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Heat Treatment of a Candidate Material for 700 °C A-USC Power Plants
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ５,２ ２( ２):１ ５ ０ Ｇ １ ５ ６
He a tTr e a tme n to faCand i da t eMa t e r i a lf o r ７００ ℃ AＧUSCPowe rP l an t s YanCHONG１ ２ , Zheng Ｇ dongLIU２ , AndyGODFREY１ , Lu WANG２ , We iLIU１ , Yu Ｇ i ng WENG２ q ,
( １． Schoo lo fMa t e r i a l sSc i enc eandEng i ne e r i ng,Ts i nghuaUn i ve r s i t i i ng１０００８４,Ch i na; ２．Cen t r a lI r on y,Be j andS t e e lRe s e a r chI ns t i t u t e,Be i i ng１０００８１,Ch i na) j Ab s t r a c t:Thep r e l imi na r c a lc ompo s i t i onop t imi z a t i onandhe a tt r e a tmen tpa r ame t e r so fI nc one l７４０H we r e ychemi i nve s t i t edsy s t ema t i c a l l S i xhe a t so fexpe r imen t a la l l oy s( de s i t eda she a t４０１t ohe a t４０６)wi t hva r i edchemi Ｇ ga y． gna c a lc ompo s i t i onswe r esub e c t edt os t anda r dhe a tt r e a tmen ta tf ou rd i f f e r en ts o l u t i ont empe r a t u r e s．Duet oi t ssupe r i Ｇ j o rc omb i na t i ono fs t r eng t h,duc t i l i t oughne s st oge t he rwi t hi t smi no rme chan i c a lp r ope r t sa td i f f e r en t y,andt ychange s o l u t i ont empe r a t u r e s,he a t４０５wa scho s ena sanop t imi z edonet oc onduc tf u r t he rhe a tt r e a tmen ti nve s t i t i ons．The ga e vo l u t i ono fg r a i ns i z ewi t hs o l u t i ont empe r a t u r ef o rhe a t４０５wa ss t ud i edandt heop t ima ls o l u t i ont empe r a t u r ewa s de t e rmi ned．Af t e rs o l u t i ont r e a tmen ta tt heop t ima lt empe r a t u r e,f ou rd i f f e r en tc oo l i ngr a t e swe r eapp l i edt oi nve s t i Ｇ t et hee f f e c to fc oo l i ngr a t eont hes i z ed i s t r i bu t i onmoda landme anr ad i uso ft heγ ′p r e c i i t a t e s．Nob i Ｇmoda ls i z e ga p d i s t r i bu t i ono fγ ′p r e c i i t a t e swa sf oundf o ra l lc oo l i ngr a t e sandwa t e rc oo l i ngwa sr e c ommendedf o rI nc one l７４０H． p I nadd i t i on,t hee f f e c to fp r e Ｇ ag i nga t８００ ℃f o r１６hont hemi c r o s t r uc t u r eo fI nc one l７４０Hagedf o ral ongt imewa s s t ud i ed． I ti sf oundt ha tp r e Ｇ ag i nga t８００ ℃ wou l dr e su l ti nb i Ｇmoda ls i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e sa f t e rl ong p t imeag i nga t７５０ ℃ c ompa r ed wi t h mono Ｇmoda ls i z ed i s t r i bu t i oni ns amp l e s wi t hou tp r e Ｇ ag i ng,wh i ch mi tbe gh c aus edbyt hed i f f e r enc ei ni n i t i a ls i z ed i s t r i bu t i on moda lbe f o r eOs twa l dr i i ngo fγ ′p r e c i i t a t e si ns amp l e swi t h pen p andwi t hou tp r e Ｇ ag i nga t８００ ℃． Ke r d s:I nc one l７４０H;he a tt r e a tmen t;g r a i ns i z e;γ ′p r e c i i t a t e;me chan i c a lp r ope r t p y ywo
Du et ot h ei n c r e a s i nge n e r ema nd sa nda c c e l e r Ｇ gyd , a t e de nv i r onme n t a li s s u e st h e r ei sanu r tne edt o gen imp r ovet het he rma le f f i c i enc fc oa l Ｇ f i r ed powe r yo l an t s,e spe c i a l l nCh i na,whe r ec oa lr e s ou r c e sa r e p yi abundan tandt hee l e c t r i c i t r a t edbyc oa l Ｇ f i r ed ygene rp l an t smakeupt hema o r i t ch i evet h i s powe j y．Toa , ( ) o a l t h e a d v a n c e d u l t r a Ｇ s u e r c r i t i c a l A Ｇ U S C g p , rp l an t s ope r a t i ng a ts t e am t empe r a t u r e so f powe ７００－７５０ ℃ ands t e am p r e s su r eupt o３７ ５ MPa, a r eunde rdeve l opmen t．Thei nc r e a s edope r a t i ngpa Ｇ r ame t e r sa r esuppo s edt oi nc r e a s et het he rma le f f i Ｇ c i enc r om ４１％ (HHV,h i a t i ng va l ue)a t yf gh he [ １, ２] ( ) , r e s e n tt on e a r l ５ ０％ HHV ． H o w e v e r t h e p y i nc r e a s edope r a t i ngpa r ame t e r sp l a c emo r es t r i ngen t r equ i r emen t sont hep r ope r t i e so fc and i da t e ma t e r i Ｇ a l s,i nc l ud i ng c r e ep s t r eng t h and ox i da t i onr e s i s t Ｇ anc e．Conven t i ona lf e r r i t i candaus t en i t i cs t e e l sc an
ha rd l e tt her equ i r emen t st husa r esuppos edt o y me ber ep l a c edby Ni Ｇba s edsupe r a l l oys． I ncone l７４０H,deve l oped by Spe c i a l Me t a l s Co r ,Hun t i ng t on,We s tVi r i n i a,USA,i soneo f p g t he mos tp r omi s i ngc and i da t e Ni Ｇba s edsupe r a l l oys f o rt hema i ns t e am p i e so f７００ ℃ USCpowe rp l an t s． p I ti st hemod i f i edve r s i ono fI ncone l７４０,wh i chsu f Ｇ f e r edf r om mi c r os t ruc t ur a li ns t ab i l i t i ng l ong y dur t imeag i nga t７５０ ℃．Thenomi na lcompos i t i ono f I ncone l７４０H (ma s s％ )i sCr２５,Co２０,Mo０ ５, Nb１ ５,Ti１ ４,Al１ ４,Mn０ ３,Fe０ ０３,C０ ０３ andNiba l anc e．Compa r edwi t hI ncone l７４０,t her a Ｇ t i oo fTit oAli nI ncone l７４０Hi sl owe r edi no rde rt o e l imi na t et heex i s t enc eo fηpha s ea tg r a i nbounda Ｇ r i e sf oundi nI ncone l７４０a f t e rp r o l ongedag i ng a t [ ３ Ｇ ７] , ７５０ ℃ ． I nadd i t i on t heNbandBcon t en t si nI n Ｇ cone l７４０H a r ebo t hr educ edt oimp r ovet he we l d Ｇ
Founda t i onI t em: I t em Spons o r edbyHi ＧTe chRe s e a r chandDeve l opmen tPr o e c to fCh i na ( ２１０２AA０３A５０１) gh j B i o r aphy: YanCHONG,Do c t o r; E Ｇma i l: chongyan８７１２１０＠s i na c om; Re c e i v e dDa t e:Oc t obe r３１,２０１３ g
I s sue２ He a tTr e a tmen to faCand i da t eMa t e r i a lf o r７００ ℃ AＧUSCPowe rP l an t s
ab i l i t ft h i sa l l oy．Thes t anda r dhe a tt r e a tmen to f yo I ncone l７４０Hr e c ommendedbySpe c i a lMe t a l sCo r p． wa s１１５０ ℃ × ３０ mi nf o l l owed by WQ (wa t e r ) ( i ng p l us８００ ℃ ×１６hf o l l owedby AC a i r quench coo l i ng)．Thes amp l e sa f t e rs t anda r dhe a tt r e a tmen t a r el ongt imeagedo rc r e ept e s t eda t７５０ ℃． Fo rt hepu rpo s eo ff u r t he rchemi c a lc ompo s i t i on op t imi z a t i onandl o c a l i z a t i ono fI nc one l７４０Hi nCh i Ｇ na,de t a i l edi nve s t i a t i o n so nt h ee f f e c to fc h e m i c a l g compo s i t i onsonme chan i c a lp r ope r t i e sa swe l la st he e f f e c to fhe a tt r e a tmen tpa r ame t e r son mi c r o s t ruc Ｇ t ur ea r er equ i r ed．Thei nve s t i t i onsi nt hep r e s en t ga s t udyi nc l udepr e l imi na r ompo s i t i onop t imi z a t i on yc ba s ed ont he me chan i c a lp r ope r t i e sa f t e rs t anda rd , he a tt r e a tmen t t hee f f e c to fs o l u t i ont empe r a t ur e ong r a i ns i z e,t hee f f e c to fc oo l i ngr a t eont hes i z e d i s t r i bu t i ono fγ ′p r e c i i t a t e sandt hei n f l uenc eo f p r e Ｇ ag i nga t８００ ℃f o r１６hons i z ed i s t r i bu t i ono fγ ′ p r e c i i t a t e s． I nt heend,t her e c ommenda t i onsabou t p p chemi c a lc ompo s i t i on op t imi z a t i on and he a tt r e a t Ｇ men tpa r ame t e r sf o rI nc one l７４０Ha r ep r ov i ded．
１ Exp e r imen t a lPr o c e du r e
S i xhe a t so fI nc one l７４０H ( de s i t eda she a t gna ４０１t ohe a t４０６)wi t ht hechemi c a lc ompo s i t i onsl i s Ｇ
１５１
