High Entropy Alloys - Science of New Class of Materials Based on Elemental Multiplicity and Heterogeneity

金沢大学理工研究域機械工学系近年，従来合金には見られない得意で優れた力学特性を示すハイエントロピー合金(High entropy alloy: HEA)の，加工熱処理による組織制御が報告されている．多様な構成原子間の相互作用による単純な混合則では表現できないカクテル効果によって，HEAは高電気抵抗率を示すとされる．しかしながら，組織変化に伴う電気特性の変化は不明である．その為，本研究では従来用いられてきた(1)アーク溶解炉と，ナノ結晶を作製可能な(2)スパッタ装置を用いて作製した試料に対して加工熱処理を施し，格子欠陥量（転位密度・粒界密度）の変化に伴う電気特性の変化を測定する．fcc単相のCantor alloy (CrMnFeCoNi合金)およびbcc単相のRefractory HEA (TiZrNbHfTa合金)に対して，最大で90%までの冷間圧延を行った．各圧下率の試料に対して，液体窒素温度および室温における電気抵抗率測定を行った．また，組織観察としてEBSD測定，X線回折測定，力学試験としてビッカース硬さ試験を行った．EBSD測定結果より，塑性加工の進展に伴って結晶粒微細化が起こっていることが判明した．X線回折結果より，圧下率を大細で90%まで増加させても，Cantor alloy とRefractory HEAはそれぞれ，fcc単相とbcc単相を維持していた．X線ラインブロードニング解析より，塑性加工の進展に伴って転位密度の増加が起こっていることを確認した．ビッカース硬さ試験結果より，圧下率の増加に伴ってビッカース硬さは増加し続けた．ビッカース硬さの増加は，組織変化，つまり，結晶粒微細化と転位密度の増加による，結晶粒微細化強化と加工硬化によって説明が可能である．それに対して，電気抵抗率は，従来の純金属や希薄合金で見られたように，塑性加工の進展に伴って増加しなかった．これは，ハイエントロピー合金が5種類以上の当モルの元素より構成されているため，短範囲秩序を持つことが原因だと考えられる．短範囲秩序は，単結晶のX線回折によって得られる散漫散乱の解析や，透過型顕微鏡観察を用いて評価されることは知られている．一般的に，十分大きな単結晶の作製は困難なことが多く，透過型顕微鏡観察は局所情報となる．そのため，今回の電気抵抗率の変化が短範囲秩序によるものであると考えられるため，ハイエントロピー合金の短範囲秩序の評価のみならず，別の合金系でも短範囲秩序が見られる場合には，電気抵抗率測定が有効であることが判明した．ハイエントロピー合金の特異な力学特性や物性には短範囲秩序が影響しているという報告もあるため，今後は別種のハイエントロピー合金の電気特性の測定が期待される．研究課題/領域番号:19H05168, 研究期間(年度):2019-04-01 – 2021-03-31出典：研究課題「スパッタおよび加工熱処理によって作製したハイエントロピー合金の電気特性」課題番号19H05168（KAKEN：科学研究費助成事業データベース（国立情報学研究所）） （https://kaken.nii.ac.jp/ja/grant/KAKENHI-PUBLICLY-19H05168/）を加工して作

Optical skin: Sensor-integration-free multimodal flexible sensing

The biological skin enables animals to sense various stimuli. Extensive efforts have been made recently to develop smart skin-like sensors to extend the capabilities of biological skins; however, simultaneous sensing of several types of stimuli in a large area remains challenging because this requires large-scale sensor integration with numerous wire connections. We propose a simple, highly sensitive, and multimodal sensing approach, which does not require integrating multiple sensors. The proposed approach is based on an optical interference technique, which can encode the information of various stimuli as a spatial pattern. In contrast to the existing approach, the proposed approach, combined with a deep neural network, enables us to freely select the sensing mode according to our purpose. As a key example, we demonstrate simultaneous sensing mode of three different physical quantities, contact force, contact location, and temperature, using a single soft material without requiring complex integration. Another unique property of the proposed approach is spatially continuous sensing with ultrahigh resolution of few tens of micrometers, which enables identifying the shape of the object in contact. Furthermore, we present a haptic soft device for a human-machine interface. The proposed approach encourages the development of high-performance optical skins.Comment: 13 pages, 11 figure

Effects of Rolling Reduction and Strength of Composed Layers on Bond Strength of Pure Copper and Aluminium Alloy Clad Sheets Fabricated by Cold Roll Bonding

