High-temperature internal friction peak in high-purity aluminium associated with quenching from high temperatures

Scripta METALLURGICA et MATERIALIA

Vol. 25, pp. 2827-2832, 1991 Printed in the U.S.A.

HIGH-TEMPERATURE ALUMINIUM

INTERNAL

Pergamon Press plc All rights reserved

FRICTION PEAK IN HIGH-PURITY

ASSOCIATED WITH QUENCHING

FROM HIGH TEMPERATURES

P. Cui, X.S. Guan, T.S. K~,(Gc Tingsui) L~boratory of Internal Friction and Defects in Solids, Institute of Solid State Physics, Academia Sinica, Hefei 230031, China ( R e c e i v e d S e p t e m b e r 3 , 1991) ( R e v i s e d O c t o b e r 7, 1991) In a preceding paper concerning the effect of high-temperature quenching on grain boundary relaxation in pure aluminium, an internal friction peak was observed for the first time on the high-temperature side of the grain boundary internal friction peak when the quenching temperature is sufficiently high[i]. In this paper, the conditions for the appearance of this new internal friction peak will be described in detail. It was found that the presence of bamboo boundaries in the specimen is another requirement for the appearance of this peak, in addition to quenching at sufficiently high temperatures. The activation energy associated with this peak was found to bc very high. Furthermore, a strong anomalous amplitude dependent effect was observed within the temperature region of the internal friction peak. Discussions ensued on the possible origin of this peak. I.

Specimens and Experimental Procedure

The aluminium used, produced in Japan, was of 99.999% purity. The specimen was completely rccrystallized by annealing at 350t3 for lh after a prior cold-work of 90% reduction in area. Internal friction was measured with an inverted torsion pendulum on specimens with a diameter of 1 ram. The frequency of vibration is about 1.6Hz. The specimen was heated in-situ of the torsion apparatus to successively higher temperatures and then quenched and furnace-cooled, respectively. Internal friction measurements were then taken at ascending temperatures according to a procedure similar to that described in the preceding paper[l]. 11. II.l.

Experimental Results

Effect of Quenching Temperature The grain boundary internal friction peaks for the 99.999% aluminium specimen quenched and furnace-cooled,

respectively, from 500E are shown by curves 1,2 of Fig.l. It is seen that the grain boundary peak for the quenched specimen (curve 1) shifted to a lower temperature relative to the furnaced--coolcd specimen (curve 2), as has been previously reported[l]. A hump appeared on the high temperature side of the grain boundary peak of the specimen quenched from 530E, as shown by curve 1 of Fig.2. Such a hump was absent in the case of the furnace-cooled specimen (curve 2 of Fig.2). This indicates that the appearance of this hump is connected with the quenching treatment. The hump becomes more pronounced with quenching from 550E, as shown in Fig.3a. The dashed curves are the extrapolation of the high temperature background corresponding to curves I and 2. Curves 1 and 2 of Fig.3b show the corresponding grain boundary peaks with the high-temperature background subtracted. The dashed curve is a symmetrical curve of the low-temperature branch of curve 1. It was drawn based on the assumption that the genuine grain boundary peak should be symmetrical on either side of the peak on a Q-I vs 1 / T plot. Curve 3 was then ob. mined by subtracting the dashed curve from curve i.

It is seen that a small internal friction peak emerged around

350E for the quenched specimen (curve 3 of Fig.3b). When the specimen was quenched from 600E, the high temperature side of the grain boundary peak for the quenched specimen is raised considerably (Fig.4a), indicating that the new high-temperature peak is considerably enhanced. Curves 1 and 2 of Fig.4b show the corresponding grain boundary peaks with the high-temperature back. ground subtracted. It is seen that the peak 3 (obtained according to similar procedure described above) emerged to a height of about 0.07.The shape of the peak indicates a fine structure since the lower temperature side of the peak is

2827 0036-9748/91 $3.00 + .00 Copyright (c) 1991 Pergamon Press plc

2828

INTERNAL FRICTION

IN A1

Vol.

