LOW TEMPERATURE INTERNAL FRICTION OF COLD WORKED ZIRCONIUM

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LOW TEMPERATURE INTERNAL FRICTION OF COLD WORKED ZIRCONIUM

E. Savino, E. Bisogni

To cite this version:

E. Savino, E. Bisogni. LOW TEMPERATURE INTERNAL FRICTION OF COLD WORKED ZIRCONIUM. Journal de Physique Colloques, 1971, 32 (C2), pp.C2-209-C2-213.

�10.1051/jphyscol:1971246�. �jpa-00214572�

JOURNAL

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Colloque C2, supplt!ment au a0 7, tome 32, Juillet 1971, page C2-209

LOW TEMPERATURE INTERNAL FRICTION OF COLD WORKED ZIRCONIUM

E. J. SAVINO and E. A. BISOGNI (")

Departamento de Metalurgia, C. N. E. A., Buenos Aires, Argentina

Rbum4. - Le spectre de frottement interne a basse frkquence du Zirconium de haute puretk a kt6 ktudie au moyen d'un pendule de torsion type Kg qui permet d'effectuer des deformations in-situ soit a tempkrature ambiante, soit 78 OK. Aprh dkformation a tempQature ambiante, il apparait un pic de frottement interne centre a environ 150 OK (a 1 Hz). Aprks variation de la frkquence de mesure, les valeurs obtenues pour A H et

sont respectivement 3 f 0.4 kcal/mole et 10-5-1-1 S. Quand les Bchantillons sont d6form8s B la temperature de l'azote liquide et que le frotte- ment interne est mesure au cours du rkchauffement, il apparait un faible maximum P i 130 OK et des pics

et

a 210-230 OK. I1 est aussi detect6 une augmentation du frottement interne ainsi qu'un defaut de module 80 OK.

Ces resultats sont analyses en relation avec diverses causes de dissipation d'energie dans les mBtaux Ccrouis.

Abstract. - The internal friction spectrum at low frequencies of high purity Zirconium has been studied by means of a conventional Ke type torsion pendulum, yhich allowed for in situ deformations either at room temperature or 78

After room temperature deformation an internal friction peak P I centered at about 150 OK (for 1 Hz) was found. Changes of the measuring fre- quency yields values of A H and

of 3 f 0.4 kcal/mol and 10-5*1 s respectively. When samples were deformed at liquid nitrogen temperature and the internal friction measured during warm-up, it was detected the appearance of a small maximum P i at 130

and peaks

and

at 210°-230 OK. It was also detected an increase of internal friction and a modulus defect at 80 OK.

These result are analysed in terms of possible sources of energy dissipation in cold worked metals.

Introduction.

In the last few years, considerable work has been done to study the internal friction peaks introduced by cold work in pure or lightly alloyed f. c. c. metals. Among these maxima, the Bordoni peak has been extensively studied [I]. Several theories have been advanced for its interpretation [2,7]

and it seems to exist now agreement [ l , 81 that the Bordoni peak in the f. c. c. metals is associated with the thermal generation of kinks pairs in dislocations lying nearly parallel to Peierl's valleys, in general accord with the modified Seeger's theory [6, 91.

The secondary features of the peak have been recently incorporated to this model, as being caused by the diffusion of kinks along the dislocation line [lo, 111.

There are other internal friction peaks that have been observed in cold worked f. c. c. metals at tempe- ratures higher than that of the Bordoni peak [12, 161.

These maxima seem to be related to the interaction of dislocations with deformation produced point defects.

There are in the litterature several references to the existence of internal friction peaks introduced by

(*)

Present adress

Service de Physique ^du Solide, C . E. N.,

Grenoble.

cold work in metals of h. c. p. structure, such as Zn [17, 181, Mg [19, 211, Ti and Co [12], Zr and Zr-Cu alloys [12, 221. Some of these peaks show the characteristic features of the Bordoni maxima in f. c. c. metals and have been interpreted in that manner [19, 221. Hasiguti et al. [12] interpreted their Pd peaks in Ti, Co and Zr as being due to the interac- tion of a relatively stable configuration of point defects with dislocations, though did not rule out the possibility that these peaks might be of the Bordoni type.

It is the purpose of the present work to study the internal friction spectrum at low frequencies of high purity Zirconium, after deformation at ambient and liquid nitrogen temperatures.

Experimental results.

The internal friction mea- surements were performed at frequencies of the order of 1 Hz, in the temperature range 77O-300

by means of a conventional KC type pendulum which allowed for in situ deformation either at room temperature or at 77 OK. Two purities of Zirconium were used : 99.99 % and 99.999 % as specified by the manufacturers. Prior to any measurement, the samples were annealed a t 700 OC at pressures less than l o p 6 torr.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971246

C2-2 10 E. J. SAVINO AND E. A. BISOGNI

The internal friction of a Zr wire, in the annealed condition and after different amounts of cold work, is shown in figure 1. It is apparent that deformation

FIG. 1. - Internal friction of Zr after different treatments

curve A

annealed ; curve B (El) after 6 % extension a t room temperature ; curve C (0) after 15 %extension a t room tempe-

rature.

at room temperature has produced a large internal friction maximum centered at about 1500K for a measuring frequency of the order of 1 Hz. The height of this peak, which we shall call P I , increases with the amount of deformation up to a maximum

Q - I

value of about 9 x obtained either after

15 % extension or after 8 % extension followed by 15 % reduction in area by drawing, a process which is thought to produce a more severe deformation.

