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京都大学 / 新制・課程博士 / 博士(工学) / 甲第23900号 / 工博第4987号 / 新制||工||1779(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 邑瀬 邦明, 教授 宇田 哲也, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Clad metals are extensively used for their multi-functionality and their optimal combination of quality and cost. Roll bonding is an effective and economic processing approach to making clad metals. This dissertation presents an experimental investigation of the roll cladding process as well as thermo-mechanical modeling of mechanism for roll bonding of clad metals. The objectives of this research are to investigate the bonding mechanism of dissimilar metals in a warm rolling process and to advance the knowledge of the roll cladding process. To accomplish the objectives, aluminum 1100 sheet (Al 1100) and stainless steel 304 sheet (SST 304) are bonded by warm rolling under controlled conditions. The 180 degrees peel test is used to determine the bonding property of those clad metals. The experimental results show that the rolling thickness reduction and the entry temperature are two major factors of bonding strength. Minimum thickness reduction at a particular entry temperature is required to bond Al 1100 and SST 304. Increasing of either thickness reduction or entry temperature significantly improves the bonding strength between the two metals. X-ray microanalysis is also performed to characterize the diffusion state at the bonding interface. The diffusion coefficients of aluminum and iron are estimated through experimental method. A thermo-mechanical model was developed to describe the rolling plastic deformation of component metal sheets and the diffusion evolution during a roll bonding process of dissimilar metals. The effect of various rolling conditions on the contact area ratio was quantitatively discussed. Finite element simulation of 2-D diffusion under the rolling created boundary conditions was performed. The peel strength during the diffusion evolution was predicted by the integrated roll bonding model. The modeling predictions correspond to the experimental results well. The correspondence validates the effectiveness of the thermo-mechanical roll bonding model. Based on experimental observation, this research presents a bonding mechanism for the roll cladding process of dissimilar metals. The roll bonding model can help optimize rolling parameters for varying bonding strength depending on the demands of the application. It can also provide insights into design and analysis of rolling bonding process of other groups of dissimilar metal sheets.

In this studing, application of the digital image correlation method (DIC) for determining the coefficient of thermal expansion (CTE) of Indium Tin Oxide/Polyethylene Terephthalate(ITO/PET) thin film/flexible substrate was proposed and the effects of thinkness variations of ITO and PET, respectively, on the CTE of the specimens was disscussed. The observation range of experimental temperature was chosen from room temperature to the glass transfer temperature of PET, 70¢J. A novel DIC experimental process for reducing the errors caused from the variations of the refractive index of the surrounding heated air was proposed. As a result, the experimental error of CTE measurement was reduced form 10~17% to less than 5%. The experimental results showed that the CTE of ITO/PET specimen is anisotropic. Futhermore, the CTE of an ITO/PET specimen will be increased by decreasing the thinkness of PET flexible substrate, and increased by increasing the thinkness of ITO film - which means decreasing the surface resistance of ITO film.

Ce travail est né de l'idée d'associer l'ingénierie des matériaux sous forme de couches minces, domaine qui motive depuis de nombreuses années les chercheurs du LMGP, à des substrats piézoélectriques à fort coefficients de déformation. Les matériaux piézoélectriques peuvent convertir une énergie électrique en une énergie mécanique (de déformation) et vice-versa. Il est alors aisé d'imaginer qu'une couche mince synthétisée à la surface d'un substrat piézoélectrique profitera de la déformation de ce dernier quand il est soumit à un champ électrique. Le substrat mis en jeu est le PMN-PT, composé qui présente de forts coefficients de déformation. Dans cette étude le film synthétisé et mis en œuvre est le LaNiO3. Il cristallise dans une structure pérovskite ABO3. Cette structure présente l'avantage de permettre une grande variété de distorsions structurales et peut accueillir un grand nombre d'éléments chimiques. / This work was born from the idea of ​​combining materials in thin films form, an area that motivates many years researchers LMGP, to substrates with high piezoelectric coefficients of deformation. Piezoelectric materials can convert electrical energy into mechanical energy (strain) and vice versa. So we can imagine that a thin film synthesized on the surface of a piezoelectric substrate will benefit from the substrate deformation when subjected to an electric field. The substrate involved is the PMN-PT, a compound that shows high piezoelectric coefficient. In this study the film synthesized is the LaNiO3. It crystallizes in a perovskite structure ABO3. This structure has the advantage of a wide variety of structural distortions and can accommodate a large number of chemical elements.

