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Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment D. Praveen Kumar ⇑, S. Kumaran Department of Metallurgical and Materials Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu 620015, India
a r t i c l e
i n f o
Article history: Received 17 October 2019 Accepted 23 October 2019 Available online xxxx Keywords: Inconel 718 Spark plasma sintering Diffusion bonding Double aging Corrosion behaviour
a b s t r a c t Spark plasma assisted resistant heating process is an emerging technique for joining materials in a short duration. In this paper, diffusion bonding of Inconel 718 alloy was carried out by spark plasma sintering (SPS) at a temperature of 850 °C (Heating rate of 50 °C/min) with the pressure of 50 MPa and holding time of 5 min. The diffusion bonded samples were solutionized and double aged. Microstructural analysis of bonded samples was analyzed through an optical microscope. The mechanical tests such as hardness and tensile tests were carried out to understand the strength of the diffusion bonded samples at various conditions. The corrosion behavior of samples was studied and analzysed. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction Inconel 718 is a Ni-Cr-Fe based superalloy. This alloy is generally strengthened by solid solution strengthening and precipitate hardening mechanism to withstand the working temperature of 650 °C. Phases like c00 -(Ni3 (NbAlTi)), c0 -(Ni3 (AlTiNb)), d (Ni3Nb) and Nb rich M23 C6 are present in double aged condition [1]. Inconel 718 has high fatigue, creep, oxidation and corrosion resistance. Formation of laves phases in fusion welding leads to the initiation of strain cracking during post-weld heat treatment, solidification cracking and liquation cracking [2]. Diffusion bonding of materials using spark plasma sintering (SPS) is an emerging technique [3,4]; breaking of the surface oxide layer on the diffusion zone is done within a fraction of seconds in SPS heating process. The very short duration of holding time makes the SPS diffusion bonding more effective in time consumption while compared to conventional diffusion bonding. Usage of low voltage DC pulse current with faster heating and cooling rate are some of the advantages in SPS heating technique. The alloy 718 has been strengthened by precipitates like c00 and c0 , which have been formed at the double aging heat treatment condition [5]. In this study, the SPS diffusion bonded samples were tested before and after the double aging, the tests like hardness,
⇑ Corresponding author. E-mail address: [email protected] (D. Praveen Kumar).
tensile test and corrosion were done in order to correlate the structure and properties. 2. Materials and methods The chemical compositions of Inconel 718 is shown in Table 1. The Inconel alloy718 was received at solutionized (980 °C) and precipitation hardened condition. Two samples of diameter 20 mm and height of 10 mm were polished to mirror finish, attaining a surface roughness of 0.08 (Mitutoyosurftesr SJ-210) and cleaned in acetone using an ultrasonic bath for 5 min. SPS machine (SPS SYNTEX INC, DR.SINTER LAB Model: SPS-515S, Japan) was used for diffusion bonding at a vacuum atmosphere of 10-2torr. SPS diffusion bonded samples have been defined in Fig. 1 (a). Fig. 1 (b) represents the double aging heat treatment curve of the diffusion bonded sample of diameter and height of 20 mm respectively. In this system, the solutionizing temperature was maintained at 1010 °C for 1 h 30 min and double aging heat treatment process was maintained at 720 °C and 620 °C (ASM standardsAMS 5664). Optical microscopy (Olympus BX53) was used to study the microstructure. Hardness variations were analyzed through Vickers Microhardness (M/s Wilson hardness Machine 402 MVD with ASTM E92-16). The bonding strength was examined through the universal testing machine (Dak system inc, model: T-72302) at a strain rate of 10-3s-1according to ASTM E8-04 standards. Electro-chemical linear polarization and Impedance (Biologic instruments- SP 150, France) studies was performed in 3.5% NaCl solution under ASTM G102-89 standards [6].
https://doi.org/10.1016/j.matpr.2019.10.163 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: D. Praveen Kumar and S. Kumaran, Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.163
2
D. Praveen Kumar, S. Kumaran / Materials Today: Proceedings xxx (xxxx) xxx
Table 1 Chemical compositions of the as-received Inconel 718. Material
Cr
Fe
Mn
Nb
Al
Mo
Ti
C
Si
Ni
Inconel-718
18.2
19.5
0.1
5.2
0.6
2.8
1
0.05
0.1
Bal
Fig. 1. (a) SPS diffusion bonded sample with the graphite die and plungers, (b) Solutionizing and Double aging treatment of Inconel 718.