t edi nTab l e１we r ep r oduc edi nCh i naI r onandS t e e l Re s e a r chI ns t i t u t e( CISRI)by VIM ( va cuumi nduc Ｇ t i on me l t i ng)＋ VAR ( va cuum a r cr e Ｇme l t i ng)． The s ei ngo t swe r et henf o r n t or ods． Fo rp r e l imＧ gedi i na r c a lcompos i t i on op t imi z a t i on,s amp l e s y chemi cu tf r omt her odswe r es t anda rdhe a tt r e a t eda tf our d i f f e r en tso l u t i ont empe r a t ur e s( １１２０,１１５０,１１８０ and１２００ ℃ )． Impa c tt e s t so fCha r t chs amＧ py VＧno l e sc u t f r o mt h e s t a n d a r dh e a t t r e a t e ds a m l e sw e r e p p r f o rmeda tr oom t empe r a t ur e．Tens i l et e s t sbo t h pe a tr oomt empe r a t ur eanda t７５０ ℃ we r ec a r r i edou t i nahyd r au l i ct e s ts t emequ i t hat empe r a Ｇ ys ppedwi t ur e Ｇ con t r o l l ed f urna c e．The t empe r a t ur ef l uc t ua Ｇ t i onswe r ekep twi t h i n３ ℃．Al lme chan i c a lt e s tex Ｇ r imen t swe r econduc t edona tl e a s tt hr e es amp l e s． pe Thes t anda rdhe a tt r e a t edspe c imenso fhe a t４０５a t d i f f e r en t so l u t i on t empe r a t ur e s we r eg r ound and l i shedf o l l owi ngs t anda rd me t a l l og r aph i c a lme t hＧ po odsandt henchemi c a l l t chedi naf r e shso l u t i ono f ye HCl,HNO３andH２O wi t ht hevo l umep r opo r t i ono f １０∶１∶１０a t５０ ℃ f o r１５ mi n．Op t i c a l mi c r o s c opy ( OM) i nve s t i t i onswe r econduc t edunde ranOl ga ymＧ c r os cope．Theave r ageg r a i ns i z e swe r e pusGX５１ mi me a sur edby me anso fal i ne a ri n t e r c ep tme t hod． Fo rt hei nve s t i t i onabou tt hee f f e c to fcoo l i ng ga
Tab l e１ Ch emi c a lc ompo s i t i on so fs i xh e a t so fI nc on e l７０４Hi nv e s t i a t e di nt h i ss t udy ma s s％ g
He a t ４０１ ４０２ ４０３ ４０４ ４０５ ４０６
Cr
２４ ３８ ２５ ３０ ２５ ０８ ２５ ４８ ２５ ５７ ２５ ５２
Co
２０ ０４ ２０ ２０ ２０ ２６ ２０ １７ １９ ９２ ２０ ０２
Mo
０ ５１ ０ ５２ ０ ５２ ０ ５２ ０ ５０ ０ ５１
Ti
１ ６４ １ ２８ ０ ８７ １ ２２ １ ３８ １ ５９
Al
１ ０８ １ ４６ １ ４６ １ ４３ １ ４７ １ ４７
Nb
１ ９８ １ ９６ １ ５０ １ ５３ １ ４８ １ ５９
Fe
０ ０３４ ０ ０３３ ０ ０３３ ０ ０３３ ０ ０３２ ０ ０３３
r a t eons i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e s,f ou rd i f Ｇ p f e r en tc oo l i ngr a t e s,i nc l ud i ng wa t e rc oo l i ng (WC), o i lcoo l i ng (OC),a i rc oo l i ng andf u rna c ec oo l i ng ( FC),we r eadop t edonhe a t４０５a f t e rs o l u t i onan Ｇ ne a l i nga t１１５０ ℃．Thes o l u t i onanne a l eds amp l e s we r eageda t８００ ℃ f o r１６ handa i rc oo l ed．The ma s sf r a c t i ono ft heγ ′p r e c i i t a t e swa sa s c e r t a i ned p t hr ough mi c r o Ｇ chemi c a lpha s eana l i s me t hod．The ys γ ′p r e c i i t a t e s we r ee l e c t r o l t i c a l l t r a c t edi nan p y yex ( ) aqueouss o l u t i onc on t a i n i ng１％ NH４ ２SO４and１％ C６H８O７ H２Of r om０t o５ ℃．Acu r r en tdens i t f yo ２ / ０ ０５A cm wa sus ed．Thepa r t i c l es i z ed i s t r i bu t i on and me and i ame t e ro ft heex t r a c t ed γ ′p r e c i i t a t e s p we r ede t e rmi nedus i nganXＧ r ayd i f f r a c t r o Ｇ spe c t r omＧ e t e requ i t ha Kr a t hysma l lang l es c a t t e r i ng pped wi ( SAXS)gon i ome t e r．
C
０ ０２４ ０ ０２２ ０ ０２０ ０ ０２３ ０ ０２３ ０ ０２２
Mn
０ ３３ ０ ３２ ０ ３３ ０ ３４ ０ ３４ ０ ３４
S i
０ ０６７ ０ ０５４ ０ ０５１ ０ ０５２ ０ ０４９ ０ ０４８
B
０ ００２１ ０ ００１０ ０ ００１２ ０ ０００６ ０ ０００５ ０ ０００５
S
０ ００１ ０ ００１ ０ ００２ ０ ００１ ０ ００１ ０ ００１
Ni
Ba l anc e Ba l anc e Ba l anc e Ba l anc e Ba l anc e Ba l anc e
Fo rt hei nve s t i t i onabou tt hee f f e c to fp r e Ｇ ag Ｇ ga i nga t８００ ℃ ont hes i z ed i s t r i bu t i ono fγ ′p r e c i i pＧ , t a t e sa f t e rl ongt imeag i nga t７５０ ℃ bo t hso l u t i on anne a l edandso l u t i onanne a l ed p l us p r e Ｇ ageds amＧ l e so fhe a t４０５ we r el ongt imeageda t７５０ ℃ f o r p ８０００h．Thes amp l e sf o rs c ann i nge l e c t r onmi c r os co Ｇ SEM)obs e r va t i on we r ep r epa r edf o l l owi ngt he py ( r oc edur e sde s c r i bedabove．TheSEM expe r imen t s p we r econduc t edonaTe s c anLYRA３ mi c r os copeop Ｇ e r a t eda t２０kV．
２ Re s u l t sandDi s c u s s i on
２ １ Pr e l imi na r ompo s i t i onop t imi z a t i on yc Asl i s t edi nTab l e１,t hechemi c a lcompos i t i ons o ft hes i xhe a t so fI ncone l７４０Hcou l dbed i v i dedi n t o twoc a t ego r i e sa c co rd i ng t ot he Nb con t en t,wi t h
１５２
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
he a t s４０１and４０２c on t a i n i ng２ ０ ma s s％ Nb,wh i l e t her e s tf ou rhe a t sc on t a i n i ng１ ５ma s s％ Nb．Toi n Ｇ ve s t i a t e t h ee f f e c to ft h eT i t o A lr a t i oo nt h e m i Ｇ g , c r os t ruc t u r es t ab i l i t chan i c a lp r ope r t i e st he yandme r a t i oso fTit oAli ne a chc a t ego r r ede s i o y we gnedt exh i b i tat r ans i t i ona lchangef r oml owt oh i hl e v e l ． g , I nadd i t i on t he r ewe r ea l s od i f f e r enc e si nt hecon Ｇ t en to ft r a c ee l emen tsucha sB． Thet ens i l et e s tr e su l t so ft hes i xhe a t sa tr oom t empe r a t u r eand７５０ ℃ a r eshowni nF i １and２, gs r e spe c t i ve l c tt oughne s sr e su l t sa tr oom y．Theimpa t empe r a t u r ea r e shown i nF i ３．Fo r me chan i c a l g r ope r t i e s,i nt hef i r s tp l a c e,t heduc t i l i t fhe a t p yo ４０１ wa s muchl owe rc ompa r ed wi t ht heo t he rf i ve he a t sa ta l ls o l u t i ont empe r a t u r e si nve s t i t ed． I ti s ga suppo s edt obec o r r e l a t ed wi t ht hef o rma t i on o fη s ea tt heg r a i nbounda r i e si nhe a t４０１wi t hah i pha gh ( / ) , ( Tit oAlr a t i o １ ６４ １ ０８ a sshowni nF i ４ a)． g Evenwo r s e,t hef o rma t i ono fηa tt heg r a i nbounda Ｇ r i e s wa s de t r imen t a lt ot heimpa c tt oughne s sa t ( ) , r oomt empe r a t u r e F i ３ wh i chwa sa l s or epo r t ed g [] byZhaoi nh i si nve s t i t i onsonI nc one l７４０４ ． S imi Ｇ ga
l a r l heduc t i l i t fhe a t４０６a t７５０ ℃ wa sex Ｇ y,t yo t r eme l ow,wh i chi sa t t r i bu t edt ot hef o rma t i ono f yl ( ) ) c e l l u l a rM２３C６c a r b i d e s( F i ４ b a t t h e r a i nb o u n d a Ｇ g g [] r i e so fhe a t４０６８ ．Thei n t e r f a c eo fc e l l u l a r M２３C６ c a r Ｇ b i d eand ma t r i xp r ov i dedan e a s i e r pa t hf o rc r a ck r opaga t i on．Af t e rp r e c l ud i nghe a t s４０１and４０６,t he p f ur t he rchemi c a lcompos i t i onop t imi z a t i onwa sma i n Ｇ l s edont hef l uc t ua t i onso fme chan i c a lp r ope r t yba y a td i f f e r en tso l u t i ont empe r a t ur e s．I ti sf oundt ha t t hes t r eng t hf l uc t ua t i onso fhe a t４０２a tbo t hr oom t empe r a t ur eand７５０ ℃ we r er a t he rl a r r e Ｇ ge．The , f o r ei t wa sp r e c l udedf o rcons i de r a t i on．Al t hough s e s s i ngt heh i s timpa c tt oughne s s,t hey i e l d pos ghe s t r eng t handt ens i l es t r eng t ho fhe a t４０３ we r et he l owe s tbo t ha tr oom t empe r a t ur eand７５０ ℃．I ti s r a l l l i evedt ha tt he y i e l ds t r eng t ha th i gene y be gh t empe r a t ur eha sac l os er e l a t i onsh i t ht hec r e ep p wi , rup t ur es t r eng t h．Asar e su l t he a t４０３ wa sa l so ru l edou tf o rcons i de r a t i on,l e av i ng on l a t s４０４ y he and４０５． I tc anbes e enf r om F i ha the a t s gs．１－３t ４０４ and ４０５ exh i b i t ed a good ba l anc e among s t r e ng t h,du c t i l i t c tt oughne s s．Asar e su l t, yandimpa
F i １ Ev o l u t i ono fs t r eng t handdu c t i l i t fI nc on e l７４０Ha tr o omt emp e r a t u r ewi t hs o l u t i ont emp e r a t u r e g yo
F i ２ Ev o l u t i ono fs t r eng t handdu c t i l i t fI nc on e l７４０Ha t７５０ ℃ wi t hs o l u t i ont emp e r a t u r e g yo
I s sue２ He a tTr e a tmen to faCand i da t eMa t e r i a lf o r７００ ℃ AＧUSCPowe rP l an t s
１５３
F i ３)．Howe v e r,whe nt het emp e r a t u r ewa s１１２０ ℃ , g i twa sno th i od i s so l vea l lt hec a rb i de s． ghenought The s eund i s so l ved p r ima r c a r b i d e s w i t hl a r es i z e y g wou l dr ema i ni nt hemi c r os t ruc t ur eanda c ta si n i t i a l c r a cks i t e sdur i ngc r e ep．The r e f o r e,t hesu i t ab l eso Ｇ l u t i ont empe r a t ur ef o rI ncone l７４０H wa s１１５０ ℃ a t wh i cha l lt hep r ima r a rb i de swe r ed i s so l vedwi t hＧ yc ou texc e s s i veg r a i ncoa r s en i ng．
F i ３ Ev o l u t i ono fimpa c tt oughn e s sa tr o om g t emp e r a t u r ewi t hs o l u t i ont emp e r a t u r ef o r s i xh e a t so fI nc on e l７４０H
( a)１１２０ ℃ ; ( b)１１５０ ℃ ; ( c)１１８０ ℃ ; ( d)１２００ ℃．
F i ４ Gr a i nbounda r r e c i i t a t e si nh e a t４０１ ( a)and g yp p h e a t４０６ ( b)
