INTERNAL FRICTION IN RHENIUM

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INTERNAL FRICTION IN RHENIUM

M. Raadschelders, R. de Batist

To cite this version:

M. Raadschelders, R. de Batist. INTERNAL FRICTION IN RHENIUM. Journal de Physique Collo- ques, 1971, 32 (C2), pp.C2-179-C2-181. �10.1051/jphyscol:1971240�. �jpa-00214566�

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JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 7, tome 32, Juillet 1971, page C2-179

INTERNAL FRICTION IN RHENIUM

(*) M. RAADSCHELDERS (**) and R. D E BATIST (***) Solid State Physics Department, S. C. K./C. E. N., B-2400 MOL, Belgium

Rburnk. - Le frottement intkrieur du rhknium a êt6mesure entre 100 et 350 OK a une frkquence d'environ 300 Hz. Les 6chantillons krouis presentent un pic a 275 OK et un deuxikme, moins prononce, vers 230 ÔK.Si ce pic est attribue it la relaxation des dislocations, la valeur de l'enthalpie d'activation est alors estimee ît0,6 eV. Quelques rksultats concernant des effets de traitements thermiques ou d'irradiation aux Clectrons de 12 MeV B temperature ambiante sont kgalement presentes ^;a 100 OC des effets de restauration sont observes.

Abstract.

-

Preliminary results of internal friction measurements in rhenium between 100 and 350 OK are reported. For a frequency of about 300 Hz, an internal friction peak is observed in cold-rolled specimens at about 275 OK, together with a shoulder near 230 ^OK.Assuming that this peak is due to dislocation relaxation, an activation enthalpy of approximately 0.6 eV is estimated.

Some results due to thermal treatment and/or irradiation near room temperature with 12 MeV electrons are also discussed ^;it is shown that recovery occurs at 100 @C.

1. Introduction. - Investigations on metals crys- tallizing with the hexagonal close-packed structure appear to be much less numerous than those on cubic metals. Progress in the understanding of the properties of defects in cubic metals has been stimulated by the often conflicting interpretations put forward by different investigators. Unfortunately, research on hexagonal metals has all too often tended to remain the work of only a very few persons. It is hoped therefore that the' work on the high-melting point hexagonal metal rhenium, initiated in our laboratory, might stimulate other people to extend it so as to reach a degree of understacding at least comparable to that in cubic crystals.

The recovery of the changes in electrical resistivity caused in rhenium by plastic deformation or irradiation is being studied by Nihoul et al. [l], 121. In the present contribution, a few preliminary observations made in the course of a study of the internal friction charac- teristics of polycrystalline rhenium strips are described.

In particular, the influence on the internal friction spectrum between 100 and 350 OK of various thermal treatments and of irradiation (at room temperature) with 12 MeV electrons is discussed. It should be stressed from the beginning that this research is being continued presently and that some of the results shown here require further investigation. This implies also that the interpretation of the results can only be of a tentative nature.

(*) Work performed for the Association R. U. C. A.-S. C. K./

C . E. N.

(**) Rijksuniversiteit Gent, Belgium.

Based on a thesis submitted in partial fulfilment of the require- ments for the degree of licentiate in physics at the Rijksuniversi- teit Gent.

(***) Also at Rijksuniversitair Centrum Antwerpen, Belgium.

2. Experimental details. - The specimens are made of polycrystalline 99.997

%

pure rhenium strips of 30 pm thick and 4 mm wide. These strips are mounted as a cantilever beam, the free part being approximately 8 mm long. The corresponding resonance frequency for bending vibrations is about 300 Hz. The specimen is driven electro-magnetically (a short strip of soft- iron being spot-welded to the rhenium) and the displacement detected capacitively. A detailed description of the experimental set-up has been published earlier [3].

Some specimens are annealed at about 2 500 OK under flowing helium gas. The annealing treatments carried out at lower temperature (300-650 OK) are done in air. The electron irradiations are made by means of the Linac of the Rijksuniversiteit at Gent. Typical beam conditions are about 1-2 pA of 12 MeV electrons over a cross-section of 1-2 cm2, resulting in irradiation doses of several times 1016 e/cm2.

