Thermoelastic behavior of the martensitic transformation in ß′ NiAl alloys

Scripta METALLURGICA

Vol. 6, pp. 1209-1214, 1972 P r i n t e d in the U n i t e d States

P e r g a m o n Press,

T H E R M O E L A S T I C B E H A V I O R OF THE M A R T E N S I T I C T R A N S F O R M A T I O N IN ~' NiAI ALLOYS Y. K. Au and C. M. W a y m a n D e p a r t m e n t of M e t a l l u r g y and M i n i n g E n g i n e e r i n g and Materials Research Laboratory U n i v e r s i t y of Illinois at U r b a n a - C h a m p a i g n , Urbana, Illinois

(Received O c t o b e r

61801

27, 1972)

INTRODUCTION The i n t e r m e d i a t e p h a s e 8' NiAI extends over a large c o m p o s i t i o n 1 range. G u a r d and T u r k a l o 2 f i r s t o b s e r v e d that some n i c k e l rich alloys undergo a martensitic from the h i g h

transformation when quenched

t e m p e r a t u r e B' phase.

s t r u c t u r e of the m a r t e n s i t e served no m a r t e n s i t i c

to room t e m p e r a t u r e

Rosen and G o e b e l 3 d e t e r m i n e d

to be the o r d e r e d CuAu type

transformation

( L I ) and obo in s p e c i m e n s q u e n c h e d to 0°C from

temperatures below

1000°C or in any alloy c o n t a i n i n g

ic % Ni.

the d e p e n d e n c e of the M

However,

the

less than 62 atom-

t e m p e r a t u r e on c o m p o s i t i o n 1-3 these e a r l i e r i n v e s t i g a t i o n s . Litvinov, S

remains et al.,

unclear, 4

were

condition

considering

the first to i n d i c a t e

for the m a r t e n s i t i c

demonstrated

this b y p l o t t i n g

after a s l o w h e a t i n g

that q u e n c h i n g

transformation

is not a n e c e s s a r y

in NiAI.

These authors

the d i l a t a t i o n of a t r a n s f o r m e d 6 4 % Ni alloy

and cooling cycle

(ranging from room t e m p e r a t u r e

to 500°C). 10°C.

F r o m the d i l a t a t i o n curves, the M S was found to be i00 I+ 5 Recently, Enami and N e n n o r e p o r t e d a shape m e m o r y e f f e c t to be

associated with later,

Enami,

the m a r t e n s i t i c p h a s e in an A I - 6 3 . 2 % Ni alloy,

Nenno,

that the m a r t e n s i t e [iii}

twins.

and

and S h i m i z u 6 d e t e r m i n e d b y e l e c t r o n m i c r o s c o p y substructure

However,

in an A I - 6 3 . 2 % Ni alloy consists

of

Enami and N e n n o 5 claimed that the shape

m e m o r y e f f e c t in this alloy does not c o r r e s p o n d

to the reverse trans-

formation

the shape m e m o r y be-

to the 8' phase.

havior observed

in o t h e r alloys. 7

that p r e r e q u i s i t e s transformation phases

Wayman

and S h i m i z u 7 h a v e s u g g e s t e d

for the shape m e m o r y b e h a v i o r

is t h e r m o e l a s t i c ,

are ordered,

it remains

This c o n t r a s t s w i t h

and

are

(i) the m a r t e n s i t i c

(2) the p a r e n t and the m a r t e n s i t i c

(3) the m a r t e n s i t e

to be shown if the m a r t e n s i t i c 1209

is i n t e r n a l l y twinned. transformation

Hence,

in NiAI alloys

Inc

1210

MARTENSITIC

TRANSFORMATION

IN 8' NiAI ALLOYS

Vol.

6, No.

is thermoelastic. The present communication the NiAI martensitic

reports on further characteristics

transformation,

with emphasis

of

on alloys contain-

ing less than 64% Ni and their low temperature behavior. EXPERIMENTAL RESULTS Specimens

containing 60.0%,

63.4%,

64.0%,

and A1

(99.999)

62.0%,

62.4%,

62.8%,

63.1%,

and 65.0% Ni were prepared by arc melting Ni

63.2%,

(99.999)

on a water cooled copper hearth under one atmosphere

of high purity argon.

