京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19999号 / 工博第4243号 / 新制||工||1657(附属図書館) / 33095 / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 三浦 清貴, 教授 田中 勝久, 教授 平尾 一之 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

This thesis encompasses a feasibility study of using low-cost materials to manufacture microfluidic chips that can perform the same functions as chips manufactured using traditional methods within an acceptable range of efficiency of chips created with more exotic methods and materials. The major parts of the project are the selection and characterization of the fabrication methods for creating the channels for fluid flow, the methods for sealing the channels to create a usable chip and the electrophoretic separations of carboxylated microspheres of different potentials. In this work we seek to answer the question if laser-etched PMMA microfluidic chips are comparable in functionality to microfluidic chips created with PDMS or glass. In the process of answering this question we will touch on FEA modeling, characterization of the manufacturing process and multiple prototype designs while keeping within the low-cost theme. The purpose of capillary electrophoresis is to separate proteins based on their inherent electric charge. Capillary electrophoresis is a standard chip design used in the microfluidics world to prove a new fabrication method or chip material before branching out to other experiments because it is a fairly simple and robust design. Common problems associated with the manufacturing methods and materials were taken into account such as electroosmotic flow and chip sealing. CZE designs from literature were referenced to create a chip that would separate carboxylated microbeads with reasonable resolution. Wire electrodes were affixed to the chip to induce electric fields for the electrophoresis experiments. The goal of this thesis is to prove the manufacturing methods and attain results within 70% of literature standards.

Chalcogenide glasses are well known to have good transparency into the infrared spectrum. These glasses though tend to have low thresholds as compared to oxide glasses for photo-induced changes and thermally-induced changes. Material modification such as photo-induced darkening, bleaching, refractive index change, densification or expansion, ablation of crystallization have been demonstrated, and are typically induced by a thermal furnace-based heat treatment, an optical source such as a laser, or a combination of photo-thermal interactions. Solely employing laser-based heating has an advantage over a furnace, since one has the potential to be able to spatially modify the materials properties with much greater precision by moving either the beam or the sample. The main properties of ChG glasses investigated in this study were the light-induced and thermally-induced modification of the glass through visible microscopy, white light interferometry, and Raman spectroscopy. Additionally computational models were developed in order to aid in determining what temperature rise should be occurring under the conditions used in experiments. It was seen that ablation, photo-expansion, crystallization, and melting could occur for some of the irradiation conditions that were used. The above bandgap energy simulations appeared to overestimate the maximum temperature that should have been reached in the sample, while the below bandgap energy simulations appeared to underestimate the maximum temperature that should have been reached in the sample. Ultimately, this work produces the ground work to be able to predict and control dose, and therefore heating, to induce localized crystallization and phase change.

<p> Microarchitectural or nano- functional materials are critical to industry and scientific research owning to their special properties derived from their tiny sizes and subsequently increased surface area. However, they are also expensive and a pain to make. </p> <p>The large-scale manufacturing of microarchitectural functional materials can often be complex and difficult. Considering the following factors: (1) the capability of attaining the desired physical and chemical properties and morphology for target nano-materials; (2) the quality of nano-materials in industrial-scale production; (3) the ability to incorporate nanosized materials into a matrix of standard material to form strengthened nano-composites; (4) the feasibility to transfer laboratory-scale research to industrial manufacturing; (5) the stability of reliability of manufacturing technique; and (6) cost and environmental safety of the process, the industrial use of nano-materials faces many obstacles as there is no suitable technique to meet every demands. </p> <p>Laser processing has a wide range of applications from micro/nano fabrication to surface treatment, re-construction, element doping, composition modification, and shock peening. Compared to the longer pulse width lasers, ultrafast laser pulses are unique in the incredibly high peak intensities and the laser-matter interactions on a timescale faster than lattice disorder and heat diffusion do. These two features enable ultrafast laser to precisely tune and engineer the states of materials. Herein, we utilized picosecond (ps) laser as energy source with multiple field (thermal, magnetic, pressure, etc.) to explore the feasibility of large-scale manufacturing microarchitectural materials with desired functions.</p>

Multi-pass fusion welding by a filler wire (welding electrode) is normally carried out to join thick steel sections used in most engineering applications. Welded joints in an installation, is the area of critical importance, since they are likely to contain a higher density of defects than the parent metal and their physical properties can differ significantly from the parent metal. Fusion arc welding process relies on intense local heating at a joint where a certain amount of the parent metal is melted and fused with additional metal from the filler wire. The intense local heating causes severe transient thermal gradients in the welded component and the resulting uneven cooling that follows produces a variably distributed residual stress field. In multi-pass welds, multiple thermal cycles resulted in a variably distribution of residual stress field across the weld and through the thickness. These complex thermal stresses generated in welds are undesirable but inevitable during fusion welding. Presence of such tensile residual stresses can be detrimental to the service integrity of a welded structure. In addition to a complex distribution of residual stress state, multi-pass welds also forms dendritic grain structure, which are repeatedly heated, resulting in segregation of alloying elements. Dendritic grain structure is weaker and segregation of alloying elements would result in formation of corrosion microcells as well as reduction in overall corrosion prevention due to depletion of alloying elements.