he a t s４０４ and ４０５ we r e cho s en a st he op t imi z ed he a t st oc onduc tf u r t he ri nve s t i t i onsont hehe a t ga t r e a tmen to fI nc one l７４０H．Neve r t he l e s s, i ti swo r t h no t i ngt ha tt heabovechemi c a lc ompo s i t i onop t imi Ｇ z a t i oni sr a t he rr ough, wh i ch r equ i r e sf u t u r er e Ｇ s e a r ch wi t hr e spe c tt ot he mi c r o s t ruc t u r es t ab i l i t y andc r e eps t r eng t h． ２ ２ Ef f e c to fs o l u t i ont empe r a t u r e I nt he s t anda r d he a tt r e a tmen to fI ncone l ７４０H,t hes o l u t i ont empe r a t u r ei s１１５０°C． I no rde r t oi nve s t i t et hee f f e c to fs o l u t i ont empe r a t u r eon ga t heg r a i ns i z eo fI nc one l７４０H,t heop t i c a l mi c r o Ｇ r aphso ft hehe a t４０５he a t Ｇ t r e a t eda tf ou rd i f f e r en t g so l u t i ont empe r a t u r e swe r et akenanda r eshowni n F i ５． I ti sf oundt ha t,whent hes o l u t i ont empe r a Ｇ g t ur ewa sbe l ow１１５０ ℃ ,t heg r a i ns i z eo fhe a t４０５ kep ta r ound１００μm,whe r e a sexc e s s i veg r a i nc oa r s Ｇ en i ng wa sobs e r ved whent hes o l u t i ont empe r a t ur e wa sh i rt han１１５０ ℃．Theave r ageg r a i ns i z e so f ghe t hes amp l e st r e a t eda ts o l u t i ont empe r a t u r e so f１１８０ and１２００ ℃ we r el a r rt han２２０μm．Theexc e s s i ve ge r a i nc oa r s en i ngl edt oasha r r opo fimpa c tt oughＧ g pd ne s sa tr oom t empe r a t u r ef o rhe a t４０５ ( showni n
F i ５ Op t i c a lmi c r o s c op e so ft h es amp l e ss o l u t i on g t r e a t e da td i f f e r en tt emp e r a t u r e s
２ ３ Ef f e c to fc oo l i ngr a t e Thee f f e c to fcoo l i ngr a t ea f t e rso l u t i ont r e a t Ｇ men tont hes i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e sha s p [ ] be eni nve s t i t edi no t he rNi Ｇba s edsupe r a l l oys９Ｇ１８ ． ga I ti sf oundt ha tf a s tcoo l i ng r a t e,such a s wa t e r i ng,t i c a l l e adst ot hef o rma t i ono fmono Ｇ quench yp yl [ ] moda ls i z ed i s t r i bu t i ono fr e f i nedγ ′p r e c i i t a t e s９Ｇ１１ ． p Ont hecon t r a r l owe rcoo l i ng r a t el e adst ot he y,s f o rma t i on o fb imoda lsome t ime seven mu l t imoda l , s i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e s wh i chi sbe l i eved p t or e su l tf r om mu l t i l ed i s t i nc tbur s t so fnuc l e a t i on p o fγ ′p r e c i i t a t e sa td i f f e r en tunde r coo l i ngsdur i ng p con t i nuouscoo l i ng．Whent hea l l oyi scoo l edt oar e l Ｇ a t i ve l i rt empe r a t ur ej us tbe l ow γ ′p r e c i i t a t e yh ghe p so l vust empe r a t ur e,t hef i r s tnuc l e a t i onbur s twi t h l ow d r i v i ngf o r c eandh i i f f us i v i t ake sp l a c e, gh d yt br i ng i ngou tt hef o rma t i ono ft hef i r s tgene r a t i ono f γ ′p r e c i i t a t e s w i t hl o w e r n u m b e r d e n s i t ．T h e s e p y coa r s eγ ′p r e c i i t a t e sa r eo f t enr e f e r r edt oa spr ima Ｇ p r ′p r e c i i t a t e s．Whent hea l l oyi sf ur t he rcoo l ed, yγ p l owe rd i f f us i v i t i rd r i v i ngf o r c ewou l dl e ad yandh ghe t ot hesupe r s a t ur a t i ono fγ ′ Ｇ f o rmi nge l emen t saway f r omt hed i f f us i onf i e l dso fg r owi ngp r ima r ′p r e Ｇ yγ , c i i t a t e s ． A s a r e s u l t t h e s e c o n db u r s t o fγ ′ r e c i i Ｇ p p p t a t enuc l e a t i onhappens．Thes e conda r ′p r e c i i Ｇ yγ p t a t e shavet i c a l l i ne rs i z eand h i r numbe r yp yf ghe
１５４
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
dens i t Subs equen tag i ngf o rasho r tt imei susua l l y． y c a r r i edou tt omagn i f hed i f f e r enc ebe twe ent hes i Ｇ yt [ １６ Ｇ １８] z e so ftwogene r a t i onso fγ ′p r e c i i t a t e s ． p I nt he pr e s en ts t udy,f ou rd i f f e r en tc oo l i ng r a t e sr ang i ngf r om wa t e rc oo l i ngt of u rna c ec oo l i ng we r eadop t edf o rhe a t４０５a f t e rs o l u t i ont r e a tmen ta t １１５０ ℃ f o r３０ mi n．Thes o l u t i onanne a l eds amp l e s we r et henageda t８００ ℃ f o r１６hf o l l owedbya i r coo l i ng．Theγ ′pr e c i i t a t e sw e r et h e ne x t r a c t e db p y t hemi c r o Ｇ chemi c a lpha s eana l i sme t hod．Thema s s ys f r a c t i ono fγ ′pr e c i i t a t e si ne a chs amp l ewa sde t e r Ｇ p mi ned．Ther e su l ti sshowni nF i ６． I ti sf oundt ha t g s l owc oo l i ngr a t el edt oal a r to fγ ′p r e c i i Ｇ geamoun p t a t e s．The ma s sf r a c t i onso fγ ′p r e c i i t a t e si nt he p a i r Ｇ coo l edandf u rna c e Ｇ c oo l eds amp l e s we r ea r ound １５ ma s s％ c ompa r ed wi t h１３ ma s s％ i nt he wa t e r Ｇ coo l edando i l Ｇ c oo l eds amp l e s．Thes i z ed i s t r i bu t i ons o ft he s e ex t r a c t ed γ ′p r e c i i t a t e s de t e rmi ned by p SAXS me t hodf o rd i f f e r en tc oo l i ngr a t e sa r eshown i nF i ７． Th ec o r r e spond i ngme and i ame t e r so ft heγ ′ g
F i ６ Ma s sf r a c t i ono fγ ′p r e c i i t a t e sa td i f f e r en t g p c o o l i ngme t hod sa f t e rs o l u t i ont r e a tmen t
r e c i i t a t e sa r ea l so g i ven．I n gene r a l,nob imoda l p p s i z ed i s t r i bu t i onso fγ ′p r e c i i t a t e swe r eobs e r vedf o r p a l lt hef ourcoo l i ngr a t e s．Thes i z ed i s t r i bu t i onso fγ ′ r e c i i t a t e sf o ra l lt hes amp l e swe r emonomoda land p p t he me an d i ame t e rde c r e a s ed wi t ht hei nc r e a s eo f coo l i ngr a t e．
D )—S i z ed i s t r i bu t i on; D — Me ans i z e． f( ( a)WC; ( b)OC; ( c)AC; ( d)FC．
F i ７ SAXSr e s u l t so fγ ′p r e c i i t a t e so fI nc on e l７４０Ha td i f f e r en tc o o l i ngme t hod sa f t e rs o l u t i ont r e a tmen t g p
I nt hepr ev i ousi nve s t i t i ons,whe r eb imoda l ga , s i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e sw a so b s e r v e d t h e p t i c a lc oo l i ngr a t e swe r ewe l lbe l ow５ K/mi n．Fo r yp
i ns t anc e,i nt hei nve s t i t i ono fRene１０４bySa r os i ga [ ] e ta l １２ ,t hec oo l i ngr a t ewa sa sl owa s５ K/mi nt o r oduc eb imoda ls i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e s． p p
I s sue２ He a tTr e a tmen to faCand i da t eMa t e r i a lf o r７００ ℃ AＧUSCPowe rP l an t s
S imi l a r l n as t ema t i cs t udy on t he e f f e c to f y,i ys coo l i ngr a t eonγ ′p r e c i i t a t e ss i z ed i s t r i bu t i on,Ra Ｇ p [ ] d i se ta l １５ c onc l udedt ha tc oo l i ngr a t el owe rt han２ / K mi ni senought oc aus eb imoda ls i z ed i s t r i bu t i on o fγ ′pr e c i i t a t e s． I nt hep r e s en ts t udy,t hec oo l i ng p r a t eo ff u rna c ec oo l i ngwa sa r ound１０K/mi nwh i ch, , i nt heau t ho r s ′op i n i on wa s no ts l ow enought o c aus et heb imoda ls i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e s． p Be s i de s,t hel a r and i ame t e ro fγ ′p r e c i i t a t e s ge me p a s soc i a t edwi t hs l owc oo l i ngr a t ewa sde t r imen t a lt o t hes t r eng t ho ft h i sa l l oy．The r e f o r e,f r omt hepo i n t , o fv i ew o f me and i ame t e ro fγ ′p r e c i i t a t e s wa t e r p coo l i nga f t e rs o l u t i ont r e a tmen ti sp r e f e r r edf o rI n Ｇ cone l７４０H．
１５５
