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Superplasticity and diffusion bonding of IN718 superalloy
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ScienceDirect
Acta Metall. Sin. (Engl. Lett.) Vol.20 No.4 pp307-312 Aug. 2007
ACTA METALLURGICA SINICA (ENGLISH LETTERS)
www.atns,org.cn
SUPERPLASTICITY AND DIFFUSION BONDING OF IN718 SUPERALLOY W.B. Han', K.F. Zhang, B. Wang, and D.Z. Wu School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China Manuscript received 8 June 2007
The superplasticity and dimion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at direrent temperatures and various initial strain rates using the tensile speed mutation method; m reached its maximum value 0.53 at an initial strain rate of 1 x 104s-' at 12.5311: The d i h i o n bonding parameters, including the bonding temperature T, pressure p. and time t, affected the mechanism of joints. When the bonded specimen with 2 5 thick nickelfoil interlayerwas tensile at room temperature, the shearfracture of thejoints with nickel foil interlayer took place at the IN718 part. Microstructure study was camed out with the bonded samples. The microstmcture shows an excellent bonding at the interfaces. The optimum parameters for the dimion bonding are: T = 1273-I323K, p = 20-30MPa, t = 45-Mlmin. KEY WORDS superphticity; di@ion bonding; nickel foil; IN718 alloy
1. Introduction IN7 18 is a nickel-base superalloy, and possesses an advantageous combination of properties. It is the most widely used superalloy and accounts for 35% of the total superalloy production. IN7 18 superalloy was mainly used to manufacture complex welding sheet components in the 1960s, and it was used to produce parts of turbine, which had service life of more than ten thousand Now, IN71 8 alloy is practically used in high effective turbines, such as turbine disk, axle, blade, guide blade, shell, etc. to satisfy the increasing demands for higher temperature environment['I. To fulfill the requirements of product applications, the superplasticity and diffusion bonding of IN7 18 have been investigated in detail.
2. Microstructure Features of IN718Superalloy 2.1 Material IN718 superalloy used in the tensile experiment was Imm thick sheet. The analyzed composition (wt%) of the alloy is given as folloows: C 0.067, S 0.005, P 0.008, Cr 19.26, Ni 53.67, Ti 1.13, Cu 0.072, 'Corresponding author. Tel.: +86 451 86403016; fax: +86 451 86402382. E-moil address: [email protected] ( W . B . Han)
~
.
308
Mg ~ 0 . 0 1 ,Mn 0.03, Si 0.08, Mo 3.26, Nb 5.38, Al 0.55, Co 0.05, B 0.008. The specimen used to evaluate the strain rate sensitivity m was heat treated in 1193K for 30minL21.
2.2 Microstructural features The first detailed characterization of superplasticity was presented by Hayden etal.E3]for alloys in the NiFe-Cr system. In the superplastic condition, superalloys are characterized by a fine grained (generally lOpm or less), two-phase microstructure. The microstructure of the IN718 alloy is shown in Fig.1. For this alloy, the second phase is essential in ordered face centered cubic y’. The presence of a second phase is essential so that the microstructure remains stable throughout hot deformation[’”].
Fig. 1 Microstructure of Inconel7 18 superalloy. 06 -A-3 -*-9
2X104 6M04
2.3 Superplasticity of Inconel718 superalloy Early references have appeared relating to the observation of superplasticity in nickel-base alloys at a 1220 1230 1240 1250 wide temperature range of 1213 to 1293K and a strain Temperature T, K rate range of 1O4 to 10”s-l L51. Fig.2 The relationshipbetween the strain rate sensiFig.2 shows the relation of the strain rate sensitivtivity m and temperature. ity m and the test temperature at various initial strain rates. The value of rn increases with the decrease of the strain rate and the rise of temperature and reaches its maximum value at an initial strain rate of 1x 104s-’ at 1253K.
3. Diffusion Bonding of Inconel718 Superalloy In case of diffusion bonding of Inconel7 18 alloy, 25pm thick nickel foil interlayer is adopted. The effects of the diffusion bonding parameters, such as temperature T, pressure p , and time t, were investigated.