Vanadium or titanium was melted for gettering

before melting the alloys.

Each alloy was melted six times,

quartz capsules with argon,

and homogenized

Such specimens were water-quenched

sealed in

at 1200°C for three days.

to room temperature.

The alloys

were then chemically analyzed to determine both the impurities exact compositions. method,

and

The former, b y the flame emission spectroscopic

resulted in parts per million

impurities

The latter,

W

less than i00

V

I0

Cu

i0-i00

Fe

5-50

done by a wet titration method,

accurate

resulted in 0.2% agreement with the values calculated

to 0.3-0.4%, from the amount

of starting materials. All the alloys were polished reagent 2°8 was used as an etchant. were observed

for microscopic observation. Alloys containing

to be completely martensitic

Marble's

63.4% Ni or higher

at room temperature.

Mar-

tensitic structures were not observed at room temperature in specimens containing

less than 63.2% Ni.

The alloys containing

less than 63.2% Ni

were studied with a metallograph equipped with a cooling stage, formation of martensite was determined b y surface relief. ture of investigation

The tempera-

ranged from room temperature to approximately -196°C.

It was observed that the M centration.

and the

decreases linearly with a decrease in Ni cons The data are plotted in Fig. i, and the linear behavior

12

Vol.

6, No.

12

extrapolates

MARTENSITIC

to the M

measured

TRANSFORMATION

by

Litvinov,

IN 6' NiAI

et al.,

4

ALLOYS

1211

for a 6 4 % Ni a l l o y

S

using was

the d i l a t a t i o n

observed

A s , and Af

to b e

m e a s u r e m e n t method.

thermoelastic

temperatures

are w i t h i n

lief

for a 6 3 . 1 % Ni a l l o y

Fig.

2.

relief

When

and h e a t e d

slowly

the s p e c i m e n

disappeared

was

in r e v e r s e

for m a n y

with

cycles

tion.

was h e a t e d

The

elastic

relief

approximately

The

still

show

and

the

the M

to room

same the

was

The s u r f a c e

temperature,

specimen same

could be

relief

martensitic

to o b s e r v e

reverse

10°C.

the Ms,

the M s to Mf is shown

completely

in a w a t e r b a t h

in character,

from

order.

transformation

small h y s t e r e s i s :

slowly heated

and

caused by

very

cooled

The 63 .4,% Ni a l l o y w h i c h was perature

The m a r t e n s i t i c

the

measured

to be

at room

in the

cooled

tem-

transforma-

is also

60°C

re-

sequences.

reverse

transformation

Mf,

thermo-

+ 5°C.

S

The The

6 3 . 1 % Ni a l l o y w a s

a l l o y was

ture

(above

were

The

specimens

the Ms),

they w e r e

pletely,

after being

ductile.

to room

and

but

temperature,

there was

to make

little

no r e m a i n i n g

in an a l c o h o l

could b e b e n t

the o r i g i n a l surface

18mm x

at room

to the m a r t e n s i t i c

specimens

effect.

specimens

ductility

immersed

completely Such

the shape m e m o r y

polished

exhibited

transformed

comparatively

When heated

to e x a m i n e

cut and m e c h a n i c a l l y

4 m m x 0.3mm.

-20°C,

used

shape w a s

tempera-

bath phase

at and

to some

3-4%.

recovered

com-

relief.

DISCUSSION The p r e s e n t transformation alloys

experiments

in NiAI

containing

formation

Combining

of o t h e r w o r k e r s , 3'6 it is NiAI

satisfies

is t h e r m o e l a s t i c , (3)

(2)

the m a r t e n s i t e

specimen

that

the

found

It has b e e n

a sub-ambient

results that

the m a r t e n s i t i c verified

martensitic

of the p r e s e n t w o r k

the m a r t e n s i t i c

using trans-

and

that

transformation

in

p r e r e q u i s i t e s for the shape m e m o r y b e h a v i o r as 7 and Shimizu, namely, (i) the m a r t e n s i t i c t r a n s f o r m a t i o n

In the p r e s e n t NiAI

Ni

that

certain

noted by Wayman

and

established

is t h e r m o e l a s t i c .

