STUDY OF GRAIN BOUNDARIES IN ICE BY INTERNAL FRICTION MEASUREMENT

(1)

HAL Id: jpa-00226273

https://hal.archives-ouvertes.fr/jpa-00226273

Submitted on 1 Jan 1987

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

STUDY OF GRAIN BOUNDARIES IN ICE BY INTERNAL FRICTION MEASUREMENT

J. Tatibouet, J. Perez, R. Vassoille

To cite this version:

J. Tatibouet, J. Perez, R. Vassoille. STUDY OF GRAIN BOUNDARIES IN ICE BY INTERNAL FRICTION MEASUREMENT. Journal de Physique Colloques, 1987, 48 (C1), pp.C1-197-C1-203.

�10.1051/jphyscol:1987128�. �jpa-00226273�

(2)

JOURNAL DE PHYSIQUE

Colloque C1, suppl6ment au no 3, Tome 48, mars 1987

STUDY OF GRAIN BOUNDARIES IN ICE BY INTERNAL FRICTION MEASUREMENT

J. TATIBOUET, J. PEREZ and R. VASSOILLE

Groupes d'Etudes de Metallurgie Physique et de Physique des Materiaux ( U A 341), INSA d e Lyon, ~ 8 t . 502, 20, Avenue Albert Einstein, F-69621 V i l l e u r b a m e Cedex, France

R B S U ~ - Le pic de relaxation associB aux joints de grains dans la glace a 6th 6tudi6 par des mesures de frottement interne tr&s basses frequences (1-10-~HZ). Lf Bnergie dq activation apparente du phenomgne a 6tB determinee avec precision sur diffhrents types df6chantillons : bi-cristaux, polycrys- taux isotropes & petits grains, specimens dopks avec HF. La valeur impor- tante de cette Bnergie dfactivation (1.26 B 1.38 eV) ne permet pas de conclure & un mecanisme simple de dissipation d18nergie par des dislocations. Le pic de joints de grains observ6 est cependant caractgris- tique dfun Btat de plus basse Bnergie du joint et le phenomgne peut 6tre attribue au mouvement reversible des dislocations intrinsgques du joint de grains.

Abstract - The relaxation peak associated to grain boundaries in ice has been studied by using very low frequencies internal friction measurements (1-10-3 Hz). The apparent activation energy of the phenomena has been determined accuratly on different types of specimens : bicrystals, fine-grained polycrystals, HF doped specimens. The important value of activation energy (1,26 to 1.38 eV) cannot be explained by a simple mechanism of dislocation.

However it appears that the tfgrain-boundaryfs peak observed is characteristic of a state of lower energy in the boundary and that it can be attributed to the reversible motion of intrinsic grain-boundary dislocations.

INTRODUCTION

The understanding of physical processes that take place when polycristalline ice is plastically deformed has led for several years to many studies (see review 1, 2, 3).

These studies show that above 255 K the situation is very complex and point out that it is necessary to improve our knowledge about dynamic properties of grain-boundary in ice.

Internal friction measurements in this temperature range on polycristalline samples seem to be an interesting tool to study grain-boundaries properties. So, Kurofwa (4) working in the kilohertz range has given an interpretation of the internal friction rise that he observed near the melting point as a phenomenon attributed to grain- boundary sliding. But the measurements made at too high frequencies could not put in evidence the existence of a relaxation peak. Results from Gavrilo et a1 (5) confirmed these results. Kuroiwa (4) using the assumption of KG (6) described this phenomenon in terms of viscous flow located at grain-boundaries. Values of the activatian energy of the phenomenon, determined only with the rise of internal friction showed only a dependence on impurities segregation at boundaries and not on structure of grain-boundary.

Using low frequencies measurements (cv 1 Hz), the same. phenomenon were studied by Perez et a1 (7). In this case, internal friction measurements in polycristalline ice exhibited a relaxation peak near the melting point and this peak was associated with grain-boundary movements.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987128

(3)

C1-198 3OURNAL DE _PHYSIQUE

BY using very low frequencies technique (1-10-~HZ), we have studied this relaxation peak at lower temperatures. It leads to a full separation between this peak and the high temperature internal friction rise previously attributed to lattice dislocations movement in the case of single crystals (8,g).

The conditions in the observation of the relaxation peak on different types of specimens are discussed and a qualitative model based on grain-boundary dislocations movement is proposed.

