MICRO-MECHANICAL BEHAVIOR STUDY OF NON-METALLIC INCLUSIONS IN P/M DISK SUPERALLOY RENE 95

Transcription

1 Superlloys 2004 Eite y K.A. Green, T.M. Pollok, H. Hr, T.E. Howson, R.C. Ree, J.J. Shirr, n S, Wlston TMS (The Minerls, Metls & Mterils Soiety), 2004 MICRO-MECHANICAL BEHAVIOR STUDY OF NON-METALLIC INCLUSIONS IN P/M DISK SUPERALLOY RENE 95 Xishn Xie 1, Lin Zhng 1,2, Ming Zhng 1, Jinxin Dong 1, Kenneth Bin 3 1 High Temperture Mterils Reserh Lortories, University of Siene & Tehnology Beijing, Beijing , Chin 2 Eletron Mirosopy Lortory, Shool of Mterils Siene n Engineering, Tsinghu University, Beijing , Chin 3 GE Airrft Engines, Cininnti, Ohio 45215, USA Keywors: P/M Superlloy Rene 95, Non-metlli Inlusion, Miro-mehnil Behvior Astrt Speilly esigne SEM in-situ tensile n ftigue tests hve een onute to tre the entire proess of rk initition n propgtion till frture in Al 2 O 3 seee P/M Rene 95 superlloy. Speil thin foil TEM smples (with inlusions) were refully prepre n etil oservtions were onute with eletron mirosopy. The istriution of stress n strin fiel roun inlusions hs een lulte y mens of n elsto-plsti finite element metho FEM moel with the ommeril softwre, ANSYS. The results of this work re helpful to estlish the prtil life preition moel for the hrteristi inlusion prmeters in P/M superlloy omponents. Introution The mehnil properties, espeilly low yle ftigue properties (LCF), of P/M superlloys hve een seriously egre y the existene of non-metlli inlusions whih re introue into the lloy uring power metllurgy proessing [1-7]. From the 1980 s, extrinsi ermi inlusions hve een stuie, n mny reserh progrms hve een one to investigte this prolem. The work inlues inlusion hrteriztion n the effet of inlusions on mehnil properties espeilly LCF ility. Aoring to these investigtions, the min ompositions of ermi inlusions re Al, Si, C, Mg, n Zr, n the typil inlusions re Al 2 O 3 n SiO 2. The size rnge of efets is from severl nnometers to severl hunre mirometers. Extrinsi inlusions t s origins for ftigue rks, n erese tensile properties n LCF pility of P/M superlloys. Numerous experimentl results show tht the LCF life of P/M superlloy is losely relte to the size, lotion n numer of inlusions. The inlusion omposition or type sometimes is not signifint ftor. When the inlusion is t surfe of omponent (or speimen), it is esier to form ftigue rk initition thn if it is internl. With the inrese of inlusion size for oth surfe n internl inlusions, the LCF life of P/M superlloy ereses. Mny methos hve een investigte to ope with inlusion prolem [8]. These methos my e ivie into two kins y purpose. One is to iminish inlusion mount, while the other is to erese inlusion size. However, getting ompletely len superlloy is not urrently possile. In orer to ssure the sfety of P/M superlloy omponents, it eomes impertive to urtely preit the LCF life of P/M superlloy with extrinsi inlusions [9, 10]. So the etil informtion of inlusions must e lerne, espeilly the inlusion ehvior uring loing proess. Up to te, only few of pulitions hve een stuie on the miromehnil ehvior of inlusions in P/M superlloy n few systemtil investigtions or tests hve een rrie out. In this pper, miro-mehnil ehvior, suh s rk initition n propgtion, of ermi inlusions in P/M superlloy Rene 95 hs een investigte. Experimentl Mterils & Methos For expeiently unerstning the inlusion effet on rk initition n propgtion t ifferent stress onitions, GE Airrft Engines prepre the speil P/M Rene 95 experimentl mteril ope with lumin (Al 2 O 3 ) sees. Fine powers (-270 mesh) of Rene 95 lloy n Al 2 O 3 prtiles were mixe n proesse y routine P/M Rene 95 isk proution. SEM in situ tension n ftigue tests n trking oservtions were onute in this projet to iretly monitor inlusion ehvior t tension n ftigue stress onitions. A reful speimen preprtion ws onute. The flt tension n ftigue speimens with imension mm (see Fig.1) inluing the oserve inlusions were seletively ut from the test mterils. These inlusions must e lote t the surfe in the guge length setion of speimens. Eh smple ws mehnilly polishe n immersion ethe for SEM oservtion. Inlusion Fig.1 Shemti of SEM in-situ test speimen SEM in-situ tension tests were onute on the tensile loing stge in the hmer of SEM equipment whih n ontrol the lo n isplement t mient temperture. Similr with insitu tension tests, LCF in-situ tests were onute on the ftigue loing stge in the hmer of SEM, whih n ontrol the yli stress n numer of yles t mient temperture. The yli loing is in sine wve form. For miro-sle nlyses on inlusion/mtrix interfes, eformtion hrteristis, islotion onfigurtions n miro rking ehviors, speil thin foil TEM smples (with inlusions) were refully prepre n etil oservtions were onute with TEM. Furthermore, stress n strin istriution roun the simplifie inlusions uner tensile lo hs een lulte using the ommeril finite element metho (FEM) softwre ANSYS to ugment the tests results. 451