62.0-63.2%

occurs.

have

the p a r e n t

and

is i n t e r n a l l y

experiments

corresponds

with

the that

the m a r t e n s i t i c

phases

are ordered,

twinned. shape of the

recovery

process

transformation

of a d e f o r m e d back

to the

1212

MARTENSITIC

p a r e n t phase.

TRANSFORMATION

IN 8' NiAI A L L O Y S

Vol.

6, No.

Thus,

the shape m e m o r y b e h a v i o r in NiAI is s i m i l a r to 7 that in a n u m b e r of materials, e.g., TiNi, CuZn, CuAiNi, and FePt.

ACKNOWLEDGMENTS This r e s e a r c h was

s u p p o r t e d b y the U. S. A t o m i c E n e r g y C o m m i s s i o n

(Contract A T ( I I - I ) - I I 9 8 )

through the M a t e r i a l s

the U n i v e r s i t y of Illinois at U r b a n a - C h a m p a i g n .

R e s e a r c h L a b o r a t o r y at The authors w o u l d also

like to thank P r o f e s s o r S. N e n n o for a p r e p r i n t of r e f e r e n c e 6, and Mrs.

J u d i t h Baker

for c a r r y i n g out the c h e m i c a l analysis.

REFERENCES

i.

M. Hansen: " C o n s t i t u t i o n of B i n a r y A l l o y s , " M c G r a w - H i l l , N e w Y o r k (1958), p. 119.

2.

R . W . Guard and A. M. Turkalo: "Mechanical P r o p e r t i e s of I n t e r m e t a l l i c C o m p o u n d s , " W i l e y and Sons, N e w York (1959), p. 141.

3.

S. Rosen and J. A. Goebel: pp. 722-24.

4.

V. S. Litvinov, L. P. Z e l e n i n and R. Sh. Shklyar: Met. and M e t a l l o q r a p h y , 31, i, (1971), pp. 137-41.

5.

K. Enami and S. Nenno: pp. 1487-90.

6.

K. Enami,

7.

C. M. W a y m a n

8.

G. Kehl: "Principles of M e t a l l o g r a p h i c L a b o r a t o r y P r a c t i c e , " 3rd ed~, M c G r a w - H i l l , N e w Y o r k (1949), p. 415.

Trans.

TMS-AIME,

Metallurqical

S. N e n n o and K. Shimizu: and K. Shimizu:

Trans.,

2nd ed.,

242,

2,

(1968), Phys.

(1971),

to be p u b l i s h e d .

M e t a l S c i e n c e Journal,

in press.

12

Vol.

6, No.

12

MARTENSITIC

I

I

TRANSFORMATION

I

IN 6' NiAI A L L O Y S

i I

I

I I I

I00 I I I

/

50

0

-50 °C -I00

-

-150

-

- 200

-

o

present experiment

o Litvinov, et. al. ( 4 ) I I I I I

-250

I I

-

I

61

60

I I

I

62

I 63

I 64

I 65

Atomic % Ni Fig.

i.

M

t e m p e r a t u r e of ~' NiAI alloys as a f u n c t i o n of s Ni c o n c e n t r a t i o n .

1213

1214

MARTENSITIC

Fig.

2.

TRANSFORMATION

S u r f a c e relief

IN ~' NiAI A L L O Y S

Vol.

6, No.

for an A I - 6 3 . 1 % Ni alloy d e m o n s t r a t i n g

the t h e r m o e l a s t i c b e h a v i o r of the m a r t e n s i t i c

trans-

formation.

frames

The d i f f e r e n c e b e t w e e n s u c c e s s i v e

A through H is I°C.

Magnification

24x.

12