Advanced Materials Research Vol. 1154

Abstract: Bulk metallic glasses (BMGs) and their composites (BMGMC) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very high elastic strain limit. However, they suffer from a lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which render them to failure without appreciable yielding owing to mechanisms of rapid movement of shear bands all throughout the volume of the material. This severely limits their use in fabricating structural and machinery parts. Various mechanisms have been proposed to counter this effect. Introduction of secondary ductile phase in the form of in-situ nucleating and growing dendrites from melt during solidification have proved out to be best solution of this problem. Nucleation and growth of these ductile phases have been extensively studied over the last 16 years since their introduction for the first time in Zr-based BMGMC by Prof. Johnson at Caltech. Data about almost all types of phases appearing in different systems have been successfully reported. However, there is very little information available about the precise mechanism underlying their nucleation and growth during solidification in a copper mould during conventional vacuum casting and melt pool of additively manufactured parts. Various routes have been proposed to study this including experiments in microgravity, levitation in synchrotron light and modelling and simulation. In this report consisting of two parts which is a preamble of author’s PhD Project, a concise review about evolution of microstructure in BMGMC during additive manufacturing have been presented with the aim to address fundamental problem of lack in ductility along with prediction of grain size and phase evolution with the help of advanced modelling and simulation techniques. It has been systematically proposed that 2 and 3 dimensional cellular automaton method combined with finite element (CAFE) tools programmed on MATLAB® and simulated on Ansys® would best be able to describe this phenomenon in most efficient way. Present part consists of general introduction of bulk metallic glass matrix composites (BMGMC), problem of lack of ductility in them, measures to counter it, success stories and their additive manufacturing.

Abstract: . Bulk metallic glasses (BMGs) and their composites (BMGMC) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very high elastic strain limit. However, they suffer from a lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which render them to failure without appreciable yielding owing to mechanisms of rapid movement of shear bands all throughout the volume of the material. This severely limits their use in the manufacture of structural engineering parts. Various theories and mechanisms have been proposed to counter this effect. Introduction of secondary ductile phase in the form of in-situ nucleating and growing dendrites from melt during solidification have proved out to be best solution of this problem. Nucleation and growth of these ductile phases have been extensively studied over the last 16 years since their introduction for the first time in Zr-based BMGMC by Prof. Johnson at Caltech. Data about almost all types of phases appearing in different systems have been successfully reported. However, there is very little information available about the precise mechanism underlying their nucleation and growth during solidification in a copper mould during conventional vacuum casting and melt pool of additively manufactured parts. Various routes have been proposed to study this including experiments in microgravity, levitation in synchrotron light and modelling and simulation. In this report, which is Part B of two parts comprehensive overview, state of the art of development, manufacturing, characterisation and modelling and simulation of BMGMCs is described in detail. Evolution of microstructure in BMGMC during additive manufacturing have been presented with the aim to address fundamental problem of lack in ductility along with prediction of grain size and phase evolution with the help of advanced modelling and simulation techniques. It has been systematically proposed that 2 and 3 dimensional cellular automaton method combined with finite element (CAFE) tools programmed on MATLAB® and simulated on Ansys® would best be able to describe this phenomenon in most efficient way. Present part B focuses on methodology by which modelling and simulation can be adopted and applied to describe evolution of microstructure in this complex class of materials.

Abstract: Double rare-earth (La; Sm/Gd) substituted Aurivillius family of Bismuth Layered Structured Ferroelectrics (BLSF) namely Bi_2.6Sm_0.2La_0.2TiNbO₉ (BSLT; sample-A), Bi_2.6Gd_0.2La_0.2TiNbO₉ (BGLT; sample-B), single phase ceramics were prepared by solid state route. In addition, intergrowth (x BSLT - (1-x) BGLT, where x=0.49; sample-C) and solid solution (BSLT_­x - BGLT_y; where x + y=0.4; sample-D) materials were prepared. Dielectric, ferroelectric and Raman spectroscopic properties were studied on the said above materials. The X-ray diffraction analysis and Raman spectra revealed well-formation of stable structure. Though, the sample-C and sample-D have lower coercive field, compared to the sample-A and sample-B, but they exhibited sharp hysterisis loop. Therefore the instrinsic defects of sample-D inhabits more sensitivity towards the ferroelectric behaviour. The results were corroborated to the impedance and dielectrical data. The results were consistent with the SEM micrographs and complex impedance plots. An attempt is made to understand the effect of rare-earth ions on A-site of layered-pervoskite structure, defined as: (Bi₂O₂)²⁺(A_n-1B_nO_3n+1)^2-.The term n represents number of pervoskite blocks interleaved with the bismuth oxide layers.

