HIGH DAMPING CAPACITY OF Mn-BASE γ-PHASE ALLOYS

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HIGH DAMPING CAPACITY OF Mn-BASE γ-PHASE

ALLOYS

K. Ito, M. Kobayashi, M. Tsukishima

To cite this version:

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JOURNAL DE PHYSIQUE

CoZZoque C5, suppZe'n~ent au n020, Tome 42, octobre 1982 page C5-641

HIGH DAMPING CAPACITY OF Mn-BASE y-PHASE ALLOYS K. Ito, M. Kobayashi and M. Tsukishima

Department of MetaZZmgy and Materials Science, Facutty o f Engineering, University of Tokyo, 11 3 Bunkyo-ku, Tokyo, Japan

Abstract The damping capacity as well as Young's modulus has been measured by flexural vibration(220-310Hz) as a function of temperature(125-370K) for (Mnl-XFex)O.95CuO.05(X=O.146-0.279) and Mnl-xNiX(X=0.096-0.240) alloys quenched from the Y-phase state. The temperature dependence of axial ratio of the metastable Y-phase has been determined and some alloys have been further examined by torsional vibration(l.2-1.6Hz).

Provided that the fct/fcc critical tempe5ature is high enough, the alloys show high damping capacity(Q =0.01-0.02) at 250-350K which consists of at least two peaks. They have both the character of the relax2tion type damping with the almost equal activation energy 5x10 J/mol. The damping behaviour of the examined alloys is essentially the same as known for Mn-Cu alloys.

1. Introduction The high damping capacity1) of manganese-r ich Mn-Cu alloys quenched from the high temperature face centred cubic Y-phase state has been revealed to be associated with the presence of micro- twins2)in the metastable face centred tetragonal ~ - ~ h a s e ~ - * ) . Mn-base alloys with many elements, including nicke19)and ironlO),are known to 1 1 ) show tetragonality corresponding to the anti-ferromagnetic ordering

,

when quenched to retain the metastable Y-phase.

It will be reasonably inferred from analogy to the Mn-Cu alloys that the Mn-base alloys of the face centred tetragonal Y-phase should

Table 1 Annealing temperatures (K)

*1) applied to specimens for damping measurement (A.C.)

*2) applied to specimens for lattice parameter measurement (W.Q.) " 3 ) applied to specimens for damping as well as lattice parameter

measurement (A.C.)

*4) No single Y-phase structure was obtained by air cooling.

"5) Lattice parameters were not determined for these alloys.

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c5-642 JOURNAL DE PHYSIQUE

Atomic fraction of Mn as 1-x

Temperature

/

K Fig.2 Characteristic tempera-

Fig.1 Young's modulus as a function tures. See text for definition of temperature and alloying concent- of Tx-ray and TEl. The data of ration. The latter is shown by fig- Mn-Fe a$$pys were reported ures (100 x X = ) 27.9 22.9 etc. earlier

.

yield commonly a high damping capacity. This was really observed in some Mn-Ni a l 1 0 ~ s ~ ' ~ ~ ) a n d the a ~ t h o r s ~ ~ ) f o u n d it earlier in Mn-Fe alloys. In the present work, the damping capacity as well as Young's modulus and tetragonality is measured as a function of temperature for Mn-Ni and Mn-Fe-Cu alloys. Binary Mn-Fe alloys were diffi- cult to quench13&o that copper was added in this time as was done by Endoh and 1shikawa14)

.

2. Experimentals The alloys were prepared from electrolytic raw metals by high-frequency induction melting in magnesia crucibles under flowing argon gas and were cast into either cylinders 40mm in diameter using a steel mould (Mn-Ni alloys of X>0.153) or sheets 2.5mm thick using a copper mould (Mn-Fe-Cu alloys and Mn-Ni alloys of X(0.168). They were processed by cold working, being intermitted several times by inter- mediate annealings followed by water quenching, to sheets 0.75mm in thickness or to wires 0.38mrn in diameter. By final annealings, specimens were sandwiched by titanium sheets 0.8mm thick and held lOmin at the temperatures shown in Table 1. They were then water quenched (W.Q.) or pulled out to cooling zone of the furnace kept at room temperature

(A.C.). These annealing conditions were determined to obtain the single Y-phase structure. The annealings were made in the argon atmosphere. Only Mn-Ni alloys of X>0.153 were annealed in fused silica tube for 48h at 1223K in the course of the processing.

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-

Oo 5 10 1

shear strain

Fig.3 Damping capacity vs. strain amplitude (1.3Hz).

.

(Mm,FeXWw05

O '

. ~ b #

. . ~ A O

' 3 ~ 0 ' 4 & ' ~ Temperature

/

K

Fig.4 Damping capacity of higher concentration alloys. free decay curves of the flexural vibration of sheet specimen (220 -

310Hz) and Young's modulus was calculated from the resonant frequency. Wire specimens of some characteristic alloys were further examined by an inverted torsional pendulum method (1.2

-

1.6Hz). The maximum shear

strains at the specimen surface were 1 x if not stated specially.