The exciting thermomechanical properties of nickel-titanium shape memory alloys have sparked significant research efforts seeking to exploit their exotic capabilities. Until recently, the performance capabilities of nickel-titanium devices have been inhibited by the retention of only one thermomechanical characteristic. However, laser processing technology promises to deliver enhanced material offerings which are capable of multiple functional responses. Presented in this thesis, is an investigation of the effects of laser processing on the thermomechanical behaviour of nickel-titanium shape memory alloys. In the context of this work, laser processing refers to removal of alloy constituents, as in the case of laser ablation, or alternatively, addition of elements through laser alloying. The effects of laser ablation on the composition, crystallography and phase transformation temperatures of a nickel-titanium strip have been studied. Application of laser energy was shown to ablate nickel constituents, induce an austenite-martensite phase change and cause an increase in phase transformation onset temperatures, which correlated well with reported findings. Laser processing of a nickel-titanium wire was shown to locally embed an additional thermomechanical response which manifested as unique shape memory and pseudoelastic properties. Localized alloying of ternary species via laser processing of nickel-titanium strip was investigated. Synthesis of a ternary shape memory intermetallic within the laser processing region was achieved through melting of copper foils. Results from thermoanalytical testing indicated that the ternary compound possessed a higher phase transformation temperature and reduced transformation hysteresis in comparison to the reference alloy. Indentation testing was used to demonstrate the augmented thermomechanical characteristics of the laser processed shape memory alloy. In order to demonstrate the enhanced functionality of laser processed nickel-titanium shape memory alloys, a self-positioning nickel-titanium microgripper was fabricated. The microgripper was designed to actuate through four different positions, corresponding to activation of three embedded shape memory characteristics. Thermoanalytical and tensile testing instrumentations were used to characterize the thermomechanical performance of the laser processed nickel-titanium microgripper. Results indicated that each of the laser processed microgripper components possessed unique mechanical and shape memory recovery properties.

The unique performance offerings of NiTi based shape memory alloys (SMAs), which includes the shape memory effect (SME), pseudoelasticity (PE) and biocompatibility have led to widespread acceptance of these alloys as valuable engineering materials. Over the past several decades the complex metallurgy behind the SME and PE properties has for the most part been uncovered and the design and engineering knowhow has been demonstrated; facilitating successful application of NiTi devices in numerous industries. Specifically, more mature applications in the medical industry including medical devices such as, catheters, guide wires, orthodontic arch wires, maxillofacial reconstruction implants, minimally invasive surgical tools, and arterial and gastrointestinal stents, have become common practice in modern medicine. Recently however, there has been a drive for more demanding functionality of SMAs for example to locally modify properties creating tuneable or gradient SME and PE performance. Unique processing protocols are therefore necessary to meet these demands and allow SMAs to reach their full potential in a wider range of applications. The current thesis successfully details the application of pulsed Nd:YAG laser processing along with post-processing techniques to locally tune both the SME and PE functional properties of monolithic binary NiTi wires and strip, while maintaining confidence in the retained corrosion performance and limited release of biologically harmful Ni ions. This extensive study contains three distinct parts which include: i) application of a laser induced vaporization protocol to locally embed multiple memories in a monolithic wire actuator; ii) uncovering the process, structure, and performance relationship of combined laser, cold working, and heat treatment processes; and iii) comprehensive characterization of surface characteristics and their relationship with corrosion performance and Ni ion release from laser processed material.

The exciting thermomechanical properties of nickel-titanium shape memory alloys have sparked significant research efforts seeking to exploit their exotic capabilities. Until recently, the performance capabilities of nickel-titanium devices have been inhibited by the retention of only one thermomechanical characteristic. However, laser processing technology promises to deliver enhanced material offerings which are capable of multiple functional responses. Presented in this thesis, is an investigation of the effects of laser processing on the thermomechanical behaviour of nickel-titanium shape memory alloys. In the context of this work, laser processing refers to removal of alloy constituents, as in the case of laser ablation, or alternatively, addition of elements through laser alloying. The effects of laser ablation on the composition, crystallography and phase transformation temperatures of a nickel-titanium strip have been studied. Application of laser energy was shown to ablate nickel constituents, induce an austenite-martensite phase change and cause an increase in phase transformation onset temperatures, which correlated well with reported findings. Laser processing of a nickel-titanium wire was shown to locally embed an additional thermomechanical response which manifested as unique shape memory and pseudoelastic properties. Localized alloying of ternary species via laser processing of nickel-titanium strip was investigated. Synthesis of a ternary shape memory intermetallic within the laser processing region was achieved through melting of copper foils. Results from thermoanalytical testing indicated that the ternary compound possessed a higher phase transformation temperature and reduced transformation hysteresis in comparison to the reference alloy. Indentation testing was used to demonstrate the augmented thermomechanical characteristics of the laser processed shape memory alloy. In order to demonstrate the enhanced functionality of laser processed nickel-titanium shape memory alloys, a self-positioning nickel-titanium microgripper was fabricated. The microgripper was designed to actuate through four different positions, corresponding to activation of three embedded shape memory characteristics. Thermoanalytical and tensile testing instrumentations were used to characterize the thermomechanical performance of the laser processed nickel-titanium microgripper. Results indicated that each of the laser processed microgripper components possessed unique mechanical and shape memory recovery properties.

