Cr GRAIN BOUNDARY DIFFUSION IN Cr2O3

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Cr GRAIN BOUNDARY DIFFUSION IN Cr2O3

A. Sabioni, B. Lesage, A. Huntz, J. Besson, C. Dolin, C. Monty

To cite this version:

A. Sabioni, B. Lesage, A. Huntz, J. Besson, C. Dolin, et al.. Cr GRAIN BOUNDARY DIFFUSION IN Cr2O3. Journal de Physique Colloques, 1990, 51 (C1), pp.C1-611-C1-616. �10.1051/jphyscol:1990196�.

�jpa-00230365�

COLLOQUE DE PHYSIQUE

Colloque Cl, suppl6ment au n o l , Tome 51, janvier 1990

Cr GRAIN BOUNDARY DIFFUSION IN Cr,O,

A.C.S. S A B I O N I ( ~ ) , B. LESAGE, A.M. HUNTZ, J. BESSON", C. DOLIN*' and C.

MONTY* *

ISMA, CNRS URA 1107, Laboratoire d e Metallurgie Structurale, Bdt 413, yniversite Paris X I , F-91405 Orsay Cedex, France

E.N.S.M.P., Centre des MatBriaux, BP. 87, F-91003 Evry Cedex, France

X *

CNRS, Laboratoire de Physique des Materiaux, Bellevue, F-92195 Meudon, France

RCsum6

-

La diffusion intergranulaire du chrome dans des polycristaux denses de Cr203 a CtC mesurCe en utilisant l'isotope stable 5 4 ~ r . Les profils de pCnCtration ont CtC Ctablis par SIMS

.

A 1200 et 1300°C, sous une pression de 5.10-5 atm. (5 Pa), les valeurs trouvCes pour Dj sont respectivement de 1,03.10-15 et 4,72. 10-l4 cm2.s-l en prenant lnm comme largeur de joint et en utilisant les valeurs de coefficient de diffusion en volume mesurkes dans les monocristaux (1,0.10-l8 cm2.s-1

B

1200°C et 4,8.10-18 cm2.s-l 2 1300OC)

.

Ces valeurs sont plus faibles que celles publiCes prCc6dernment dans le domaine de temphatures et de pression d'oxyg5ne

.

Abstract Cr grain boundary diffusion has been measured in dense polycrystals of Cr203 using S4cr as a stable tracer and depth profiling by SIMS

.

At 1200 and 130O0C, in an oxygen pressure of 5.10-5 a m , (5 Pa), it was found 1.03.10-15 and 4.72.10:14 cm2.s-l respectively for the grain boundary diffusion, considering the width of the grain boundary equal to 1 nm and using lattice diffusion values obtained on single crystals (1.0.10-l8 cm2.s-l at 1200°C and 4.8.10-18 cm2.s-l at 1300°C)

.

These values are smaller than those previously published in the same range of temperatures and oxygen pressure

.

The study of self-diffusion in m 3presents a great technological interest because its knowledge is necessary to interpret the mechanism of Cr203 scale growth on chromium -rich alloys at high temperature

.

However, up to now, there is a lack of data in l i t e r a m about chromium and oxygen diffusion in CqOg, especially with respect to grain boundary (GB) diffusion

.

This work deds with the Cr diffusion

.

In all earlier experiments 11-51, the chromium radioactive isotope S1Cr was used

.

In such cases, the concentration profile of the tracer is determined by sectioning the sample in thin layers, mechanically or by ion beam sputtering, and counting the radioactivity remaining in the sample or in each layer. The purpose of this paper is to determine new values of the lattice and grain boundary diff~sion coefficients in Cr2O3 using an original technique

.

It consists of using the s4Cr, the less abundant of the natural chromium stable isotopes, and depth profiling by secondary ion mass spectrometry (SIMS)

.

Our results are compared to literature data.

11- EXPERIMEKTAL PROCEDURE 11-1 Material

Polycrystalline Cr2O3 was prepared by hot-pressing at 1450°C, 48 MPa during 40 min., using high purity Cr2O3 powder, (impurity contents < 10 pprn), obtained from Johnson Matthcy Corp.

