- Email: [email protected]
NiCr laminated composite to Ti-6Al-4V joint without interlayer
Vacuum 143 (2017) 195e198
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Short communication
Effect of bonding time on interfacial microstructure and shear strength of vacuum diffusion bonding super-Ni/NiCr laminated composite to Ti-6Al-4V joint without interlayer Kun Liu a, Yajiang Li a, *, Chunzhi Xia b, Juan Wang a a b
Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, China Provincial Key Laboratory of Advanced Welding Technology, Jiangsu University of Science and Technology, Zhenjiang 212003, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 May 2017 Received in revised form 8 June 2017 Accepted 15 June 2017 Available online 16 June 2017
Super-Ni/NiCr laminated composite was successfully joined with Ti-6Al-4V by vacuum diffusion bonding at 950 C temperature. Results show that the bonding interface was composed of sequentially Ni3Ti, NiTi and NiTi2 layers. The interfacial phase constituents were similar although the joints were obtained with different bonding time. But the bonding time had a significant effect on the interfacial microstructure when the bonding time was prolonged from 30 min to 90 min. The morphology of NiTi2 layer transformed from serrate to straight and eutectoid products (Ni3Ti and NiTi2) were formed in NiTi layer whose width increased significantly. The maximum shear strength of joint is 69.2 MPa obtained at 60 min. Most joints fractured at the super-Ni/Ni3Ti interface. The shear strength of joint is mainly attributed to the plastic deformation and shifting of super-Ni crystals. © 2017 Published by Elsevier Ltd.
Keywords: Diffusion bonding Laminated composite Microstructure Shear strength
1. Introduction Ni-base superalloys have promoted the development of jet turbine engines due to its superior mechanical properties at high temperature and good corrosion resistance [1e3]. Super-Ni/NiCr laminated composite as a promising new structural material is composed of super-Ni cover layers and Ni80Cr20 sintered alloy base layer, which can be applied for a variety of high-temperature burner environment, especially, in the field of aerospace [4]. In order to combine perfect properties of different materials, it is essential to bond laminated composite with other alloys including Ti-6Al-4V as one of the most popular aero materials. Xia et al. [5] pointed out a serious problem that super-Ni cover layer was easy to separate from Ni80Cr20 base layer during heated by a welding arc. The separation would deteriorate the laminated structure. Wu et al. [6] reported that the brittle Ni-P phase in the center of brazed zone was detrimental to the property of joint when brazing superNi/NiCr laminated composite to stainless steel using NiCrP filler metal. Therefore, fusion welding and brazing with filler metal introducing other elements could both weaken the bonding of laminated composite with other metals.
* Corresponding author. E-mail address: [email protected] (Y. Li). http://dx.doi.org/10.1016/j.vacuum.2017.06.025 0042-207X/© 2017 Published by Elsevier Ltd.
Diffusion bonding as an advanced joining process has been applied in joining dissimilar metals [7]. Both residual stress induced by shrink effect during solidification process and impurity elements from interlayer can be ignored when adopting diffusion bonding without interlayer to join super-Ni/NiCr laminated composite with Ti-6Al-4V. Much work has been made on diffusion bonding Ti-6Al4V alloy with other metals including stainless steel, aluminum alloy and intermetallic compounds [8e10]. However, the investigation on the effect of bonding time on interfacial diffusion and microstructure has rarely reported. In current work, diffusion bonding was used to join laminated composite with Ti-6Al-4V and effect of bonding time on interfacial microstructure and properties of joints was studied.
