INTERNAL FRICTION MEASUREMENTS APPLIED TO THE STUDY OF REVERSE MARTENSITE TRANSFORMATION IN A Cu - Zn - Al ALLOY

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INTERNAL FRICTION MEASUREMENTS APPLIED TO THE STUDY OF REVERSE MARTENSITE TRANSFORMATION IN A Cu - Zn - Al ALLOY

Z. Bojarski, J. Ilczuk, T. Panek, H. Morawiec

To cite this version:

Z. Bojarski, J. Ilczuk, T. Panek, H. Morawiec. INTERNAL FRICTION MEASUREMENTS APPLIED TO THE STUDY OF REVERSE MARTENSITE TRANSFORMATION IN A Cu - Zn - Al ALLOY. Journal de Physique Colloques, 1983, 44 (C9), pp.C9-241-C9-246.

�10.1051/jphyscol:1983932�. �jpa-00223379�

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JOURNAL DE PHYSIQUE

Colloque C9, supplgment au n012, Tome 44, d k e r n b r e 1983 page C9-241

INTERNAL FRICTION MEASUREMENTS APPLIED TO THE STUDY OF REVERSE MARTENSITE TRANSFORMATION IN A Cu

-

^Zn- A1 ALLOY

2. B o j a r s k i , J . I l c z u k , T. Panek and H . Morawiec

I n s t i t u t e of t h e Physics and Chemistry of Metals, S i l e s i a n University, 40-00 7 Katowice, Bankowa 12, Poland

~Gsurng

-

On a e'tudi6 l'influence des transformations martensi- tiques cycliques,rkversibles sur les changements de frottement interne pour l'alliage CU-(14.5%en pds)~n-[8.5%en pds)~l. On a observ6 l'abaissement des temperatures caract6ristiques de la transformation apres le deuxihe cycle par rapport aux dchanti- llons tremp&s des hautes tempkratures. La cause essentielle du caractkre diffkrent de la marche de transformation martensiti- que inverse est la diff6rence des concentrations des lacunes trempkes.

Abstract- Investigations were made of the influence of cyclic reversible martensitic transformations on variations in internal friction for a Cu- (14.5%wt.) Zn-(8.5%wt.) A1 al1oy.A drop in characteristic transformation temweratures was found after the second cycle relative to those for samples quenched from high temperatures.The fundamental reason that the reverse martensitic transformation for samples obtained after quenching is different from that obtained after successive cycles is the difference in concentration of quenched in vacancies.

1. INTRODUCTION

.

Cu-Zn-A1 alloys,which after quenching show martensitic structure,exhi- bit the shape memory effect.Bearing in mind the potential importance of these alloys for practical applications,the influence of cyclic reversible martensitic transformations on the stability of their properties including the percentage shape recovery and characteristic temperatures of transf~rmation~is of particular significance.

Investigations of changes in properties and structure after successive transformation cycles and low temperature annealing in the range of the parent phase have been reported in several papers [l

-

7 1 .Due to appreciable differences in the chemical compositions of the alloys tested by these authors and the selective nature cf the investigations, considerable difficulties are encountered in drawing definitive conclusions from the published results.

The object of the studies reported here was to study the differences in the course of the reverse martensitic transformation M-fil in samples quenched from high temperature and after successive "heating

=

cooling" cyclesfand also the consequent changes in the properties and structure of the martensite.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983932

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JOURNAL DE PHYSIQUE

2. MATERIALS AND METHOD

.

Alloy of composition Cu

-

( 14.5%wt.) ~n

-

( 8.5%wt .) A1 was melted in an induction furnace; the purity of the materials was: Cu

-

99.97 %,

A1

-

99.95 %, Zn - 99.95 %.After homogenising annealing at 1220 K for 12 hours the ingot was hot rolled to a thickness of 0.7 mm.Samples were quenched from temperatures 970,1070 and 1170 K in ice water-Curves of internal friction (IF) against temperature were measured using a ty- pe RAK

-

1 audio frequency relaxator for samples of dimensions 35 x 10 x 0.7 mm in the temperature range 270

-

⁵²⁰^Kwith fregyencies range from 400 to 700 Hz and deformations amplitudes &-2.10

.

^{Rate of}

temperature change was 1-2 K/min.Supplementary methods emploved were positron annihilati~n~electron microsc~py~high temperature X-ray diffraction and measurement of mechanical properties.

3. RESULTS

.

