- Email: [email protected]
Phase compositions and lattice misfit in CMSX-11B partition coefficients in single crystal nickelbase superalloys
Scripta mater. 44 (2001) 731–736 www.elsevier.com/locate/scriptamat
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B PARTITION COEFFICIENTS IN SINGLE CRYSTAL NICKELBASE SUPERALLOYS Claudia Schulze and Monika Feller-Kniepmeier Technische Universita¨t Berlin, Institut fu¨r metallische Werkstoffe, BH 18, Straße des 17. Juni 135, 10623 Berlin, Germany (Received August 4, 2000) (Accepted in revised form October 18, 2000) Keywords: Nickelbase superalloys; Phase composition; Lattice misfit Introduction The non Re-containing nickelbase single crystal superalloy CMSX-11B [1] has been designed for industrial turbine application. As compared to superalloys of the first generation the Cr content was raised resulting in good hot corrosion and oxidation resistance. High strength is achieved by an elevated Ti: Al level and a moderate Ta content. Due to dendritic solidification of superalloys, phase compositions in dendrites and interdendritic areas can differ greatly in the as cast condition [2]. The applied solution heat treatment is aimed to level out these differences as element enrichment or impoverishment would decrease the alloys strength. We therefore intended to measure phase compositions in dendrites and interdendritic areas applying energy dispersive X-ray analysis, a method with high spatial resolution. In addition, the local lattice parameters were determined by convergent electron diffraction in order to determine the lattice misfit between ␥⬘ phase and matrix, which is needed for modelling creep stresses. Experimental A single crystal bar of CMSX-11B [1] was provided by DONCASTERS Feingußwerk, Bochum and heat treated by CANNON-MUSKEGON, Muskegon. The nominal analysis is given in Table 1 together with the applied heat treatment. After heat treatment, the mean ␥⬘ edge length in dendrites was (400 ⫾ 106) nm and the width of the matrix channels (41 ⫾ 10) nm. In interdendritic areas these values are (389 ⫾ 114) nm and (50 ⫾ 32) nm. A multistep procedure was applied in order to produce thin foils suitable for transmission electron microscope (TEM) inspection. First, 200m thin discs with a diameter of 3mm and [001] orientation were polished electrolytically (80% ethanol, 10% perchloric acid and 7% glycerine) until a hole appeared. In a second step, we performed two hours of ion milling with Ar ions in order to obtain foils of unique thickness. The mean thickness of the foils was 250nm. The dendritic macrostructure of the foils relative to the hole was made visible by backscattered electrons in a scanning electron microscope (SEM). These foils were used to measure the ␥⬘ phase composition by energy dispersive X-ray analysis (EDX) in a TEM and the local lattice constants in both phases by convergent beam electron diffraction 1359-6462/01/$–see front matter. © 2001 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved. PII: S1359-6462(00)00670-9
732
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
Vol. 44, No. 5
TABLE 1 Nominal Analysis and Heat Treatment of CMSX-11B
weight % atomic % Solutioning 1540 K/4h
Al
Cr
Co
Mo
3.6 7.85
12.5 14.14
7.0 6.99
0.5 0.31
Ti
Ta
W
Nb
Hf
Ni
4.2 5.0 5.0 0.1 5.16 1.63 1.60 0.14 Annealing 1394 K/5h, 1144 K/24h, 1033 K/30h
0.04 —
62.1 62.21
(CBED). The mean spot size was between 3.6 – 8.5 nm. First the CBED measurements and the analysis of the ␥⬘ phase were performed. As the matrix channels contained small secondary ␥⬘ particles after heat treatment, that would falsify the matrix analysis, a second etching with 25 ml acetic acid, 25 ml nitric acid and 37 ml hydrochloric acid was applied in order to solve the secondary ␥⬘ precipitates. This resulted in a complete dissolution of ␥⬘ particles in parts of the thin foil located close to the hole. As the ␥ channels were also attacked by the etchant, a grid of very thin ␥ channels (⬇ 100 nm) was produced. In order to make sure that only grid parts with no interior ␥⬘ particles were analysed dark field images with a ␥⬘ superlattice reflection were made. For all measurements a double tilt specimen holder cooled with liquid nitrogen was used. Calibration of the acceleration tension of our Philips CM30 TEM yielded (302.1 ⫾ 0.3)kV. CBED patterns were taken for the [1 1 19] direction, which is 4° off the [001] oriented ␥/␥⬘ phase boundaries. The CBED patterns were recorded with a GATAN TV-camera and integrated over several TV-frames. The digitization and the integration were performed by the program “ImageCBED⫹⫹” developed by R. Vo¨lkl [3] for image analysis and CBED pattern simulation. We considered 13 intersections between 7 HOLZ lines. Results Microstructure and Phase Compositions As result of the applied heat treatment, CMSX-11B has a tendency to recrystallize. Fig. 1 shows a high angle grain boundary decorated with precipitates. EDX-analysis in the TEM revealed that the grain boundary precipitates are high in Cr and Ni added by Co, W and Mo (Table 2).
