Energy-Beam Processing Studies on Ta/U and Ir/Ta Systems
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ENERGY-BEAM PROCESSING STUDIES ON Ta/U AND Ir/Ta SYSTEMS. E. N. KAUFMANN,* P. S. PEERCY,** D. C. JACOBSON,+ C. W. Draper,++ F. J. Huegel,* C. J. Echer,* D. M. Makowiecki+ and J. D. Balser* *Lawrence Livermore National Laboratories, Livermore, CA 94550; **Sandia National Laboratories, Albuquerque, NM87185; +Bell Laboratories, Murray Hill, NJ 07974; ++Western Electric Engineering Research Center, Princeton, NJ 08540 ABSTRACT Films of Ta metal on uranium and of Ir metal on tantalum have been irradiated and melted by pulses from Q-switched Ruby and frequency-doubled Nd:YAG lasers to investigate the nature of the resulting mixtures in light of the very different binary-phase diagrams of the two systems. In addition, a two-phase Ir-Ta alloy has been surface-processed with CWC02 -laser radiation and with an electron beam in order to study microstructure refinement and test the advantage of using alloys as opposed to film-on-substrate combinations for the developement of claddings. INTRODUCTION The binary phase diagram for the Ta-U system [1] shows no intermetallic phases, complete miscibility in the liquid phase, and little or no mutual solubility in the solid phase. Whereas pure tantalum metal displays a bcc crystal structure up to its very high melting point at 2996°C, pure uranium is polymorphic displaying a (orthorhombic), 8 (tetragonal) and y (bcc) phases with rising temperature to its melting point at 1125°C. The maximum solid solubility of U in Ta is ^.2at.% and of Ta in U is ,v0, -,, 0, and ,, 1.5 at.% in a, 8, and y phases, respectively. On the other hand, Nb, which is similar in many respects to Ta, shows a continuous series of bcc solid solutions with y-U [2]. The question arises whether the rapid quench of the liquid alloy obtained by pulse-laser melting will form an extended bcc solution of U in Ta or of Ta in y-U or the two phase mixture, Ta + a-U. The effect of two practical difficulties, ie., the wide disparity in melting point and the extreme susceptibility of uranium to oxidation, is also of interest. The Ir-Ta binary system shows several intermetallic phases and a eutectic at 55 at.% Ta. The eutectic temperature of 1950°C is to be compared with the melting points of Ta (2996 0 C) and Ir (2454°C). For this combination, it is interesting to find if an amorphous phase will form in rapid quenching near the eutectic composition. A practical question for cladding applications is whether sufficient energy can be transmitted to the high melting substrate to cause melting (possibly via eutectic formation) before the lower melting film is vaporized. THE TANTALUM ON URANIUM CASE In a preliminary study, 2400A of Ta metal was sputter deposited on an electropolished high-purity depleted-uranium substrate and irradiated with a single 25ns pulse from a Q-switched Ruby laser at a series of power levels in air. At lower powers, a substantial fraction of the treated area 2 remained covered by what appeared to be partially melted Ta. At 3.2J/cm Mat.
Res.
Soc. Symp.
Proc.
Vol.
23 (1984)
Published by Elsevier Science P
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