Viscosities of nickel base super alloys

Transcription

1 Vscostes of nckel base super s Y.Sato, K.Sugsawa, D.Aok and T.Yamamura Department of Metallurgy, Graduate School of Engneerng, Tohoku Unversty, Senda , Japan. Emal: satoz@materal.tohoku.ac.jp ABS TRACT The vscostes of molten nckel base super s of TMS-75, CM-247LC, CMSX-4 and INCO-73C have been measured precsely by means of an oscllatng vscometer. The hghest and lowest vscosty were found for TMS-75 and INCO-73C, respectvely, although all of them were relatvely hgher than that of nckel. As the super s are mult component systems, the composton dependence of the vscosty may be complcated. Then, the estmaton of the vscosty on the molten super s were tred based on the results on the bnary melts. The calculated values agreed well wth the measured vscostes and t was consdered that the estmaton method was effectve to predct the vscosty of mult component melts. INTRODUCTION The vscostes of molten metals are very mportant not only n academc feld but also n ndustry because the vscosty s related to many ndustral processes such as castng, smeltng weldng etc. The demand for precse vscosty as a physcal parameter s ncreasng n the computer smulaton of the processes. For example, nckel base super s wth hgher strength at hgh temperatures are used n hgh technology feld such as the turbne blade of jet engne whch s manufactured n undrectonal castng or sngle crystal castng. Therefore, the progress of the smulaton of soldfcaton process s strongly requred. However, on the other hand, t s dffcult to measure precse vscosty of molten metals and bg dscrepances are frequently found among the reported values, especally at hgher temperatures. Authors have developed an oscllatng vscometer avalable up to 6 o C wth hgh precson [] and measured vscostes of hgh meltng temperature metals such as ron group elements [2]. On the other hand, nckel base super s are mult components, namely they contan many ng elements such as Co, Cr, Al, W, Ta, Mo, Hf, Re, Zr etc. Therefore, the authors planned to measure the precse vscosty of super s, TMS-75, CM-247LC, CMSX-4 and INCO-73C, and addtonally to estmate ther vscostes based on the vscostes on the nckel base bnary s obtaned by authors. EXPERIMENTAL As the vscosty of molten metals s low n general and the nckel base super s have hgh meltng ponts, the method for measurng vscosty s actually lmted to only the oscllatng method. A feature of the oscllatng vscometer s the good adaptablty to lower

2 vscosty and the precson s very good compared wth other hgh temperature vscometers such as a rotatonal vscometer. Also another feature s the wde choce on the materal as the melt contaner. It s the great advantage, especally at hgh temperatures. Present authors have developed the oscllatng vscometer wth a cylndrcal crucble [,2] to measure the molten salts and molten metals. In ths work, the vscometer was mproved for hgh temperatures wth hgh relablty. It conssts of a suspenson system, an oscllaton detecton system and a heatng system. The suspenson and detecton system of the vscometer s shown n Fg.. A torson wre made of platnum suspends a crucble connected through a tungsten rod, an nerta dsk and a mrror block. The mrror block reflects ncdent lght from a He-Ne laser and the lght s focused as a small spot of about.mm on the detector whch conssts of three photo transstors. Then four tme ntervals between the tmes when locus passes through the detectors are determned by usng a computer n the resoluton of.ms. Rotatonal force s gven to the nerta dsk made of alumnum to start the oscllaton electromagnetcally by means of the cols located above and under the dsk. The reproducblty of the tme measurement was excellent, for example, the standard devaton of the perod of oscllaton n actual measurement at hgh temperatures was typcally less than.%. The perod of the oscllaton and the logarthmc decrement were determned from the four tme ntervals by means of the algorthm developed by authors as descrbed earler [2]. The vscosty was calculated based on Roscoe s equaton [3] usng the perod of the oscllaton, the logarthmc decrement and some other physcal parameters. The whole apparatus s shown n Fg.2 schematcally. The torson wre was kept 38.2K to mantan the constant rgdty by crculatng warm water n the copper tube wound around the wre housng. Data processng computer. (PC-98) Tme Counter Photo transstor Wre(Pt-3%Rh) Laser lght Mrror(Al) Inerta dsc He nlet : Head Corn 2: Gas Inlet 3: Torson Wre 4: Water Crculaton Ppe 5: Reflecton Mrror 6: Wndow 7: Inerta Dsk 8: Oscllaton Intator 9: Water Jacket : W Rod : Mo plate 2: Crucble 3: Three dvded Furnace 4: Zr sponge 5: Thermocouple L L Colmator lens Convex lens Oscllaton ntator Tungsten rod 9 Coolng Water He-Ne laser Crucble Coolng Water 5 9 Fg. Suspenson and detecton system of oscllaton. Fg.2 Schematc vew of the whole apparatus of the oscllatng vscometer. The heatng system s also essentally mportant because the crucble of about 85mm long must be heated unformly to prevent the convecton flow n the crucble and to determne the absolute temperature precsely although t s very dffcult to obtan good temperature 2