Abstract: Electropolishing is an attractive method for surface smoothing of cardiovascular stent. This study investigated the effect of times of electropolishing on the surface characteristics both are upper surface and surface of the strut of cardiovascular stent after the by die sinking electrical discharge machining (EDM). The observed surface characteristics of the strut were recast layer, surface roughness and brightness. The weight analysis, and the reduction of the width strut were conducted. The recast layer was analyzed by optical microscope qualitatively, the surface roughness was measured by surface texture measuring instrument, the weight analysis and the reduction of width strut were calculated. The stent was made from steel AISI 316 L. The times which were used in the electropolishing were 3 minutes, 7 minutes, and 11 minutes. The experimental results show that the time for smoothing and brightening of stent at room temperature and low voltage 5 V is 7 minutes. The times affect the upper and EDM surface roughness, the weight of stent and the width of strut. The results show that increasing of times, than the value of surface roughness, the weight of stent and the width of strut will decrease, and vice versa. The average surface roughness of EDM surface after electropolishing is in the range of 3.49 – 1.62 µm. The average surface roughness of upper surface after electropolishing is in the range of 0.55-0.22 µm. The weight analysis show that the loss of weight is in the range of 0.12-1.12 %, and the reduction of width strut is in the range of 11.02 – 69.3 %.

Abstract: In this article, simulation results of novel and facilitated heterostructures of the Second Generation (2G) Thin-film Solar Cells (TFSCs): hydrogenated amorphous Silicon (a-Si:H), Cadmium Telluride (CdTe), and Copper Indium Gallium di-Selenide (Cu(In,Ga)Se₂ or CIGS) have been presented to compare their performances. The solar cells have been modeled and analyzed for investigating optimized structure with higher stabilized efficiency. Entire simulations have been accomplished using Analysis of Microelectronic and Photonic Structures – 1 Dimensional (AMPS-1D) device simulator. The thickness of the absorber layer was varied from 50 nm to 1400 nm for a-Si:H and from 50 nm to 3 μm for both CdTe and CIGS cells to realize its impact on cell performance. The utmost efficiency, η of 9.134%, 20.776%, and 23.03% were achieved at AM 1.5 (1000 W/m²) for a-Si:H, CdTe, and CIGS material cells, respectively. Lastly, the operating temperature of the three cells was varied from 280°K to 328°K to realize its effect on the cell PV performances.

Abstract: By a theoretical consideration of a viscous body it has been deduced a formula for the description of the fatigue properties of ductile metals and plastic materials. This formula has been compared with experimental fatigue data of Wöhler-curves (S-N curves). For cellulose acetate, iron, copper, nickel, silver, zinc and, to a restricted degree, also for aluminum a sufficient accordance between the experimental data and the theoretical curves has been reached. With this procedure it is possible to determine fatigue limits for these materials. Similar results are obtained for the creep of brass. It is supposed that the cause of the fatigue limit is the near surface stress of the specimen.

Abstract: The Electrochemical frequency modulation and Reactivation investigation results have shown that the anticorrosion inhibitors of 3a,6a- bistolylthioglycoluril, 4,5-dihydroxy-4,5-bistolylimidazolidine-2-thione and 5,5-bistolyl-2-thione-4-imidazolidone maximally reduced H⁺ impacts on metal surface so these inhibitors have decreased the degree of sensitization to intergranular stress corrosion cracking on N80 steel surface.

Abstract: Studies have revealed that wood ash cement concrete just like other pozzolanic cement concrete has lower early strength compared to plain cement concrete. Nanoparticles have been found to improve the early strength of concrete due to its small size and large surface area. This paper reports the findings on influence of nanosilica on the workability and compressive strength of wood ash cement concrete. Wood ash was obtained as a waste product from Ladoke Akintola University of Technology (LAUTECH) bread bakery, Ogbomoso. Biological synthesis of nanosilica using kola pod extract and silica precursor (1:5) was conducted at Nanotechnology research group laboratory at LAUTECH. The chemical composition, specific gravity and grading of wood ash, fine and coarse aggregate used were determined. Concrete with 10% wood ash replacement for cement was produced using 1:2:4 mix proportion and water to binder ratio of 0.5. Nanosilica was added at 0.5, 1.0, 1.5 and 2.0% levels. Concrete with no wood ash and nanosilica served as the control. Workability and compressive strength of the plain and composite concrete were determined. The results showed that concrete workability was enhanced with introduction of nanosilica. The compressive strength also increased with the addition of nanosilica. Maximum compressive strength of 27.53MPa was achieved at 90 days with 1.5% nanosilica addition. It was concluded that nanosilica enhanced workability and improved both early and later strength development in wood ash concrete with 1.5% as the optimum addition.

Abstract: Before and after the completion of a project we often encounter unforeseen events that affect the sustainability of the project. We understand that engineers and practitioners need to look for the best average or process in terms of quality and cost, to ensure project maintenance. Among the possible methods; we can quote the concrete reinforced by the metallic fibers between the pavement and asphalt concrete pavement, the latter will ensure the continuity between two materials (flexible-rigid). This work consists of studying the formulation of a metal fiber concrete based on local materials (cement, gravel and sand) and studying the effect of fibers. The results of this study highlighted the improvement of both the mechanical properties of concrete and the problem of cracking between the pavement and pavement concrete joints.