Felületkezelés és amorfizáció nagy plasztikus deformációval = Surface mechanical treatment and amorphization by severe plastic deformation

A pályázat keretében a nagy plasztikus deformáción alapuló felületkezelés (SMAT), ill. nagynyomású csavarás (HPT) hatására kialakuló (részleges) szilárdfázisú amorfizáció jelenségét vizsgáltam. Szinkrotronos, röntgendiffrakciós és mikroszkópos vizsgálatok alapján megmutattam, hogy a Cu hordozó mellett őrölt Zr-Ti porkeverék egy homogén bevonatot eredményez, melynek előnyös mechanikai tulajdonságai az alkalmazhatóság szempontjából is fontos. Megmutattam, hogy binér kristályos Cu-Zr rendszer a HPT módszer segítségével az extrém deformációnak köszönhetően már szilárdfázisban eredményezhet tisztán amorf tartományokat. A hagyományos módszerekkel tömbi formában Al-alapú amorf ötvözetek nem állíthatók elő. Új kompaktálási eljárásként, sikerrel alkalmaztuk a nagynyomású csavarást amorf Al-Ce-Ni-Co, Al-Gd-Ni-Co és Al-Y-Ni-Co ötvözetek esetén. | In the present project the effect of surface mechanical attrition treatment (SMAT) and high pressure torsion (HPT) on the (partial) solid state amorphization was studied. It was shown by synchrotron measurements, conventional X-ray diffraction and microscopic studies that milling the mixture of Zr and Ti powders near a Cu target provides a homogeneous coating exhibiting enhanced mechanical properties which may lead to industrial applications. Due to the extreme deformation of HPT, some regions of the binary crystalline Cu-Zr system transform in to amorphous. It is well known that the synthesis of Al-based bulk amorphous alloys is strongly restricted. As a new method of compaction, we have shown that HPT of rapidly quenched amorphous Al-Ce-Ni-Co, Al-Gd-Ni-Co and Al-Y-Ni-Co can successfully be applied

Preparation, structure and giant magnetoresistance of electrodeposited Fe Co/Cu multilayers

No systematic studies have been carried out on the giant magnetoresistance (GMR) of electrodeposited (ED) Fe-Co/Cu multilayers since the elaboration of a method for the optimization of the Cu layer deposition potential. In this paper, we present results on the electrochemical optimization of the Cu layer deposition potential which was found to depend on the relative iron concentration in the bath. An X-ray diffraction study of ED Fe5Co95(1.5 nm)/Cu(dCu) multilayers with dCu ranging from 0.8 nm to 10 nm revealed an fcc structure. For most of the multilayers, weak superlattice satellite reflections could be identified. The room-temperature magnetoresistance was studied in detail as a function of the individual layer thicknesses. Multilayers with Cu layer thicknesses above about 1.5 nm were found to exhibit a GMR behavior with a maximum GMR of about 5 % and a typical saturation field of 1 kOe. The GMR magnitude decreased with increasing Fe-content in the magnetic layer. The spacer layer thickness evolution of the MR data was established in detail after separating the ferromagnetic and superparamagnetic GMR contributions and no oscillatory GMR was found. A comparison with literature data on both physically deposited and ED Fe-Co/Cu multilayers is also made

Structural and hydrogen storage characterization of nanocrystalline magnesium synthesized by ECAP and catalyzed by different nanotube additives

Ball-milled nanocrystalline Mg powders catalyzed by TiO2 powder, titanate nanotubes and carbon nanotubes were subjected to intense plastic deformation by equal-channel angular pressing. Microstructural characteristics of these nanocomposites have been investigated by X-ray diffraction. Microstructural parameters, such as the average crystallite size, the average dislocation density and the average dislocation distance have been determined by the modified Williamson–Hall analysis. Complementary hydrogen desorption and absorption experiments were carried out in a Sieverts’ type apparatus. It was found that the Mg-based composite catalyzed by titanate nanotubes exhibits the best overall H-storage performance, reaching 7.1 wt% capacity. The hydrogenation kinetic curves can be fitted by the contracting volume function for all the investigated materials. From the fitted parameters, it is confirmed that the titanate nanotube additive results in far the best kinetic behavior, including the highest hydride front velocity

High glass forming ability correlated with microstructure and hydrogen storage properties of a Mg-Cu-Ag-Y glass

