Metallurgical and Materials Transactions a Volume 14 Issue 9 1983 [Doi 10.1007_bf02645557] R. a....

8/10/2019 Metallurgical and Materials Transactions a Volume 14 Issue 9 1983 [Doi 10.1007_bf02645557] R. a. Outlaw; D. T.

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Th e iffusivi ty of H ydro ge n in N b Stabilized Stainless Steel

R . A . O U T L A W a nd D . T. P E T E R S O N

The evolu t ion of hydrogen f rom 347 s ta in less s tee l has been s tudied by us ing a rea l t ime dynamictechnique unde r u l t rah igh vacuu m condi t ions . A uger e lec t ron spec t roscopy was used to de termine thesur face composi t ion as a func t ion of t ime and tempera ture . The sur face f i lm on the e lec t ropol i shedsamples was fou nd to be approx imate ly 1 5/~ th ick and cons is ted of a carbon -oxyg en comp lex and ameta l ox ide (Fex0y) . Upo n hea t ing to 400 ~ the carbon-o xygen comple x desorbed as CO andthe remain ing oxygen and carbon began to incorpora te . Also a t th i s tempera ture su l fur began todi ffuse out of the bulk to the sur face and a t approxima te ly 800 ~ form ed a comple te monolayer.A t 900 ~ ca rbon and oxygen v i r t ua l ly d i sap pea red , l e av ing t he m ono lay e r o f su l fu r a s theon ly su r f ace con t aminan t . The hy d ro gen d i f fu s iv i t y was fo u nd t o f o l l o w c lo s e ly t he e qua t i onD = 7 .01 x 10 7 ex p [ -4 8 . 0 /R T ] m 2 p e r s e c on d ov e r th e e n t ir e t emp e ra tu r e r an ge s t u d ie d , t husindica ting tha t hydro gen evo lu t ion i s no t s igni f icant ly a ffec ted by the changing sur face composi t ion .The som ewhat h ighe r va lue of the d i ffus iv i ty obta ined in th i s work com pared to pas t measurem entsin aus ten i t ic s ta in less s tee ls may indica te the impor tance of sample preprocess ing and u l t rah ighvacuum condi t ions in minimiz ing the e ffec ts of sur face layers .

I . I N T R O D U C T I O N

LTHOUGH he re a r e ex t ens ive d i f fu s ion s t u d i e s o fhyd roge n in othe r a ustenit ic stainless steels , 1 '2 '3 ver y l i t t leinformat ion ex is t s on the d i ffus iv i ty of hydrogen in 347stainless steel . 4 '5 This part icular meta l is cha racteriz ed b ythe addit ion of n iobium (Nb + Ta ~ 10 t imes the carbonconcent ra t ion) to prevent chromium carb ide prec ip i ta t iona t the gra in boundar ies . The s tab i l iza t ion preserves goodcorros ion res i s tance fo l lowing weld ing or exposure a t t em-pera tures up to 900 ~ thus making i t a h ighly funct iona lmater ia l for many appl ica t ions in the space program. Thispaper presents measurem ents of the hydrogen d i ffus iv i ty in347 s ta in less s tee l as de termined by a rea l t ime dynamictechnique appl ied under u l t rah igh vacuum (UHV) condi -t i ons . The UHV fu rnace and t he dynamic t e ch n iq ue em-

p loy ed have been r ep o r t ed e l s ewh e re . 6 Da t a a r e a l sopresented on the changing sur face comp osi t ion of the meta las a func t ion of t ime and tempera ture .