Changing the measuring frequency between 0.5 and 1.8 Hz, shifted the position of the maximum, allowing for the determination of the associated activation energy and frequency factor. When data obtained on the same specimen were compared, values of AH

3 + 0.4 kcal/mol and

10- * ' ^s

were found, in reasonable agreement with the values given by Hasiguti et al. [12]. The position of the peak was found to depend on the purity of the mate- rial, being displaced to lower temperature for the higher purity, as it is shown in figure 2. This plot includes also values reported by Hasiguti et al. [12]

and Gibbons [23] for Zr, and Boch and de Fouquet for Zr-Cu alloys [22] (the value of the peak tempe- rature, given by Hasiguti et al. for a frequency of 1 kHz, was also comptetd using their ^z, and AH values, for the indicated measuring frequency of 185 Hz). If a line is drawn through all these points values of AH of 7 kcal/mol and z0 of about lo-" s are obtained which differ markedly from the values previously given. They should however be taken with caution since were obtained by comparison of specimens of much different purity and state of deformation for which different values of the relaxa- tion time may be expected.

Using for AH a value of 3 kcal/mol, it was found

FIG. 2. - Frequency dependence of the peak temperature. 0

present work, Zr 99.99 % ;

present work, Zr 99.999 %

I? data of Hasiguti et al. (12) ; I? data of Boch and de Fouquet

(22) ; x data of Gibbons (24).

that the experimental half width of the peak is about two times larger than the value expected for a process with a unique relaxation time. Some specimens showed a pronounced substructure of the P, peak, suggesting that the observed maximum is due to the superposition of several elementary contributions. Measurements were taken with maximum strain values of 1.5 and 6.5 x l o d 5 ; no amplitude dependence was observed in the region of the peak, but a slight increase of the internal friction for the higher amplitude measurements was observed in the temperature region 2100-270 OK, as shown in figure 3.

To determine the stability of the peaks, samples were annealed under high vacuum at temperatures up to 350 OC. It was found that for a sample extended 6 %, the peak recovers noticeably at 150 0C and completely anneals out after 30 mn at 250 OC.

It was also found that the peak produced by cold drawing was more stable compared to that obtained by simple extension.

The internal friction spectrum for a Zirconium

sample extended 10 % ^{in situ} at liquid nitrogen tempe-

rature, is shown in figure 4. In addition to a peak Pi

appearing at about 130 OK, two other peaks P,,

and P,, have developped (curve A). After annealing

the sample for 40 mn at room temperature and

re-measuring from liquid nitrogen up (curve B)

LOW TEMPERATURE INTERNAL FRICTION O F COLD WORKED ZIRCONIUM C2-211

FIG.

Amplitude dependence of the internal friction of Zr deformed a t room temperature. Curve A (0)

6.5 x 10-5

curve B

FIG. 4.

Internal friction of Zr after 10 % extension in

at 80 OK

Curve A (0) first run after deformation

curve B (0)

second run after 40 mn at room temperature.

it was found that P; shifted to higher temperatures (to finally stabilize at 150 OK for longer holding times at room temperature) while the peaks P,, and P,, decreased in magnitude (to finally disappear). In addition it can be seen that the large background internal friction present near 80 OK immediately after deformation, is considerably reduced by this treatment.

In an effort to study the transient behaviour of the internal friction peaks, the sample was heated after low temperature deformation to successively increasing temperatures, the frequency of vibration and the internal friction being measured from liquid nitrogen temperature up after each treatment. It was found that after heating the sample for few minutes at 165O-170 OK the peak Pi had completely disappeared while P,, and P,, were fully developped (curves A, B ; Fig. 5). Curves C, D of the same figure, show the behaviour after holding the sample at room temperature, for a few minutes and 24 hours respec- tively.

I

I

100 150 ZOO 250

T'K

FIG. 5. - Internal friction and dynamic modulus of Zr after 10 % extension in situ at 80 OK. Curve A (0) warmed to 170°K

curve B (0) second run, warmed to 270 OK

curve C

third run, after few minutes at 270 OK

curve D (3) fourth run,

after 24 hours at room temperature.

A sample was deformed in situ at a temperature close to 170 OK, cooled down to liquid nitrogen and the internal friction measured during warm up. It can be seen (curve A, Fig. 6) that the peak Pi is not present ; it suffices however to attain room temperature for only few minutes (curve B) for the peak to reappear at its stable position near 150 OK. Variations of the elastic modulus, computed as the square of the measuring frequency are also shown in figures 5 and 6.

It can be seen that deformation at 77O or 1700K, has produced a modulus defect at 770K which recovers upon annealing in the temperature range 2100-270 OK.

Discussion.

We shall first consider the peak P, which appears after room temperature deformation.