The use of ultrafast lasers in material surface engineering has gained pre-eminence in recent years. This is due to optimal utility arising from their versatility, better process control, repeatability and high precision fabrication, without need for post processing. Reported in this thesis are experimental results on the use of picosecond laser to produce micro-patterns on cyclone components and their effects on flow characteristics. Results show that micro- dimples achieved reduction in dust accumulation within a multi-cyclone system considered, up to 78%. These micro-dimples when applied on the cyclone roof effected a 3% reduction in inlet velocity and 5% reduction on the dynamic pressure across the cyclone, without dust introduction. Results support the possibility for energy savings, without compromise on cyclone overall separation efficiency. Findings further demonstrated the effects of micro-riblets on cyclonic airflow at the wall boundary. Research outcomes supported the view that surface roughness of the cyclone roof could contribute on its dust separation capacity. Injection moulding was used to produce bumps on ABS plastic materials utilising picosecond laser machined micro-dimples on H13 tool steel. A statistical model detailing the interactions between the critical factors involved with picosecond laser interaction with H13 for micro-patterning was proposed. Critical factors identified were laser fluence, scanning speed and number of laser scans. In addition, results demonstrated the suitability of predicting depth of 40 - 100 µm for H13 tool steel, with 96% accuracy. The findings in this research could be explored to develop embedded micro/nano-wires within riblets through injection moulding, to effect electrically biased charging within the internal walls of a cyclone to aid dust separation processes.

Dans les piles à combustible SOFC (Solid Oxide Fuel cell) de type monochambre (SC-SOFC), l’anode et la cathode, séparées par un électrolyte, sont situées dans une même chambre alimentée par un mélange de combustible et d’oxygène. L’électrolyte, n’ayant alors plus le rôle d’étanchéité entre les compartiments anodique et cathodique, peut être mis en forme par sérigraphie. Cependant, il est nécessaire d’avoir une barrière pour éviter la possible diffusion de l’hydrogène produit localement à l’anode vers la cathode, ce qui peut générer une chute de la tension. L’objectif de ce travail de thèse est de créer une barrière de diffusion localisée via la densification de la surface de l'électrolyte par un traitement laser. Le matériau sélectionné pour l’électrolyte est un oxyde mixte Ce0,9Gd0,1O1,95 (CGO) qui est déposé par sérigraphie sur une anode composite NiO-CGO. Deux types de lasers impulsionnels sont utilisés : un laser UV (λ = 248 nm) et un laser IR (λ = 1064 nm). Les caractérisations microstructurales réalisées ont permis de mettre en évidence les effets du traitement laser pour certaines combinaisons fluence – nombre de tirs, montrant un grossissement de grain de l’électrolyte ou bien des surfaces densifiées mais fissurées. Des modifications structurales et chimiques sur la surface ont été évaluées ainsi que la diffusion de gaz au travers des électrolytes modifiés tout comme leur conductivité électrique. Afin de mieux comprendre l'interaction laser-matière, une modélisation thermique a également été mise en œuvre. Finalement, les performances de piles SC-SOFC ont été améliorées pour les dispositifs présentant un grossissement de grain à la surface de l'électrolyte. / In single-chamber solid oxide fuel cells (SC-SOFC), anode and cathode are placed in a gas chamber where they are both exposed to a fuel/air mixture. Similarly to conventional dual-chamber SOFC, the anode and the cathode are separated by an electrolyte, but in the SC-SOFC configuration it does not play tightness role between compartments. For this reason, a porous electrolyte can be processed by screen printing. However, it is necessary to have a diffusion barrier to prevent the transportation of hydrogen produced locally at the anode to the cathode through the electrolyte that reduces fuel cell performances. This study aims to obtain directly a diffusion barrier through the surface densification of the electrolyte by a laser treatment. The material chosen for the electrolyte was cerium gadolinium oxide Ce0.9Gd0.1O1.95 (CGO) which is deposited by screen printing on a composite NiO-CGO anode. UV laser and IR laser irradiations were used at different fluences and number of pulses to modify the density of the electrolyte coating. Microstructural characterizations confirmed the modifications on the surface of the electrolyte for appropriate experimental conditions showing either grain growth or densified but cracked surfaces. Structural and chemical modifications on the surface were evaluated as well as the gas diffusion through the electrolytes and their electrical conductivity. In order to understand interaction between the laser and the material, thermal modelling was also developed. Finally, SC-SOFC performances were improved for the cells presenting grain growth at the electrolyte surface, particularly, the power density has been enhanced by a factor 2.