I I E X P E R I M E N T A L

Cyl indr ica l samples 12 .5 m m in d iameter and 25 turn inlength were cu t f rom an annealed rod wi th AST M gra in s izeno . 8 obta ined f rom A1-Tech Specia l ty S tee l Company,Durki rk , New York . A weight percent ana lys is of th i s rodshowed Cr = 16 .47 , Ni = 9 .73 , Mn = 1 .33 , Nb = 0 .90 ,Si = 0 .17 , S = 0 .00 9 and C = 0 .01 . Suff ic ien t hydrog enexis ted in the as - rece ived samples to obvia te the needfor charg ing . The samples were e lec t rop ol i shed wi th ame than o l 6 pc t by vo lum e pe r ch lo r i c a c id so l u t i on a t- 8 0 ~ for f ive minutes , r insed wi th methanol , and thenquickly hot a i r d ried before inser t ion in to the UH V furnace

R . A . O U T L A W i s R e s e a r c h S c i e n ti s t N A S A L a n g l e y R e s e a r c h C e n -te r Ham pton VA 23665 . D T. PETE RSO N i s Meta l lu rg i s t 222 Me ta l sD e v e l o p m e n t A m e s L a b or a to r y A m e s 1 A 5 0 0 11.

Manu scr ip t submi t t ed March 21 1983.

or sur face ana lys is sys tem. Elec t ropol i sh ing lowered thesur face roughness to near one , as ind ica ted by the h igh

surface re f lec t iv i ty, and minimized the amount of sur facecontaminants and the th ickness of the oxide layer.

Samples were loaded in to a 347 s ta in less s tee l sampleholder ( tha t had been previous ly vacuum degassed for twohours a t 1200 ~ and then inser ted in the UH V furnace ,shown schemat ica l ly in F igure 1 . Af ter lower ing the sampleto poin t A where i t was kept a t room tempera ture byexterna l forced a i r cool ing , the sample exch ange reg ion wasthen baked for 36 hours a t 150 ~ Fol lowing cool down , theiso la t ion va lve was opened and the furnace hea ted to theexper ime nt tempera ture . Suff ic ien t t ime was a l lowed forthe furnace components to degas and the pressure to reacha s tab le va lue of approximate ly 1 10 -7 Pa in the measure-men t vo l ume . Th e s a m p le an d ho lde r we r e t hen qu i ck lylowered in to the hot zone where the sample tempera tureincreased a t a ra te of 60 ~ per minute in i t ia l ly and thendecreased to average of about 20 ~ per minute . The de-sorbed gas was channeled by the furnace tube up in to themeasu r e m e n t v o lu m e w he r e i t was s i m u l t a neous ly pumpedthrough a ca l ibra ted res t r ic t ing annular conductance in tothe lower volume where the pressure was approximate ly1 1 0 - 9 Pa. A ca l ibra ted quadrupole mass spec t rometermeasured the composi t ion and pressure of the gas evolvedfrom the sample and a l lowed a de term inat ion of the d i f -fus ion coeff ic ien t f rom the var ia t ion in hydrogen pressure asa func t ion of t ime. The concent ra t ion f rac t ion ,C t)/Coo fhydrogen in the s ta in less s tee l sample a t any t ime was de ter-

min e d b y

C( / ) _ 1 2 6 ( 'Co VkTCo Jo P t) dt [1]

where P t) i s the pressure in the measu remen t volum e, T i sthe sys tem tempera ture , 6 i s the conductance of the annularop e n in g b e t wee n t h e m e a s u remen t vo l u me and t he l owervolume (6 .27 l i te rs per second) , V i s the volume of thesample , t i s the desorp t ion t ime, k i s Bol tzm ann 's cons tan t ,and Co is the total concentrat ion in the sample.

METALLURGICAL TRANSACTIONSA U . S . GOVERNMENT WORK VOLUME 14A SEPTEMBER1 9 8 3 1 8 6 9NOT PROTECTED BY U . S. COPYRIGHT


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3 0 l i t e r s / s e c

r , t )Upper vo lume

p ,

0.013 JJP t wi re J

Rad iatio n Y. [shields ~ _-W-'~ -[]-

347 s t a in l e s s j ~ ~steel sample

C apede stal --j

r IG

Sightport

5N3

Sample~ xchange

port

~ Isolat ionvalve

S L .