25, No.

12

much wider than the high temperature side. It can be seen by comparing Fig.3b and Fig.4b that the new internal friction peak is enhanced and shifts to higher temperature with increasing quenching temperature. Furthermore, the height of the peak decreased slowly upon aging at the peak temperature. I1.2.

On the Relaxation Behavior of the New Internal Friction Peak FigureSa shows the internal friction curves when the specimen was quenched and furnac~--cooled, respectively,

from 600~ and measured with a lower frequency of vibration (0.4HZ). Correspondingly, Fig.Sb shows the cases when the high-temperature background was subtracted. Peak 3 obtained has a height of about 0.08. The irregular shape of the peak also indicates a fine structure. Since the shape of peak 3 determined with two frequencies, as shown in FigsAb and 5b, are quite different, it is rather difficult to determine the activation energy by method of changing frequency (1.6 and 0.4 Hz) utilizing the data given by Fig.4b and 5b. However, the peak shifted definitely toward a lower temperature for a lower frequency of vibration. A rough estimation gives an activation energy ranging from 2.2 to 2.6 eV, which is much higher than the activation energy associated with volume diffusion in aluminium (l.SeV). 11.3. Effect of the Grain Size of the Specimen In paragraph II.l, attention was placed on the effect of quenching temperature. It is well-known that the excess vacancies created will be more in number the higher the quenching temperature. The experimental fact showing that the new peak begins to appear when the quenching temperature is 530E or higher may indicate that only then is the content of excess vacancies high enough to give rise this new peak. The decay of the peak during aging may indicate the escaping of the excess vacancies. However, it is also well-known that the grain size of the specimen will increase by heating to high temperatures. The internal friction curves shown in Fig.l are for the specimen heated to 500~C, for which the specimen was fine-grained, with a grain size smaller than the diameter of specimen.

After heating to

530~, some of the grains in the specimen grew and ran across the diameter of the specimen so that bamboo boundaries appeared. More bamboo boundaries formed when the specimen was heated successively to higher temperatures and, finally, the specimen consisted completely of bamboo crystals. Accordingly, it is conceivable that the appearance of the new internal friction peak may also be connected with the presence of bamboo boundaries in the specimen. The following experiment is designed to examine the validity of this proposition. A nearly single crystal specimen of 99.999% aluminium was prepared by the dynamic annealing method, with a critical previous deformation of 3% elongation. This specimen contains only 5 bamboo boundaries in a length of l0 cm. The grain boundary peak disappeared in this specimen and the new internal friction peak is absent, as shown in Fig.6 for the specimen quenched and furnace-cooled, respectively, from 600E. Whereas for Fig.4b, a high internal friction peak appeared around 380E for the specimen containing about 30-40 bamboo boundaries in a length of l0 cm. Furthermore, for a specimen containing 13 bamboo boundaries in a length of l0 cm, the corresponding internal friction curves are shown in Fig.7. It is seen that both the grain boundary peak and the new internal friction peak appeared. However, the heights of both peaks are lower than the corresponding cases shown in Fig.4b. It is, thus, evi. dent that the height of the new internal friction peak increases with the increasing number of bamboo boundaries in the specimen. 11.4.

Effect of Strain Amplitude

Experiments showed that the new internal friction peak is not affected by the application of tensile and twisting deformatiom However, it exhibits a strong anomalous amplitude dependent effect as shown in Fig.S. This curve was taken at the temperature point 380t2 on curve i of Fig.4a. Further results on the amplitude effect will be reported in a later paper. HI. Discussion To sum up, the conditions for the appearance of the new internal friction peak arc the creation of enough excess vacancies after quenching treatment and the presence of bamboo boundaries in the specimen. The characteristics of this new peak include the relaxation behavior associated with a high activation energy, the appearance at a rather

Vol.

25, No.

