Rotating Electrode Method Research Articles

Electric spark alloying of steel, titanium and niobium alloys using rotating electrode method

The article presents the results of a study of electrospark coatings on metals and alloys using the rotating electrode method. The influence of various parameters on the formation of an electrospark coating on steel 20, titanium VT1-0, niobium and niobium alloy 5VMTs, on titanium VT1-0, niobium and niobium alloy 5VMTs with subsequent siliconization has been studied. The dependences of the growth of the thickness of the electrospark coating with increasing doping time, current in the circuit, and electrode rotation speed were obtained. It has been established that with increasing thickness of the electrospark coating, the thickness of the silicide layer increases. Electric spark alloying leads to an increase in the heat resistance of steel 20 with an aluminum coating by 1.5—3.0 times, of titanium by 2—9 times, and of titanium with a nichrome coating by 2 times. The heat resistance of titanium with a copper electrospark coating after siliconization increases up to 2—10 times, depending on the thickness of the electrospark layer and the siliconization temperature.

Deuterium desorption and retention of Beryllium intermetallic compounds for fusion applications

Beryllium intermetallic compounds (beryllides) such as Be12Ti and Be12V are the most promising advanced neutron multipliers in demonstration (DEMO) power reactors because of their low swelling and high stability at high temperatures. In this work, beryllides pebbles with binary and ternary compositions were successfully fabricated by combining plasma sintering and rotating electrode methods. After 3 keV D2+ ions were implanted to the beryllides pebbles, the deuterium desorption and retention properties were investigated by thermal desorption spectroscopy to investigate hydrogen desorption and retention of these materials for fusion application.The desorption properties and retention of hydrogen isotopes (deuterium) using the newly developed beryllide pebbles indicated that the beryllide pebbles exhibited better deuterium desorption properties, such as lower starting-up temperature, total retention, and activation energy for deuterium desorption than beryllium.

A recycling process on vanadium beryllium intermetallic compounds as advanced neutron multipliers for DEMO fusion applications

Abstract Beryllium intermetallic compounds (beryllides) are known as promising materials for advanced neutron multipliers for fusion applications owing to their high stability and low swelling. Because a large amount of beryllium is used for each solid breeding blanket in fusion reactors, the development of effective and efficient recycling processes is essential. In this study, a proper recycling process of Be12V pebbles was proposed, which combines a plasma sintering and a rotating electrode method for the fabrication of beryllide pebbles. As a result of experiments, it is determined that the rotating electrode method is available to reduce oxygen impurities, whereas the plasma sintering process can eliminate Li impurities and hydrogen isotope depending on sintering temperature. Regarding the recycling process, the beryllide pebbles used can be recycled into rods by plasma sintering, in which Li impurity and tritium can be eliminated. Then, recycled rods can be granulated by the rotating electrode method. During this process, it is anticipated that oxygen impurities and irradiation defects can be eliminated because the rotating electrode method includes the melting process. Thus, the current process was determined to be appropriate as a recycling process for beryllide pebbles.

Study on Microstructure and Mechanical Properties of Powder Metallurgy TA15 Titanium Alloy

TA15 pre-alloyed powder chosen in this paper is made by plasma rotating electrode method. The powders were used to prepare fully dense TA15 alloy ingots by the means of hot isostatic pressing(HIP) forming technology. The optimum parameter of the HIP process is 900°C /120MPa/3h. After the process of hot isostatic pressing, the powders were pressed into a fully dense ingot. An optital microscope was used to observe the microstructure of the ingot specimen and its formation mechanism was analysized. The microstructure of the TA15 alloy prepared by hot isostatic pressing of pre-alloyed powder is composed of fine α-equiaxed grains along lamellar colony boundaries. The mechanical properties exceed that of the casting level, which is close to the forging level. A typical TA15 alloy component was finally produced by HIP-PM process.

Synthesis and magnetic performance of gadolinium powder produced with rotating disk atomization

ABSTRACT Spherical powder is key for achieving good heat transfer and maintaining low pressure drop for heat transfer fluid in magnetocaloric regenerator. Obtaining relatively large spherical powder of rare earth metals that are extremely sensitive to oxygen is challenging. Comparing to gas atomization and plasma rotating electrode methods, rotating disk atomization (RDA) method is more robust for obtaining a small amount of powder with a short turn-around time, thereby, more suitable for research and development of new magnetocaloric materials. In this work, commercially bulk gadolinium was successfully atomized to produce spherical powder in the targeted 150–250 μm range. The obtained powder exhibited the expected magnetocaloric performance with a maximum change of magnetic entropy of 12.1 J/kg K and a maximum adiabatic temperature change of 12.8 K with an applied magnetic field of 7 T.