2. Experimental procedure Super-Ni/NiCr laminated composite with a sandwich structure composed of two super-Ni cover layers (Ni%>99.5% and thickness of 0.3 mm per layer) and Ni80Cr20 base layer (thickness of 2 mm) and Ti-6Al-4V (thickness of 6 mm) with nominal composition of 6 wt.% Al, 4 wt.% V and balanced Ti were used as base materials in this study. The sandwich structure of laminated composite and joint configuration are shown in Fig. 1. Prior to bonding, the mating surfaces of base materials were prepared by conventional grinding
196
K. Liu et al. / Vacuum 143 (2017) 195e198
Fig. 1. Structure of laminated composite and joint configuration: (a) sandwich structure of laminated composite, (b) configuration of vacuum diffusion bonding without interlayer, (c) schematic diagram of shear test experiment.
technique and polishing down to 1000 grid SiC paper and then were cleaned with ethanol. Vacuum diffusion bonding trials were carries out in Workhorse-Ⅱ bonding installation providing a vacuum condition of 106 Pa and a series of controlled thermal parameters of bonding temperature 950 C, compressive force 5 MPa and bonding time in a series of 30 min, 60 min and 90 min. The effect of bonding time on the interfacial microstructure and properties of joint was investigated by means of metallography, HITACHI SU-70 field-emission scanning electron microscopy (FESEM) and
energy dispersive spectrum (EDS). The shear strength of joints was measured using SANS CMT5205 testing machine at a loading rate of 0.5 mm/min, as illustrated in Fig. 1c. 3. Results and discussion Interfacial microstructure of super-Ni/Ti-6Al-4V joints produced at 950 C for different bonding time was shown in Fig. 2. An obvious bonding interface between super-Ni and Ti-6Al-4V was formed. It is
Fig. 2. Effect of bonding time on interfacial microstructure: (a) 30 min, (b) 60 min, (c) 90 min, (d) scanning line analysis of interface with bonding time of 60 min, (e) the effect of bonding time on with of interfacial layers.
K. Liu et al. / Vacuum 143 (2017) 195e198
known that the interface obtained by directly diffusion bonding is different from that archived by transient liquid bonding (TLP) [11]. The formation of interface in current study was mainly attributed to the mutual diffusion of elements in base materials and interfacial reaction at elevated temperature with a press. Fig. 2a indicates that the interface at 30 min is not straight. The interface was divided into three layers marked A, B and C. Based on the Ni-Ti binary phase diagram, three Ni-Ti intermetallic compounds (IMCs) are likely to form. In order to identify the phase constituents of reaction layers, EDS was carried out to reveal the composition of interface. Results of EDS spot analysis listed in Table 1 show that A, B and C layer are composed of Ni3Ti, NiTi and NiTi2, respectively. NiTi layer is much wider than other two layers. Ni3Ti layer is not continuous and there are voids between super-Ni and Ni3Ti layer in the case of 30 min, which is attributed to the short bonding time resulting in the inefficient diffusion. It can be also observed that the morphology of NiTi2 layer is serrated. With prolonging the bonding time to 60 min and 90 min, the serrate of NiTi2 layer disappeared and the morphology was transformed to straight. Some eutectoid products (Ni3Ti and NiTi2) in dark fine stripe morphology can be observed in NiTi layer near NiTi2. The eutectoid reaction can be expressed as NiTi / Ni3Ti þ NiTi2. In the case of 60 min, although there are little voids between super-Ni and Ni3Ti layer, the morphology of Ni3Ti is continuous as shown in Fig. 2b. When bonding time increasing to 90 min, discontinuous fracture between super-Ni and Ni3Ti layer can be found, which was caused by large stress of thin super-Ni at the elevated temperature with so long time. It is worth mentioning that the width of NiTi layer increased significantly with prolonging the bonding time while the width of other layers (Ni3Ti and NiTi2) did not change obviously, as shown in Fig. 2e. It can be inferred that the growth of NiTi layer resulted in the widening of interface. According to the element distribution as shown in Fig. 2d, the high concentration of Ni and Ti element in NiTi layer indicates that the diffusion of base materials could provide sufficient atoms (Ni and Ti) for the growth of NiTi layer. In addition, the growth of Ni3Ti layer was controlled by the diffusion of Ti atom moving across NiTi2 layer and NiTi layer successively while the