3.1 Effect of the diffusion bonding temperature T on the shear strength of joint The temperature of diffusion bonding greatly affects the plastic deformation, creeping resistance, and the diffusion behavior of the joint. The diffusion bonding temperature is increased properly because of the high thermal resistance of Ni based superalloy. Based on the suitable combination of the parameters of pressure, temperature, and time, the diffusion bonding temperature must be in the range of 1273- 1323K. Fig.3a shows the relationship between the shear strength of the joints and the temperature in this temperature range. It can be seen that the strength of the joints increases with the increasing bonding temperature.
3.2 Effect of the difision bonding pressure p on the tensile strength of the joint The diffusion bonding pressure is important to control the properties of the joint. The main function
309 .
320
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280
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h h-
S
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1260 -
6
240 1201 I 1170
1200
1230
1260
1290
-
I
1320
10
Bonding temperature T, K
15
20
25
30
Bonding pressure p, MPa
Fig.3 Relationship between the shear strength ofjoint and the diffusion bonding parameters: (a) shear strength-bondingtemperature curve; (b) shear strength-bonding pressure curve; (c) shear strength-bonding time curve. I 10
I 20
30
40
50
60
Bondingtime t. min
of the pressure is to increase the bonding area and decrease the cavity at the joint owing to the local plastic deformation, and therefore obtain a high strength joint. However, the high precision of the bonded structure cannot be maintained if the plastic deformation is very large. The optimum pressure is 20MPa at T= 1323K and t=45min. Fig.3b shows the relationship between the shear strength of the joints and the diffusion bonding pressure.
3.3 Effect of the difision bonding time t on the shear strength of joint The determination of the diffusion b h d i n g time depends on the pressure and temperature. In case of diffusion bonding of IN7 18 superalloy, at a lower bonding temperature, the joint strength is lower owing to the reduction of the contact area between materials. Elemental diffusion of IN7 18 alloy can be improved by prolonging the holding time. However, the increase of bonding time cannot improve the strength of the joint because the contact area cannot be increased. At higher bonding temperatures, the contact area between materials increases, and in this case, the increase of bonding time has an opposite effect on the joint strength. Increasing the bonding time will cause a sufficient elemental diffusion, leading to the increase of the joint strength. F i g . 3 ~depicts the relationship between the shear strength and the bonding time. In this article, the optimum time is 60min at T= 1253K andp=20MPa.
3.4 Effect of interlayer on the shear strength of joint The difision bonding of IN7 18 superalloy used nickel foil for the interlayer has been studied in this paper. Ni is the most suitable material for the interlayer used in the diffbsion bonding of Ni based superalloys. The effect of interlayer on the shear strength of the joint was studied and the result is shown in Fig.4. The thickness of the nickel interlayer is 25pm. Thus, to obtain suitable properties of the joint, the nickel interlayer must be decided.
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310 .
Without interlayer
300
8 a
240
c-
r
5 b
180 120
I 60
n 1170
1200
1230
1260
1290
1320
Bonding temperature T, K
Fig.4 Effect of diffusion bonding with interlayer and without interlayer on the shear strength ofjoints.
4. Properties and M i m c t u r e of the Diffusion Bonding Parts Based on the above experimental results, the optimum parameters are: T = 1273 - 1323K, p = 20 30MPa, and f = 45 -60min. Fig.5 is a SEM (scanning electron microscope) image of the bonded joint, showing layer dimple type ductile fracture surface, which indicates good ductile bonding. Fig.6 is the microstructure of the bonding interfaces. The results indicate that no defect and intermetallic compound can be found in the joint. Fig.7 is an EPMA (electron probe microanalysis) micro-area line analysis element distribution curve of the bonded joint. It indicates that a certain amount of diffusion occurs b e h e e n the interlayer metal Ni
Fig5 SEM image of the bonded joint (T=1323K, p=lOMPa, t=30min).
Fig.6 Examples of microstructure of bonding interfaces.
. 311
.
Fig.7 EMPA micro-area line analysis element distribution curve of the bonded joint: (a) T= 1323K,p=IOMPa. r=ISmin; (b) T=1323K,p= IOMPa, 1=30min.
Fig.8 Rupture of the specimen.
and based alloy, and a mutual diffusion layer in which the composition changes gradually is formed near the interface. The width and quantity of the diffision area increase with the increase of the bonding time. The bonded parts fractured at based alloy with an average tensile strength of 1089MPa when the tensile test was carried out at room temperature, as shown in Fig.8.