Granulation of Be12V pebbles using the rotating electrode method

Hydrogen generation via the oxidation of beryllium (Be) in the presence of water vapor at high temperatures needs to be minimized in fusion reactors because of safety concerns. Advanced neutron multipliers with increased stability at high temperatures are desirable in pebble bed blanket design with water coolant. Beryllium intermetallic compounds (e.g., vanadium beryllide Be12V) are a promising material that can be used as advance neutron multipliers. Granulation aims to produce beryllide pebbles that are a critical element in the development of advanced neutron multipliers.Based on previous trial granulations of beryllides, a rotating electrode method (REM) was selected [1–3]. Furthermore, its experimental dataset is broad, covering beryllium and metallic pebbles. Rod-shaped beryllide blocks are necessary to fabricate beryllide pebbles via the REM. Hot isostatic pressing and casting have been proposed to synthesize beryllides. However, pure beryllium-based intermetallic compounds have very limited plasticity at high rotational speeds. The use of Be–V rods containing pure beryllium phase was considered a reasonable solution to this problem. The microstructure of Be–V rods and pebbles confirmed that the REM produced single-phase Be12V pebbles from multiphase Be–V rods. Special emphasis has been placed on the yield properties, size distribution, and sphericity of vanadium beryllide pebbles fabricated under different granulation conditions. The effect of rotational speed and electric current on pebble fabrication with the REM is discussed in this study. Taking into account the high costs and restricted availability of beryllium products, the perspective of material re-use was also considered by the process development and appropriate granulation trials were performed.

Fabrication and characterization of Be-Zr-Ti ternary beryllide pebbles

Beryllium intermetallic compounds (beryllides) such as Be12Ti, Be13Zr and Be12V are the most promising advanced neutron multipliers for DEMO reactors (DEMOnstration fusion power plant). Plasma sintering and the rotating electrode methods for the fabrication of beryllide rods and pebbles have been established and a new chemical composition has been suggested as development of more advanced neutron multipliers. By using these methods, preliminary synthesis of the ternary Be-Zr-Ti pebbles has been conducted. In the Be13Zr1-xTix composition (x = 0.1, 0.3, 0.5, 0.7 and 0.9), some of the pebbles showed the existence of a Be phase on the surface, which results in mass gain and hydrogen generation. Ternary beryllide pebbles were successfully fabricated from mixtures of Be12Ti and Be13Zr with ratios of 1:1, 1:0.6, 1:0.4, 1:0.2 and 1:0.1. As a result of the SEM observations, it was clear that no Be phase was found on the surface of the pebbles despite of the fact that some fractions were identified inside the pebbles. For stability with 1% water vapor of as-received ternary pebbles at high temperatures, it was clear that those indicated much lower hydrogen generation, which corresponds to much higher stability than Be pebbles at high temperatures.

Thermal properties of beryllides as advanced neutron multipliers for DEMO fusion application

The hydrogen generation with steam is a major drawback of using beryllium (Be) as neutron multipliers in water-cooled blankets. Advanced neutron multipliers having considerable stability at high temperatures are desirable and beryllides depict a strong potential to be applied. Be12V pebbles were successfully fabricated directly using the rotating electrode method. Hydrogen generation ratio and heat of reaction due to the hydrogen generation reaction of Be12V was observed to be two orders of magnitude less than that of Be. Be12V exhibited good resistance to steam. By performing computer simulations at the loss of coolant accident (LOCA), thermal excursion was observed to be very sensitive to the initial temperature under Be pebble packed blanket conditions. However, better thermal stability was observed for the beryllide-steam reaction.