2 Results n Disussion P/M Rene 95 lloy for this investigtion hs nominl hemil omposition (in wt%) of 0.065C, 13Cr, 8Co, 3.5Al, 2.5Ti, 3.5N, 3.5Mo, 3.5W, n lne Ni n hs een hrterize s fine grin size ASTM 8 to 10. The primry ' (Ni 3 (Al,Ti,N)) of 1~5 m in imeter minly lotes t grin ounries s shown in Fig.2. Seonry ' (~0.1 m) n tertiry ' preipittes re very fine n ispersively istriute in grins (see Fig.3). A few MC (NC) rie prtiles rnomly istriute t grin ounries n in the grins oth. () 10 m Fig.2 OPM struture of P/M Rene 95 The white loky prtiles inite primry () Fig.5 Inlusion istriution imge of P/M Rene 95 etete y ultrsonindt (white spots inite inlusions 50 m) () P/M Rene 95 smple lok ( mm) () setion of P/M Rene 95 experimentl isk 80nm Fig.3 TEM struture of preipitte prtiles 10 m 10 m Fig.4 SEM frtogrphy of ommeril P/M Rene 95 LCF file smple Fig.6 OPM morphology of Al 2 O 3 inlusions with ifferent sizes (polishe surfe of smple) 452

3 LCF test results show tht nonmetlli inlusions were the origins of ftigue rks in PM Rene 95. Fig.4 shows SEM frtogrphy of ommeril P/M Rene 95 smple fter LCF test to filure. The frture ws initite t piee of nonmetlli inlusion s shown y the rrow in Fig.4. Fig.5 shows the istriution imge of inlusions in smple lok n n experimentl isk ope y Al 2 O 3 sees. Fig.6 illustrtes optil mirosopy morphology of Al 2 O 3 inlusions with ifferent sizes in the investigte mteril. Some of them re ompose of severl piees, whih were roken own from one inlusion prtile uring mnufturing proess. The interfes of inlusions/mtrix re just mehnilly ontte ut not metllurgilly one. There is no trnsition zone etween mtrix n inlusions. SEM In-situ Tension Oservtion Surfe Inlusion. Aoring to the results of the SEM in-situ tension oservtion, the rks n initite t ermi inlusion, n the effet of inlusions with ifferent sizes on rking ehviors is ifferent. Figure 7 shows the results of in-situ tensile test speimen with smll Al 2 O 3 inlusion. A tringulr Al 2 O 3 prtile out 10 m in size is shown in Fig.7 efore loing. The loing iretion is horizontl s shown y the rrows. The morphology of inlusion or mtrix hs no hnge until the tensile stress is up to the yiel strength ( s ) level. Fig.7 illustrtes the morphology of inlusion n mtrix fter the yieling of lloy. There re slip ns throughout mtrix n the surfe of the speimen eomes srggly. With the inresing of the lo, sliing eformtion eomes severe n rking ours in the inlusion (s rrow inite in Fig.7). The rk wiens ontinuously with the inrese in stress until the speimen fils n the smll tringle inlusion is ivie into two piees (Fig.7). Fig.7 A smll tringulr inlusion ehvior uring SEM in-situ tension proess () efore loing () fter speimen frture Figure 8 shows the results of n in-situ tensile test of speimen with reltively lrge ermi Al 2 O 3 inlusion, whih is out 50 m in mximl length. This inlusion hs een roken into severl piees uring mteril proessing efore loing s shown in Fig.8. After loing, t the stress level even lower thn yiel (point ), it is ifferent from the smll inlusion ehvior s shown in Fig.7. Crks initite t the inlusion/mtrix interfes s shown in Fig.8. This ours t stress levels lower thn the yiel stress. The sliing eformtion in the mtrix hs not hppene. It n e seen tht smll rk lso initites t one of the left orner of the inlusion. At this moment, the mtrix oes not eform n the lo is out 0.8 s of the mtrix. It shows tht the rks initite t the inlusion/mtrix interfe efore mtrix yieling. With inresing of externl tension loing, the initite rks t the inlusion/mtrix interfe wien. The rks join eh other n propgte into mtrix (Fig.8). The inlusion n e seprte from the mtrix n the eformtion of mtrix eomes ovious. As the speimen fils, the rks eome wier, n some piees of the inlusion hve lrey fllen out from mtrix (Fig.8). Su-surfe Inlusion. Besies surfe inlusion, the su-surfe inlusion (inlusion ner to the surfe) is lso signifint. Figure 9 shows pir of mthing frture surfes of P/M Rene 95 with inlusions fter in-situ tensile loing test to filure. The rk 453