r ima r ′i nl a r i z e． S imi l a r l hes e condnuc l e Ｇ p yγ ges y,t a t i onbur s to fγ ′p r e c i i t a t e st ookp l a c edur i ngsub Ｇ p s equen tag i nga t７５０ ℃ ,wh i chi st e rmeda ss e cond Ｇ , a r ′．Att hebeg i nn i ngo fag i nga t７５０ ℃ t hes i z e yγ o ft hes e conda r ′p r e c i i t a t e s wa ssma l l e rcomＧ yγ p r edwi t ht ha to ft hep r ima r ′p r e c i i t a t e s．Af t e r Ｇ pa yγ p , wa rds bo t hp r ima r e conda r ′p r e c i i t a t e s yands yγ p unde rwen tt hep r oc e s so fg r owi ngandOs twa l dr i Ｇ pe n i ng． I ti sbe l i evedt ha t,dur i ng Os twa l dr i i ng, pen t heg r owt ho ft hel a r rp r e c i i t a t e si sa tt heex Ｇ ge p eo ft heg r owt ho fsma l l e rp r e c i i t a t e s．The r e Ｇ pens p f o r e,t hep r ima r ′p r e c i i t a t e scou l dg r owi n t oa yγ p muchl a r rs i z e． Be s i de s,t heg r owt ho ft hes e cond Ｇ ge a r ′p r e c i i t a t e s wa sa lwayssupp r e s s ed by t he yγ p Os twa l dr i i ngo fp r ima r ′p r e c i i t a t e s,wh i ch pen yγ p r e su l t edi nt heb imoda ls i z ed i s t r i bu t i ono fγ ′p r e c i Ｇ p i t a t e sa sobs e r veda f t e rl ong Ｇ t imeag i nga t７５０ ℃．
２ ４ Ef f e c to fpr e Ｇ a i nga t８００ ℃ f o r１６h g I nt he s t anda r d he a tt r e a tmen to fI ncone l , ７４０H apr e Ｇ ag i nga t８００ ℃ f o r１６hi sr equ i r ed． I n t her e s e a r che sonI nc one l７４０pe r f o rmedbyZhaoe t [ ] a l ３Ｇ５ ,t hemi c r o s t ruc t u r eevo l u t i onandme chan i c a l r ope r t i e swe r es t ud i edons amp l e swh i chwe r eso l u Ｇ p t i onanne a l edandl ong Ｇ t imeageda t７５０ ℃．Node Ｇ t a i l ed mi c r o s t ruc t u r eobs e r va t i ons we r ec a r r i edou t on s amp l e s wh i ch we r e aged a f t e rs t anda r d he a t t r e a tmen t,no rwa st hec ompa r i s onbe twe ent hemi Ｇ c r os t ruc t u r e so fageds amp l e swi t handwi t hou tp r e Ｇ , ag i nga t８００ ℃．The r e f o r ei nt hep r e s en ti nve s t i Ｇ ga t i on,wi t ht hepu r s eo fa s s e s s i ngt hene c e s s i t f po yo , r e Ｇ a i n a t８ ０ ０ ℃ f o r I n c o n e l ７ ４ ０ H b o t hs o l u t i o n p g g anne a l edands t anda r dhe a t Ｇ t r e a t edI nc one l７４０Ha l Ｇ l oyswe r el ong Ｇ t imeageda t７５０ ℃ f o r８０００h．The SEM r e su l t so fbo t hs amp l e sa r eshowni nF i ８． g Themi c r o s t ruc t u r e so fhe a t４０５ageda f t e rs o l u t i on anne a l i nga r eshowni nF i ８( a)and８( c),wh i l e gs ( a),( c)So l u t i ont r e a tmen t＋７５０ ℃×８０００h,AC; t hemi c r o s t ruc t u r e so fhe a t４０５ageda f t e rs t anda rd ( b),( d)So l u t i ont r e a tmen t＋８００ ℃×１６h,AC＋ he a tt r e a tmen ta r eshowni nF i ８( b)and８( d)． I n gs ７５０ ℃×８０００h,AC． t hes amp l e wi t hou tp r e Ｇ ag i nga t８００ ℃ ,c oa r s eγ ′ F i ８ Mo rpho l o fγ ′p r e c i i t a t e sa f t e r g g yo p ( ) r e c i i t a t e s a r ound１５０nmi nd i ame t e r wi t hcu Ｇ d i f f e r en th e a tt r e a tmen t s p p bo i dshape we r eobs e r ved,wh i chi sbe l i evedt obe ti sr epo r t edi no t he ri nve s t i t i onso fNi Ｇba s ed ga t hecommonr e su l to fOs twa l dr i i ng． I nc on t r a s t, I pen , s u e r a l l o s t h a t t h e e x i s t e n c eo f s e c o n d a r a n d t e r t i Ｇ p y y i nt hes amp l ewi t hp r e Ｇ ag i nga t８００ ℃ twogene r a Ｇ r ′p r e c i i t a t e swi t hf i nes i z ei sbene f i c i a lt obo t h yγ p t i onso fγ ′pr e c i i t a t e swe r eobs e r vedi nt he mi c r o Ｇ a p [ , ] ens i l eandc r e eps t r eng t ha th i empe r a t ur e s１９ ２０ ． ght s t ruc t u r e． I nadd i t i ont ot hel a r i dγ ′p r e c i i Ｇ t gecubo p nt hec a s eo fI ncone l７４０H,t hecomb i nede f f e c t so f t a t e swi t hne a r l hes ames i z et ot ha ti nt hes amp l e I yt r e Ｇ ag i nga t８００ ℃f o r１６handsubs equen tag i nga t wi t hou tpr e Ｇ ag i ng,as e c ondgene r a t i ono fγ ′p r e c i i Ｇ p p an p r oduc es e conda r ′p r e c i i t a t e s wi t h yγ p t a t e swi t ha muchsma l l e rs i z e we r ea l s oobs e r ved ７５０ ℃ c i nes i z ei nadd i t i ont ot hel a r i dp r ima r ′ gecubo yγ be twe ent hel a r ′p r e c i i t a t e s．Theave r aged i amＧ f geγ p r e c i i t a t e sa f t e rl ong Ｇ t imeag i ng．Att hes amet ime, p e t e rf o rt hes e c ondgene r a t i ono fγ ′p r e c i i t a t e swa s p p s i r eds i dee f f e c t swe r eobs e r ved．The r e f o r e, a r ound４０nm． I ti sp r opo s edt ha t,du r i ngp r e Ｇ ag i ng nounde , i t i ss u e s t e dt h a t r e Ｇ a i n a t８ ０ ０ ℃ i sn e c e s s a r gg p g g y a t８００ ℃ t hef i r s tnuc l e a t i onbu r s to fγ ′p r e c i i Ｇ p o rI ncone l７４０Ht oimp r ovei t spe r f o rmanc ea th i gh t a t e st ookp l a c e,wh i chr e su l t edi nt hef o rma t i ono f f
１５６
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
t empe r a t u r e s．
３ Conc l u s i on s
( １) Among t hes i x he a t so fI nc one l７４０H manu f a c t u r ed i n t he l abo r a t o r he op t imi z ed y, t chemi c a lc ompo s i t i oni sp r e l imi na r i l d e t e r m i n e dt o y , bet ha to fhe a t s４０４and４０５ ba s edont heme chan i Ｇ c a lpr ope r t i e sa f t e rs t anda r dhe a tt r e a tmen ta td i f f e r Ｇ en tso l u t i ont empe r a t u r e s． ( ２)Thes o l u t i ont empe r a t u r ei sf i xedt obe １１５０ ℃ t od i s s o l vea l lt hec a rb i de s wi t hou texc e s Ｇ s i veg r a i nc oa r s en i ng． ( ３)Nob imoda ls i z ed i s t r i bu t i onso fγ ′p r e c i i Ｇ p t a t e swe r eobs e r vedi na l ls amp l e sa td i f f e r en tcoo l Ｇ i ngr a t e sa f t e rs o l u t i ont r e a tmen t．Wa t e rc oo l i ngi s r e commendeda si tl e adst ot hef i ne s tγ ′p r e c i i t a t e s． p ( ４)Pr e Ｇ ag i nga t８００ ℃ f o r１６hi sne c e s s a r y , f o rI n c on e l７４０H s i n c ei tr e s u l t si nb imod a ls i z ed i s t r i Ｇ bu t i ono fγ ′p r e c i i t a t e sa f t e ra i nga t７５０ ℃ ,wh i c hi s p g be l i evedt obebene f i c i a lt ot hec r e eps t r eng t h． Re f e r enc e s:
[ １] R．Vi swana t han,J F．Henr o sh,G． S t anko,J． Sh i n Ｇ y,J．Tanz l ede cke r,B．Vi t a l i s,R．Pur r t,J．Ma t e r．Eng．Pe r f o rm． １４ g ge ( ２００５)２８１ Ｇ ２９２． [ ２] R．Vi swana t han,K．Co l eman,U．Rao,I n t． J．Pr e s s．Ve s s e l s P i ８３ ( ２００６)７７８ Ｇ ７８３． p． [ ３] S． Zh a o,X．X i e,G D． Smi t h,S J． Pa t e l,Ma t e r．Le t t． ５８ ( ２００４) １７８４ Ｇ １７８７． [ ４] S． Zhao,X．Xi e,GD．Smi t h,S J．Pa t e l,Ma t e r．Sc i．Eng．A ３５５ ( ２００３)９６ Ｇ １０５．
[ ５] S． Zh a o,X．X i e,G D． Smi t h,S J．Pa t e l,Ma t e r．De s． ２７ ( ２００６) １１２０ Ｇ １１２７． [ ６] ND．Evans,P J．Ma z i a s z,R W．Swi ndeman,GD．Smi t h, Sc r i t a Ma t e r． ５１ ( ２００４)５０３ Ｇ ５０７． p [ ７] J P．Sh i ng l ede cke r,GM．Pha r r,Me t a l l．Ma t e r．Tr ans．A４３ ( ２０１２)１９０２ Ｇ １９１０． [ ８] Y．Chong,Z．L i u,A．God f r ey,W．L i u,Y．Weng,Ph i l．Mag． Le t t． ９３ ( ２０１３)６８８ Ｇ ６９６． [ ９] S S．Babu,MK．Mi l l e r,J M．Vi t ek,S A．Dav i d,Ac t a Ma Ｇ t e r． ４９ ( ２００１)４１４９ Ｇ ４１６０． [ １０] J Y．Hwang,R．Bane r e e,J．Ti l ey,R．Sr i n i va s an,GB． j Vi swa n a t h a n,HL． Fr a s e r,Me t a l l．Ma t e r．T r a n s．A４０ ( ２００９)
２４ Ｇ ３５． [ １１] D N． Se i dman,C K． Sudbr a ck,KE．Yoon,JOM５８ ( ２００６) ３４ Ｇ ３９． [ １２] P M．S a r o s i,B．Wa ng,J P．S immon s,Y．Wa ng,MJ．Mi l l s, Sc r i t a Ma t e r． ５７ ( ２００７)７６７ Ｇ ７７０． p [ １３] Y H．We n,J P．S immon s,C．Sh e n,C．Wo o dwa r d,Y．Wa ng, Ac t a Ma t e r． ５１ ( ２００３)１１２３ Ｇ １１３２． [ t aMa t e r． P． S immons,Y．Wang,Ac １４] YH．Wen,B．Wang,J ５４ ( ２００６)２０８７ Ｇ ２０９９． [ １５] R．Rad i s,M． Scha f f e r,M．Al bu,G．Ko t h l e i t ne r,P． Pö l t,E． Ko z e s chn i k,Ac t a Ma t e r． ５７ ( ２００９)５７３９ Ｇ ５７４７． [ １６] AR P． S i ngh,S．Nag,J Y．Hwang,GB．Vi swana t han,J． i n i va s an, HL．Fr a s e r, R．Bane r e e, Ma t e r． Ti l ey,R．Sr j Cha r a c t． ６２ ( ２０１１)８７８ Ｇ ８８６． [ l ey, t t opadhyay,Y．Ren,J．Ti １７] AR P． S i ngh,S．Nag,S．Cha , GB．Vi swana t han,HL．Fr a s e r,R．Bane r e e A c t a M a t e r． j ６１ ( ２０１３)２８０ Ｇ ２９３． [ P．Va z e,D U． ng,K．Ra １８] J．Ma o,K M．Ch a ng,WH．Ya y,S Fe r r e r,Me t a l l．Ma t e r．Tr ans．A３２ ( ２００１)２４４１ Ｇ ２４５２． [ D．Wh i t i s, １９] GB．Vi swana t han,P M． Sa r o s i,MF．Henr y,D WW．Mi l l i l l s,Ac t a Ma t e r．５３ ( ２００５)３０４１ Ｇ gan, MJ．Mi ３０５７． [ ２０] C Y．Cu i,YF．Gu,Y．Yuan,T．Os ada,H．Ha r ada,Ma t e r． Sc i．Eng．A５２８ ( ２０１１)５４６５ Ｇ ５４６９．