Figure 1. High angle grain boundary in CMSX-11B with precipitates.
Vol. 44, No. 5
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
733
TABLE 2 Mean Phase Composition of Grain Boundary Precipitates in CMSX-11B
weight % atomic %
Cr
Ni
Co
W
Mo
Ta
Al
Ti
39.03 0.21 50.82
20.73 0.44 23.9
10.73 0.13 12.34
22.96 0.13 8.46
4.63 0.17 3.27
1.61 0.32 0.60
0.12 0.05 0.31
0.19 0.08 0.27
We were not able to conduct a full structure analysis from our CBED patterns. The measured interlattice plane distances however suggest that the precipitates are isomorph with the -(Cr-Ni-Mo) phase. A relatively high concentration of dislocations is observed in the microstructure of after heat treatment (Fig. 2). This is an unusual result for a monocrystalline nickelbase superalloy but corresponds with the tendency of CMSX-11B to recrystallize during heat treatment. The mean phase composition of the ␥⬘ phase, as determined from 50 measurements in dendrites is listed in Table 3. The ␥⬘ phase composition was found equal in dendrites and interdendritic areas. Mean compositions of the matrix in the dendritic macrostructure are compiled in Table 4. All elements are distributed evenly in dendrites and interdendritic areas except of W which is enriched in dendrites. By applying the lever rule and considering all detected elements, a ␥⬘ volume fraction of V␥⬘ ⫽ 67% is calculated from the measured phase compositions. CBED Measurements Average lattice constants resulting from 50 measurements each in dendrites lead to a ␥⬘ ⫽ (0,35803 ⫾ 0,000028)nm for the ␥⬘ phase and a ␥ ⫽ (0,35857 ⫾ 0,00030)nm for the matrix. Fig. 3 shows the course of local misfit between ␥⬘ phase and matrix as function of the dendritic macrostructure. Plotted is the constrained misfit in the foil perpendicular to the ␥/␥⬘ interface: ␦⬜foil ⫽ 2(a␥⬘ ⫺ a␥)/(a␥⬘⫹ a␥). Measurements and FEM calculations on superalloys CMSX-10 [2], CMSX-4 [4] and SRR99 [4] have shown that the unconstrained misfit ␦u is approximately 45% smaller than ␦⬜foil. The unconstrained misfit is therefore estimated to be ␦u ⫽ ⫺1.4 䡠10⫺3 in dendrites.
Figure 2. High concentration of dislocations in heat treated CMSX-11B.
734
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
Vol. 44, No. 5
Figure 3. Course of misfit ␦⬜foil as function of the local macrostructure; D: dendrite center, SA: secondary arm, ID: interdendritic area.
