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

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

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

Composition, morphology and electrical transport properties of Co-Pb electrodeposits

Bath compositions were elaborated for the codeposition of Co and Pb by taking into account the chemical compatibility of Co2+ and Pb2+ with the appropriate anions. Electrolytes containing either acetate, chloride or nitrate anions were tested, but only the acetate bath proved to be appropriate for the preparation of compact Co-Pb films. Deposits were obtained with constant current, with constant potential or by using various current and potential pulses in order to investigate the possibility of multilayer formation. The variation in deposit composition as a function of the deposition parameters was elucidated by using cyclic voltammetry, current transient measurements and gravimetry. X-ray diffraction (XRD) patterns recorded for two-pulse plated deposits revealed a nanocrystalline structure with grain sizes in the range 5 to 20 nm. The XRD peaks could be well indexed to pure face-centered cubic Co and Pb, indicating that the Pb codeposited with Co is not dissolved in Co but is segregated. Both the d.c.-plated and the two-pulse plated deposits exhibited anisotropic magnetoresistance without an indication for a noticeable giant magnetoresistance contribution. This means that the observed magnetoresistance arises from spin-dependent electron scattering events dominantly within the sufficiently large Co regions and not along electron paths between two Co regions via the Pb regions. Low-temperature resistivity measurements revealed a superconducting transition slightly below that of pure Pb. This may be ascribed to a proximity effect: the ferromagnetic Co grains suppress somewhat the superconductivity of the Pb phase due to the nanoscale phase mixture of the two constituents

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

Hydrogen storage of nanocrystalline Mg-Ni alloy processed by equal-channel angular pressing and cold rolling

Ball-milled nanocrystalline Mg2Ni powders were subjected to intense plastic straining by cold rolling or equal-channel angular pressing. Morphological and microstructural evolution during these processes has been investigated by scanning electron-microscopy and X-ray diffraction line profile analysis, respectively. Complementary hydrogen absorption experiments in a Sieverts’ type apparatus revealed that there exists some correlation between the micro- and nanostructure and hydrogen storage properties of the severely deformed materials