JOURNALOFIRON ANDSTEELRESEARCH,INTERNATIONAL２ ０ １ ５,２ ２( ２):１ ５ ０ Ｇ １ ５ ６
He a tTr e a tme n to faCand i da t eMa t e r i a lf o r ７００ ℃ AＧUSCPowe rP l an t s YanCHONG１ ２ , Zheng Ｇ dongLIU２ , AndyGODFREY１ , Lu WANG２ , We iLIU１ , Yu Ｇ i ng WENG２ q ,
( １． Schoo lo fMa t e r i a l sSc i enc eandEng i ne e r i ng,Ts i nghuaUn i ve r s i t i i ng１０００８４,Ch i na; ２．Cen t r a lI r on y,Be j andS t e e lRe s e a r chI ns t i t u t e,Be i i ng１０００８１,Ch i na) j Ab s t r a c t:Thep r e l imi na r c a lc ompo s i t i onop t imi z a t i onandhe a tt r e a tmen tpa r ame t e r so fI nc one l７４０H we r e ychemi i nve s t i t edsy s t ema t i c a l l S i xhe a t so fexpe r imen t a la l l oy s( de s i t eda she a t４０１t ohe a t４０６)wi t hva r i edchemi Ｇ ga y． gna c a lc ompo s i t i onswe r esub e c t edt os t anda r dhe a tt r e a tmen ta tf ou rd i f f e r en ts o l u t i ont empe r a t u r e s．Duet oi t ssupe r i Ｇ j o rc omb i na t i ono fs t r eng t h,duc t i l i t oughne s st oge t he rwi t hi t smi no rme chan i c a lp r ope r t sa td i f f e r en t y,andt ychange s o l u t i ont empe r a t u r e s,he a t４０５wa scho s ena sanop t imi z edonet oc onduc tf u r t he rhe a tt r e a tmen ti nve s t i t i ons．The ga e vo l u t i ono fg r a i ns i z ewi t hs o l u t i ont empe r a t u r ef o rhe a t４０５wa ss t ud i edandt heop t ima ls o l u t i ont empe r a t u r ewa s de t e rmi ned．Af t e rs o l u t i ont r e a tmen ta tt heop t ima lt empe r a t u r e,f ou rd i f f e r en tc oo l i ngr a t e swe r eapp l i edt oi nve s t i Ｇ t et hee f f e c to fc oo l i ngr a t eont hes i z ed i s t r i bu t i onmoda landme anr ad i uso ft heγ ′p r e c i i t a t e s．Nob i Ｇmoda ls i z e ga p d i s t r i bu t i ono fγ ′p r e c i i t a t e swa sf oundf o ra l lc oo l i ngr a t e sandwa t e rc oo l i ngwa sr e c ommendedf o rI nc one l７４０H． p I nadd i t i on,t hee f f e c to fp r e Ｇ ag i nga t８００ ℃f o r１６hont hemi c r o s t r uc t u r eo fI nc one l７４０Hagedf o ral ongt imewa s s t ud i ed． I ti sf oundt ha tp r e Ｇ ag i nga t８００ ℃ wou l dr e su l ti nb i Ｇmoda ls i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e sa f t e rl ong p t imeag i nga t７５０ ℃ c ompa r ed wi t h mono Ｇmoda ls i z ed i s t r i bu t i oni ns amp l e s wi t hou tp r e Ｇ ag i ng,wh i ch mi tbe gh c aus edbyt hed i f f e r enc ei ni n i t i a ls i z ed i s t r i bu t i on moda lbe f o r eOs twa l dr i i ngo fγ ′p r e c i i t a t e si ns amp l e swi t h pen p andwi t hou tp r e Ｇ ag i nga t８００ ℃． Ke r d s:I nc one l７４０H;he a tt r e a tmen t;g r a i ns i z e;γ ′p r e c i i t a t e;me chan i c a lp r ope r t p y ywo
Du et ot h ei n c r e a s i nge n e r ema nd sa nda c c e l e r Ｇ gyd , a t e de nv i r onme n t a li s s u e st h e r ei sanu r tne edt o gen imp r ovet het he rma le f f i c i enc fc oa l Ｇ f i r ed powe r yo l an t s,e spe c i a l l nCh i na,whe r ec oa lr e s ou r c e sa r e p yi abundan tandt hee l e c t r i c i t r a t edbyc oa l Ｇ f i r ed ygene rp l an t smakeupt hema o r i t ch i evet h i s powe j y．Toa , ( ) o a l t h e a d v a n c e d u l t r a Ｇ s u e r c r i t i c a l A Ｇ U S C g p , rp l an t s ope r a t i ng a ts t e am t empe r a t u r e so f powe ７００－７５０ ℃ ands t e am p r e s su r eupt o３７ ５ MPa, a r eunde rdeve l opmen t．Thei nc r e a s edope r a t i ngpa Ｇ r ame t e r sa r esuppo s edt oi nc r e a s et het he rma le f f i Ｇ c i enc r om ４１％ (HHV,h i a t i ng va l ue)a t yf gh he [ １, ２] ( ) , r e s e n tt on e a r l ５ ０％ HHV ． H o w e v e r t h e p y i nc r e a s edope r a t i ngpa r ame t e r sp l a c emo r es t r i ngen t r equ i r emen t sont hep r ope r t i e so fc and i da t e ma t e r i Ｇ a l s,i nc l ud i ng c r e ep s t r eng t h and ox i da t i onr e s i s t Ｇ anc e．Conven t i ona lf e r r i t i candaus t en i t i cs t e e l sc an
ha rd l e tt her equ i r emen t st husa r esuppos edt o y me ber ep l a c edby Ni Ｇba s edsupe r a l l oys． I ncone l７４０H,deve l oped by Spe c i a l Me t a l s Co r ,Hun t i ng t on,We s tVi r i n i a,USA,i soneo f p g t he mos tp r omi s i ngc and i da t e Ni Ｇba s edsupe r a l l oys f o rt hema i ns t e am p i e so f７００ ℃ USCpowe rp l an t s． p I ti st hemod i f i edve r s i ono fI ncone l７４０,wh i chsu f Ｇ f e r edf r om mi c r os t ruc t ur a li ns t ab i l i t i ng l ong y dur t imeag i nga t７５０ ℃．Thenomi na lcompos i t i ono f I ncone l７４０H (ma s s％ )i sCr２５,Co２０,Mo０ ５, Nb１ ５,Ti１ ４,Al１ ４,Mn０ ３,Fe０ ０３,C０ ０３ andNiba l anc e．Compa r edwi t hI ncone l７４０,t her a Ｇ t i oo fTit oAli nI ncone l７４０Hi sl owe r edi no rde rt o e l imi na t et heex i s t enc eo fηpha s ea tg r a i nbounda Ｇ r i e sf oundi nI ncone l７４０a f t e rp r o l ongedag i ng a t [ ３ Ｇ ７] , ７５０ ℃ ． I nadd i t i on t heNbandBcon t en t si nI n Ｇ cone l７４０H a r ebo t hr educ edt oimp r ovet he we l d Ｇ
Founda t i onI t em: I t em Spons o r edbyHi ＧTe chRe s e a r chandDeve l opmen tPr o e c to fCh i na ( ２１０２AA０３A５０１) gh j B i o r aphy: YanCHONG,Do c t o r; E Ｇma i l: chongyan８７１２１０＠s i na c om; Re c e i v e dDa t e:Oc t obe r３１,２０１３ g
I s sue２ He a tTr e a tmen to faCand i da t eMa t e r i a lf o r７００ ℃ AＧUSCPowe rP l an t s
ab i l i t ft h i sa l l oy．Thes t anda r dhe a tt r e a tmen to f yo I ncone l７４０Hr e c ommendedbySpe c i a lMe t a l sCo r p． wa s１１５０ ℃ × ３０ mi nf o l l owed by WQ (wa t e r ) ( i ng p l us８００ ℃ ×１６hf o l l owedby AC a i r quench coo l i ng)．Thes amp l e sa f t e rs t anda r dhe a tt r e a tmen t a r el ongt imeagedo rc r e ept e s t eda t７５０ ℃． Fo rt hepu rpo s eo ff u r t he rchemi c a lc ompo s i t i on op t imi z a t i onandl o c a l i z a t i ono fI nc one l７４０Hi nCh i Ｇ na,de t a i l edi nve s t i a t i o n so nt h ee f f e c to fc h e m i c a l g compo s i t i onsonme chan i c a lp r ope r t i e sa swe l la st he e f f e c to fhe a tt r e a tmen tpa r ame t e r son mi c r o s t ruc Ｇ t ur ea r er equ i r ed．Thei nve s t i t i onsi nt hep r e s en t ga s t udyi nc l udepr e l imi na r ompo s i t i onop t imi z a t i on yc ba s ed ont he me chan i c a lp r ope r t i e sa f t e rs t anda rd , he a tt r e a tmen t t hee f f e c to fs o l u t i ont empe r a t ur e ong r a i ns i z e,t hee f f e c to fc oo l i ngr a t eont hes i z e d i s t r i bu t i ono fγ ′p r e c i i t a t e sandt hei n f l uenc eo f p r e Ｇ ag i nga t８００ ℃f o r１６hons i z ed i s t r i bu t i ono fγ ′ p r e c i i t a t e s． I nt heend,t her e c ommenda t i onsabou t p p chemi c a lc ompo s i t i on op t imi z a t i on and he a tt r e a t Ｇ men tpa r ame t e r sf o rI nc one l７４０Ha r ep r ov i ded．
１ Exp e r imen t a lPr o c e du r e
S i xhe a t so fI nc one l７４０H ( de s i t eda she a t gna ４０１t ohe a t４０６)wi t ht hechemi c a lc ompo s i t i onsl i s Ｇ
１５１
t edi nTab l e１we r ep r oduc edi nCh i naI r onandS t e e l Re s e a r chI ns t i t u t e( CISRI)by VIM ( va cuumi nduc Ｇ t i on me l t i ng)＋ VAR ( va cuum a r cr e Ｇme l t i ng)． The s ei ngo t swe r et henf o r n t or ods． Fo rp r e l imＧ gedi i na r c a lcompos i t i on op t imi z a t i on,s amp l e s y chemi cu tf r omt her odswe r es t anda rdhe a tt r e a t eda tf our d i f f e r en tso l u t i ont empe r a t ur e s( １１２０,１１５０,１１８０ and１２００ ℃ )． Impa c tt e s t so fCha r t chs amＧ py VＧno l e sc u t f r o mt h e s t a n d a r dh e a t t r e a t e ds a m l e sw e r e p p r f o rmeda tr oom t empe r a t ur e．Tens i l et e s t sbo t h pe a tr oomt empe r a t ur eanda t７５０ ℃ we r ec a r r i edou t i nahyd r au l i ct e s ts t emequ i t hat empe r a Ｇ ys ppedwi t ur e Ｇ con t r o l l ed f urna c e．The t empe r a t ur ef l uc t ua Ｇ t i onswe r ekep twi t h i n３ ℃．Al lme chan i c a lt e s tex Ｇ r imen t swe r econduc t edona tl e a s tt hr e es amp l e s． pe Thes t anda rdhe a tt r e a t edspe c imenso fhe a t４０５a t d i f f e r en t so l u t i on t empe r a t ur e s we r eg r ound and l i shedf o l l owi ngs t anda rd me t a l l og r aph i c a lme t hＧ po odsandt henchemi c a l l t chedi naf r e shso l u t i ono f ye HCl,HNO３andH２O wi t ht hevo l umep r opo r t i ono f １０∶１∶１０a t５０ ℃ f o r１５ mi n．Op t i c a l mi c r o s c opy ( OM) i nve s t i t i onswe r econduc t edunde ranOl ga ymＧ c r os cope．Theave r ageg r a i ns i z e swe r e pusGX５１ mi me a sur edby me anso fal i ne a ri n t e r c ep tme t hod． Fo rt hei nve s t i t i onabou tt hee f f e c to fcoo l i ng ga
