積層スマート材料グループ

積層スマート材料グループでは、ジェットエンジンやガスタービンなど高温エネルギー機器で利用される耐熱材料について研究を行っています。

【グループ研究概要】

特に過酷な環境から保護するためのコーティング技術、原料粉末から複雑な三次元構造を直接作る3D積層造形プロセス、また高温で材料を塑性変形させ目的の形状に加工する鍛造プロセス、これらによる材料開発を進めています。さらに開発材料の組織と力学特性の相関解明や、信頼性確保のための新しい非破壊評価技術について研究しています。

関連画像


【研究テーマ】

【3D造形】
【溶射コーティング】
  • Effects of Gun Scanning Pattern on the Structure, Mechanical Properties and Corrosion Resistance of Plasma-Sprayed YSZ Coatings
  • Effects of amorphous phase on hot corrosion behavior of plasma-sprayed LaMgAl11O19 coating
【非破壊検査】
  • Evaluation of 3D-Printed titanium alloy using eddy current testing with high-sensitivity magnetic sensor
  • Terahertz Magneto-Optic Sensor/Imager
  • Mid-infrared pulsed laser ultrasonic testing for carbon fiber reinforced plastics
【鍛造】
  • Effect of α precipitation on β texture evolution during β-processed forging in a near-β titanium alloy


【3D造形】
Image Segmentation and Analysis for Microstructure and Property Evaluations on Ti6Al4V Fabricated by Selective Laser Melting

The selective laser melting could be employed in fabrication of near-net shape products for airplane and biomedical applications from Ti-6Al-4V alloy, which is difficult-to-process material. In this method, the localized laser irradiation forms the unique Ti-6Al-4V microstructures which correspond to the laser scanning patterns and local thermal history as it could be observed from sample cross-sections with OM or SEM. In this study, the effects of heat treatments on mechanical properties of Ti6Al4V samples produced by selective laser melting are discussed based on quantitative analysis of microstructures with image processing and machine learning tools. It was found that microstructures of heat-treated samples retained their original morphologies and secondary Alpha phase precipitated regularly at Beta grain boundaries with increased treatment time. These microstructures were appropriately segmented and classified. Each Alpha particle geometrical characteristics were successfully extracted and evaluated by image analysis. Importantly, the hardness of the heat-treated samples was lower compared to that of as-built ones and it tended to increase with the area fraction of Alpha phase, the Alpha particle width, and the nearest neighbor distance between Alpha particles.

Shiho Miyazaki, Masahiro Kusano, Dmitry S. Bulgarevich, Satoshi Kishimoto, Atsushi Yumoto, Makoto Watanabe, Materials Transactions, Vol. 60, No. 4 (2019) pp. 561- 568, https://doi.org/10.2320/matertrans.MBW201806(別ウィンドウで開きます)  

「Scheme of image analysis (a) SEM images, (b) phase classification using machine learning with RF algorithm, (c) classified images, (d) Alpha particles segmentation at k = 0.7, (e) ellipse approximation and (f) NND between a particles.」の画像

Scheme of image analysis (a) SEM images, (b) phase classification using machine learning with RF algorithm, (c) classified images, (d) Alpha particles segmentation at k = 0.7, (e) ellipse approximation and (f) NND between a particles.




【溶射コーティング】
Effects of Gun Scanning Pattern on the Structure, Mechanical Properties and Corrosion Resistance of Plasma-Sprayed YSZ Coatings

(別ウィンドウで開きます)Due to the non-symmetric distribution of sprayed particle plume in conventional plasma spraying caused by the radial injection of feedstock powder into a plasma jet, significant influence of the gun scanning pattern can appear in the structure of the sprayed coatings. Especially, the portion of poorly treated powder flux can be a cause of horizontal cracking as well as poor coating adhesion. In this study, three different scanning patterns of an air plasma spray gun were adopted with a commercial ZrO2-8 mass% Y2O3 (YSZ) powder. The cross sections of the obtained YSZ coatings were observed by SEM, while interfacial fracture toughness was measured by the indentation method, and hot corrosion testing was conducted. It was found that by modification of the gun scanning pattern, it is possible to decrease the possibility of horizontal weak bonding between spray passes and improve the coating adhesion and corrosion resistance.

