Abstract: Co-free AB5-type LaxMm1-x(NiMnSiAlFe)4.9 (x = 0, 0.45, 0.75, 1) hydrogen storage alloys were prepared by casting and rapid quenching. The phase structures and microstructures of the as-cast and quenched alloys were analyzed and observed by XRD and SEM. The electrochemical performances of the as-cast and quenched alloys were measured. The effects of La content and quenching rate on the microstructures and electrochemical properties of the alloys were investigated comprehensivel y. The obtained results indicate that the Co-free AB5-type hydrogen storage alloy with excellent synthetical electrochemical performances can be prepared by adjusting La content and employing appropriate rapid quenching technique.
Abstract: In this work, the electrochemical discharge capacity of melt-spun (MmY)1 (NiCoMnAl)5 ribbons, in which the content of yttrium was 0-2.5wt%, was studied in the temperature range of 30~80oC. It was found that adding element yttrium made the electrochemical capacity of the compounds increased. The capacity obtained was 333mAh/g at 30 oC and 247 mAh/g at 80oC when the content of yttrium was 2.0wt%. In addition, 70~85% recovery of the capacity was obtained due to better antioxidation. The increase of charging/discharging efficiency with yttrium substitution for Mm in melt-spun ribbons illustrated by the potential characteristics of charging/discharging is ascribed to the flatter and lower hydride formation potential, as well as the higher hydrogen evolution potential. Moreover, This effect is more prominent with increasing yttrium content.
Abstract: Hydrogen absorption-desorption cycling induced by pressure change in a closed system were carried out with LaNi5, La0.7Ce0.3Ni4Cu and TiFe0.9Ni0.1 alloys. PC isotherms measured during the cycling showed some changes in hydrogen storage capacity, plateau pressure and hysteresis of the alloys. . The half capacity life of LaNi5 alloy can be projected as 70,000 cycles for room temperature pressure cycling. When La0.7Ce0.3Ni4Cu alloy was pressure cycled both of the plateau pressures were decreased significantly and continuously. TiFe0.9Ni0.1 alloy showed a good resistance to cyclic degradation. Heat treatments of the degraded alloys under 1 atm of hydrogen gas recovered most of the hydrogen storage properties to the initial level even though they were degraded again more rapidly
upon subsequent cycling.
Abstract: Tritium radioluminography has been applied to Ti50Cr50 and Ti40Cr60 alloys with
two-phase structure of BCC phase and Laves phase by examining hydrogen distributions and by measuring a hydrogen penetration profiles. Hydrogen diffusion coefficients in these alloys have been successfully determined by analyzing the tritium depth profile to be 3.3×10-12 m2/s and 1.3× 10-12 m2/s, respectively. This value has been suggested that the hydrogen diffusion in the Laves phase is slower than that in the BCC phase.
Abstract: MmxMl1-xNi4.14Cu0.5Al0.3Zn0.06 (Mm=Ce-rich misch-metal, Ml=La-rich misch-metal, x=0, 0.2, 0.4, 0.6, 0.8, 1) alloys have been synthesized by the inter-media alloy method. The properties of these alloys have been systematically investigated by means of X-ray diffraction (XRD), pressure-composition isotherms (PCT), electrochemical impendence (EIS) and cyclic voltammogram (CV). The X-ray diffraction results indicated that these alloys had a CaCu5-type hexagonal crystal structure. With increasing the Mm content, the plateau pressure and volume expansion of their hydrides were increased, but the volume of unit was decreased.
