Hydrogen transport during deformation in nickel: Part II. Single crystal nickel
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I.
INTRODUCTION
A previous investigation has detailed several effects of tensile deformation on hydrogen permeation fluxes in polycrystalline nickel. ~At a fast strain rate, the hydrogen permeation flux decreased during deformation due to dynamic trapping by newly created dislocations. At a slower strain rate, less of a decrease in the flux occurred as a result of lattice refilling during the experiment. Finally, at a very slow strain rate where total lattice refilling was possible, a decrease in the specimen thickness and an increase in input concentration during deformation resulted in an increase in the hydrogen flux. No unambiguous evidence of dislocation transport was observed in polycrystalline nickel. The above findings do not preclude, however, the possibility that dislocation transport occurred but was dominated by the other influences. In the present investigation, the same experiments were performed on single crystal slices of nickel. In the easy glide region (or Stage I) of single crystal deformation, dislocations have a long mean free path and thus move long slip distances with little interaction from other dislocations. Therefore, the conditions of easy glide should be the best possible for observing dislocation transport.
II.
EXPERIMENTAL
The electrochemical permeation technique modified to allow for simultaneous deformation 2 was utilized in this study. The procedure has been described in detail elsewhere. ~,3 The single crystal rods were grown from ultra high purity nickel of composition shown in Table I. Slices 350/~m thick were spark cut from the rods and the edges of the slices were then trimmed by a string saw to result in a specimen width of about 1 cm. The orientation of the tensile axis of each slice was about 10 deg from the (110) and 5 deg from the (331). The faces of the slices had an orientation about 4 deg from that for the emission of pure edge dislocations) The slices were annealed under argon at 1000 ~ for 2 days after heating at a rate of 100 ~ Annealing G. S. FRANKEL was formerly Graduate Student, The H. H. Uhlig Corrosion Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 and is currently Postdoctoral Associate, Institute for Materials Chemistry and Corrosion, Swiss Federal Institute of Technology, Zurich, Switzerland. R. M. LATANISION is Shell Professor of Materials Science, Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted April 29, 1985.
METALLURGICALTRANSACTIONS A
Table I. Chemical Composition of the Nickel Single Crystal Rods in ppm (Balance Ni) C S Fe Cu Si Mg Ti Zr Pb Mo A1 Ag
8 < 1 < 10 < 10
/ O far) hi tY
o') ).l Q. "~ Run IA
Run9A Stress
~
Current
0.1
I i 0.2 RESC)IVFr)
I 0.3 SHFAR
I
0.4
8 7 0 - - V O L U M E 17A, MAY 1986
, I 0.5
I
I 0.6
STRAIN
Fig. 2 - - P a s s i v a t i o n current c h a n g e and resolved shear stress
The extent of easy glide, determined by the intersection of the extrapolated Stage I and Stage II regions, was very different for the two conditions. The effects of a passive f
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