Mössbauer study of precipitation in FeNiMo and FeNiCoMo maraging alloys

Mössbauer study of precipitation in FeNiMo and FeNiCoMo maraging alloys

Scripta METALLURGICA Vol. Printed 8, pp. 15-22, in the U n i t e d 1974 States Pergamon Press, Inc. MOSSBAUER STUDY OF PRECIPITATION IN Fe-Ni-...

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Scripta

METALLURGICA

Vol. Printed

8, pp. 15-22, in the U n i t e d

1974 States

Pergamon

Press,

Inc.

MOSSBAUER STUDY OF PRECIPITATION IN Fe-Ni-Mo AND Fe-Ni-Co-Mo MARAGING ALLOYS G E N I N , G. LE CAER de M4tallurgie , Ecole des Mines 54000 Nancy , France. Ph. MAITREPIERRE and B.J. THOMAS Groupe M@tallurgie Physique , Institut de Recherches de la Sid@rnrgie FranQaise , 78104 Saint-Germain-en-Laye,France. J.M.

Laboratoire

Received

October

25,

1973)

MSssbauer spectroscopy is potentially a very valuable technique for the study of precipitation phenomena in iron-base alloys since

~TFe is one of the few natu-

rally occuring isotopes which give rise to a large MSssbauer resonance

(1,2). The

technique has been notably applied to the study of precipitation in iron rich Fe-Mo alloys by Marcus, quenched alloys,

Schwartz and Fine

(3,4). These authors observed that, in the as-

the six peaks of the iron spectrum were broadened into six envelopes

which were analysed as a superposition of three sets of peaks one set each for iron atoms with 0,1 and 2 molybdenum atoms amongst their nearest neighbours.

During aging

the form of the peaks was observed to change progressively with aging time. This behaviour corresponds to modifications in the relative intensities of the three subspectra and was attributed to a redistribution of the Mo atoms in the alloy.

Simulta-

neously a new peak appeared in the center of the spectrum due to the precipitation of a paramagnetic phase containing a fraction of the iron atoms. The isomer shift associated with this peak was shown to be compatible with the isomer shifts of Fe Mo intermetallic compounds studied by the same authors (3). The interpretations x y were largely supported by the results obtained using other techniques on these and similar alloys (3, 4, 5). MSssbauer spectroscopy has recently been applied to ternary Fe-Ni-Mo and quaternary Fe-Ni-Co-Mo alloys (6, 7, 8).

The results obtained are quali-

tatively similar to those described above for Fe-Mo alloys.

In the present work MSssbauer spectroscopy has been used to study the aging behaviour of an Fe-12.2 at % Ni - 6.2 at % Mo alloy and an Fe-17.3 at % Ni-8.4 at % Co-2.9 at % Mo alloy for which a considerable amount of information relative to the precipitation processes had already been obtained by classical techniques electron microscopy,

X-ray diffraction

(hardness,

(9, 10, 11). The MSssbauer experiments were

performed at room temperature on electrolytically thinned 20 ~ - thick foils using an ELRON transmission MSssbauer spectrometer and a 57Co source in a palladium matrix. 15

16

MOSSBAUER

STUDY

OF

PRECIPITATION

IN M A R A G I N G

ALLOYS

Vol.

8, No.

Fe-No-Mo alloy. The first

set of M S s s b a u e r

6.2 Mo alloy a s - q u e n c h e d at 450°C.

spectra was obtained from samples of the F e - 1 2 . 2 N i -

and q u e n c h e d

This a g i n g t e m p e r a t u r e

observations

and aged for 2, 8, 16, 30, 64 and 122 hours

was chosen because previous

(11) has shown that a single p r e c i p i t a t i o n

times up to 200 hours at 450°C. of the m a r t e n s i t e logy. R e v e r s i o n

The p r e c i p i t a t e s

process was active for a g i n g

nucleate

rapidly

and their growth leads to a characteristic

austenite

is not observed before

electron m i c r o s c o p y

on the d i s l o c a t i o n s

" ribbon-like

" morpho-

200 hours aging.