Discussion From the results of the phase analyses it can be concluded that the applied heat treatment is sufficient for industrial application. The different W contents in dendrites and interdendritic regions however give rise to quite different misfit values and thereby coherency stresses. The increased mean dislocation density of CMSX-11B after heat treatment can not be related to coherency stresses. The measured constrained misfit values ␦⬜foil in dendrites and interdendritic regions are relatively low and do not differ more than in other nickelbase superalloys that exhibit only low mean dislocation densities. Recently R. Bu¨rgel et al. [5] have shown that in CMSX-11B already 2% of plastic strain is sufficient to fully recrystallize the alloy during solutioning. They conclude that the dislocation structure supplies the mechanical energy for primary recrystallization. It seems obvious that the enlarged mean dislocation density is already produced by plastic strains during the casting process. In order to compare the equilibrium phase compositions of different superalloy generations, the partitioning ratios of elements (ci␥⬘/cin) 䡠V␥⬘ in the ␥⬘ phase and (cimatrix/cin)䡠(1-V␥⬘) in the matrix after standard heat treatment are listed in Tables 5 and 6. cin is the nominal composition of element i in atomic % and V␥⬘ the volume fraction of the ␥⬘ phase. In addition to CMSX-11B we choose nickel base superalloys that have been analysed in recent years as SRR99 [6] and the Re containing superalloys CMSX-4 [7] and CMSX-10 [2]. The nominal compositions and ␥⬘ volume fractions of these superalloys are given in Table 7. From the values of the partition ratios two groups of alloys can be distinguished: the Re containing and the non Re-containing superalloys. The Re containing alloys CMSX-4 and CMSX-10 have identical partition ratios for both ␥⬘ phase and matrix, despite of the great variations in their nominal Cr, Co and Ti content. Also, the partition coefficients of SRR99 and CMSX-11B are quite similar although they have considerable differences in their nominal composition, especially in Cr, Co, W, Ta and Ti. From our results, we conclude that for the groups of Re containing and of non-Re containing nickel base superalloys, the phase compositions can be estimated quite well from our measured partition ratios, if the ␥⬘ volume fraction is known. The occurrence of the -phase in heat treated CMSX-11B is discussed in terms of the electronvacancy concept of d-shells [11]. As has been found empirically by Woodyatt et al. [12] nickelbase superalloys are prone to -precipitation if the average number of electron vacancies in electron d-subshells in the matrix is greater than N v ⫽ 2.52. Using the analysis values from Table 2 and the values of electron vacancies numbers calculated in [10], N v ⫽ 3.28 is obtained for CMSX11-B, where the -phase is precipitated after the applied heat treatment. From their matrix phase compositions and
Vol. 44, No. 5
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
735
TABLE 3 Composition of ␥⬘ Phase in CMSX-11B
dendrite weight % atomic %
Cr
Co
Mo
W
Ta
Al
Ti
Ni
2.79 0.18 3.14
3.17 0.55 3.15
0.14 0.07 0.09
2.38 0.31 0.76
8.19 0.38 2.65
4.77 0.43 10.34
