3 4Y5b 0514733 4

This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuiacy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.

ORNL- TM-3 73 4

Contract No. W-7405-eng-26

MIEALS AND CERAMICS DIVISION

EFFECT OF AGING TIME AND TEMPERATURE ON THE IMPACT AND

TENSILE BEWiVIOR OF L-605 - A COBALT-BASE ALLOY

D. T . Bourgette

APRIL 1973

OAK RIDGE NATIONAL LABORATORY Oak Ridge, T e n n e s s e e 37830

UNION CARBIDE CORPORATION operated by

3 4456 OSL4733 i?~

iii

CONTENTS

Page

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1nt;soduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Ex-perimental Procedure . . . . . . . . . . . . . . . . . . . . . . . 3

?.laterials . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Specimen Machining and Heat Treatment . . . . . . . . . . . . . 4 Impact Testing . . . . . . . . . . . . . . . . . . . . . . . . 5 T e n s i l e T e s t i n g . . . . . . . . . . . . . . . . . . . . . . . . 6

Discussion of Resul ts . . . . . . . . . . . . . . . . . . . . . . . . 6 Impac tTes t s . . . . . . . . . . . . . . . . . . . . . . . . . 6

Aged at; 870°C . . . . . . . . . . . . . . . . . . . . . . 7 Aged at 760°C . . . . . . . . . . . . . . . . . . . . . . 13 Aged below 760°C . . . . . . . . . . . . . . . . . . . . . 16 Reentry Heating Ef fec t s . . . . . . . . . . . . . . . . . 16

T e n s i l e T e s t s . . . . . . . . . . . . . . . . . . . . . . . . . 16 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2 . StSSJECG CATEGORY NO.

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EFFECT OF AGING TIME AND TEMPE-RAT'URE OBT THE IMPACT hr'\sD

TENSILE BEHAVIOR OF L-605 - A COBALT-BASE ALLOY

D. T. Bourgette

ABSTRACT

The e f f e c t of aging temperature and time on the impact and t e n s i l e behavior of L-605 was s tudied over t h e range o f '7413 t o 870°C and 50 t o 4000 h r . temperatures r e su l t ed i n severe a l l o y embrittlement. The p r i n c i p a l embr i t t l i ng r eac t ion was the p r e c i p i t a t i o n o f t h e Laves phase, CozW. A t t h e lower temperatures, hDwever, t he p r e c i p i t a t i o n of CojW may have contr ibuted t o embrit t lement. Maximum aging embrittlement occurred a f t e r 5OG h r a t 8'70°C.

Prolonged exposure a t these

Impact t e s t i n g of identica1.1 y aged specimens a t temperatures of 315 t o 7170°C revealed t h a t 33% of t h e toughness was l o s t a t t h e highest t e s t temperature and t h a t a l l f r a c t u r e s were i n t e r - granular . Impact t e s t i n g a t lower temperatures revealed a g rea t e r loss of toughness.

Specimens aged a t 760, 815, and 870°C and t e n s i l e t e s t ed a t room temperature and 540°C showed a severe loss of d u c t i l - i t y , t h e g r e a t e s t l o s s occurring i n specimens aged at; 870°C. Specimens aged a t 760°C for 1000 h r exhib i ted a d u c t 5 l i t y ~f 10% a t r m m temperature and 2cS$ a t 540'C. ( a t 740°C) resuLted i n a continued loss of d u c t i l i t y .

Longer aging times

INTROIYJC TI ON

The Co-Cr-W alloy, L-605 (Haynes a l l o y No- ? 5 ) , i s genera l ly regard-eci as one of t he most proven cobalt-base alloys commercially ava i l ab le . T h i s a1:Loy i s used i n many common engineering appl ica t ions ranging from j e t engine components t o fbrnace muffles operat ing i n environments such 8s

a i r and low-pressure ni t rogen o r oxygen. Sn addi t ion, L-6G5 is u s e d i n the cons t ruc t ion of l i q u i d metal hea t - t r ans fe r loops and accessory equip- ment - The exce l l en t oxidat ion res i s tance , ' corrosion r e s i s t ance i n l i q u i d

~ ~~~

'Haynes Alloy No. 25 Ihta Folder, Haynes S t e l l i t e Company, Kokomo, Indiana, ,June 1962. Now S t e l l i t e Division, Cabot Corporation, Kokomo, Indiana 46'301.

2

metals, * high-temperature s t r eng th , ' y 4 and good f a b r i c a b i l i t y and welda- b i l i t y promote t h e use of t h i s a l l o y i.n these app l i ca t ions ,

The use of L-605 i n an environment such as the hard v&cuurn ih space f o r times i n excess of 10,300 h r may, however, l ead t o se r ious problem

as soc ia t ed wi th low post-age duc t i l i t y5Y6 and w e l d fusion l i n e f a i l u r e s .

I n add i t ion , r e s i s t a n c e t o thermal cycle f a i l u r e could be low because of t h e l o s s of low-temperature d u c t i l i t y .

