ON THE 0.4 TM PEAK IN F.C.C. PURE METALS

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ON THE 0.4 TM PEAK IN F.C.C. PURE METALS

A. Rivière, J. Woirgard, J. de Fouquet

To cite this version:

A. Rivière, J. Woirgard, J. de Fouquet. ON THE 0.4 TM PEAK IN F.C.C. PURE METALS. Jour- nal de Physique Colloques, 1985, 46 (C10), pp.C10-343-C10-346. �10.1051/jphyscol:19851076�. �jpa- 00225461�

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ON THE 0 . 4 T, PEAK I N F . C . C . PURE METALS

A. RIVIERE, J. WOIRGARD AND J. DE FOUQUET

Laboratoire de Mbcanique et Physique des Materiaux, U A C N R S 863, ENSMA 86034 Poitiers Cedex, France

ABSTRACT :

An internal friction relaxation peak-located about 0.4 TM for a vibration frequency of 1 Hz is observed in poly and single crystals of pure F.C.C.

metals (A1 -Ag-Cu-Ni-Pd). The re1 ating activation energy is always close to 0.5 H , H being the self diffusion energy.

~ c c o r a i n ~ ~ t h e experimental results, the peak can be associated with motion of dislocation loops belonging either to fragments of cells destroyed in heavily cold-rol led polycrystal , or freshly created dislocations in high temperature annealed poly or single crystals.

The observed effects can be explained by a mechanism involving dislocation climb enhanced by vacancy core diffusion.

I - INTRODUCTION

High temperature internal friction spectra in F.C.C. metals exhibit several maximal superimposed on to an exponentially increasing background /1,2,3,4,5/. Some of these maxima are not true relaxation peaks but have been proved to be transient effects connected to the experimental conditions : heating or cooling rates /6,7/ and hysteristic effects sensitive to the strain amplitude but independent of the vibration frequency /7,8/. Nevertheless an accurate determi nation of the re1 axation parameters, deduced from measurements at constant temperatures and very low strain amplitudes, indicates the presence of several true relaxation peaks. The same peaks have been obtained in different purity specimens and in both single crystals and polycrystals /8/.

This paper deals with the lowest temperature peak located about 0.4 TM, for a vibration frequency of 1 Hz.

I1

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EXPERIMENTAL METHOD

Results were obtained with an evacuated flexural pendulum for vibration frequencies ranging between 0.3 and 5 Hz, and with a variable frequency torsion pendulum a1 lowing measurements between and 160 Hz. Damping curves corresponding to the null strain amplitude are ext apolated

grom

measurements performed at strain amplitudes ranging between 2.10- and 8.10-. 7

Five F.C.C. pure metals were tested.

- polycrystals and single crystals of 5 N silver and 4N5 nickel.

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polycrystals of 4 N palladium and 5 N copper

- polycrystals and single crystals of 3 N and 5 N aluminium.

111- EXPERIMENTAL RESULTS

In heavi 1 y rolled specimens, the relaxation peak appeared only after annealing at temperatures above the recrystallization temperature. Figure 1 shows the increase in damping associated with the recrystallization (curve a) and the low temperature peak (0.4 T 1 appearing after annealing at 700 K (curve b). In metals with a high stackia fault energy, recrystal l i zation corresponds to an important internal

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19851076

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C10-344 JOURNAL DE PHYSIQUE

f r i c t i o n maximum. The r e s u l t s of f i g u r e 2, obtained with a torsional variable frequency pendulum and plotted versus temperature, show t h a t t h e observed large damping maximum i s not a t r u e relaxation peak since i t i s not s h i f t e d when t h e vibration frequency i s changed.

In t h e case of s i n g l e c r y s t a l s or polycrystals annealed a t high temperature, the 0.4 TM peak appears a f t e r a s l i g h t deformation. as shown f o r aluminum i n f i g u r e 3 f o r an 5 N s i n g l e crystal and i n f i g u r e 4 f o r an 3 N polycrystal.

In high stacking f a u l t energy metals, t h e 0.4 TM peak disappears a f t e r a f u r t h e r annealing a t a temperature close t o 0.5 TM

.