15

l i t e r s / ~ e

UHV furnace

P t / P t R hI thermocouple

f

400 l i t e r s / se c I P

Fig. I --S chcm atic of the UHV furnace and desorption system. Pressure in thc measurcmcnt chambcr withfurnace at 900 ~ was ~-l x l0 -7 Pa.

The diffusion coefficient was determined from a logP t )vs t plot and is given by

2.3mD = [2]

wh ere m is the slope, l is the length of the sample, d is thediameter of the sample, and fl, is the root of the Besselfunction J0(~,) = 0. This equation is similar to that usedby Hill and Johnson7 but the technique used he re was tomeasure the pressure ch anges in real t im e and u nder UHVconditions rather than b y a cum ulative metho d employinga storage volume.

AES experiments were performed using a Varian cylin-drical mirror analyzer and scanning electron gun within anion/sublimation-pumped, metal sealed, stainless steel UHVsystem with a base residual pressure of < 1 x 10 -8 Pa. Re-

sidual gases in the system were analy zed using a UT I massspectrometer and consisted largely of H2, CO, CO2, andmino r traces o f CxHy. Thin disk shaped electropolishedsamples 7.5 mm in diameter and 0.25 m m thick of the 347stainless steel were admitted into the U HV surface analysischamber by a UHV vacuum sample transfer system, thusemploy ing an identical procedu re to that described above forthe hydrogen evolution m easurements. A 5 keV, 1 /xA pri-mary beam was used to make the AES measurements alongwith a 2 eV peak-to-peak mo dulatio n voltage. A V arianmultiplexer was used to sw eep the cylindrical m irror ana-lyzer through Auger peaks of interest.

I I I. R E S U LT S A N D D I S C U S S I O N

An AES survey of the electropolished stainless beforebeating is shown in Figure 2(a). In addition to the Fe LMM

1870--VOLUME 14A SEPTEMBER 1983 METALLURGICAL TRANSACTIONS A


3/6

CFe

oi

200 400 600t I . t I

8 0 0 1 0 0 0

E l e c t r o n e n e r g y , e V

a)

Z

~ J J J

0 200 400 600 800 1000

E l e c t r o n e n e r g y , e Va)

4

C~

O

7 m

f

6 /Fe LMM

4

1 - ~ M V V

I I t 1 l I i

0 3 6 9 12

t , r a i n

b)Fig, 2 - - a) AES survey of the 347 stainless steel surface com posit ion afterthe methanol-perchloric acid electropolish and before heating. b) Sputterprofi le throughthe surface f i lm to the ulk metal . Film thickness wasapproxim ately 15 ,~, thick. LM M, KLL, and MV V are the specific Aug erelectron transitions monitored.

series, peaks from oxy gen, carbon, and chlorine are quiteapparent. S putter profiling by 3 kV argon ions through thissurface film is shown in Figure 2(b). A s soon as sputteringwa s initiated, C1 disappeared within secon ds. Af ter the car-bon was sputtered away, the oxygen signal from the under-lying metal oxide became the prominent peak. Thesechanges could be explained by an adso rbed carbon-oxygenlayer on a metal oxide layer. The slope change in the Fe

peaks after three minutes probably represents sputteringthrough the carbon-oxygen complex into the m etal oxide(Fe~Oy). A fter a short sputtering pe riod , a clean 34 7 stainlesssteel spectrum w as observed. Co mparison of the peak-to-peak amplitudes of the Fe LM M and the Fe M VV electrontransistions before and after sputtering gave an estimatedthickness of approximately 15 A for the oxide plus carbon-oxyg en surface film. s

The AES survey of an unsputtered sample at 900 ~ isshown in Figure 3(a). The expected Fe, Cr, and Ni peakshave becom e quite prominent while C and O are virtuallygone. Sulfur has becom e the predominant contaminant onthe surface. Althou gh S constitutes o nly 0.016 at. pc t in the