A miniature, ultra-low power, sensitive, microbridge gas sensor has been developed.The heat loss from the bridge is a function of the thermal conductivity of thegas ambient. Miniature thermal conductivity sensors have been developed for gaschromatography systems [1] and microhotplates have been built with MEMS technologywhich operates within the mW range of power [2]. In this work a lower power microbridgewas built which allowed for the amplification of the effect of gas thermalconductivity on heat loss from the heated microbridge due to the increase inthe surface-to-volume ratio of the sensing element. For the bridge fabrication,CMOS compatible technology, nanolithography, and polysilicon surfacemicromachining were employed. Eight microbridges were fabricated on each die,of varying lengths and widths, and with a thickness of 1 μm. A voltagewas applied to the sensor and the resistance was calculated based upon thecurrent flow. The response has been tested with air, carbon dioxide, helium,and nitrogen. The resistance and temperature change for carbon dioxide was thegreatest, while the corresponding change for helium was the least. Thus the selectivity of the sensor todifferent gases was shown, as well as the robustness of the sensor. Another aspect of the sensor is that it hasvery low power consumption. The measuredpower consumption at 4 Volts is that of 11.5 mJ for Nitrogen, and 16.1 mJ forHelium. Thesensor responds to ambient gas very rapidly. The time constant not only showsthe fast response of the sensor, but it also allows for more accuratedetection, given that each different gas produces a different correspondingtime constant from the sensor. The sensor is able to detect differentconcentrations of the same gas as well. Fromthe slopes that were calculated, the resistance change at 5 Volts operation wasfound to be 2.05mΩ/ppm, 1.14 mΩ/ppm at 4.5 Volts, and 0.7 mΩ/ppm at 4 Volts. Thehigher voltages yielded higher resistance changes for all of the gases thatwere tested. Theversatility of the microbridge has been studied as well. Experiments were donein order to research the ability of a deposited film on the microbridge, inthis case tin oxide, to act as a sensing element for specific gases. In thissetup, the microbridge no longer is the sensing element, but instead acts as aheating element, whose sole purpose is to keep a constant temperature at whichit can then activate the SnO film, making it able to sense methane. In conclusion,the microbridge was designed, fabricated, and tested for use as an electrothermalgas sensor. The sensor responds to ambient gas very rapidly with differentlevels of resistance change for different gases, purely due to the differencein thermal conductivity of each of the gases. Not only does it have a fastresponse, but it also operates at low power levels. Further research has beendone in the microbridge's ability to act as a heating element, in which the useof a SnO film as the sensing element, activated by the microbridge, was studied. REFERENCES: 1. D. Cruz,J.P. Chang, S.K. Showalter, F. Gelbard, R.P. Manginell, M.G. Blain," Microfabricated thermal conductivity detector for themicro-ChemLabTM," Sensors andActuators B, Vol. 121 pp. 414-422, (2007). 2. A. G. Shirke, R. E. Cavicchi, S. Semancik, R. H. Jackson, B.G. Frederick, M. C. Wheeler. "Femtomolar isothermal desorption usingmicrohotplate sensors," J Vac Sci TechnolA, Vol. 25, pp. 514-526 (2007).

Les travaux de thèse se sont attachés à développer des outils permettant :(i) d'estimer par nanoindentation le niveau de contraintes résiduelles locales de type biaxial introduit dans un alliage d'aluminium 2050-T8. Nous proposons une méthode d'estimation qui couple des essais expérimentaux de nanoindentation, l'observation des empreintes résiduelles et une analyse numérique de l'effet de contraintes résiduelles élastiques biaxiales sur la géométrie des empreintes résiduelles d'indentation. et (ii) de déterminer par nanoindentation le comportement mécanique d'un film d'oxyde ultra-mince, d'épaisseur variant entre 15 et 20nm, formé sur un acier inoxydable biphasé de type Duplex. Nous avons développé une méthode de caractérisation de films ultra-minces qui couple la réalisation et l'analyse d'essais expérimentaux à l'aide d'indenteurs dont le défaut de pointe est déterminé, et la reproduction de ces essais en simulation numérique 3D à l'aide des géométries réelles des indenteurs. / Works performed during this thesis were dedicated to development of tools allowing:(i) To estimate using nanoindentation tests the level of biaxial residual stresses introduced within a 2050-T8 aluminium alloy. We propose an estimation method that couples experimental nanoindentation tests, residual imprints observation and numerical evaluation of the impact of elastic biaxial residual stresses on the geometries of residual indentation imprints. And (ii) the determination by nanoindentation of the mechanical behavior of an ultra-thin oxide film, between 15 to 20nm thickness, formed on a dual phased Duplex stainless steel. We developed a characterization method that couples analysis of experimental nanoindentation tests using several indenters with known tip defects, and reproduction of these tests in 3D finite element simulations using the true indenters' geometries.

