Aluminizing of Nickel-Based Superalloys Grade IN 738 by Powder Liquid Coating

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1 Mterils Trnstions, Vol. 51, No. 5 (2010) pp. 982 to 987 #2010 The Jpn Institute of Metls Aluminizing of Nikel-Bse Superlloys Gre IN 738 y Power Liqui Coting Ptm Visuttipitukul 1; *, Nuntiy Limvnutpong 2 n Pnywt Wngyo 1; * 1 Deprtment of Metllurgil Engineering, Fulty of Engineering, Chullongkorn University, Thiln 2 Grute Shool of Engineering, Fulty of Engineering, Chullongkorn University, Thiln Nikel-se superlloy gre IN738 hs superior reep resistne, however, oxition resistne is the min limittion of this lloy for prtil pplitions t high temperture. Coting of nikel luminie ompouns whih hve high oxition resistne on the IN738 lloys surfe n remrkly inrese the oxition resistne y formtion of Al 2 O 3 film s protetive lyer. Aluminizing y power liqui oting methos is pplie in this reserh. Mixe slurries of Al n Al 2 O 3 powers re pste onto IN 738 smples n hete t 1273 K in rgon tmosphere for 3.6 to 14.4 ks (1 to 4 h). Slurries n e lssifie into four ifferent rtios of Al : Al 2 O 3 : 10 : 0, 7:3, 5:5n 3:7. The mirostruture ws investigte y snning eletron mirosope (SEM) n optil mirosope. Phses in the ote lyer re hrterize y Glning Inient-ngle X-ry Diffrtometer (GIXD) n Eletron Proe Miro Anlysis (EPMA). The results show tht the ote lyer is forme y issolution of nikel into liqui luminum t luminizing temperture resulting in formtion of intermetlli ompoun lyer. The ote lyer onsists of Ni 2 Al 3 s min phse with smll mount of NiAl 3 n AlCr 2. AlCr 2 exists mostly t the lyer jent to the top surfe. For 8.1 n 14.4 ks (2.25 n 4 h) holing time, formtion of AlCr 2 t the interfe of mtrix n ote lyer ours ue to iffusion of luminum from ote lyer into nikel mtrix. The effet of time shows tht longer luminizing time les to formtion of uniform ote lyer. The Al : Al 2 O 3 rtio of either 10 : 0 or 7:3will rete uniform ote lyer with thikness more thn 200 mm. [oi: /mtertrns.m ] (Reeive Novemer 18, 2009; Aepte Ferury 15, 2010; Pulishe April 7, 2010) Keywors: luminizing, nikel luminie, IN738, power liqui oting 1. Introution Tle 1 Chemil omposition of IN738. Nikel-se superlloys gre IN738 is well known s high temperture mteril ue to its superior reep resistne. 1) However, this lloy suffers from low oxition n orrosion resistne. In orer to pply nikel-se superlloys gre IN738 s mhine prts in hot setion uner severe oxitive n orrosive tmosphere, surfe moifition to improve oxition n orrosion resistne is neessry. Mny reserh ttempts relte to protetive film oting hve een one to improve hot orrosion n oxition resistne of IN ) Formtion of intermetlli ompoun, for exmple nikel luminie, overing entire surfe is one wy to inrese oxition resistne of IN738. The nikel luminie lyer ts s n luminum sink, therefore, lumin film n form t high temperture s protetive lyer retring oxygen iffusion s well s oxition. 6) There re severl methos to inrese luminum ontent t the surfe yieling formtion of nikel luminie on the surfe of IN 738. A reently evelope proess is the so-lle power liqui oting proess pplie for luminizing steel. This proess employs psting slurries, whih t s soure for oting mterils, on to the surfe followe y susequent het tretment. The slurry ontins oting metl power, whih is luminum power for luminizing, mixe with other high melting point power, suh s Al 2 O 3. Aition of Al 2 O 3 power helpe retining n ispersing molten luminum to over ll oting res, preventing olesene of molten luminum into seprte pools. Therefore oting lyer ws forme uniformly n evenly on the entire surfe. 