András Szalay

Fabrication of bimetallic rods by explosive cladding and warm extrusion

Abstract The fabrication of bimetallic aluminium sheathed/copper axisymmetric rods by explosive cladding and subsequent warm extrusion is reported. The effect of the cladding and the extrusion parameters on the macro- and the microscopic features and the soundness of the product at the various stages of the fabrication are indicated using microhardness testing and optical metallography. By employing warm extrusion as a post-welding forming technique, instead of the cold extrusion, the soundness of the components is improved due to advantageous plastic flow of the extruded composite rod at elevated temperatures and the minimization of the characteristic extrusion defects. A theoretical analysis pertaining to the extrusion of axisymmetric bimetallic rods is proposed.

Three phase inductive HTS fault current limiter for the protection of a 12 kVA synchronous generator

The concept of high temperature superconducting (HTSC) mini power plant model is presented. An HTSC fault current limiter (FCL) for the protection of a generator unit was designed. The simulation and test results of a one phase overload case are shown. Duration tests to reveal the dependency of the limited current and the FCL voltage on the activation number were performed. A new representation of the sudden short circuit current and voltage are proposed.

Fabrication of multi-layered steel/superconductive ceramic (YBaKCuO)/silver rods by explosive powder compaction and extrusion

Abstract Axisymmetric explosive powder compaction and subsequent direct extrusion are employed to fabricate a multi-layered metal/high-Tc ceramic rod consisting of a silver mandrel, a potassium doped YBa2Cu3O7 core and a steel sheath. Experimental investigations regarding the ‘soundness’ and the superconducting properties of the component at the various stages of the fabrication are reported. Microstructural/crystallographic changes, macro- and micro-defects of the ‘green’ compacted billet and the extruded rod are also indicated and discussed.

Requirements for the industrial application of superconducting rotating electrical machines

The objective of the project reported in the paper is the design and construction of an experimental high Tc (HTS) synchronous machine. The machine is excited with rare-earth permanent magnets on the rotor and rod-shaped armature conductors on the stator. The machine incorporates Bi-based HTS conductors supplied with electrical contacts. In the design procedure special attention has been paid to the considerations regarding industrial applications of HTS rotating electrical machines both in motor and generator modes of operation. Possible applications have been analyzed to formulate the requirements for the machine to be applied and calculations have been performed to check how the above requirements can be met by HTS machines. Comparisons have been made between conventional and HTS machines designed for particular practical cases.

Design and construction of a small-scale model of a high-temperature superconducting magnetically levitated vehicle

The design of a small-scale model of a magnetically levitated vehicle is presented in the paper. The model has been constructed on the basis of the calculation of the magnetic field and forces between permanent magnets and high temperature superconducting materials prepared by different fabrication techniques. The fabrication of the superconductor play a fundamental role in designing the vehicle since large enough levitation forces can be achieved only with superconductors that have large pinning forces. The fabrication processes, the design with a special emphasis on the calculation of the magnetic field and model construction are reported.

Upgrading electric power quality by superconducting flywheels

Abstract An experimental flywheel based on high temperature superconductors was constructed. The aim of the study is to investigate the possible use of this technology to improve electric power quality against voltage disturbances. Some preliminary results on the flywheel performance are reported.

The effect of heat treatment on explosively compacted (YBaKCuO) superconductive powders

Abstract A ceramic powder mixture corresponding to the stoichiometric ratio of YBa 1.95 K 0.05 Cu 3 O y superconducting ceramic with 10% w/w Ag was heat treated at 950°C for 3 h in flowing oxygen. The resultant superconducting powder was consolidated in a silver tube by the explosive compaction technique (pre-heat treated ceramic). The same fabrication technique, i.e. explosive compaction, was employed to the initial stoichiometric powder mixture, without prior heat treatment and the green product was subsequently subjected to a series of heat-treating cycles (920°C, 70 h), in order to obtain the required superconducting properties (post-heat treated ceramic). The microstructure and physical properties of the pre- and post-heat treated ceramics were analyzed and compared using various characterization techniques. X-ray diffraction performed on the pre-heat and post-heat treated ceramics indicated that maximum 123-phase content retained in the former case (pre-heat treated ceramic), whilst DC magnetic susceptibility measurements have shown the characteristic Meissner shielding effect at 99 and 92 K, respectively. Furthermore, the pre-heat treated compacted billet was characterized by a critical current density, J c equal to 2800 A/cm 2 at 77 K after suitable annealing at 850°C for 10 h in oxygen stream.

Characterization and Comparison of Rapidly Solidified Al Particles Mechanically Milled Nanostructures and their Consolidated Structures Made by High Energy Rate Forming (HERF) Technique

The aim of the present work is to produce new types of solid nanomaterials for different purposes (coatings, fillers, foams, bulk pieces, etc.). Technologies such as RS Al flake production, high energy mechanical milling and high energy rate forming technology (HERF) for compacting are used. The products are analyzed mainly by XRD, SEM and TEM methods. It was shown that the new-type of RS Al “flake” material is suitable not only for pigments but also for powder metallurgical purposes, i.e. Al based nanocomposites. By choosing suitable parameters for mechanical alloying with the Fritsch Planetary mill 4, very fine, alloyed and composited nanostructures can be produced (Al-4.5w%Cu- 10w%Al2O3, Al-15w%Pb) Dynamic compaction (HERF) using explosive techniques seems to offer a good way for the compaction of Al (metal) matrix nanostructured composites.

Effect of explosive compaction on microstructure and the physical properties of ceramic superconducting materials produced by different techniques

Cryomagnetic applications of high-T c superconductors require the fabrication of bulk ceramics with different shapes and sizes, high critical current density and magnetic levit ation force. Larger grain size and orientation of the superconducting YBa 2Cu3Oy (123) crystallites can improve the grain connection and thus the above mentioned superconducting properties. The addition of KF is favourable to the YBa 2Cu3Oy (123) crystal growth [1, 2] while using of melt-powder-melt-growth (MPMPG) technique [3, 4] for production of polycrystalline superconductor s results in oriented microstructure of the platelike superconducting grains with the most rapid-growth direction within the a-b plane. In this highly oriented structure the finely dispersed YBaCuO 5 (211) grains act as flux pinning centres and increase the magnetic levitation forces [5]. Bulk polycrystalline superconductors with complicated geometry can be easily fabricated by explosive cladding technique [6]. During this compaction technique the pr operties of the starting superconducting materials can be changed. In this study these chang es were investigated in the case of polycrystalline superconducting materials prepared by different technique s.

Fabrication of an HTSC electrical switch

Abstract The possibility and apparent ease of transferring superconductors from the superconducting (i.e., ideally conducting) into the normal (i.e., well insulating) state and back has attracted interest in utilizing this specific feature of superconductors in the field of electrical switches. The discovery of high-temperature superconductors (HTSCs) in 1986 opened up new prospects. Due to the possibility of liquid-nitrogen cooling, devices made up of HTSC materials may be more simple and economical. The problem of the application of HTSC materials in electrical switches has been formulated by a Hungarian power engineering company. The investigation under this project is aimed at the creation of a prototype controlled HTSC switch. The use of the proposed switch would offer a novel way of suppressing the arcs developing in heavy current-switching equipment. This paper describes the results of the first stage of the project. This stage includes the fabrication of silver-sheathed bulk YBaCuO samples and that of metal contacts.