Papers by Keyword: Crystallization

Abstract: Amorphous alloys are promising structural materials because of their high mechanical strength. Their drawbacks are low ductility and severe size restrictions for components obtained by casting. Additive manufacturing by selective laser melting (SLM) consists in successive fusion of small portions of material to add to a growing part. Each portion is subjected to a short thermal cycle favorable for amorphization. Thus, one can build an amorphous part as large as necessary. We study the microstructure of cast samples of a zirconium-based bulk metallic glass after laser processing with the parameters typical for SLM. Scanning electronic microscopy has shown partial crystallization in the heat affected zone of the laser beam. The spatial distribution and the volume fraction of the crystalline phase can be controlled by laser processing parameters. The obtained amorphous-crystalline structures are promising to increase the ductility of bulk metallic glasses.

Abstract: A review of publications on metallurgical and foundry production showed that many authors, when analyzing the properties of liquid metals and alloys, proceed from the concept of their cluster structure. The cluster structure of a liquid is a hypothesis, but it is confirmed by studies of diffraction of X-rays, electrons and neutrons reflected from its surface. This paper considers the existing concept that a cluster is a crystal-like concentration of atoms. Around the clusters there is a weakened zone, which consists of disordered atoms, the volume of which does not exceed 3 ... 5%, and this provides the fluidity of many melts. The authors of the publications have achieved success in explaining the forming structure of ingots, proceeding from the cluster mechanism of the crystallization of liquid metals and alloys. The authors of this work suggested that the superheated liquid metal in the head of the bath, which has smaller clusters, moves under the action of magnetic fields to its tail, and provides refinement of the weld metal structure during welding with the action of a control transverse magnetic field.

Abstract: In this study, Aluminum (Al) and Manganese (Mn) co-doped ZnO thin films were successfully synthesized into glass substrates by the sol-gel dip-coating method with different Al concentrations (1%, 3%, and 5%). The structural, morphological, and optical properties of the obtained thin films were characterized by X-ray diffraction (XRD), Atomic force microscopy (AFM), and UV–VIS spectroscopy. XRD pattern revealed that the films have a polycrystalline hexagonal structure with a preferred orientation along (101) for undoped ZnO thin films, further the co-doped ZnO thin films show a shift in the preferred orientation to (002) direction without any Mn or Al related phases. The morphological analysis showed that the films have a uniform and dense ZnO grains, without any voids and cracks, and it was found that the surface roughness (RMS) increases from 8,27 to 14,43 nm when the Al doping concentration increased from 1% to 3%; however, when Al doping concentration is 5%, the RMS value decreased to 2,80 nm. From the optical analysis, the higher average transmittance was found to be corresponding to 5% Al doping concentration.

Abstract: The properties of bulk metal products are formed when molten metal transforms from an unstructured liquid into a solid crystal state. We suggest a new approach to the automation of the control over crystallized metal shrinkage compensation based on controlling the law of change in pressure applied to crystallizing metal through a program taking into account the transition process in the hydraulic system of the production equipment. We observed the increase in rigidity, durability, and pliability of В95-alloy samples as compared to cast aluminum alloys. The metal utilization rate can be increased up to 0.90 of the liquid metal volume.

Abstract: The article deals with the influence of crystallization additives on the life of self-compacting concrete (so-called SCC concrete), which are exposed to chemically aggressive environments. The focus is not only on the effect of the crystallization additive on the characteristics of the capillary-pore structure of SCC concrete, but especially long life durability of self-compacting concrete (two years expozition). The effect of individual types of aggressive environment is assessed on the basis of a set of physico-mechanical and physico-chemical analyzes.

Abstract: The article examines the process of crystallization of Wood alloy using the ultrasonic method. The dependence of the determination of the speed of sound in three aggregate states of the alloy (liquid, solid, transition (liquid-solid)) was derived. The relation-ship with the amplitude values of the sound signal, a single pulse in determining the speed of sound, as well as in determining the state of the alloy is carried out. The data obtained allow us to analyze the state of the alloy and the measurement time and the specified frequency range directly in the process of crystallization.