Tab l e１ Ch emi c a lc ompo s i t i on so fs i xh e a t so fI nc on e l７０４Hi nv e s t i a t e di nt h i ss t udy ma s s％ g
He a t ４０１ ４０２ ４０３ ４０４ ４０５ ４０６
Cr
２４ ３８ ２５ ３０ ２５ ０８ ２５ ４８ ２５ ５７ ２５ ５２
Co
２０ ０４ ２０ ２０ ２０ ２６ ２０ １７ １９ ９２ ２０ ０２
Mo
０ ５１ ０ ５２ ０ ５２ ０ ５２ ０ ５０ ０ ５１
Ti
１ ６４ １ ２８ ０ ８７ １ ２２ １ ３８ １ ５９
Al
１ ０８ １ ４６ １ ４６ １ ４３ １ ４７ １ ４７
Nb
１ ９８ １ ９６ １ ５０ １ ５３ １ ４８ １ ５９
Fe
０ ０３４ ０ ０３３ ０ ０３３ ０ ０３３ ０ ０３２ ０ ０３３
r a t eons i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e s,f ou rd i f Ｇ p f e r en tc oo l i ngr a t e s,i nc l ud i ng wa t e rc oo l i ng (WC), o i lcoo l i ng (OC),a i rc oo l i ng andf u rna c ec oo l i ng ( FC),we r eadop t edonhe a t４０５a f t e rs o l u t i onan Ｇ ne a l i nga t１１５０ ℃．Thes o l u t i onanne a l eds amp l e s we r eageda t８００ ℃ f o r１６ handa i rc oo l ed．The ma s sf r a c t i ono ft heγ ′p r e c i i t a t e swa sa s c e r t a i ned p t hr ough mi c r o Ｇ chemi c a lpha s eana l i s me t hod．The ys γ ′p r e c i i t a t e s we r ee l e c t r o l t i c a l l t r a c t edi nan p y yex ( ) aqueouss o l u t i onc on t a i n i ng１％ NH４ ２SO４and１％ C６H８O７ H２Of r om０t o５ ℃．Acu r r en tdens i t f yo ２ / ０ ０５A cm wa sus ed．Thepa r t i c l es i z ed i s t r i bu t i on and me and i ame t e ro ft heex t r a c t ed γ ′p r e c i i t a t e s p we r ede t e rmi nedus i nganXＧ r ayd i f f r a c t r o Ｇ spe c t r omＧ e t e requ i t ha Kr a t hysma l lang l es c a t t e r i ng pped wi ( SAXS)gon i ome t e r．
C
０ ０２４ ０ ０２２ ０ ０２０ ０ ０２３ ０ ０２３ ０ ０２２
Mn
０ ３３ ０ ３２ ０ ３３ ０ ３４ ０ ３４ ０ ３４
S i
０ ０６７ ０ ０５４ ０ ０５１ ０ ０５２ ０ ０４９ ０ ０４８
B
０ ００２１ ０ ００１０ ０ ００１２ ０ ０００６ ０ ０００５ ０ ０００５
S
０ ００１ ０ ００１ ０ ００２ ０ ００１ ０ ００１ ０ ００１
Ni
Ba l anc e Ba l anc e Ba l anc e Ba l anc e Ba l anc e Ba l anc e
Fo rt hei nve s t i t i onabou tt hee f f e c to fp r e Ｇ ag Ｇ ga i nga t８００ ℃ ont hes i z ed i s t r i bu t i ono fγ ′p r e c i i pＧ , t a t e sa f t e rl ongt imeag i nga t７５０ ℃ bo t hso l u t i on anne a l edandso l u t i onanne a l ed p l us p r e Ｇ ageds amＧ l e so fhe a t４０５ we r el ongt imeageda t７５０ ℃ f o r p ８０００h．Thes amp l e sf o rs c ann i nge l e c t r onmi c r os co Ｇ SEM)obs e r va t i on we r ep r epa r edf o l l owi ngt he py ( r oc edur e sde s c r i bedabove．TheSEM expe r imen t s p we r econduc t edonaTe s c anLYRA３ mi c r os copeop Ｇ e r a t eda t２０kV．
２ Re s u l t sandDi s c u s s i on
２ １ Pr e l imi na r ompo s i t i onop t imi z a t i on yc Asl i s t edi nTab l e１,t hechemi c a lcompos i t i ons o ft hes i xhe a t so fI ncone l７４０Hcou l dbed i v i dedi n t o twoc a t ego r i e sa c co rd i ng t ot he Nb con t en t,wi t h
１５２
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
he a t s４０１and４０２c on t a i n i ng２ ０ ma s s％ Nb,wh i l e t her e s tf ou rhe a t sc on t a i n i ng１ ５ma s s％ Nb．Toi n Ｇ ve s t i a t e t h ee f f e c to ft h eT i t o A lr a t i oo nt h e m i Ｇ g , c r os t ruc t u r es t ab i l i t chan i c a lp r ope r t i e st he yandme r a t i oso fTit oAli ne a chc a t ego r r ede s i o y we gnedt exh i b i tat r ans i t i ona lchangef r oml owt oh i hl e v e l ． g , I nadd i t i on t he r ewe r ea l s od i f f e r enc e si nt hecon Ｇ t en to ft r a c ee l emen tsucha sB． Thet ens i l et e s tr e su l t so ft hes i xhe a t sa tr oom t empe r a t u r eand７５０ ℃ a r eshowni nF i １and２, gs r e spe c t i ve l c tt oughne s sr e su l t sa tr oom y．Theimpa t empe r a t u r ea r e shown i nF i ３．Fo r me chan i c a l g r ope r t i e s,i nt hef i r s tp l a c e,t heduc t i l i t fhe a t p yo ４０１ wa s muchl owe rc ompa r ed wi t ht heo t he rf i ve he a t sa ta l ls o l u t i ont empe r a t u r e si nve s t i t ed． I ti s ga suppo s edt obec o r r e l a t ed wi t ht hef o rma t i on o fη s ea tt heg r a i nbounda r i e si nhe a t４０１wi t hah i pha gh ( / ) , ( Tit oAlr a t i o １ ６４ １ ０８ a sshowni nF i ４ a)． g Evenwo r s e,t hef o rma t i ono fηa tt heg r a i nbounda Ｇ r i e s wa s de t r imen t a lt ot heimpa c tt oughne s sa t ( ) , r oomt empe r a t u r e F i ３ wh i chwa sa l s or epo r t ed g [] byZhaoi nh i si nve s t i t i onsonI nc one l７４０４ ． S imi Ｇ ga
l a r l heduc t i l i t fhe a t４０６a t７５０ ℃ wa sex Ｇ y,t yo t r eme l ow,wh i chi sa t t r i bu t edt ot hef o rma t i ono f yl ( ) ) c e l l u l a rM２３C６c a r b i d e s( F i ４ b a t t h e r a i nb o u n d a Ｇ g g [] r i e so fhe a t４０６８ ．Thei n t e r f a c eo fc e l l u l a r M２３C６ c a r Ｇ b i d eand ma t r i xp r ov i dedan e a s i e r pa t hf o rc r a ck r opaga t i on．Af t e rp r e c l ud i nghe a t s４０１and４０６,t he p f ur t he rchemi c a lcompos i t i onop t imi z a t i onwa sma i n Ｇ l s edont hef l uc t ua t i onso fme chan i c a lp r ope r t yba y a td i f f e r en tso l u t i ont empe r a t ur e s．I ti sf oundt ha t t hes t r eng t hf l uc t ua t i onso fhe a t４０２a tbo t hr oom t empe r a t ur eand７５０ ℃ we r er a t he rl a r r e Ｇ ge．The , f o r ei t wa sp r e c l udedf o rcons i de r a t i on．Al t hough s e s s i ngt heh i s timpa c tt oughne s s,t hey i e l d pos ghe s t r eng t handt ens i l es t r eng t ho fhe a t４０３ we r et he l owe s tbo t ha tr oom t empe r a t ur eand７５０ ℃．I ti s r a l l l i evedt ha tt he y i e l ds t r eng t ha th i gene y be gh t empe r a t ur eha sac l os er e l a t i onsh i t ht hec r e ep p wi , rup t ur es t r eng t h．Asar e su l t he a t４０３ wa sa l so ru l edou tf o rcons i de r a t i on,l e av i ng on l a t s４０４ y he and４０５． I tc anbes e enf r om F i ha the a t s gs．１－３t ４０４ and ４０５ exh i b i t ed a good ba l anc e among s t r e ng t h,du c t i l i t c tt oughne s s．Asar e su l t, yandimpa
F i １ Ev o l u t i ono fs t r eng t handdu c t i l i t fI nc on e l７４０Ha tr o omt emp e r a t u r ewi t hs o l u t i ont emp e r a t u r e g yo
F i ２ Ev o l u t i ono fs t r eng t handdu c t i l i t fI nc on e l７４０Ha t７５０ ℃ wi t hs o l u t i ont emp e r a t u r e g yo
I s sue２ He a tTr e a tmen to faCand i da t eMa t e r i a lf o r７００ ℃ AＧUSCPowe rP l an t s
１５３
F i ３)．Howe v e r,whe nt het emp e r a t u r ewa s１１２０ ℃ , g i twa sno th i od i s so l vea l lt hec a rb i de s． ghenought The s eund i s so l ved p r ima r c a r b i d e s w i t hl a r es i z e y g wou l dr ema i ni nt hemi c r os t ruc t ur eanda c ta si n i t i a l c r a cks i t e sdur i ngc r e ep．The r e f o r e,t hesu i t ab l eso Ｇ l u t i ont empe r a t ur ef o rI ncone l７４０H wa s１１５０ ℃ a t wh i cha l lt hep r ima r a rb i de swe r ed i s so l vedwi t hＧ yc ou texc e s s i veg r a i ncoa r s en i ng．
F i ３ Ev o l u t i ono fimpa c tt oughn e s sa tr o om g t emp e r a t u r ewi t hs o l u t i ont emp e r a t u r ef o r s i xh e a t so fI nc on e l７４０H
( a)１１２０ ℃ ; ( b)１１５０ ℃ ; ( c)１１８０ ℃ ; ( d)１２００ ℃．
F i ４ Gr a i nbounda r r e c i i t a t e si nh e a t４０１ ( a)and g yp p h e a t４０６ ( b)
