TIME AND HEATING RATE DEPENDENT CONTRIBUTIONS IN THE INTERNAL FRICTION

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TIME AND HEATING RATE DEPENDENT

CONTRIBUTIONS IN THE INTERNAL FRICTION

S. Kiss, W. Benoit, I. Harangozó, F. Kedves, G. Posgay, R. Schaller

To cite this version:

S. Kiss, W. Benoit, I. Harangozó, F. Kedves, G. Posgay, et al.. TIME AND HEATING RATE

DEPENDENT CONTRIBUTIONS IN THE INTERNAL FRICTION. Journal de Physique Colloques,

1987, 48 (C8), pp.C8-329-C8-333. �10.1051/jphyscol:1987848�. �jpa-00227152�

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JOURNAL DE PHYSIQUE

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

TIME AND HEATING RATE DEPENDENT CONTRIBUTIONS IN THE INTERNAL FRICTION

S. KISS, W. BENOIT*, 1.2. HARANGOZO, / F.3. KEDVES, G. POSGAY and R. SCHALLER'

Kossuth University, Department of Solid State Physics, PO Box 2, H-4010 Debrecen, Hungary

' ~ c o l e Polytechnique FkdBrale de Lausanne, Institut de Genie Atomique. PHB Ecublens, CH-1015 Lausanne, Switzerland

The internal friction (i.f.1 back round of pure A1 and Al- -

i

s higher for higher heating or cooQing rates. Heatlng rate or time dependent effects were also found i n the case of precipitation or dissolution (AlAg, AlCu, AlZn, recrystallization, or structural relaxation (metallic glasses). One part of these changes can be attributed to continuous transformation of the structure which can be monitored mainly by the change of the modulus. Also an extra damping was detected depending on the intensity of the transformation processes.

Introduction

Kost of the internal friction (i.f.) measurements are made during continuous heating or cooling. On the spectra obtained in this way one can find relaxational peaks, and non relaxational ("pseudo") peaks due to the structural transformation (precipitation, dissolution, recrystalli- z a t i o n , structural relaxation or crystallization and so on). Usually the heating or cooling rate is kept at a nearly constant value. But very often n o t - e n o u g h care i s taken of the value of the heating o r cooling rate (T). In this work w e show the importance of this parameter for s o m e cases. For different materials and different transformation processes the obtained I.f. and dynamical modulus (d.m.1 values can greatly depend on the T parameter.

Our measurements were made i n torsional enduluns of different types.

Most of the results were obtained o n A1 and

AP

alloys (5NA1, A14wt%Cu, A10.3wt%Mn, A15wt%Ag and A125wt%Zn) using K G pendulums. The measurements on metallic glasses (Fe80820, Ni80.6P19.4 and multicomponent CoNiFe based alloys) were made in a normal torsional pendulum with low inertia and under low axial stress. The heat capacity of the furnace

; : a s snal.1 in all c a s e s ; s o we could stop heating o r cooling and could

~ I I ~ I - 1 to isothernal il~asltrement in a short tine.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987848

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JOURNAL DE PHYSIQUE

Results and discussion

It w a s shown 11) that the i.f. background i s higher when the heating _{- -} or cooling r a t e i s greater. This result was found for high purity and recrystallized aluminium when the heating or cooling i s interrupted.

T h u s , turning to a n isothermal measurement w e observed an i.f: decrease and d.m. increase at higher temperatures. As can be s e e n i n Fig.1. this

Fig.1. Isothermal i.f. and frequency changes for A15N

behaviour does not depend o n the earlier decreasing or increasing run of the i.f. during the temperature dependent measurement. The isothermal change is bigger for higher temperature and f o r higher heating or cooling rate. Similar isothermal changes were found for different A1 alloys but it w a s greater for higher purity

This general behaviour leads to higher i.f. background for higher heating or cooling rate. This extra damping can be caused by a continuous change of the structure during heating or cooling (allchange of the vacancy concentration, e.g.1. On the other hand local damping increases due to the higher heating rate can b e found on the spectrum of materials undergoing structural transformation during heating or cooling. Such an effect was found near the solvus temperature for AlCu AlZn and AlAg alloys when precipitation or dissolution occurs L27.

During heating the i.f. decreases (forming a non relaxational pseudo peak i n this way). This peak is accompanied by a rather great decrease in the modulus. A similar effect i n the opposite sense can be observed at a slightly lower temperature when cooling down is continuous. These peaks due to dissolution and precipitation c a n be seen i n Fig.2. when

Fig.2. The i.f. peaks due to precipitation and dissolution are stron ly de-

pendent o n the heaving rate Fig.3. Heating rate dependent damping f o r AlZn alloy

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the very strong heating rate dependence i s also represented. Similar behaviour can be observed from AlZn alloy but in this c a s e even the shape of the heating and cooling curve i s rather different. The heating rate dependence of the peak occureing during heating i s shown i n Fig.3.

The peak and the inflexion point of the modulus curve shift to higher temperatures if the T i s greater. This fact can be explained by the time needed for the transformation ( 3 ) . In addition a certain extra damping occurs i n the temperature range of the transformation. Also the heating rate dependent extra damping occurs f o r different rnateri- als when the structure is transformed to a more stable state with a higher atomic order. For instance investigating the i.f. of a plasti- cally deformed crystalline material, the damping decrease suddenly due to the recrystallization. On the spectrum measured under such circumstances the i.f. is greater i n the temperature. range of the transformation if the heating rate i s greater. Other examples of this type of effect are the strcutural relaxation and the crystallization of metallic glasses. In the t o p o l o g ~ c a l and chemical ordering of the amorphous material the i.f. i s also T dependent (Fig.4). During the crystallization and phase transformations at higher temperatures a sudden damping decrease occurs again.