Takuma Ohnuki, Seiji Kuroda, Hiroshi Araki, Xiaolong Chen, Makoto Watanabe & Yukihiro Sakamoto
Journal of Thermal Spray Technology volume 29, pages60–73(2020),https://doi.org/10.1007/s11666-019-00925-6 (別ウィンドウで開きます)

「Appearance of plasma spray plumes with different powder feed gas flow rates; (a) 2 L/min, (b) 5 L/min」の画像

Appearance of plasma spray plumes with different powder feed gas flow rates; (a) 2 L/min, (b) 5 L/min




【溶射コーティング】
Effects of amorphous phase on hot corrosion behavior of plasma-sprayed LaMgAl11O19 coating

Plasma-sprayed LaMgAl11O19 (LaMA) coating as a novel thermal barrier coating candidate has been studied for more than a decade, but it tends to contain significant amounts of non-equilibrium amorphous phase due to rapid solidification. The microstructure of such as-sprayed LaMA coating was first studied in detail by a transmission electron microscope (TEM), which revealed that the coating consisted mostly of an amorphous phase but with very thin layers of crystalline (thickness ~ 100 nm) phase at the boundary of neighboring sprayed particles. A hot corrosion test was also conducted on an as-sprayed LaMA coating as well as on a fully-crystallized coating after heat treatment by a molten V2O5-Na2SO4 mixture at 1100 °C. The coatings' cross sectional observation showed that the as-sprayed coating was affected over a wider area by the corrosion reaction than the crystallized coating. To clarify the intrinsic reactivity of the amorphous and crystalline LaMA phases with the molten salt, a piece of as-sprayed coating was crushed into powder, mixed with a salt, and tested at temperatures below and above the crystallization temperature. The reacted powder was analyzed by an X-ray diffractometer (XRD) to quantify the amounts of various phases in the sample as a function of time. The results revealed that the amorphous LaMA has a remarkably higher reaction rate with the molten salt than the crystalline phase. In fact, at the testing temperature of 1100 °C, corrosion of the sprayed LaMA powder proceeded much faster than crystallization, as almost 90% of LaMA was corroded within 30 min. 

S.Tsukada,S.Kuroda,M.Nishijima,H.Arakia,A.Yumoto,M.Watanabe,Surface and Coatings Technology ,Volume 363, 15 April 2019, Pages 95-105,https://doi.org/10.1016/j.surfcoat.2019.01.097(別ウィンドウで開きます)


【非破壊評価】【3D造形】
Evaluation of 3D-Printed titanium alloy using eddy current testing with high-sensitivity magnetic sensor

We developed ECT systems using high-sensitivity magnetic sensors with small size; and used the systems to evaluate a titanium alloy sample prepared by a 3D laser printer. Two systems were used. In the first system, a small excitation coil was wrapped around the amorphous wire, and the excitation frequency was chosen to be 100 kHz. In the second system, a large circular coil was used to surround the test sample, and the excitation frequency was chosen to be 70 kHz. The image of the scanning result shows that both ECT excitation methods were able to detect the positions of flaws in the test sample. Moreover, the sizes of the flaws could be seen in the phase image result of the first ECT excitation method, and the interaction between the eddy current and the flaws could be observed in the amplitude imaging result of the second ECT excitation method. We also compared the results with that of traditional inductive coil ECT system.

Dongfeng He, Zhi Wang, Masahiro Kusano, Satoshi Kishimoto, Makoto Watanabe, NDT & E International Volume 102, March 2019, Pages 90-95,https://doi.org/10.1016/j.ndteint.2018.11.007(別ウィンドウで開きます)

「Schematic of the experimental setup for the ECT system with small excitation coil.」の画像

Schematic of the experimental setup for the ECT system with small excitation coil.




【非破壊評価】
Terahertz Magneto-Optic Sensor/Imager

We are reporting a new type of compact magneto-optic sensor constructed from terahertz-wave spintronic emitter and electro-optic detector. The corresponding terahertz polarization output of the emitter and the detection phase-sensitivity of the detector depend on the vector of the external magnetic field. The emitter/detector pair consists of two small and thin wafers sandwiched together and capped with a thin gold mirror. As a result, the use of bulky terahertz steering/collection optics was completely eliminated in our magneto-optic imager. With such simple on-chip generation/detection scheme for terahertz time-domain setup in reflection-type geometry, we were able to record the raster-scanned image contrast of a permanent magnet in the proximity of the sensor surface. The contrast strongly varies with the magnet orientation and its position with respect to the sensor. The imager spatial resolution depends on chip optical quality for tight femtosecond-laser pump/probe cross-focusing at detector/mirror interface and terahertz generation/detection efficiency. In this respect, the chip robustness to the pump/probe fluences is also an important factor to consider.