(')supported by U n i v e r s i t y o f Ouro P r e t o and CNPq ( B R A Z I L )

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990196

Cl-612 COLLOQUE DE PHYSIQUE

The volumic mass of the hot-pressed Cr203 samples is quite equal to 100% of the theoretical volumic mass of this oxide, and its microstructure after thermal etching is shown in Fig.1

.

The diffusion samples were cut into small parallelepipeds of 3 x 5 ~ 1 mm3 from the hot-pressed compacts.

The largest surface was used as diffusion surface after diamond polishing

.

Fig. 1- Microstructure of the polycrystalline Cr203 after thermal etching at 1 100°C, 15 min., air.

Single crystals of Cr203 of 99.9% purity were purchased from Labelcomat (Belgium)

.

These samples were used as disks of 2mm thickness and 5mm in diameter

.

The 5 4 ~ r used as stable tracer was obtained through CEA (France)

.

Its chemical composition is given in Table 1

.

Table 1

Isotopic composition

Chemical Impurities

11-2 Diffusion ex~eriments

The diffusion experiments were performed by the following procedure : Element

2

-Samples were preannealed in oxygen pressures corresponding to the diffusion test conditions, during a time longer than the diffusion time

.

- Samples were polished again to eliminate the thermal etching at the surface

-

S4Cr was deposited by vacuum evaporation at 104 Pa

.

Ca

1

^Fe

I

^{S i}

I

^Pb

I

^Sn

⁽

^A1

0.02 0.02

1

^0.05

1

^0.01 ( ^0.02

1

^q0.005

1

^0.03

NI

<0.01

- Oxidation of the 54Cr film was performed by heating at 5W°C, in air during 30 min.

Cu 0.01

- Giffi~sion annealing were then conducted in 5.10-5 atm ( 5 Pa) PO:! at 12(X) and 1300°C.

11-3 Devth profiling bv SIMS

The depth profiles were determined by SIMS using a 10 KeV Csf ion source

.

The scanned area was 250x250 pm2

.

The concentration was determined from the 50Cr-, 5 2 ~ r - , 5 3 ~ 1 - and 5 4 ~ ~ - signals using the expression C = IC54 / ( 150 + 152

+

153 + 154 ), where I', are the count numbers of each chromium isotope. IC54 is the count number on ion 54 corrected from a background obtained by calibrating the signal far from the diffusion zone

.

The penetration depths were obtained assuming a constant sputtering rate and measuring the final depth of the crater.

111- RESULTS

This paper presents the results obtained for experiments performed at 1200 and 1300°C in argon (5.10-5 atm 02)

.

The concentration profile of 54Cr in polycrystalline Cr2O3 for one of these experiments is shown in Fig.2

.

DEPTH ( n m )

Fig.2- S4cr concentration profile in polycrystalline C r ~ 0 3 after the diffusion annealing

.

The figure 3 shows a penetration plot for 54Cr in Cr203 single crystal 161 at the same temperature and oxygen pressure ^, The comparison between the plots of figures 2 and 3 allows to know the region where lattice diffusion becomes negligible in our experimental conditions

.

Our diffusion experiments correspond to the type-B diffusion / 7 / . In this case, Le Claire I81 has shown that the product D'6, where D' is the GB diffusion coefficient and 6 the width of the grain boundary, is given by the following expression :

d L n c 4D

D'6 = 0.661 ( - --- )-S13 ( --- )l12

dx615 t

where D is the lattice diffusion coefficient

.

This relation is valid if the parameter

P

= --- --- is 7 10

D

6

l'he D values used to deduce D'd were taken from the experiments performed on siligle crystals

COLLOQUE DE PHYSIQUE

0 20 CO 60

DEPTH ( n m l

Fig. 3- Penetration plot of Cr in Cr2O3 single crystal after diffusion annealing 161.