Impact, loading of L-605 hardware af ter long-term aging at 500 'co 900°C i s possible i n some aerospace appl icat ions.

gat ion the re fo re w a s concerned wi th 'che e f f e c t of long-term aging on t h e

microstructure, impact, and t ens i - l e behavior of L-605.

"he present i n v e s t i -

Alloy 1,-605 derives i t s s t r e n g t h pr imari ly from so l id - so lu t ion har-

dening, but a d d i t i o n a l s t r eng th can be acquired by aging. Cobalt i s hexag-

ona l c lose packed a t room temperature but changes to face-centered cubic

above d18"C.

t h i s polymorphic transformation of t h e matrix, wi th t h e hexagonal close-

packed l a t t i - c e being associated wi th t h e less duc1;ile s t r u c t u r e s . Tungsten

and chromium r a i s e and n i c k e l and i r o n luier the transformation tempera-

t u r e . For L-605, transformation from face-centered cubi.c t o hexagonal

The d u c t i l i t y of a cobalt-base a l l o y i s often a f f e c t e d by

2D. H. Jansen and E . E. Hoffman, Type 316 S ta in l e s s S tee l , Tnconel, ~ - - and Haynes Alloy N o . 25 Natural-Circulation Boiling-Potassi.um Corrosion Test Loops, ORNL-3970 (June 1965).

'R. Wid-mer, J. M. Dhosi, and N. J. Grant, Mechanisms Associated wi th Long Tjme Creep Phenomena -____., Technical Report AFML-TR-65-181, Pa r t I T , 1967.

'C, J. Slunder, Short 'Term Tensile Propert ies Qf t h e Co-20 Cy15 W-10 Ni. Cobalt-Base Alloy (L-S05), DMTC Memo No. 179, l h t t e l l e Memorial I n s t i t u t e (Sept. 27, 1963) .

Report No. 817-1390, Haynes S t e l l i t e Company, Kokomo, lndiana (May 21, 1958).

5E. E . Jenkins, Einbrittlement of iIaynes Alloy No. 25 lhiring Brazing,

6S. T. Wlodek, Embrittlement of a C o - C r - W (I,-605) Alloy, R-61-FPD-538 (Dee. 1, 1941.).

7R. W, Sw1 ndeman, Oak Ridge Nati.osa1 Laboratory, p r i v a t e c o m n i c a - t lon, February 1.969.

'F. S. Badger and F. C. Kraft, Jr., "Cobalt-Base and Nickel-Ease Alloys f o r Ultrahigh Temperature, ' I Metal Progr. - 52, 39.: (1947).

-

c lose packed can be expected between 650 and 300°C, hut only a f t e r very

long times.

high-temperature s t r eng th over long periods of time.

This sluggishness i s a p re requ i s i t e f o r r e t en t ion of 9710

EXPER1MF;NTAL PROCDURE

The purchasing of mater ia l s , machining o f t h e t e s t specimens, and

aL1 heat t reatments i n a i r were completed a t t he Nartin-Marietta Corpora- t i on , t h e b h r t i n Company, Baltimore, Maryland. The impact t e s t i n g was conducted a t t h e B a t t e l l e Memorial I n s t i t u t e , Columbus, Ohia, while t h e

t ens i l e t e s t i n g was completed a t t h e Martin Company. Evaluation of all . Clata, m t a l l o g r a p b i c examination, hardness and g ra in s i z e determinations, chemical. ana lys i s , and f i n a l repor t ing were completed a t ORNL. A-dditional

impact specimens were machined, aged i n argon, and t e s t e d a t ORNL for t h e purpose of determining environmental e f f e c t s and the aging response

of L-605 a t lower t emperatzlres .

Materials

Two pieces of L-605 were purchased f r o m t h e IJCC S t e l l i t e D i v i s i m i n accordance wi th aerospace ma te r i a l s p e c i f i c a t i o n AN3-5537B.

chemical composition, mechanical proper t ies (vendor 's ) , and heat; i d e n t i - f i c a t i o n s a r e given i n Table 1. The material. as received had been solu-

t i o n hea t - t r ea t ed ( i n a i r ) at 1230°C f o r a period of not less t'nan 0. 25 hr.

'Die

9W. Koster, "On t h e Inf luence of t h e Elements on t h e Pol-ymorphic Transformation of' Cobalt, " Z . Metallk. L+3, 297 (1952).

Nickel on t h e Alpha/Beta Transformation arid Gamma P r e c i p i t a t i o n i n Cabal t- Chromium Alloys, 'I Trans. AIME 188, 154 (1350)

__ ''A. R. Elsea and C. C . McBride, "The Effec ts of Nitrogen, I ron, and

I_ I_

Table l. Analyses of Commercial L-605

He a t Nunib e r

(0.056 i n . shee t ) (0.500 i n . p l a t e )

a 186-6-1843 186- 5- 1737 Compos it ion Mechanical

( T i t %) Proper t ies

C r 20.24 20.37

15.02 3-4.81 W Fe 2.00 1.80

N i 10.24. 10.00

MI1 1.35 1.43

C 0.09 0.1-1

Si 0.03 0.18

S 0.005 0.014

P 0.007 0.016

co Balance Balance

Ultimate t e n s i l e 136,650 129,800

Yield s t r eng th 0.2% 64,750 59,200

~ u c t i l . i t y , i n 2 i n . 56.5% 64 $

s t rength , p s i

o f f s e t , p s i

a Vendor's ana lys i s .