3. Results, - In presenting the experimental results obtained thus far during the present investigation, it is convenient to consider separately the specimens in the

(( as-received condition (rolled to thickness at an unspecified temperature by the manufacturer), the influence of various annealing treatments and the effect of electron irradiation.

The internal friction spectrum of some of the as-received specimens is shown by figure 1. The resonance frequencies measured at room temperature for the specimens presented here vary between 190 and 390 Hz. One notices a rather complicated peak structure between 200 and 300 OK, with a pronounced peak at about 270 OK and a second, shallower one at about 2250K. Especially noteworthy is the wide variation in peak height between different specimens.

Although this might be caused partly by the strongly

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971240

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C2-180 M. RAADSCHELDERS AND R. DE BATIST

FIG. 1. -Internal friction spectra for various G as received rhenium specimens.

anisotropic plastic behaviour of hexagonal crystals, it seems more likely that it is the result of the very high sensitivity of the present material to relatively low temperature annealing. Indeed, even though storage at room temperatures does not appear to affect the internal friction spectrum at reduced temperature, annealing the specimen at 100 OC strongly diminishes the height of the 270 OK peak. This is shown by figure 2, where the spectrum of specimen R e 4 is

FIG. 2. -Internal friction spectra for rhenium specimens following heat-treatment at the indicated temperatures.

plotted following the measurement up to 360°K shown by figure 1. Figure 2 also shows how annealing at 400 OC further depresses the internal friction over the whole temperature range. Such a treatment appears to yield the lowest overall values of internal friction in the peak region. In a specimen annealed at over 2 000 OC, there remains a noticeable contribution of the peak between 230 and 3000K ; in a specimen which had been treated at 1 OOOOC, prior to the determination of the internal friction spectrum, a very distinct 270 OK peak is observed. Finally, the effect of irradiation with 12 MeVelectrons is typified by figure 3, showing the disappearance of the peak structure between 2250K and 3000K following a dose of 2 ^X 1016 and of 8 ^X 1016 e/cm2. This figure also shows the results obtained with a specimen pre- annealed at 400 OC so as to suppress completely the peak structure. Here, electron irradiation appears to introduce three very small peaks at about 175, 205

FIG. 3. -Internal friction spectra of electron irradiated rhenium.

1. Re 11, cf. figure 1.

2. Following irradiation with 2 X 1016 e/cmz.

3. FoIIowing additional irradiation with 6 X 1016 e/cmz.

4. Re 4, cf. figure 2.

5. Following irradiation with 8 ^X1016 elcrnz.

6. Following heating to 200 OC.

Notice the displacement of the origin of the ordinate between curves 3 and 4.

and 235 OK. These three peaks persist after annealing at l00 OC, but following annealing at 200 OC, only the peak at 175 OK remains. Unfortunately it has not been possible yet to duplicate these results in another specimen.

4. Discussion. - In view of the scarcity of the irradiation data, it is premature to discuss this aspect of t h e experimental results at the present stage. Howe- ver, it should be pointed out that no measurement of the specimen temperature has been made during irradiation. Since the specimen is in good thermal contact with the surroundings, it was hoped that the temperature rise during irradiation would be negligible. As it turned out in the course of the investigation that warming to 100 OC caused already drastic changes of the internal friction spectrum, this hope may have been too naive.

Two further aspects of the observations deserve closer discussion. These are firstly the recovery occur- ring between room temperature and 100 OC, and secondly the nature of the internal friction maxima observed between 230 OK and 300 OK. Vandenborre et al. [I] have shown that recovery of the electrical resistivity of rhenium plastically deformed at room temperature starts already below 325 OK. The present data confirm that indeed some defect becomes mobile in this temperature range and that the defect, responsible for the recovery of the electrical resistivity, is also responsible for the disappearance of the internal friction peaks between 230 and 300OK. It might be added here that also the resonance frequency data present evidence of this recovery, even in specimens where the friction peak is not pronounced. Following a first annealing at 100 OC, the resonance frequency is usually increased with a few Hz. This occurs even in a specimen which has been heat-treated at a higher

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INTERNAL FRICTION IN RHENIUM C2-18 1

temperature. Apparently, the handling involved in mounting the specimen is sufficient to increase the modulus defect. On the other hand, no clear evidence has been found for changes in the anelastic properties of rhenium in the temperature ranges where the electrical resistivity shows more pronounced recovery effects (500 OK, 600 OK, cf. [l], [2]).