Dmitry S. Bulgarevich, Yusuke Akamine, Miezel Talara, Valynn Mag-usara, Hideaki Kitahara, Hiroyuki Kato, Masaki Shiihara, Masahiko Tani & Makoto Watanabe,Terahertz Magneto-Optic Sensor/Imager. Sci Rep 10, 1158 (2020). https://doi.org/10.1038/s41598-020-58085-5(別ウィンドウで開きます)

「MOI results with different permanent magnet orientation with respect to the on-chip THz sensor (see text for more details). The magnet in (a) and (b) was ~5 mm above the spintronic layer surface. The waveform colours correspond to ones of the circles, which indicate the spatial positions on images for their collections. The photos of used magnet positioned above and below of the MFVS are in (c) together with other drawings and data for magnet properties.」の画像

MOI results with different permanent magnet orientation with respect to the on-chip THz sensor (see text for more details). The magnet in (a) and (b) was ~5 mm above the spintronic layer surface. The waveform colours correspond to ones of the circles, which indicate the spatial positions on images for their collections. The photos of used magnet positioned above and below of the MFVS are in (c) together with other drawings and data for magnet properties.




【非破壊評価】
Mid-infrared pulsed laser ultrasonic testing for carbon fiber reinforced plastics

Laser ultrasonic testing (LUT) can realize contactless and instantaneous non-destructive testing, but its signal-to-noise ratio must be improved in order to measure carbon fiber reinforced plastics (CFRPs). We have developed a mid-infrared (mid-IR) laser source optimal for generating ultrasonic waves in CFRPs by using a wavelength conversion device based on an optical parametric oscillator. This paper reports a comparison of the ultrasonic generation behavior between the mid-IR laser and the Nd:YAG laser. The mid-IR laser generated a significantly larger ultrasonic amplitude in CFRP laminates than a conventional Nd:YAG laser. In addition, our study revealed that the surface epoxy matrix of CFRPs plays an important role in laser ultrasonic generation.

 MasahiroKusano,HidekiHatano,MakotoWatanab,ShunjiTakekawa,HisashiYamawaki,KanaeOguchi,ManabuEnoki,Ultra sonics Volume 84, March 2018, Pages 310-318,https://doi.org/10.1016/j.ultras.2017.11.015(別ウィンドウで開きます)


【鍛造】
Effect of α precipitation on β texture evolution during β-processed forging in a near-β titanium alloy

 The effects of α precipitation on β texture development during β-processed forging in Ti–6Al–2Sn–4Zr–6Mo alloy were investigated. Typical {001} and {111} β textures of β phase were developed, and the {001} texture intensity monotonically increased with increasing deformation ratio during forging in the β single-phase region with its promotion because of dynamic recrystallization (DRX), where DRX grains inherited the crystal orientation of the parent β phase. However, the {001} texture intensity decreased, accompanied by α precipitation during forging in the (α + β) dual-phase region, where the forging was performed after cooling from the β single-phase region. DRX hardly occurred during forging in the (α + β) dual-phase region. The precipitated α phase showed strong {11–20} transformation texture according to the Burgers orientation relationship under deformation. The {10–11}<11–20> pyramidal slip system was dominant in the α phase, which is nearly parallel to several {110}<111> β slip systems. It enhanced slip transmission between α and β phases increasing the {110}<111> slip activity in the β phase and it weakened the {001} β texture intensity after α precipitation.
L.Meng,T.Kitashima,T.Tsuchiyama,M.Watanabe,Materials Science and Engineering: A Volume 771, 13 January 2020, 138640,https://doi.org/10.1016/j.msea.2019.138640(別ウィンドウで開きます)

「β-Phase orientation maps of Ti-6246 at different forging temperatures and ratios: (a)1030℃, 45%; (b) 1030℃, 75%; (c) 980℃, 45%; (d) 980℃, 75%; (e)920℃, 15%; (f) 920℃, 45%; (g) 920℃, 60%; (h) 920℃, 75%;」の画像

β-Phase orientation maps of Ti-6246 at different forging temperatures and ratios: (a)1030℃, 45%; (b) 1030℃, 75%; (c) 980℃, 45%; (d) 980℃, 75%; (e)920℃, 15%; (f) 920℃, 45%; (g) 920℃, 60%; (h) 920℃, 75%;