Deuterium retention and desorption properties of ternary beryllide pebbles as advanced neutron multipliers

Beryllium intermetallic compounds (beryllides) such as Be12Ti and Be12V are the most promising advanced neutron multipliers in demonstration (DEMO) power reactors because of their low swelling and high stability at high temperature. In this work, single-phase Be12Ti and Be12V pebbles produced by a novel process combining plasma sintering and rotating electrode methods were successfully fabricated. In parallel to the successful fabrication of binary beryllide pebbles, new research and development on ternary beryllides was begun to determine preferable pebble compositions in terms of mass production and improved properties. The desorption properties and retention of hydrogen isotopes (deuterium) using the newly developed ternary beryllide pebbles indicated that the ternary pebbles exhibited better deuterium desorption properties, such as lower starting-up temperature, total retention, and activation energy for deuterium desorption, than these for beryllium.

Experimental Study on the Machining of Inclined Holes for Thermal Barrier-Coated Nickel Superalloys by EDM

Thermal barrier coatings (TBCs) are used to thermally insulate superalloy components from the hot gas streams in gas turbine engines. In this work, electrical discharge machining (EDM) was used to machine different inclined holes in TBC-coated nickel superalloys by integrating the inner-jet-liquid rotating electrode method and the assisting electrode method. The influences of the inclination angle (i.e., from 0° to 60°) and EDM parameters (i.e., peak current, pulse duration, duty factor and flushing pressure) on the machining time and electrode wear were investigated. The surface morphologies and elemental distribution were analyzed using a scanning electron microscope and an energy dispersive spectroscope. The results of the analysis showed that the 8YSZ ceramic coating is more prone to brittle fracture and cracking than the IN718 substrate and NiCoAlY bond coating, and pits and cracks become more pronounced as the inclination angle increases. The damage on the trailing edge is primarily caused by the thermal stress fracture, and the damage on the leading edge is mainly caused by thermal erosion. Using high-energy parameters, a delamination with dimensions of 28 μm (W) × 200 μm (L) occurs on the trailing edges of the coating/substrate interface.

Beryllide pebble fabrication of Be–Zr compositions as advanced neutron multipliers

Fusion reactors require advanced neutron multipliers with high stability at high temperatures. Beryllium intermetallic compounds (beryllides) have a universally robust potential for high temperature use. Fabrication of beryllide pebbles of Be–Zr compositions was conducted from the viewpoint of pebble mass production. Prototypic pebbles were successfully fabricated using the plasma-sintered electrodes with high Be and Zr contents for enhanced of the thermal shock resistivity of the electrodes during granulation by a rotating electrode method. From the results of granulation examinations, it was revealed that granulation yields varied greatly depending on compositions of the plasma-sintered electrodes themselves. By utilizing plasma-sintered electrodes with high Be and Zr contents, Be13Zr pebbles had a high granulation yield of 84%. Moreover, the Be13Zr pebbles displayed better oxidation properties as compared to pure Be pebbles.

Synthesis and characteristics of ternary Be–Ti–V beryllide pebbles as advanced neutron multipliers

A new combined plasma sintering and rotating electrode method for fabricating beryllide rods and pebbles has been suggested. Using these methods, preliminary synthesis of ternary beryllide pebbles with different chemical compositions, Be12Ti1−xVx (x=0.1, 0.3, 0.5, 0.7, 0.9 and 1.0), was successful. Scanning electron microscopy observations revealed that grain size on the surface decreased, whereas the area fraction of the Be phase in the cross-section decreased as the amount of V increased. These decreases may be attributed to the fact that the chemical composition of the pebble was closely varied to single-phase Be12V, with no peritectic reaction as the amount of V increased, while the Be, Be12Ti, and Be17Ti2 phases were formed with large grains caused by a peritecic reaction in Be12Ti. This feature influenced the variation of reactivity with 1% water vapor at high temperatures. It was concluded that weight gain and H2 generation decreased with decreases in grain size as well as Be phase on the surface, as the amount of V increased in Be12Ti1−xVx. Based on cross-sectional observations after oxidation measurement for 24h, we found that Be12Ti0.3V0.7 and Be12Ti0.1V0.9 pebbles showed high phase stability.