Table 1 Results of EDS spot analysis in interface with bonding time of 30 min. Point
A B C
Element (at. %)
197
growth of NiTi2 layer was dominated by the diffusion of Ni atom moving across Ni3Ti layer and NiTi layer in sequence. Due to the limit of diffusion distance, it is difficult for Ni3Ti and NiTi2 to grow greatly. To explore the effect of bonding time on the shear strength of joints produced at 950 C, the relationship between the shear strength and the bonding time is illustrated in Fig. 3. During shear test, most samples fractured at the interface between super-Ni and Ni3Ti layer, which indicated the weakest zone of joint was located at the super-Ni/Ni3Ti interfaces. Considering the different coefficients of linear expansion between thin super-Ni and Ni3Ti IMCs, it was easy for residual stress to remain in the thin super-Ni (only 0.3 mm thickness) after cooling from high temperature so voids and cracks were likely to form. From the load-displace curve shown in Fig. 3a, it can be seen that the plastic deformation was improved by increasing the bonding time and some drapes can be observed on the fracture surface of super-Ni. Fig. 3b shows a trend of shear strength from rising to drop with prolonging bonding time. The maximum value of shear strength obtained at bonding time of 60 min is 69.2 MPa compared with 45.4 MPa and 47.4 MPa in the case of 30 min and 90 min, respectively. In order to further reveal the fracture mechanism of joints, SEM and EDS were carried out to characterize the morphology and to measure composition of fracture surfaces. Fig. 4 shows the fracture morphology of interface. Two different fracture morphologies including dark bulk zone and white dense dimples can be observed from Fig. 4a. The dark bulk zone with a large size is composed of Ni3Ti IMCs, presenting a brittle fracture mode. Some voids near super-Ni/Ni3Ti interface acted as crack initiation sites. It was easy for facture to occur when crack extended to the brittle Ni3Ti IMCs with the increase of stress. It should be noted that the white dense fine dimples play a role of suppressing the cracks. Fig. 4b shows the fine microstructure of dense dimples. Some raptured polylateral crystals with the size of about 3 mm expose smooth and flat crystal planes which indicate the brittle and ductile mixed fracture mode. EDS analysis of feature point implies the polylateral crystal is superNi as shown in Fig. 4c. Large crystal spacing and plastic deformation zone can be observed on other crystal planes of super-Ni where there is more resistance to cracks under shear load. Therefore, the shear strength of joint is mainly attributed to the plastic deformation and shifting of super-Ni crystals.
Phase
Ti
Ni
26.95 53.32 67.80
73.05 46.68 32.20
4. Conclusions Ni3Ti NiTi NiTi2
Super-Ni/NiCr laminated composite and Ti-6Al-4V were bonded by vacuum diffusion without interlayer at 950 C temperature for
Fig. 3. Effect of bonding time on shear strength of joints: (a) load-displace curve, (b) shear strength of joints.
198
K. Liu et al. / Vacuum 143 (2017) 195e198
Fig. 4. Fracture of joints: (a) fracture surface, (b) polylateral crystals, (c) EDS results.
various bonding time. The interface was composed of sequentially Ni3Ti, NiTi and NiTi2 layers. As the bonding time increased, the morphology of NiTi2 layer transformed from serrate to straight and eutectoid products (Ni3Ti þ NiTi2) were formed in NiTi layer whose width increased significantly. Shear strength of joints presented a trend from rising to drop and plastic deformation was improved by prolonging the bonding time. The maximum value of shear strength is 69.2 MPa obtained at bonding time of 60 min. Most joints fractured at the super-Ni/Ni3Ti interface. Acknowledgements This project was supported by National Natural Science Foundation of China (grant number 51575316) and the Natural Science Foundation of Shandong Province, China (grant number ZR2015EM040). References [1] J.H. Perepezko, The hotter the engine, the better, Science 326 (5956) (2009) 1068e1069. [2] L. Lan, W.D. Xuan, J. Wang, C.J. Li, Z.M. Ren, J.B. Yu, J.C. Peng, Interfacial microstructure of partial transient liquid phase bonding of Si3N4 to nickelbase superalloy using Ti/Au/Ni interlayers, Vacuum 130 (2016) 105e108.