6. Conclusions (1) IN718 superalloy exhibits satisfying superplasticity at an initial strain rate of l x I04s-' at 1253K. (2) IN7 18 superalloy can be joined by the diffusion bonding method and the optimum parameters are: T = 1273- i323K, t = 45-60rnin, and p = 20-30MPa. (3) The 25pm thickness of nickel foil used for the interlayer in the joint can increase the properties of the bonded specimens by mechanical test and microstructure study. (4) At room temperature, the fracture of the bonded specimens takes place in the based alloy parts.
312 REFERENCES 1 M.S. Yeh and T.H. Chuang, Welding Research 5 (1997) (Supp1.)197. 2 W.B. Han, D.Z. Wu, G.F. Wang, and M.J. Tong, Materials Science Forum 551-552 (2007) 163. 3 R.G. Liu, H.M. Jiang, and Y. Jiang, J. Aerospace Materials & Technology 28(2) (1998) 36. 4 S.C. Medeiros, Y.V.R.K. Prasad, W.G. Frazier, and R. Snnivasan, MateriuLs Science and Engineering A 293 (2000) 198. 5 B.P.Kashyap and M.C.Chaturvedi, Scr. Mater. 43 (2000) 429. 6 O.A. Idowu, N.L. Richards, and M.C. Chaturvedi, Materials Science and Engineering A 397(25) (2005) 98. 7 F. Jalilian, M. Jahazi, and R.A.L. Drew, Materials Science ond Engineering A 423(15) (2006) 269. 8 L.I. Duarte, AS. Ramos, M.F. Vieira, F. Viana, M.T. Vieira, and M. KO&, Intermetdlics 14(10-11) (2006) 1 151 9 X.F. Wang, M. Ma, X.B. Liu, X.Q. Wu, C.G. Tan, R.K. Shi, and J.G. Lin, Transactions of Nonferrous Metals Society of China 1q5) (2006) 1059. 10 S. Kundu, M. Ghosh, and S. Chattejee, Materials Science and EngineeringA 428(1-2) (2006) 18. 11 H.J. Lu, X.C. Jia, K.F. Zhang, and C.G. Yao, Moterials Science and EngineeringA 326 (2002) 382.
.J'
--##
ScienceDirect
Acta Metall. Sin. (Engl. Lett.) Vol.20 No.4 pp307-312 Aug. 2007
ACTA METALLURGICA SINICA (ENGLISH LETTERS)
www.atns,org.cn
SUPERPLASTICITY AND DIFFUSION BONDING OF IN718 SUPERALLOY W.B. Han', K.F. Zhang, B. Wang, and D.Z. Wu School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China Manuscript received 8 June 2007
The superplasticity and dimion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at direrent temperatures and various initial strain rates using the tensile speed mutation method; m reached its maximum value 0.53 at an initial strain rate of 1 x 104s-' at 12.5311: The d i h i o n bonding parameters, including the bonding temperature T, pressure p. and time t, affected the mechanism of joints. When the bonded specimen with 2 5 thick nickelfoil interlayerwas tensile at room temperature, the shearfracture of thejoints with nickel foil interlayer took place at the IN718 part. Microstructure study was camed out with the bonded samples. The microstmcture shows an excellent bonding at the interfaces. The optimum parameters for the dimion bonding are: T = 1273-I323K, p = 20-30MPa, t = 45-Mlmin. KEY WORDS superphticity; di@ion bonding; nickel foil; IN718 alloy
1. Introduction IN7 18 is a nickel-base superalloy, and possesses an advantageous combination of properties. It is the most widely used superalloy and accounts for 35% of the total superalloy production. IN7 18 superalloy was mainly used to manufacture complex welding sheet components in the 1960s, and it was used to produce parts of turbine, which had service life of more than ten thousand Now, IN71 8 alloy is practically used in high effective turbines, such as turbine disk, axle, blade, guide blade, shell, etc. to satisfy the increasing demands for higher temperature environment['I. To fulfill the requirements of product applications, the superplasticity and diffusion bonding of IN7 18 have been investigated in detail.
2. Microstructure Features of IN718Superalloy 2.1 Material IN718 superalloy used in the tensile experiment was Imm thick sheet. The analyzed composition (wt%) of the alloy is given as folloows: C 0.067, S 0.005, P 0.008, Cr 19.26, Ni 53.67, Ti 1.13, Cu 0.072, 'Corresponding author. Tel.: +86 451 86403016; fax: +86 451 86402382. E-moil address: [email protected] ( W . B . Han)
~
.