Thermal characterization of an as-cast Mg54Cu28Ag7Y11 bulk metallic glass revealed that this alloy exhibits excellent glass forming ability. High-resolution X-ray diffraction study and transmission electron microscopy show that heating and isothermal annealing treatment results in the nucleation of nanocrystals of several phases. The average size of these nanocrystals (~15-20 nm) only slightly varies with prolonged annealing, only their volume fraction increases. High-pressure calorimetry experiments indicate that the as-cast fully amorphous alloy exhibits the largest enthalpy of hydrogen desorption, compared to partially and fully crystallized states. Since the fully crystallized alloy does not desorb hydrogen, it is assumed that hydrogen storage capacity correlates only with the crystalline volume fraction of the partially crystallized Mg54Cu28Ag7Y11 BMG and additional parameters (crystalline phase selection, crystallite size, average matrix concentration) do not play a significant role

Electrodeposition of Ni from various non-aqueous media: the case of alcoholic solutions

Although electrodeposition from aqueous media has been widely used to obtain metallic deposits, there are cases where the application of non-aqueous solutions offers advantages over the traditional baths or even represents the only way to electrodeposit some metals. For this reason, a study of the electrodeposition of Ni from various alcoholic solutions was performed. Apart from a detailed cyclic voltammetry study of these solutions, the surface morphology, crystal structure and texture as well magnetic properties of the deposits have also been investigated. The best results were obtained with methanol as solvent, so results on Ni deposits prepared from this solution will be presented in more detail whereas the case of the other alcoholic solutions investigated will be summarized only briefly. Structural and magnetic properties of the deposits obtained have been compared to literature data on Ni samples obtained from various non-aqueous solvents

Evaluation of scalability in the Fission serverless framework

The efficient code execution often requires concurrency, so many programming languages, libraries and framework aim at parallelism. Based on the granularity and abstraction level, many approaches of concurrency are available. However, concurrency carries difficulties but modern ways try to make it more convenient. A rather new solution is cloud computing which enhances the concurrency in a way that standalone virtual machines utilize the shared hardware. Containerization takes advantage of lightweight virtual machines called containers because they use a shared kernel of the operating system. Conteiner orchestration (e.g. Kubernetes) enables containerization among multiple hosts. Serverless programming supports container orchestration for individual function so every trigerred function may run in a different container which is inside a cluster of hosts. In this paper, we briefly present the modern cloud computing ways of concurrency. This subtle distributed approach requires a comprehensive evaluation. We take advantage of the open source Fission serverless framework and implement some distributed algorithms in this realm using the Python programming language. For a deeper comprehension, we measure and evaluate the scalability of Fission framework and the entire system. We execute the distributed algorithms with different sizes of input and we fine-tune the configuration of the Fission framework

Structure and giant magnetoresistance of electrodeposited Co/Cu multilayers prepared by two-pulse (G/P) and three-pulse (G/P/G) plating

The giant magnetoresistance (GMR) was investigated for electrodeposited Co/Cu multilayers. In order to better understand the formation of individual layers and their influence on GMR, multilayers produced by two different deposition strategies were compared. One series of Co(2 nm)/Cu(tCu) multilayers with tCu ranging from 0.5 nm to 6 nm was produced with the conventional two-pulse plating by using a galvanostatic/potentiostatic (G/P) pulse combination for the magnetic/non-magnetic layer deposition, respectively, whereby the Cu layer deposition was carried out at the electrochemically optimized potential. Another Co(2 nm)/Cu(tCu) multilayer series with the same tCu range was prepared with the help of a G/P/G pulse combination. In this latter case, first a bilayer of Co(2 nm)/Cu(6 nm) was deposited in each cycle as in the G/P mode after which a third G pulse was applied with a small anodic current to dissolve part of the 6 nm thick Cu layer in order to ensure the targeted tCu value. The comparison of the two series revealed that the G/P/G pulse combination yields multilayers for which GMR can be obtained even at such low nominal Cu layer thicknesses where G/P multilayers already exhibit bulk-like anisotropic magnetoresistance only. Surface roughness measurements by atomic force microscopy revealed that the two kinds of pulse combination yield different surface roughness values which correlate with the structural quality of the multilayers as indicated by the absence or presence of multilayer satellite reflections in the X-ray diffraction patterns. A separation of the superparamagnetic (SPM) contribution from the total observed GMR provided useful hints at the understanding of differences in layer formation between samples prepared with the two kinds of pulse combination. The results of multilayer chemical analysis revealed that mainly an increased Cu content of the magnetic layer is responsible for the onset of SPM regions in the form of Co segregations in the G/P/G multilayers with small Cu layer thicknesses. Magnetization measurements provided coercive force and remanence data which gave further support for the above interpretation of the GMR data