality without any stiction problem between valve components, and provided a very effective evaporation protection barrier for the microfluids in the device. Successful evaporation control by the liquid-film-embedded (LiFE) microfluidic valve has been demonstrated. In addition, guided actuation of the microfluidic valve along predefined paths was successfully achieved using newly developed oil-repellent surfaces, which were later used for developing ‘virtual walls’ for confining low surface tension liquids within predefined areas. Moreover, bioinspired slippery surfaces for aiding the microfluidic valve along the ejector surface have also been developed. These slippery surfaces were evaluated for their effectiveness in reducing microfluidic valve driving voltages. Finally, a sliding liquid drop (SLID) shutter technique has been developed for a normally closed functionality with aid from nanostructures. The SLID shutter resolves many issues found in the previous LiFE microfluidic valve. Smooth and successful printing results of highly volatile bio-fluids have been demonstrated using the SLID shutter technique. I envision that these demonstrated techniques and developed tools have immense potential in various microfluidic applications

Polymorphic transformations in oxides and metals processed by electric discharge assisted mechanical milling: indirect assessment of plasma temperature via microscopic and crystallographic approach

The aim of the following thesis was to develop a fundamental understanding about the processing temperatures and mechanisms occurring during Electric Discharge Assisted Mechanical Milling (EDAMM). This was done through processing of a variety of materials which exhibit a phase transformation or polymorphic transformation in a known temperature

Laser Remelting of Yttria Stabilized Zirconia Coatings Deposited by Suspension Plasma Spraying

ABSTRACT Laser Remelting of Yttria Stabilized Zirconia Coatings Deposited by Suspension Plasma Spraying ASHKAN BAADI CONCORDIA UNIVERSITY, 2020 Thermal barrier coatings (TBCs) are applied as a protective layer in a range of applications, mainly in the aero-engine and power generation industries to protect the metallic parts from high operating temperatures, especially in gas turbine-engines. One way to improve the efficiency of the engines is to increase the combustion temperature; in order to reduce potential damage to the metallic parts, TBCs are commonly applied to these components. The TBC comprises a bond coat and a top coat. Since Yttria Stabilize Zirconia (YSZ) has the best combination of properties among the various options, this material is most commonly used as the top coat on commercial TBCs. The top coat in TBCs can be applied by different methods, including Electron Beam - Physical Vapour Deposition (EB-PVD), Atmospheric Plasma Spraying (APS) and the recently developed Suspension Plasma Spraying (SPS) which is one of the newest methods in applying top coat layers. SPS has the potential to generate columnar microstructures with a beneficial range of porosity: these columns reduce thermal stresses in the TBCs and at the same time provide an acceptable range of porosity which reduces the thermal conductivity of the coated layers. The columnar structure of this type of coating, despite having a potential to increase the life cycle of the top coat in terms of thermal stresses, can be a way of penetration for calcium–magnesium– aluminosilicates (CMAS) into the TBC structure, which will result in deterioration of the TBC.IV In this thesis, the formation of a variety of top coats using Suspension Plasma Spraying SPS method is used in order to obtain the desired columnar microstructure. Subsequently, these layers are laser treated to study the possibility of creating a remelted layer across the TBC surface which should reduce the CMAS penetration. In this regard, advantages and disadvantages of the major laser parameters such as scanning speed, output power, power density and energy density were observed. Based on the experimental tests on columnar structures, it was found that increasing scanning speed and power does not have a linear relation and that increasing the laser travel speed above 2 m/min will cause nonuniform melting and create different phases on the surface of the substrate. At the same time, decreasing power below a certain amount will not cause significant changes to the substrate. A specific range of energy and power density need to be considered in order to obtain a uniform melted layer over the substrate