7.39 0.15 9.02
71.18 0.85 70.87
TABLE 4 Composition of Matrix in Dendrites and Interdendritic Areas in CMSX-11B
dendrite weight % atomic % Interdendrite weight % atomic %
Cr
Co
Mo
W
Ta
Al
Ti
Ni
30.79 0.22 35.81 31.13 0.38 35.81
11.11 0.22 11.40 11.60 0.31 11.77
1.14 0.19 0.72 1.02 0.38 0.64
10.51 0.31 3.46 9.00 0.46 2.93
0.40 0.19 0.13 0.31 0.29 0.10
0.77 0.10 1.77 0.74 0.13 1.64
0.44 0.19 0.56 0.22 0.05 0.28
44.91 0.29 46.19 45.97 0.48 46.84
TABLE 5 Partition Coefficient in the ␥⬘ Phase (ci␥⬘/cin) 䡠 V␥⬘ for Different Single Crystal Nickelbase Superalloys
SRR99 CMSX-4 CMSX-10 CMSX-11B
Ni
Cr
Co
Mo
W
Ta
Re
Al
Ti
0.8 0.8 0.8 0.8
0.2 0.3 0.5 0.1
0.4 0.5 0.5 0.3
— 0.5 0.6 0.2
0.5 0.7 0.8 0.3
1.1 1.0 1.1 1.1
— 0.2 0.3 —
1.0 0.9 1.0 0.9
1.0 1.2 1.2 1.2
TABLE 6 Partition Coefficient in the Matrix (cimatrix/cin) 䡠 (1⫺V␥⬘) for Different Single Crystal Nickelbase Superalloys
SRR99 CMSX-4 CMSX-10 CMSX-11B
Ni
Cr
Co
Mo
W
Ta
Re
Al
Ti
0.2 0.2 0.2 0.2
0.7 0.7 0.6 0.8
0.5 0.5 0.5 0.6
— 0.5 0.4 0.8
0.4 0.3 0.3 0.7
0.1 0.0 0.0 0.1
— 1.0 1.0 —
0.1 0.0 0.0 0.0
0.1 0.0 0.1 0.0
TABLE 7 Nominal Composition and Volume Fraction V␥⬘ of SRR99 [8], CMSX-4 [9] and CMSX-10 [10] in Atomic %
SRR99 CMSX-4 CMSX-10
Ni
Cr
Co
Mo
W
Ta
Re
Al
Ti
V␥⬘ [%]
66.7 62.3 74.2
9.6 7.3 2.4
5.0 9.8 3.2
— 0.4 0.3
3.0 2.1 1.7
0.9 2.2 2.8
— 1.0 2.0
12.0 13.7 13.2
2.7 1.2 0.3
71 [4] 78 [5] 83.7 [2]
736
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
Vol. 44, No. 5
electron vacancy numbers, N V ⫽ 1.79 is obtained for SRR99, N V ⫽ 2.06 for CMSX-4 and N V ⫽ 1.29 for CMSX-10. Consequently, all these alloys are not prone to -phase precipitation. References 1.
G. L. Erickson, in Superalloys 1996, ed. R. D. Kisinger, D. J. Deye, D. L. Anton, A. D. Cetel, M. V. Nathal, T. M. Pollock, and D. A. Woodford, p. 45, The Minerals, Metals and Materials Society, Warrendale, PA (1996). 2. C. Schulze and M. Feller-Kniepmeier, Mater. Sci. Eng. A281, 204 (2000). 3. R. Vo¨lkl, Schriftenreihe Werkstoffwissenschaften, Bd. 12, Verlag Dr. Ko¨ster, Berlin (1997). 4. R. Vo¨lkl, U. Glatzel and M. Feller-Kniepmeier, Acta Mater. 46, 4395 (1998). 5. R. Bu¨rgel, P. D. Portella, and J. Preuhs, in Superalloys 2000, ed. T. M. Pollock, R. D. Kissinger, R. R. Bowman, K. A. Green, M. McLean, S. Olson, and J. J. Schirra, p. 229, The Mineral, Metals and Materials Society, Warrendale, PA (2000). 6. R. Schmidt und M. Feller-Kniepmeier, Metall. Trans. A. 23, 745 (1992). 7. U. Hemmersmeier und M. Feller-Kniepmeier, Mater. Sci. Eng. A248, 87 (1998). 8. D. A. Ford and R. P. Arthey, in Proceedings of the 5th International Symposium on Superalloys, Seven Springs, PA, p. 115, AIME (1984). 9. D. J. Frasier, J. R. Whetstone, K. Harris, G. L. Erickson, and R. E. Schwer, in High Temperature Materials for Power Engineering 1990, ed. E. Bachelet et al., p. 1281, D. Reichel, Dordrecht (1990). 10. G. L. Erickson, in Superalloys 1996, ed. R. D. Kissinger, D. J. Deye, D. L. Anton, A. D. Cetel, M. V. Nathal, T. M. Pollock, and D. A. Woodford, p. 35, The Minerals, Metals and Materials Society, Warrendale, PA (1996). 11. D. K. Das, S. P. Rideout, and P. A. Beck, Trans. AIME. 200, 253 (1954). 12. I. R. Woodyatt, C. T. Sims, and H. J. Beattie, Trans. AIME. 239, 519 (1966).