12

INTERNAL

FRICTION

IN A1

2829

high temperature with a high relaxation strength, and the exhibition of an anomalous amplitude dependcnt effect. The appearance of high-temperature relaxation peaks in pure metals has bccn aptly reviewed by Gleitcr and Chalmers[2]. A n internal friction peak above the temperature of the "orthodox" grain boundary peak was observed in 99.9998% A u by Marsh and Hall[3] after annealing at temperatures between about 650 and 1040~. This peak ap~ars at 404~ (f- IHz) with an activation energy of 2.52 eV, which is much higher than that of the "orthodox" grain boundary peak. This high temperature peak is absent after annealing at temperatures outside the range mentioned above and is also absent in commercially pure A u (99.98%) regardless of the annealing treatment. The authors attri. buted this peak to the presence of some grains formed by secondary recrystallization. In the case of Cu, Peters et al.[4]observed an internal friction peak at a temperature (700~C) higher than the orthodox grain boundary peak (280~) in 99.999% copper by annealing at 823~ for long times to produce secondary recrystaUization but not in commercially pure O F H C copper. Further expcrimcntal results wcrc reported by De Morton and Leak [5],who found that the high-temperature peak was sensitive to the annealing time at 900~, increasing with increasing time.The height of the peak increased by a factor of 3 aftcr an anncaling at 1000~. This peak, which behaves similarly to that in Au, is characterized by its high activation cncrgy (4.52 eV), high rclaxation strcngth, and its large width. A systematic study on Cu by Williams and Lcak[6] showcd that the high tcmperaturc peak appeared around 700~ is absent in a single crystal copper specimen. They suggcstcd that this peak is probably d uc to stress-induced grain boundary sliding which occurs only when thc grain size is largc cnough for grain boundaries to extend across the specimen diameter. In the case of Ni, Datsko and Parlor[7] noted a similar high-temperature pcak after a series of deformation and annealing treatments. They concluded that this peak resulted from the strcss rclaxation along polygonizcd sub-boundaries which they believed to be present. This interpretation differs from those of othcrs [5,6]who suggested that the relaxation process is associated with the special "bamboo-type" boundarics produced by high-temperature annealing. Experiments with 99.999% Ni by Robert and Barrand[8] showed that the high-tcmpcrature peak (800~) was most prominent in the specimen with a fully developed bamboo structure produced by high-tcmperaturc annealing. Also, the activation energy for the peakin Ni was higher than that for volume self-diffusion. In the case of At, Williams and Leak[6] observed a " high-tempcraturc peak"

around 560~ (l Hz) in

spcctroscopicaUy pure aluminium from Johnson Matthey and Co., Ltd. The orthodox grain boundary peak appcarcd at about 300~C .The "high-temperature peak" briefly reported by them is quite different from those observed in other metals. According to the internal friction curves they reported, a small h u m p began to emerge on the high temperature side of the grain boundary peak when the grain size of the spccimcn was 0.300 m m

produced by annealing at

615~C. This grain size is much smaller than the specimen diameter of 0.76 m m . A conspicuous peak appeared after annealing at a stillhigher temperature (not mentioned by the authors) whcn thc grain size was 0.380 ram, which is still smaller than the specimen diameter.As the high-temperature peak appcarcd only whcn the grain size cxcccdcd the specimen diameter as reported for other metals, it seems that the 500~ peak obscrvcd by Williams and Lcak may bc caused by other happenings. The optimum temperature of the new internal friction pcak wc observcd in 99.999% aluminium quenched from 600~ is around 350 to 380~, which is much lower than the S60~ they reported. The absence of the real high temperature peak in Williams ~ and Leak's experiment may bc duc to the low purity of the aluminium specimen they used. There are two reasons for this belief.A grain size of 0.300 m m obtained after an annealing at 615~ indicates that the purity of the specimen is lower and is certainly less than 99.999%. Our cxpcri. ments showed conclusively that the grain size should be very large after 615~C annealing in the case of 99.999% aluminium (Japance produced). Furthermore, the optimum temperature 300~ (IHz) of the grain boundary peak is too high, as it should be 272~ for 99.999% aluminium[l]. It is interesting to notice that the manifestations of the high-tcmpcraturc peaks observed in Au, Cu and Ni are very similar to the new internal friction peak that wc observed in 99.999% At qucnchcd from 530~C or highcr. However, the peaks in Au, Cu and Ni appeared after the specimens wcrc anncaled at a dcfinite range of tcmpcraturc

2830

INTERNAL

FRICTION

IN AI

Vol.