7) The purpose of this stuy ws to pply power liqui oting proess to frite nikel luminie lyer whih ws well known s protetive lyer for *Corresponing uthor, E-mil: ptm.v@hul..th, pnywt@ hotmil.om Element Ni Cr Co Ti Al W Mo T C mss% Bl t% Bl oxition in nikel se superlloys. Effet of proessing prmeters whih were slurry omposition n het tretment time on mirostruture n phses of the frite lyer ws investigte. 2. Experimentl Proeure 2.1 Smple preprtion Nikel-se superlloy gre IN738 (hemil omposition shown in Tle 1) ws ut into retngulr shpe with the size of 5 mm 10 mm 5 mm. All smples were polishe y SiC pper to numer 4000 gre. The smples were then rinse in etone y ultrsoni lening mhine for 300 seons. 2.2 Coting Coting slurries were prepre from mixture of Al n Al 2 O 3 powers with vrious Al : Al 2 O 3 rtios: 10 : 0, 7:3, 5:5n 3:7. Alumin power with size of 160 mm ws mixe with 3 mm luminum power. Ethylene glyol ws e into the mixture of Al n Al 2 O 3 powers to liquefy the mixture n this eme the oting slurries. The slurries were pste onto the smples with ensity of 1 kg/m 2 (0.1 g/m 2 ) n were hete uner rgon tmosphere t 473 K, n hel t this temperture for 5.4 ks in orer to remove the ethylene glyol. After tht, the temperture ws inrese to luminizing temperture t 1273 K, n hel for 3.6 ks (1 h), 8.1 ks (2.25 h), n 14.4 ks (4 h). The oting onitions re summrize in Tle 2.

2 Aluminizing of Nikel-Bse Superlloys Gre IN 738 y Power Liqui Coting st su lyer 2 n su-lyer 1 st su-lyer 2 n su-lyer Fig. 1 Cross-setionl mirostruture of IN738 luminize t 1273 K for 3.6 ks with Al : Al 2 O 3 rtio of () 10 : 0, () 7:3, () 5:5n () 3:7. Smple No. Al : Al 2 O 3 power rtio Tle 2 Coting onitions. Time (ks) Temperture (K) Atmosphere 1 10 : Argon 2 7:3 (1 h) 3 5:5 4 3:7 AlCr 2 NiAl 3 Ni 2 Al : :3 (2.25 h) 7 5:5 8 3: : :3 (4 h) 11 5:5 12 3:7 2.3 Chrteriztion Surfe n ross-setionl mirostruture of the ote smples were oserve y n optil mirosope n snning eletron mirosope (SEM). Energy ispersive spetrosopy (EDS) n eletron proe miro nlysis (EPMA) were performe to investigte the istriution of elements in the ote lyer. Phse formtion in the ote lyer ws hrterize y n X-ry iffrtrometer (XRD) n gling inient ngle X-ry iffrtometer (GIXD) t the inient ngle of 5 egree. 3. Results n Disussion 3.1 Phses n mirostruture hrteriztion Figure 1 shows ross-setionl mirostruture of smples whih were luminize y slurries with ifferent Al : Al 2 O 3 rtios for 3.6 ks (smple No. 1 to 4 in Tle 2). It n Fig. 2 GIXD profiles of IN738 luminize t 1273 K for 3.6 ks with ifferent Al : Al 2 O 3 rtios. e seen tht the ifferent Al : Al 2 O 3 rtios ffet uniformity n thikness of the oting lyer. The slurry with higher Al : Al 2 O 3 rtio proues thiker n more uniform ote lyer. In the se of 5:5n 3:7mixing rtios the ote lyer oes not over the entire surfe of IN738 mtrix. This is euse the mount of luminum in the slurries is not suffiient to e uniformly istriute. Moreover, luminum nnot wet nikel surfe euse the formtion of nikel luminie lyer seprtes the liqui luminum n the nikel mtrix elow. Nikel luminie lyer prevents liqui luminum from spreing, therefore nnot over the entire surfe of nikel sustrte. 8) Figure 1() shows the luminize lyer forme on the top surfe of IN738 smple. This mirostruture shows tht nikel n other lloying elements re issolve into liqui luminum t the luminizing temperture resulting in the formtion of luminize lyer on the top surfe. GIXD nlysis t the surfe of Nos. 1 to 4 smples is shown in Fig. 2. At the surfe of smple Nos. 1, 2 n 3, the ote lyer onsists of NiAl 3,Ni 2 Al 3 n AlCr 2, while only

