Preliminary List of Abstracts (Alphabetical Order)

2ND INTL. SYMP. ON QUASI-CRYSTALS, METALLIC ALLOYS, COMPOSITES, CERAMICS AND NANO MATERIALS

One of the most effective solutions for reducing environment-damaging emissions and improving fuel economy is to implement lightweight materials in ground vehicles. With the ultra-lightweight feature, high strength-to-weight ratio and superior damping capacity, magnesium has recently emerged as a promising material in the lightweight design and construction for energy efficiency in the automotive and aerospace industry. Despite the potential of substantial reductions in weight, most wrought magnesium alloys exhibit a high degree of mechanical anisotropy and tension-compression yield asymmetry due to the presence of strong crystallographic texture owing to their hexagonal close-packed structure and limited deformation modes. For the vehicle components subjected to dynamic cyclic loading, such problems could exert an unfavorable influence on the material performance. These problems could be tackled through texture modification via alloy composition adjustment, i.e., an addition of rare-earth (RE) elements into magnesium alloys. Despite the fact that the addition of RE elements sheds some light on the alteration in the mechanical anisotropy, the potential advantage of such RE-Mg alloys as structural components under cyclic loading condition has not been well appreciated. An understanding of cyclic plastic deformation is essential for the critical engineering application of Mg-RE alloys. The aim of the present study was, therefore, to identify the cyclic deformation characteristics of RE-Mg alloys under varying strain amplitudes, with particular attention to the effect of RE elements. It was found that the Mg-RE alloy contains a large number of precipitates and possesses a fairly weak texture, which gives rise to much relieved tension-compression yield asymmetry and enhanced fatigue fracture resistance in comparison with the RE-free extruded Mg alloys. The fatigue life of the present alloy was observed to be longer than that of the RE-free extruded Mg alloys. Details about the cyclic deformation behavior of RE-Mg alloys will be presented.

The alloy is a recent introduction in the 8XX.X series of aluminium alloys and hence information about these alloys is very scarce in literatures. The present study involves optimizing thermal treatments parameters of ANSI 852.0 alloy. This alloy is mainly used in bushings and bearings applications due to its antifriction and antisoaring properties enhanced to it by addition of Sn (5.5-7.0%). For this particular application, 165 Mpa Tensile Strength is needed. In this present research work, the attempt was made to optimize the properties of alloy by designing the Heat Treatment Cycle. The various parameters involved are temperature and time function of ageing treatment. Hence 4 treatment cycles have been designed and then experiments were performed subsequently with variation of temperatures and time periods of the stages of treatment cycles. These cycles were designed for Double Ageing treatments. Single ageing was carried out at 220°C for 8 hours Design matrix of 2^2 was developed. The characterization was carried out in view of understanding microstructure, tensile properties, hardness profile, toughness & fractography of samples.

Existing technological synthesis capabilities let you receive samples of macroscopic size only for a limited number of single-quasicrystalls. However, the traditional applications of single crystals in the functional electronics (for example, multiple acoustic wave sensors) may be actual for single-quasicrystalls. The main criteria for such applications of single-quasicrystalls are macroscopic material constants and characteristics of acoustic waves with propagation in them.In this work, pulsed ultrasonic method in macroscopic samples single-quasicrystalls Ag42In42Yb16 with linear dimensions about 1 cm investigated characteristics of acoustic waves' propagation. The elastic constants are analyzed in the isotropic and cubic approximations on the basis of the experimentally determined values of the bulk acoustic waves' velocities. The attenuation coefficients of longitudinal and shear acoustic modes for different directions of propagation determined by attenuation of the reflected pulses series.

In recent years, interest has evolved in electrochemically deposited hydroxyapatite (HAp) and other calcium phosphates as an alternative to the traditional plasma-sprayed (PS) process for coating of orthopedic and dental implants. Thus, we have deposited such coatings on commercially pure Ti and Ti-6Al-4V samples by cathodic polarization. The reaction kinetics was found to be controlled by charge transfer at the interface. As in the human body, HAp formed via transformation of a precursor phase (octacalcium phosphate). The effects of bath pH and temperature were studied experimentally, while a speciation-precipitation model was applied for understanding the effects of bath conditions. Corrosion tests confirm that the porous coatings did not introduce any localized corrosion issues. The effects of mechanical and chemical surface pre-treatments and a surface electron post-treatment on the adhesion strength, surface morphology, wettability and interactions with bone-forming cells and bacteria were also studied.Animal studies were used to quantify osseo-integration and evaluate the level of cracking compared to commercial PS coatings. The importance of coating solubility in vivo will be discussed. The coatings developed in the lab are currently being commercialized.

