18 research outputs found
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Oxygen stabilized rare-earth iron intermetallic compounds
A new, oxygen-stabilized intermetallic compound was identified in sintered, pre-alloyed rare-earth iron powder samples. Its composition corresponds to formula RFeO and its crystal structure belongs to space group Im3m. The presence of these compounds was observed, so far, in several R--Fe--O systems, with R = Gd, Tb, Dy, Ho, Er, and Y. (auth
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BINARY AND TERNARY NIOBIUM-BASE SUPERCONDUCTORS BY THE INFILTRATION PROCESS
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THE EFFECT OF MAGNETICALLY ALIGNED POWDER ON THE MAGNETOSTRICTION OF SINTERED RARE EARTH-IRON LAVES PHASE COMPOUNDS
A powder metallurgical approach is utilized to prepare grain oriented Laves phase compounds of Tb{sub x}Dy{sub 1-x}Fe{sub 2}. The magnetostrains observed in the oriented compounds, though containing {approx}20% porosity as presently prepared, are far superior to those of arc cast and highly dense liquid phase sintered materials. Also, it is shown that the alignment achieved is strongly dependent on the Tb/Dy ratio
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A15 multifilamentary superconductors by the infiltration process
The inherent brittleness of the A15 compounds, and the requirement for a filamentary morphology, led to a heavy reliance on a powder approach for the preparation of superconducting tapes and wires. The quench-age technique, a non-powder process, was employed for the niobium-aluminum system, following the special features of the equilibrium phase diagram. The powder approach proved particularly effective for binaries, such as Nb-Sn, and for the ternaries Nb(Al,Ge) and Nb(Al,Si). Two variations of the powder process were assessed. One involved the use of precompounded powder of the desired stoichiometry but required simultaneous application of heat and pressure. The second variation was the infiltration process. This process involves the preparation of a ductile niobium matrix containing a controlled network of interconnected pores which are subsequently infiltrated with liquid metals (Sn) or low melting-point eutectics (e.g., Al-Ge, Al-Si). The composite is then subjected to a thermomechanical treatment to form a multiply connected array of A15 filaments in a niobium matrix. Multifilamentary conductors, based on Nb/sub 3/Sn, Nb/sub 3/Al, Nb/sub 3/ (Al,Ge) and Nb/sub 3/ (Al,Si), were readily obtained. Nb/sub 3/Sn conductors made by the infiltration process exhibit a critical temperature (Tc) of 18.1 K and a critical current carrying capacity (I/sub c/) of 8 x 10/sup 4/ amp.cm/sup -2/ at 12 Tesla
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Binary and ternary niobium-base superconductors by the infiltration process
This report summarizes the work on high field superconducting materials and processes performed at the Materials and Molecular Research Division of the Lawrence Berkeley Laboratory. Two major interrelated focal points characterize this research. One was the decision to restrict the effort to A-15 compounds because of their superior critical temperatures and critical fields. The inherent brittleness of these compounds along with the requirement for a filamentary morphology led to the second focal point: a heavy reliance on a powder approach for the fabrication of superconducting tapes and wires. There have been exceptions to the use of powder techniques where special circumstances such as the nature of a particular alloy system suggested on alternative approach. The quench-age technique described herein is an example of a non-powder approach. Here the niobium-aluminum system is involved and the methodology is based on the fact that in a certain composition range a solid solution of aluminum in niobium is the stable phase at elevated temperatures (1950/sup 0/C), whereas at lower temperatures (< 1100/sup 0/C) the stable phase is the desired A-15 compound. Additionally, niobium forms deformation twins which were found to be effective sites for the nucleation of the A-15 phase
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