TTT DIAGRAM OF A NEWLY DEVELOPED NICKEL-BASE SUPERALLOY ALLVAC 718PLUS

Transcription

1 Superlloys 718, 625, 706 nd Derivtives 2005 Edited y E.A. Lori TMS (The Minerls, Metls & Mterils Soiety), 2005 TTT DIAGRAM OF A NEWLY DEVELOPED NICKEL-BASE SUPERALLOY ALLVAC 718PLUS Xishn Xie 1, Chunmei Xu 1, Gilin Wng 1, Jinxin Dong 1, Wei-Di Co 2, Rihrd Kennedy 2 1 High Temperture Mterils Reserh Lortories, University of Siene & Tehnology Beijing; Beijing , Chin 2 ATI Allv; n Allegheny Tehnologies Compny, 2020 Ashrft Avenue, Monroe, NC 28110, USA Keywords: 718Plus, TTT Digrm, δ Phse, γ' Phse, γ" Phse Astrt A new nikel-se superlloy designted s Allv 718Plus hs een developed y ATI Allv to e used t 700 C. For phse hrteriztion, het tretment seletion nd struture stility evlution in high temperture rnge, the determintion of TTT digrm for lloy 718Plus is not only si reserh issue ut lso n importnt mtter for the lloy pplition t high tempertures. The onventionl lloy 718 hs een lso studied for omprison. Both lloys were solution treted t 1040 C for full solution of preipitted phses exept stle ride MC. After solution tretment oth lloy smples were het treted t 649 to 954 C for the times from 3-6 minutes till 100 hrs. Phse identifition ws minly y mens of SEM, XRD nd prtilly TEM nd SAD. Hrdness test ws lso onduted on the smples s the indition of γ" nd γ' preipittion hrdening. The experimentlly determined T-T-T digrms nd disussion on the phse formtion in lloys 718 nd 718Plus re desried in this pper. Introdution The first T-T-T digrm for wrought lloy 718 ws presented y Eiselstein in 1965 [1]. However, the omposition of erly mteril used y Eiselstein s well s the therml history hve hnged over the yers nd some of the phses Eiselstein reported re not urrently found. Sine the pioneering work y Eiselstein, mny investigtors hve produed TTT digrms determined on lloys solution treted to e strin free. [2-6] All these ltter studies differed from the former one y the ft tht rittle Lves phse ws not found to preipitte t short holding time s reported y Eiselstein nd nother ft tht the delt phse formed in shorter times thn tht reported y Eiselstein. Reently V. Beuois et l. [7] further studied short term preipittion kinetis of delt phse in strin free 718 lloy. This preipittion hs een studied on oth s reeived nd solution-treted onditions in the temperture rnge 650 to 1020 C nd for times up to 10 h. The results indite tht the strt of preipittion of delt phse in lloy 718 in the high temperture rnge where forming is rried out seems to proeed t higher tempertures nd shorter times thn reported in most previous work. From ll pulished literture on lloy 718, it is ler tht the eginning of preipittion nd the type of preipittion is dependent on the nture of the strting mteril, i.e. the degree of residul strin, the mount of delt produed y the solid solutioning step, nd proly the most importnt is the degree of N segregtion left fter the proessing yles. Oviously it is very dependent on the experimentl onditions. 193

