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Submitted on 1 Jan 1971
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ULTRASONIC ATTENUATION STUDY OF THE INTERACTION OF IRRADIATION PRODUCED
PINNING POINTS WITH DISLOCATIONS IN COPPER
A. Ostermann, D. Lenz, K. Lücke
To cite this version:
A. Ostermann, D. Lenz, K. Lücke. ULTRASONIC ATTENUATION STUDY OF THE INTERAC- TION OF IRRADIATION PRODUCED PINNING POINTS WITH DISLOCATIONS IN COPPER.
Journal de Physique Colloques, 1971, 32 (C2), pp.C2-149-C2-150. �10.1051/jphyscol:1971232�. �jpa- 00214558�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 7, tome 32, Juillet 1971, page C2-149
ULTRASONIC ATTENUATION STUDY OF THE INTERACTION OF IRRADIATION PRODUCED PINNING POINTS
WITH DISLOCATIONS IN COPPER
by A. OSTERMANN*, D. LENZ and K. LUCKE
Institut fiir Allgemeine Metallkunde und Metallphysik, T. H. Aachen, Deutschland
RksumB. - Le depikgeage thermonlkcanique des lignes de dislocations a et6 ktudik dans un monocristal de cuivre en fonction de la contrainte exterieure appliquee, en utilisant la mesure de I'attknuation ultrasonique. La production de points d'ancrage a et6 obtenue par une irradiation de l'echantillon aux rayons-y
a
la tempkrature de 295 OK, suivie de recuits par &tapes successives jusqu'a 400 OK. En utilisant le frottement intkrieur dtia
la resonance des dislocations ainsi que les theories du depiegeage, on a determine par I'analyse des courbes a(z) I'energie de liaison des points d'ancrages avec les dislocations. L'6nergie de liaison croit linkairement avec la densite des points d'ancrages produits par irradiation. Elle decroit lineairement aussi lorsque la densite des points d'ancrages diminue au cours d'un recuit de 1'8chantillon entre 500 et 650 OK.Abstract. - The stress-induced breakaway of dislocations from their pinning points has been studied in Cu single crystals by measuring the ultrasonic attenuation a as a function of the externally applied stress z. The pinning points under consideration were produced by y-irradiation at 295 OK and subsequent step-wise annealing up to 400 OK. Using dislocation resonance damping and breakaway theories, the analysis of the a(z) dependence yielded the binding energy of the pinning points to the dislocations. The binding energy increases linearely with increasing density of irradiation-induced pinning points. It decreases linearly as the density of pinning points is reduced during annealing of the sample between 500 and 650 OK.
In order to investigate the breakaway of disloca- tions from pinning points an external stress (uniaxial compression) has been applied to Cu single crystals (99.999 % purity) under simultaneous measurement of their ultrasonic attenuation (10 and 170 MHz ; pulse echo method with automatic attenuation recording [l]).
The attenuation which, up to 90 %, is due to disloca- tion resonance damping [2] is used in order to measure changes in free dislocation loop length caused either by dislocation pinning during irradiation or by break- away during stress loading. The experiments were carried out on well annealed and then y-irradiated crystals and on irradiated and then stepwise isochro- nically annealed (up to 650 OK) crystals.
As an example figure 1 shows the dislocation atte- nuation as function of the resolved shear stress in the glide system during loading after different y-irradia- tions at 295 OK (the y-dose of 1 pAh yields about 4.7 X 10'' Frenkel defects/cm3 131). With increasing stress an increase in attenuation is observed which is caused by an increase of the loop length of the dislo- cations due to breakaway from their pinning points.
With increasing dose the zero stress attenuation decreases due to irradiation pinning and the onset of breakaway is shifted to higher stress values.
If after irradiation at 295 OK the sample is annealed
Shearstress 'C [p/rnrn2]
FIG. l. -Dislocation attenuation as function of resolved shear stress for a Cu sample irradiated at 295 OK with the
y-doses indicated.
at stepwise increased temperatures one finds further pinning up to about 400 OK followed by complete thermal depinning between 500 and 650 OK [4].