By means of a combination of SEM, TEM and HREM techniques, the strengthening structures and their changes in heat treated Mg-Gd-Nd and Mg-Gd-Y-Zn alloys have been investigated. HREM observations directly show that the early-aging-stage structure in the Mg-15. 4Gd-1. 6Nd (wt. %) alloy aged at 200°C is characterized by formation of various local ordering of RE solute atoms due to their rearrangements in the Mg matrix. These local ordered structures, which can act as embryos of precipitates are quite small with a size of only a few nanometers. For the Mg97.4-xGd1.8Y0.8Znx (at. %) alloy system, we have found that Zn-content can improve the aging-hardening response at 200°C significantly, and also can affect the formation and stability of long-period stacking (LPS) structure. Various strengthening phases formed at different aging states have been identified and their structural evolutions during aging processes revealed by HREM will be reported.

In the Al-Cu-Fe phase diagram, quasicrystals occupy a narrow region normally surrounded by crystalline and amorphous phases. In particular, a small variation of the ideal quasicrystalline composition means a new crystalline structure like the w-Al70Cu20Fe10 phase (w-phase). Consequently, the w-phase is a simple crystalline phase which can help us to understand the effect of microstrain in Al-Cu-Fe phases due to the nanostructuration of the samples. In this context, in the present work we study the influence of the mechanical milling on the microstrain of nanostructured w-Al70Cu20Fe10 phase. The bulk samples were prepared by arc furnace and then nanostructured by means of mechanical milling in a high energy ball milling equipment SPEX 8000 for different time periods (0-5 hours).The results indicate that the synthesized sample (with tetragonal unit cell and space group P4/mnc) have a high structural quality. The study of the line-broadening intensity and the diffraction line of the un-milled (bulk) and milled (nanostructured) samples using Rietveld method indicates a slight increase of the microstrain from 0.00(5)% up to 0.19(2)%, respectively. Furthermore, the average grain size decreases up to an average value of 12.79(3) nm for the 5 hours milled sample. Additionally, the only increase of the c lattice parameter from c=14.80(8) A… up to c=14.83(1) A… suggests a unidirectional lattice expansion due to the mechanical milling process.

The formation and growth of a magnetic interstitial region after reducing the grain size has been investigated in i-Al64Cu23Fe13 quasicrystalline and w-Al70Cu20Fe10 crystalline phases. The Al-Cu-Fe samples were obtained by arc furnace technique and then nanostructured by means of mechanical milling. The results indicate that the solid samples present a weak ferromagnetic behavior at 300 K, showing a saturation magnetization of 0.124 emu/g for the icosahedral phase (i-phase) and 0.449 emu/g for the tetragonal phase (w-phase). These small values indicate that only a few percentage of the Fe atoms carry magnetic moment. The magnetic response in the nanostructured w-phase increases up to 3.5 times higher than its corresponding solid counterpart.Surprisingly, for the case of the i-phase this increment is about 16 times, which implies a larger magnetic interstitial region in this phase. Moreover, the speed of the variation of the studied physical parameters after reducing the average grain size has been obtained from the exponent of a power law fit of the experimental data. The values of this exponent, corresponding to the magnetic response, are slightly different in each phase, which should be related to the different chemical composition and/or the type of long range order.

Automotive and aerospace sectors have currently a pressing need for structural components that are lighter and stronger, aiming to improve energy efficiency and reduce anthropogenic climate-changing and environment-damaging emissions, while guaranteeing safety and reliability of vehicles. Lightweight aluminum has already a wide variety of structural applications in the transportation industry due to their excellent properties, such as good ductility, formability and thermal conductivity. The structural application of aluminum alloys inevitably involves welding and joining of dissimilar Al-to-steel and Al-to-copper, since both combinations have many potential engineering applications in the automotive and electronic industries, respectively. However, traditional fusion welding of dissimilar Al-to-steel and Al-to-Cu alloys is very challenging, since it produces coarse grains and some defects such as hot cracks. Thus, special attention has recently been paid to the solid-state welding processes. Friction stir welding has been reported to generate brittle intermetallic compounds of Al3Fe and Al5Fe2 in the Al-to-steel dissimilar joints and Al2Cu and Al4Cu9 in the Al-to-Cu dissimilar joints, which decreases considerably the mechanical properties of the welded joints. This study was aimed at exploring the potential of joining dissimilar Al-to-steel and Al-to-Cu alloys using another solid-state joining process - ultrasonic spot welding (USW) technique, and examining the formation mechanisms of the intermetallic compounds during USW using scanning electron microscope, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The effect of welding conditions on the interface microstructure and mechanical properties of the joints such as microhardness, lap shear strength, and fatigue life was evaluated. It was observed that a zinc interlayer placed in-between the two faying surfaces could be used to avoid the formation of the brittle intermetallic compounds, and thus to enhance the bonding strength of the welded joints. Details will be presented at the Symposium.