3 unformty at the hgh temperature. The furnace conssts of three spral MoS 2 heaters (Kanthal, superthal heater) controlled ndependently each other. Addtonally, about 25 reflecton plates of molybdenum were nstalled n an outer alumna tube to mnmze the thermal radaton vertcally. The temperature profle was checked and the furnace controller was fne tuned carefully every measurement to obtan the best temperature unformty. As a result, unform temperature profles wthn.5k n whole length of the crucble was obtaned whle the temperature of upper part was set to be slghtly hgher than that of lower part. The atmosphere nsde was helum whch was nert and gave least effect on the measurement due to the lower vscosty. The zrconum sponge was placed under the crucble to keep the least oxygen partal pressure n the atmosphere. RESULTS AND DISCUSSION In ths work, hgh purty alumna crucble of 6 mm I.D. was used and the radus at hgh temperature was corrected by the expanson coeffcent of alumna [4]. As the densty s the most mportant parameter for determnng the vscosty, those of the molten super s used were the data measured by Muka et al. [5]. The results obtaned are shown n Fg.3. Ther vscostes are smlar each other and are hgher than that of molten nckel. TMS-75 and INCO-73C show hghest and lowest vscostes. The actvaton energes of all the super s are consderably hgher than that of molten nckel. As mentoned above, the super s are the complex mult component system as shown n Table. Major components are cobalt, chromum and alumnum based on the atomc fracton. Alumnum and nckel form very stable compound wth hgher meltng pont. It s very nterestng to estmate the vscosty of mult component system such as super as a functon of the composton. Log (Vscosty, η / mpa s ) TMS-75 CM-247LC CMSX-4 INCO-73C (Temperature, T ) - / -3 K - Fg.3 Vscostes of molten super s obtaned. Table Chemcal compostons of super s. TMS-75 CM247-LC CMSX-4 INCO-73C Element wt% at% wt% at% wt% at% wt% at% Co Cr Al Mo W Ta Nb Re T Zr Hf B balance balance balance balance Vscosty, η / mpa s 3

4 Authors have already measured fve bnary nckel base s, -Co [2], -Cr, -Al, -Ta and -W [6] at the compostons nearby nckel. Therefore, It was tred to estmate based on the results of above bnary melts. Although the addtvty s most useful for prmary estmaton of the composton dependence for many propertes of the melt, t s recognzed that the logarthmc addtvty s more probable than the smple addtvty for the vscosty. Generally, the vscosty s expressed as a functon of the temperature lke equaton (). E η = η exp( ) () The logarthmc vscosty s expressed n two terms as shown n equaton (2). Here, the parameters, lnη and E are ndependent of the temperature, respectvely. Then, t s possble to assume these as the functons of only compostons. Where, lnη = lnη lnη and E = E E. lnη = lnη = ( x E lnη = (lnη n n x lnη x lnη ) ( x x lnη ) ( E = n n E x E n n x E ) xe ) (2) The lnη and E were defned n low concentraton range of -th component n the bnary s and they were determned based on the prevous results mentoned above. However, the parameters have not been obtaned for Mo, Nb, Re, T, Zr, Hf and B. To resolve the problem, n ths work, ndvdual element was classfed n the meltng pont and was assgned to the bnary that consst of correspondng element wth smlar meltng pont. Boron was neglected here. Fgure 4 shows the results of the estmaton for same temperature range to the measurement. They are also hgher than the vscosty of molten nckel and the order of magntude among the s s almost same to measured results. However, the dfference of the actvaton energes among the s s less than that among the measurement, and the order of the magntude of the actvaton energy s almost same to that of the absolute vscosty values Log (Vscosty, η / mpa s ) TMS-75 (estmated) CM-247LC (estmated) CMSX-4 (estmated) INCO-73C (estmated) Vscosty, η / mpa s Log (Vscosty, η / mpa s ) TMS-75 CM-247LC CMSX-4 INCO-73C TMS-75 (estmated) CM-247LC (estmated) CMSX-4 (estmated) INCO-73C (estmated) Vscosty, η / mpa s (Temperature, T ) - / -3 K - Fg.4 Estmated vscostes of molten super s (Temperature, T ) - / -3 K - Fg.5 Comparson between measured and estmated vscostes. 4

5 Fgure 5 shows the overlapped comparson between the estmated vscostes and measured ones. The dfferences between the measured and estmated vscostes are less than 4% as seen n the fgure. The result of the comparson ndcates that the estmaton method s successvely adapted to predct the vscosty based on the addtvty of the logarthmc vscosty by usng the data of bnary melts. CONCLUSION In order to clarfy the fludty of molten nckel base super s, the vscostes of four super s were measured by means of the oscllatng vscometer up to about 88K. All of ther vscostes and ther actvaton energes were hgher than those of molten nckel although the vscostes are smlar each other. As the super s are typcal mult component system, the predcton of the vscosty was tred by usng the vscosty data of nckel base bnary melts. The vscostes measured were well represented by the estmaton wthn 4%. It was consdered that the estmaton method based on the addtvty of the logarthmc vscosty was very effectve to predct the vscosty of mult component melt. ACKNOWLEDGEMENT Ths work was performed as a part of Research and Development of Innovatve Castng Smulaton supported by New Energy and Industral Technology Development Organzaton (NEDO), through the Japan Space Utlzaton Promoton Center(JSUP), Report to the Mnstry of Economy, Trade and Industry (METI), Japan. REFERENCES. Y.Sato, Y.Kameda, T.Nagasawa, T.Sakamoto, S.Morguch, T.Yamamura and Y.Waseda, J.Cryst.Growth., 249, 44 (23). 2. Y.Sato, K.Sugsawa, D.Aok and T.Yamamura, Meas.Sc.Technol., 6, 363 (25). 3. R.Roscoe, Proc.Phys.Soc. 72, 576 (958). 4. Y.S.Touloukan, R.K.Krby, R.E.Taylor and T.Y.R.Lee, Thermophyscal Propertes of Matter, Vol.3, Thermal Expanson (IFI/Plenum, New York, 977), K.Muka, Z.L and L.Fang, Mat.Trans.Jpn.Inst.Met., 45, 2987 (24). 6. Y.Sato, K.Sugsawa, D.Aok and T.Yamamura, to be publshed. 5