Figure 2 shows how the attenuation vs. stress curves are influenced by such an annealing treatment after a 50 pAh irradiation at 295 OK. As long as addi- tional pinning takes place (solid lines) a(z) changes in a similar way as in figure 1 with increasing
* Now with Mahle KG, Stuttgart-bad Cannstatt, Deuts- dose. During thermal depinning (broken lines) the
chland. curves shift in the reversed direction until finally
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971232
C2-150 A. OSTERMANN, D. LENZ AND K. LUCKE
1,s - stage 111, and at 367 OK, i. e. in stage IV. The fact that
Annealing
~ ~ u r e t ~ ] U*(p) is independent of the temperature of irradiation indicates that in both stages the same type of pinning point is formed. This can be explained most easily by assuming that in both stages the same type of irradia- tion produced point defect anneals out at the dislo- cations.
The increase in U* with p can be explained by assu- ming that pinning is caused by defect clusters which increase in size (and also in binding energy) during pro- longed irradiation. This assumption is in agreement o 10 20 30 40 with recent irradiation and recovery experiments in
Shearstress r [plmm2] CU [3, 7 , 81.
The broken lines in figure 3 give the range of U*
FIG. 2. - Dislocation attenuation as function of resolved from the annealing experiment (Fig. 2). They show shear stress for a Cu sample irradiated at 295 OK with a y-dose close agreement with the u y p ) values from the iso- of 50 pAh and then annealed 15 min at the temperatures indicated.
the a(z) behaviour of the unirradiated sample is restored. The interesting result of this depinning expe- riment is that the measured a(z) curves depend only upon a(0). This means that the shapes of the curves a vs z are about equal for equal a(0) no matter whether the curve is obtained in the course of a pinning or depinning experiment. It means further that the binding strength of the pinning points is determined only by a(O), i. e. by the density of the pinning points, no matter whether this density as obtained by pinning or depinning.
Using the theory of dislocation resonance damping [2] and the theory of thermally activated dislocation breakaway [5,6] a quantitative description of the present results has been given [l]. From this an appro- ximation has been derived by which a relative binding energy U* = U,/Uo can be obtained from the onset of breakaway. Here U,, U, are the effective binding- energies of pinning points in the irradiated and unirra- diated state, respectively.
Figure 3 shows U* as function of p, the number of irradiation induced pinning points per initial mean loop length L,. The points given in the figure refer to isothermal irradiations at 295 OK, i.e. in annealing
0
I
0 9 5 1.0 1,5 2.0 2.5
Additional pinning points per L.
FIG. 3. - Relative binding energy U* as function of the number p of irradiation induced pinning points. The data points refer to isothermal irradiations at 295 and 367OK, respectively.
The dashed lines indicate the range of values of U* obtained from the annealing experiment.
thermal irradiation experiment. The fact that during thermal depinning, i. e. with decreasing p, U* decreases indicates that the loss in pinning points is accompa- gnied by a loss in pinning strenght of the remaining pinning points.
References
[l] OSTERMANN A., Thesis T H Aachen, 1970. [6] TEUTONICO L. J., LUCKE K., HEUSER F. W., GRANATO [2] GRANATO A. V., LUCKE K., J. appl. phys., 1956,27,583. A. V . , J. Acbust. SOC. Am., 1969, 45, 1402.
[3] WINTERHAGER P., Thesis TH Aachen, 1969. [7] THOMPSON D. O., BUCK O., BARNES R. S., HUNTING- [4] INAGAKI H., HULTGREN F. A., LUCKE K., Acta Met.,
1970. 18, 713. TON H. B., J. appI phys., 1967, 38, 3051.
[5] L ~ ~ C K E K.; G ~ N A T O A. V., TEUTONICO L. J., J . appl. [8] KEEFER D., ROBINSON J. C., SOSIN A., Acta Met., 1965,
Phys., 1968, 39, 5181. 13, 1135.
