ULTRASONIC ATTENUATION IN POLYCRYSTALLINE 5N ALUMINIUM

HAL Id: jpa-00227111

https://hal.archives-ouvertes.fr/jpa-00227111

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 pub- lished 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.

ULTRASONIC ATTENUATION IN POLYCRYSTALLINE 5N ALUMINIUM

W. Alnaser, D. Niblett

To cite this version:

W. Alnaser, D. Niblett. ULTRASONIC ATTENUATION IN POLYCRYSTALLINE 5N ALU- MINIUM. Journal de Physique Colloques, 1987, 48 (C8), pp.C8-77-C8-82. �10.1051/jphyscol:1987807�.

�jpa-00227111�

JOURNAL DE PHYSIQUE

Colloque C8, supplkment au n012, Tome 48, dbcembre 1987

ULTRASONIC ATTENUATION IN POLYCRYSTALLINE 5N ALUMINIUM

W.E. ALNASER") and D.H. NIBLETT

Physics Laboratory, The University, GB-Canterbury C T 2 7 N R , Kent, Great-Britain

The ultrasonic attenuation of 5N purity polycrystalline aluminium has been measured over the temperature range from 110 to 300K at a frequency of 10 MHz, using a conventional pulse echo technique with a single quartz transducer. Five specimens were used and each was subjected to a series of deformations by compression, the plastic strain ranging up to about 20%.

For the higher deformations two dislocation relaxation peaks (Bordoni and Niblett-Wilks peaks) were observed at about 226 and 168K respectively, superimposed on attenuation due to other sources. The Bordoni peak was not observed after low levels of deformation, only the Niblett-Wilks peak being evident at these strains. Our results are compared with previous measurements on similarly-strained 5N aluminium at other frequencies and

indicate that the activation energies for the Bordoni and Niblett-Wilks peaks are about 0.22 and 0.15 eV respectively.

1. INTRODUCTION

In the early work carried out at megahertz frequencies (Hutchison and ~ilmer,l Kamigaki and ~ i r o n e ~ and Mongy et a13) a single attenuation peak was reported in polycrystalline and single crystal aluminium of purity 4N4, 4N and 4N4 respectively.

This peak was classified as the Bordoni peak. Hutchison and Filmer found the peak in a specimen strained 1.4% to occur at 155K for a frequency of 5 MHz. Kamigaki and Hirone made measurements at 5 and 15 MHz and reported the peak to occur at 152 and 165K respectively, while Mongy et a1 observed the peak at 143, 160 and 180K for measurements at 10, 20 and 50 MHz respectively.

These temperatures are very near to those found when the Bordoni peak was measured at kilohertz frequencies. For example. Fanti and ~ u o v o ~ reported the Bordoni peak at a frequency of 140 kHz to occur at a temperature of 138K for polycrystalline aluminium of 4N5 purity and they also found the Niblett-Wilks peak at 101K. Since the Bordoni and Niblett-Wilks peaks are relaxation peaks, it is expected that they should shift to a higher temperature as the frequency is increased. For example, Baxter and wilks5 found that the Bordoni peak moved from 95K to 119K when the frequency was increased from 1Hz to 1080 Hz; similarly the Niblett and Wilks peak shifted from 65K to 83K. The reported Bordoni peak temperatures at megahertz frequencies are thus not consistent with the measurements at lower frequencies.

Instead they appear to correspond to the low frequency measurements of the

Niblett-Wilks peak. Therefore we decided to investigate whether the peak reported at megahertz frequencies is the only peak that can be observed, as predicted by Routbort and sack6, or whether two peaks can be found when a range of deformation is employed. In this way it was hoped to be able to calculate a more reliable value for the activation energy of the Bordoni peak in aluminium.

2. EXPERIMENTAL PROCEDURES

Five polycrystalline aluminium specimens were supplied by Metal Crystals Ltd in the form of rods 10 mm long and 12 mm in diameter, having a purity of 5N. Details of the procedures for preparing the specimens for the attenuation measurements are described elsewhere

.