After quenching the samples exhibited martensite of 18R and 2H structure determined by electron diffraction method. X-ray diffraction tests on these samples showed the presence of small quantities of (3, phase.Measurement of mechanical properties showed significant diffe

-

rences between those properties found for samples quenched from 970K and for those after the first reversible transformati0n.A marked drop in strength and yield point and increase in extension are exhibited by the samples after the first transformations cycle relative to samples quenched from high temperature.Electron microscopy examination of samples after quenching and after cyclic transformations showed no significant differences in the martensite structure. For this reason the defect structure of the markensite and the matrix phase was studied using positron annihilation.Measurements made of maximum annihilation quanta unidimensional angular distribution, i.e. N(@= 0 ) after successive 293=353 K and 2 9 3 z 4 7 3 K cycles are shown on Fig. la.

A considerable change in number of counts after the first transformation may be seen,both for the martensite and the matrix phase,which is the result of reduction in concentration of quenched-in vacancies during cooling from high temperature.The energy of vacancy formation in the

p

phase [8] of Cu-Zn alloys is very low which means a very high concentration of vacancies, cv = low4 to in the quenched samples.

Such a large vacancies concentration causes an increase in strenath,as ascertained for Cu-Zn by Green and Brown [9]

.

Analysis of positron annihilation parameters in successive 293=473 K transformation cycles ( Fig. lb ) indicates the generation of new defects, that is dislocations[6,7]

.

p&q,-&a. Variations of norma-

lised number of cases of two- photon positron annihilation for collinear gamma quanta N

(0

= 0 )

.

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The significant differences between the first reverse martensitic transformation and successively following transformations shown up on the internal friction temperature curves.

Fig,-&&, The normalized area

---

( A ) under the inverted parabo- P

la as a function of the number of reversible martensite cycles

2 4 6 8 ^{( n ) .}

Fig.2 shows the IF curves found for a sample quenched from 970 K,then heated to 420 K and cooled from that temperature-On the heating curve no clear peak corresponding to the M-bl transformation can be seen.

riq.

2. Curves of internal friction as a function of temperature for a sample quenched from 970K for the first transformations cycle:

A

-

heating curve, B

-

cooling curve,

f

-

⁴²⁰^Hz

^,

E - 2 . 1 0 - ~

.

The cooling curve shows a high IF maximum corresponding to the transformation taking place which is evidence that a transformation from martensite to the parent phase took place during the preceding Qeating process although no corresponding peak is to be seen on the Q- = f ( ~ ) curve. When heating the quenched sample to higher temperatures a distinct IF peak appears at temperature 480 K associated with the process taking place in the (jl matrix phase ( ~ i g . 3 )

,

while on the cooling curve this peak is not observed. The IF curves obtained for the second heating and cooling cycle for the same sample are shown on Fig.4:. The Q - ~ ( T ) curve obtained during heating of the sample exhibits a double peak attributed to the reverse martensitic transformation ( T1 = 317 K and T2 = 329 K )

,

while during cooling the peak corress- ponding to the

b,-M

transformation appears at T3 = 311 K. Similar results as for the second cycle were also found for the next two con- secutive cycles and for the samples quenched from 1170 K.

For the purpose of verifying the IF measurement results direct examination of these transformations was made using the high temperature X-ray method. The obtained results are as follow: 1-st cycle As =358K;

Af = 393 K, Ms = 308 K, Mf = 293 K, 2 -end cycle As = 308 K,

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c9-244 JOURNAL DE PHYSIQUE

Af - = 338K, Ms = 303K, M f = 293K. Shifting of these transformations to- wards lower temperatures after the second heating cycle, relative to those for the prior quenched samples,is clearly visible.

Fig1-?, Curve of internal friction as a function of temperature for a sample quenched from 1070K for the first transformations cycle: A

-

^heating,B

-

cooling, f

-

~ O O H Z , ~ ~ 2 . 1 0 - ~ .

F&g,-4+ The curve Q - ~ = f (T) for the second transformations cycle: f

-

⁴⁸⁰^Hz,^E^{- 2}

Similar results were achieved by Dejonghe et al. [ 5 ] who explained the absence of a peak on the IF curve during heating of the quenched martensite by the pinning of the martensite plate interfaces. The asymme- tric form of the IF peaks,as seen on Fig.3 and 4,is explained by dis- continuity of the martensite transformation.

Yening et al. [lo] stated that the dampYng due to the martensitic transformation is similar to that caused by pinning of dis1ocations.Hence it would appear to be justified to attribute the peak on the IF curve

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to dislocations on the interfaces.