Fig. 2. The optical microstructure of Inconel718 (a) as-received condition, (b) SPS diffusion bonded zone at 850 °C, (c) The microstructure of Inconel 718 after bonding, (d) SPS diffusion bonded zone after double aging, (e) Microstructure after double aging.
Please cite this article as: D. Praveen Kumar and S. Kumaran, Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.163
3
D. Praveen Kumar, S. Kumaran / Materials Today: Proceedings xxx (xxxx) xxx
3. Results and discussion
3.2. Mechanical properties of diffusion bonded alloy
3.1. Microstructural studies
3.2.1. Hardness Fig. 3 (a) shows the hardness of the alloy. The as-received sample gives the average hardness of 541 Hv. The hardness of diffusion bonded sample is 268 Hv. They were heat treated to double aging condition and its average hardness rises back to 502 Hv
Fig. 2 (a) shows the microstructure of solutionized and Inconel 718 alloy. The microstructure shows fine austenitic equiaxed grains with annealing twins having an average grain size of 9 mm. Fig. 2 (b), and (c) represent the microstructure of diffusion bonded samples at 850 °C with the average grain size of 17 mm. Fig. 2 (d) and (e) show the double aged heat treated samples average grain size is 42 mm.
3.2.2. Bonding strength The bonding strength of the diffusion bonded samples was tested through the universal testing machine. The failure occurs
Fig. 3. (a) Vickers Microhardness of Inconel 718 at different conditions, (b) Engineering stress strain curve for the SPS diffusion bonded samples.
Fig. 4. (a) Electro-Chemical Polarisation curve and (b) Impedance curves for the as-received, diffusion bonded and double age-hardened samples.
Table 2 Data derived from tafel plot. S.NO
Condition
Ecorr (V)
icorr (mA/cm2)
Corrosion rate (mm/yr)e3
1 2 3
As-received Bonded at 850 °C Bonded and double aged
0.33 0.311 0.172
0.188 0.123 0.089
2.71 1.77 1.29
Please cite this article as: D. Praveen Kumar and S. Kumaran, Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.163
4
D. Praveen Kumar, S. Kumaran / Materials Today: Proceedings xxx (xxxx) xxx
age-hardened sample shows higher value compared to the other two conditions. An increase in the grain size is the reason for higher corrosion resistance in the double age-hardened sample when comparing the other two samples in the system. Fig. 5 clearly shows that there is an increase in the grain size from as received to double aged condition and a reduction in corrosion rate. In Inconel 718, grain boundaries are highly corrosive when compared to the main matrix, because of the presence of M23C6 rich phase in the grain boundaries makes it highly corrosive in nature. 4. Conclusions
Fig. 5. Bar chart comparing average grain size to corrosion rate of three different systems.