Effect of titanium content on mechanical properties and reactivity of titanium beryllide pebbles

A combinational process for the fabrication of beryllide pebbles, consisting of a plasma-sintering method and the rotating electrode method for fabrication of electrode rods and pebbles, respectively, is proposed. To investigate the effect of Ti content in titanium beryllide pebbles on the pebbles’ crush strength and oxidation resistance, beryllide pebbles with 3–10.5at.% Ti were fabricated. Scanning electron microscopy (SEM) observations demonstrated that the surfaces of Be – 3 and 5at.% Ti pebbles contained a Be phase, whereas the surfaces of Be – 7–10.5at.% Ti pebbles did not. Moreover, according to cross-sectional SEM images, the area fraction of the Be phase decreased with increasing Ti content in beryllide pebbles with 3–9at.% Ti, whereas the pebble with 10.5at.% Ti consisted primarily of the Be17Ti2 phase. With regard to the mechanical properties of the pebbles, their strength and elongation decreased with increasing Ti content because of the brittleness of the Be phase. The weight gain and the amount of H2 generated by the pebbles under reaction with 1% H2O/Ar decreased with increasing Ti content, whereas the stability of the pebbles was strongly dependent on the presence of the Be phase on their surface.

Fabrication and hydrogen generation reaction with water vapor of prototypic pebbles of binary beryllides as advanced neutron multiplier

Advanced neutron multipliers such as beryllides with high stability at high temperatures are desired for demonstration power plant (DEMO) reactors. Prototypic pebbles 1mm in diameter of single phase Be12Ti beryllide were successfully fabricated by a combination process involving plasma sintering, a rotating electrode method, and a homogenization treatment. Relative to the non-treated, multi-phase pebbles, the homogenized Be12Ti pebbles demonstrated an increased reactivity because the homogenization treatment caused an increase in the specific surface area of the treated pebbles. To prevent increased hydrogen generation, prototypic Be17Ti2 pebbles were successfully fabricated without homogenization. The Be17Ti2 prototypic pebbles where shown to have a good oxidation resistance.

Synthesis of Be–Ti–V ternary beryllium intermetallic compounds

Beryllium intermetallic compounds (beryllides) such as Be12Ti and Be12V are the most promising advanced neutron multipliers in demonstration power reactors. Advanced neutron multipliers are being developed by Japan and the EU as part of their Broader Approach activities. It has been previously shown, however, that beryllides are too brittle to fabricate into pebble- or rod-like shapes using conventional methods such as arc melting and hot isostatic pressing. To overcome this issue, we developed a new combined plasma sintering and rotating electrode method for the fabrication of beryllide rods and pebbles.Previously, we prepared a beryllide pebble with a Be–7.7at.% Ti composition as the stoichiometric value of the Be12Ti phase; however, Be17Ti2 and Be phases were present along with the Be12Ti phase that formed as the result of a peritectic reaction due to re-melting during granulation using the rotating electrode method. This Be phase was found to be highly reactive with oxygen and water vapor. Accordingly, to investigate the Be phase reduction and applicability for fabrication of electrodes prior to granulation using the rotating electrode method, Be–Ti–V ternary beryllides were synthesized using the plasma sintering method.Surface observation results indicated that increasing plasma sintering time and V addition led to an increase in the intermetallic compound phases compared with plasma-sintered beryllide with a Be–7.7at.% Ti composition. Additionally, evaluation of the reactivity of samples with water vapor at high temperature revealed that specimens with larger fractions of Be phases experienced larger weight gains and H2 generation rates because of oxidation, as Be12Ti and Be12V phases have a similar oxidation tendency.

TEM study of impurity segregations in beryllium pebbles

Beryllium is planned to be used as a neutron multiplier in the Helium-cooled Pebble Bed European concept of a breeding blanket of demonstration power reactor DEMO. In order to evaluate the irradiation performance, individual pebbles and constrained pebble beds were neutron-irradiated at temperatures typical of fusion blankets. Beryllium pebbles 1mm in diameter produced by the rotating electrode method were subjected to a TEM study before and after irradiation at High Flux Reactor, Petten, Netherlands at 861K. The grain size varied in a wide range from sub-micron size up to several tens of micrometers, which indicated formation bimodal grain size distribution. Based on the application of combined electron energy loss spectroscopy and energy dispersive X-ray spectroscopy methods, we suggest that impurity precipitates play an important role in controlling the mechanical properties of beryllium. The impurity elements were present in beryllium at a sub-percent concentration form beryllide particles of a complex (Fe/Al/Mn/Cr)B composition. These particles are often ordered along dislocations lines, forming several micron-long chains. It can be suggested that fracture surfaces often extended along these chains in irradiated material.

