ASSOCIATION OF DEFECTS WITH IRON IMPURITIES IN FCC ALUMINIUM

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ASSOCIATION OF DEFECTS WITH IRON IMPURITIES IN FCC ALUMINIUM

R. Preston, S. Nasu, U. Gonser

To cite this version:

R. Preston, S. Nasu, U. Gonser. ASSOCIATION OF DEFECTS WITH IRON IMPURI- TIES IN FCC ALUMINIUM. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-564-C2-565.

�10.1051/jphyscol:19792196�. �jpa-00218574�

JOURNAL DE PHYSIQUE Colloque C2, supplkment au n O 3, Tome 40, mars 1979, page ~ 2 - 5 6 4

A S S O C I A T I O N OF DEFECTS W I T H I R O N I M ? U R I T I E S I N FCC A L U M I N I U M

R.S. Preston, S. Nasu and U. Gonser

Fachbereich Angewandte Physik, Universitat des SaarZandes, 6600 Saarbriicken, Germany

RCsum6.- Nous avons dtudid par spectroscopie ~gssbauer les effets d'un revenu isochrone sur un 6chan- tillon de Al-O,OI% Fe aprPs une d6formation 3 77 K. Les plus remarquables effets que nous avons ob- servds sont dans le domaine de tempdrature compris entre 210 K et 350 K oii des lignes satellites apparaissent par suite d'une association des atomes de Fe avec des lacunes.

Abstract.- We have used ~Gssbauer spectroscopy to monitor the isochronal annealing of A1

-

0.01% Fe after cold working at 77 K. The most striking results are for the annealing range from 210 K to 350 K where the growth and decay of a satellite line due to the association of Fe atoms with vacancies can be seen.

The Msssbauer spectrum of very dilute 5 7 ~ e in aluminium is primarily a sharp single line represen- ting isolated iron atoms on substitutional lattice sites. If lattice defects such as vacancies, inters- titials and dislocations are introduced by irradia- tion, by quenching from high temperature or by de- formation of the specimen, one may expect the hyper- fine interactions of the iron atoms to be perturbed when they associate with these defects. In radiation damage studies Manse1 and Vogl / I / have found a satellite line due to 5 7 ~ o associated with intersti- tial A1 atoms. Recently a group at Tokyo University /2,3/ observed a somewhat different satellite line for 5 7 ~ e and 5 7 ~ o in aluminium quenched from high temperature. They attributed this satellite to asso- ciated vacancies, although Janot and Georges-Gibert /4/, Sdrensen and Cotterill /5/, and Ward /6/ have performed similar quenching experiments without fin- ding any satellite lines attributable to vacancies.

In order to clarify this situation we have per formed a Msssbauer study on aluminium containing

"Fe. We did not succeed in forming Fe-vacancy pairs by rapid quenching of a 50 ppm specimen, although we used a single crystal in an effort to reduce the loss of vacancies during quenching. However, we did find clear satellite lines due to associated defects in a 100 ppm specimen which had been deformed while at liquid nitrogen temperature. In this paper we re-

port primarily the results from the deformation experiments.

Aluminium containing 100 ppm 5 7 ~ e was prepared by melting 99.999 % aluminium with enriched iron foil. After rolling to 0.6 mm thickness and long annealing at high temperature the specimen grains were 2

-

3 nnn in diameter and the Msssbauer

spectrum at 77 K was a single line with a half width of 0.248

+

0.001 m / s and shifted to 0.569

+

0.001 mm/s relative to room-temperature a-Fe. From this

spectrum it was clear that all the Fe atoms were in isolated substitutional sites in the aluminium ma- trix.

This specimen was then sandwiched between stain- less steel plates 1 rnm thick and cooled to 77 K in a liquid nitrogen bath where it was rolled to about 50 % of its original thickness. Except for short annealing periods the sample was kept at liquid ni- trogen temperature for the duration of the experi- ment.

We then annealed the specimen isochronally for I minute periods at intervals of Zoo, measuring the Msssbauer spectrum at 77 K after each annealing.

Every spectrum made after the cold rolling contained a satellite (Fig. 1).

Using these spectra we can divide the recovery process into three stages. The first stage is from 77 K (the as-rolled condition) to 190 K. In this region we were unable to fit the satellite to either a single line or a symmetric doublet. According to the resistivity measurements of Panseri et al. /7/

and Ceresara et al. /8/ bhe spectrum for the as- rolled state should reflect the association of in- terstitial~ with Fe atoms.

The second stage is from 210 K to 350 K where we were able to fit the satellite to a single line 0.28

+

0.02 mm/s wide with a shift of 0.25 f 0.01 mm/s relative to room temperature a-Fe. This satel-

lite appears to be the same as the one observed in the quenching experiments by the Tokyo group and is seen in approximately the temperature region where vacancy migration should occur /7,8/. Therefore we

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792196

attribute this stage to the association of vacancies with Fe atoms. Satellite intensity vs. temperature is shown in figure 2.

unique atomic configuration. The simplest assumption is that this configuration consists of an Fe atom associated with a monovacancy or, possibly, a diva- cancy.

Experiments are in progress to determine the dynamical properties of defect-associated Fe atoms and the kinetics of trapping and de-trapping in the second stage.

Acknowledgements.- This work was supported by the DFG. Technical assistance by Nessrs. H. Staats and 3. Welsch is gratefully acknowledged.

References

/I/ Mansel, W., Vogl, G., J . Phys. F : Metal Phys.l (1977) 253. This paper contains references to related earlier work.

/ 2 / Ichinose, H., Sassa, K., Ishida, Y., Kato, M.,

Scr. Metall.

2

(1977) 539.

/3/ Sassa, K., Goto, H., Ishida, Y., Kato, M., Scr.

Metall.

11

(1977) 1029.

/4/ Janot, Ch., Georges-Gibert, H., J. Phys. F : Metal Phys.

1

(1977) 231.This paper contains re- ferences to related earlier work.

092 92 /5/ sdrensen, K.O., Cotterill, R.M.J., Acta Metall.

1 o 1 -1 0 1

-

22 (1974) 1331.

YELOCITY Imn/sl /6/ Ward, J.B., Scr. Metall.

9

(1975) 1211.

Fig. 1 : Mgssbauer spectra of cold-worked specimen. / 7 / Panseri, C., Ceresara, S., Federighi, T., Nuovo The velocity scale is relative to a-Fe at room tem- Cimento

9

(1963) 1223.

perature. /8/ Ceresara, S., Elkholy, H., Federighi, T., Philos

Mag.

12

(1965) 1105.

L.

,

O 200

I

KO 300 3!h l b )

TEWERATURE ( K 1

Fig. 2 : Satellite areal intensity as a function of the isochronal annealing temperature.

In the third stage, from 370 K to 450 K, the satellite is again very weak and no reliable fit is possible. It may be that in this stage Fe atoms are associated with dislocations and subboundaries. We are continuing the isochronal annealing to higher temperatures.

Since we have attributed the satellite in our second stage to Fe vacancy associations and since we are able to fit this satellite with a very narrow line, we infer that Fe-vacancy associations have a