METALLURGICAL TRANSACTIONS A

12

I0

~3

-

c ~ 4

O K L L

C K L L

F e L M M

S L M M

O 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0

Ts , ~

b)Fig. 3 -- a ) AES survey of the 347 stainless steel surface at 900 ~Carbon and oxygen have virtually disappeared, and sulfur peak representfull mon olayer coverag e. b) Surface comp osit ion change as a function oftemperature after steady state was reached at each temperature. LM M andKLL are the specific Aug er electron transit ions monitored.

bulk, it is well know n to segrega te to grain boundaries andfree surfaces.9'~~Figure 3(b) rep resents the chang e in surface

composition after reaching s teady state at each temperature.The surface composition seem ed to change very little untilabout 400 ~ at wh ich the residual gas analyzer indicatedthe start of desorption of CO from th e surface. At approxi-mately 600 ~ the CO desorption was comp leted. Based onthe absence of any deso rbing species at this tim e, it appearsthat the continued decreasing O signal was du e to oxyg enincorporation into the bulk. Sulfur began to appear at ap-proximately 400 ~ probably because of the beginningde~orption of CO and the incorporation of ox ygen from themetal-oxide freeing up s urface sites. The surface concen-tration of the sulfur rapidly increa sed at 550 ~ and ap-proached a full m on olay er at a temperatu re of about 800 ~

VOLUME14A,SEPTEMBER1983-- 1871


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In previous studies on 304 stainless steel heated to 750 ~for 10 minutes su l fur was observ ed to increase gradual ly toan average sur face concent ra t ion of about 25 a t . pc t wi th thesul fur aggregated in to d iscre te pa tches ra ther than un i formlydis t ribu ted o ver the sur face . 9 Tho maset al. ,ohave a l so ob-served su l fur segrega t ion to the f ree sur face of pure i ronsamples tha t were e i ther vacuum mel ted or zone re f ined .They noted tha t su l fur and oxygen rep laced each o ther ac-cord ing to the gra in or ien ta t ion , the re la t ive concent ra t ions ,the d i ffus iv i t ies of su l fur and oxy gen, and the re la t ive b ind-

ing energ ies to a par t icu lar sur face . T hey a lso observed thedesorp t ion of SO2 f rom the Fe sur faces. In the present work ,no SO2 desorp t ion was observed , but Auger mapping d idindica te some minor su l fur aggregat ion super imposed on auni form su l fur sur face coverage . Essent ia l ly, the sur facedur ing the d i ffus iv i ty measurements underwent s igni f icantchemica l changes f rom 400 to 800 ~ but above 800 ~ hascons tan t composi t ion ,i . e . , the m onolay er of su l fur.

H y d r o g e n e v o l u t i o n e x p e r i m e n t s w e r e c o n d u c t e d o nthe cy l indr ical s tee l samples ove r the tempera ture range o f400 to 900 ~ in 100 ~ increments . A typica l desorp t ioncurv e at 800 ~ is show n in Figure 4. Ini t ial ly, CO w as theonly s igni f icant sur face gas desorbed f rom the spec imen~4 00 ~ and was fo l l owed by hyd rogen d e so rpt i o n f r om

the bulk . A smal l H2 peak f rom the sur face was observed ,but th is may have been f rom CO rep lacement of adsorbed H2on the wal l s of the measurem ent chamber. Th e to ta l quant i tyof CO desorbed was ca lcu la ted us ing E q. [1]C t ) = O,t ---> equil ibrium ) and co rrespon ds to single m ono laye r cov-erage ove r the area of the cylindrica l samp les ~ 12 cm2). I ti s unc lear whether the sur face was covered wi th CO or acarbon-ox ygen complex tha t reac ted at tempera ture to formCO, but the monolay er quant ity desorbed s t rongly sugges tstha t the carbon and oxygen were in the form of CO. Theshape of the hydrog en desorp t ion curve appears normal forevolu t ion tha t i s d i ffus ion cont ro l led . At a l l t empera tures ,the evolu t ion of the bulk hydrogen fo l lowed CO sur facedesorp t ion . This behavior has been observed in o ther sys-tems and sugges ts poss ib le CO blocking of hydrogen evo-lu t ion . H The sample reached a tempera ture of 800 ~ af te rabout 35 minutes and the H2 decay as a func t ion of t imebecam e l inear on a semi log sca le . Equ at ion [1] was used tode termine the re la t ive hydrogen concen t ra t ion in the sam pleas a func t ion o f t ime.