Three types of clad sheets, Cu/Al, Cu/AA5052, and Cu/AA5083, were produced by cold roll bonding with the rolling reduction of 50% and 75%. Tensile shear tests which give tensile shear strength were performed in order to assess the bond strength. Scanning electron microscopy was performed on the fractured interface produced by the tensile shear tests, which suggests that the fracture occurs within the Al alloy layer. The tensile shear strengths considering the area fraction of deposit of Al alloy on Cu side were compared with the shear stress converting from the ultimate tensile strengths. As a result, the tensile shear strength of the clad sheets is attributed to the shear strength of Al alloy layer close to the well bonded interface. A simple model was proposed that explains the effects of the rolling reduction and area fraction of deposit of Al alloy

Destruction of mesoscopic chemically modulated domains in single phase high entropy alloy via plastic deformation

Chemically modulated mesoscopic domains in a fcc single phase CrMnFeCoNi equi-atomic high entropy alloy (HEA) are detected by small angle diffraction performed at a synchrotron radiation facility, whereas the mesoscopic domains cannot be detected by conventional X-ray diffraction and 2D mappings of energy dispersive X-ray spectroscopy by scanning electron microscopy and scanning transmission electron microscopy. The mesoscopic domains are deformed and shrieked, and finally destructed by plastic deformation, which is supported by the comprehensive observations/measurements, such as electrical resistivity, Vickers hardness, electron backscattering diffraction, and hard X-ray photoemission spectroscopy. The destruction of the mesoscopic domains causes the decrease in electrical resistivity via plastic deformation, so called K-effect, which is completely opposite to the normal trend of metals. We confirmed that the presence and the size of local chemical ordering or short-range order domains in the single phased HEA, and furthermore, Cr and Mn are related to form the domains

Electronic properties of pulsed laser deposited amorphous carbon and carbon nitride thin films.

This thesis is concerned with the electrical properties of the disordered amorphous material, amorphous carbon and carbon nitride films. At first, hydrogenated amorphous carbon was deposited using rf plasma enhanced chemical vapour deposition with methane as a precursor. Changing the deposition parameter, such as the input power results in the negative self bias modification and thus changes in the properties of the deposited film. The hydrogen condition in the deposition chamber is important for the growth of these films. With the demonstration of an achieve electronic device, a resonance tunnel diode, was reported using pulsed laser deposition; pulsed laser deposited amorphous carbon and carbon nitride thin films were studied. To understand the electrical properties of these films, a wide range of measurements were performed. The surface morphology was examined using atomic force microscopy and scanning tunnelling microscopy. The microstructure was investigated using electron energy loss spectroscopy giving data on the sp2 fraction, density, nitrogen content and Raman spectroscopy showed the degree of sp2 clustering. The band structure was investigated using electron energy loss spectroscopy, scarnning tunnelling spectroscopy and ultraviolet photoelectron spectroscopy, giving information on the density of empty conduction band states, close to the Fermi level and the occupied valence band states. The joint density of states was also measured by ultraviolet-visible-infrared optical transmittance, spectroscopic ellipsometry and Photothermal deflection spectroscopy. Electrical characterisations were carried out using both sandwich and coplanar structures. Pulsed laser annealing of amorphous carbon films was also studied, and the change on the surface morphology, microstructural and electrical properties studied. The conduction mechanism in amorphous carbon films at high electric fields was found to be based on classical Poole-Frenkel conduction, and the dielectric constants estimated from the model were found to be consistent with optical measurements. The neutral trapping centres were postulated to be localised sp2 sites below the conduction band according the analysis of the total band structure. Low field conduction in amorphous carbon films were thought to be controlled by band tail hopping through localised sp2 sites. Laser annealing shows the increase of the number of the sp2 sites which increase the conductivity of the film. However, the sp2 clustering does not necessarily increase the conductivity of the film. The optical band gap in high stress amorphous carbon films can be smaller than the other reports, as a bandtail exists in the bandgap which contributes to the hopping and Poole- Frenkel conduction process. The influence to the nitrogen atoms incorporated to laser deposited amorphous carbon nitride films was also studied. It was found that the nitrogen gas background pressure in the deposition chamber strongly affects the properties of the films. It was demonstrated that a higher nitrogen pressure does not always give rise to higher nitrogen content in the films. Higher nitrogen pressure reduces the velocity of the incident carbon species ablated by the laser, and less dense (less stress) films were deposited. Consequently, the conductivity of the film was reduced. However, the conduction mechanism appears still to be similar to that of amorphous carbon. The analysis of the change in the band structure due to the incorporation of the nitrogen atoms supports the analysis. Thus, the entire band structure of amorphous carbon was linked to the electrical conduction mechanism at both high and low electric fields, including the effect of nitrogen atom incorporation, and pulsed laser annealing. In this thesis we report the highest field effect mobility of a-C and a-CNx films ever reported in the literature of 0.01-0.02 cm2/Vs. This mobility is obtained due to the very high electric field that can be applied to our devices

Electronic properties of pulsed laser deposited amorphous carbon and carbon nitride thin films.