The mechanical behavior of bundles of ceramic fibers exhibits a characteristic rupture process when subjected to traction, known as avalanche failure. This process is related to the load sharing between bundle fibers once some of the elements begin to fail. Mechanical tests were performed with bundles and Weibull statistics were used to interpret the results of the maximum stress supported by the bundles before the avalanche failure. A computational simulation was originally adapted introducing load sharing models. The simulations were compared to experimental results. Finally, the newly proposed load model was considered to be a better approach for the understanding of the rupture avalanche effect.

It is commonly accepted that an observation of wetting phenomenon requires participation of at least one liquid phase. In the present work, we report on observation of wetting-like phenomenon at interaction between two solid nano-size particles of metals. Merging of silver and gold nanoparticles was observed at their spontaneous contact at room temperature. The experimental part of the study was done with transmission electron microscope (TEM ). The TEM observations were supported with molecular dynamics simulation. Wetting-like behavior of silver on gold was independent on the shape of interacting nanoparticles (sphere-like or rod-like): Silver behaved as a soft matter, while gold was as a hard surface being wetted and retaining its original morphology. The observed type of wetting results in merging of interacting nanoparticles which, then, share a stable atomic interface without detectable alloying. We discuss the observed phenomenon as an interplay between thermodynamics and local redox chemistry at nano-scale.

This study investigates the numerical simulation and theoretical modeling of longitudinal and transverse compressive failure in fiber reinforced composite materials. Firstly the numerical simulation of longitudinal compressive failure is conducted. The simulated results show that at one moment of the loading, the localized deformation catastrophically appears in the material, and the reduction of tangent shear stiffness plays an important role in this initiation of the localized deformation. Then a set of mathematical equations is obtained for the deformation of composite materials, and the mathematical solution of the equations is considered. There exists a state where arbitrariness occurs in solution of equations expressing deformation of composite materials. It is indicated that onset of arbitrariness in solution of equations expressing the deformation of composite materials is closely related with the initiation of longitudinal compressive failure, and also related with the initiation of narrow localized band in the materials. Secondly the transverse compressive failure is investigated. In the numerical simulation, multiple shear bands appear in the material, and one of the shear bands develops to the entire material, and the transverse compressive failure is formed in the material. The theoretical model of transverse compressive failure shows that the critical stress value is represented by fiber volume fraction, matrix Poisson's ratio, matrix yield stress and angle of shear band. Finally the numerical simulation of compressive failure in quasi-isotropic laminate is conducted. The localized deformation also appears in the laminate, and the simulated deformation of the material agrees with the microscope picture of the experimental result.

G. Stewart's sibotaxes are prominent among the quasi-crystal theories. More recently, an equivalent term "cluster" was coined. The following example is of particular interest for metallurgists. The icosahedronic symmetry is observed in the recently discovered (1984) state of a substance possessing a special type of the long-range order, the state being referred to as quasi-crystal. First, it was discovered by D. Shechtman in the Al-Mn melts, then in many other metal melts after quench hardening. The materials possessing similar structure were also termed as "shechtmanit". The fact that the quasi-crystal state is fixed as a result of melt rapid quenching is an evidence of the atoms being put in such order.The concept of the quasi-chemical model of the liquid micro-non-uniform composition is being developed under the supervision of B.A. Baum in our laboratory. According to it, the metal melt consists of space areas (groups, sibotaxes or clusters) within which the atom arrangement is characterized by certain ordering "short-range" order.The unique technology of the melt time-temperature treatment has been developed taking into account the above concept and research made on the physical properties of the metal- and cobalt-based melts being crystallized. Amorphous ribbons produced with this technology require optimal annealing temperatures to be specifically selected. The results of studying nano-crystal magnetic circuits' properties and their structure in the course of annealing at temperatures below and above the optimal one are presented.The proposed approaches, which are scientifically justified, enabled producing magnetic soft nano-crystal magnetic circuits possessing an extremely low coercive force (about 0,1 A/m) and high initial magnetic permeability (about 200 000) with the saturation magnetic induction of 0,4 T. The maximum relative magnetic permeability is less than 600 000.