0.12

0.10 0.06 0.0~

0.05 0.O4

'¢ o,04 0.02

0.02

O.Ob

3 7

(~

5

4

~

2

".

oF_.~-~-~-4-~-2

i

~~'~

VELOCITY(mm,'=)

~'4

~

6

-a-

-b-

0.12

0.10

O.O8

Fi~. I - R o o m - t e m p e r a t u r e M S s s b a u e r spectra of the Fe-12.2 Ni-6.2 Mo (at %) alloy. - a - As-quenched - b - Aged 30 hours at 450°C - c - Aged 122 hours at 450°C.

z I-

i ,,¢

r

o.o4

+

o e,

,

,~,

,~

,_, _1 2 1

,

0

1

,

2

,

VELOCITy(minis) -C-

Three

selected

from the u n a g e d

spectra are shown in Fig.

sample

ding to 3 distinct

(Fig.

fields are r e s p e c t i v e l y

I. The fine structure

I a) can be d e c o m p o s e d

environments

of the Fe atoms

into 3 basic

(labelled

of the spectrum

spectra correspon-

I, 2 and 3)- The hyperfine

H I = 337 ~ 0.5 k O e , H 2 = 293 ± 2 k O a a n d H 3 = 250 ~ 5 kO e

F o l l o w i n g the i n t e r p r e t a t i o n

of Marcus and A1.

atoms which have no i n t e r a c t i o n

with Mo atoms.

-~

VELOCITY(r.,,./=)

(3,4), peak I can be a s s o c i a t e d This means

to

that these atoms have no

1

Vol.

8, No.

1

Mo n e i g h b o r s

MOSSBAUER

in the first

Peaks 2 and 3 c o r r e s p o n d determining

STUDY

OF

two shells

(12) or p o s s i b l y

the areas u n d e r the various peaks,

obtained from various models It was shown

(11) that,

to the p r e c i p i t a t i o n

tent. A f t e r phase.

The i n t e n s i t i e s

peak is c l e a r l y apparent

Measurement

(Fig.

(Fig.

compounds

In order to study the k i n e t i c s

where X is the fraction

of the p a r a m a g n e t i c

can be

Fe con-

peak shows that

The isomer shift

of the p r e c i p i t a t i o n

process

of Fe atoms in the p r e c i p i t a t e

experiment

on a sample

of Xp with time is p l o t t e d

Q9

phase,

of the precipifor Fe Mo x y

through the variawe define Xp = X/X F

after a given aging time and

process.

A value

of X F

~

0.122 was

in which the p r e c i p i t a t i o n in Fig.

,

was com-

2.

r

~

,

,

r

I

i

.#

Q8

o7

i

I

// /

"1

/'

X

/

/ s

J

o~

ts

o,3

/

I

/

/

/

/

o

/

X

0,2

sharply and a paraThis decrease

with the isomer shift m e a s u r e d

at the end of the p r e c i p i t a t i o n

The v a r i a t i o n

of the various

phase with an a p p r e c i a b l e

of Fe atoms in the p r e c i p i t a t e

obtained from a separate plete.

of Mo

(3) (13).

tion of the c o n c e n t r a t i o n

X F the f r a c t i o n

sites.

Ic) most of the Mo is in the p r e c i p i t a t e

intensity

~ - 0.28 mm/s w h i c h is compatible

intermetallic

lattice

intensity

of peaks 2 and 3 decrease

of a M o - c o n t a i n i n g

of the relative

of

to those

a random d i s t r i b u t i o n

Ib) the relative

11.8 % of the Fe atoms are in the precipitate. tate is

on the C.C.

sample,

By

the p r o p o r t i o n

can be compared

in the center of the spectrum.

122 h o u r s a g i n g at 450°C

(5).

spectra.

A f t e r a g i n g at 450°C for 30 hours peaks changes markedly.