In order to study the time dependence of the i.f. and d.m. in the temperature ranges of the transformationg, isothermal measurements were also made. Not considering the general T and time dependence of the background mentioned above [I] i.f. and d.m. changes with longer characteristic times were found for the different transformations. During the isothermal period the i.f. and d.m. tend to an equilibrium value which is characteristic of the equilibrium structure at that temperature. In this way the intensity of the transformation process or the transformed part of the material c a n be monitored by the anelastic parameters. Making measurements during recrystallization w e obtained rather great and sudden isothermal i.f. decreases, but only small effects

Fig.4. lhe i.f. de- pends on the ? ⁱⁿ the range of the structural relaxation and crystallization of metallic glasses

were found at lower or higher temperatures (Fig.5). This i.f. decrease i s usually accompanied by a d.m. increase showing that the modulus of the more perfect material is higher. Similar isothermal i.f. and d.m.

behaviour was found for metallic glasses during the structural relaxation and crystallization [4]. This can be attributed to the higher modulus and lower damping i n the relaxed amorphous o r the crystalline state[5]. Similar i.f. behaviour has been found for martensitic transformation too f6]

.

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C8-332 JOURNAL DE PHYSIQUE

More detailed investigations were necessary i n the case of reversible precipitation and dissolution transformations. In order to avoid the transient behaviour just after stopping the change o f the temperature, and to avoid the influence of the general isothermal i.f. de- T crease and d.m. increase under such (K) circumstances, only the changes of

the measured parameters after 1 0 minutes were considered. The reason 800 f o r not counting the first 1 0 mi-

nutes can be seen i n Fig.6.(627 K) where the i.f. decreases at the beginning but this i s followed by a damping increase for longer periods.

6m For the AlAg alloy cooled from homogenisation temperature, isothermal i.f. decrease and d.m. increase due t o the precipitation COO process were found. These changes

were observed in the temperature range of the non relaxational i.f.

peak which appeared during cooling 100 200 300 t(rnin1 :2]

.

On the other hand starting from

a precipitated state and stopping Fig.5. Great isothermal i.f. the heating, the frequency, f , (and

changes in the temperature e d.m. being proportional to the ran e of recrystallization

:'

decreased to a great extent and only a smafl d.m. increase w a s observed at the beginning of the dlsso- lution. The behaviour of the i.f. during the dissolution i s more compli- cated (Fig.6). I t decreases by a great amount at the beginning and at the end of the temperature range of the dissolution peak on the spectrum (at 6 3 2 K f o r instance).

(Hz)

0.7 5

0.70

065.5

~

Fig.6. Isothermal measurements in the temperature range of dissolution This fact has a special importance because during continuous heating be- low the peak temperature the i.f. w a s always increasing. This result shows that the equilibrium structure at a certain temperature after the partial dissolution causes lower damping than at the beginning of the process. Performing isothermal measurements in a narrow temperature range at about 6 2 5 K i.f. increase w a s observed due to the change of the

structure (at 6 2 7 K on the Fig.6).

f b - 4

.

²

Al Swt

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Ag ^T

A

659

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650-

600-

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550-

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f

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f <

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Measuring isothermal1 in the temperature range of the precipitation and dissolution effecY using the above method, we can compare the results with those observed during continuous changing of the temperature, From the measurements at different heating or cooling rates we have found that the peak temperature of the.precipitationa1 and disso- lutional peak are closer to each other if T is smaller. Taking the extrapolated equilibrium vaiues of the,i.f. and d,.,m. and plottin these against the temperature, a quasi statlc spectrum c6n be obtaine!.

These are two different peaks for precipitation and dissolution, but they are only about 10 K apart from each other (Fig.7). This must be due to the fact that the peaks on the normal spectra are greater; the

Fig.7. Normal and "quasi static" spectra the energy needed for the observed during dissolution transformations can be taken

(heating) and precipitation from the mechanical vibration.

(cooling) In order to clear further de-

tails af this behaviour i.f.

measurements with different oscillation amplitudes should be made. On the other hand, we can conclude that this effect must be taken into con- sideration during the analysis of the i.f. spectra.

damping is higher if measuring takes place during heating or cooling.

References

(11 S. Kiss,

R.

Schaller, W. Benoit:

Phys.Stat.So1. (a) Vol. 92, K109 (1985) 121 S. Kiss, R . Schaller, W. Benoit:

Acta Met. Vol. 3 4 , No 11. 2151 (1986) [3] P . M . Anderson I11 and A.E. Lord J r . :

Mater. Sci. Eng. Vol. 43, 9 3 (1980)

141 S. Kiss, G. Posgay, 1.2. Harangozb, F.J. Kedves:

Journ. de Phys. Tome 42, ~'10. C5-529 (1981) 151 Editors: H . Beck, H.I. Guntherodt:

Glassy Metals 11, Springer-Verlag (1983) 161 M. Morin, G. Guenin, S. Etienne, P.F. Gobin:

Trans. Jap. Inst. Met. Vo1.22, 1 (1981)

f Summarizing all the results we can see that during the irreversible, and (in most

(HZ)

cases) during the reversible transformations, the d.m. is decreasing and 1.f. is In- creasing. In spite of these facts, if the temperature changes, the i.f. increases,

' 0 9 and the higher the heating or

cooling rate the greater the damping. From this we can conclude that the i.f. is deter- mined not only by the actual structure, but an extra damping due to the transformation 0.6 process also appears. This

.-.

a d

3

2

1

'O0 600 650 7 0 0 ~ ( ~ 7 5 0 ' means that a certain part of

A15wt%Ag

/

-

- -

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