Abstract: The high-pressure synthesis of new hydrides of Mg-RE-H systems, where RE = La, Ce and Pr, were conducted by using a cubic-anvil-type apparatus, and their crystal structure, thermal stabilities and hydrogen contents were investigated. In MgH2-xmol%REH (REH = LaH3, CeH2.5 and PrH3), new hydrides with primitive tetragonal structure were synthesized around x = 25 - 33 under GPa-order high pressures. The lattice constants were a = 0.8193 nm, c = 0.5028 nm, a = 0.8118 nm, c = 0.4979 nm and a = 0.8058 nm, c= 0.4970 nm at x = 25 in Mg-La, Ce and Pr systems, respectively. The hydrogen contents of the novel compounds were 4.1 mass%, 3.7 mass% and 3.9 mass% in Mg-La, Ce and Pr systems, respectively, and the chemical formulas were found to correspond to Mg3LaH9, Mg3CeH8.1 and Mg3PrH9. The new hydrides decomposed into Mg and rare-earth hydride at about 600 K (Mg3LaH9: 614 K, Mg3CeH8.1: 609 K, Mg3PrH9: 630 K) with an endothermic reaction.
Abstract: Microstructural features, mechanical properties, and corrosion properties of a SAF2205 duplex stainless steel (DSS) were systematically investigated as functions of cooling rate during casting and heat treatment conditions. The choice of a duplex stainless steel was a SAF2205 alloy, of which composition is 0.03C, 21~23Cr, 4.5~6.5Ni, 2.5~3.5Mo, 0.08~0.2N, 1.0Si, and 2.0Mn with remaining Fe. A 5-stepped sand mold and the permanent Y-block mold were used to check the effect
of cooling rate during solidification. The microstructural characteristics, such as grain size, the d/γ ratio, the existence of the carbides and σ phase has been noticed to greatly change with the variation of cooling rate during the casting procedure. Various heat treatment conditions were also examined to achieve the optimized mechanical properties of DSS. Based on the preliminary examination, the
feasibility study of utilization of centrifugal casting has been carried out for the production of better quality DSS pipe components. Melting and casting practices of DSS during centrifugal casting in an air atmosphere were systematically investigated in order to obtain the optimized process parameters.
Abstract: Die design rule for semi-solid die casting (SSDC) with A356 electromagnetic stirring (EMS) aluminum alloy, was proposed. The die design rule included inspection of machine, part requirements, parting line determination, sleeve, plunger, gating system, overflow, air vent, ejector pin, and heating line design. The specification of gating system, overflow, air vent, plunger tip, and sleeve suitable for respective part were regulated. Two steps die system of lower-positioned gate and
three steps die system of center-positioned gate were manufactured for 4 automobile suspension parts, based on the die design rule. For the sound filling pattern and solidification behavior, injection speeds of 4 parts were summarized to the interval (from V1 to V4). As a result of observing the microstructure of 4 parts after T6 heat treatment, primary Al-α phase was globularized and fine Si particles were distributed around the grain boundary. The mechanical properties of 4 parts with T6 heat treatment were investigated and showed ultimate tensile strength (UTS) of 330 MPa, yield strength (YS) of 250 MPa, and elongation of 7.5% as average.
Abstract: Small amounts of various alloying elements were added to a high strength Al-Zn-Mg-Cu alloy and their effects on the microstructure, mechanical properties, and casting characteristics were investigated. Silicon additions with or without extra Mg to the Al-Zn-Mg-Cu alloy could enhance the castability such as fluidity, feedability, and hot tearing resistance significantly while maintaining a high strength. However, in these alloys containing silicon the compositional adjustment was necessary to prevent the Mg2Si phase formation from degrading the precipitation of MgZn2 phase that is responsible for the high strength. Zr addition to the base alloy was also observed to improve the feedability without deteriorating the tensile strength.
Abstract: In this study, melt protection property of SF6+synthetic air and HFC-134a+synthetic air cover gas mixtures were investigated for most commonly used magnesium alloys, AZ91D and AM60B. Each alloy was melted in mild steel crucible with different temperature, cover gas concentrations and sealing conditions. HFC-134a+synthetic air cover gas mixtures offered better melt protection property for all variables of temperatures, alloys, cover gas concentrations and sealing conditions. However, crucible (AISI 1020) surface that is exposed to HFC-134a cover gas mixtures was seriously damaged due to the corrosive characteristics of HFC-134a in molten