DISLOCATION PINNING RATE IN X-RAY-IRRADIATED COPPER BETWEEN 78-240 °K

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DISLOCATION PINNING RATE IN

X-RAY-IRRADIATED COPPER BETWEEN 78-240 °K

G. Roth, G. Sokolowski, K. Lücke

To cite this version:

G. Roth, G. Sokolowski, K. Lücke. DISLOCATION PINNING RATE IN X-RAY-IRRADIATED COPPER BETWEEN 78-240 °K. Journal de Physique Colloques, 1971, 32 (C2), pp.C2-145-C2-146.

�10.1051/jphyscol:1971230�. �jpa-00214556�

JOURNAL DJ2 PHYSIQUE Colloque C2, supplment au no 7 , tome 32, Juillet 1971, page C2-145

DISLOCATION PINNING RATE

IN X-RAY-IRRADIATED COPPER BETWEEN 78-240 "K

G. ROTH, G. SOKOLOWSKT and K. LUCKE

Institut fiir Allgemeine Metallkunde und Metallphysik der Technischen Hochschule Aachen und Van de Graff-Labor Aachen der Kernforschungsanlage Jiilich

Rhum6. - Le taux d'ancrage des dislocations dans le cuivre a kte determine par des mesures du frottement intkrieur et du module de torsion au cours d'irradiations isothermes auxrayons-X dans le domaine de temperature de 78 a 210 ^{O K .} I1 semble d'apres le resultat des mesures de frottement intkrieur qu'on verifie l'existence d'un minimum du taux d'ancrage ^8, la temperature de 160 ^{O K} comme il a et6 indiquk par Thompson et Buck. Puisque, par ailleurs, on n'a pas obtenu de minimum par la mesure du module et qu'en outre on a observe une dkpendance de l'ancrage apparent en fonction de la temperature de mesure, il apparait maintenant douteux que le minimum observe soit vkitablement un effet du taux d'ancrage.

Abstract. - The dislocation pinning rate in copper was determined by measurements of internal friction and torsion modulus during isothermal irradiation with x-rays in the temperature range between 78 and 210 ^{O K .} The evaluation of the damping measurements seems to verify a minimum of the pinning rate at 160 OK as reported by Thompson and Buck. Since, however, this minimum was not obtained from the evaluations of the modulus measurements and, moreover, a dependance of the apparent pinning upon the temperature of measurement was observed, it seems now doubtful that the mininlunl is a true effect of pinning rate.

Introduction. - Recently, Thompson and Buck [ l ] reported an effect of irradiation temperature on dislocation pinning of copper during Co60-y-irradia- tion. By means of internal friction measurements they observed a pronounced minimum of the pinning rate at 160 OK. These authors and later Seeger [2]

interpreted this minimum as to be due to the thermal conversion of interstitials during their migration to the dislocations.

Roth, Sokolowski and Liicke [3] found for 3 MeV- electron irradiations from damping measurements also a minimum of pinning rate at 160 OK, but a much smaller one. There was, however, no indication of a minimum if the torsion modulus measurements were evaluated. The authors concluded that this is in contradiction to the assumption of Thompson and Buck that the minimum deduced from damping is really due to a minimum in pinning rate.

I n the present paper results for irradiations with x-rays will be reported. In particular, additionally to the influence of the temperature of irradiation the influence of the temperature of measurement will be investigated.

Experimental Procedure and Results. - In the present experiments the same type of samples (poly- crystalline sheets of 0.1 mm thickness of 99.999 %

purity ASARCO-copper excited to torsional vibrations of 5 kHz) and the same experimental set up as des- cribed in [3] for the electron irradiations were used.

Only the kind of irradiation was changed by stopping the 3 MeV-electron beam by a gold target situated about 2 cm before the sample. Therefore in the present case the radiation damage was caused by the x-rays generated in the gold target.

Under these conditions the defect production rate was about a factor of 7 smaller than in the case of the electron irradiation [3] and a factor of 60 larger than

in the case of the ~ o ~ ~ - y - i r r a d i a t i o n of Thompson and Buck [l]. These relations are estimated from a MHz-pinning experiment [4], in which the electron irradiation was compared with the 3 MeV-Brems- strahlung of a gold target and with the irradiation of a calibrated C ~ ~ ~ - s o u r c e . The total time of irra- diation was 150 hours in the experiments of Thompson and Buck [l], 5 hours in the present experiments, and 0.5 hours in the case of electron irradiation [3].

Therefore the final defect concentration was nearly the same in all three cases and was of the order of magnitude of 10-'.

