DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

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ability to manipulate composition variations due to the use of powder bed platforms. Laser Engineered Net Shaping (LENS) 3 could produce composition variations in space, but it uses of focused high power radiation, as also seen in SLS and EBM, creates high thermal stress and may cause cracks in ceramic-metal composites. Methods like Three- Dimensional Printing (3DP) 7 and Fused Deposition Modeling (FDM) 4 use high binder content and face a significant binder removal issue in the finishing steps. New methods and material systems have to be developed for SFF to overcome the inherent difficulties and limitations in the context of ceramic-metal composites. 1.2. Thesis Objective The overarching objective of the work described in this thesis is assembly of a complex, three-dimensional structure of ferroelectric BaTiO3 ceramic along with Ni metal. This dissertation details the evolution of a SFF technique called Robocasting to assemble functional, ceramic-metal composites with controlled structure on a sub- millimeter length scale. The Robocasting method was originally developed at Sandia National Laboratories and is similar to other extrusion-based SFF methods in print strategy. The extruded filament, however, is unique. The printing ink requires colloidal processing of materials in a concentrated, aqueous-gel form. The ink is robotically patterned by controlled extrusion followed by drying, binder burnout, and co-sintering of composite green compacts. To realize the goal of SFF of functional metal-ceramic composites requires building upon an existing knowledge-base of colloidal processing of polyelectrolyte stabilized ceramic and metallic sols, co-sintering of base metal electrodes with ferroelectric ceramics and the diverse field of functionally graded materials. The intersection of these fields generates new knowledge about the importance of controlling 2
and characterizing rheological properties to facilitate assembly of complex heterogeneous structures. Likewise, exploring the impact of process variations, such as liquid phase sintering to enable successful co-sintering of devices while maintaining the overall properties of the metal and ceramic phases, is a new area for SFF. Insights from this work reveal several key requirements for metal-ceramic composite SFF, namely: formulation of the appropriate colloidal gels of fugitive, ceramic, metal, and flux- containing materials, successful co-sintering of composite structures, and understanding of the limitations of the chosen materials system and processes. 1.3. Thesis Scope The major task of this project is to develop aqueous colloidal inks for fabrication of ceramic-metal composite structures, focusing on the following aspects: 1) to formulate an aqueous colloidal fugitive ink with appropriate rheological properties and chemistries based on carbonaceous materials so that long-spanning and cantilevered features may be created by SFF; 2) to develop compatible aqueous colloidal ceramic and metal inks and evaluate their relevant chemistries and material properties; 3) to produce ceramic-metal composite powder preforms through serial printing of colloidal inks; 4) to consolidate these preforms and study the effects of process variables including ink composition, temperature profile, and sintering strategy. Finally, fabrication of disparate, heterogeneous, geometrically complex ceramic-metal composites is demonstrated. 1.4. Thesis Organization This thesis is organized into seven chapters. Chapter one states the motivation of this work, thesis objectives, thesis scope, and thesis organization. Chapter two provides 3
Page 1 and 2: DESIGN, ASSEMBLY AND CHARACTERIZATI
Page 3 and 4: ACKNOWLEDGEMENTS First and foremost
Page 5 and 6: CHAPTER 5 BARIUM TITANATE NICKEL CO
Page 7 and 8: Table 6.1 Formulations of aqueous c
Page 9 and 10: Figure 2.12 Schematic illustrations
Page 11 and 12: Figure 2.35 Schematic of the SHS pr
Page 13 and 14: Figure 4.9 Sintered nickel lattices
Page 15 and 16: Figure 6.12 Optical image of the cr
Page 17: 1.1. Motivation CHAPTER 1 INTRODUCT
Page 21 and 22: 2.1. Materials System CHAPTER 2 BAC
Page 23 and 24: 2.2. Reentrant Structures and Ceram
Page 25 and 26: devices would provide self-sustaini
Page 27 and 28: a) b) Figure 2.4 Schematic illustra
Page 29 and 30: production of concept models, injec
Page 31 and 32: Fused Deposition Modeling (FDM) was
Page 33 and 34: Laser Engineered Net Shaping (LENS)
Page 35 and 36: Inkjet printing (IP) 27 is based on
Page 37 and 38: Table 2.1 Comparisons of various SF
Page 39 and 40: Figure 2.11 Processing steps involv
Page 41 and 42: 2.4.1 Colloidal Inks The printing i
Page 43 and 44: Robocasting has lacked a well-desig
Page 45 and 46: Table 2.2 Example polymers that dep
Page 47 and 48: 2.6. Sintering In robocasting, sint
Page 49 and 50: Figure 2.15 Sphere and plate model
Page 51 and 52: where
Page 53 and 54: 2.5.3 Solid State Sintering In this
Page 55 and 56: Figure 2.18 Illustration of neck gr
Page 57 and 58: 2.5.3.4 Final Stage During this sta
Page 59 and 60: Figure 2.23 Schematic diagram of th
Page 61 and 62: 2.5.4.2 Rearrangement With the form
Page 63 and 64: 2.5.4.6 Spreading of Sintering Aid
Page 65 and 66: Driven by reduction of free energy,
Page 67 and 68: 2.5.5 Sintering Atmosphere Sinterin
Page 69 and 70:
2.7. Composite Materials In this re
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Figure 2.29 Types of composite mate
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Table 2.6 Examples of composite mat
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Table 2.7 Examples of FGM applicati
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2.7.3 Processing For the fabricatio
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prepared discrete layers of uniform
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Powder densification processes gene
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The specific volume fraction beyond
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a) b) Figure 2.34 a) Volume fractio
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When the powders are densified in s
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Various FGM coating processes are a
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of FGMs, such as partially reactive
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leading to a characteristic time τ
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3.1 Introduction CHAPTER 3 AQUEOUS
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occurs in a multi-step process: fir
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a) b) Figure 3.1 a) SEM image of as
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3.2.3 Preparation of Carbon Black C