ENGINEERING SUPERHYDROPHOBIC BEHAVIOR IN 3D-PRINTED STAINLESS STEEL COMPOSITES

This thesis discusses the wettability of 316L stainless steel composites using carbon nanotubes and manufactured via a selective laser melting. Superhydrophobicity is created through the combination of low surface tension and surface roughness at a micro to nanoscopic scale, and it has become a topic of vigorous study over the past 20 years. Previous studies have relied primarily on processes such as etching and nanomaterial arrays to generate surface roughness, followed by the application of harmful chemicals (e.g., fluorosilanes) to modify surface energy and achieve superhydrophobicity. Stainless steel powder (316L) was combined with carbon nanotubes, which demonstrate near-hydrophobic properties, via high energy ball milling in attempts to reduce the materials surface energy. An ideal pillared surface geometry based on natural superhydrophobicity was produced through additive manufacturing using multiple concentrations of carbon nanotube composites. Through material characterization including sessile water drop contact angle measurements, optical profilometry, and microscopy, it was determined that all samples remained hydrophilic in nature due to insufficient surface energy modification using carbon nanotubes. However, trends indicate that further increasing CNT concentration, controlling printing laser energy density, and slight model modifications could demonstrate hydrophobic effects.Ensign, United States NavyApproved for public release. Distribution is unlimited

Microdevices and Microsystems for Cell Manipulation

Microfabricated devices and systems capable of micromanipulation are well-suited for the manipulation of cells. These technologies are capable of a variety of functions, including cell trapping, cell sorting, cell culturing, and cell surgery, often at single-cell or sub-cellular resolution. These functionalities are achieved through a variety of mechanisms, including mechanical, electrical, magnetic, optical, and thermal forces. The operations that these microdevices and microsystems enable are relevant to many areas of biomedical research, including tissue engineering, cellular therapeutics, drug discovery, and diagnostics. This Special Issue will highlight recent advances in the field of cellular manipulation. Technologies capable of parallel single-cell manipulation are of special interest

Multi-scale multi-dimensional imaging and characterization of oil shale pyrolysis

In recent years, oil shale has attracted renewed attention as an unconventional energy resource, with vast and largely untapped reserves. Oil shale is a fine-grained sedimentary rock containing a sufficiently high content of immature organic matter from which shale oil and combustible gas can be extracted through pyrolysis. Several complex physical and chemical changes occur during the pyrolysis of oil shale where macromolecular network structures of kerogen are thermally decomposed. The pyrolysis of oil shale leads to the formation of a microscopic pore network in which the oil and gas products flow. The pore structure and the connectivity are significant characteristics which determine fluid flow and ultimate hydrocarbon recovery. In this thesis, a state-of-the-art multi-scale multi-dimensional workflow was applied to image and quantify the Lacustrine Eocene Green River (Mahogany Zone) formation, the world’s largest oil shale deposit. Samples were imaged before, during and after pyrolysis using laboratory and synchrotron-based X-ray Micro-tomography (µCT), Optical Microscopy, Automated Ultra-High Resolution Scanning Electron Microscopy (SEM), MAPS Mineralogy (Modular Automated Processing System) and Focused Ion Beam Scanning Electron Microscopy (FIB-SEM). Results of image analysis using optical (2-D), SEM (2-D), and µCT (3-D) reveal a complex fine-grained microstructure dominated by organic-rich parallel laminations in a tightly bound heterogeneous mineral matrix. MAPS Mineralogy combined with ultrafast measurements highlighted mineralogic textures dominated by dolomite, calcite, K-feldspar, quartz, pyrite and illitic clays. From high resolution backscattered electron (BSE) images, intra-organic, inter-organic-mineral, intra and inter-mineral pores were characterised with varying sizes and geometries. A detailed X-ray µCT study with increasing pyrolysis temperature (300-500°C) at 12 µm, 2 µm and 0.8 µm voxel sizes illuminated the evolution of pore structure, which is shown to be a strong function of the spatial distribution of organic content. In addition, FIB-SEM 3-D visualisations showed an unconnected pore space of 0.5% with pores sizes between 15 nm and 22 nm for the un-pyrolysed sample and a well-connected pore space of 18.2% largely with pores of equivalent radius between 1.6 µm and 2.0 µm for the pyrolysed sample. Synchrotron 4-D results at a time resolution of 160 seconds and a voxel size of 2 µm revealed a dramatic change in porosity accompanying pyrolysis between 390-400°C with the formation of micron-scale heterogeneous pores followed by interconnected fracture networks predominantly along the organic-rich laminations. Combining these techniques provides a powerful tool for quantifying petrophysical properties before, during and after oil shale pyrolysis. Quantitative 2-D, 3-D and 4-D imaging datasets across nm-µm-mm length scales are of great value to better understand, predict and model dynamics of pore structure change and hydrocarbon transport and production during oil shale pyrolysis.Open Acces