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B PARTITION COEFFICIENTS IN SINGLE CRYSTAL NICKELBASE SUPERALLOYS Claudia Schulze and Monika Feller-Kniepmeier Technische Universita¨t Berlin, Institut fu¨r metallische Werkstoffe, BH 18, Straße des 17. Juni 135, 10623 Berlin, Germany (Received August 4, 2000) (Accepted in revised form October 18, 2000) Keywords: Nickelbase superalloys; Phase composition; Lattice misfit Introduction The non Re-containing nickelbase single crystal superalloy CMSX-11B [1] has been designed for industrial turbine application. As compared to superalloys of the first generation the Cr content was raised resulting in good hot corrosion and oxidation resistance. High strength is achieved by an elevated Ti: Al level and a moderate Ta content. Due to dendritic solidification of superalloys, phase compositions in dendrites and interdendritic areas can differ greatly in the as cast condition [2]. The applied solution heat treatment is aimed to level out these differences as element enrichment or impoverishment would decrease the alloys strength. We therefore intended to measure phase compositions in dendrites and interdendritic areas applying energy dispersive X-ray analysis, a method with high spatial resolution. In addition, the local lattice parameters were determined by convergent electron diffraction in order to determine the lattice misfit between ␥⬘ phase and matrix, which is needed for modelling creep stresses. Experimental A single crystal bar of CMSX-11B [1] was provided by DONCASTERS Feingußwerk, Bochum and heat treated by CANNON-MUSKEGON, Muskegon. The nominal analysis is given in Table 1 together with the applied heat treatment. After heat treatment, the mean ␥⬘ edge length in dendrites was (400 ⫾ 106) nm and the width of the matrix channels (41 ⫾ 10) nm. In interdendritic areas these values are (389 ⫾ 114) nm and (50 ⫾ 32) nm. A multistep procedure was applied in order to produce thin foils suitable for transmission electron microscope (TEM) inspection. First, 200m thin discs with a diameter of 3mm and [001] orientation were polished electrolytically (80% ethanol, 10% perchloric acid and 7% glycerine) until a hole appeared. In a second step, we performed two hours of ion milling with Ar ions in order to obtain foils of unique thickness. The mean thickness of the foils was 250nm. The dendritic macrostructure of the foils relative to the hole was made visible by backscattered electrons in a scanning electron microscope (SEM). These foils were used to measure the ␥⬘ phase composition by energy dispersive X-ray analysis (EDX) in a TEM and the local lattice constants in both phases by convergent beam electron diffraction 1359-6462/01/$–see front matter. © 2001 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved. PII: S1359-6462(00)00670-9
732
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
Vol. 44, No. 5
TABLE 1 Nominal Analysis and Heat Treatment of CMSX-11B
weight % atomic % Solutioning 1540 K/4h
Al
Cr
Co
Mo
3.6 7.85
12.5 14.14
7.0 6.99
0.5 0.31
Ti
Ta
W
Nb
Hf
Ni
4.2 5.0 5.0 0.1 5.16 1.63 1.60 0.14 Annealing 1394 K/5h, 1144 K/24h, 1033 K/30h
0.04 —
62.1 62.21
(CBED). The mean spot size was between 3.6 – 8.5 nm. First the CBED measurements and the analysis of the ␥⬘ phase were performed. As the matrix channels contained small secondary ␥⬘ particles after heat treatment, that would falsify the matrix analysis, a second etching with 25 ml acetic acid, 25 ml nitric acid and 37 ml hydrochloric acid was applied in order to solve the secondary ␥⬘ precipitates. This resulted in a complete dissolution of ␥⬘ particles in parts of the thin foil located close to the hole. As the ␥ channels were also attacked by the etchant, a grid of very thin ␥ channels (⬇ 100 nm) was produced. In order to make sure that only grid parts with no interior ␥⬘ particles were analysed dark field images with a ␥⬘ superlattice reflection were made. For all measurements a double tilt specimen holder cooled with liquid nitrogen was used. Calibration of the acceleration tension of our Philips CM30 TEM yielded (302.1 ⫾ 0.3)kV. CBED patterns were taken for the [1 1 19] direction, which is 4° off the [001] oriented ␥/␥⬘ phase boundaries. The CBED patterns were recorded with a GATAN TV-camera and integrated over several TV-frames. The digitization and the integration were performed by the program “ImageCBED⫹⫹” developed by R. Vo¨lkl [3] for image analysis and CBED pattern simulation. We considered 13 intersections between 7 HOLZ lines. Results Microstructure and Phase Compositions As result of the applied heat treatment, CMSX-11B has a tendency to recrystallize. Fig. 1 shows a high angle grain boundary decorated with precipitates. EDX-analysis in the TEM revealed that the grain boundary precipitates are high in Cr and Ni added by Co, W and Mo (Table 2).