Development of Advanced Neutron Multipliers for DEMO Blankets

Advanced neutron multipliers with low swelling and high stability at high temperatures are desired for the pebble bed blankets of demonstration fusion power (DEMO) reactors. Beryllium intermetallic compounds (beryllides) such as Be12Ti are the most promising material for this purpose. To fabricate the beryllide pebbles, a new granulation process has been established that combines a plasma sintering method for beryllide synthesis and a rotating electrode method using a plasma-sintered electrode for granulation. In trial granulation examinations, prototypic beryllide pebbles 1 mm in diameter were successfully fabricated. This study describes the results of a crush test and the characterization of the oxidation properties of the prototypic beryllide pebbles compared with those of Be pebbles. The crush test revealed that the prototypic beryllide pebble was more brittle than a Be pebble, and its crush load is one-third that of a Be pebble. The oxidation experiment showed that the weight gain ratios of the prototypic beryllide pebbles were significantly smaller than those of pure Be pebbles. The results confirmed that the prototypic beryllide pebbles have better oxidation resistance than pure Be pebbles.

Fabrication of beryllide pebble as advanced neutron multiplier

Fusion reactors require advanced neutron multipliers with great stability at high temperatures. Beryllium intermetallic compounds, called beryllides such as Be12Ti, are the most promising materials for use as advanced neutron multipliers. However, few studies have been conducted on the development of mass production methods for beryllide pebbles. A granulation process for beryllide needs to have both low cost and high efficiency. To fabricate beryllide pebbles, a new granulation process is established in this research by combining a plasma sintering method for beryllide synthesis and a rotating electrode method using a plasma-sintered electrode for granulation. The fabrication process of the beryllide electrode is investigated and optimized for mass production. The optimized beryllide electrode exhibits higher ductility and can be sintered at a lower temperature for a shorter time, indicating that it is more suitable not only for withstanding the thermal shock from arc-discharge during granulation but also for producing the beryllide pebbles on a large scale. Accordingly, because these optimization results can reduce the time required for electrode fabrication by 40%, they suggest the possibility of great reductions in time and cost for mass production of beryllide pebbles.

Preliminary synthesis and mechanical property of titanium beryllide pebbles with different chemical compositions

Abstract Beryllide is well-known as the most promising candidate for advanced multipliers in demonstration fusion reactors. However, due to its brittleness, it is difficult to fabricate a pebble-type beryllide. Here, we report the synthesis and analysis of beryllide pebbles with different chemical compositions. In order to clarify the effect of the content of Ti on the fabrication of beryllide pebbles, a rotating electrode method was applied using a plasma-sintered beryllide rod jointed by two beryllide blocks and powder. The beryllide pebbles were successfully fabricated accompanied by phase changes induced by re-melting during the rotating electrode method. The SEM images of the rods and the cross-section of the pebbles demonstrated that the phases of the plasma-sintered beryllide rods with 6 at.%, 7 at.%, and 7.7 at.% Ti were transformed to the peritectic Be 12 Ti phase with a Be 17 Ti 2 phase due to re-melting whereas pebbles with 3 at.% and 5 at.% Ti showed similar phases as the plasma-sintered beryllide rods. Additionally, the dependence of the Ti amount on crush load depicted that the pebbles with the larger area fraction of Be indicated the higher crush load as well as longer displacement because the Be contributed to increase of ductility in the pebbles.

TEM study of beryllium pebbles after neutron irradiation up to 3000 appm helium production

Beryllium is planned to be used as a neutron multiplier in the Helium Cooled Pebble Bed (HCPB) European concept of a breeding blanket of DEMO. In order to evaluate the irradiation performance, individual pebbles and constrained pebble beds were neutron irradiated at temperatures typical for fusion blanket. Beryllium pebbles with a diameter of 1mm produced by the Rotating Electrode Method were subjected to a TEM study after irradiation at the HFR, Petten, at temperatures of 686, 753, 861, and 968K. The helium production in the pebbles was calculated in the range from 2090 to 3090appm. Gas bubbles as disks of hexagonal shape were observed for all four irradiation temperatures. The disks were oriented in the (0001) basal plane with a height directed along the [0001] “c” axis. The average diameters of the bubbles increase from 7.5 to 80nm with increasing irradiation temperature, the bulk densities accordingly decrease from 4.4×1022 to 3.8×1020m−3. With increasing irradiation temperature, the swelling of the pebbles increases from 0.6% at 686K up to 6.5% at 968K.