17

richer Mo environments.

one can calculate

of Mo atoms d i s t r i b u t i o n s

even in the a s - q u e n c h e d

ALLOYS

the first three shells

I, 2 and 3. The results

atoms cannot account for the observed

attributed

IN M A R A G I N G

to Fe atoms with p r o g r e s s i v e l y

Fe atoms with the e n v i r o n m e n t s

magnetic

PRECIPITATION

,," 01

,/

0,1 !

o

Fig.2 -

i

lo

i

i

10o

Aging time {hours)

A l l o y Fe-12.2 Ni - 6.2 Mo(at %). V a r i a t i o n of X_(o) and XTT (e) • with a g i n g t±me at 450°C~

I0

~)o

Aging time (hours)

Fig. ~ - A l l o y Fe-12.2 Ni-6.2 Mo (at %). I V a r i a t i o n of Log ( ~ ) with o I-X a g i n g time at 450 C. P

9

18

MOSSBAUER

STUDY

OF

PRECIPITATION

IN M A R A G I N G

ALLOYS

The variation with aging time of the hyperfine field without Mo near neighbors

Vol.

8, No.

1

(h.f.) H I (Fe atoms

) was also followed by computing the ratio ~ = ( H I - H I O ) / H I F ,

were H10 is the hyperfine

field in the as-quenched sample ( ~ 337 kOe), H I the h.f. F field after a given aging time and H I the h.f. field after complete precipitation ( ~ 342 kOe).

The variation

of X H with time is

clearly seen that the h.f. field increase

the Fe atoms have gone into the precipitate

fraction of

phase. This shows that Mo atoms cluster

during the early stages of the aging process, 1 In figure 3, Log - - ~

also plotted in Fig. 2. It can be

starts before any noticeable

as suggested by various authors

(5) (7).

is plotted versus aging time on a Log scale. The short-

comings of this type of analysis are well known, but the fact that only one precipitation reaction occurs at 450°C up to 122 hours aging justifies

its use in the pre-

sent context. A straight line of slope n ~ 1 is thereby obtained, ponent of time in the Johnson-Mehl

formula Xp = 1 - exp(-ktn).

in good agreement with theoretical

predictions

ders of precipitate

Such a value of n is

(14) for the thickening of long cylin-

phase. This is indeed the case beyond 8 hours aging at 450°C,

since electron microscopy red by precipitates

where n is the ex-

observations

have shown that all the dislocations

are cove-

at that stage of aging (11).

In the publication

already quoted

followed by measurements

kinetics at 450°C were

(11), the precipitation

of the matrix lattice parameter.

/

Fig. 4 - Alloy Fe-12.2 Ni-6.2 Mo (at %). Comparison of MSssbauer spectroscopy results with lattice parameter measurements

(Xp)

(Xa).

Q5

I

~

I

I

J

i

i

i

i

Xo a

In Figure 4, Xp

is plotted versus X a , defined as Xa

the lattice parameter in the as-quenched

state,

a the lattice

-

a

a° _ aF o

, where a ° is parameter

after a given aging time at 450°C and a F the lattice parameter after complete precipitation.

The good agreement between the two methods is clearly apparent.

Vol.

8,

No.

1

M'OSSBAUER STUDY OF P R E C I P I T A T I O N

IN MARAGING ALLOYS

19

Fe-Ni-Co-Mo alloy. A limited number of MSssbauer experiments were performed on a quaternary Fe-17.3 Ni-8.4 Co-2.9 Mo as-quenched and aged at 350°C. It has been previously shown that on aging this type of alloy at temperatures below about 450°C,

the precipitates

are not nucleated on dislocations but instead are randomly distributed throughout the matrix

(9, 10, 15, 16). These precipitates are small spheroidal particles 20-30

in diameter with an ordered structure derived from the BCC lattice. The superlattice has lower symmetry than the parent lattice and appears in 4 distinct orientations relative to the matrix

(9, 10, 15). Similar precipitates are also observed in certain

ternary Fe-Ni-Mo alloys

(10). Yedneral and Perkas

(15) have shown that the super!at-

tice diffraction spots can be accounted for by segregation of molybdenum atoms onto every third plane of a given (111],i family. The aim of the present work was to try to obtain some information concerning the arrangement

of the Fe atoms in the super-

lattice.

