Designing of Interfacial Structures in Advanced Materials and their Joints

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Authors: Masaaki Naka
Abstract: Strength of nanostructured Cr-B and Cr-Ni alloys prepared by sputtering was related with grain size. The alloying of B or Ni to Cr reduces the grain size of the alloys. The increase in volume of grain boundaries or amorphous phase induced by alloying elements causes the departure of strength of nanostructured Cr alloys from the values estimated by the Hall-Petch relation. The formation and microhardness of Cr or Ti base amorphous alloys could be discussed by the chemical bonding between elements. The strength of dissimilar joints was dominated by the thickness and structure of the interfacial reaction zone between SiC and metal. The formation of interfacial reaction zone is discussed by the change of chemical potentials of elements between ceramics and metal.
Authors: Yukichi Umakoshi, Hiroyuki Y. Yasuda, Toshiya Sakata
Abstract: Crystallographic relation between NiAl (β ) grains and Ni3Al (γ ' ) precipitate was examined using Ni-38at%Al bicrystals with an oriented grain boundary. Microstructure and texture in B2 type intermetallic compounds such as NiAl and FeAl were controlled by a thermomechanical process focusing on obtaining highly developed <111> texture and improving ductility.
Authors: Adina Berbecaru, Masaaki Naka, Julius C. Schuster
Abstract: The ternary system Cu-Si-Ti was investigated using XRD, SEM-EDX, and DTA. The existence of two ternary phases τ1-CuSiTi and τ2-TiSi2-xCux as well as their crystal structures are confirmed. The isothermal section at 800°C is corroborated. From DTA data of equilibrated alloys a reaction scheme linking the isotherm at 700°C with the liquidus surface is derived. Using data on primary crystallisation of as cast alloys a projection of the liquidus surface is proposed.
Authors: J.E. Indacochea, J. Beres, A. Polar
Abstract: There is need for efficient energy conversion systems based on domestic fossil or biofuels. Solid Oxide Fuel Cells (SOFC's) are attractive in this case, however sealing is a critical issue in SOFC development. The purpose of this investigation is to find a procedure to seal yttria stabilized zirconia (YSZ) electrolyte to the stainless steel electrical interconnect or gas manifold. The seal is usually exposed to high temperatures in the range of 500 to 1000°C. Brazing by in-situ alloying of nickel and titanium foils was performed to braze zirconia to 444- stainless steel. Different combinations of nickel/titanium foils were used; brazing was done in vacuum at 6 x 10-6 torr at 960°C, 1010, and 1030°C for different brazing times. The braze and interfacial microstructures were characterized by optical microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). This paper assesses the effect of process parameters on the development and stability of the braze metal and the interactions of the filler metal with the two substrates.
Authors: Wolfgang Tillmann, Miriam Gathen, Artur Martin Osmanda
Abstract: Currently there is an increasing demand for composites and joints composed of hard materials, such as ceramics, superabrasives or metal-carbides, and metals. Wear pads, welded or brazed machining tools or composites employed for grinding tools are typical fields of application. All those various materials solutions have in common that there are interfaces between materials that typically have a covalent or ionic bonding and metals. Consequently, wetting and bonding problems arise. The paper presents different examples and discusses them with emphasize on the corresponding interfacial interactions. Furthermore measures are analysed that can be taken to influence the intensity and strength of the interfacial bonding between the materials to be joined.
Authors: Jindřich Musil, P. Zeman
Abstract: This article reports on a new class of amorphous a-Si3N4/MeNx nanocomposite coatings with a high (≥50 vol.%) content of Si3N4 phase; here Me=Zr, Ta, Mo and W. These nanocomposites exhibit high (>1000°C) thermal stability against crystallization and high (>1000 °C) oxidation resistance if the metal Me incorporated in the nanocomposite is correctly selected. It was found that the Zr-Si-N film deposited on Si(100) substrate exhibits no increase of the mass (m=0) in thermogravimetric measurements performed in flowing air up to 1300 °C, i.e. up to the temperature that is the thermal limit for Si substrate but not for nanocomposite.
Authors: Lin Wu, Hai Chao Li, Hong Ming Gao, Guang Jun Zhang
Abstract: This paper presents a generic design and implementation of a telerobotic system application for the remote welding of unstructured and hazardous environment. The objective is to establish a remote welding telerobotic system that is flexibility to carry out welding seam tracing and welding remotely. According to the difference of welding task and environment, this paper presents human machine cooperative control strategies that integrate sensor and model-based computer assistance. The human operator decision and control commands participate into every control level of the teleoperation system. The specific control modes have been presented to integrate into human machine interface (HMI).
Authors: J.C. Feng, Peng He, Heinz Hackl
Abstract: Distribution of Zn and interfacial microstructure of braze-welding CMT joints between aluminium and galvanized steel sheets were researched. The results showed, except the gas porosity contains a little Zn, the other areas of fusion zone almost have no Zn. Temperature plays a decisive role in the distribution of Zn. The content of Zn is higher in the dendritic crystal than the intergranular part. The Zn coat adjacent to the joint is almost evaporated entirely. The Zn coat of steel sheet in the heat-affected zone around the joint is badly destroyed, and the corrosion resistance of the joint will decline. There are FeAl3 intermetallics and Al-Fe-Zn triphase solid solution formed at the interface.
Authors: Toshiharu Fukunaga, Keiji Itoh, Kazuhiro Mori, Masaaki Sugiyama
Abstract: Reverse Monte Carlo (RMC) modeling, based on diffraction data, was applied to various kinds of amorphous materials to visualizing the three-dimensional atomic arrangement and to elucidate topological characteristics. For an as-grown amorphous carbon nanocoil, it could be clarified that graphene sheets are winding and the regular ABAB… stacking is lost and the configuration gradually changes to the hexagonal network with great regularity through heat treatment. Voronoi analysis of the RMC model could characterize the atomic configurations for NiZr2 and CuZr2 metallic glasses. The Zr environments are very similar in the two systems, but there are marked differences between the polyhedra around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by prismatic-like polyhedra. In contrast, icosahedron-like polyhedra are preferred for Cu.
Authors: Shuji Ogata, Takahisa Kouno
Abstract: There is growing demand to perform dynamic, atomistic computer-simulation of nano-scaled interfaces. For dynamic simulation of interesting processes at the nano-interfaces, we have been developing the hybrid simulation schemes by concurrently coupling the quantum description as the electronic density-functional theory and the classical description as the classical molecular dynamics. A quantum (QM) region composed of a relatively small number of atoms, is embedded with the novel buffered-cluster method in a classical (CL) region of atoms interacting through an empirical inter-atomic potential. The hybrid QM-CL simulation scheme is applied to various kinds of nano-processes including implantation of oxygen atoms to a Si slab relating to SIMOX technology.

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