2 Allv 718Plus lloy is new Ni-se superlloy developed t ATI Allv, nd it hs high strength t high temperture, good struture stility ompred with onventionl 718 lloy nd n e used up to 704 C [8-11]. To tilor the mirostruture for properties, n understnding of phse stility with time nd temperture is essentil. Therefore, this investigtion ws initited to determine the T-T-T digrm for lloy 718Plus, whih is not only si reserh ut lso n importnt mtter for the lloy pplition t high tempertures. Alloy 718 hs een lso studied for omprison. Experimentl Method nd Mterils The lloy 718Plus used in this study ws supplied y ATI Allv s 20 mm RCS rolled rs. Alloy 718 offered y Fushun Steel Compny hs lso een studied for omprison. Chemil omposition of the mterils is reported in Tle I. Smples mm were ut from the srolled rs, then solution treted for 1 hour t 1040 C nd wter quenhed for full dissolution of preipitted phses exept stle ride MC. After solution tretment oth lloy smples were het treted in the temperture rnge of 649 C to 954 C for 3-6 minutes to 100 hours nd wter quenhed. Phse identifition ws minly onduted y mens of SEM, XRD nd prtilly TEM nd SAD. Hrdness tests were lso onduted on the smples s the indition of γ" nd γ' preipittion hrdening. Tle I. Chemil Composition (wt%) Alloy C Cr Mo W Co Fe N Al Ti Ni Bl 718Plus Bl Hrdness Results nd Disussion Figure 1 shows Time- Temperture-Hrdness (TTH) urves for lloy 718 nd lloy 718Plus speimens exposed in the temperture rnge of 649 to 954 for 3-6 minutes to 100 hours. The Vikers hrdness for lloys 718 nd 718Plus is 225HV nd 223HV, respetively, fter solution tretment t 1040 C for 1 hour. γ /γ strt to preipitte in the mtrix when the Vikers hrdness exeeds 225HV nd 223HV, respetively, during the ging tretment. γ'/γ" solvus in Figure 1 hve een otined from Thermo-Cl thermodynmi lultion. It n e seen tht the preipittion hrdening proess in lloy 718Plus is little it fster thn tht in lloy 718. Evolution of Mirostruture with Time nd Temperture Figure 2 shows optil nd SEM pitures of lloy 718 fter solution tretment. The verge grin size of lloy 718 is 44 µm, equivlent to ASTM 6. After solution tretment t 1040 C for 1 hr, lloy 718 ontins minly MC rides (N nd Ti rides) nd no dditionl preipittion ould e oserved y SEM on exposure t 649 C up to 100 hrs. Figure 3 shows photogrphs of lloy 718 speimens exposed t 732 C for 0.5, 1 h, nd 100 hours. No dditionl preipittion ould e oserved on exposure t 732 C for 0.5 hour. With inresing exposure time to 1 hour, grin oundry preipittes n e oserved. At 100 h exposure, grin oundries re essentilly overed with preipittes nd the mtrix hs mottled pperne typil of overged γ"/γ'. Alloy 718 speimens exposed t 816 C for 0.5 h shows grin oundry preipittes only nd intrgrnulr mottled overged γ"/γ' lso pper with inresing exposure time to 50 h, Figure 4. Grin oundry preipittes hve ppered fter 194

3 exposed t 850 C for 0.1 h nd intrgrnulr mottled overged γ"/γ' is oserved fter exposure for 5 h nd 30 h, Figure () 900 γ /γ Solvus (886 ) Temperture, o C >225HV Time (h) γ /γ Solvus (989 ) () Temperture, o C >223HV Time (h) Figure 1 Time-Temperture-Hrdness Plots of the Mterils Solution Treted t 1040 for 1h nd Exposed in the Temperture Rnge of 649 ~954 for the Time of 3-6 Minutes to 100h. () Conventionl Alloy 718 () Modified Alloy 718Plus 195

4 100 m Figure 2 Optil () nd SEM () Pitures of Alloy 718 fter Solution Tretment (1040 /1h) Prior to Therml Aging Figure 3 Mirostruture of Alloy 718 Speimens Exposed t 732 for () 0.5 h, () 1 h, () 100 h Figure 4 Mirostruture of Alloy 718 Speimens Exposed t 816 for () 0.1h, () 0.5h, () 50h Figure 5 Mirostruture of Alloy 718 Speimens Exposed t 850 for () 0.1 h, () 5 h, () 30 h 196

5 Figure 6 Mirostruture of Alloy 718 Speimens Exposed t 900 for () 0.1 h, () 5 h, () 10 h Figure 7 Mirostruture of Alloy 718 Speimens Exposed t 954 for () 0.1 h, () 10 h, () 50 h An exposure t 900 C for 0.1 h revels grin oundry preipittes only, Figure 6. However, with inresing exposure time t 900 C to 5 h nd 10 h, inter- nd intrgrnulr plte-like preipittes hve een oserved, Figure 6 nd 6. Asene of intrgrnulr mottled pperne suggests tht γ"/γ' preipittes re in solution t 900 C. An exposure t 954 C for 0.1 h revels grin oundry preipittes only, Figure 7. With inresing exposure time t 954 C to 10 h nd 50 hours lerly show inter- nd intrgrnulr plte-like preipittes, Figure 7 nd 7. Oviously the volume frtion nd size of the plte-like preipittes for 50 h exposure re lrger thn those of 10 h exposure. Figure 8 shows optil nd SEM pitures of lloy 718Plus fter solution tretment. The verge grin size of 718Plus lloy is 79 µm, equivlent to ASTM 4. Solution treted (1040 C/1h) lloy 718Plus ontins minly MC rides (N nd Ti rides) nd no dditionl preipittion ould e oserved y SEM on exposure t 649 C till 100h. 100 m Figure 8 Optil () nd SEM () Pitures of Alloy 718Plus fter solution tretment prior to therml ging 197

