Low-temperature solubility of copper in beryllium, in beryllium-aluminum, and in beryllium-silicon using ion beams
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POLYCRYSTALLINE beryllium is prone t o brittle fracture at room temperature, a p r o p e r t y which is attributed to the deformation anisotropy of the hexagonal crystal lattice. 1,2 In structural applications this tends t o offset the advantage of a very high r a t i o of elastic modulus t o density.3 A possible remedy for this problem was proposed some time ago by Damiano e t a l ,4 who predicted that the c r a c k propagation energy of beryllium would be increased by adding a few percent of a monovalent element in solution. Recent experiments by Wilhelm and Aldinger 2 on single-crystal m a t e r i a l have shown this t o be true at room temperature for copper concentrations up to about 1.3 a t . pet. The m a x i m u m energy inc r e a s e is about one o r d e r of magnitude. Above 1.3 a t . pct the propagation energy decreases, which these workers have explained as b e i n g due to a change in the dominant mechanism of cracking. The solubility of copper in beryllium is comparable t o the concentration levels b e i n g considered for solution strengthening, and therefore it is des i r a b l e t o determine this solubility for all temperatures w h e r e the atomic diffusivity is sufficient for precipitation. Also t o be considered is the possibility of strong t e r n a r y reactions with impurities, analogous t o those observed in the berylliumaluminum-iron system? Previously, the solubility of copper in pure beryllium has been reported only above 873 K,6'~ while ternary effects have not been investigated. In the present work w e have used recently developed ion beam techniques s to m e a s u r e the S. M.MYERS is Member, Technical Staff, Sandia Laboratories, Albuquerque, NM 871 l5, and J. E. SMUGERESKY is Member, Technical Staff, Sandia Laboratories, Livermore, CA94550. Manuscript submittedSeptember27, 1976. METALLURGICAL TRANSACTIONS A
solubility of copper in beryllium down to 593 K. A new experimental feature, reported here for the f i r s t time, is the use of ion irradiation t o accelerate diffusion and thereby permit measurements at lower temperatures. T h e s e data make possible a reliable extrapolation to room temperature. We have also investigated the effects on the copper solubility of aluminum and silicon, two impurities which are known t o undergo t e r n a r y reactions in a beryllium m a t r i x with s e v e r a l elements from the f i r s t transition s e r i e s .8 1.0 E X P E R I M E N T A L P R O C E D U R E The experimental procedure used in this work was essentially s i m i l a r to that discussed in detail in a previous paper.5 Diffusion couples were created by implanting copper into single-crystal beryllium at room temperature, followed where appropriate by implantation of aluminum or silicon t o study the ternary r e g i m e s . The samples were then annealed isothermally at temperatures of interest, and the composition-vs-depth profiles of the implanted elements were monitored nondestructively by ion b a c k scattering analysis. Annealing produced a relatively rapid precipitation within t
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