This thesis is concerned with the electrical properties of the disordered amorphous material, amorphous carbon and carbon nitride films. At first, hydrogenated amorphous carbon was deposited using rf plasma enhanced chemical vapour deposition with methane as a precursor. Changing the deposition parameter, such as the input power results in the negative self bias modification and thus changes in the properties of the deposited film. The hydrogen condition in the deposition chamber is important for the growth of these films. With the demonstration of an achieve electronic device, a resonance tunnel diode, was reported using pulsed laser deposition; pulsed laser deposited amorphous carbon and carbon nitride thin films were studied. To understand the electrical properties of these films, a wide range of measurements were performed. The surface morphology was examined using atomic force microscopy and scanning tunnelling microscopy. The microstructure was investigated using electron energy loss spectroscopy giving data on the sp2 fraction, density, nitrogen content and Raman spectroscopy showed the degree of sp2 clustering. The band structure was investigated using electron energy loss spectroscopy, scarnning tunnelling spectroscopy and ultraviolet photoelectron spectroscopy, giving information on the density of empty conduction band states, close to the Fermi level and the occupied valence band states. The joint density of states was also measured by ultraviolet-visible-infrared optical transmittance, spectroscopic ellipsometry and Photothermal deflection spectroscopy. Electrical characterisations were carried out using both sandwich and coplanar structures. Pulsed laser annealing of amorphous carbon films was also studied, and the change on the surface morphology, microstructural and electrical properties studied. The conduction mechanism in amorphous carbon films at high electric fields was found to be based on classical Poole-Frenkel conduction, and the dielectric constants estimated from the model were found to be consistent with optical measurements. The neutral trapping centres were postulated to be localised sp2 sites below the conduction band according the analysis of the total band structure. Low field conduction in amorphous carbon films were thought to be controlled by band tail hopping through localised sp2 sites. Laser annealing shows the increase of the number of the sp2 sites which increase the conductivity of the film. However, the sp2 clustering does not necessarily increase the conductivity of the film. The optical band gap in high stress amorphous carbon films can be smaller than the other reports, as a bandtail exists in the bandgap which contributes to the hopping and Poole- Frenkel conduction process. The influence to the nitrogen atoms incorporated to laser deposited amorphous carbon nitride films was also studied. It was found that the nitrogen gas background pressure in the deposition chamber strongly affects the properties of the films. It was demonstrated that a higher nitrogen pressure does not always give rise to higher nitrogen content in the films. Higher nitrogen pressure reduces the velocity of the incident carbon species ablated by the laser, and less dense (less stress) films were deposited. Consequently, the conductivity of the film was reduced. However, the conduction mechanism appears still to be similar to that of amorphous carbon. The analysis of the change in the band structure due to the incorporation of the nitrogen atoms supports the analysis. Thus, the entire band structure of amorphous carbon was linked to the electrical conduction mechanism at both high and low electric fields, including the effect of nitrogen atom incorporation, and pulsed laser annealing. In this thesis we report the highest field effect mobility of a-C and a-CNx films ever reported in the literature of 0.01-0.02 cm2/Vs. This mobility is obtained due to the very high electric field that can be applied to our devices

微量の遷移元素添加による高比強度高比導電率Al合金の開発

金沢大学理工研究域機械工学系Dut to the recent electrification of transportation equipments, there is a need for a metal material for wires and cables having both high conductivity, high strength, and light weight. Aluminum having low specific gravity is often used for such purposes. Conventionally, high strength of metallic materials has been achieved through alloying by adding large amounts of alloying elements. However, when large amounts of alloying elements are added, free electrons are scattered by the added elements. Therefore, it has been difficult to achieve high electrical conductivity by alloying.In this study, model aluminium alloys having a small amount of transition metal elements were prepared in this study. We have shown that high strength and high conductivity can be achieved by applying spevere plastic deformation by this alloy.近年の輸送用機器の電気化に伴って，高導電率と高強度を両立し，更に軽量なワイヤー・ケーブル用金属材料が必要とされている．そのような目的には，比重の小さいアルミニウムがよく用いられる．従来，金属材料の高強度化は多量の合金元素を添加する合金化を通じて実現されてきた．しかし，多量の合金元素を添加する場合は，添加元素が自由電子を散乱する．そのため，合金化によって高導電率を実現することは難しかった．本研究では，通常用いられない遷移金属元素をアルミニウムに微量添加したモデル合金を準備した．この合金に巨大ひずみ加工を施すことで，高強度化と高導電率化が可能であることを示した．研究課題/領域番号:19K05056, 研究期間(年度):2019-04-01 - 2022-03-31出典：研究課題「微量の遷移元素添加による高比強度高比導電率Al合金の開発」課題番号19K05056（KAKEN：科学研究費助成事業データベース（国立情報学研究所））（https://kaken.nii.ac.jp/ja/report/KAKENHI-PROJECT-19K05056/19K05056seika/）を加工して作