6 Figure 9 shows photogrphs of the lloy 718Plus speimens exposed t 732 C for 0.5, 1 h, nd 100 hours. No dditionl preipittion ould e oserved on exposure t 732 C for 0.5 hour. With inresing exposure time to 1 hour, grin oundry preipittes hve een oserved. At 100 h exposure, grin oundries re essentilly overed with preipittes nd the mtrix revels mottled pperne typil of overged γ'/γ". Alloy 718Plus speimen exposed t 816 C for 0.5 h shows grin oundry preipittes only nd intrgrnulr mottled overged γ'/γ" lso pper fter 50 h exposure, Figure 10. Grin oundry preipittes hve ppered fter exposure t 850 C for 0.1 h nd intrgrnulr mottled overged γ'/γ" lso pper fter exposure for 30 h, Figure 11. Figure 9 Mirostruture of Alloy 718plus Speimens Exposed t 732 for () 0.5 h, () 1 h, () 100 h Figure 10 Mirostruture of Alloy 718plus Speimens Exposed t 816 for () 0.1 h, () 0.5 h, ()50 h Figure 11 Mirostruture of Alloy 718plus Speimens Exposed t 850 For () 0.1 h, () 10 h, () 30 h An exposure t 900 C for 0.1 h revels grin oundry preipittes only, Figure 12. However, with inresing exposure time t 900 C to 1 h nd 10 h, intrgrnulr plte-like preipittes hve een oserved, Figure 12 nd 12. The lloy 718Plus speimen exposed t 954 C for 0.1 h shows grin oundry preipittes only nd exposures for 10 h nd 50 h result ed in grin oundry preipittes, intrgrnulr mottled overged γ'/γ" nd intrgrnulr plte- like preipittes. Volume frtion nd size of the plte-like preipittes for 50 h exposure re more nd lrger thn 10 h exposure. Presene of intrgrnulr mottled pperne suggests tht γ'/γ" preipittes re not solutioned in γ-mtrix in the temperture rnge of C, Figure

7 XRD nd TEM Anlyses Figure 12 Mirostruture of Alloy 718plus Speimens Exposed t 900 For () 0.1 h, () 1 h, () 10 h Figure 13 Mirostruture of Alloy 718plus Speimens Exposed t 954 For () 0.1 h, () 10 h, () 50 h The mjor preipitted phses found in lloy 718 in this study y isotherml tretments up to 100 h re γ', γ", nd δ phses. While the phses found in lloy 718Plus re γ', γ", δ, nd Ni 3 Al 0.5 N 0.5 phses[12]. The differene etween lloys 718 nd 718Plus is tht the min strengthening phse in lloy 718 is γ", ut the min strengthening phse in lloy 718Plus is γ'. Moreover, new pltelike Ni 3 Al 0.5 N 0.5 with HCP struture hs een found in lloy 718Plus. The grin oundry preipittes EDX nlyses of the speimens for oth lloy 718 nd lloy 718Plus solution treted t 1040 C for 1 h nd ged t 954 C for 5 h shows definite enrihment in N nd Ni. The residues from the HCl-Methnol eletrolyti extrtion on the sme speimens ontin δ nd MC (N nd Ti ride). It onfirms tht the grin oundry preipittes re δ-ni 3 N. Moreover, seleted TEM nlyses were onduted to onfirm the presene of plte-like Ni 3 Al 0.5 N 0.5 phse[12] in ddition to plte-like δ phse in lloy 718Plus fter ging t 900 C nd 954 C for some times. Time-Temperture-Trnsformtion Digrms Bsed on the struture nlyses nd hrdness tests, two TTT digrms for lloys 718 nd 718Plus re presented in Figure 14. Chnges in hrdness (Figure 1) orrelte well with the γ'/γ" preipittion. γ'/γ" strt to preipitte in the mtrix when the Vikers hrdness exeeds 225HV nd 223HV for lloy 718 nd lloy 718Plus respetively during the ging tretment. γ'/γ" nd δ solvus in Figure 14 nd 14 hve een otined from Thermo-Cl thermodynmi lultion. Figure 14 shows the TTT urve for lloy 718 nd the nose of the TTT urve for γ'/γ" preipittion ours t out 850 C for less thn 0.1 h nd the nose of the TTT urve for grin oundry δ preipittion ours t out 900 C for muh less thn 0.1 h. It is found tht δ phse preipittion is muh fster thn reported in most previous work. The right prt of Figure 14 lso shows the lrge plte-like δ preipittion urve. The lrge plte-like δ phse n form t higher temperture rnge fter severl hours ging. Figure 14 shows the TTT urve for lloy 718Plus nd the nose of the TTT urve for γ'/γ" preipittion ours t out 900 C for less thn 0.1 h nd the nose of the TTT urve for δ preipittion ours t out C for less thn 0.1 h. The plte-like Ni 3 M preipittion n form t 900 C for only 1hr therml ging. It n e 199