^Onthe other land,in low stacking f a u l t energy metals as s i l v e r ( f i g u r e 5 ) i t i s necessary t o anneal a t temperatures as high as 0.9 Tiq t o eliminate i t completly.

The 0.4 TM peak has been observed i n polycrystals and single c r y s t a l s of d i f f e r e n t purity metals as shown i n f i g u r e 6 f o r 3 N and 5 N aluminum.

IV

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DISCUSSION

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CONCLUSION

The c h a r a c t e r i s t i c s of t h e peak are l i s t e d i n t a b l e 1 f o r different metals /8,9,10/.

Table 1

* Hv : s e l f -diffusion energy Metal

Tp/TM a t 1 Hz H eV

H,/HV*

T.E.M. and X. Rays observations seem t o indicate t h a t the peak i s related t o the motion of dislocation loops belonging, e i t h e r t o fragment of destroyed c e l l s i n heavily cold-rolled specimens, or t o f r e s h l y created dislocations i n specimens annealed a t high temperatures.

Since t h e c e l l s a r e destroyed by dislocation climb, t h e d i f f e r e n t behaviour mentionned above can be simply explained :

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i n high stacking f a u l t energy metals (Al, N i , Pd) i n which climb occurs a t moderate temperatures /11,12/ t h e c e l l s a r e completly destroyed a f t e r annealings a t intermediate temperatures ( 0.7 T M ) and t h e 0.4 TM peak disappears rapidly.

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i n low stacking f a u l t energy metals (Ag, C u ) very high temperature annealings ( 0.9 T M ) a r e necessary t o eliminate completly t h e c e l l walls and t o make the peak t o disappear.

A1 0.43 0.74 0.50

As regards the elementary mechanism responsible f o r t h e motion of t h e dislocations we can note t h a t t h e activation energy has been found close t o 0.5 H v , a value which can correspond t o dislocation climb by pipe-diffusion of vacancies along t h e dislocation l i n e s /13/.

V

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REFERENCES

Ag 0.37 1 0.52

/1/ WOIRGARD J., These Doctorat 6s Sciences, Poitiers (1974).

/2/ DATSKO, 0. I and PAVLOV, V.A., Relaxation phenomena i n Metals and A1 loys, Ney-York (1963) 174.

Cu 0.41 0.96 0.47

N i

0.42 1.39 0.46

pd

0.40 1

0.40

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/7/ RIVIERE, A., AMIRAULT, J.P. and WOIRGARD, J., ICIFUAS-7, J. Phys. C5 (1981 439.

/8/ RIVIERE, A., These Doctorat 6s Sciences. Poitiers (1984).

/9/ RIVIERE, A. and WOIRGARD, J., Scripta Met. 17 (1983) 269.

/lo/ RIVIERE,A. and WOIRGARD, ECIFUAS-4, J.Phys. C9 (1983) 741.

/IT/ HASEGAWA, T. and KOCKS, V.F. , Acta Met. 27, (1979) 1705.

/12/ SCATTERGOOD, R.O. and HASEGAWA, T., Scripta Met. 13 (19791, 723.

/13/ WOIRGARD, J., Phil. Mag. 33 (1976) 623.

LOO, 6 00 K

I I : I 1 1 1 1 1

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Figure 1 - Polycrystal 5N Silver - 3 Hz a ) as rolled

b ) annealed at 700 K.

Figure 2 - Polycrystal 5N Aluminum Cold-rolled 20 %.

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C10-346 JOURNAL DE PHYSIQUE

Figure 3 - S i n g l e c r y s t a l 5N A1 - 5 Hz Figure 4 - Polycrystal 3N A1 - 1 Hz a ) S l i g h t l y deformed a ) S l i g h t l y deformed b ) Annealed a t 670 K. b ) Annealed a t 670 K.

Figure 5 - Polycrystal 5N S i l v e r - 3 HZ a ) Annealed a t 700 K

b) Annealed a t 1000 K C ) Annealed a t 1200 K.

Figure 6 - Frequency and tempera- t u r e p o s i t i o n of t h e 0.4 TM peak i n Al.