Rapid Heat Cycle Research Articles

Development of Microtubular SOFCs

Microtubular solid oxide fuel cells (SOFCs) have successfully demonstrated their advantages over conventional (planar) SOFCs, such as high thermal stability during rapid heat cycling and large electrode area per volume, which enables one to realize SOFC systems applicable to portable devices and auxiliary power units for automobile. In this study, the fabrication method of the microtubular SOFCs was examined. Shrinkage behavior and the microstructure of electrolyte/anode as a function of sintering temperature were shown and correlated with densification of the electrolyte during cosintering process.

RHCM(TM)-Rapid Heat Cycle Molding : The Innovative Molding Technology Creating Infinite Texture

RHCM(TM)-Rapid Heat Cycle Molding : The Innovative Molding Technology Creating Infinite Texture

Development of cube-type SOFC stacks using anode-supported tubular cells

Tubular SOFCs have shown many desirable characteristics such as high thermal stability during rapid heat cycling and large electrode area per unit volume, which can accelerate to realize SOFC systems applicable to portable devices and auxiliary power units for automobile. So far, we have developed anode-supported tubular SOFCs with 0.8–2 mm diameter using Gd-doped CeO 2 (GDC) electrolyte, NiO-GDC anode and (La, Sr)(Co, Fe)O 3 (LSCF)-GDC cathode. In this study, a newly developed cube-type SOFC stack which consists of three SOFC bundles was designed and examined. The bundle consists of three 2 mm diameter tubular SOFCs and a rectangular shaped cathode support where these tubular cells are arranged in parallel. The performance of the stack whose volume is less than 1 cm 3 was shown to be 2.8 V OCV and over 1 W at 1.6 V under 500 °C. Cathode loss factor due to current collection from cathode matrix was also estimated using a proposed model.

Fabrication of Micro-Tubular SOFC Stack Using Ceramic Manifold

Micro tubular SOFCs have been expected to overcome shown many desirable characteristics over conventional (planar) SOFCs such as high thermal stability during rapid heat cycling and high packing density of the cells, which enables to realize micro SOFC systems applicable to portable devices and auxiliary power units for automobile. Our research project Advance Ceramic Reactors aims to develop innovative processing method to fabricate such new micro tubular SOFCs and their stacks. In this study, new micro tubular SOFC stacks was fabricated and the performance of the stack was investigated.

Brazing of Inconel X-750 to stainless steel 304 using induction process

The proposed paper discusses results of the joining of Inconel X-750 to stainless steel 304 by induction brazing. The experimental brazing was carried out at 1423 K using a nickel-based brazing BNi-2 (Ni–7Cr–3Fe–3.2B–4.5Si–0.06C wt.%) filler metal. By means of induction heating, joining process can be completed within seconds in argon ambient. The effects of joining time on the microstructures of joint and base materials, elemental distribution within the brazed joint, and the joint shear strengths were investigated. Experimental results show that BNi-2 containing boron and silicon melting point depressants can achieve good wetting and spreading between Inconel X-750 and stainless steel 304. Joint shear strengths of as high as 483 MPa were obtained when processed at approximately 1423 K for 180 s. The width of the braze-affected zone increases with increasing joining time but it does not cause any significant reduction in the joint strength. Inconel X-750 and stainless steel 304 exhibited no noticeable change in their microstructures due to the rapid heating cycle of induction processing.

Joining of Hastelloy X to Inconel 718 using an infrared process

Joining of Hastelloy X to Inconel 718 by a rapid infrared processing technique has been investigated at 1150 °C using a nickel-based brazing alloy AMS 4777, Ni7Cr3Fe3.2B4.5Si0.06C in wt.%. With this infrared technique, joining typically was completed in seconds in ambient argon. The effects of the infrared joining time on the joint and base material microstructures, elemental distribution within the microstructures and the resulting joint shear strength were investigated. Results show that excellent joint shear strengths of as high as 503 MPa were obtained when processed at approximately 1150 °C for 120 s. Micro-structural examinations of the joint with an optical microscope and a scanning electron microscope indicate that good wetting existed between the brazing alloy and both Hastelloy X and Inconel 718. The braze-affected zone width increased with increasing joining time but did not show a direct correlation with the joint strength. Hastelloy X and Inconel 718 exhibited no noticeable change in microstructures due to the rapid heating cycle of infrared processing.