at the bonded zone for all the samples and it is a brittle fracture. The engineering stress–strain curve for the SPS bonded samples and double age-hardened bonded samples are shown in Fig. 3 (b). The SPS diffusion bonded sample shows an ultimate tensile strength of 583 MPa and a strain rate of 2.5%. After double aging heat treatment process, UTS is reduced to 493 with increasing elongation of 4.20%. due to partially stress relieved during heat treatment process, which leads to the reduction in ultimate tensile strength and increase in the elongation of the bonded zone. There is no variation in the yield strength for both the conditions, the SPS bonded sample attain a strength of 454 MPa and followed by agehardened sample shows the yield strength of same 454 MPa. There is no variation in the bonded strength of the material after the heat treatment. 3.3. Corrosion behavior Fig. 4(a) shows the electro-chemical polarization curves for the samples at three different conditions. Table 2 shows the data derived from Tafel plot. There is a shift in Ecorr values moving towards the positive side in both bonded (0.311) and age hardened (0.172) samples when compared to as-received one (0.33). Fig. 4 (b) shows the impedance curves at three different conditions, higher charge transfer resistance is visible at the double aged sample when compared to bonded and as-received samples. Warburg impedance also proves the same that the double
There is an increase in grain size during SPS bonding due to the reduction in interfacial energy at high temperature. The metastable phases are dissolved during diffusion bonding which leads to dropping in hardness. There is no improvement in the bonding strength after the heat treatment process. The secondary phases like d-phase at the grain boundaries may result in the discontinuous and inhomogenous passive film that leads to higher corrosion.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] A.S.M. International, A. Rights, ASM specialty handbook: nickel, cobalt, and their alloys, 2013. doi:10.5860/choice.38-6206. [2] J.T. Tharappel, J. Babu, Welding processes for Inconel 718 – a brief review, IOP Conf. Ser. Mater. Sci. Eng. 330 (2018), https://doi.org/10.1088/1757-899X/330/ 1/012082. [3] P. Pripanapong, Bonding mechanism of Ti / AZ80 dissimilar materials fabricated by spark plasma sintering, 2 (2016) 1009–1013. [4] K. Zhao, Y. Liu, L. Huang, B. Liu, Y. He, Diffusion bonding of Ti-45Al-7Nb-0 . 3W alloy by spark plasma sintering, J. Mater. Process. Technol. 230 (2016) 272–279. [5] X. Li, J.J. Shi, G.H. Cao, A.M. Russell, Z.J. Zhou, C.P. Li, G.F. Chen, Improved plasticity of Inconel 718 superalloy fabricated by selective laser melting through a novel heat treatment process, Mater. Des. 180 (2019), https://doi. org/10.1016/j.matdes.2019.107915 107915. [6] N. Anbarasan, S. Jerome, N. Arivazhagan, Argon and argon-hydrogen shielding gas effects on the laves phase formation and corrosion behavior of Inconel 718 gas tungsten arc welds, J. Mater. Process. Technol. 263 (2019) 374–384, https:// doi.org/10.1016/j.jmatprotec.2018.07.038.
Please cite this article as: D. Praveen Kumar and S. Kumaran, Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.163
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment D. Praveen Kumar ⇑, S. Kumaran Department of Metallurgical and Materials Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu 620015, India
a r t i c l e
i n f o
Article history: Received 17 October 2019 Accepted 23 October 2019 Available online xxxx Keywords: Inconel 718 Spark plasma sintering Diffusion bonding Double aging Corrosion behaviour
a b s t r a c t Spark plasma assisted resistant heating process is an emerging technique for joining materials in a short duration. In this paper, diffusion bonding of Inconel 718 alloy was carried out by spark plasma sintering (SPS) at a temperature of 850 °C (Heating rate of 50 °C/min) with the pressure of 50 MPa and holding time of 5 min. The diffusion bonded samples were solutionized and double aged. Microstructural analysis of bonded samples was analyzed through an optical microscope. The mechanical tests such as hardness and tensile tests were carried out to understand the strength of the diffusion bonded samples at various conditions. The corrosion behavior of samples was studied and analzysed. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction Inconel 718 is a Ni-Cr-Fe based superalloy. This alloy is generally strengthened by solid solution strengthening and precipitate hardening mechanism to withstand the working temperature of 650 °C. Phases like c00 -(Ni3 (NbAlTi)), c0 -(Ni3 (AlTiNb)), d (Ni3Nb) and Nb rich M23 C6 are present in double aged condition [1]. Inconel 718 has high fatigue, creep, oxidation and corrosion resistance. Formation of laves phases in fusion welding leads to the initiation of strain cracking during post-weld heat treatment, solidification cracking and liquation cracking [2]. Diffusion bonding of materials using spark plasma sintering (SPS) is an emerging technique [3,4]; breaking of the surface oxide layer on the diffusion zone is done within a fraction of seconds in SPS heating process. The very short duration of holding time makes the SPS diffusion bonding more effective in time consumption while compared to conventional diffusion bonding. Usage of low voltage DC pulse current with faster heating and cooling rate are some of the advantages in SPS heating technique. The alloy 718 has been strengthened by precipitates like c00 and c0 , which have been formed at the double aging heat treatment condition [5]. In this study, the SPS diffusion bonded samples were tested before and after the double aging, the tests like hardness,
⇑ Corresponding author. E-mail address: [email protected] (D. Praveen Kumar).
