Key Engineering Materials Vol. 804

Abstract: Graphene-aluminum (Gr/Al) composite laminated by aluminum (Al) and graphene sheets alternately has excellent mechanical properties thanks to the high strength, high Young’s modulus and the two-dimensional atomic structure of graphene. In this study, the uniaxial tensile properties of Gr/Al nano-laminated composite are studied by molecular dynamics (MD) method. It is found that the thickness of Al layer has a significant effect on the tensile strength and Yang’s modulus of the Gr/Al composite. Composite with a smaller thickness of Al layer shows better properties. Graphene not only block propagation of dislocations, but bear most of the loads, resulting in higher Young's modulus, tensile strength and failure strain of the composites than those of pure Al. The simulation of temperature-effect shows that the Gr/Al composite is difficult to arise plastic deformation at low temperature, which lead to a higher strength and modulus of the composite. In addition, the effect of graphene stacking on the properties of composites is investigated. Through tensile tests at the vertical and parallel interfaces, it is found that graphene stacking may lead to a reduced performance of the composite.

Abstract: The purpose of incorporating CNTs into ceramic materials is to enhance the toughness of ceramic materials, in which the interface plays a key role. Due to the nanoscale of nanocomposites, however, it is not easy to acquire a direct knowledge of the interface behavior. In this research, we simulated the dynamics of CNT/SiC and branched CNT/SiC under uniaxial tensile stress using molecular dynamics method (LAMMPS). The simulation method using molecular dynamics provide an insight into designing an effectively toughened ceramic nanocomposite materials.

Abstract: This paper considers a problem of detecting nanosheets which are moving in colloidal liquid from confocal laser scanning microscopy (CLSM) images. Introducing the deep learning approach, we particularly develop a scheme for constructing the so-called `detection map’ consisting of the brightness value information on the area of nanosheets in CLSM images. Therein, we use an architecture of deep learning network ‘U-net’ and present how to implement such a network. The performance is demonstrated by some experimental studies.

Abstract: A soft actuator is expected to be applied in the next generation of robotics. This study focuses on soft gel actuators hybridized with nanosheet liquid crystals. The resulting soft actuator has a highly hydrophilic property, and is suitable for underwater use. When the gel in water is heated to more than the transition temperature, the gel contracts; conversely, it swells when it is cooled. This gel actuator remarkably has an anisotropic contraction characteristic because the orientation of the nanosheets is uniformly arranged. However, little is known about its dynamic characteristics of the thermal contraction. As a basic analysis, this paper investigates the heating step response through experiments, and reveals the variation of the time constant against the dimensions.

Abstract: In this study, Mg-based alloys were prepared by rapid solidification of twin roll casting (TRC), then microstructure and element distribution were investigated respectively with Scanning Electron Microscope (SEM) and Electron Probe Micro Analyzer (EPMA). What’s more, in order to analyze microstructure and crystal structure of Mg-based alloys, experiments on specimens with the usage of X-ray diffraction (XRD) and Transmission Electron Microscope (TEM) were also carried out. At last, the designed Mg-Re magnesium alloy with quasi-amorphous phase plus fine crystalline phase dual phase microstructure produced with our rapid solidification of TRC process. The rapid solidification process realized with a faster casting speed and a thinner roll gap that does not need any anther additional devices and vacuum environment. EPMA results and TEM analyses show that the quasi-amorphous phase has a high concentration in Al and RE element. There are quasi-amorphous phase in the middle of Mg-Re alloy cross section surrounded by dendrites phase and normal crystals. Acknowledgement. This work was supported by Cooperative Research and Development Center for Advanced Materials (CRDAM) funded by the Institute for Materials Research (IMR), Tohoku University (Project Number 18G0042).

Abstract: In this study, magnesium alloy AZ31 was successfully welded with aluminum alloy 6061 by diffusion bonding method. In addition, annealing process was applied to refine micro-structure and improve mechanical property. Microstructure and elemental distribution of interface were investigated with Scanning Electron Microscope (SEM) and Electron Probe Micro Analyzer (EPMA). Furthermore, experiments on diffusion bonded specimens with the usage of Transmission Electron Microscope (TEM) were carried out. At last, tensile strength was measured. It can be obtained that the width of diffusion layers increase with the increasing annealing temperatures. Elemental distribution of specimens with annealing were more uniform than that without annealing. The intermetallic compounds in diffusion layers are Al₃Mg₂ and Al₁₂Mg_17, their crystal structure are respectively face-centered cubic (fcc) and body-centered cubic (bcc). What’s more, tensile strength turns to be strongest after annealing at 250°C.

Abstract: This study proposed the new method of preparing Mg-based composite by mixed powder Ni and Ti onto the surface of pure Mg ingot. The prepared method caused that hydrogen absorbing phase Mg₂Ni and catalytic phase NiTi generated and distributed regularly. The pure Mg ingot as the center and the powder Ni and Ti as cladding material on the surface were formed and sintered, in which the temperature range of generated alloy phase Mg₂Ni and NiTi was confirmed at first; according to the temperature range, the size of Mg₂Ni and NiTi crystal grains at 650°C and 850°C were analyzed and compared, respectively; The size of Mg₂Ni alloy phase at the surface and center was calculated by comparing the atomic radius of Ni, Ti to confirm that Mg₂Ni distributed on the surface due to the atom Ti replaced the atom Ni in Mg₂Ni to generate the alloy phase NiTi; the capacity of the hydrogen desorption reached 4wt% within 5min. The disadvantages that easy to chalking and difficult to activate in the conventional method were avoided and achieved the application of the multilayer composite material in hydrogen storage field.

Abstract: In recent years, global warming is a serious international problem. We focused on dielectric elastomer power generation to solve the problem. The dielectric elastomer generation has characteristics such as compactness and flexibility. The dielectric elastomer generation can harvest electric energy from renewable energy sources such as sea wave, wind, and human motion. However, the dielectric elastomer generation has a weakness dependent on an external power supply. In this paper, we proposed a self-excited dielectric elastomer generation circuit using piezoelectric elements. As a circuit verification method, circuit simulations are performed using MATLAB / Simulink, and the circuit behavior is confirmed from the results. From results, it is considered that dielectric elastomer generation can be performed without using the external power supply.

Abstract: The bond coat plays an important role in the failure of the thermal barrier coating (TBC) system used for gas turbines ^{[1, 2]}. In this research, the CoNiCrAlY coated Ni-base superalloy specimens were used for developing evaluation method for interfacial damage in the coat. Samples were exposed at 1000°C and 1100°C for up to 1000 hours. The morphology and residual stress in the thermally grown oxide (TGO) layer on the CoNiCrAlY coating were characterized by microscopic observation and luminescence spectroscope, respectively. The microstructure and damage o\n both the coating surfaces and the cross sections were observed by optical microscope and scanning electron microscope. According to the results, the low pressure plasma sprayed CoNiCrAlY coating (LPPS) showed the thinnest TGO layer and lowest residual stress.Residual stress decreased with an increase in exposure time, depending on the morphology of TGO layer. The effects of thermal spraying methods on the oxidation of yttrium in TGO layer and BC layer and its influence on interfacial damage were discussed.