3 984 P. Visuttipitukul, N. Limvnutpong n P. Wngyo AlCr2 NiAl3 Ni2Al3 Fig. 3 GIXD profiles of the smple luminize t 1273 K for 3.6 ks using Al : Al2 O3 rtio of 10 : 0 t the vrious epths from the surfe. Ni2 Al3 peks re etete on the surfe of smple No. 4. It n e seen tht the reltive intensities, whih express volume frtions, of NiAl3 n AlCr2 erese with eresing mount of Al in the slurries ut volume frtion of Ni2 Al3 inreses. The ontrst in ross-setionl mirostruture long the epth from the surfe inites tht severl phses exist in the ote lyer. The ote lyer n e ivie into 2 sulyers: the first su-lyer is the grey olor lyer lote next to the IN738 mtrix, n the seon su-lyer is t the top surfe. It is minly white in olor with some splsh of grey olor phse, s n e seen in Fig. 1(). Investigtion of phses existing t vrious epths from surfe ws one y GIXD s shown in Fig. 3. The GIXD profiles show tht there re NiAl3, Ni2 Al3 n AlCr2 t the surfe. The reltive intensity shows tht the min phses t the top surfe, whih is the seon su-lyer, re NiAl3 n AlCr2. At inresing epth from the surfe, the reltive intensities of NiAl3 n AlCr2 eome lower while the reltive intensity of Ni2 Al3 eomes higher. At epth greter thn 150 mm from the surfe, the first su-lyer, Ni2 Al3 is the min phse. Distriution of luminum, nikel, n hromium elements ws investigte y EDS s shown in Fig. 4. The ote lyer hs higher ontent of luminum thn tht of IN738 mtrix. The first su-lyer hs lower ontent of luminum thn the seon su-lyer, n vie vers for nikel n hromium ontents. The istriution of these elements orrespons well with the result from GIXD, in tht Ni2 Al3 in the first su-lyer hs lower mount of Al thn NiAl3 in the seon su-lyer. EDS line nlysis of the seon sulyer shows lrge mount of luminum t the top surfe, whih eomes less t inresing epth from the surfe. In ontrst, nikel ontent is lowest t the top lyer. Distriution n onentrtion grient of nikel n luminum suggests tht nikel toms iffuse through soli Ni2 Al3 lyer n then issolve into liqui luminum t the luminizing temperture. Effet of luminizing time is shown in Fig. 5. At short luminizing time, there re two istint su-lyers. When the luminizing time is inrese, the thikness of the first sulyer remrkly inreses, where s the thikness of the seon su-lyer ereses. At suffiiently long luminizing time, the seon su-lyer isppers; the mirostruture of ote lyer eomes phsi uniform n ontins only the first su-lyer. Therefore, smple No. 6, whih hs only first su-lyer uniformly ote on the IN 738 is selete for mirostruture n phse nlysis. Smple No. 6 is luminize t 1273 K for 8.1 ks, using slurry of 7 : 3 Al : Al2 O3 rtio. Its EDS nlysis is shown in Fig. 6. The first su-lyer ontins nikel, lrge ontent of luminum n smll ontent of hromium. Figure 7() shows SEM mirogrph of the first su-lyer forme on surfe of smple No. 6. High mgnifition SEM mirogrph of the first su-lyer n the first su-lyer/mtrix interfe re Fig. 4 EDS nlysis of luminize smple t 1273 K for 3.6 ks with Al : Al2 O3 rtio of 7 : 3 () seonry eletron imge () istriution of Ni () istriution of Al n () istriution of Cr.