EXPERIMENTAL PROCEDURE

Internal friction measurements were performed by using an inverted torsional ap- paratus developed in the laboratory (70). The frequency of the stress or strain is in the range 10'3-1 Hz. All experiments were made at E = 2.10-5. Plastic deformation (up to 3%) by creep in torsion is also possible in sltu.

Specimens are obtained from the "Laboratoire de Glaciologie CNRS" in Grenoble.

Isotropic polycrystals are prepared by packing sieved ice grains into cylindrical molds, saturating with cooled de-ionized water under vacuum and freezing the whole mixture. This method produces fine-grained ice with randomly oriented crystals of about 1 mm in diameter without bubbles. By using doped crystals and HF solutions, isotropic doped polycristals can be obtained by the same way. Orientations of grains in the case of bicrystals are determined by X-ray Laue diagrams.

EXPERIMENTAL RESULTS a) bi-crystals

The internal friction spectrum of pure ice bi-crystals exhibits clearly a peak due to grain-boundary as shown in fig: 1. The temperature of this peak is depending on measurement frequency and in the case of non-deformed specimens the peak is well separated from the rise of internal friction associated with dislocation movements at higher temperature (8,9). Orientations of the two grains and of the boundary are shown on the same figure. In figure 2, we show the internal friction spectrum obtained on the same specimen after deformation by creep in torsion at 265 K up to 1%.

It can be noted remarkable increase of the rise of high temperature internal friction.

Figure 1 Internal Friction vs Temperature Figure 2 Same bicrystal as in figure 1 Artificial bicrystal - ^kmaX⁼^2.10-5 _-after plastic deformation

( & = 1 % at 265 K)

---annealing treatment (48 h at 270 K) ,.annealing treatment (168 h at 270 K)

(4)

This phenomenon also observed on deformed single crystals is attributed to the increase of intragranular dislocation density (8). An important feature in this spectrum is the remarkable decrease of the height of the grain boundary peak. The peak has nearly disappeared in 1 Hz experiment.We have made on this deformed specimen a annealing treatment at 270 K as shown in figure 2. We can observe the modifi- cations of internal friction spectrum after 48 and 168 hours of annealing treatment.

The high temperature rise decreases and the grain-boundary peak becomes higher particularly in 10-I and 1 Hz experiments. The effect of this annealing for the high temperature internal friction is quite different from that obtained on single crystal as shown on figure 3.

In order to investigate the influence of the orientation of grain-boundary prior to the torsion axis, a specimen issued from the same bicrystal as in first experiment, has been cutted with the grain-boundary perpendicular to the torsion axis. Results are shown on figure 4. The amplitude of the grain-boundary peak is lowered. The high temperature internal friction rise remains the same as the first specimen.

Figure 3 Plastically deformed single Figure 4 Artificial bicrystal

crystal : (GB perpendicular to torsion axis)

-

after plastic deformation ( & = 1,3 at 265 K)

-- --annealing treatment (190 K at 268 K) b) isotropic ~olycrystals

Figure 5 exhibits results obtained from isotropic fine-grained specimens (d = 1 mm).

Grains-boundary peak appears at the same temperature as in bicrystals, but we can observe a broadening of the peaks. The peak temperature is shifted towards the high temperature when HF-doped specimen is measured

.

In this case, HF concentration is estimated to 5 ppm from the peak temperature for the low temperature relaxation

(11).

CHARACTERISTICS OF THE GRAIN-BOUNDARY PEAK

As it was pointed out by Kuroiwa (4) and Perez et a1 (7) the phenomenon as described above has not been observed in single-crystals. We have also verified this fact, and even in polygonized single crystals, no grain-boundary peak can be observed.

Contrary to the case of metals, where a similar peak can be observed in Single crystals (121, it seems that the peak in ice has to be associated with grain- boundary properties.

(5)

JOURNAL DE PHYSIQUE

Figure 5 Isotropic polycrystals (d = 1 mm)-pure ice.

-

^{- -}^HF^{doped ice}⁽^{5 ppm)}

Figure 6 Arrhenius plot for relaxation time.