The specimens were deformed by compression at room temper-

("present address : Physics Department. Bahrain University, PO Box 1082, Bahrain

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987807

C8-78 JOURNAL DE PHYSIQUE

ature using a Hounsfield tensometer. The deformation range normally extended to about 20%. Prior to the deformation and after the specimen preparation, each specimen was annealed in argon for one hour at 350°C. An X-cut quartz crystal transducer having a fundamental frequency of 10 MHz was used to generate mechanical waves in the specimen. To get the optimum exponential decay of the pulses, the diameter of the transducer used was 6 mm and it was bonded to the specimen by means of 2-cyano ethyl methyl silicone. A conventional pulse echo technique was used for the attenuation measurements.

Two tests were used to compare the purity of the specimens. The first used a scanning electron microscope (SEM). The number of X-ray photons emitted per second is plotted in Fig.1 against the photon energy. The purest specimen should emit the highest number of photons. The second used the ARL inductively coupled plasma (ICP) atomic emission spectrometer to analyse the specimens for trace impurities. The results of this test are shown in Table 1.

Table 1

-

Analysis of aluminium specimens used in this research for trace impurities.

Phatan Energy (teV)

Total Impurities (mg/kg)

70 3 3 26 18 28

s

1 I I 1 I

I '

140

,

P. ^{Specimen 4}

-

- ^-

- -

Specimen 3 Specimen 1

3 100

-

5

=

0

e

80

-

'.- -

C

.- 0 V)

g)

1 6

2 6

3 4

4 4

5 6

.? 60

I

E 0

% 40

=

a

20

Fig.1

-

Purity test using the scanning Fig.2 - The ultrasonic attenuation of

electron microscope. specimen 1.

Zn (mglkg)

6 0 25 20 14 20 Fe

(mglkg) 3 2 2 2

1

2.0

- - i

^15-

m

Z

c 0

-

4.8

;

^1.0-

a

L,

-z

0 5

, _I i 1. 8

-

I 1

-

_I ^{I I} t ¹ _t

-

I t

I I

-

_I ^{/ t}

,

₈

-

/ 3

.

⁸

- - - - I I I I t I I

o As-received specimen, after lapping and polishing.

Mg (ng/kg)

1

* I I I ⁴

- -

?".

.*'.-.,

0 " .

, =.

^.,*

^-

*.

'

O0oo =i

ooo.,

" .. ..

00.

.. _-

0 - ,

.-•

- 0 O O o " ^{0 . .}

00 ₀ L

.=

0

.=

-

e

I I I

1.3 1 . 4 1.5 1.6 1.7 1.8

x After annealing at 350°C for one hour

-

measurements made while cooling.

100 150 200 2M)

-

Temperature ( K )

e As above - measurements made during subsequent heating.

3. RESULTS

Although all the specimens were supplied as having a purity of 5N, the SEM and ICP tests showed that some specimens are more pure than others. Specimen No.4 was found to be the purest, while specimens 3 and 5 appear to be more pure than

specimens 1 and 2, although the two tests do not give completely consistent results The ultrasonic attenuation at room temperature depends on the dislocation loop length and the dislocation density (Granato and Lucke8), so for specimens having the same deformation, the one that has the highest purity, ie. longest loop length, should also have the highest attenuation. However, the measured value of the attenuation includes contributions from other factors, eg. bond losses, diffraction losses and non-parallelism losses, which may vary between different experiments, so that it is difficult to determine precisely the dislocation contribution to the room temperature attenuation; our measurements were unable to distinguish between the slightly different purities.

These factors are less troublesome when the temperature dependence of the ultra- sonic attenuation is considered, although the absolute values of the attenuation may be affected when a specimen is remounted after each deformation. The artenuation was measured between llOK and room temperature after about twenty different amounts of deformation for each of the five aluminium specimens. The principal features of the results may be described as follows:

(i) Some specimens, especially when measured immediately after annealing or after a small deformation, showed a sudden decrease in the ultrasonic attenuation when the temperature was increased above about 200K, as in Fig.2. This was attributed to the quartz-sample deformation (QSD)

,

which has been observed in copper and other metals and explained by Lenz and ~ u c k e ~ , Winterhager and ~ u c k e l ~ , Kaufmann et allll and Schulz and Lenz12. This QSD effect was found to become smaller when the amount of deformation was increased.

