INTERACTION BETWEEN DISLOCATIONS AND H ATOMS IN α-Fe

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INTERACTION BETWEEN DISLOCATIONS AND H

ATOMS IN α-Fe

M. Hermant

To cite this version:

JOURNAL DE PHYSIQUE Colloque C 3, supplément au no 7-8, Tome 27, juillet-août 1966, page C 3-209

INTERACTION BETWEEN DISLOCATIONS AND

H ATOMS IN &-Fe

Natuurkundig Laboratorium, Universiteit van Amsterdam, The Netherlands

There is still discussion about the question regarding the interaction between H atoms and dislocations in a-Fe. During the last 10 years many experiments have been performed in connection with this problem. These experiments can be roughly divided into 2 groups. The first group deals with the possible exis- tence of an upper yield point in deformed a-Fe due to H (e. g. Rodgers [l] and Adair and Hook [2]). The second group deals with the internal friction below room temperature of analogous materials (Weiner and Gensamer [3], Maringer a. o. [4], Heller [5] and Our own experiments [6].

The observation of characteristic yield points and damping peaks in these measurements upon the introduction of H are sometimes explained in terms of a hydrogen-dislocation interaction. However, an important group of authors believes these phenomena to be solely due to the deformations introduced. Thereby they point to the fact that, because of the extremely low solubility of H in a-Fe, the introduction of relatively large quantities of hydrogen inevitably Ieads to the creation of cracks filled with molecular

H, at high pressures, and thus to deformations

(e. g. Tetelman [7] and Farrell [8]).

In order to investigate this point in more detail, we performed a number of internal friction measurements on a-Fe containing H. Initially we discovered, that the appearance of an internal friction peak at about 1300K (see also [3, 4, 51) without exception was connected with the presence of cracks in Our samples (see above). This result, of course, did not solve the problem. Thereafter we tried to separate the effects of deformation and H on the appearance of the peak. First, we measured the damping of a-Fe wires, cold deformed in several ways, such as to imitate as closely

as possible the deformation due to cracks. It can be definitely stated, that below 170 OK no internal fric- tion peaks are present. The subsequent introduction of H such that no cracks were created did not signi- ficantly change the results obtained. These experiments point to the fact, that deformation alone is not able to give rise to a damping peak in the 130 OK range. Finally we performed a number of measurements, the variables with respect to the treatment of Our wires were plastic strain, charging with H (without the crea- tion of cracks) and copper plating. Al1 possible combi- nations and orders of succession were applied, with the exception of copper plating before charging. It appeared, that the 130 OK peak could be observed only, in case al1 three treatments had been applied. Thereby the order of succession played no significant role. Therefore these results give the conclusive proof, that the 130 OK peak is connected with the simulta- neous presence of H and dislocations, and thus imply an interaction between H and dislocations in a-Fe to be present.

Bibliographie

[ l ] RODGERS (H. C.), Acta Met., 1954, 2 , 167 ; ibid., 1957,

5, 112.

[2] A D ~ I R (A.), HOOK (R.), Acta Met., 1962, 10, 741 ; ibid., 1963, 11, 81.

[3] WEINER (L.), GENSAMER (M.), Acta Met., 1957, 5, 692. [4] MARINGER (R.), SWETNAM (E.), MARSH (L.), MAN-

NING (G.), N. A. C. A., Technical. Note 4328, 1958.

[5] HELLER (W.), Acta Met., 1961, 9, 600.

[6] HERMANT (M. E.), Thesis, University of Amsterdam, 1966.

[7] TETELMAN (A.), Fracture of Solids, John Wiley &

Sons, New York, 671, 1963.

[8] FARRELL (K.), Journ. Iron St. Inst., 1965, 203, 71.