Laser transformation hardening of a high-purity iron-carbon-chromium alloy

Successful laser transformation hardening of steel surfaces requires that the absorbed laser energy is sufficient to austenitize the initial microstructure to a depth of 0.5 mm or more. Hardening is accomplished when rapid cooling by conduction of heat away from the surface causes transformation of the austenite layer to martensite. Heating and cooling rates of 10/sup 4/ K/s or greater are typical of the laser hardening process and the entire thermal cycle may be accomplished in less than 0.1 s. In an earlier study, laser surface hardening of commercial plain carbon and chromium alloyed steels was examined. It was shown that in the alloyed steel chromium enrichment of the cementite in the initial microstructure could prevent complete transformation of pearlite to asutenite during the very rapid laser heating cycle. However, interpretation of the results was complicated somewhat by the fact that manganese was also partitioned to the cementite. The purpose of this work was to conduct selected identical laser heating experiments on a high-purity Fe-C-Cr alloy to test the effect of chromium unequivocally, i.e., in the absence of manganese and other elements normally present in commercial steels.

The Metallurgy of Continuous-Annealed Drawing-Quality Sheet Steel

Continuous annealing can provide products for the automotive and appliance industries which exhibit more uniform mechanical properties, better shape (flatness), and cleaner surfaces than batch annealing. Continuous annealing (CA) is especially suited for the high-strength steel grades required by the automotive industry. Because of the rapid heating cycle encountered in continuous annealing, drawing-quality steels produced on a CA line do not have properties equivalent to steels produced by batch annealing (BA). However, the latest continuous-annealing technologies combined with proper control of chemistry, have developed products with properties approaching those obtained with BA. This paper reviews the metallurgical concepts of these technologies.

Trans-Varestraint試験法による溶接金属の凝固割れ感受性の研究(1)

In fusion welding of constructional ferrous and non-ferrous materials solidification cracking frequently occurs in the weld metal when a great deal of distortion and shrinkage takes place in the parent and weld metals due to a local rapid weld heat cycle. The occurrence of this solidification cracking, which is a kind of hot cracking, often gives rise to serious problems for some constructional materials from a view-point of weldability.Meanwhile those constructional materials including commercially pure metals have a brittleness temperature range during solidification whose ductility is very low to cracking.The properties in the solidification brittleness range such as temperature difference, minimum ductility and shape of ductility curve depend upon the kind and amount of impurities or alloying elements in the materials. Increasing the temperature interval and decreasing the minimum ductility are considered to increase the susceptibility of solidification cracking for the material in general.Unfortunately, however, there are few reports, so far, concerning the properties in the solidification brittleness range during welding of the constructional materials in spite of their close relation to solidification cracking.In this report authors have firstly investigated the nominal susceptibility of solidification cracking during TIG arc bead-on-plate welding for various constructional materials of carbon steels, low alloy high tensile strength steels, austenitic stainless steels, aluminum and aluminum alloys and brass, using the Trans-Varestraint Tester which was modified from the original Varestraint. Secondly, utilizing the relationship between the maximum crack length occurring in the center of weld metal with the Trans-Varestraint Test and the temperature distribution during welding which was actually measured, the properties of the solidification brittleness range have been investigated for the weld metals of the materials.Lastly, authors have proposed new indices, the critical strain rate for temperature drop (CST), which reasonably evaluates the solidification crack susceptibility of material during welding and the critical strain rate to time (CSS), which is easy to measured and is substituted for (CST) under a limited condition.

Vacuum Heat Treating Using Plasma EB

This paper describes a semicontinuous heat treatment equipment with some of its operating results for metal strips or foils. Work accelerated electron flux from a hot hollow cathode discharge is used for bombarding the strip. Use of hot hollow cathod discharge for annealing of a metal strip was briefly discussed by Morley in 1963. (see Ref. 1.) Smith, Jr. and Hunt reported in 1965 (Ref. 2) the use of high-voltage high-vacuum electron beam for continuous annealing of metal strips. Homogeneous thermal history, rapid heating cycle, and a very high temperature processing are obtainable by using an electron bombardment heating for running strips. Processing of metal strips while running will also be desirable for high temperature treatment where adhesion between layers of a roll may cause defects. The high-voltage high-vacuum EB is advantageous in obtaining higher energy density than the use of hot hollow cathode EB. The latter, however, operates at a low voltage and often more economically than the former. Less evaporation of a volatile component can be another factor to be considered for some alloys. Thus refractory alloys strip rolls that require high temperature contamination free environment, minimum vaporization of volatile component, and nonsticking between layers will be suitable for the plasma EB semicontinuous or continuous processing.