Specimen Machining and Heat Treatment

The Charpy V-notch impact spechiens and sheet t e n s i l e speclmens

were machined i n accordance wi th Fig. 1. All. specimens were subsequently

so lu t ion annealed a t 1230°C f o r a per iod of not Less than 0.25 hr. The impact specimens were aged i n a i r a t 8'70°C: f o r peri.ods of 50, 1-00, 500,

1000, 2500, and 4000 hr . The shee t t e n s i l e specimens were aged i n a i r a t 760, 820, and 870"i! f o r per iods of 50, 100, 500, 1000, and /(to00 hr . Additional impact specimens were machined, so lu t ion annealed at 1230°C

f o r 1 hr i.n vacuum, and. aged i n argon a t 650, 760, and 870°C f o r 50, 200, 500, and 1000 h r . These add i t iona l specimens were machined fYom

t h e same hea t (186-5-1737) as were t h e air-aged specimens.

5

i3RNL-OWG 70-24 5 8

SOLUTION ANNEAL AFTER MACHINING -t230°C - 0.25 hr

0.0 i O ~ o . o o ' RADIUS NOTCH DETAIL

CHARPY V-NOTCH IMPACT SPECIMEN

TYPE 304 STAINLESS STEEL TABS

THREE SIDES (TYP.)

\HOLE 0.374 -0.381 DlAM

FROM SPECIMEN END FUSION WELDED TO SPECIMEN ON LOCATE ON CENTER 5 k m .

0.05f0.00~

1 t I I ! I / I f 1

HIGH TEMPERATURE TENSILE SPECIMEN DIMENSIONS ARE IN INCHES

Fig. 1. Specimen Spec i f ica t ions for L-605 Aging Study.

Impact Testing

A c e r t i f i e d Richle impact t e s t e r ( s e r i a l No. €?A-17876) was used t o test t h e specimens aged i n a i r - Specimens were impact t e s t e d i n a i r a t 31!S, 427, 538, 649, and 760°C. A t r a n s f e r time from t h e mrnace t o t h e t e s t i n g block of 4 t o 5 sec necess i t a t ed a temperature c a l i b r a t i o n of the specimen t o co r rec t for r e s u l t i n g thermal lo s ses .

machined i n a spare specimen t o permit a Chromel-%Alumel thermocouple

(28-gage wi re ) t o be located d i r e c t l y behind t h e notch.

couple connected to a high-speed recorder showed t h a t specimens impact t e s t e d a t t h e above temperatures had t o be heated to 31'7, 430, 543, 656,

and 77OoC, respec t ive ly . The instrumented specimen was heated w i t h t h e

A small hole was

The thermo-

6

specimen t o be t e s t e d as a more accura te ind ica to r of spc imen tempera-

t u r e .

same temperature.

I n an e f f o r t t o simulate the h e a t i n g b y r een t ry i n t o t h e e a r t h ' s

Two specimens of each aging treatment were impact t e s t e d a t the

atmosphere, impact specimens aged i n ajr f o r 4000 hr a t 870°C wel-e heated

t o 1110°C and t e s t e d at a p p o x i m t e l y 1080°C. The impact specimens so lu t ion annealed i n vacuu111 and aged i n argon

were impact t e s t e d a t 316°C wi th a Baldwin t e s t e r ( s e r i a l No, 1075).

The specimens were superheated 2 t o 3 ° C . Spare specimens aged i n a i r

were impact t e s t e d on t h e Baldwin machine; t h e r e s u l t s were i d e n t i c a l

t o those obtained on t h e Hichle t e s t e r a t t h e Uattel-le Memorial I n s t i t u t e .

Tensi le Testing

A c e r t i f i e d Baldwin Lima Hamilton Universal t e n s i l e t e s t i n g machine

was used i n making t e n s i l e measurements of a i r -aged specimens. The ten-

s i l e t e s t e r was equipped w i t h a pacing device f o r t h e measurement and

control. o f Lhe s t r a i n r a t e a t 0.05 i.n./inr.

aged condi t ion were t e n s i l e t e s t e d a t 5 L , O o C , and one specimen of each

aged condi t ion was t e s t e d a t room temperature.

imens aged for 4000 h r a t 870°C were t e n s i l e t e s t e d a t 1080°C i n an e f f o r t t o sirnul a t e r een t ry heating.

Three specimens of each

I n addi t ion, t h ree spec-

DISCUSSION OF RESULTS

Impact Tests

I n i t i a l l y , it should be understood t h a t t h e uninstrumented- Charpy V-notch impact t e s t possesses many shortcomings. numerical information t h a t can be used d i r e c t l y i n design cal.cu1 a t ions ,

t h e s t r e s s d i s t r i b u t i o n during f r a c t u r e i s unknown, t he resisLance of

the mater ia l t o crack i n i t i a t i o n and propagation cannot be obtained, and conditions of the t e s t do not adequately r e f l e c t ac txa l se rv ice condi- t i o n s .