4 V V H Fig.8 SEM in-situ tension oservtion of lrger Al2O3 inlusion in P/M Rene 95. () efore loing () fter speimen frture 30Pm 30Pm Fig.9 A pir of mthing frture surfe with inlusions ner to the smple surfe origin is luster of Al2O3 inlusion ner to the surfe, ut not the surfe inlusion. It shows tht when the inlusion ner to the surfe is igger thn the surfe one, the former is still the rk initition site. Filure ours from the ig su-surfe inlusion ut not from the smller surfe inlusion. efore mtrix yieling. Seon, the rks initite t ifferent lotions. For the smll inlusions, the rk usully forms in the inlusion. For the igger Inlusion, the rk initites t the inlusion/mtrix interfe esily. This is why the inlusion with ig size is more etrimentl to mehnil properties of P/M Rene 95. The results of the SEM in-situ tension oservtion revel tht the effets of inlusions with ifferent sizes on the rking ehvior re ifferent in two spets. First, for the smll tringulr Al2O3 prtile (out 10 Pm), the rk ours fter smple yieling, while the rk initites t the igger inlusion (out 50Pm) SEM In-situ Ftigue Oservtion SEM in-situ ftigue tests with stresses of sine wve form n ifferent mplitues were onute in stress rtio of 0.1(ie. R=0.1). 454