Abstract: At present, casting and wrought high-strength and light aluminum alloys are widely used in the creation of a number of products and units in mechanical engineering, aviation and space technology. The process of developing alloys includes the formation of initial design data covering the operating conditions, the necessary physical, mechanical and other characteristics of products, and also considers the requirements of manufacturability in their manufacture and ensuring a given structure. To achieve these goals, when smelting aluminum alloys, Al-Mg, Al-Cu, Al-Mn, Al-B, Al-Ti ligatures are used. Despite the widespread use of ligatures, there is no single set of requirements for their quality. However, recent studies in the field of structural heredity in the "charge - melt - cast product" system have shown that the structure of the ligature has a significant hereditary effect on the crystallization process, structure and properties of the modified alloy. In this work, a study of the Al-5Ti-1B master alloy was carried out using synchronous thermal analysis, which made it possible to establish such properties as: the magnitude of the thermal effect, the temperature of its onset, enthalpy, and the crystallization interval. The results obtained make it possible to expand the bank of initial data to improve existing programs for modeling casting processes and to develop new ones.

Abstract: Sulphated zirconia (SZ) is one of the most important solid acid catalysts was synthesize at different operating conditions,different calcination temperature and sulfonating time has been used. The prepared catalyst was distinguished by X-ray Diffraction (XRD), particle size and morphology of catalyst were checked by atomic force microscopy (AFM) and scanning electron microscopy (SEM) respectively, in addition to analysis by (DTA) Differential thermally and Energy Dispersive X-Ray (EDX). Finally, the N2 adsorption-desorption was used to measure the surface area (BET) and pore volume. High degree of tetragonal crystallinity was obtained 90 %, and surface area of 169 m²/g and pore volume of 0.39 cm³g^-1 at 600°C calcination temperature for 3 hrs and 6 hrs time of impregnation in H₂SO₄. nanoparticle size of sulphated zirconia was produced with an average of 73.48 nm.

Abstract: In this report the problem of control of solidification crack formation in welded plates is considered. In this problem the welding source is determined in dependence on the preset configuration and curvature of the rear part weld pool. A double ellipsoid model of weld pool with preset semi-axes may be used for the first approximation of preset weld pool configuration. It is an inverse problem which may be more efficiently solved as optimal control problem. The Function of welding source as a controlling function obtained in the result of solution is determined in a class of piecewise continuous functions which is more common class and the continuous-smooth functions are special partial case of common class. Recent methods of optimal control which use for solution of optimal control problems require to present the controlling functions in class of piecewise constant functions. Laser influence, electron beam, plasma, arc and submerged arc are the welding sources with high concentrated energy. A mathematical models of these welding sources may be introduced in class of piecewise continuous function with an efficient accuracy.

Abstract: The incorporation of filler and plasticizer provides effective nucleation and mechanical reinforcement in polymer composites to impart flexibility, toughness, thermal stability and tensile strength of PLA composites that can be used in the development of packaging applications. In this paper, the inclusion of plasticizer and reinforcement of nanofiller in PLA matrix prepared using solvent casting method aims to improve the thermomechanical properties that consequently alter the crystallization and melting behavior of PLA composites. Plasticized PLA with different percentages of TiO₂ at 2.0, 3.5, 5.0 and 7.0 % w/w were dispersed in PLA solution using mechanical mixer and ultrasonication technique to introduce a matrix reinforcing nanophase within the composite. The thermomechanical properties and thermal behavior of PLA nanocomposites were characterized using dynamic mechanical analysis (DMA) and differential scanning calorimeter (DSC). DSC cooling curves at low scanning rate of 2.0 K·min^-1 proved that the presence of TBC in PLA matrix increased the crystallinity of plasticized PLA nanocomposites that initiated the formation of perfect spherulites. TBC increased the crystallization activity during cooling, which in turn reduced the recrystallization effect on heating, in parallel with DMA results that revealed small peak of cold-crystallization activity on PLA nanocomposites with the addition of plasticizer observed at temperature range of 80 °C to 100 °C. Nanofiller induced nucleation for crystallization of PLA matrix and plasticizer accelerated the overall crystallization process. Considerable adjustments of plasticizer and nanofiller in PLA matrix in having a good balance of stiffness and flexibility are a practical strategy that has a potential in biopolymer medical engineering and in the development of packaging applications.