8 seen tht the TTT urves of γ'/γ" nd δ preipittion for lloy 718Plus hve shifted to the higher temperture for shorter time thn for onventionl lloy 718. γ'/γ" nd δ solvus (989 C nd 1060 C) for lloy 718Plus otined from Thermo-Cl thermodynmi lultion re muh higher thn tht for onventionl lloy 718. It explins tht the preipittion hrdening phses in lloy 718Plus re more stle t higher temperture thn tht in lloy δ Solvus (1027 () Temperture, o C δ (GB) γ /γ Solvus (886 γ /γ Plte-like γ /γ Solvus (989 ) Time (h) δ Solvus (1060 () Temperture, o C δ (Grin γ /γ Plte-like Ni 3 M δ+ni 3 Al 0.5 N Time (h) Figure 14 Time-Temperture-Trnsformtion Curves () Conventionl Alloy 718, () Alloy 718Plus 200

9 Conlusions 1. In lloy 718 only γ', γ", nd δ phses n e found in ddition to the primry MC (N nd Ti ride) phses, while in lloy 718Plus dditionl plte-like Ni 3 M (Ni 3 Al 0.5 N 0.5 ) phse with HCP struture hs een found. The morphology of Ni 3 Al 0.5 N 0.5 phse is similr to the δ phse ut diffiult to differentite from δ phse. No α-cr, σ phses were found in this study, whih re often found when stress is pplied or in very long time exposures. 2. The strt of preipittion of γ'/γ" nd δ phses in lloy 718 seems to proeed in shorter times thn reported in most previous work. Menwhile, the strt of preipittion of γ'/γ" nd δ phses in lloy 718Plus proeeds t higher tempertures nd shorter times thn those in onventionl lloy In ompring the phse formtion urves in lloy 718Plus with onventionl lloy 718, ll urves move to higher temperture nd shorter times. It is proly the effet of high luminum ontent (1.45%Al) in lloy 718Plus whih promotes γ preipittion nd lso my led to the formtion of the Ni 3 Al 0.5 N 0.5 in omprison with lloy 718. Aknowledgement The uthors would like to thnk ATI Allv nd Fushun Steel Compny for the mterils used in this study. The finnil support of ATI Allv is most ppreited. Referenes 1. H. L. Eiselstein, Metllurgy of Columium-Hrdened Nikel-Chromium-Iron Alloy, ASTM Speil Tehnil Pulition, 1965, 369, pp J. F. Brker, Long Time Behvior of Turine Mterils, GE Report R65FPD51, Ferury 5, R. F. Deker, Strengthening Mehnisms in Nikel-Bse Superlloys, Steel Strengthening Mehnisms Symposium, Zurih, Switzerlnd, W. J. Boesh nd H. B. Cnd, Preipittion Retions nd Stility of Ni 3 C in Inonel 718 Alloy, J. Met., 1969, 10, p J. W. Brooks nd P. J. Bridges, Metllurgil Stility of Inonel Alloy 718, 1988, Wrrendle, PA, TMS, p Ordei-Bsile nd J. F. Rdvih, A Current T-T-T Digrm for Wrought Alloy 718, Superlloys 718, 625 nd Vrious Derivtives, ed., E. A. Lori, TMS(1991), p V. Beuois, J. Huez, S. Coste, O. Bruelle nd J. Lze, Short Term Preipittion Kinetis of Delt Phse in Strin Free Inonel 718 Alloy, Mterils Siene nd Tehnology, 2004, Vol. (20), 8, p W.D. Co, US Ptent No.: 6, B2, W.D. Co nd R.L. Kennedy, Superlloy 2004, ed. K.A. Green et l, TMS, 2004, p R.L. Kennedy, W.D. Co, T.D. Byh nd R. Jeniski, Nioium, High Temperture Applitions, ed. Y.W. Kim et l., TMS, 2003, p W.D. Co nd R.L. Kennedy, At Metllugi Sini Vol. 18, 2005, p

10 12. Xishn Xie, Gilin Wng, Jinxin Dong, Wei-Di Co, Rihrd Kennedy, Struture Stility Study on Newly Developed Modified 718Alloy Allv 718Plus, Superlloys 718, 625, 706 nd Vrious Derivtives, TMS (2005). Allv nd 718Plus re trdemrks of ATI Properties, In. 202