0,I0 0,I0

o

tl

tI

t~

! o.o~; 0,02 -8

7

6

-5

-4

-3

2

-1

I 0

1

2

3

4

5

6

7

8

5 6 7 8

VELOCITY(mmll)

VEL~ITY(mmls)

-aFig.

-b-

5 - Room-temperature spectra of the Fe-17.3 Ni-8.4 Co-2.9 Mo (at % ) - a - As-quenched. - b - Aged 1024 hours at 350°C.

The spectrum obtained in the as-quenched martensitic main Fe environments

state (Fig.5a) shows two

(there might be a very small peak corresponding to a third type

of environment but its intensity is too weak to be included in the analysis).

The

h.f. fields were respectively H I ~ 347 kO e and H 2 ~ 303 kO e. After aging for 1024 hours at 350°C

(an advanced stage of homogeneous precipitation)

peak 2 has all but

vanished and the spectrum corresponds to that of a nearly molybdenum-free matrix with H I ~

355 kO e (Fig. 5b). Moreover there is no evidence of a paramagnetJc

peak

in the center of the spectrum which shows that the precipitate contains very few iron atoms, but does not preclude the presence of nickel and/or cobalt atoms.

Discussion and conclusions. The results of the MSssbauer study of precipitation at 450°C in the Fe-12.2Ni-6.2

20

MOSSBAUER

STUDY

OF P R E C I P I T A T I O N

Mo alloy are complementary

IN M A R A G I N G

ALLOYS

Vol.

to the results obtained by electron microscopy

8, No.

and

lattice parameter measurements.

Firstly,

the precipitation

wholly compatible

Secondly,

kinetics

(n ~ I

with the observed "ribbon-like"

by combining an analysis

in the Johnson-Mehl morphology

of the MSssbauer

equation)

spectrum obtained from the

specimen aged for 122 hours with the lattice parameter measurements specimen,

it is possible

precipitate

to make an estimate

at the end of the precipitation

of the composition reaction.

are

of the particules.

from the same

of the matrix and the

The results which are presented

in the table below were obtained in the following way

:

TABLE I Composition of precipitate and matrix at the end of precipitation (for 100 atoms of alloy).

Alloy

Fe

Ni

Mo

81.6

12.2

6.2

9.7

0.7

5.2

71.9

11.5

Precipitate Matrix

The number of Fe atoms in the precipitate intensity

of the paramagnetic

was calculated from the relative

peak as described earlier.

number of iron atoms was obtained with corresponds of the alloy). the MSssbauer matrix,

This gives by difference

A value of 11.8 % of the

to 9.7 atoms of Fe (for 100 atoms

71.9 Fe atoms remaining in the matrix.

spectrum shows that there are very few molybdenum

the ratio of nickel

I

to iron in the matrix can be estimated by comparing

h.f. field of peak I (H I = 342 k0 e) with recently determined values in binary Fe-Ni alloys

ponds to 11.5 nickel atoms in the matrix.

analysis.

As pointed out by Marcus and al.

in the matrix.

These calculations of the precipitation

~

I

(4) when the molybdenum

concen-

concerning

However by comparing the lattice parameter measurements

as a function

mated that approximately

contain

has already been shown by

spectroscopy yields little information

of the matrix at the end of precipitation lattice parameters

of the h.f. field

It follows the precipitates

of nickel in the precipitates

tration is very small MSssbauer the molybdenum

the

(17). The value of Ni/Fe thus obtained was 0.16 which corres-

nickel atom. The presence chemical

Since

atoms remalng in the

(2.874 ~) with previous measurements

of nickel and molybdenum

contents

of

(11) it was esti-

I Mo atom remains in the martensite.

suggest that the composition

process approximates

of the precipitate

to the formula

at the end

(Fe,Ni)2Mo rather than to

1

Vol.