The investigations of Gotthardt and Mercier [ll] showed that the interfaces between the martensite plate and the

b1

phase are formed of many dislocations which are mobile and move durinq deformation. From consideration of this data it was decided to investigate the influence of martensite deformation achieved after quenchinq from a high temperature on the form of the IF curve during cyclic heating and cooling processes.Results obtained for the first " heatingzcooling " cycle are shown on Fi9.5.

F&q,-s, Curves of internal friction as a function of

temperature for a sample quenched from 1070K and deformed by 0.6 % in a tensile test; first " heatingzcooling I'

cycle, A

-

^heating,^B

-

cooling, f N 560 HZ, E 2

Martensite deformation after high temperature quenchinq does not change the form of the IF curves obtained during the first heating,that is no distinct M - 4 transformation peak occurs,but an additional peak,relative to the non-deformed sam~le,appears at T -440K. At temperature -510K one more peak is found whose occurrence was also ascertained in [12] where it was interpreted as being due to the effect of dislocations interaction with a stress field from the copper atom pairs occupying the lattice points of the zinc sublattice. The appearance of the peak at ~ 4 4 0 K could not be fully explainediit also occurs in further heatinq cycles.

Using various methods it was ascertained that in the tested alloy there are differences in temperatures of reverse martensitic transformation ( As and Af) as between martensite obtained after quenching from a high temperature ( fi phase) and martensite obtained after cyclic heating and cooling transformations in the range of the

4

^pha-

se of DOj structure-The martensite obtained after cyclic treatment from the 6, phase region exhibits lower transformations temperatures them the martensite quenched from the (?I phase. The greatest differences occur for transformation points As and between the first and second heatinq cycles. The lowering of temneratures found after cyclic heating and cooling is in agreement with the data given in C1,4] but the authors of [ 2 , 3 ] reported a rise in transformation tem~erature following additional thermal treatment-It is noteworthy that some of the Cu -Zn

-

A1 alloys studied by various authors had widely varied chemical compositions which causes significant differences in the temperature of ordering transition from B2 to DO3 as well as in martensitic transformation temperature and can even cause a tendency to decom-

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C9-246 JOURNAL DE PHYSIQUE

position of the

b1

phase in the equilibrium phases.

4. CONCLUSIONS.

1. In the tested alloy significant changes in the physical and mechanical properties were found as between the martensite obtained after quenching and that obtained after the first reversible transformation.

2. The esse'tial cause of the changes in physical and mechanical pro- n pertiesfand particularly internal friction, of the martensite and in the characteristic transformation temperatures is the difference in concentration of quenched-in vacancies.

3. Deformation of the quenched martensite does not influence the form of the IF curve in the first heating cycle,i.e. the reverse transformation process M

-PI

is not reflected.

5. REFERENCES.

1. RAPACIOLI R.,CHANDRASEKARAN M.,DELAEY L.,Shape Memorv Effects in Alloys,ed.by J. Perkins,Plenum Press,New York 1975,p.365 2. SCHOFIELD D.,MIODOWNIK A.P., Met. Technology &(1980)167

3. PLANES A.,MACQUERON J.L.,MORIN M.,GUENIN G., Phys.Stat.Solidi(a) 66 ( 1 9 8 1 ) 717

-

4. KOVAL JU.N.,KONDRATEV S.JU., MUSIENKO R.JA.,HANDROS L.G., JAROSLAVSKIJ G.JA., Fiz.Met.Metalov.

50

( 1 9 8 0 ) 1326

5. DEJONGHE W.,DELAEY L.,DE BATIST R., VAN HUPBEECK J.,Met.Sci.

11 ( 1 9 7 7 ) 523

-

6. PERKINS J.,Met.Trans.

4

( 1 9 7 3 ) 2709

7. MA1 C.,GUENIN G.,MORIN M.,LIVET F.,GOBIN P.F., Mater.Sci.Eng.

4 5 ( 1 9 8 0 ) 217

-

8. PAEVEL J.

,

COTTAM R., DELAEY L.

,

^Z

.

^Metallk.

66

( 1975 ) 453 9. GREEN H.,BROWN N., Trans. AIME

197

( 1 9 5 3 ) 1240

10. YBWING W.,HUIMIN S.,ZIRAN X., YIFENG Z.,JINSONG Z.,ZHIFANG Z., ZHAOJIN Y., J. Physique

42

( 1 9 8 1 ) C5-1049

11. GOTTHARDT R. ,MERCIER O., J. Physique

42

( 1981) C5-995

12. GHILARDUCCI DE SALVA A.,AHLERS M.,J. Physique

42

( 1 9 8 1 ) C5-1001