Figure 1. High angle grain boundary in CMSX-11B with precipitates.
Vol. 44, No. 5
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
733
TABLE 2 Mean Phase Composition of Grain Boundary Precipitates in CMSX-11B
weight % atomic %
Cr
Ni
Co
W
Mo
Ta
Al
Ti
39.03 0.21 50.82
20.73 0.44 23.9
10.73 0.13 12.34
22.96 0.13 8.46
4.63 0.17 3.27
1.61 0.32 0.60
0.12 0.05 0.31
0.19 0.08 0.27
We were not able to conduct a full structure analysis from our CBED patterns. The measured interlattice plane distances however suggest that the precipitates are isomorph with the -(Cr-Ni-Mo) phase. A relatively high concentration of dislocations is observed in the microstructure of after heat treatment (Fig. 2). This is an unusual result for a monocrystalline nickelbase superalloy but corresponds with the tendency of CMSX-11B to recrystallize during heat treatment. The mean phase composition of the ␥⬘ phase, as determined from 50 measurements in dendrites is listed in Table 3. The ␥⬘ phase composition was found equal in dendrites and interdendritic areas. Mean compositions of the matrix in the dendritic macrostructure are compiled in Table 4. All elements are distributed evenly in dendrites and interdendritic areas except of W which is enriched in dendrites. By applying the lever rule and considering all detected elements, a ␥⬘ volume fraction of V␥⬘ ⫽ 67% is calculated from the measured phase compositions. CBED Measurements Average lattice constants resulting from 50 measurements each in dendrites lead to a ␥⬘ ⫽ (0,35803 ⫾ 0,000028)nm for the ␥⬘ phase and a ␥ ⫽ (0,35857 ⫾ 0,00030)nm for the matrix. Fig. 3 shows the course of local misfit between ␥⬘ phase and matrix as function of the dendritic macrostructure. Plotted is the constrained misfit in the foil perpendicular to the ␥/␥⬘ interface: ␦⬜foil ⫽ 2(a␥⬘ ⫺ a␥)/(a␥⬘⫹ a␥). Measurements and FEM calculations on superalloys CMSX-10 [2], CMSX-4 [4] and SRR99 [4] have shown that the unconstrained misfit ␦u is approximately 45% smaller than ␦⬜foil. The unconstrained misfit is therefore estimated to be ␦u ⫽ ⫺1.4 䡠10⫺3 in dendrites.
Figure 2. High concentration of dislocations in heat treated CMSX-11B.
734
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
Vol. 44, No. 5
Figure 3. Course of misfit ␦⬜foil as function of the local macrostructure; D: dendrite center, SA: secondary arm, ID: interdendritic area.