[3] L. Jiang, S.Q. Guo, Y.Y. Bian, M. Zhang, W.Z. Ding, Interfacial behaviors of magnesia partially stabilized zirconia with nickel-based superalloy, Mat. Lett. 181 (2016) 313e316. [4] N. Wu, Y.J. Li, Q.S. Ma, Microstructure evolution and shear strength of vacuum brazed joint for super-Ni/NiCr laminated composite with Ni-Cr-Si-B amorphous interlayer, Mat. Des. 53 (2014) 816e821. [5] C.Z. Xia, Y.J. Li, U.A. Puchkov, J. Wang, Microstructural study of super Ni laminated composite/1Cr18Ni9Ti steel dissimilar welded joint, Mat. Sci. Tech. 26 (11) (2010) 1358e1362. [6] N. Wu, Y.J. Li, J. Wang, U.A. Puchkov, Vacuum brazing of super-Ni/NiCr laminated composite to Cr18-Ni8 steel with NiCrP filler metal, J. Mat. Process. Tech. 212 (4) (2012) 794e800. [7] S. Wang, Y.H. Ling, J.J. Wang, G.Y. Xu, Microstructure and mechanical properties of W/Cu vacuum diffusion bonding joints using amorphous FeeW alloy as interlayer, Vacuum 114 (2015) 58e65. [8] M.S. Kenevisi, S.M. Mousavi Khoie, A study on the effect of bonding time on the properties of Al7075 to Tie6Ale4V diffusion bonded joint, Mat. Lett. 76 (2012) 144e146. [9] S. Zakipour, M. Samavatian, A. Halvaee, A. Amadeh, A. Khodabandeh, The effect of interlayer thickness on liquid state diffusion bonding behavior of dissimilar stainless steel 316/Ti-6Al-4V system, Mat. Lett. 142 (2015) 168e171. [10] J.K. Liu, J. Cao, X.T. Lin, H.Y. Chen, J. Wang, J.C. Feng, Interfacial microstructure and joining properties of TiAl/Ti3AlC2 diffusion bonded joints using Zr and Ni foils as interlayer, Vacuum 102 (2014) 16e25. [11] X.J. Yuan, C.Y. Kang, Microstructural characteristics in vacuum TLP (Transient Liquid Phase) bonds using a novel iron-based interlayer based on duplex stainless steel base metal alloyed with a melting-point depressant, Vacuum 99 (2014) 12e16.
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Short communication
Effect of bonding time on interfacial microstructure and shear strength of vacuum diffusion bonding super-Ni/NiCr laminated composite to Ti-6Al-4V joint without interlayer Kun Liu a, Yajiang Li a, *, Chunzhi Xia b, Juan Wang a a b
Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, China Provincial Key Laboratory of Advanced Welding Technology, Jiangsu University of Science and Technology, Zhenjiang 212003, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 May 2017 Received in revised form 8 June 2017 Accepted 15 June 2017 Available online 16 June 2017
Super-Ni/NiCr laminated composite was successfully joined with Ti-6Al-4V by vacuum diffusion bonding at 950 C temperature. Results show that the bonding interface was composed of sequentially Ni3Ti, NiTi and NiTi2 layers. The interfacial phase constituents were similar although the joints were obtained with different bonding time. But the bonding time had a significant effect on the interfacial microstructure when the bonding time was prolonged from 30 min to 90 min. The morphology of NiTi2 layer transformed from serrate to straight and eutectoid products (Ni3Ti and NiTi2) were formed in NiTi layer whose width increased significantly. The maximum shear strength of joint is 69.2 MPa obtained at 60 min. Most joints fractured at the super-Ni/Ni3Ti interface. The shear strength of joint is mainly attributed to the plastic deformation and shifting of super-Ni crystals. © 2017 Published by Elsevier Ltd.