It does not provid-e

I n t h i s s tudy the (notched) impact t e s t was used t o determine

7

r e l a t i v e changes i n t h e toughness 3f L-605 microstructures t h a t r e s u l t e d from thermal treatments which w i Z i be encountered i n se rv i ce and which

a r e known t o cause a l l o y embrit t lement. These r e s u l t s coupled wi th ca l -

cu la t ions of r e e n t r y v e l o c i t i e s and impact forces assoc ia ted w i t h reent ry

and launch pad abor t s w i l l hopefully determine the s e r v i c e a b i l i t y of

L-605 under impact loads. In addi t ion, t h e notched specimen geometry

may simulate notches of t h e type encountered i n welds and regions of high stress concentrat ion.

The Charpy V-notch impact t e s t i s a severe mechanical t e s t . An a l l o y withstanding a Charpy t e s t without exhib i t ing much l o w energy

cleavage has an exce l l en t chance of withstanding a cleavage f r a c t u r e i n

se rv i ce a t t h e t e s t temperature. When t h e maximum f r a c t u r e toughness is

g r e a t e r than nominally 100 f't-lb ( a t LOO$ t e a r ) , it i s considered suf - f i c i e n t l y high t o guarantee aga ins t f a i l u r e by low energy t e a r , a t l e a s t

i n medium-strength ma te r i a l s . Conversely, when t h e fYactxre toughness

is low ( 5 t o 2 0 f t - l b ) and t h e f r a c t u r e i s p r i n c i p a l l y by cleavage o r

is in te rgranular , t h e a l l o y i s very suscept ib le t o b r i t t l e f a i l u r e .

Aged. at 870" C

%ne f r a c t u r e toughness of 21-695 aged i n air a t 870°C genera l ly decreased with aging time at all t e s t temperatures. decrease occurred a f t e r aging f o r 50 h r .

observed after the 100-hy aging t rea tment , but thereaf te r . t h e toughness

continued t o decrease f o r aging times t o ~+/to1X1 hr. This behavior i s

i l l u s t r a t e d i n Fig. 2. For specimens impact t e s t e d a t 42'?*C, a 100% f ibrous f r a c t u r e was obtained f o r t h e solution-annealed condi t ion, while subsequent aging t reatments r e s u l t e d i n s l i g h t cleavage, gross i-nter- g ranular f r a c t u r e s , and a smll increase i n g ra in s i ze .

Lreatments , f o r example, r e s u l t e d i n about 2076 cleavage ( t ransgranular t e a r without deformation) , while after the lOO-hr aging t reatment , cleav- age f r a c t u r e s were very scarce and in t e rg ranu la r f r a c t u r e s were obtained. Aging t i m e s longer than 100 hr r e s u l t e d i n t o t a l in te rgranular f a i l u r e s . Hardness behavior (Fig. 3) and l a t e r a l expansion f u r t h e r i nd ica t e a l l o y embrittlement and loss of toughness w i t h aging t i m e .

The greatest,

A recovery i n toughness was

The 50-hr aging

8

ORNL-OWG 70-2461

250

240

230

220

c

'7 0 - D - + .I- v

& 60 (r W z W

$ 5 0 3 t- 0 Q [L LL.

4c

3c

2c

4 (

C

+- -4

......... __ 1 -I- + 4' . . . . . . .

1 ' :

HT-1230°C FOR 0.25 hf

@ @

I I I 100 200 300 4 00 5 00 so0 700 800

IMPACT TEST TEMPERATURE ("C)

Fig. 2. Influence of Test, Temperature and Aging Time i n A i r a t 870°C on t h e Fracture Toughness of L-605.

340

330

$ 320 z 0 LT

3 310 z b- 0 Q

2 0 2 a (5 290

300

0 (2-3)

0 500 1000 1500 2000 2500 3000 3500 4000 AGING TIME (hr)

Fig. 3 . Effec t of Aging Time a t 870°C on t h e Hardness of L-405.

Typical mic ros t ruc tu ra l changes are presented i n Fig. 4. The

s o l u t ion-annealed microstructure i s e s s e n t i a l l y a single-phase matrix wi th s c a t t e r e d heterogeneous carbide d ispers ions , probably t h e M G C type.

Transgranular t e a r wi th considerable deformation w a s observed. This

condi t ion i s t y p i c a l of a ma te r i a l wi th high f r a c t u r e toughness. Specimens aged a t 870°C f o r 50 hr f r ac tu red in t e rg ranu la r ly wi th

considerable deformation; however, s l i g h t t ransgranular tear was a l s o observed. This behavior i s a t t r i b u t e d i n p a r t t o t h e p r e c i p i t a t i o n of an i r r e g u l a r , blocky carbide i n t h e g ra in matrices and m almost con-

t inuous sphero ida l carbide i n t h e g ra in boundaries, as shown i n Fig. 5. The r e s u l t s of Yukawa and Sato'' (at 700 and 800°C) ind ica t e t h a t t h e

I I N . Yukawa and K. Sato, "The c o r r e l a t i o n Between Microstructure and S t r e s s Rupture Proper t ies of a Co-Cr-ITi-W (13s-25) Alloy," Japan I n s t . Metals - 9 9 (Supplement) (1968).

