The influence of hydrogen and the interface phase on fracture in Ti code 12
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A1 Coating Polarization Current Density DA ThickneSs, (/xm) Transient (mA/cm 2) (cmZ/sec) 0.064 1st 2 3.1 X 10 -16 2nd 2 2.8 • 10 -16 0.2 1st 20 1.8 X 10-15 2nd 20 5.9 x 10-15
diffusivities calculated from the first permeation transients where all trap sites are empty, to subsequent transients, when strong sites are permanently filled. 7'1~ Results from these tests are summarized in Table II, showing little difference between diffusivities calculated from first and second transients; thus, the irreversible trap density is likely low and a large concentration of weaker (reversible) traps plus a low lattice solubility more likely accounts for the large DL/Da ratio. The fine grain size and a high point defect concentration, both of which are common in vapor deposited material, are likely trap candidates to explain the results. In summary, we have been able to measure with some confidence the room temperature effective hydrogen diffusivity in vapor deposited aluminum using a composite specimen. The value found, 10-15 to 10 -16 c m 2 per second, is lower than originally estimated, 4 but is comparable with recent measurements by others on aluminum alloys.t6 The large trap density inferred from this study suggests that grain boundaries can be one of perhaps a number of very effective hydrogen traps in aluminum, consistent with our observation of hydrogen-induced intergranular failure in a high purity aluminum alloy. 2 This also implies that such boundaries are not efficient short circuit diffusion paths. So long as this purified aluminum model system reflects the hydrogen response in aluminum alloys, these results provide support for the contention2 that hydrogen transport of mobile dislocations is a necessary transport mode to rationalize the extent and kinetics of hydrogen embrittlement of aluminum. Of equal interest, the composite technique should be able to be used to study transport behavior in other pure metals and alloys with similar hydrogen characteristics.
7. G.M. Pressouyre and I.M. Bernstein: Metall. Trans. A, 1978, vol. 9A, p. 1571. 8. R.G. Meyers and R.P. Morgan: in Trans. of the Vacuum Metall. Conf., 1966, p. 271. 9. U. Koster, E S. Ho, and M. Ron: Thin Solid Films, 1980, vol. 67, p. 35. 10. I.M. Bernstein and A.W. Thompson: in Advanced Techniques for the Characterization of Hydrogen in Metals, N.F. Fiore and B.J. Berkowitz, eds., TMS, Warrendale, PA, 1982, p. 89. 11. G.S. Frankel and R.M. Latanision: Scripta Met., 1982, vol. 16, p. 1091. 12. M.A. Devanathan and Z. O. J. Stachursky: Proc. Royal Society, 1962, vol. A270, p. 90. 13. See, for example, "Hydrogen in Metals", G. Alefeld and J. Vokl, eds., Topics in Applied Physics, Springer, Berlin, 1978. 14. W.M. Robertson: Metall. Trans. A, 1979, vol. 10A, p. 489. 15. R.A. Oriani: Acta Metall., 1970, vol. 18, p. 147. 16. G.M. Scamans: Alcan Ltd., private communication, 1983.
The Influence of Hydrogen and the Interface Phase on Fracture in Ti Code 12 N.R. MOODY, F.A. GREULICH, and S. L. ROBINSON Two phase a/fl titanium alloys often exhibit an interface phase
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