(ii) When the specimens were given low deformation (in the range from 2% to 4%) one peak was generally observed at a temper- ature around 160 to 170K, as in Fig.3. This peak is believed to be the Niblett-Wilks peak.

(iii) When the specimens were given a deformation in the range from 4% to 7% two peaks were generally observed. The first occurred at the same temperature as the previous-mentioned peak (160

-

^170K)

and the second, believed to be the Bordoni peak, occurred in the region of 220 to 230K (Fig.4). From the mean of a large number of measurements the temperatures of the peaks were estimated to be 168 and 226K.

(iv) At higher levels of deformation the Niblett-Wilks peak becomes less evident, so that in some measurements only the Bordoni peak was observed (Fig.5).

Routbort and sack6 collected results obtained by different authors on aluminium at different frequencies. They found that the ratio of the height of the Bordoni peak to that of the Niblett-Wilks peak was 1.4 at frequencies around 1Hz while at kilo- hertz frequencies the ratio was 1.0. They added that, if this is a systematic trend, the Niblett-Wilks peak will be the only peak observable at megahertz

frequencies. This suggests that in the early measurements on aluminium at megahertz frequencies the peak reported as the Bordoni peak is in fact the Niblett-Wilks peak.

This is consistent with the fact that the peak occurs at a temperature which corresponds to those observed for the Niblett-Wilks peak at lower frequencies.

The measurements we report here have shown that it is possible, at megahertz frequencies, to observe either the Niblett-Wilks peak or the Bordoni peak alone, or both peaks together, depending on the amount of prior deformation of the speci- men. The early workers are believed to have used small deformations, at which we have found that only the Niblett-Wilks peak is observed at megahertz frequencies.

C8-80 J O U R N A L D E PHYSIQUE

Fig.3 - The ultrasonic attenuation Fig.4

-

The ultrasonic attenuation of specimen 4 after strain of 3.2% of specimen 4 after strain of 6.4%

(stress = 25 N nun-2). ^t stress = 32 N nun-2).

2 0

- -

'5

m

3 5 - .- 0 4 . 2 3 E a

C

"1.0

Fig.5

-

The ultrasonic attenuation Fig.6 - Frequencv deoendence of tne of specimen 4. relaxation peaks in 5N aluminium.

I I I

- -

..

^I

.=

= = .

' * * = *

-

1 Z

-

^-

I I I

o strain = 10.1% (stress = 36 N nun-')

- - -

-

-

Bordoni peak

110 160 210 260

Temoerarure ( K )

w Strain = 20.4X (stress = 51 N mm-2) Niblett-Wilks peak

e

Panti & ~ u o v o ~ @ Esnouf et all6

8

Routbort & sack6 d) Volkl et a117

@ Tsui .(see ref . 6 ) 0 Riggauer(see ref.

0

~ o u t b o r t l ~ 0 ~ a s s a n l ~ Deterre et a115 0 This research

Since the temperature of the Bordoni peak varies with purity (Hassan and ~iblettl~), we have used only measurements on aluminium of 5N purity to estimate the activ- ation energies of the relaxation processes responsible for the peaks in Fig.6.

The broken line relates to the Bordoni peak and corresponds to an activation energy, W, of 0.22 eV and an attempt frequency, fo, of 6.4 x 1011 Hz. The full line belongs to the Niblett-Wilks peak and corresponds to an activation energy of 0.15 eV and an attempt frequency of 3.7 x 1011 Hz.