Trans . -

10

Photcr 98586

50

- 1c

In - ? 0

W

500

4000

INTER109 SECTIONS FRKTURE SECTIONS OXIDIZED SURFACES

Fig. I+. Microstructural Changes i n L-605 Aged in A i r a t 870°C and Impact Teslxd at 315°C. Etchant : 100 ml H20 i- 40 ml CF13COOH + L+O ml HC1 + 15 ml lI2SO4 + 25 e; FeCI.3. 500X. Reduced 16.5%.

Fig. 5. L-605 Aged for 50 h r a t 870°C i n A i r and Impact Tested a t 315°C. + 25 g FeC13. 2OCOX.

Etchant: l C 0 ml H20 + A0 ml- CH3COOH f 40 m l HC1 f 15 m l HzSO,:

bl-ocky carbide is of t h e M23C6 type, which i n i t i a l l y p r e c i p i t a t e s i n t h e grarin boundaries and subsequently wi th in t h e g ra ins . More important,

however, i s t h a t t h e present s tud ie s , conducted a t a s l i g h t l y g r e a t e r

temperature ( 8 7 O o C ) , have shown t h a t a cobal t - tungsten Laves phase a l s o

p r e c i p i t a t e d (discont inuously) near t h e g r a i n boundaries during the

50-hr aging t reatment and i n p a r t i s responsible for t h e in t e rg ranu la r f a i l u r e s and loss of toughness. These r e s u l t s are i l l u s t r a t e d i n Figs. 5 and 6. t h e i n i t i a l p r e c i p i t a t i o n of t h e Laves phase adjacent t o t h e grain boundaries.

The mic ros tmc tu re i l l u s t r a t i n g t h e 50-hr age i n F i g . 6 shows

&ing for lof) h r r e su l t ed i n f u r t h e r d i s s o l u t i o n o r t ransformation of the g r a i n boundary sphero ida l carbide t o a finer carbide d i spe r s ion

3.2

PHOTO 97101

F3.g. 6. Electron Micrographs Illustrating t h e Aging Behavior o f 1;-605 at 870°C. ( c ) Aged 4000 h r , 5000X.

( a > Aged 50 hr, SOOOX. (b) Aged 500 hr, 5000x. (d) Aged 4000 h r , 12,500X.

13

i n t h e matr ix . Grain boundaries and adjacent areas , however, contained

an increased amount of Laves phase. YUkawa,12 Jenkins,13 and Wlodek14 showed t h a t blocky M ~ ~ C F , transforms t o MgC and t h a t a f t e r 100 h r a t

temperatures above 800cC, t h e Laves phase, (Co, N i ) , ( C r , W ) , p r e c i p i t a t e s near t h e gra in boundaries a s elongated p l a t e l e t s and subsequently as

i n t e rg ranu la r p a r t i c l e s .

ment w i t h t h e r e s u l t s of t h e previous inves t iga t ions . For s impl ic i ty ,

t h e Laves phase w i l l be designated C02W.

The results of t h e present s tudy a r e i n agree-

Continued aging f o r times t o 4000 h r at 870°C merely r e s u l t e d i n a f i n e d ispers ion of t he Mc;C carbide and an increased amount of CozW, which

p r e c i p i t a t e d i n the g ra in boundaries, on t w i n boundaries, and probably on s tacking f a u l t s . A t an intermediate aging time of 500 h r , t h e behavior

i s i l l u s t r a t e d i n Fig. 6. The Laves phase thickened and coarsened with

t i m e and depleted t h e m t r i x of some components. For example, chemical ana lys i s showed t h a t t h e tungsten concentrat ion i n t h e matrix decreased

from 14.81 t o 7.46 w t $ during 1000 Inr at 870°C. f r a c t u r e toughness and apparent loss of d u c t i l i t y a r e a t t r i b u t e d pr in- c i p a l l y to t h e p r e c i p i t a t i o n of t h e Laves phase i n the gra in boundaries.

Tine d r a s t i c loss of

Aged a t 760°C

The f r a c t u r e toughness r e s u l t i n g from aging i n argon a t 760°C i s

shown i n Fig. '7 f o r an impact t e s t temperature of 316°C. The g r e a t e s t

l o s s of f r a c t u r e toughness due t o aging a t 760°C again occurred during the i n i t i a l 50 hr . The 100-hr age, however, did not r e s u l t i n a recovery

a f f r a c t u r e toughness. Instead, t h e toughness gradual ly decreased wi th

aging time at a r a t e less than f o r specimens aged a t 8'70°C. i s a t t r i b u t e d t o t h e slower p r e c i p i t a t i o n r a t e of t h e embr i t t l i ng laves

phase a t 760" C.

This behavior

Metallographic examination supported the contention t h a t

- I%. Yukawa and K. S a b , "The Corre la t ion Between f i c r o s t r u e t u r e

and Stress Rqtu re Proper t ies of a Co-Cr-Ni-W (HS-25) Alloy, " Trans. Japan Ins t . Metals 2, -- (Supplement) !1968) ~

I3E. 3. Jenkins, Embrittlement of Hsynes Alloy No. 25 During Brazing, Report PJo . 817-13'3(7, Haynes S t e l l i t e Company, Kcikomo, Indiana, (May 21, 1958).