Crystallography has been one of the mature sciences. Over the years, the modern science of crystallography that started by experimenting with x-ray diffraction from crystals in 1912, has developed a major paradigm - that all crystals are ordered and periodic. Indeed, this was the basis for the definition of "crystal" in textbooks of crystallography and x-ray diffraction. Based upon a vast number of experimental data, constantly improving research tools, and deepening theoretical understanding of the structure of crystalline materials no revolution was anticipated in our understanding the atomic order of solids. However, such revolution did happen with the discovery of the Icosahedral phase, the first quasi-periodic crystal (QC) in 1982, and its announcement in 1984 [1, 2]. QCs are ordered materials, but their atomic order is quasiperiodic rather than periodic, enabling formation of crystal symmetries, such as icosahedral symmetry, which cannot exist in periodic materials. The discovery created deep cracks in this paradigm, but the acceptance by the crystallographers' community of the new class of ordered crystals did not happen in one day. In fact it took almost a decade for QC order to be accepted by most crystallographers. The official stamp of approval came in a form of a new definition of "Crystal" by the International Union of Crystallographers. The paradigm that all crystals are periodic has thus been changed. It is clear now that although most crystals are ordered and periodic, a good number of them is ordered and quasi-periodic. While believers and nonbelievers were debating, a large volume of experimental and theoretical studies was published, a result of a relentless effort of many groups around the world. Quasi-periodic materials have developed into an exciting interdisciplinary science. This talk will outline the discovery of QCs and describe the important role of electron microscopy as an enabling discovery tool.[1] D. Shechtman, I. Blech, Met. Trans. 16A (June 1985) 1005-1012.[2] D. Shechtman, I. Blech, D. Gratias, J.W. Cahn, Phys. Rev. Letters, Vol 53, No. 20 (1984) 1951-1953.

It was a surprising discovery nearly ten years ago that the ground state Bohr radius of hydrogen atom is divided into two Golden sections pertaining to the electron and proton. This resulted in the cascade of findings which led to the general result that the bond lengths d(AA) between two atoms of the same kind are sums of the cationic and anionic radii. This enabled to establish that atomic and Golden ratio based ionic radii are additive in the bond lengths of small as well as large molecules. Further, the covalent bond lengths of elements were shown to be linearly related to their Bohr radii obtained from their first ionization potentials and that for all elements the ratio of the covalent radii to their Bohr radii is a simple function of the Golden ratio.

We shall illustrate the fundamental role played by nanoplasmonics in a number of nanodevices showing different characteristics in terms of topological and material point of view, and oriented to different applications. In particular, we shall start by describing how superhydrophobicity can be used to go beyond the diffusion limit, hence allowing the realization of devices capable of detecting, in a very short time, an extremely small number of molecules [1,2]. We shall proceed by introducing 3D suspended devices which, similarly to the hydrophobic ones, can find suitable applications in the SERS field but, on the other hand, do not need to reproduce a superhydrophobic layout. Finally, by joining the concept of adiabatic compression and hot electrons, we shall demonstrate how nanoplasmonics can, once again, amaze us by allowing the realization of a new kind of nanoscopy [3].[1] Nature Nanotechnology (doi:10.1038/nnano.2009.348).[2] Nature Photonics (doi:10.1038/nphoton.2011.222).[3] Nature Nanotechnology (doi:10.1038/nnano.2013.207).

Monolayer or a few atomic layer thick graphene coatings on metals (Figure (left)) have been shown to improve their corrosion resistance by nearly orders of magnitude (Figure (right)). Though there are very few studies reported on the topic of corrosion resistance due to graphene coating, there is still considerable variability in the degree of improvement. For example, improvement in aqueous corrosion resistance of copper due to graphene coating is reported to vary from insignificant to nearly 2 orders of magnitude, whereas the improvement for nickel can be in excess of an order of magnitude. This presentation will review the most recent (2010-14) research on graphene that has been claimed as 'the thinnest known corrosion-protecting coating', and potential application of such disruptive approach to corrosion resistance of steels.The second part of the presentation will focus on the remarkable resistance to oxidation as result of the nanocrystalline alloy structure. This will include an elaborate description of the author's own hypothesis that nanocrystalline structure can impart extraordinary oxidation resistance, and the validation of this hypothesis. A thorough surface/subsurface characterization of oxidized alloys, using secondary ion mass spectrometry has provided a sound mechanistic understanding of the remarkable improvement in oxidation as result of nanocrystalline structure. The data to be presented will include the results establishing that a Fe-Cr nanocrystalline alloy with only 10wt% Cr can provide as much oxidation resistance as a Fe-20Cr alloy, suggesting possibility of Fe-Cr alloys with the necessary corrosion resistance at much lower Cr contents. As another exciting potential application of this work, the nanocrystalline powders of Fe-Cr alloys synthesized in this study could be used for developing corrosion resistance coating having considerably low Cr contents.

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