5 Fig.10 shows the in-situ ftigue oservtion on surfe Al 2 O 3 inlusion with mx = 1000MP. The inlusion size is out m 2. The initil morphology of this inlusion in mtrix is shown in Fig.10. At N=5000 yles, the rk t inlusion/mtrix interfe egn to grow. After N=6000 yles, the rk propgte rpily. When N=7000 yles, the speimen file. Fig.10() n( ) re the mthe frture surfes from two file prts of speimen. Fig.11 isplys the result of in-situ ftigue oservtion on P/M Rene 95 with surfe inlusion luster when mximum stress is 600MP. The loing iretion is shown y lk rrows. Fig.11 shows the originl morphology of n inlusion efore yli loing. This inlusion is out 60 m in size. There re two smll inlusion prtiles ner the right orner of the ig inlusion. With inresing ftigue yles, n interfe of the inlusion/mtrix is seprte n smll rk ours (see Fig.11). Initil rks t the interfes of ig inlusion/mtrix n smll inlusion/mtrix (see Fig.11) wien ontinuously, n t yle numer N=116316, two rks onnete together through the mtrix etween ig n smll inlusions. The eformtion of mtrix roun inlusions is so intense tht prt of the ig inlusion prtile hs een pulle out from the mtrix (s shown in Fig.11). The onnete lrge rk grows into the mtrix step y step from oth sies of the ig Al 2 O 3 prtile. When N= yles, the rk propgtes rpily until filure. A piee of ig inlusion prtile still remins in the mtrix s shown in Fig.11f. () N=0 () N=7000 () N=5000 ( ) N=7000 Fig.10 Inlusion ehvior uring SEM in-situ ftigue test ( =1000MP, R=0.1) The experimentl results show tht inlusions will esily initite ftigue rks even when the stress level is fr lower thn the yiel stress of P/M Rene 95. When the LCF stress is higher, the ftigue rk initites erlier t inlusions. TEM Oservtion SEM in-situ tension n ftigue tests inite tht rks ten to form t ermi inlusions ue to the lol stress onentrtion. Fig.12 represents the islotion onfigurtion ner very smll inlusion. It implies tht stress onentrtion existe t the inlusion/mtrix interfe efore loing. The stress onentrtion oul e inue uring the P/M mteril mnufturing proess. Fig.13 shows reltive lrge ermi inlusion. The islotion onentrtion n even smll rk n e oserve insie the inlusion prtile. Uner loing, the existing stress onentrtion eomes intense n the miro-rks (vois) t inlusion/mtrix interfe or in the inlusion n evelop or expn. When the stress is higher thn the yiel stress, the rks will form t inlusion/mtrix interfe or in the inlusion. When the inlusion size is very smll, the rk initition in PM Rene 95 n lso hppen t the interfes of primry /mtrix. Fig.14 shows the TEM imge of islotion onentrtions roun primry prtile. SEM in-situ tension test speimens without surfe inlusions inite tht the rk initites t primry / mtrix interfes n propgtes into long rk (Fig.15). TEM of n in-situ tension test ws onute n the results suggest tht the rk n grow long primry prtiles. Fig

6 V e f Fig.11 Inlusion ehvior uring SEM in-situ ftigue test (Vmx=600MP) () N=0, () N=2068, () N=101335, () N= (e) N=158116, (f) N= illustrtes TEM of n in-situ tension test with miro-rk hnging its propgting orienttion ue to the existene of two lrge primry J prtiles. FEM Anlysis Finite element simultion of surfe semispheril Al2O3 n P/M Rene 95 mtrix uring tensile proess ws onute to investigte the stress-strin fiel evelopment roun n inlusion prtile. The inlusion size n loing proess simulte tht of the in-situ mehnil tests. Fig.17 illustrtes the simultion results. The tensile loing iretion is long xis Z. From Fig.17 ()()(), show the stress fiel t surfe inlusion n mtrix re t ifferent stress levels. Clultion results show tht stress onentrtes t the pole re of the inlusion n its viinity (s 150nm Fig.12 TEM oservtion of very smll ZrO-Al2O3 inlusion prtile 456

7 2Pm Fig.15 Crk initites t n propgtes long primry J phse y SEM in-situ oservtion on speimen without surfe inlusion Primry J Primry J Fig.13 TEM imge of reltive lrge Al2O3 prtile of P/M Rene 95 Crk Fig.16 A miro-rk hnges its growing orienttion ue to the existene of two primry J prtiles t TEM in-situ tension test primry J The results of this investigtion n offer n experimentl sis for physil n mehnil moeling for the life of P/M Rene 95 mteril in the presene of inlusions. Aoring to experimentl results, it n e ertinly foun out tht ritil inlusion size exists. When n inlusion is smller thn the ritil size, the erliest rk my not initite t the inlusion for the tensile stress level lower thn yiel stress. These smll size inlusions my not e hrmful to the mehnil properties suh s tensile strength n LCF life. At this onition rks my initite t the interfes of ig primry J/mtrix n propgte long the ig primry J. More etile work shoul e one on the miro-mehnil ehvior of inlusions in P/M Rene 95 to gin vlue of ritil inlusion size for resonle life time preition on the P/M superlloy. 400nm Fig.14 Dislotions roun the primry J prtile shown y the rrow in Fig.17()). The stress reues grully from the pole of inlusion to equtor fe. During in-situ tension testing, surfe inlusion/mtrix interfes re only mehnilly one. Crks n form y seprting the interfe of inlusion prtile n mtrix t lo out 0.8Vs. Crk lotion will e t the pole re of the inlusion. The simultion results re in greement with the in-situ tensile experiments. The stress onentrtion roun the inlusion inreses with inresing in tensile stress. When the tensile stress V rehes 1120MP, tht is out 0.8Vs (Vs is yieling strength of the lloy), lol plsti eformtion (see Fig.17 ( )) ours in the mtrix ner the inlusion. If the interfe strength is low, rk n initite t the inlusion/mtrix interfe. Conlusions 1. The inlusion ehvior in lumin (Al2O3) seee P/M Rene 95 superlloy hs een investigte y SEM in-situ tension n ftigue tests. Diret oservtions of inlusion ehvior revels, tht uring the loing proess, rks initite t the inlusion/ 457