The characteristic features of this peak can be summa-

rized as : i) the peak is not present in well annealed

material, but appears as a result of cold work. Its

magnitude increases with the amount of deformation

showing a tendency for saturation ; ii) the height and

position of the peak depend slightly on the impurity

content : the height increasing and the temperature

of the peak decreasing for increasing purity ; iii) the

shape and position of the peak up to strains of

6.5 x are not amplitude dependent ; iv) the

peak can be removed by annealing at temperatures

C2-212

E. J. SAVINO AND E. A. BISOGNI

FIG. 6 . -Internal friction and dynamic modulus of Zr after 8 % extension at 170

Curve A (0) first run

curve B (0)

second run, after 24 hours at room temperature.

of the order of 300 OC ; v) changes of the measuring frequency shifts the position of the peak in the manner predicted for a thermally activated process. These properties are very similar to those reported [I]

as being characteristic of the Bordoni peaks in f. c. c.

metals.

It has been reported [24] that Zirconium deforms, in the temperature range 770-575 OK, by simultaneous twinning in several systems and by glide only in the prismatic (10i0) < 1210 > system (other slip systems have been reported to occur, though very rarely [25)].

Anelastic effects related to twin movements have been reported [26] to take place at room temperature with a relaxation time of the order of hours. It is unlikely that these type of processes should make a contribution to the internal friction below room temperature.

We must then admit that the PI peak is related to the dislocation structure produced by room tempera- ture deformation. We cannot decide however with the available information if it is related to some intrinsic properties of dislocations, or to the interaction of some stable configuration of point defects with dislocations. The high value of the frequency factor z0 suggests that dislocation movement is the rate controll- ing factor. If we assume that PI is a Bordoni type peak and consider valid the Seeger model (3), it is possible to deduce, from the value of the activation energy A H

3 kcal/mol, a value of the Peierl's stress which compares well with the extrapolated value

at 0 OK of the critical shear stress of Zr in the prismatic plane [24]. Using this value of the Peierl's stress, the zo factor predicted by the Seeger model is much lower than the value found either by Hasiguti et al. [I21 or our results for the same specimen (Fig. 2).

When a sample deformed at liquid nitrogen tem- perature is annealed at 170 OK, or directly deformed at that temperature, no internal friction peak can be detected in the temperature region 100°-200 OK (Fig. 5 and 6). The absence of the P;-PI peaks implies that at this particular temperature (near 1700K) there is either some dislocation rearrangement or migration of point defeccts which interact with dislocations and prevent the peak to occur. It has been reported [27] the presence, in Zr containing 0.07 % oxygen deformed at 4 OK, of a small recovery stage of the electrical resistivity at 190 OK. This stage has been interpreted as being due to the release of interstitial Zr atoms from oxygen traps. For higher purity Zr, equivalent to that used in the present work, no recovery stage was found in this tempera- ture range either after deformation [27] or electron irradiation [28] at 40K. These results give support to the idea that the dominant process taking place around 170 OK is dislocation rearrangement. The high value found for z0 and the sensitivity of PI to dislocation rearrangements after low temperature deformation are points that deserve further study.

It was found that the treatment that supresses the maximum PI has no effect on either the modulus defect or the background internal friction at 80 OK.

Both these quantities recover in the temperature range 210°-2700K, seeming to be closely related.

Their origin may be accounted for in several ways.

It may be that we are observing the high temperature side of a relaxation peak occurring at lower tempe- ratures, in which case the modulus defect will be a measure of its relaxation strength. With this assump- tion, Q-I (max) should be of the order of 5 x This hypothetical peak, could be caused either by dislocations, point defects or interaction of point defects with dislocations. If it is due to some reorien- tation of point defects, the fact that it recovers at temperatures much higher than that of the peak, implies that the reorientation energy of the particular defect should be much smaller than its long range migration energy. If it is caused by point defects

dislocations interaction, its annealing behaviour suggests that the configuration responsible for the peak is destroyed upon annealing at 2100-2700K.

Finally, if the increase in the internal friction and the

modulus defect at 80 OK are due solely to higher

dislocation mobility, its recovery might be considered

as an indication of restricted mobility. In this case,

if we accept that PI is related to dislocation move-

ments, it would imply the existence of two distinct

dislocation configurations which behave differently

upon annealing treatments either at 170° or in the

range 2100-270 OK. In the lack of enough information

LOW TEMPERATURE INTERNAL FRICTION OF COLD WORKED ZIRCONIUM C2-213

all these considerations remain highly speculative. Acknowledgements. - One of us (E. A. B.) wishes More experimental work is needed before the present to express its gratitude to the Centre d'Etudes Nuclt- observations will be uniquely interpreted. It will aires de Grenoble, Service de Physique du Solide for be desirable to have results in single crystal specimens, its hospitality, and in particular to Dr. J. Hillairet for know the effect of irradiation and make measurements numerous discussions, during the preparation of this at other frequencies. These experiments are currently manuscript. This work was sponsored by the Comision being performed and will be published elsewhere [29]. Nacional de Energia Atomica, Argentina.

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1291 SAV~NO (E.) and BISOGNI (E. A.), to be published.