308
Mg ~ 0 . 0 1 ,Mn 0.03, Si 0.08, Mo 3.26, Nb 5.38, Al 0.55, Co 0.05, B 0.008. The specimen used to evaluate the strain rate sensitivity m was heat treated in 1193K for 30minL21.
2.2 Microstructural features The first detailed characterization of superplasticity was presented by Hayden etal.E3]for alloys in the NiFe-Cr system. In the superplastic condition, superalloys are characterized by a fine grained (generally lOpm or less), two-phase microstructure. The microstructure of the IN718 alloy is shown in Fig.1. For this alloy, the second phase is essential in ordered face centered cubic y’. The presence of a second phase is essential so that the microstructure remains stable throughout hot deformation[’”].
Fig. 1 Microstructure of Inconel7 18 superalloy. 06 -A-3 -*-9
2X104 6M04
2.3 Superplasticity of Inconel718 superalloy Early references have appeared relating to the observation of superplasticity in nickel-base alloys at a 1220 1230 1240 1250 wide temperature range of 1213 to 1293K and a strain Temperature T, K rate range of 1O4 to 10”s-l L51. Fig.2 The relationshipbetween the strain rate sensiFig.2 shows the relation of the strain rate sensitivtivity m and temperature. ity m and the test temperature at various initial strain rates. The value of rn increases with the decrease of the strain rate and the rise of temperature and reaches its maximum value at an initial strain rate of 1x 104s-’ at 1253K.
3. Diffusion Bonding of Inconel718 Superalloy In case of diffusion bonding of Inconel7 18 alloy, 25pm thick nickel foil interlayer is adopted. The effects of the diffusion bonding parameters, such as temperature T, pressure p , and time t, were investigated.
3.1 Effect of the diffusion bonding temperature T on the shear strength of joint The temperature of diffusion bonding greatly affects the plastic deformation, creeping resistance, and the diffusion behavior of the joint. The diffusion bonding temperature is increased properly because of the high thermal resistance of Ni based superalloy. Based on the suitable combination of the parameters of pressure, temperature, and time, the diffusion bonding temperature must be in the range of 1273- 1323K. Fig.3a shows the relationship between the shear strength of the joints and the temperature in this temperature range. It can be seen that the strength of the joints increases with the increasing bonding temperature.
3.2 Effect of the difision bonding pressure p on the tensile strength of the joint The diffusion bonding pressure is important to control the properties of the joint. The main function
309 .
320
-
300
-
280
-
h h-
S
4L
1260 -
6
240 1201 I 1170
1200
1230
1260
1290
-
I
1320
10
Bonding temperature T, K
15
20
25
30
Bonding pressure p, MPa
Fig.3 Relationship between the shear strength ofjoint and the diffusion bonding parameters: (a) shear strength-bondingtemperature curve; (b) shear strength-bonding pressure curve; (c) shear strength-bonding time curve. I 10
I 20
30
40
50
60
Bondingtime t. min
of the pressure is to increase the bonding area and decrease the cavity at the joint owing to the local plastic deformation, and therefore obtain a high strength joint. However, the high precision of the bonded structure cannot be maintained if the plastic deformation is very large. The optimum pressure is 20MPa at T= 1323K and t=45min. Fig.3b shows the relationship between the shear strength of the joints and the diffusion bonding pressure.
3.3 Effect of the difision bonding time t on the shear strength of joint The determination of the diffusion b h d i n g time depends on the pressure and temperature. In case of diffusion bonding of IN7 18 superalloy, at a lower bonding temperature, the joint strength is lower owing to the reduction of the contact area between materials. Elemental diffusion of IN7 18 alloy can be improved by prolonging the holding time. However, the increase of bonding time cannot improve the strength of the joint because the contact area cannot be increased. At higher bonding temperatures, the contact area between materials increases, and in this case, the increase of bonding time has an opposite effect on the joint strength. Increasing the bonding time will cause a sufficient elemental diffusion, leading to the increase of the joint strength. F i g . 3 ~depicts the relationship between the shear strength and the bonding time. In this article, the optimum time is 60min at T= 1253K andp=20MPa.