The average co ncent ra t ion de termined for the as - rece ivede l ec t ropo l i shed 347 s t a i n l e s s s t e e l s amp le s w a s Co =0.49 cm3/100 g 2 .1 x 10TMa toms/cm3) . Th is va lue agreedfavorably wi th da ta taken us ing a hot ex t rac t ion method.Rep re sen t a t i ve cu rves o fC t ) / C o f o r e ach t em pe r a tu r es tudied are presented in F igure 5 . I t should be noted heretha t comple te evolu t ion of hydrogen f rom the samples a tt he l ower t empe ra tu r e s r equ i r e s ve ry l ong t i m e s ,e . g . ,C t ) / C o = 0 .99 af te r 24 hours for T = 500 ~

The d i ffus ion coeff ic ien ts were de termined f rom Eq. [2]and the s lope of desorp t ion curves such as shown in F ig-ure 4 . Care w as taken to insure the equi l ibr ium tempe ra turehad been achieved usua l ly a f te r 35 minutes) before tak ingthe s lopes . T he d i ffus ion coeff ic ien ts a re p lo t ted as a func-t ion of rec iproca l tempera ture in F igure 6 . The va lue of thepreexponent ia l fac tor and the ac t iva t ion energy de terminedfrom a least squares f i t of the data are Do = 7.01x 10 7 .m zpe r s econd and AH = 48 .0 k J /mo le . Comp a r i son o f thepresent da ta to tha t o f Gibson , Jones , and Evans 4 for 347

/ T S a m p l e s u r l a c e d e s o r p t i o n1 0 - 1 ~ . J -

10 2

1 0 - 3

1 0 4

10

Sample bulk d e s o r p t i o n

. . . '

co

\

2 0 4 0I I ~ I

6 0 8 0 1 0 0

t mln

9 0 0

8 0 0

7 0 0

600

500

r

4 0 0

3

2 0 0

1 0 0

Fig . 4 - - Ty p ic a l desorp t ion spec t ra o f cy lindr i ca l samples o f 347 s t a in les s800 ~ Note the desorp t ion o f the CO a t ~4 00 ~ and then the inc reas ing

Hz signal .

9

C t) /Co

.4

.2

0 100 200 300 400 500

t , minF ig . 5 - Var ia t ion o f the obse rved f r ac tiona l concen t ra t ion as a func t ion ot ime and t empera tu re . A t 500 ~C t)/Co= 0 .99 a f t e r 24 h .

s ta in less s tee l i s a lso presented in F igure 6 . T hey conductedpermeat ion exper iments , no t under UHV condi t ions , andrepea ted the i r exper iments many t imes not ing tha t the per-meabi l i ty increased dur ing cont inued exposures to hydro-gen . Exposure o f the ir samples to a i r subs tan t ia l ly decreasedthe permeabi l i ty, so i t i s l ike ly tha t cont inued exper imen-ta t ion in hydrogen a t tempera ture reduced the i r sur facecontaminat ion . Compared to the present work , the i r va luesDo = 1 x 10 -7 m 2 per second, AH = 44 .4 kJ /m ole) g ive

di ffus iv it ies tha t a re much lower. Louth an and D err ick 1havereviewed the d i ffus iv i ty of deuter ium in o ther aus ten i t icstainless steels and found them to f i t Do = 4.7x 10 7 m 2