8, No.

the formula

1

M O S S B A U E RSTUDY OF PRECIPITATION IN MARAGING ALLOYS

(FsNi)Mo which was obtained by chemical

microanalysis

on extracted precipitates

It should again be emphasised ful information

concerning

21

analysis and electron probe

(11).

that M8ssbauer

the kinetics

spectroscopy not only yields use-

of the actual precipitation

process

( varia-

tion of Xp with aging time ) but also gives some insight into the simultaneous

rear-

rangement

of

of the atoms in the matrix solid solutions as shown by the variation

the h.f. field.

The MSssbauer

experiments

clearly that the homogeneous

(and in certain Fe-Ni-Mo alloys to molybdenum

performed

on the quaternary Fe-Ni-Co-Mo

precipitation (10))

alloy show

observed at low temperature

corresponds

rich zones which are virtually

to the segregation

in Fe-Ni-Co-Mo of Mo atoms in-

iron free. This confirms again the gene-

ral tendancy of Mo to cluster in these Fe-Ni and Fe-Ni~Co matrices.

In terms of the

model proposed by Yedneral and Perkas these results imply that the formation of the ordered structure third (111)~

involves not only the segregation

plane but also the replacement

within the precipitates

It would be quite interesting

is limited to molybdenum

of the V and VI groups

atoms onto every

of iron atoms on the other (111)~ planes

by nickel and/or cobalt atoms.

to confirm whether this behaviour to other elements

of molybdenum

or whether it also applies

such as Nb, W, Ta, as might be expected.

Acknowledgments. The authors wish to thank Mr. J. BOURGEOT

for his continued aid in this research.

References. I.

H. FRAUENFELDER,

2.

N.M. GREENWOOD and T.C. CIBB, MSssbauer London (1971).

3.

H.L. MARCUS,

4.

H.L. MARCUS and L.H.

5.

T. ERICSSON,

S. NOURIKIS

6.

H.L. MARCUS,

L.H. SCHWARTZ and M.E. FINE, Trans. ASM, 59, 468 (1966)..

7.

P.L. GRUZIN, Y.L. RODIONOV, Y.D. ZHAROV, V.S. MKRTCHYAN, M.D. PERKAS, Soviet Phys. Doklady, 17, 64 (July 1972).

8.

P.L. GRUZIN,

The MSssbauer

M.E. FINE and L.H. SCHWARTZ,

effect. W.A. Benjamin,

SCHWARTZ,

Science, ~ , 901

and Y.A.LI,

2 b 475 (1972). 9.

B.J. THOMAS,

M4m.

Sci. Rev. M4t.,

58, 4750 (1967).

162, 259 (1967).

J. Mat.

V.S. MKRTCHYAN

(1962).

Champan et Hall Ltd.,

J. Appl. Phys.,

Phys. Rev.,

and J.B. COHEN,

Y.L. RODIONOV,

spectroscopy.

Inc. New-York

68, n ° 3, 212 (1971).

(1970).

A.F. YEDNERAL

and

Soviet Phys. Deklady,

22

M O S S B A U E R STUDY OF P R E C I P I T A T I O N

IN M A R A G I N G ALLOYS

Vol.

8, No.

10.

J. BOURGEOT, Ph. MAITREPIERRE, J. MANENC and B.J. THOMAS, in Electron Microscopy and Structure of Materials, G. THOMAS and al., Ed. p. 818 (Berkeley 1971).

11.

J. BOURGEOT, Ph. MAITREPIERRE, J. MANENC and B.J. THOMAS, M@m. Sci. Rev. M~t., 70, n ° 2, 125 (1973).

12.

VINCZE and I.A. CAMPBELL,

13.

R. COURRIER, Th~se de Doctorat, University of Nancy (1972).

14.

J.W. CHRISTIAN, The theory of transformation in metals and alloys. Pergamon Press, Oxford (1965).

15.

A.F. YEDNERAL and M.D. PERKAS, Phys. Met. and Metallography, 33, n° 2, 89 (]973).

16.

G. MAEDER and C. SERVANT, 16~me Colloque de M~tallurgie, Saclay (France), June 1973.

17.

G. LE CAER and R. COURRIER,

J. Phys. F. : Metal Phys., ~,647 (1973).

Unpublished results.

1