he a t s４０４ and ４０５ we r e cho s en a st he op t imi z ed he a t st oc onduc tf u r t he ri nve s t i t i onsont hehe a t ga t r e a tmen to fI nc one l７４０H．Neve r t he l e s s, i ti swo r t h no t i ngt ha tt heabovechemi c a lc ompo s i t i onop t imi Ｇ z a t i oni sr a t he rr ough, wh i ch r equ i r e sf u t u r er e Ｇ s e a r ch wi t hr e spe c tt ot he mi c r o s t ruc t u r es t ab i l i t y andc r e eps t r eng t h． ２ ２ Ef f e c to fs o l u t i ont empe r a t u r e I nt he s t anda r d he a tt r e a tmen to fI ncone l ７４０H,t hes o l u t i ont empe r a t u r ei s１１５０°C． I no rde r t oi nve s t i t et hee f f e c to fs o l u t i ont empe r a t u r eon ga t heg r a i ns i z eo fI nc one l７４０H,t heop t i c a l mi c r o Ｇ r aphso ft hehe a t４０５he a t Ｇ t r e a t eda tf ou rd i f f e r en t g so l u t i ont empe r a t u r e swe r et akenanda r eshowni n F i ５． I ti sf oundt ha t,whent hes o l u t i ont empe r a Ｇ g t ur ewa sbe l ow１１５０ ℃ ,t heg r a i ns i z eo fhe a t４０５ kep ta r ound１００μm,whe r e a sexc e s s i veg r a i nc oa r s Ｇ en i ng wa sobs e r ved whent hes o l u t i ont empe r a t ur e wa sh i rt han１１５０ ℃．Theave r ageg r a i ns i z e so f ghe t hes amp l e st r e a t eda ts o l u t i ont empe r a t u r e so f１１８０ and１２００ ℃ we r el a r rt han２２０μm．Theexc e s s i ve ge r a i nc oa r s en i ngl edt oasha r r opo fimpa c tt oughＧ g pd ne s sa tr oom t empe r a t u r ef o rhe a t４０５ ( showni n
F i ５ Op t i c a lmi c r o s c op e so ft h es amp l e ss o l u t i on g t r e a t e da td i f f e r en tt emp e r a t u r e s
２ ３ Ef f e c to fc oo l i ngr a t e Thee f f e c to fcoo l i ngr a t ea f t e rso l u t i ont r e a t Ｇ men tont hes i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e sha s p [ ] be eni nve s t i t edi no t he rNi Ｇba s edsupe r a l l oys９Ｇ１８ ． ga I ti sf oundt ha tf a s tcoo l i ng r a t e,such a s wa t e r i ng,t i c a l l e adst ot hef o rma t i ono fmono Ｇ quench yp yl [ ] moda ls i z ed i s t r i bu t i ono fr e f i nedγ ′p r e c i i t a t e s９Ｇ１１ ． p Ont hecon t r a r l owe rcoo l i ng r a t el e adst ot he y,s f o rma t i on o fb imoda lsome t ime seven mu l t imoda l , s i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e s wh i chi sbe l i eved p t or e su l tf r om mu l t i l ed i s t i nc tbur s t so fnuc l e a t i on p o fγ ′p r e c i i t a t e sa td i f f e r en tunde r coo l i ngsdur i ng p con t i nuouscoo l i ng．Whent hea l l oyi scoo l edt oar e l Ｇ a t i ve l i rt empe r a t ur ej us tbe l ow γ ′p r e c i i t a t e yh ghe p so l vust empe r a t ur e,t hef i r s tnuc l e a t i onbur s twi t h l ow d r i v i ngf o r c eandh i i f f us i v i t ake sp l a c e, gh d yt br i ng i ngou tt hef o rma t i ono ft hef i r s tgene r a t i ono f γ ′p r e c i i t a t e s w i t hl o w e r n u m b e r d e n s i t ．T h e s e p y coa r s eγ ′p r e c i i t a t e sa r eo f t enr e f e r r edt oa spr ima Ｇ p r ′p r e c i i t a t e s．Whent hea l l oyi sf ur t he rcoo l ed, yγ p l owe rd i f f us i v i t i rd r i v i ngf o r c ewou l dl e ad yandh ghe t ot hesupe r s a t ur a t i ono fγ ′ Ｇ f o rmi nge l emen t saway f r omt hed i f f us i onf i e l dso fg r owi ngp r ima r ′p r e Ｇ yγ , c i i t a t e s ． A s a r e s u l t t h e s e c o n db u r s t o fγ ′ r e c i i Ｇ p p p t a t enuc l e a t i onhappens．Thes e conda r ′p r e c i i Ｇ yγ p t a t e shavet i c a l l i ne rs i z eand h i r numbe r yp yf ghe
１５４
J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
dens i t Subs equen tag i ngf o rasho r tt imei susua l l y． y c a r r i edou tt omagn i f hed i f f e r enc ebe twe ent hes i Ｇ yt [ １６ Ｇ １８] z e so ftwogene r a t i onso fγ ′p r e c i i t a t e s ． p I nt he pr e s en ts t udy,f ou rd i f f e r en tc oo l i ng r a t e sr ang i ngf r om wa t e rc oo l i ngt of u rna c ec oo l i ng we r eadop t edf o rhe a t４０５a f t e rs o l u t i ont r e a tmen ta t １１５０ ℃ f o r３０ mi n．Thes o l u t i onanne a l eds amp l e s we r et henageda t８００ ℃ f o r１６hf o l l owedbya i r coo l i ng．Theγ ′pr e c i i t a t e sw e r et h e ne x t r a c t e db p y t hemi c r o Ｇ chemi c a lpha s eana l i sme t hod．Thema s s ys f r a c t i ono fγ ′pr e c i i t a t e si ne a chs amp l ewa sde t e r Ｇ p mi ned．Ther e su l ti sshowni nF i ６． I ti sf oundt ha t g s l owc oo l i ngr a t el edt oal a r to fγ ′p r e c i i Ｇ geamoun p t a t e s．The ma s sf r a c t i onso fγ ′p r e c i i t a t e si nt he p a i r Ｇ coo l edandf u rna c e Ｇ c oo l eds amp l e s we r ea r ound １５ ma s s％ c ompa r ed wi t h１３ ma s s％ i nt he wa t e r Ｇ coo l edando i l Ｇ c oo l eds amp l e s．Thes i z ed i s t r i bu t i ons o ft he s e ex t r a c t ed γ ′p r e c i i t a t e s de t e rmi ned by p SAXS me t hodf o rd i f f e r en tc oo l i ngr a t e sa r eshown i nF i ７． Th ec o r r e spond i ngme and i ame t e r so ft heγ ′ g
F i ６ Ma s sf r a c t i ono fγ ′p r e c i i t a t e sa td i f f e r en t g p c o o l i ngme t hod sa f t e rs o l u t i ont r e a tmen t
r e c i i t a t e sa r ea l so g i ven．I n gene r a l,nob imoda l p p s i z ed i s t r i bu t i onso fγ ′p r e c i i t a t e swe r eobs e r vedf o r p a l lt hef ourcoo l i ngr a t e s．Thes i z ed i s t r i bu t i onso fγ ′ r e c i i t a t e sf o ra l lt hes amp l e swe r emonomoda land p p t he me an d i ame t e rde c r e a s ed wi t ht hei nc r e a s eo f coo l i ngr a t e．
D )—S i z ed i s t r i bu t i on; D — Me ans i z e． f( ( a)WC; ( b)OC; ( c)AC; ( d)FC．
F i ７ SAXSr e s u l t so fγ ′p r e c i i t a t e so fI nc on e l７４０Ha td i f f e r en tc o o l i ngme t hod sa f t e rs o l u t i ont r e a tmen t g p
I nt hepr ev i ousi nve s t i t i ons,whe r eb imoda l ga , s i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e sw a so b s e r v e d t h e p t i c a lc oo l i ngr a t e swe r ewe l lbe l ow５ K/mi n．Fo r yp
i ns t anc e,i nt hei nve s t i t i ono fRene１０４bySa r os i ga [ ] e ta l １２ ,t hec oo l i ngr a t ewa sa sl owa s５ K/mi nt o r oduc eb imoda ls i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e s． p p
I s sue２ He a tTr e a tmen to faCand i da t eMa t e r i a lf o r７００ ℃ AＧUSCPowe rP l an t s
S imi l a r l n as t ema t i cs t udy on t he e f f e c to f y,i ys coo l i ngr a t eonγ ′p r e c i i t a t e ss i z ed i s t r i bu t i on,Ra Ｇ p [ ] d i se ta l １５ c onc l udedt ha tc oo l i ngr a t el owe rt han２ / K mi ni senought oc aus eb imoda ls i z ed i s t r i bu t i on o fγ ′pr e c i i t a t e s． I nt hep r e s en ts t udy,t hec oo l i ng p r a t eo ff u rna c ec oo l i ngwa sa r ound１０K/mi nwh i ch, , i nt heau t ho r s ′op i n i on wa s no ts l ow enought o c aus et heb imoda ls i z ed i s t r i bu t i ono fγ ′p r e c i i t a t e s． p Be s i de s,t hel a r and i ame t e ro fγ ′p r e c i i t a t e s ge me p a s soc i a t edwi t hs l owc oo l i ngr a t ewa sde t r imen t a lt o t hes t r eng t ho ft h i sa l l oy．The r e f o r e,f r omt hepo i n t , o fv i ew o f me and i ame t e ro fγ ′p r e c i i t a t e s wa t e r p coo l i nga f t e rs o l u t i ont r e a tmen ti sp r e f e r r edf o rI n Ｇ cone l７４０H．
１５５