3.4 Effect of interlayer on the shear strength of joint The difision bonding of IN7 18 superalloy used nickel foil for the interlayer has been studied in this paper. Ni is the most suitable material for the interlayer used in the diffbsion bonding of Ni based superalloys. The effect of interlayer on the shear strength of the joint was studied and the result is shown in Fig.4. The thickness of the nickel interlayer is 25pm. Thus, to obtain suitable properties of the joint, the nickel interlayer must be decided.
.
310 .
Without interlayer
300
8 a
240
c-
r
5 b
180 120
I 60
n 1170
1200
1230
1260
1290
1320
Bonding temperature T, K
Fig.4 Effect of diffusion bonding with interlayer and without interlayer on the shear strength ofjoints.
4. Properties and M i m c t u r e of the Diffusion Bonding Parts Based on the above experimental results, the optimum parameters are: T = 1273 - 1323K, p = 20 30MPa, and f = 45 -60min. Fig.5 is a SEM (scanning electron microscope) image of the bonded joint, showing layer dimple type ductile fracture surface, which indicates good ductile bonding. Fig.6 is the microstructure of the bonding interfaces. The results indicate that no defect and intermetallic compound can be found in the joint. Fig.7 is an EPMA (electron probe microanalysis) micro-area line analysis element distribution curve of the bonded joint. It indicates that a certain amount of diffusion occurs b e h e e n the interlayer metal Ni
Fig5 SEM image of the bonded joint (T=1323K, p=lOMPa, t=30min).
Fig.6 Examples of microstructure of bonding interfaces.
. 311
.
Fig.7 EMPA micro-area line analysis element distribution curve of the bonded joint: (a) T= 1323K,p=IOMPa. r=ISmin; (b) T=1323K,p= IOMPa, 1=30min.
Fig.8 Rupture of the specimen.
and based alloy, and a mutual diffusion layer in which the composition changes gradually is formed near the interface. The width and quantity of the diffision area increase with the increase of the bonding time. The bonded parts fractured at based alloy with an average tensile strength of 1089MPa when the tensile test was carried out at room temperature, as shown in Fig.8.
6. Conclusions (1) IN718 superalloy exhibits satisfying superplasticity at an initial strain rate of l x I04s-' at 1253K. (2) IN7 18 superalloy can be joined by the diffusion bonding method and the optimum parameters are: T = 1273- i323K, t = 45-60rnin, and p = 20-30MPa. (3) The 25pm thickness of nickel foil used for the interlayer in the joint can increase the properties of the bonded specimens by mechanical test and microstructure study. (4) At room temperature, the fracture of the bonded specimens takes place in the based alloy parts.
312 REFERENCES 1 M.S. Yeh and T.H. Chuang, Welding Research 5 (1997) (Supp1.)197. 2 W.B. Han, D.Z. Wu, G.F. Wang, and M.J. Tong, Materials Science Forum 551-552 (2007) 163. 3 R.G. Liu, H.M. Jiang, and Y. Jiang, J. Aerospace Materials & Technology 28(2) (1998) 36. 4 S.C. Medeiros, Y.V.R.K. Prasad, W.G. Frazier, and R. Snnivasan, MateriuLs Science and Engineering A 293 (2000) 198. 5 B.P.Kashyap and M.C.Chaturvedi, Scr. Mater. 43 (2000) 429. 6 O.A. Idowu, N.L. Richards, and M.C. Chaturvedi, Materials Science and Engineering A 397(25) (2005) 98. 7 F. Jalilian, M. Jahazi, and R.A.L. Drew, Materials Science ond Engineering A 423(15) (2006) 269. 8 L.I. Duarte, AS. Ramos, M.F. Vieira, F. Viana, M.T. Vieira, and M. KO&, Intermetdlics 14(10-11) (2006) 1 151 9 X.F. Wang, M. Ma, X.B. Liu, X.Q. Wu, C.G. Tan, R.K. Shi, and J.G. Lin, Transactions of Nonferrous Metals Society of China 1q5) (2006) 1059. 10 S. Kundu, M. Ghosh, and S. Chattejee, Materials Science and EngineeringA 428(1-2) (2006) 18. 11 H.J. Lu, X.C. Jia, K.F. Zhang, and C.G. Yao, Moterials Science and EngineeringA 326 (2002) 382.