8 Pole re equtor fe Y X Z () 500MP () 800MP () 1120MP ( ) Distriution of 1 st priniple stress of mtrix ( ) Lol plsti eformtion of mtrix Fig.17 Distriution of 1 st priniple stress of simulte tensile proess y mens of FEM moel on P/M Rene95 with surfe inlusion mtrix interfe, n my lso initite t shrp orners of inlusions. Crks n propgte into the mtrix for further stress relese. The rk my lso initite insie the inlusion. The rk my propgte iretly into or through the inlusion n the inlusion n e ut or roken into two or more piees. 2. TEM oservtion revels the islotion onfigurtion t the inlusions. When the islotion rrys meet the inlusion (s stle ostle), they pile up to form stress onentrtion t the inlusion/mtrix interfe for rk initition n propgtion. 3. FEM simultion shows tht stress onentrtion ours t the pole re of spheril inlusion uner tensile loing. The stress onentrtion inreses with lo or inlusion size. Given n inlusion of set size, lol plsti eformtion initilly ours t the mtrix sie of inlusion/mtrix interfe. This ours t the stress level lower thn the yiel strength of Rene 95. The mismth of eformtion etween inlusion n mtrix les to rk initition n propgtion t interfe efore the lloy mtrix yiels. 4. A ritil inlusion size shoul exist oring to SEM in-situ tests. A ritil size of inlusion, whih is hrmful for mehnil properties (suh s tensile n LCF), n e foun y the further experimentl n moeling investigtion. Aknowlegments: This projet ws supporte y GE Airrft Engines, Cininnti, USA. Referenes 1. C. E. Shmlen et l, Effet of Inlusions on LCF Life of HIP Plus Het Trete Power Metl Rene95, Metll. Trns. B, 168 (1985), Eri S. Huron, Pul G. Roth., The Influene of Inlusion on Low Cyle Ftigue Life in P/M Nikel-Bse Disk Superlloy, (Pper presente t Symposium of Superlloy 1996), P. G. Roth et l., Hevy Liqui Seprtion: Relile Metho to Chrterize Inlusions in Metl Power, (Pper presente t onferene of Avnes in Power Metllurgy n Prtiulte Mterils, Cn, 1994), D. R. Chng et l., Superlloy Power Proessing, Properties n Turine Disk Applitions, (Pper presente t meeting of Superlloys 1984), J. C. Lutriou et l, Effet of Inlusions on LCF Life of PM Superlloys for Turoengine Diss, (Pper presente t onferene of High Temperture Mterils for Power Engineer, 1990), Prt II, J. M. Hyzk, I M Bernstein., The Effet of Defets on the Ftigue Crk Initition Proess in Two P/M Superlloys, Prt1, Ftigue Origins, Metll. Trns. A, 13 (1982), J. M. Hyzk, I. M. Bernstein., The Effet of Defets on the Ftigue Crk Initition Proess in Two P/M Superlloys. Prt2, Surfe-susurfe Trnsition, Metll. Trns. A, 13(1982), T. S. Cokrof et l., Inlusions n the EB Refining of Superlloys., (Pper presente t the meeting of Eletron Bem Melting n Refining Stte of the Art, USA, 1992), J. Grison, L. Remy., Ftigue Filure Proility in Power Metllurgy Ni-se Superlloy, Engineering Frture Mehnis, 57(1997), A. Brukner-Foit, H. Jkels, U. Qufsel, Preition of the Lifetime Distriution of High-Strength Components Sujete to Ftigue Loing, Ftigue Frt. Engng Mter. Strut., 16(1993),