In discussing the nature of the peaks observed between 230 OK and 300 OK, the following observations have to be explained. The peaks appear to exist in most of the << as-received (i. e. cold-rolled) specimens.

They disappear upon warming up to 100 OC, although a clear peak is observed in a specimen annealed at 1 000 OC and some structure exists in one annealed at 2 350 OC. There is evidence of at least two peaks, one centred about 230 OK and one centred about 275 OK.

The frequency range covered in this investigation does not allow one to decide about the frequency depen- dence of the peak temperatures. The complex peak structure and the similarity of the peak shape with the observations in other hexagonal metals (see e. g.

[4], also [5], [6]) suggest that the peak could be due to dislocation relaxation effects. A possible interpretation of the recovery behaviour could then go as follows. Upon heating to 100 OC, point defects migrate towards the dislocations and reduce the relaxation strength. At 1000 OC, these point defects disappear from the dislocations and the peak is restored. At 2 350 OC, recrystallization reduces the dislocation density, but apparently sufficient dislocation lines remain to yield still some relaxation strength.

If it is admitted that the peaks are caused by dislocation relaxation, an estimate of the activation enthalpy

H can be obtained from the peak temperature by assuming a value for the pre-exponential factor z0 in the Arrhenius expression for the relaxation time z = 7, exp(H/kT) which is representative for dislocation relaxation (e. g. z0 = 10-l2 S). In this way an activation enthalpy of about 0.6 eV is found. When this value is used in the Seeger-Donth-Pfaff [7] theory for the Bordoni peak, the ratio of the Peierls stress to the shear modulus turns out to be about 5 X 10-4, which compares well with the results obtained in other systems [4].

5. Conclusion. - The preliminary results reported here and the tentative interpretations put forth suggest a number of further experiments. One should first of all extend the frequency range, for instance by carrying out experiments with a torsion pendulum. Also, it is important to find out whether the relaxation peaks can be reintroduced by plastic deformation or by annealing at 1 000 OC following an annealing at 100 OC of a cold-worked specimen. Finally, irradiations performed at reduced temperature may reveal effects lost during room temperature irradiation experiments.

6. Acknowledgements. - The authors are pleased to thank Prof. J. Verhaeghe and Prof. S. Amelinckx for the close co-operation between the university of Gent and S. C. K./C. E. N. and for their continued interest in the progress of this work. They also thank Ir. Kiezel for his help with the irradiation of the specimens. They greatly appreciated discussions with H. Vandenborre, Dr Nihoul and Dr Stals, as well as the technical assistance of M. Delcon and R. Van Hoof.

References

[l] VANDENBORRE (H.), STALS (L.), NIHOUL (J.), KFA [4] DE BATIST (R.), Internal Friction of Structural Defects Jelich Rep. Jul. Conf., 1968, 2 , 802. in Crystalline Solids, North Holland, to be

published.

['l VANDENBORRE (H')7 STALS (L.)' (J')' _[5]TSUI (R. T. C.), SACK (H. S.), Acta Met., 1967, 15,1715.

stat. sol., 1969, 35, 1009. [6] BORDONI (P. G.), NUOVO (M.), VERDINI (I,.), NUOVO [3] STRUMANE (R.), DE BATIST (R.), AMELINCKX (S.), Cim. Ser., 10, 1960, 16, 373.

Phys. stat. sol., 1963, 3, 1379. [7] SEEGER (A.), DONTH (H.), PFAFF (F.), Disc. Faraday Soc., 1957, 23, 19.