1872--VOL UM E 14A, SEPTEMBER 1983 METALLURGICAL TRANSACTIONS


5/6

i0 8

Quick and Johnson [

: : : : : : n :on:D e g: CEkvan /

e ~

5

10 9

lO 1 O

\ \ \\ \ \ \

\ \ \x\ \ \

\ \ \ \

\ \ \ \

\ \ \ \

\ \ \ \

\ \ \ \ \\\ X k \ ~ \

\ \ , \ \

.8 1.0 1.2 1.4 1.6 10 3

I/T, K IFig. 6- -A rrh en ius plots of the diffusion coefficients of hydrogen in 347stainless steel. Comp arisons with Gibson Jones and Evans Louthan andDerrick and Quick and Johnson are also presented. The error bar repre-sents a 99 pct confidence interval.

pe r second and AH = 54 .0 k J /mo le wh ich fo r hyd rogen , i fthe c lass ica l iso tope ra t io of 1 .41 for Do is obey ed, w ould beDo = 6.63 l 0 -7m 2 pe r second and AH = 54 .0 k J /m o le .The ac t iva t ion energy for d i ffus ion found in the presentwork i s thus subs tant ia l ly less than tha t observed by L outhanand Derr ick for o ther aus teni t ic s ta in less s tee ls , but becauseof the i r s imi lar preexponent ia l the d i ffu s iv i ty a t 1173 K islower only by a fac tor of 2 . They were c lear ly concernedabout the sur face condi t ion of the s ta in less s tee l spec imensand n oted tha t much o f the d i ffus ion da ta on aus teni t ic stee lsma y be suspect because of the effec t of sur face f i lms . Theoxide f i lm th ickness es t imated in the i r work was < 0.2 5 /zmand was not charac ter ized for chemical cons t i tuency. Thesurface layers on the s ta in less s tee l spec imens in th is wo rkdid not seem to a ffec t the ra te of hydr ogen evo lu t ion or ac ta s a s i gn i f i can t impedance t o hyd rog en f l ow. The l ogC t ) /C o v s t ime p lo ts became l inear wi th t ime jus t as i sexpected fo r d i ffus ion cont ro l led evolu t ion wi th no sur face

impedan ce . Su rface bar rie rs usual ly resul t in s low evolu t ionta i l s and unreproducib le va lues for the evolu t ion curves . Theplo t of logD v s l I T was a lso l inear over the tempera turerange f rom 400 to 900 ~ a l though the sur face comp osi t ionc h a n g e d f r o m a c o m p l e x c a r b o n - o x y g e n - i r o n l a y e r a t400 ~ to a mon olayer of su l fur cover ing an oxide free , 347s ta in less s tee l sur face enr iched in chr om ium at 900 ~Probably the most s t r ik ing observat ion i s the good agree-ment be tween o ur resul ts and tho se of Q uick and John son. 12Quick and Johnson s tud ied t he d i f fu s iv i t y o f hy d rogen in310 s ta in less s tee l in UHV us ing a monopole gas analyzerand d e t e rmine d Do = 5 .15 10 -7 m 2 pe r s econd andAH = 48.8 k J /m ole . In the i r s tudy, they took grea t care to

e l iminate sur face effec ts and even p la ted the spec imen sur-faces wi th pa l lad ium to insure unobs t ruc ted ent rance andegress of hydro gen. The y were a lso able to show pe rmeat ionra tes tha t var ied wi th pressure in a way cons is tent wi th nosurface contro l . The effec t of th icker oxide and con taminan tlayers in changing the observed d i ffus ion coeff ic ients hasbeen reported m an y t im es. 13,14 Usu ally, the obse rved valu esof the d i ffus ion coeff ic ients a re lower, par t icu lar ly a t low ertempera tures , and the observed ac t iva t ion energies a re un-usual ly h igh . The inf luence of sur face layers on hydrogen

evolut ion i s obvious ly an in teres t ing and imp or tant researchsubjec t , but one tha t must be ext remely complex because o fthe in terp lay of th ickness , com posi t ion , s t ruc ture , tempera-ture , and t ime. In the case of commercia l a l loys tha t canshow par t i t ioning of minor meta l l ic and nonmeta l l ic con-st i tuents to the surface, the complexity is even greater.