"S. T. Wlodek, Einbrittlement of a Co-Cr-W ( L - 4 0 5 ) Alloy, R-61-FPD-538 (Dee. 1, ~ 3 h l ) .

1 4

ORNL- DWG 70- 2462

2 5 40* 2 5 lo3 2 5 to4 AGING TIME Ihr)

Fig. 7. Effect of Time on t h e Fracture Toughness of T,-605 Aged in Argon a t 760°C and Tested a t 3 1 6 ° C .

t h e r e was v a s t l y l e s s k v e s phase i n t h e g ra in boundarks of specimens

aged a t ’760°C f o r equal periods mid t h a t f o r -times t o 500 h r consi.d.erably more cleavage f a l l u r e was present. A comparison of Fig, 8 w i . t h Fig. L

w i l l i l l u s t r a t e t hese observations. In add i t ion , it i s seen t h a t aging i.n sir oxidizes t h e surface of L-605 p r i n c i p a l l y a t t h e gr-ain bo-undaries to depths t h a t increase with t i m e ; however, these e f f e c t s are not considered se r ious i n terms of impact r e s h t a n c e -

A shortage of specimens prevented agi.ng treatments longer than 1000 hr

a t 769°C. However, t h e necessi.ty o f huw-ing longer term behavior r e s u l t e d i n t h e extyapolation shown i n Fig. ‘7. I-t i s app%i-ent t h a t t h e f m c t u r e

toughness decreased a t a rapid rake , and thal; specimens aged f o r 448 h r (Fig. 8) exhibited. t o t a l i n t e rg ranu la r frac-Lure. it was concluded., -there- f o r e , that L-605 aged for g r e a t e r periods than 11100 h r a t ‘760°C wou1.d be b r i t t l e , be sens i t i ve t o impac-t loading, and frackure a t impact energies be-tween 20 and 30 f t - l b .

0

Lo

9

W

W

0

3

cn Z

t- 0

W

cn

E! w QI 3 c- 0 6

LL LL

cn z

0

e

0

W

cn 11c

LL W

I- 0

z

16

Aged below 760°C -- The e f f e c t of aging temperature on the f r a c t u r e toughness of' L-605

i s shown i n Fig , 9. A t temperatures gene ra l ly above 7 O O 0 C , aging i n a i r

o r an i n e r t atmosphere f o r 500 h r or longer w i l l cause ernbrittlement.

aging temperatures of 650°C OT lower, t h e f r a c t u r e toughness (240 f t - l b )

f o r an aging time of 448 h r i s t h e same as f o r t h e solution-annealed

condition.

Yukawa and Satol* ind ica t e s t h a t ti1ous.xnd.s o f hours a r e necessary for.

embr i t t l i ng phase t o p r e c i p i t a t e a t t h e s e lm temperatures The f r a c t u r e

mode of' specimens aged at, t h e l m e r temperatures i s t ransgranular (high energy) t e a r wi th considerable deforimtion.. A t y p i c a l high-energy t e a r

fracture shown i n Fig. 1.0 was obtained. a f t e r aging at 650°C and testing

a t 316°C.

A t

The time-tempe7nati~re-transfoz.-f~tioil diagrani derived by

Reentry Heating Effects

Reentry heat ing caused by t h e e a r t h ' s atmosphere was s i m u l a k d by

heat ing aged specimens t o 1.1 . lO"C f o r 200 see.

f o r LO00 h r at 870°C were impact t e s t e d a t 1080°C. Nine specimens showed f r a c t u r e toughnesses i n the range 18.0 t o 20.5 f t - l b , and one he ld a-t 1110°C f o r 400 sec showed 21.0 f t - l b . These values are about whst would

be expected by extrapolahion of t h e cume f o r 4000 h r aging i n E'ig. 2 (p. 9 ) . Thus, r een t ry heat ing tines of 200 t o 400 sec are apparently not s u f f i -

c i e n t l y long for toughness recovery.

For example, spechens aged

Tensile Tests

The s t r a i n r a t e s associated wi th normal t e n s i l e t e s t s a r e many times

l e s s than those encountered during jmpact loading. However, t h e conclu-

si.ons regarding t h e ernbrittlement of 1,-605 due t o aging are t h e sane as those obtained f r o m t h e impact tests. The L-605 a.3.7.oy-, over the w i d e range of aging conditions s tudied, r e t a i n e d s u f f i c i e n t t e n s i l e s t r eng th

and ductl1it.y for many conventional ( tensi . le) applicatj .ons a t temperatures above 540" C.

The e f f e c t o f aging t i m e and temperature on the -'ierisile behavior ol" L-605 i s i3_lust,rated i n P'igs. II. and 1 2 . The increase i n y i e l d and u l t i - mate t e n s i l e s t r eng th occurring d-iiring t h e i n i t i a l 500 h r of aging a t

E7

ORNL-DWG 70-2463 280 -

Fig. 9. Effec t o f Aging Temperature on t h e Fracture Toughness of L A 0 5 Aged i n Argon f o r U+8 hr and Tested a t 316°C.