HF doped (1,37 eV)

bicrystal pure ice (1,26 eV) A polycrystal pure ice (1,38 eV) Results from Kuroiwa (4) and Perez et a1 (71, exhibiting no peak when bicrystals are made by welding two single crystals seem indicate that grain-boundary peak can be observed only when the boundary is in its lower energy state. In our case the effect of plastic deformation confirms this result. Figure 2 shows that in effect, plastic deformation increases the dislocation density and leads to the disappearance of the grain boundary peak. This effect can be due either to the interaction between intragranular dislocations and intrinsic grain boundary dislocations or to the disor- ganization of the intrinsic grain boundary dislocation array when plastic deformation occurs. An annealing treatment close to the melting point leads to a recovery of the grain-boundary structure and gives again an internal friction peak. These results are in agreement with those observed when experiment is performed with a high amplitude cyclic stress ( & = ^4.10-~)^(7).

A other feature concerning the grain-boundary peak is the relation between total area of the boundaries and the relaxation intensity.figures 1 and 4, showing results obtained with bi-crystals from the same origin (same desorientation between crystals) exhibit a very important difference between relaxation intensities. The intensity ratio is, in that case, significantly different from the area ratio. Experi- ments done on fine-grained polycrystals are also in agreement with the fact that relaxation intensity does not depend directly on the area of crystals boundaries but rather on the geometrical properties of the moving species responsible for the grain boundary peak.

On the other hand, figure 6 shows an Arrhenius plot of the relaxation time associated to the grain-boundary peak assuming that we have a single relaxation time (Wx=

1). On bicrystals as in polycristals the apparent activation energy Eap can be derived and is between 1.26 and 1.38 eV. These values are very high compared to activation energies found in ice for mechanisms involving either self-diffusion of water molecules or point defects movements or even basal dislocations glide. These high values are to be compared with those obtained for creep of polycrystalline ice when temperature is above 263 K (2, 3). In our case, the apparent activation energy is the same at temperatures as low as 220 K. It is also worthy to notice that higher Eap values are obtained when high temperature internal friction rise is higher

(higher intragranular dislocation density).

(6)

Similarly, it is observed that the pre-exponential factor is unusually low (about

~ o - ~ ~ s . ) : phenomenologically these features seem to imply a characteristic time proportional to ( 1, exp u/~T)'/" with o < ⁿ< ¹^(13).

Let us consider a general pattern allowing a qualitative interpretation of the results hereabove presented.

The structure of grain boundary (GB) in ice can be described using coincidence site lattice (CSL) concept (14, 15). A general grain boundary can be seen equivalently as the sum of a CSL boundary and of a dislocation wall or sub-boundary. These dislocations, obviously constituting the GB, will be called intrinsic grain boundary dislocation (IGBD) and can be distinguished from intragranular dislocations (ID).

It is well known that, when a stress is applied on a crystal with sub-boundaries, a force appears on the walls resulting in a displacement of defects : thus several cases can be invoked ; with a one-degree of freedom sub-boundary, the wall is moved as a whole or with two-degrees of freedom the wall can be splitted in two different dislocations arrays. In both cases, the displacement of dislocations corresponds to a separation of IGBD, from the CSL boundary thus implying a increase of the free energy of the crystal : such a possibility is summarized in figure 7.

Figure 7 a) Schematic structure of grain boundary b) Energy vs distance from GB

In these conditions two situations can be discussed :

(i) when a periodic stress is applied as during internal friction measurements IGBD are moving at short distance from the GB as long as deformation is low ( 10'~) and the energy profile shown in 7 (b) implies a relaxation phecomenon leading to an internal friction peak.

(ii) when a static stress or periodic stress inducing high amplitude oscillations

(& = 10-31, IGBD, move at longer distance resulting in a decompositon of the

previous GB and a subsequent increase of ID in the vicinity of the GB.

Such a pattern, although qualitative could explain the experimental results.

a) when GB in bicrystal is orientated as in fig. 1 (grain boundary parallel to torsion axis) the deformation in the vicinity of GB is very low (total deformation = 2 10-5)* So, cyclic stress induced reversible movements fo IGBD, (situation i) and a relaxation peak is observed.

b) When specimen is plastically deformed, IGBD move at long distance thus inducing an increase of ID density in both grains (situation (ii)).so, only the high temperature component of internal friction due to ID is observed. If CSL boundaries movement occurs it is only for accomodation of deformations.obtained in grains ; conse- quently no relaxation peak has to be observed.