Keywords: Diffusion bonding Laminated composite Microstructure Shear strength
1. Introduction Ni-base superalloys have promoted the development of jet turbine engines due to its superior mechanical properties at high temperature and good corrosion resistance [1e3]. Super-Ni/NiCr laminated composite as a promising new structural material is composed of super-Ni cover layers and Ni80Cr20 sintered alloy base layer, which can be applied for a variety of high-temperature burner environment, especially, in the field of aerospace [4]. In order to combine perfect properties of different materials, it is essential to bond laminated composite with other alloys including Ti-6Al-4V as one of the most popular aero materials. Xia et al. [5] pointed out a serious problem that super-Ni cover layer was easy to separate from Ni80Cr20 base layer during heated by a welding arc. The separation would deteriorate the laminated structure. Wu et al. [6] reported that the brittle Ni-P phase in the center of brazed zone was detrimental to the property of joint when brazing superNi/NiCr laminated composite to stainless steel using NiCrP filler metal. Therefore, fusion welding and brazing with filler metal introducing other elements could both weaken the bonding of laminated composite with other metals.
* Corresponding author. E-mail address: [email protected] (Y. Li). http://dx.doi.org/10.1016/j.vacuum.2017.06.025 0042-207X/© 2017 Published by Elsevier Ltd.
Diffusion bonding as an advanced joining process has been applied in joining dissimilar metals [7]. Both residual stress induced by shrink effect during solidification process and impurity elements from interlayer can be ignored when adopting diffusion bonding without interlayer to join super-Ni/NiCr laminated composite with Ti-6Al-4V. Much work has been made on diffusion bonding Ti-6Al4V alloy with other metals including stainless steel, aluminum alloy and intermetallic compounds [8e10]. However, the investigation on the effect of bonding time on interfacial diffusion and microstructure has rarely reported. In current work, diffusion bonding was used to join laminated composite with Ti-6Al-4V and effect of bonding time on interfacial microstructure and properties of joints was studied.
2. Experimental procedure Super-Ni/NiCr laminated composite with a sandwich structure composed of two super-Ni cover layers (Ni%>99.5% and thickness of 0.3 mm per layer) and Ni80Cr20 base layer (thickness of 2 mm) and Ti-6Al-4V (thickness of 6 mm) with nominal composition of 6 wt.% Al, 4 wt.% V and balanced Ti were used as base materials in this study. The sandwich structure of laminated composite and joint configuration are shown in Fig. 1. Prior to bonding, the mating surfaces of base materials were prepared by conventional grinding
196
K. Liu et al. / Vacuum 143 (2017) 195e198
Fig. 1. Structure of laminated composite and joint configuration: (a) sandwich structure of laminated composite, (b) configuration of vacuum diffusion bonding without interlayer, (c) schematic diagram of shear test experiment.
technique and polishing down to 1000 grid SiC paper and then were cleaned with ethanol. Vacuum diffusion bonding trials were carries out in Workhorse-Ⅱ bonding installation providing a vacuum condition of 106 Pa and a series of controlled thermal parameters of bonding temperature 950 C, compressive force 5 MPa and bonding time in a series of 30 min, 60 min and 90 min. The effect of bonding time on the interfacial microstructure and properties of joint was investigated by means of metallography, HITACHI SU-70 field-emission scanning electron microscopy (FESEM) and
energy dispersive spectrum (EDS). The shear strength of joints was measured using SANS CMT5205 testing machine at a loading rate of 0.5 mm/min, as illustrated in Fig. 1c. 3. Results and discussion Interfacial microstructure of super-Ni/Ti-6Al-4V joints produced at 950 C for different bonding time was shown in Fig. 2. An obvious bonding interface between super-Ni and Ti-6Al-4V was formed. It is
Fig. 2. Effect of bonding time on interfacial microstructure: (a) 30 min, (b) 60 min, (c) 90 min, (d) scanning line analysis of interface with bonding time of 60 min, (e) the effect of bonding time on with of interfacial layers.