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3.2.5 Drying Shrinkage Characteriza
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the optimized surfactant concentrat
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The storage modulus of a colloidal
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For HA ink, yield stress
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In the case of the aqueous carbon b
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PPO units of Pluronic F-127 may ads
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a) b) Figure 3.6 A carbon black lat
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a) b) Figure 3.7 SEM images of a) c
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TGA plot is in agreement with previ
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a) b) Figure 3.9 Thermogravimetric
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3.3.8 Fabrication of Complex Cerami
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c) d) 109
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3.4 Conclusion A fugitive support m
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metal inks have been reported for R
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Midland, MI) 5% by weight stock sol
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4.2.5. Thermal Degradation of Binde
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4.3. Results and Discussion 4.3.1.
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4.3.2. Preparation of Nickel Ink Su
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260 °C for 8 hours, the residual c
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Table 4.1 Calculated residual carbo
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a) b) Figure 4.6 Sintered Ni struct
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temperature 138, 139 lead to 92-95%
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Figure 4.8 Scanning electron microg
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c) Figure 4.9 Sintered nickel latti
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5.1. Introduction CHAPTER 5 BARIUM
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materials within the overall struct
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40:60, 60:40, 80:20 are separately
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5.2.3. Rheological Characterization
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5.2.5. Co-sintering and Re-oxidatio
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mixing, BT and Ni phases appear uni
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The combined use of PAA and PAA-90K
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To quantify this difference in sint
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As the BT and Ni particles used in
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The reducing atmosphere used in the
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Figure 5.7 Vickers hardness number
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5.3.6. Fabrication of BT-Ni composi
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modify the sintering kinetics of th
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a) b) Figure 5.10 Co-sintered compo
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5.4. Conclusions Freeform fabricati
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Liquid phase sintering involves usi
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(pH=4.4, 31.5% by weight) (Adva Flo
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concentration of 7 mg/mL in the aqu
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Table 6.1 Formulations of aqueous c
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thickness. Each layer of the struct
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6.2.6. Hardness Test Microindentati
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micrographs for these two powders.
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Second, the added LiAC∙2H2O is am
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Figure 6.3 Oscillatory behavior for
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a) b) Figure 6.4 Sintering strain c
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mass transport in LFBT network. 167
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The above discussion is mainly focu
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Figure 6.8 shows the bowtie-shaped
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Figure 6.10 A NPR composite of para
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etween BT and Ni phases. But Zn ele
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Figure 6.13 Scanning electron micro
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Figure 6.15 shows the mapping of Ti
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Figure 6.17 and Figure 6.18 show el
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Figure 6.19 shows element mapping f
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6.3.7. Piezoelectricity and Dielect
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6.4. Conclusions Aqueous colloidal
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geometric features, including non-s
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3. Development of aqueous colloidal
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7.2. Recommendations In the context
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gelation behavior. κ-carrageenan i
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REFERENCES 1. Larsson 9301647, 1993
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29. Simchi, A.; Petzoldt, F.; Pohl,
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61. Bouvard, D., Acta Metallurgica
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92. Morissette, S. L.; Lewis, J. A.
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120. Boehm, H. P., Some Aspects of
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150. Atkinson, A., Growth of Nio an
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APPENDICES A. Mathematical Modeling
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and
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conditions: Equation A.12 is solved
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and with
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a) b) Figure B.1 a) Freeze-dried st
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a) Figure C.1 Cr-Ni lattices of 5Cr
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E. Binary Phase Diagram of ZnO-B2O3
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References A.1. Du, Z., Sarofim, A.
Page 259:
Name: Jian Xu Date of Degree: May,
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