25, No.

12

while our peak appeared after the specimen was quenched from suitable high temperatures but was absent when tile specimen was furnace-cooled. A possible explanation for this difference is that the cooling rate after annealing adopted by the previous researchers on Au, Cu and Ni was not slow enough, so that at least an appreciable fraction of the excess vacancies still survived aRer cooling the specimens to lower temperatures.

The dis~uvery of the effect of quenching on the appearance of the high-temperature peak shed light on the understanding of the origin of this peak because, now, the role of vacancies must be taken into account. The requirement of the presence of bamboo boundaries is c o m m o n for the previous and the present works. The high value of the activation energy associated with this peak suggests that if may have originated from the climbing of free dislocations in the specimen. A simplified model may, thus, be contemplated in terms of the stress-induced climb of a long and free segment of dislocation, with both its ends anchored at two adjacent bamboo boundaries (that may bc parallel to each other). Such a long and free dislocation segment can only survive in a high-purity specimen aRcr having heated to sufficientlyhigh temperatures. The controlling factor of the process may be the formation of jogs on the dislocation and the migration of jogs along with the dislocation.The delayed motion of the dislocation under the action of the applied stress and its recovery of its original state upon the removal of the applied stresscan give rise to the main characteristicsof an anclastic relaxation peak. In order to account for the large relaxation strength associatcd with this peak, the joggcd dislocation should bc able to bow out to a sufficientextent. This requires a jog density on the dislocation much highcr than the equilibrium concentration. It has been shown [9] that the segregation of supersaturated vacancies around a dislocation line can produce jogs in a noncquilibrium nucleation process so that the number of jogs can be considerably larger than the equilibrium concentration of jogs[10] on the dislocation segment. A supply of supersaturated vacancies can be furnished by means of a quenching treatment. Such excess vacancies can segregate to the dislocation segment directly and more vacancics-~ originally accumulated at the bamboo boundaries can migrate to the dislocation through pipe diffusion. Finally, the anomalous amplitude dependent effect can bc attributed to the shiftof the anchoring sitesof the dislocation segment terminating at the bamboo boundaries under the application of a higher applicd stress.Such a shift can take place along with the viscous sliding of the bamboo boundaries. This will lead to a decrease of internal friction with an increase of applied stress or strain amplitude. Rcfcrcnces [I] P.Cui, X.S. Guan, and T.S. K~(Ge Tingsui), comm. to Scripta Mctallurgica et Matcrialia(1991). [2] H. Glcitcr and B. Chalmers, High-Angle Grain Boundaries, Pergamon Press, Oxford, (1972), Chap. 8. [3] D.M. Marsh and L.D. Hall, J. Metals 5, 937(1953). [4] D.T. Peters, ].C. Bisseliches, and J.W. Spretnak, Trans. A I M E 230, 530(1964). [5] M.E. Dc Morton and G.M. Leak, Acta. Met. 14, 1140(1966). [6] M. Williams and G.M. Leak, Acta Met. 15, l I I I(1967). [7] O.T. Datsko and V.A. Pavlov, in:'Rclaxation Phenomena in Metals and Alloys" [8]

N e w York Consultant% Bureau, (1963), p. 174. (cf.[gD. I.T.A. Roberts and P. Barrand, J. Inst. Metals 96, 172(1968).

[9]

R.M. Thomson and R.W. Balluffi,J. Appl. Phys. 33, 803(1962).

[10] J.P. Hirth and J. Lothe, Theory of Dislocations, 2nd cd., McGraw-Hill Publ. Co., (1982), p.570.

Vol.