Discussion From the results of the phase analyses it can be concluded that the applied heat treatment is sufficient for industrial application. The different W contents in dendrites and interdendritic regions however give rise to quite different misfit values and thereby coherency stresses. The increased mean dislocation density of CMSX-11B after heat treatment can not be related to coherency stresses. The measured constrained misfit values ␦⬜foil in dendrites and interdendritic regions are relatively low and do not differ more than in other nickelbase superalloys that exhibit only low mean dislocation densities. Recently R. Bu¨rgel et al. [5] have shown that in CMSX-11B already 2% of plastic strain is sufficient to fully recrystallize the alloy during solutioning. They conclude that the dislocation structure supplies the mechanical energy for primary recrystallization. It seems obvious that the enlarged mean dislocation density is already produced by plastic strains during the casting process. In order to compare the equilibrium phase compositions of different superalloy generations, the partitioning ratios of elements (ci␥⬘/cin) 䡠V␥⬘ in the ␥⬘ phase and (cimatrix/cin)䡠(1-V␥⬘) in the matrix after standard heat treatment are listed in Tables 5 and 6. cin is the nominal composition of element i in atomic % and V␥⬘ the volume fraction of the ␥⬘ phase. In addition to CMSX-11B we choose nickel base superalloys that have been analysed in recent years as SRR99 [6] and the Re containing superalloys CMSX-4 [7] and CMSX-10 [2]. The nominal compositions and ␥⬘ volume fractions of these superalloys are given in Table 7. From the values of the partition ratios two groups of alloys can be distinguished: the Re containing and the non Re-containing superalloys. The Re containing alloys CMSX-4 and CMSX-10 have identical partition ratios for both ␥⬘ phase and matrix, despite of the great variations in their nominal Cr, Co and Ti content. Also, the partition coefficients of SRR99 and CMSX-11B are quite similar although they have considerable differences in their nominal composition, especially in Cr, Co, W, Ta and Ti. From our results, we conclude that for the groups of Re containing and of non-Re containing nickel base superalloys, the phase compositions can be estimated quite well from our measured partition ratios, if the ␥⬘ volume fraction is known. The occurrence of the -phase in heat treated CMSX-11B is discussed in terms of the electronvacancy concept of d-shells [11]. As has been found empirically by Woodyatt et al. [12] nickelbase superalloys are prone to -precipitation if the average number of electron vacancies in electron d-subshells in the matrix is greater than N v ⫽ 2.52. Using the analysis values from Table 2 and the values of electron vacancies numbers calculated in [10], N v ⫽ 3.28 is obtained for CMSX11-B, where the -phase is precipitated after the applied heat treatment. From their matrix phase compositions and
Vol. 44, No. 5
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
735
TABLE 3 Composition of ␥⬘ Phase in CMSX-11B
dendrite weight % atomic %
Cr
Co
Mo
W
Ta
Al
Ti
Ni
2.79 0.18 3.14
3.17 0.55 3.15
0.14 0.07 0.09
2.38 0.31 0.76
8.19 0.38 2.65
4.77 0.43 10.34
