フェムト秒レーザーを用いた酸化物内部局所領域における欠陥制御および応用

京都大学0048新制・課程博士博士(工学)甲第15385号工博第3264号新制||工||1491(附属図書館)27863京都大学大学院工学研究科材料化学専攻(主査)教授 平尾 一之, 教授 横尾 俊信, 教授 田中 勝久学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA

Morphology change from nanocrack into periodic pore array formed by femtosecond laser pulses

Defects inside single crystals are an important concern because they directly affect the physical or chemical properties of the material, especially in sapphire used as substrates for semiconductors. We have investigated the thermally activated transformations of nanometer-scale cracks and phase transitions inside sapphire by femtosecond laser irradiation and successive heat treatments. The nanocracks transformed into periodic arrays of pores and dislocations that aligned along the {1Ī02} planes after heat treatments above 1300 °C. The amorphous phase at the focal point recovered into the initial single crystalline phase after the heat treatments. Our study provides useful information on the recovery behavior of nanometer-scale defects in a single crystal

Formation of a Cr3+-rich luminescent thin phase along a grain boundary of alpha-Al2O3

An α-Al2O3 bicrystal doped with Cr3+ was fabricated by diffusion bonding at high temperatures. It was found that a ruby phase with approximately 200 nm thickness was formed along the grain boundary. This thin phase shows Cr3+:Al2O3-induced luminescence, confirmed by confocal micro-luminescence spectroscopy

A new strengthening mechanism driven by disruptive shear and solute segregation during warm rolling in 1.4 GPa class 12.5 wt% Al added-FeMnC ultra-lightweight steel

Novel strengthening of Fe‒29.1Mn‒12.5Al‒1.35C‒4.95Cr steel achieved by warm rolling was investigated. The solution-treated steel consisted of a γ-matrix containing nano-sized κ-carbide ((Fe,Mn)3AlC) and elongated prior ferrite, which was transformed into FeAl-type B2 and Fe3Al-type D03 phases. The solution-treated steel exhibited poor strain hardening owing to glide softening associated with κ-carbide shearing by dislocations. However, after warm rolling with a reduction ratio of 30% at 300 °C, the yield and tensile strengths significantly increased from 917 to 1300 MPa and 1025 to 1419 MPa, respectively. The tensile test conducted at 300 °C to simulate warm rolling exhibited serrated flows, indicating dynamic strain aging (DSA). Atom probe tomography exhibited that the C atoms in κ-carbide were swept away along the slip direction by disruptive shear during rolling at 300 °C. The swept C atoms along the slip direction interacted strongly with dislocations at 300 °C, with repeated pinning and breakaway of dislocations from the C atoms. This contributed to significant strengthening owing to the formation of a solute-rich atmosphere after warm rolling. The results of the tensile tests at 300 °C indicated that the degree of strengthening was proportional to the pre-strain level. Tensile strength of 1.4 GPa can be achieved with good ductility (17% elongation) by warm rolling. This novel warm-rolling strengthening method expedites the potential application of Fe‒29.1Mn‒12.5Al‒1.35C‒4.95Cr as a 1.4 GPa class ultra-lightweight steel. © 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.FALS

Reverse partitioning of Al from κ-carbide to the γ-matrix upon Ni addition and its strengthening effect in Fe–Mn–Al–C lightweight steel