25,

No.

12

INTERNAL

FRICTION

IN A 1

2831

~°C

500 kO0 I

'

i

300

200

i

i

,

600 500 t,O0 I

'

I

'

I

'

300

200

i

i

500 I

400

300

200

i

I

'

10

8 B

? ×

J i

I

1.2

~

4

l

l

l

1.6

,

I

,

l

,

2.0

1.5

1.1

1.9

11lxIO)(IIK) Fig.1.

,-

, ~

,

I

Z.,~

2.3

I

0 1.2

I

=

Internal friction curves of

Fig.2.

Quenched (1) and furnace-cooled(2)

Fig.3(a).

[

M

I

I

I

2.0

2A

The dashed curves are

extrapolations from curves 1

from 530~.

furnace-cooled (2) from 500~.

¢

11"i" x 103(1/K)

IITxIOXIIK)

99.999% AI quenched (i) and

I

1.6

and 2. Quenched (1) and furnace-cooled (2) from 550113.

~°C 600 500 t+O0 300 200

°C ~oo

300

2oo

,

,

,

IO

r

.

t

,

i

I

,

,

i

~°C 300 ZOO

600 500 400

f

i

,

I

,

I

'

I

,

I

12 B

~6

%B x

2

f

0

Ii~

Fig.3Co).

,,

1.6

-.,,

1.8

2.0 2.2 l/Tx 103(1/K)

0

2.4

Same as in Fig.3(a) with

high temperature background subtracted. Curve 3: new internal friction peak for the quenched specimen.

,

I

1.0

,

1.~

Fig.4(a).

,

I

,

I

,

I

,

1.B 2.2 1/Tx103(1/K)

I

,

I

2.6

Quenched(l) and furnace-

cooled(2) from 600E. The dashed

o/.,,'!\ \ r

1.0

1.t*

Fig.4(b).

I

r

I.B 2.2 11Tx I03(IIK)

I

2.6

Same as Fig.4(a) with high

temperature background subtracted

curves arc extrapolations from

Curvc 3. New internal friction peak

curves 1 and 2.f = 1.6Hz.

for the quenched specimen.

2832

INTERNAL FRICTION

~*C 600 500 400 i

,

'

I

300 '

IN A1

Vol.

~*C 600 500 t~00 300 200

ZOO

i

i

'

i

,

r

,

I

600 .500 400

I

I

,

i

,

I

25, No.

300 ,

12

200

~

,

I

*

,

15

o

tl

~B "b

~o x

i 4

: " " ' - ' . " ,. "" "-:'. ;.+..

0

,

1.0

I

,

f

,

I

1.t+

,

I

,

I

+

f

"¢':.

-

+. :

I

,

I

,

I.~ 2.2 lIT xIO3(UK)

2.6

1.0

1.t,

Fig.5(b) Fig.5(a)

Same as in Fig.4(a). f= 0.4Hz.

2

,i .... /......

1.B 22 1/T xlO3[l/K]

0 l.O

26

Same as in Fig.5(a) with high

temperature background subtracted.

,

,

,

5 bamboo boundaries) quenched (1) and furnace-cooled(2) from 60013.

200 J

l 0.8

O.G

I f

0

m

1.0

Fig.7.

l

,

I

1.4

m

I

~

I

,

,

1.8 1/T x 103(1/K)

,

0.5

"I

2.2

Internal friction curves of

Fig.8.

I

Internal friction curves of

1.2

7:, .x~

,

1.B Z2 liT x 103(1/K1

99.999% AI specimen (containing

for the quenched specimen.

I

I

1.4

Fig.6.

Curve 3. New internal friction peak

~*C 600 500 ~+00 300

,

r

f

tO A( x I0 s

f

I

L5

*

_

2.O

Amplitude effect of the new

99.999% AI specimen (containing 13

internal friction peak. Measurements

bamboo boundaries) quenched (1) and

taken at the temperature point 38013

furnace-cooled (2) from 60013.

on curve I of Fig.4a.