tensile test and corrosion were done in order to correlate the structure and properties. 2. Materials and methods The chemical compositions of Inconel 718 is shown in Table 1. The Inconel alloy718 was received at solutionized (980 °C) and precipitation hardened condition. Two samples of diameter 20 mm and height of 10 mm were polished to mirror finish, attaining a surface roughness of 0.08 (Mitutoyosurftesr SJ-210) and cleaned in acetone using an ultrasonic bath for 5 min. SPS machine (SPS SYNTEX INC, DR.SINTER LAB Model: SPS-515S, Japan) was used for diffusion bonding at a vacuum atmosphere of 10-2torr. SPS diffusion bonded samples have been defined in Fig. 1 (a). Fig. 1 (b) represents the double aging heat treatment curve of the diffusion bonded sample of diameter and height of 20 mm respectively. In this system, the solutionizing temperature was maintained at 1010 °C for 1 h 30 min and double aging heat treatment process was maintained at 720 °C and 620 °C (ASM standardsAMS 5664). Optical microscopy (Olympus BX53) was used to study the microstructure. Hardness variations were analyzed through Vickers Microhardness (M/s Wilson hardness Machine 402 MVD with ASTM E92-16). The bonding strength was examined through the universal testing machine (Dak system inc, model: T-72302) at a strain rate of 10-3s-1according to ASTM E8-04 standards. Electro-chemical linear polarization and Impedance (Biologic instruments- SP 150, France) studies was performed in 3.5% NaCl solution under ASTM G102-89 standards [6].
https://doi.org/10.1016/j.matpr.2019.10.163 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: D. Praveen Kumar and S. Kumaran, Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.163
2
D. Praveen Kumar, S. Kumaran / Materials Today: Proceedings xxx (xxxx) xxx
Table 1 Chemical compositions of the as-received Inconel 718. Material
Cr
Fe
Mn
Nb
Al
Mo
Ti
C
Si
Ni
Inconel-718
18.2
19.5
0.1
5.2
0.6
2.8
1
0.05
0.1
Bal
Fig. 1. (a) SPS diffusion bonded sample with the graphite die and plungers, (b) Solutionizing and Double aging treatment of Inconel 718.
Fig. 2. The optical microstructure of Inconel718 (a) as-received condition, (b) SPS diffusion bonded zone at 850 °C, (c) The microstructure of Inconel 718 after bonding, (d) SPS diffusion bonded zone after double aging, (e) Microstructure after double aging.
Please cite this article as: D. Praveen Kumar and S. Kumaran, Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.163
3
D. Praveen Kumar, S. Kumaran / Materials Today: Proceedings xxx (xxxx) xxx
3. Results and discussion
3.2. Mechanical properties of diffusion bonded alloy
3.1. Microstructural studies
3.2.1. Hardness Fig. 3 (a) shows the hardness of the alloy. The as-received sample gives the average hardness of 541 Hv. The hardness of diffusion bonded sample is 268 Hv. They were heat treated to double aging condition and its average hardness rises back to 502 Hv
Fig. 2 (a) shows the microstructure of solutionized and Inconel 718 alloy. The microstructure shows fine austenitic equiaxed grains with annealing twins having an average grain size of 9 mm. Fig. 2 (b), and (c) represent the microstructure of diffusion bonded samples at 850 °C with the average grain size of 17 mm. Fig. 2 (d) and (e) show the double aged heat treated samples average grain size is 42 mm.
3.2.2. Bonding strength The bonding strength of the diffusion bonded samples was tested through the universal testing machine. The failure occurs
Fig. 3. (a) Vickers Microhardness of Inconel 718 at different conditions, (b) Engineering stress strain curve for the SPS diffusion bonded samples.
Fig. 4. (a) Electro-Chemical Polarisation curve and (b) Impedance curves for the as-received, diffusion bonded and double age-hardened samples.