Fig. 1Q. Frac ture Mode of L-605 Aged i n Argon a t 650°C for 448 h r and Impact Tested a t 3 1 6 ° C . HGL + 15 ml H2SO4 i- 40 m l HNO3 + 25 g FeC13, e lec t ropol i shed . Reduced 15%.

Etchant: 100 ml H 2 0 + 40 ml CH3COOH + 40 ml 500X.

ORNL- DIVG 70- 2464 ~ . . . ~ . . . .. .. .. ....

ULTIMATE TENSILE STRENGTH

1

....._I (x1031

~ ....

ULTIMATE TENSILE S1-HENGTH

TEMPERA1 URE ~~

~

YIELD ! j T R E N G T t i - - ( 0 . 2 70 OFFSET)

-

0 1000 2000 3000 4000

( b ) TESTED AT 540°C

AGING TIME (hrl

Fig. 11. The Effect of Aging Time and Temperature an the Tensi le Propert ies of L-505 Tested a t Room Temperature and a t 540°C.

ORNL- OWG 70- 2465

1

I I 700 800

I 9 00 4000 600

A G I N G TEMPERATURE ("C)

( U ) TESTED AT ROOM TEMPERATURE

-.

I I I 800 900 1000 600 700

AGING TEMPERATURE ('C)

( b ) TESTED AT 540T

Fig. 1 2 . The Effect of Aging Temperature on the Yield Strength (0.2% Offset) of L-505 Tested at Room Temperature and a t 540°C.

20

8 7 0 ° C i s a t t r i b u t e d to p r e c i p i t a t i o n of carbides ( M 2 j C b and M6C) Between 500 and 4030 h r t h e raves phase (Co2W) coarsened and t h e

increased (overaging) i n both the gra in boundaries and matr ices ,

and Co2W. quan t i ty

r e s u l t ing

i n a decrease i n t h e y i e l d a.nd ul t imate t e n s i l e streng-Lhs a t both room temperature and 540°C.

deplet ion of tungsten from t h e matrix.

of both t h e Laves phase (Co2W) and carbides (MZ3C6 and M b C ) also r e s u l t e d i n severe l o s s of t e n s i l e d u c t i l i t y , as i l l -ustra , ted i.n Fig. 13.

This l o s s of s t r eng th i s a t t r i b u t e d i n p a r t t o t h e Continued p r e c i p i t a t i o n and groWth

Tle ul t imate t e n s i l e s t r eng th decreased during the i n i t i a l 500 hr

as a r e s u l t of aging at 815 and 7 6 0 ° C (Fig. 1.1). :€owever, t h e yi.eld

s t r eng th (0.2% o f f s e t ) increased s l igh t , ly with a loss of t e n s i l e d l l c t i l i t y

(FTg- 13).

both y i e l d and ul t imate t ens5 le s t r eng ths and a f u r t h e r loss of d u c t i l i t y .

Tfle following is offered as an explanation f o r tinis behavior.

Aging f o r 1.000 h r at 760 a,nd 815°C r e s u l t e d i n an increase i n

Aging at 7 6 0 ° C f o r 500 h r promoted p r e c i p i t a t i o n of b C 3 , M 2 3 C 6 ,

MbC, a-C6,W, p-Co3W, and CozW (ref. YI), where t h e underlined phases a r e metastable. 1ni.tial.ly the C'L-CO3W phase 7.s coherent wi th t h e matrj.x, but

a f te r lorig aging times i-t transforms -Lo t h e noncoherent i3-Co3W phase. l5 Aging times longer than 1000 h r a t 760°C: r e s u l t e d i n g r e a t e r ul t imate tensi-le and y i e l d s t r eng ths because a t 'chis lcxw temperature t h e aging

r eac t ions are still incomplete. Microskructures i l l u s t r a t i n g t h e e f f e c t

of aging t i m e a t 760°C are shown i n Fig. 14. r e s u l t e d i n g r e a t e r p r e c i p i t a t i o n a.nd embrittlement , a s e-xhibited by t h e in t e rg ranu la r f r a c t u r e s . Aging a t 815" C v K L 1 probably r e s u l t i n Lhe same

behavior as exhibi ted af; 7 6 0 ° C bu t a t greater rtites. A t 8 7 0 ° C not only do the aging r e a c t j ons and hence embrittlement

Increased aging time merely

O c c u Y at g r e a t e r r a t e s (than at 815 and 7 4 O " C ) , but only M 2 3 C 6 , M,C, and C02W are found i n t h e microstructure.'5-17 The microstmctures of

1 5 N . Yukawa and K. Sato, "The Correlation Between Micros'Cructure and S t r e s s Ruptirre Propert ies of a Co-Cr-Ni-W (HS-25) Alloy," Trans. Japan Ins t . Metals - 9, (Supplement ) (1968). -

l6E. E. Jenkins ~ Embrittlement of Zaynes Alloy No. 25 Durin-, Report No. 817-1390, Haynes S t e l l i t e Company, Kokomo, Indiana ( k y 21, 1958).