4 Aluminizing of Nikel-Bse Superlloys Gre IN 738 y Power Liqui Coting 1st su lyer 2n su-lyer 985 1st su lyer e 1st su lyer f Fig. 5 Cross-setionl mirostruture of oting lyer of ifferent oting onitions; () smple No. 1, () smple No. 5, () smple No. 9, () smple No. 2, (e) smple No. 6 n (f) smple No µm Fig. 6 EDS nlysis of luminize smple t 1273 K for 8.1 ks with Al : Al2 O3 rtio of 7 : 3 () seonry eletron imge () istriution of Ni () istriution of Al n () istriution of Cr. shown in Fig. 7() n (), respetively. The ifferent ontrst in Fig. 7() inites three istint phses. EPMA nlysis of re in Fig. 7() is shown in Fig. 8. GIXD nlysis t vrious epth of this smple is shown in Fig. 9. From Fig. 8, it is foun tht the min phse in the first sulyer ontins luminum with high ontent of nikel, the seon phse ontins more luminum n less nikel, n the thir phse ontins high mount of hromium n luminum, with very low mount of nikel. Together with GIXD nlysis whih shows tht there re only Ni2 Al3, NiAl3, n AlCr2 in the first su-lyer, it n e ientifie tht the min phse is Ni2 Al3, the seon phse is NiAl3, n the thir phse is AlCr2. The first su-lyer/mtrix interfe in Fig. 7() ontins preipittes in form of light-olore elongte islns perpeniulr to the interfe in iretion of the first sulyer. EPMA nlysis of the re in Fig. 7() is shown in Fig. 10. It shows tht the preipitte islns re hromium rih phse. At epth etween mm, GIXD revels iffrtion peks t 20.57, n egree orresponing to (002), (110), n (103) rystllogrphi plnes of AlCr2 n iffrtion peks of Ni2 Al3. Therefore, the preipitte islns re ientifie s AlCr Mehnism of ote lyer formtion on IN 738 At luminizing temperture, nikel n lloying elements in IN738 issolve into molten luminum. The onentrtion of nikel in luminum is high t the interfe etween molten luminum n mtrix IN738. As soon s nikel ontent in molten luminum rehes the soluility limit, Ni2 Al3 is forme. Continuous formtion of Ni2 Al3 lyer is y iffusion of nikel toms through the newly forme Ni2 Al3 lyer into liqui luminum. Nikel onentrtion in molten luminum therefore inreses n Ni2 Al3 lyer grows. With inresing luminizing time, the Ni2 Al3 lyer, whih is the first sulyer, grows into liqui luminum.

5 986 P. Visuttipitukul, N. Limvnutpong n P. Wngyo AlCr2 NiAl3 Ni2Al3 Ni3Al mtrix Interfe 100 µm Coting lyer min phse 3r phse 2n phse Fig. 9 GIXD profiles of the smple luminize t 1273 K for 8.1 ks using Al : Al2 O3 rtio of 7 : 3 t the vrious epths from the surfe. 20 µm 5 µm Fig. 7 Cross-setionl mirostruture of () oting lyer () enlrge piture of oting lyer n () enlrge piture t interfe etween mtrix n oting lyer. n 2 phse Fig. 10 EPMA nlysis of interfe of ote lyer n IN738 () k sttering eleltron imge, istriution of Ni, Al n Cr. r 3 phse min phse 20 µm Fig. 8 EPMA nlysis of oting lyer () seonry eletron imge () istriution of Ni () istriution of Al n () istriution of Cr. For short luminizing time of 3.6 ks (1 h), istintion etween the first n the seon su-lyer n e esily me. The thikness of Ni2 