Table 2 Data derived from tafel plot. S.NO
Condition
Ecorr (V)
icorr (mA/cm2)
Corrosion rate (mm/yr)e3
1 2 3
As-received Bonded at 850 °C Bonded and double aged
0.33 0.311 0.172
0.188 0.123 0.089
2.71 1.77 1.29
Please cite this article as: D. Praveen Kumar and S. Kumaran, Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.163
4
D. Praveen Kumar, S. Kumaran / Materials Today: Proceedings xxx (xxxx) xxx
age-hardened sample shows higher value compared to the other two conditions. An increase in the grain size is the reason for higher corrosion resistance in the double age-hardened sample when comparing the other two samples in the system. Fig. 5 clearly shows that there is an increase in the grain size from as received to double aged condition and a reduction in corrosion rate. In Inconel 718, grain boundaries are highly corrosive when compared to the main matrix, because of the presence of M23C6 rich phase in the grain boundaries makes it highly corrosive in nature. 4. Conclusions
Fig. 5. Bar chart comparing average grain size to corrosion rate of three different systems.
at the bonded zone for all the samples and it is a brittle fracture. The engineering stress–strain curve for the SPS bonded samples and double age-hardened bonded samples are shown in Fig. 3 (b). The SPS diffusion bonded sample shows an ultimate tensile strength of 583 MPa and a strain rate of 2.5%. After double aging heat treatment process, UTS is reduced to 493 with increasing elongation of 4.20%. due to partially stress relieved during heat treatment process, which leads to the reduction in ultimate tensile strength and increase in the elongation of the bonded zone. There is no variation in the yield strength for both the conditions, the SPS bonded sample attain a strength of 454 MPa and followed by agehardened sample shows the yield strength of same 454 MPa. There is no variation in the bonded strength of the material after the heat treatment. 3.3. Corrosion behavior Fig. 4(a) shows the electro-chemical polarization curves for the samples at three different conditions. Table 2 shows the data derived from Tafel plot. There is a shift in Ecorr values moving towards the positive side in both bonded (0.311) and age hardened (0.172) samples when compared to as-received one (0.33). Fig. 4 (b) shows the impedance curves at three different conditions, higher charge transfer resistance is visible at the double aged sample when compared to bonded and as-received samples. Warburg impedance also proves the same that the double
There is an increase in grain size during SPS bonding due to the reduction in interfacial energy at high temperature. The metastable phases are dissolved during diffusion bonding which leads to dropping in hardness. There is no improvement in the bonding strength after the heat treatment process. The secondary phases like d-phase at the grain boundaries may result in the discontinuous and inhomogenous passive film that leads to higher corrosion.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] A.S.M. International, A. Rights, ASM specialty handbook: nickel, cobalt, and their alloys, 2013. doi:10.5860/choice.38-6206. [2] J.T. Tharappel, J. Babu, Welding processes for Inconel 718 – a brief review, IOP Conf. Ser. Mater. Sci. Eng. 330 (2018), https://doi.org/10.1088/1757-899X/330/ 1/012082. [3] P. Pripanapong, Bonding mechanism of Ti / AZ80 dissimilar materials fabricated by spark plasma sintering, 2 (2016) 1009–1013. [4] K. Zhao, Y. Liu, L. Huang, B. Liu, Y. He, Diffusion bonding of Ti-45Al-7Nb-0 . 3W alloy by spark plasma sintering, J. Mater. Process. Technol. 230 (2016) 272–279. [5] X. Li, J.J. Shi, G.H. Cao, A.M. Russell, Z.J. Zhou, C.P. Li, G.F. Chen, Improved plasticity of Inconel 718 superalloy fabricated by selective laser melting through a novel heat treatment process, Mater. Des. 180 (2019), https://doi. org/10.1016/j.matdes.2019.107915 107915. [6] N. Anbarasan, S. Jerome, N. Arivazhagan, Argon and argon-hydrogen shielding gas effects on the laves phase formation and corrosion behavior of Inconel 718 gas tungsten arc welds, J. Mater. Process. Technol. 263 (2019) 374–384, https:// doi.org/10.1016/j.jmatprotec.2018.07.038.
Please cite this article as: D. Praveen Kumar and S. Kumaran, Mechanical and corrosion behaviour of Inconel 718 processed through SPS diffusion bonding and double aging treatment, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.10.163