(7)

JOURNAL DE PHYSIQUE

c) when bicrystals are obtained by welding two single crystals : the situation is more complex. But it is obvious that GB is out of equilibrium and that IGBD do not exist in the situation here above invoked and no relaxation peak is observed.

d) after annealing treatment in the case of either deformed specimens or welded specimens, some dislocations move toward the grain boundary in order to obtain a state of lower energy and a regular array of IGBD is recovered : a relaxation peak can be observed.

To improve this qualitative interpretation two points must be considered : on one hand the geometrical features have to be precised ; in fact, experiments with bicrystals having a well known and variable misorientation near the coincidence would be useful. On the other hand, the dynamic behaviour of IGBD just near the GB has to be analysed in order to obtain a quantitative description of the GB internal friction peak. An evidence is that IGBD do not move with the same mechanism as for ID : the phenomenological description of the characteristic time mentioned above suggests that molecular movements occur through correlation effects (16) instead of being Bjerrum (ionic) defects assisted. Such an hypothesis would correspond to an extremely low density or mobility of points defects in the vicinity of GB.

(1) Weertman, J., Creep of Ice, in Physics and Chemistry of Ice, Edited by E.

Whalley, S.J. Jones and L.W. Gold, Ottawa, Royal Society of Canada, (1973), . .

320-337 ;

(2) Homer, D.R. and Glen, J.W. , ^J.of glaciology, vol. 21, no 85, (1978), 429-444.

(3) Mellor, -M. and Testa, R. , J. of Glaciology, vol. 8 no 52, (1969), 131-145.

(4) Kuroiwa, D., part 11, Contr. no 668, Inst. Low Temp. Sci., Hokkaido University A18, (1964). 38-48.

(5) ~avrilo, v.P., Gusev, A.V., Malikov, V.N. and Polyakov, A.P., Phys. Solid Earth USA, no 6, (1971), 448-450.

(6) Kt, T.S., Phys. Rev. 71, (19471, 533-5116.

(7) Perez, J., Mar, C., Tatiboust, J. and Vassoille, R. , Phys. Stat. Sol. (a), 52, (19791, 321-330.

(8) Tatibouet, J., Perez, J., Vassoille, R., J. Physique, 47, (1986), 51-60.

(9) TatibouEt, J. Perez, J., Vassoille, R., J. Physique, ClO, no 12, 46, ('1985), 339-342.

(10) Etienne, S., Cavaill6, J.Y., Perez, J. and Salvia M., J. Physique C5, 42, (1981), 1129-1134.

(11) Perez, J., Mai, C., TatibouBt, J. and Vassoille, R., J. of Glaciology, vol. 25, 91, (19801, 133-149.

(12) Woirgard, J. These Doctorat, Universit6 de Poitiers, (1974), (13) Jonscher, A.K., Nature, 267, (19771, 673-680.

(14) Higashi, A., J. of Glaciology, vol. 21, no 85, (19781, 589-605.

(15) Hondoh, T., Hokkaido University, no 125, (1985), 123-134.

(76) Ngai, K.L., White, C.T., Phys. Rev. B, 20 no 6, (1979), 2475-2486.

COMMENTS

L. APEKIS

Thermally Stimulated Depolarization (TSD) measurements on Polycryetalline Ih show a peak at about 220 K . The corresponding relaxation frequency is of the order of 10'3 Hz at this temperature. Do you think that the relaxation observed by your internal friction measurements might be of the same origin as the dielectric relaxation ? Have you any evidence that the grain boundaries causing the mechanical relaxation are electrically charged ?

(8)

Answer :

The relaxation peak observed by TSD measurements in polycrystalline ice is found at temperature and frequency which are in the same ranges as in our mechanical experiments but activation energies are very different (TSD Ea = 0.42 eV ; our experiments = 1.36 eV). As we have no evidence for electrically charged grain boundaries, we think that the two phenomena cannot be correlated .

L. APEKIS et al. J. Phys. Chem. 1983, 87, 4019.

T. HONDOH

1 . feel that your data could be interpreted in terms of extrinsic GB dislocations.

Why do you take only the intrinsic GB dislocations into account but exclude the extrinsic ones?

Answer :

Deformed bicrystals and single crystals exhibit many differences during annealing treatment. As internal friction increase in case of single crystals is known to be attributed only to intrinsic dislocations, the only way to explain the relaxation phenomena is in terms of intrinsic GB dislocations.