Al3 lyer is thin ue to insuffiient time for nikel iffusion through Ni2 Al3 lyer. Therefore, molten luminum remins on the top surfe. During ooling own in the furne, the remining liqui luminum with high nikel ontent trnsforms to Ni2 Al3 n NiAl3 uring soliifition. NiAl3 n only preipitte stle phse t temperture lower thn 1178 K. AlCr2, whih is foun in the seon su-lyer, lso forms uring soliifition. This is ue to the ft tht Ni2 Al3, whih is the first phse forme t the interfe, n issolve Cr out 4 t% t 1273 K, s shown y ternry phse igrm of Ni-Al-Cr in Fig. 11. Dissolve Cr must e ejete from Ni2 Al3 lyer into jent liqui luminum. This results in preipittion of AlCr2 in the lyer jent to the surfe, oexisting with NiAl3 in the seon su-lyer. For long luminizing time, 8.1 n 14.4 ks (2.25 n 4 h), there is suffiient time for nikel iffusion to grow thik Ni2 Al3 lyer; therefore, ll liqui luminum is onsume n trnsforme to Ni2 Al3 s single lyer. This oting lyer n e onsiere s high luminum onentrtion lyer. Aluminum n iffuse into IN738 mtrix t high temperture resulting in growth of Ni2 Al3 into IN738 mtrix. Ejetion of

6 Aluminizing of Nikel-Bse Superlloys Gre IN 738 y Power Liqui Coting 987 Ni 2 Al 3 lyer onsists of Ni 2 Al 3 s min phse oexisting with NiAl 3 n AlCr 2. For short luminizing time, the ote lyer n e ivie into two su-lyers: Ni 2 Al 3 rih lyer esies the IN738 mtrix n NiAl 3 rih lyer t the surfe. For long luminizing time, the ote lyer is uniform onsisting of minly Ni 2 Al 3 with some preipittes of NiAl 3 n AlCr 2. The formtion of the ote lyer is firstly ontrolle y retion of Ni 2 Al 3 formtion etween liqui luminum n nikel. After Ni 2 Al 3 lyer is forme, iffusion of nikel toms through Ni 2 Al 3 lyer ontrols growth of Ni 2 Al 3 lyer into liqui luminum. AlCr 2 islns re lso foun t the interfe etween the ote lyer n the mtrix ue to low soluility of hromium in Ni 2 Al 3. REFERENCES Fig. 11 Ternry phse igrm of Ni-Cr-Al t 1273 K. 9) hromium out of Ni 2 Al 3 ours s isusse ove. The ejete hromium rets with luminum n preipittes s AlCr 2 islns s shown in Fig Conlusions Nikel luminie lyer is suessfully forme y power liqui oting. The pproprite Al : Al 2 O 3 rtios re 7:3or 10 : 0. Thikness of ote lyer rehes to more thn 200 mm fter luminizing for 8.1 ks (2.25 h). This ote 1) R. F. Deker n C. T. Sims: The Superlloys, (John Wieley & Son In., 1972). 2) J. E. Shile: Surf. Cot. Tehnol (2000) 35. 3) G. W. Gowr: Surf. Cot. Tehnol (1998) 73. 4) M. J. Li, X. F. Sun, H. R. Gun, X. X. Jing n Z. Q. Hu: Surf. Cot. Tehnol. 167 (2003) ) R. E. Mlush, P. De n D. H. Boone: Surf. Cot. Tehnol. 36 (1988) ) S. Y. Lee, J. S. Lee, K. B. Kim, G. S. Kim, B. Y. Lee, H. S. Moon, H. B. Eun, J. H. Lee n S. Y. Lee: Intermetllis 11 (2003) ) K. Murkmi, N. Nishi, K. Osmur n Y. Tomot: At Meter. 52 (2004) ) S. W. Ip, R. Srihr, J. M. Toguri, T. F. Stephenson n A. E. M. Wrner: Mter. Si. Eng. A 244 (1998) 31. 9) B. Grushko, W. Kowlski, D. Pvlyuhkov, B. Przepiorzynski n M. Surowie: J. Alloy. Comp. 460 (2008)