7.39 0.15 9.02
71.18 0.85 70.87
TABLE 4 Composition of Matrix in Dendrites and Interdendritic Areas in CMSX-11B
dendrite weight % atomic % Interdendrite weight % atomic %
Cr
Co
Mo
W
Ta
Al
Ti
Ni
30.79 0.22 35.81 31.13 0.38 35.81
11.11 0.22 11.40 11.60 0.31 11.77
1.14 0.19 0.72 1.02 0.38 0.64
10.51 0.31 3.46 9.00 0.46 2.93
0.40 0.19 0.13 0.31 0.29 0.10
0.77 0.10 1.77 0.74 0.13 1.64
0.44 0.19 0.56 0.22 0.05 0.28
44.91 0.29 46.19 45.97 0.48 46.84
TABLE 5 Partition Coefficient in the ␥⬘ Phase (ci␥⬘/cin) 䡠 V␥⬘ for Different Single Crystal Nickelbase Superalloys
SRR99 CMSX-4 CMSX-10 CMSX-11B
Ni
Cr
Co
Mo
W
Ta
Re
Al
Ti
0.8 0.8 0.8 0.8
0.2 0.3 0.5 0.1
0.4 0.5 0.5 0.3
— 0.5 0.6 0.2
0.5 0.7 0.8 0.3
1.1 1.0 1.1 1.1
— 0.2 0.3 —
1.0 0.9 1.0 0.9
1.0 1.2 1.2 1.2
TABLE 6 Partition Coefficient in the Matrix (cimatrix/cin) 䡠 (1⫺V␥⬘) for Different Single Crystal Nickelbase Superalloys
SRR99 CMSX-4 CMSX-10 CMSX-11B
Ni
Cr
Co
Mo
W
Ta
Re
Al
Ti
0.2 0.2 0.2 0.2
0.7 0.7 0.6 0.8
0.5 0.5 0.5 0.6
— 0.5 0.4 0.8
0.4 0.3 0.3 0.7
0.1 0.0 0.0 0.1
— 1.0 1.0 —
0.1 0.0 0.0 0.0
0.1 0.0 0.1 0.0
TABLE 7 Nominal Composition and Volume Fraction V␥⬘ of SRR99 [8], CMSX-4 [9] and CMSX-10 [10] in Atomic %
SRR99 CMSX-4 CMSX-10
Ni
Cr
Co
Mo
W
Ta
Re
Al
Ti
V␥⬘ [%]
66.7 62.3 74.2
9.6 7.3 2.4
5.0 9.8 3.2
— 0.4 0.3
3.0 2.1 1.7
0.9 2.2 2.8
— 1.0 2.0
12.0 13.7 13.2
2.7 1.2 0.3
71 [4] 78 [5] 83.7 [2]
736
PHASE COMPOSITIONS AND LATTICE MISFIT IN CMSX-11B
Vol. 44, No. 5
electron vacancy numbers, N V ⫽ 1.79 is obtained for SRR99, N V ⫽ 2.06 for CMSX-4 and N V ⫽ 1.29 for CMSX-10. Consequently, all these alloys are not prone to -phase precipitation. References 1.
G. L. Erickson, in Superalloys 1996, ed. R. D. Kisinger, D. J. Deye, D. L. Anton, A. D. Cetel, M. V. Nathal, T. M. Pollock, and D. A. Woodford, p. 45, The Minerals, Metals and Materials Society, Warrendale, PA (1996). 2. C. Schulze and M. Feller-Kniepmeier, Mater. Sci. Eng. A281, 204 (2000). 3. R. Vo¨lkl, Schriftenreihe Werkstoffwissenschaften, Bd. 12, Verlag Dr. Ko¨ster, Berlin (1997). 4. R. Vo¨lkl, U. Glatzel and M. Feller-Kniepmeier, Acta Mater. 46, 4395 (1998). 5. R. Bu¨rgel, P. D. Portella, and J. Preuhs, in Superalloys 2000, ed. T. M. Pollock, R. D. Kissinger, R. R. Bowman, K. A. Green, M. McLean, S. Olson, and J. J. Schirra, p. 229, The Mineral, Metals and Materials Society, Warrendale, PA (2000). 6. R. Schmidt und M. Feller-Kniepmeier, Metall. Trans. A. 23, 745 (1992). 7. U. Hemmersmeier und M. Feller-Kniepmeier, Mater. Sci. Eng. A248, 87 (1998). 8. D. A. Ford and R. P. Arthey, in Proceedings of the 5th International Symposium on Superalloys, Seven Springs, PA, p. 115, AIME (1984). 9. D. J. Frasier, J. R. Whetstone, K. Harris, G. L. Erickson, and R. E. Schwer, in High Temperature Materials for Power Engineering 1990, ed. E. Bachelet et al., p. 1281, D. Reichel, Dordrecht (1990). 10. G. L. Erickson, in Superalloys 1996, ed. R. D. Kissinger, D. J. Deye, D. L. Anton, A. D. Cetel, M. V. Nathal, T. M. Pollock, and D. A. Woodford, p. 35, The Minerals, Metals and Materials Society, Warrendale, PA (1996). 11. D. K. Das, S. P. Rideout, and P. A. Beck, Trans. AIME. 200, 253 (1954). 12. I. R. Woodyatt, C. T. Sims, and H. J. Beattie, Trans. AIME. 239, 519 (1966).