The effect of the addition of Ni to Fe–30Mn–10Al–0.9C–0.5Si–1.5Mo (wt.%) cast lightweight steel was investigated with a focus on the precipitation behavior of (Fe,Mn)3AlC κ-carbide. The addition of 3 wt.% Ni (3Ni steel) resulted in continuous hardening of the steel during aging heat treatment at 550 °C for 100 h whereas the addition of 1.5 wt.% Ni (1.5Ni steel) led to peak hardening at 550 °C for 20 h. The size of κ-carbides after aging heat treatment for 100 h was smaller in 3Ni steel compared with 1.5Ni steel, despite its higher hardness and progressed hardening. Atom probe tomography of the aged 3Ni steel revealed that Al atoms were preferentially enriched in the γ-matrix with clustering of Ni atoms observed, resulting in the relative depletion of Al in κ-carbide. This is the first report of reverse partitioning of Al from κ-carbide to the γ-matrix through Ni addition, indicating that the affinity of C–Al is lower than that of Ni–Al. The substitution of Mn to the Al site of the κ-carbide lattice is energetically favorable when Ni–Al bonding actively occurs in the γ-matrix, as determined by first-principles calculations. This is clearly evidenced by the Mn enrichment of κ-carbide in the 3Ni steel. The amount of Ni–Al clustering resulting from the reverse partitioning of Al to the γ-matrix during the precipitation of κ-carbide could be increased according to the growth of κ-carbide. Therefore, we found that the addition of Ni led to simultaneous cooperative precipitation- and solid solution-strengthening after aging, contributing to continuous hardening by effectively suppressing the movement of dislocations. © 2021 Elsevier B.V.1

The cut-off values of surrogate measures for insulin resistance in the Korean population according to the Korean Genome and Epidemiology Study (KOGES).

OBJECTIVE:The current methods available for determining insulin resistance are complicated; hence, they are only applicable to small-scale studies. Therefore, this study aimed to classify the characteristics of surrogate measures for insulin resistance and establish valid cut-off values for predicting the development of type 2 diabetes mellitus (DM) in Korean populations. METHODS:This prospective study included 7,643 participants aged 40-69 years from the Ansung-Ansan cohort database (2001-2012). Four surrogate measures, namely homeostasis model assessment-insulin resistance (HOMA-IR), visceral adiposity index (VAI), lipid accumulation product (LAP), and triglycerides and glucose (TyG) index, were analyzed. We analyzed each measure using receiver operating characteristic (ROC) curve for the development of type 2 DM. The cut-off value was determined as the value with the highest Youden index score in the specificity dominant area. RESULTS:The area under the curve (AUC) was 0.566 (95% confidence interval [CI], 0.548-0.583) for HOMA-IR, 0.622 (95% CI, 0.605-0.639) for VAI, 0.642 (95% CI, 0.625-0.658) for LAP, and 0.672 (95% CI, 0.656-0.687) for TyG index. The AUC of TyG index was significantly higher than that of HOMA-IR, VAI, and LAP (p < 0.001). The cut-off value was 2.54 (sensitivity 36.8%; specificity 73.1%; hazard ratio [HR], 1.41, 95% CI, 1.25-1.59) for HOMA-IR, 2.54 (sensitivity 50.4%; specificity 68.8%; HR, 1.75, 95% CI, 1.55-1.96) for VAI, 36.6 (sensitivity 59.2%; specificity 63.9%; HR, 1.87, 95% CI, 1.64-2.14) for LAP, and 4.69 (sensitivity 62.1%; specificity 63.1%; HR, 2.17, 95% CI, 1.92-2.45) for TyG index. CONCLUSIONS:The TyG index was a better predictor for DM than HOMA-IR. VAI and LAP showed the modest predictability for DM. The TyG index could be a useful supplementary method for identifying individuals at risk for insulin resistance and DM development

A Study on the frequency of congenital missing, supernumerary teeth and tooth shape anomaly in unilateral cleft lip and alveolus patients

Introduction : The purpose of this study was to investigate the incidence of congenital missing, supernumerary teeth and tooth shape anomalies in the unilateral cleft lip and alveolus patients(UCLA). Methods : Congenital missing, supernumerary teeth and tooth shape anomalies are investigated in fifty-one patients with UCLA using their charts, models, radiographs and intraoral photographs. Results and conclusions : In UCLA samples, 1. The incidence of congenital missing was 33.3%, maxillary lateral incisors were common congenital missing teeth(65.2%). 2. The incidence of supernumerary teeth was 7.84%. 3. The incidence of microdontia was 74.5%, most of them were maxillary lateral incisors located on cleft side. 4. The incidence of the dilacerations was 5.9%, and the incidence of crown shape anomalies was 3.9%. All of them were located on cleft side