Using, at 1300°C, D = 4.8.10-18 cm2.s-1/61 and experimental data from Fig.4 , it was found D'S

= 4.72.10-~1 cm3.s-l and

P

⁼ 907.6. For the experiments at 1200°C, it was found the following values : D = 1.0.10-18 cm2.s-l, D'S = (1.03

+

0.38) 10-22 cm3.s-l and

P

⁼ 205

.

No additionnal fast diffusion process was observed as in King and Park's experiments /l l/

.

Fig.4- Plot of log10 ( C -

G )

versus

.

C, is the natural concentration of 5 ? ~ r in er203

.

Its value is 2.4% .

In Fig. 5 our D'6 v a l ~ ~ e s are cotnpared with earl~er data 1;:g b shows the cornparison between grain boundary and lattice diffusion in Cr207 . Whcn there is niore than one value at the sanle

temperature in a reference, only the smallest value is indicated, and for lattice diffusion data only from single crystals are shown.

Fig.6- Arrhenius plot for lattice and grain boundary diffusion (using 6 ⁼ Inm) in Cr203:

Fig.5 - @ D'& calculated by King et al. /g/ from Caplan and Sproule's oxidation data /10/.

X D'6 measured in sintered Cr203 151

1

_D'6 in low angle boundaries 141

.

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COLLOQUE DE PHYSIQUE

IV- CONCLUSIONS

The Cr diffusion along grain boundaries in Cr203 has been measured successfully using 54cr as a stable tracer and profiling by SIMS

.

The grain boundary diffusion coefficient at 1200°C and 1300°C in 5.10-5 atm 0 2 was found to be (1.03

+

0;38) 10-l5 cm2.s-l and 4.72.10-14 cm2.s-l, respectively, considering the grain boundary width equal to 1 nm

.

The results obtained with polycrystals confirm the low diffusivity of Cr in Cr203 observed previously in experiments with single crystals 161. New experiments are planned at different telperatures and oxygen pressures to know more about the role played by grain boundary diffusion in high temperature oxidation

.

V- REFERENCES

/ l / W.C. HAGEL and A.V. SEYBOLT. "Cation diffusion in Cr203", J. Electrochem. Soc.

108(12) (1961) 1146.

I21 L.C. WALTERS and R.E. GRACE. "Self diffusion of S1Cr in single crystals of Cr203". J.

Appl. Phys. 36(7) (1965) 2331.

131 K. HOSHMO and N.L. PETERSON. "Cation self diffusion in Cr203", J. Am. Ceram. Soc.

66(11) (1983) C 202.

-

141 A. ATKINSON and R.I. TAYLOR. "Diffusion of S1Cr tracer in Cr20-j and growth of C m 3 films" NATO-AS1 Ser. B

129

(1984) 285.

151 J.H. PARK, W.E. KING and S.J. ROTHMAN. "Cation tracer diffusion in Cr20-j and in Cr203 -0.09 wt% Y203", J. Am. Ceram. Soc. ZQ(12) (1987) ( 880).

161 A.C.S. SABIONI, B. LESAGE, J.C. PIVIN, C. DOLIN and C. MONTY. "Comparison of ion implantation and thick film methods to study Cr self diffusion in Cr203" Proceedings of the NATO-AS1 Conference on "Diffusion in Materials", Aussois (France), March 1989. (To be published).

/7/ L.G. HARRISON. Trans. Faraday Soc.57(1) (1961) 74.

181 A.D. LE CLAIRE. "The analysis of grain boundary diffusion measurements", Brit. J. Appl.

Phys. N ( l 9 6 3 ) 351.

191 W.E. KING, K.S. GRABOWSKI, D.F. MITCHELL and P.M. BALDO. "Rutherford backscattering study of high temperature oxidation of Y-implanted Fe-24Crn, Oxid. Met. x(3-4) (1989) 181.

I101 D. CAPLAN and I. SPROULE. "Effect of oxide grain structure on the high temperature oxidation of Cr", Oxid. Met. 3 5 ) (1975) 459.

l1 l / W.E. KING and J.H. PARK, Proceedings of IIB 89, Paris, Les Editions de Physique.