INTERNAL FRICTION OF ZINC SINGLE CRYSTALS UNDER IMPACT LOADING

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INTERNAL FRICTION OF ZINC SINGLE CRYSTALS

UNDER IMPACT LOADING

T. Yokoyama

To cite this version:

JOURNAL DE PHYSIQUE

CoZZoque C5, supple'ment au nolO, Tome 4 2 , octobre 1981 page c5-375

INTERNAL FRICTION O F ZINC SINGLE CRYSTALS UNDER IMPACT LOADING

Faculty of Science and l'echology, Meijo University, Nagoya, Japan

Abstract.- The internal friction measurements have been carr~ed out on zinc monocrystals in the mode of a flexural vibration, in an attempt to compare the dislocation damping in the basal slip system with that in the second-order pyramidal slip system. We

examined the effect of cold working by impact loading. A cold-

work peal; is observed to occur at about 230°K in the pyramidal slip system. Differences in amplitude dependent damping in an- nealed and cold-worked specimens are researched in both slip sys- tems, respectively.

1. Experiment.- Zinc crystals in 9 9 . 9 9 9 wt% nominal purity containing

Cd 5 ppm and Fe 1 ppm, were further purified by zone refining in a

carbon monoxide atmosphere. The ingots of single crystal grown bp a

modified Bridgman method, were cut into the rectangular shape with di-

mensions about 0.5X0.5 X ( 6 ' ~ 1 1 ) cm by an acid-cutter. In one kind of

specimens, the specimens were oriented so as to glide on the basal

slip plane, e.g. incling by

X

kind of them were finished to orient the basal plane nearly parallel to specimen axis, to glide preferentially on the second-order slipsys- terns. Tine internal friction measurements are done with the magnetic and receiving system and the decrements are measured by both free decay method and the ratio of the driving force to the amplitude at resonance. The impact loading is done by the striking pendulm of a me* a1 ball. One end of the specimen is struck just after being drawn up from liquid nitrogen. The elastic induced by this method is estimated

to be about 2 X 10-~.

2. Results.- 2-1. Cold work pealc. Figure 1 shows temperature dependent decrement in basal slip system of both annealed and cold worked speci- men. In the second-order slip systems a cold-work peak is observed at the temperature range of about 230 %25gaK, as shown in Fig.2.

C5-376 JOURNAL DE PHYSIQUE

Fig. l : Decrement vs tempera- Fig. 2' : Decrement vs tempera-

ture ~n the basal slip system ture in the second-order pyram-

in both annealed and cold work- idal slip system in both anneal-

ed specimen. ed and cold worked specimen.

10

2-2. Strain-amplitude dependent damping. In Fig.3 are the typical in-

. . .x103 o As annealed g***.*m- S A f t e r ~ a c t loadlnn _.* 0.

.

.-

. .

.

**...*

,-.

*..***

.

ternal friction vs strain-amplitude curves at various temperatures be-

tween 100' and 570°K in a well-annealed crystal. At about 100°K, the

behaviour of damping was reversible in both increasing and decreasing

?OO 150 200 250

amplitude. At about 300°K, however, a large hysteresis loop of damping

is observed to occur, as already The largest area of the

loop is observed at around 330°K. The break-point is shifted to lower

amplitude with the rise of temperature. Above 420°K, no hysteresis effect appeared again and damping was reversible on reducing the strain-amplitude. By impact loading, this hysteresis loop disappeared

Fig. 4 :

Average decrement vs max.,strain-am- Variation of the amplitude depew

plitude curves at various tempear- dent damping of the basal slip

tures, in a well-annealed specimen dislocation at room temperature

Fig. 5: Average decrement vs max. Fig. 6 : Variation of the ampli- strain-amplitude curves of the py- tude dependent damping of the py-

ramidal slip dislocation damping ramidal slip dislocation at room

at various temperatures, in an an- temperature by impact loading. nealed specimen oriented

X

3. Discussions.- It was already reported5that the cold-work peak in

zinc crystal occurred at 200°K and this peak was broad. De batist in- dicated 6that Bordoni peak in hexagonal crystals was broad. We have researched that the cold-work peak of the basal slip dislocation caused. by impact loading is also broad and not separated well to single peaks. The cold-work peak of the second-order pyramidal slip dislocation is clear, comparing with that of the basal slip dislocation. However, it must be more researched in future whether this peak is the relaxation type or not.

In the recent study of amplitude dependent damping of zinc crystal, two straight line of the Granato-Lucke plot was reported by Bortolotti e t a l . ! Recently ~ s a n o ~ a n d ~ o v o l o ~ h a v e improved the process of correc- tion to internal friction. The present data are translated to the in- trinsic decrement ( & , ) against the homogeneous strain-amplitude (

E,).

When the measured decrement

( S a )

(E,)

Figure 5 indicates an example of the amplitude dependent damping caused. by movable dislocations in pyramidal slip systems at various tempera- tures. The amplitude dependent damping increased gradually with the rise of amplitude. In some crystals narrow hvsteresis loops are ob- served at the same temperature range as that of the basal slip system mentioned above. It turns out that the temperature dependence of am- plitude dependent damping is not so complicated as that of the basal slip dislocation. By impact loading, the change of amplitude dependent damping occurs, but less than that of the basal slip dislocation, as

indicated in Fig.6.

L

---

-

A+AAfter Inpact load~ng

4

JOURNAL DE PHYSIQUE

$ , = A 1 2

+

B

the intrinsic amplitude dependent decrenent

( g ,

(2)

where

r

Furthermore, the dislocation strain ~ d corresponding to the energy ,

loss dissipated on internal friction, can be derived from the rela- tion la

where y is a geometrical factor.

Using eq,( 3 ) , the dislocation strain ( )is plotted against the stress, as shown in Pig.7. The dislocation strain caused by impact loading is compared in both slip systems.

Fig. 7 . : Dislocation strain ( E d )

l

idal slip system, converted from the same data as that of fig.4 and

0.01 Q1 UI

-

Results of such measurements will be discussed.

The author wish to express his gratitude to Professor R.R. Hasiguti,

Professor N. Igata and Dr. S. Asano, for their valuable discussions. References

(1) T.A. Read: Phys. Rev. 58, 371 (1940).

(2) T.A. Read and E.P.T. Tyndall: J. Appl. Phys. 17, 713 (1946).

(3) I.H. Swift and J.E. Richardson: J. Apgl. Phys. 18, 417 (1947).

(4) C.A. Wert: J. Appl. Phys. 20, 29 (1949). (5) G. Kamoshita: Thesis, Tokyo Univ. (1958).

( 7 ) A. Bortolotti, G. 5lattinelli and L. Passari: Internal Friction and

Ultrasonic Attenuation in Crystalline Solids 11, Springer-Verlag

507 (1975).

(8) S. Asano: Jap. Jr. Appl. Phys. 8, 9 (1969).

(9) F. Povolo and R. Gibala: Phil. Mag. 27, 1281 (1973).