I V. C O N C L U S I O N S

Be tween 400 ~ and 900 ~ t he su r f ace o f e l ec t ro -pol i shed 347 s ta in less s tee l s igni f icant ly changes in com-posi t ion under u l t rahigh vacuum condi t ions . An adsorbedlayer cons is t ing of a carbon-oxy gen complex desorbs as COstart ing a t 400 ~ and oxyg en in the sur face oxide begins todisappear, perhaps by incorporation into the bulk al loy. Theth ickness of the sur face layer on an e lec t ropol i shed surface ,inc luding the carbon-ox ygen layer and the meta l oxide , w asonly about 15 A a t room tempera ture . Sul fur begins to ap-pear a t the sur face above 400 ~ and a t 800 ~ cons t i tu tesa comple t e mono laye r. The evo lu t i on o f hyd rogen f rom thebulk of 347 s ta in less s tee l does no t seem to be s igni f icant lyaffec ted by the changing surface cons t i tuency as indica tedby the l inear i ty of the Arrhenius p lo t of the d i ffus ion coeff ic i en t s and t he ag reemen t w i th l ower t empera tu re mea -surements . This f i lm is apparent ly so th in tha t there i s aneg l ig ib l e e f f ec t on t he k ine t i c s o f hyd rogen evo lu t i ona l though th i cke r ox ide and con taminan t l aye r s l e ad t os t rong a t tenuat ion . This i s fur ther suppor ted by the mea-su red d i f fu s iv i t y, D = 7 .01 x 10 -7 ex p ( -4 8 . 0 / R T) m 2per second be ing somewhat la rger than tha t de termined inpas t expe r imen t s on 347 s t a in l e s s s t ee l and fo r o the raustenit ic steels.

A C K N O W L E D G M E N T S

The authors would l ike to thank Mr. Raym ond Parker forh is ass is tance in conduct ing the AES exper iments and forpar t ia l suppor t of th is research by the Direc tor for EnergyResearch Off i ce o f Bas i c Ene rgy Sc i ences, USD OE, unde rcont rac t no . W-7405-Eng-82.

R E F E R E N E S

1. M.R. Louthan Jr. and R.G. Derrick:Corrosion Science 1975vol. 15 p. 565.

2. W.G. Perkins:J. Vac . Sci. Technol. 1973 vol. 10 p. 543.3. H .L. Eschback E Gross and S. Schulieu:Vacuum 1963 vol. 13

p. 543.4 . R. Gibson P.M .S. Jones and J .A . Evans: Atomic Weapons

Research Establishment Report 0-47/65 1965.5. P.S. F lint: USAEC Report KAPL-659 1951.6. R.A . Outlaw D.T . Peterson and F. A. Schmidt:Metall. Trans. A

1981 vol. 12A p. 1807.7. M .L. Hill and E.W . Johnson:Acta Metall. 1955 vol. 3 p. 566.

METALLURGICALTRANSACTIONSA VOLUME 14A SEPTEMBER 1983--1873


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8. P.H. HoUoway: J. Vac. Sci . and Technol. 1975 vol. 12~ p. 1418.9. A. Joshi: Interfacial Segregation W.C. Johnson and J. M. Blakely

eds . ASM Metals Park OH 1979 p. 87.10. M.T. Thomas D. R. Baer R. H. Jones and S. M. Bruemmer: J. Vac.

Sci. Technol. 1980 vol. 17 p. 25.11. R. E. Cuthrell: J . Appl . Phys . 1978 vol. 49 p. 11.

12. N.R . Quick and H.H . Johnson: Metall . Trans. A 1979 vol. 10Ap. 67.

13. A.S. Zarchy and R.C. Axtman: J. Nucl. Mater. 1978 voL 79p. 110.

14. W.A . Swansiger R. G. Musket L. J. Weirick and W. Bauer: J . Nucl.Mater. 1974 vol. 54 p. 307.

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