The tetragonality c/a was measured by the standard X-ray diffracto- meter method. Each specimen was analyzed by the X-ray fluorescence.

3. Results and Discussion Younq's Modulus The temperatures of the

modulus minimum in Fig.1 are shown in Fig.2 as TEL. The agreement of these results with those of Masumoto et al15)and of Hgysch and T6r6k 16)

is poor, but fairly good with the data of Honda et a1

.

Tetragonality The temperature at which the broadening of the t311) di- ffraction line appeared and disappeared is plotted in Fig.2 as TX-ray. The coexistence of the fcc and fct phases was observed for Mn-Ni alloys in the hatched region of Fig.2, which should be attributed to the seg- regation of components, The characteristic temperatures of the Mn-Ni alloys are located in the hatched region of Hocke and Warlimont' s17) Fig.9. The Tx-ray of the Mn-Fe-Cu alloys approaches with decrease of X to the N6el point determined by Endoh and 1shikawal4). The axial ratios at the temperature of the damping peak are presented in Fig.7.

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JOURNAI. DE PHYSIQUE

Temperature

/

K

Fig.5 Damping capaci

0 X = 0.146 0 0,190 0 0.263 (1.2 -1.6 HZ ) Temperature

/

K ty of Mn-Fe-Cu alloys. 1 9 ) magnetic materials

.

Dependence of Damping Capacity on Temperature and Composition Alloys with lower characteristic temperature show a low damping capacity with a small peak at about 250K(see Fig.4). With increase of the characteristic temperature, the damping capacity at lower temperatures increases at first, and the peak at 250K grows up suddenly when the characteristic temperature goes higher than 2 5 0 K . The TE1,rather than the Tx-ray, should be adopted as the critical characteristic temperatures(cf Fig.2 with Fig.4,5, and 6)

.

The peak goes only a little higher with further decrease of the concentration but its width becomes larger to the side of higher temperatures. This broadening must be caused by appearance of at least one more peak at a higher temperature, as clearly demonstrated by Fig.: for Mn-Fe-Cu alloys. The peak at a higher temperature is less recog- nizable in the case of Mn-Ni alloys (Fig.6) and was still not reported for Mn-Cu alloys, though their peak width was known to be too large when compared with the one calculated as a single process relaxation peak8).

Dependence of Dampinq Capacity on Frequency The decrease of frequency shifted both of the two peaks in parallel to lower temperatures, from

4

which the activation energy has been calculated to be about 5 x 1 0 J/mol The values are roughly the same for both Mn-Fe-Cu and Mn-Ni alloys and

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Temperature

/

K Temperature

I

K Fig.6 Damping capacity of M n - ~ i alloys.

Formal Representation of Relaxation Dampinq The peaks must be resulted from any relaxation process associated with migration of twin bound- ariesZ0)which are at the same time anti-ferromagnetic domain boundarieg). The damping capacity can be formally expressed by a force constant K and a frictional. parameter F:

E=(U-//E$) + (x&'L)

....

(1) F(dx/dt)

+

K x

= x @ .

. . .

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The equation (1) denotes the strain & caused by the applied stress O\ and the displacement of a domain boundary x, and the equation (2) re- present$ balance of forces acting on the boundary, where ES , X I and are the elastic modulus after saturation of the boundary migration, the tetragonal distortion (=l-c/a)

,

and the width of a domain, respectively

.

These equations yield a relaxation peak with a relaxation time T = F o * exp (H/RT) /K and a relaxation strength A M / M = ~ E ~ / ( K $ )

,

under the

2

assumption that R E S /(K!)

<<

1 and F=Fo.exp(H/RT)

.

Heights of peaks (or shoulders) are normalized with respect to

2~

and shown in Fig.7 with their original values, where the damping capacity and the elastic modulus of Mn-Cu alloys are taken from the report of Sugimoto et a18). The value of

KI

is concluded from this figure to become smaller with increase of alloying concentration, on the other hand,the ratio F/K seems to be affected little by the alloying elements, that is, the peak temperatures are similarly shifted by frequency regardless of the elements. A physical meaning of both F and

K is left at present to be unclear. Acknowledgements

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C5-646 JOURNAL DE PHYSIQUE

Fig.7 Heights of damping capacity at

two peak temperatures measured by flexural vibration and corresponding axial ratio presented as a function of alloy composition.

the investigation. The torsional pendulum equipment was offered to

use by DrJ(.Iwasaki(The Institute of Physical and Chemical Research). The authors acknowledge sincerely

his courtesy. They thank also

Prof.S.Goto and Mr.I.Asakura for the advice and assistance by anal- ysis of composition. This research is indebted to Grant in Aid for Scientific Research Project No. 346167-1978.

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