I 7 S e T. Wlodek, Embrittlement of a Co-Cr-W (L-605) Alloy, R-61-FPD-538 -- (kc, 1, 1.961).

21

Fig. l3. The Effect of Aging Time and Temperature on the Tensile D u c t i l i t y of L-fLIS Tested at Room Temperature and at 540°C.

22

0

0)

m

cx) 0)

0

42

0

J3 c

..

.%.

.

23

L-605 aged f o r 30(3 h r a t 870, 815, and 760°C a r e compared i n Fig. 15. It i s qu i t e evident t h a t t h e morphology of t h e p r i n c i p a l phase changes

with temperature.

Specimens aged at 870°C for 4000 hr were heated to 1110°C f o r 200 sec

t o s imulate r e e n t r y heat ing. Results of subsequent t e n s i l e t e s t s at 1080°C showed no recovery of d u c t i l i t y .

promote d u c t i l i t y recovery i n 200 sec.

The sol-utioning r a t e i s too s luggish t o

COP?CLUS IONS

Prolonged exposure of L-605 i n vacuum, argon, o r a i r a t temperatures

ranging from 7c)O t o '300°C w i l l r e s u l t i n severe a l l o y embrittlement.

maximum rate of embrittlement occurs a t 870 t o 900°C and always within t h e i n i t i a l 50 t o 100 hr.

much less, but maxi.mum loss of toughness occurs wi th in t h e i n i t i a l 590 hr .

The

At lower temperatures t h e embr i t t l i ng rate i s

The p r i n c i p a l ernbri t t l ing r eac t ion i s t h e p r e c i p i t a t i o n of t h e Laves

phase, C02W. However, a t lower aging temperatures of 650 t o P;OO"C an added inducement t o embrittlement may w e l l be t h e p r e c i p i t a t i o n of carbides (MZ3C6, M6C, and M7C3), a-Co3W, and p-Co3W.

of toughness occurred during the i n i t i a l 50 hr. f o r longer aging times w a s only s l i g h t l y l e s s than f o r specimens aged a t 870°C.

subsequent t o an aging exposure a t 750 to 900°C for periods g rea t e r than

5 0 hr i s severe ly reduced because f r a c t u r e can occur at luw impact energies .

At '760°C t h e g r e a t e s t loss The loss of toughness

Therefore, t h e a b i l i t y of E605 t o s u s t a i n impact without f a i l u r e

The r e s u l t s of t e n s i l e tests a t room temperature and 540°C showed

t h a t aged L-605 su f fe red a severe loss of t e n s i l e d u c t i l i t y .

of' aged material were t o t a l l y in t e rg ranu la r because of g ra in boundary pre-

c i p i t a t i o n . At lower aging temperatures, s u f f i c i e n t t e n s i l e d u c t i l i t y was

r e t a ined a t 5L+O0C f o r app l i ca t ion a t and above t h i s temperature. However,

severe loss of d u c t i l i t y was exhib i ted a t room temperature. A b r i e f rehea t ing a t l l l O " C , a s might be expected on r een t ry , did not r e s t o r e duet i Lity.

A11 f r ac tu res

Fig. 15. Tensile Fractures and Kicroszructures of L-605 Aged for 533 hr and Tested at 540°C. ( a ) A& 2% 760"C, (3) aged st 815"C, end ( e ! aged a-t 870°C. Potentiostetically Etched. 13C:OX.

25

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NAVY FACILITIES ENGINEERING COMMAND, Department o f t h e Navy, Code 042, Washington, E 20390

M. D. S t a n

NAVY SPACE SYSTEMS ACTIVITY, A i r Force Unit Post Off ice , Los Angeles, CA 90045 ATTN: R. V. Silverman, Code 40

Commading Off icer

PACIFIC NORTHWEST LABORATORY, P. 0. Box 550, Richland, WA 99352

Direct o r

RADIO CORPORATI071J OF AEJlERICA, AEC, E l ec t ron ic Components and Devices, 415 S. 5th S t r e e t , Harr ison, NJ 07029 M. J. Hegarty

SATJDIA CORPORATION, P. 0. Box 5800, Albuquerque, NM 77115

J. R. Holland J. McDonald P. D. O'Brien

THF,RMO ELEXTP.ON CORPORATION, G5 F i r s t Avenue, Waltham, MA 02154

L. Benker

TFN SYSTEMS, One Space Park, Redondo Beach, CA 90278 J. Blurnenthal S. E. Bramer A. Hoffman I. Jones J. Ogren

UNION C m I D E CORPORATION, 270 Park Avenue, New York, NY 10017 T. A. Nemzek J. A. Swartout

WESTINGHOUSE ASTRONUCLFSLR M O R A T O R Y , P. 0. Box 10864, P i t t sburgh , PA 15231 W. G. Parker

IJSAEC OAK R I I X E OPERATIONS, P. 0. Box E, Oak Ridge, TN 37830 R. J. Hart Research and Technical Support

USAEC TECHNICAL INFORMATION CENTER, P. 0, Box 62, Oak R i d g e , TN 37830

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