r ima r ′i nl a r i z e． S imi l a r l hes e condnuc l e Ｇ p yγ ges y,t a t i onbur s to fγ ′p r e c i i t a t e st ookp l a c edur i ngsub Ｇ p s equen tag i nga t７５０ ℃ ,wh i chi st e rmeda ss e cond Ｇ , a r ′．Att hebeg i nn i ngo fag i nga t７５０ ℃ t hes i z e yγ o ft hes e conda r ′p r e c i i t a t e s wa ssma l l e rcomＧ yγ p r edwi t ht ha to ft hep r ima r ′p r e c i i t a t e s．Af t e r Ｇ pa yγ p , wa rds bo t hp r ima r e conda r ′p r e c i i t a t e s yands yγ p unde rwen tt hep r oc e s so fg r owi ngandOs twa l dr i Ｇ pe n i ng． I ti sbe l i evedt ha t,dur i ng Os twa l dr i i ng, pen t heg r owt ho ft hel a r rp r e c i i t a t e si sa tt heex Ｇ ge p eo ft heg r owt ho fsma l l e rp r e c i i t a t e s．The r e Ｇ pens p f o r e,t hep r ima r ′p r e c i i t a t e scou l dg r owi n t oa yγ p muchl a r rs i z e． Be s i de s,t heg r owt ho ft hes e cond Ｇ ge a r ′p r e c i i t a t e s wa sa lwayssupp r e s s ed by t he yγ p Os twa l dr i i ngo fp r ima r ′p r e c i i t a t e s,wh i ch pen yγ p r e su l t edi nt heb imoda ls i z ed i s t r i bu t i ono fγ ′p r e c i Ｇ p i t a t e sa sobs e r veda f t e rl ong Ｇ t imeag i nga t７５０ ℃．
２ ４ Ef f e c to fpr e Ｇ a i nga t８００ ℃ f o r１６h g I nt he s t anda r d he a tt r e a tmen to fI ncone l , ７４０H apr e Ｇ ag i nga t８００ ℃ f o r１６hi sr equ i r ed． I n t her e s e a r che sonI nc one l７４０pe r f o rmedbyZhaoe t [ ] a l ３Ｇ５ ,t hemi c r o s t ruc t u r eevo l u t i onandme chan i c a l r ope r t i e swe r es t ud i edons amp l e swh i chwe r eso l u Ｇ p t i onanne a l edandl ong Ｇ t imeageda t７５０ ℃．Node Ｇ t a i l ed mi c r o s t ruc t u r eobs e r va t i ons we r ec a r r i edou t on s amp l e s wh i ch we r e aged a f t e rs t anda r d he a t t r e a tmen t,no rwa st hec ompa r i s onbe twe ent hemi Ｇ c r os t ruc t u r e so fageds amp l e swi t handwi t hou tp r e Ｇ , ag i nga t８００ ℃．The r e f o r ei nt hep r e s en ti nve s t i Ｇ ga t i on,wi t ht hepu r s eo fa s s e s s i ngt hene c e s s i t f po yo , r e Ｇ a i n a t８ ０ ０ ℃ f o r I n c o n e l ７ ４ ０ H b o t hs o l u t i o n p g g anne a l edands t anda r dhe a t Ｇ t r e a t edI nc one l７４０Ha l Ｇ l oyswe r el ong Ｇ t imeageda t７５０ ℃ f o r８０００h．The SEM r e su l t so fbo t hs amp l e sa r eshowni nF i ８． g Themi c r o s t ruc t u r e so fhe a t４０５ageda f t e rs o l u t i on anne a l i nga r eshowni nF i ８( a)and８( c),wh i l e gs ( a),( c)So l u t i ont r e a tmen t＋７５０ ℃×８０００h,AC; t hemi c r o s t ruc t u r e so fhe a t４０５ageda f t e rs t anda rd ( b),( d)So l u t i ont r e a tmen t＋８００ ℃×１６h,AC＋ he a tt r e a tmen ta r eshowni nF i ８( b)and８( d)． I n gs ７５０ ℃×８０００h,AC． t hes amp l e wi t hou tp r e Ｇ ag i nga t８００ ℃ ,c oa r s eγ ′ F i ８ Mo rpho l o fγ ′p r e c i i t a t e sa f t e r g g yo p ( ) r e c i i t a t e s a r ound１５０nmi nd i ame t e r wi t hcu Ｇ d i f f e r en th e a tt r e a tmen t s p p bo i dshape we r eobs e r ved,wh i chi sbe l i evedt obe ti sr epo r t edi no t he ri nve s t i t i onso fNi Ｇba s ed ga t hecommonr e su l to fOs twa l dr i i ng． I nc on t r a s t, I pen , s u e r a l l o s t h a t t h e e x i s t e n c eo f s e c o n d a r a n d t e r t i Ｇ p y y i nt hes amp l ewi t hp r e Ｇ ag i nga t８００ ℃ twogene r a Ｇ r ′p r e c i i t a t e swi t hf i nes i z ei sbene f i c i a lt obo t h yγ p t i onso fγ ′pr e c i i t a t e swe r eobs e r vedi nt he mi c r o Ｇ a p [ , ] ens i l eandc r e eps t r eng t ha th i empe r a t ur e s１９ ２０ ． ght s t ruc t u r e． I nadd i t i ont ot hel a r i dγ ′p r e c i i Ｇ t gecubo p nt hec a s eo fI ncone l７４０H,t hecomb i nede f f e c t so f t a t e swi t hne a r l hes ames i z et ot ha ti nt hes amp l e I yt r e Ｇ ag i nga t８００ ℃f o r１６handsubs equen tag i nga t wi t hou tpr e Ｇ ag i ng,as e c ondgene r a t i ono fγ ′p r e c i i Ｇ p p an p r oduc es e conda r ′p r e c i i t a t e s wi t h yγ p t a t e swi t ha muchsma l l e rs i z e we r ea l s oobs e r ved ７５０ ℃ c i nes i z ei nadd i t i ont ot hel a r i dp r ima r ′ gecubo yγ be twe ent hel a r ′p r e c i i t a t e s．Theave r aged i amＧ f geγ p r e c i i t a t e sa f t e rl ong Ｇ t imeag i ng．Att hes amet ime, p e t e rf o rt hes e c ondgene r a t i ono fγ ′p r e c i i t a t e swa s p p s i r eds i dee f f e c t swe r eobs e r ved．The r e f o r e, a r ound４０nm． I ti sp r opo s edt ha t,du r i ngp r e Ｇ ag i ng nounde , i t i ss u e s t e dt h a t r e Ｇ a i n a t８ ０ ０ ℃ i sn e c e s s a r gg p g g y a t８００ ℃ t hef i r s tnuc l e a t i onbu r s to fγ ′p r e c i i Ｇ p o rI ncone l７４０Ht oimp r ovei t spe r f o rmanc ea th i gh t a t e st ookp l a c e,wh i chr e su l t edi nt hef o rma t i ono f f
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J ou r na lo fI r onandS t e e lRe s e a r ch,I n t e r na t i ona l Vo l ２２
t empe r a t u r e s．
３ Conc l u s i on s
( １) Among t hes i x he a t so fI nc one l７４０H manu f a c t u r ed i n t he l abo r a t o r he op t imi z ed y, t chemi c a lc ompo s i t i oni sp r e l imi na r i l d e t e r m i n e dt o y , bet ha to fhe a t s４０４and４０５ ba s edont heme chan i Ｇ c a lpr ope r t i e sa f t e rs t anda r dhe a tt r e a tmen ta td i f f e r Ｇ en tso l u t i ont empe r a t u r e s． ( ２)Thes o l u t i ont empe r a t u r ei sf i xedt obe １１５０ ℃ t od i s s o l vea l lt hec a rb i de s wi t hou texc e s Ｇ s i veg r a i nc oa r s en i ng． ( ３)Nob imoda ls i z ed i s t r i bu t i onso fγ ′p r e c i i Ｇ p t a t e swe r eobs e r vedi na l ls amp l e sa td i f f e r en tcoo l Ｇ i ngr a t e sa f t e rs o l u t i ont r e a tmen t．Wa t e rc oo l i ngi s r e commendeda si tl e adst ot hef i ne s tγ ′p r e c i i t a t e s． p ( ４)Pr e Ｇ ag i nga t８００ ℃ f o r１６hi sne c e s s a r y , f o rI n c on e l７４０H s i n c ei tr e s u l t si nb imod a ls i z ed i s t r i Ｇ bu t i ono fγ ′p r e c i i t a t e sa f t e ra i nga t７５０ ℃ ,wh i c hi s p g be l i evedt obebene f i c i a lt ot hec r e eps t r eng t h． Re f e r enc e s:
[ １] R．Vi swana t han,J F．Henr o sh,G． S t anko,J． Sh i n Ｇ y,J．Tanz l ede cke r,B．Vi t a l i s,R．Pur r t,J．Ma t e r．Eng．Pe r f o rm． １４ g ge ( ２００５)２８１ Ｇ ２９２． [ ２] R．Vi swana t han,K．Co l eman,U．Rao,I n t． J．Pr e s s．Ve s s e l s P i ８３ ( ２００６)７７８ Ｇ ７８３． p． [ ３] S． Zh a o,X．X i e,G D． Smi t h,S J． Pa t e l,Ma t e r．Le t t． ５８ ( ２００４) １７８４ Ｇ １７８７． [ ４] S． Zhao,X．Xi e,GD．Smi t h,S J．Pa t e l,Ma t e r．Sc i．Eng．A ３５５ ( ２００３)９６ Ｇ １０５．
[ ５] S． Zh a o,X．X i e,G D． Smi t h,S J．Pa t e l,Ma t e r．De s． ２７ ( ２００６) １１２０ Ｇ １１２７． [ ６] ND．Evans,P J．Ma z i a s z,R W．Swi ndeman,GD．Smi t h, Sc r i t a Ma t e r． ５１ ( ２００４)５０３ Ｇ ５０７． p [ ７] J P．Sh i ng l ede cke r,GM．Pha r r,Me t a l l．Ma t e r．Tr ans．A４３ ( ２０１２)１９０２ Ｇ １９１０． [ ８] Y．Chong,Z．L i u,A．God f r ey,W．L i u,Y．Weng,Ph i l．Mag． Le t t． ９３ ( ２０１３)６８８ Ｇ ６９６． [ ９] S S．Babu,MK．Mi l l e r,J M．Vi t ek,S A．Dav i d,Ac t a Ma Ｇ t e r． ４９ ( ２００１)４１４９ Ｇ ４１６０． [ １０] J Y．Hwang,R．Bane r e e,J．Ti l ey,R．Sr i n i va s an,GB． j Vi swa n a t h a n,HL． Fr a s e r,Me t a l l．Ma t e r．T r a n s．A４０ ( ２００９)
２４ Ｇ ３５． [ １１] D N． Se i dman,C K． Sudbr a ck,KE．Yoon,JOM５８ ( ２００６) ３４ Ｇ ３９． [ １２] P M．S a r o s i,B．Wa ng,J P．S immon s,Y．Wa ng,MJ．Mi l l s, Sc r i t a Ma t e r． ５７ ( ２００７)７６７ Ｇ ７７０． p [ １３] Y H．We n,J P．S immon s,C．Sh e n,C．Wo o dwa r d,Y．Wa ng, Ac t a Ma t e r． ５１ ( ２００３)１１２３ Ｇ １１３２． [ t aMa t e r． P． S immons,Y．Wang,Ac １４] YH．Wen,B．Wang,J ５４ ( ２００６)２０８７ Ｇ ２０９９． [ １５] R．Rad i s,M． Scha f f e r,M．Al bu,G．Ko t h l e i t ne r,P． Pö l t,E． Ko z e s chn i k,Ac t a Ma t e r． ５７ ( ２００９)５７３９ Ｇ ５７４７． [ １６] AR P． S i ngh,S．Nag,J Y．Hwang,GB．Vi swana t han,J． i n i va s an, HL．Fr a s e r, R．Bane r e e, Ma t e r． Ti l ey,R．Sr j Cha r a c t． ６２ ( ２０１１)８７８ Ｇ ８８６． [ l ey, t t opadhyay,Y．Ren,J．Ti １７] AR P． S i ngh,S．Nag,S．Cha , GB．Vi swana t han,HL．Fr a s e r,R．Bane r e e A c t a M a t e r． j ６１ ( ２０１３)２８０ Ｇ ２９３． [ P．Va z e,D U． ng,K．Ra １８] J．Ma o,K M．Ch a ng,WH．Ya y,S Fe r r e r,Me t a l l．Ma t e r．Tr ans．A３２ ( ２００１)２４４１ Ｇ ２４５２． [ D．Wh i t i s, １９] GB．Vi swana t han,P M． Sa r o s i,MF．Henr y,D WW．Mi l l i l l s,Ac t a Ma t e r．５３ ( ２００５)３０４１ Ｇ gan, MJ．Mi ３０５７． [ ２０] C Y．Cu i,YF．Gu,Y．Yuan,T．Os ada,H．Ha r ada,Ma t e r． Sc i．Eng．A５２８ ( ２０１１)５４６５ Ｇ ５４６９．