Figure l gives the initial pinning rates (i. e. the number of pinning points formed per pre-irradia- tion loop length L, of the dislocations and per

100 150 200 250 100 150 200 250

100 150 200 250

-

-

-

--

FIG. 1. - Dislocation pinning rate p versus irradiation tempe- rature, measured during irradiations with 3 MeV-Bremsstrahlung.

The results for Coao-y-irradiations by Thompson and Buck [l]

and for 3 MeV-electron irradiations by Roth, Sokolowski and Lucke [3] are given for comparison.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971230

C2- 146 G. ROTH, G. SOKOLOWSKI AND K. LUCKE unit time) as measured during irradiations with

3 MeV-Bremsstrahlung at 78 OK, 160 OK and 240 OK.

For 160 OK two runs, for each of the other two tem- peratures one run has been made. The present results are compared with the pinning rates found for the C O ~ O - ~ and for the 3 MeV-electron irradiations. The pinning rates deduced from damping measurements are plotted in the left half and those deduced from modulus measurements are plotted in the right half of the figure. The different levels of the curves for the three sets of experiments are caused to the largest part by the different defect production rates mentioned above.

One recognizes in figure 1 at about 160 OK a mini- mum for the pinning rates derived from the damping measurements. The reason for the different depth of

1 100 150 200 250 100 150 200 250

I I

hternal Fr~ction Torsion Modul?s

Measurements Measurements

10'

I Sample 4 3 MeV-Bremsstrahlung

I v Temperature of Measurement equal Temperature of lrrad~atlon r Temperature of Measurement 78'K

the minima for the three sets of experiments is not

yet completely clarified. It is already proved by a set l00 150 200 250 100 150 200 250

of electron irradiations that there is no influence of Temperature of Irradiation PK]

the defect production rate to the depth of the minimum [3]. Moreover it is shown [3] that it is rather unlikely that the different depth of the minimum is caused by different properties of the samples before irradiation, so that the most probable reason seems to be the different type of irradiation.

One recognizes further from figure 1 that the pinning rate as deduced from modulus measurements exhibits no minimum or, at least, a minimum much smaller than that deduced from damping measurement.

Thompson and Buck could not check this point, because their modulus measurements were too much affected by a warming up of their sample during the irradiations. Because of good thermal contact this difficulty did not exist in our experiments so that our modulus measurements are at least as accurate as the damping measurements.

Finally, in the present work a strong influence of the temperature of measurement upon the resulting pinning rate has been found. In figure 2 the open symbols give damping and modulus as measured a t the irradiation temperature, i. e . these symbols repre- sent the same values as given in figure 1. The closed symbols were obtained from measurements a t 78 OK after an irradiation at a temperature given by the abscissa. One recognizes, that in this case, i. e. if the temperature of measurement is kept constant, the minimum of pinning rate as function of irradiation temperature seems to disappear. It shall be mentioned that this behaviour is completely reversible, this means that the values measured at irradiation tempe- rature (open symbols) are reproducibly obtained if the sample after the cooling down and measurement at 78 OK (closed symbols) is warmed up to the irra- diation temperature.

FIG. 2.

-

~erature. measured during irradiations with 3 MeV-Brernsstrah- iung. he open symbols give the results measured at the tempe- rature of irradiation. The closed symbols give the results of the same irradiations, when the temperature of measurements was

held constant at 78 OK.

Conclusions. - The present measurements confirm the observations of Thompson and Buck that the decrease of damping during irradiation is slower at 160OK than at temperatures below and above this value. However, it is still doubtful whether this can be interpreted as a minimum of pinning rate as assumed by Thompson and Buck [I]. As already concluded by Roth, Sokolowski and Liicke [3], in this case the modulus measurements should lead to a minimum of the same depth, as deduced from damping measu- rements which is in contradiction to the experimental results. Furtheron it should be expected in this case that the same small pinning point number as found at 160° is observed when the sample is cooled down to 78 OK after irradiation. In reality, however, this procedure gives nearly the pinning point number as obtained after an irradiation at 78 OK (Fig. 2). This result and, in particular, the reversibility of this behavior seems to indicate that the damping is a function of the temperature of measurement and not, as proposed in [l] and 121, that the pinning rate is a function of the temperature of irradiation.

It appears to be very important, to clarify this point by further measurements. Until such a clari- fication is reached, however, it does not seem to be justified to use this what is called a pinning rate minimum as a proof for the thermal conversion of the interstitial.

References

[l] THOMPSON @. O.), BUCK (O.), Phys. stat. sol., 1970, [3] ROTH (G.), SOKOLOWSKI (G.) and L ~ ~ C K E (K.), Phys.

37, 53. Stat. Sol., 1970, 40, 77.

[2] SEEGER (A.), Phys. stat. sol., 1970, 38, 235. [4] JOHN (R.), WINTERHAGER (P.), private communication.