Because the temperature of the Bordoni peak shifts with deformation, especially for low values of deformation, we have compared our results with those of ~ a s s a n l ~ at kilohertz frequencies for a specimen of 5N purity aluminium subjected to the same amounts of deformation that our specimens received, so that a study of the variation of the activation energy and the attempt frequency with deformation can be achieved. Table 2 shows the results of this study for the Bordoni peak; we are not able to extend the calculations to smaller deformations because the Bordoni peak is not evident at megahertz frequencies. The results show that the activation energy and the attempt frequency both decrease as the deformation is increased.

Table 2

-

The variation of the activation energy and attempt frequency with deformation

According to the double kink generation model proposed by seeger19, the existence of two peaks in f.c.c. metals is due to the two possible orientations of the Burgers vector. He suggested that the Niblett-Wilks peak is caused by pure screw dislocations while the Bordoni peak is due to mixed dislocations. Our results suggest that low levels of deformation at room temperature favour the creation of screw dislocations rather than edge dislocations while the opposite is true for large deformations. This may be due to the higher mobility of the edge dislocations created by small deformations, whereas for large strains their mobility will be reduced by dislocation interactions. Therefore, high levels of deformation will result in the growth of the Bordoni peak and reduction in the height of the Niblett-Wilks peak.

Strain ( X ) 6 12 19

The relaxation strength of the Bordoni peak observed here at megahertz frequencies is, considerably less than that found by ~ a s s a n l ~ at kilohertz frequencies for aluminium of similar purity subjected to similar amounts of deformation. This is consistent with numerical calculations by Esnouf and Pantozzi20 of the internal friction due to double-kink formation.

REFERENCES

w

(ev) 0.22 0.21 0.20

1. HUTCHISON, T.S. and PILMER. A.J.. Can.J.Phys.,

2f?

(1956) 157.

2. KAMIGAKI, K. and HIRONE, T., Acta Met.

4

(1961) 84.

3. MONGY, M., S A W , K. and BECKMAN, 0.. Solid State Comm.,

1

(1963) 234.

4. FANTI, F. and NUOVO, M., Acta Met.

13

(1965) 89.

5. BAXTER, W.J. and WILKS, J., Acta Met.

11

(1963) 979.

6. ROUTBORT, J.L. and SACK, H.S., Phys.Stat.So1.

22

(1967) 203.

7. ALNASER, W.E., Thesis (1986). University of Kent, Canterbury.

8. GRANATO, A.V. and LUCKE, K., J.Appl.Phys.

27

(1956) 583 and 789.

fo (Hz) 7.4 x 1011 4.8 x 1011 2.3 x 1011

C8-82 J O U R N A L DE PHYSIQUE

9. LENZ, D. and LUCKE, K., Z.Metallkunde,

60

(1969) 375.

10. WINTERHAGER, P. and LUCKE, K., J.Appl.Phys.

44

(1973) 4855.

11. KAUFMANN, H.R., LENZ, D. and LUCKE, K., Proc. 5th ICIFUAS, Aachen (1975) Vol. 11, 177.

12. SCHULZ, J. and LENZ, D., Proc. 7th ICIFUAS, Lausanne, (1981) C5-151.

13. HASSAN, R.A.R. and NIBLETT, D.H., Journal de Physique,

44

(1983) C9-659 14. ROUTBORT, J.L., Thesis (1965), Cornell University.

15. DETERRE, Ph., ESNOUF, C., FANTOZZI, G., PEGUIN, P., PEREZ, J., VANONI, F. and VINCENT, A., Acta Met.

27

(1979) 1779.

16. ESNOUF, C., FANTOZZI, G. and GOBIN, P.F., Phys.Stat.Sol.(a)

2

(1975) 441.

17. VOLKL, J., WEINLANDER. W. and CARSTEN.J., Phys.Stat.So1.

10

(1965) 739.

18. HASSAN, R.A.R., Thesis (1986), University of Kent, Canterbury.

19. SEEGER, A., Phil Mag. 1 (1956) 651.

2 0 . ESNOUF, C. and FANTOZZI, G., Phys.Stat.Sol.(a)

47

⁽¹⁹⁷⁸⁾ 201.