The anodic films formed on CP-Ti in sulphuric and phosphoric acids using potentiodynamic polarization and potentiostatic anodizing were investigated. Single-barrier anodic films were created in sulphuric and phosphoric acids from 10 to 60 V. Oxygen evolution was initiated within both stages, leading to the suppression of current efficiency for the growth of anodic films. The crystalline phases assisted gas bubbles to develop within the film, resulting in the formation of the blister textures. The rupture of the anodic film was found from anodizing at 20 V in the sulphuric acid but occurred at 50 V in the phosphoric acid. The corrosion behaviour of the anodic oxide films formed on CP-Ti was studied in a 3.5% NaCl electrolyte. Ruptures and blisters of the films were found as a result of the release of a huge pressure by the bursting of oxygen bubbles. More ruptures were observed when anodizing to higher anodic voltages in the sulphuric and phosphoric acids. Further, the anodic films showed more ruptures after the anodized titanium specimens at higher anodic voltages were immersed for 60 days in the NaCl electrolyte compared with the immediate immersions. Additionally, the corrosion behaviours of the anodic films were examined by potentiodynamic polarization and electrochemical impedance spectroscopy. The corrosion resistance of the anodized titanium in the NaCl electrolyte increased with increased anodic voltage. Porous anodic films were formed on CP-Ti after anodizing at 100, 150 and 200 V for 900 s respectively. Nano-particulates were found within the pores; the size and quantity of the pores increased due to the dissolution of the particulates. The amorphous-to-crystalline transition was initiated during anodizing. It was revealed that the degree of crystallinity was greater at a higher voltage. An increased content of phosphorus species was incorporated into the porous oxide film as the voltage increased. The formation of anodic oxide films on CP-Ti in the NaTESi electrolyte was investigated. Barrier-type titanium anodic films generated after anodizing to 5, 10 and 20 V were of thickness 30, 37 and 67 nm respectively. Further, a porous anodic film of ~80.0 nm thickness was generated after anodizing to 40 V. Significant amounts of sodium species were found, which were incorporated into the anodic films. The current efficiency for the film growth was reduced at higher anodic voltages due to the formation of crystalline phases and more oxygen generation. The degree of crystallinity of the anodic film increased at higher voltages. The dielectric permittivity of the anodic film was estimated as ~2.35 according to EIS and the TEM evidence. The degradation test was carried out in a continuous climatic chamber with a humidity of 90% at 50 oC. The anodic films formed on CP-Ti in the NaTESi electrolyte showed an excellent degradation resistance. Single-lap bonding tests were operated for the study of the adhesion joint performance, and the bonding strength increased with increase of the voltage associated with a thicker anodic TiO2 coatings. The formation of anodic oxide films on the Ti6Al4V alloy in the NaTESi electrolyte at a constant current density of 20 mA cm-2 was studied. An anodic film with shallow pores was formed after anodizing to 10 V. Porous anodic films were created after anodizing to 20, 30 and 40 V respectively. Significant amounts of sodium species were incorporated into the films. The current efficiency for the anodic film growth increased from 10 to 30 V but decreased from 30 to 40 V due to oxygen evolution. The film thicknesses determined by RBS were ~15 nm, ~39 nm, ~1100 nm and 1800 nm for voltages of 10, 20, 30 and 40 V respectively. The film thickness at 10 V showed good agreement with 11 nm which was evident by TEM. The degree of crystallinity of the films was greater at a higher voltage. The dielectric permittivity of the film was ~118 according to the results of TEM and EIS. The degradation test was carried out in a continuous climatic chamber with a humidity of 90% at 50oC. Without the evidence of damages, the anodic films formed on Ti6Al4V alloy in the NaTESi electrolyte showed an excellent degradation resistance. In addition, it was evident that the film formed after anodizing to 40 V was crystallized at the thermal temperature of 50 oC. Single-lap bonding tests were employed to compare the strength of adhesively joined titanium alloy anodized with different film thicknesses, the results revealing a significant benefit from a thicker film. The ~100 nm thick 99.6% pure titanium layers were sputter-deposited on electropolished aluminium substrates by magnetron sputtering technique to investigate the anodic film growth behaviour of titanium in H3PO4. The TiO2 and the Ti layer were ruptured by the bursting of oxygen bubbles. The phosphoric acid electrolyte penetrated into the ruptured regions of the sputter-deposited titanium layer, leading to the growth of Al2O3. The thickness of TiO2 increased from 10 to 100 V but decreased from 100 to 150 V. Above 80 V, some regions of the titanium layer where were completely ruptured did not generate TiO2. Important structural details of anodic films with high quality images were obtained using the STEM-in-SEM technique, enabling the study of film morphologies, film thicknesses and oxygen bubble features. STEM-in-SEM would be used to study a large-scale morphology of the anodic film. Additionally, a 6-specimen carousel holder would provide an increase in productivity by ~20% compared with a conventional single-specimen STEM or TEM. An air-formed oxide film was stripped from CP-Ti substrate by chemical etching in the bromine-methanol electrolyte, exposing the bare titanium substrate and grain boundaries with defects. After that, pitting corrosion occurred on the bare titanium due to the attack of bromine. The corrosion pits propagated with etching time from 10 to 300 s and were displayed using white light interferometry. Increased surface roughness was identified with etching time due to the occurrence of more pitting corrosion attacks. Bromine species and TiBr4 compounds were detected by EDS and X-ray diffraction patterns, indicating that the dissolution of the titanium substrate was induced in each etching.

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