K. Liu et al. / Vacuum 143 (2017) 195e198
known that the interface obtained by directly diffusion bonding is different from that archived by transient liquid bonding (TLP) [11]. The formation of interface in current study was mainly attributed to the mutual diffusion of elements in base materials and interfacial reaction at elevated temperature with a press. Fig. 2a indicates that the interface at 30 min is not straight. The interface was divided into three layers marked A, B and C. Based on the Ni-Ti binary phase diagram, three Ni-Ti intermetallic compounds (IMCs) are likely to form. In order to identify the phase constituents of reaction layers, EDS was carried out to reveal the composition of interface. Results of EDS spot analysis listed in Table 1 show that A, B and C layer are composed of Ni3Ti, NiTi and NiTi2, respectively. NiTi layer is much wider than other two layers. Ni3Ti layer is not continuous and there are voids between super-Ni and Ni3Ti layer in the case of 30 min, which is attributed to the short bonding time resulting in the inefficient diffusion. It can be also observed that the morphology of NiTi2 layer is serrated. With prolonging the bonding time to 60 min and 90 min, the serrate of NiTi2 layer disappeared and the morphology was transformed to straight. Some eutectoid products (Ni3Ti and NiTi2) in dark fine stripe morphology can be observed in NiTi layer near NiTi2. The eutectoid reaction can be expressed as NiTi / Ni3Ti þ NiTi2. In the case of 60 min, although there are little voids between super-Ni and Ni3Ti layer, the morphology of Ni3Ti is continuous as shown in Fig. 2b. When bonding time increasing to 90 min, discontinuous fracture between super-Ni and Ni3Ti layer can be found, which was caused by large stress of thin super-Ni at the elevated temperature with so long time. It is worth mentioning that the width of NiTi layer increased significantly with prolonging the bonding time while the width of other layers (Ni3Ti and NiTi2) did not change obviously, as shown in Fig. 2e. It can be inferred that the growth of NiTi layer resulted in the widening of interface. According to the element distribution as shown in Fig. 2d, the high concentration of Ni and Ti element in NiTi layer indicates that the diffusion of base materials could provide sufficient atoms (Ni and Ti) for the growth of NiTi layer. In addition, the growth of Ni3Ti layer was controlled by the diffusion of Ti atom moving across NiTi2 layer and NiTi layer successively while the
Table 1 Results of EDS spot analysis in interface with bonding time of 30 min. Point
A B C
Element (at. %)
197
growth of NiTi2 layer was dominated by the diffusion of Ni atom moving across Ni3Ti layer and NiTi layer in sequence. Due to the limit of diffusion distance, it is difficult for Ni3Ti and NiTi2 to grow greatly. To explore the effect of bonding time on the shear strength of joints produced at 950 C, the relationship between the shear strength and the bonding time is illustrated in Fig. 3. During shear test, most samples fractured at the interface between super-Ni and Ni3Ti layer, which indicated the weakest zone of joint was located at the super-Ni/Ni3Ti interfaces. Considering the different coefficients of linear expansion between thin super-Ni and Ni3Ti IMCs, it was easy for residual stress to remain in the thin super-Ni (only 0.3 mm thickness) after cooling from high temperature so voids and cracks were likely to form. From the load-displace curve shown in Fig. 3a, it can be seen that the plastic deformation was improved by increasing the bonding time and some drapes can be observed on the fracture surface of super-Ni. Fig. 3b shows a trend of shear strength from rising to drop with prolonging bonding time. The maximum value of shear strength obtained at bonding time of 60 min is 69.2 MPa compared with 45.4 MPa and 47.4 MPa in the case of 30 min and 90 min, respectively. In order to further reveal the fracture mechanism of joints, SEM and EDS were carried out to characterize the morphology and to measure composition of fracture surfaces. Fig. 4 shows the fracture morphology of interface. Two different fracture morphologies including dark bulk zone and white dense dimples can be observed from Fig. 4a. The dark bulk zone with a large size is composed of Ni3Ti IMCs, presenting a brittle fracture mode. Some voids near super-Ni/Ni3Ti interface acted as crack initiation sites. It was easy for facture to occur when crack extended to the brittle Ni3Ti IMCs with the increase of stress. It should be noted that the white dense fine dimples play a role of suppressing the cracks. Fig. 4b shows the fine microstructure of dense dimples. Some raptured polylateral crystals with the size of about 3 mm expose smooth and flat crystal planes which indicate the brittle and ductile mixed fracture mode. EDS analysis of feature point implies the polylateral crystal is superNi as shown in Fig. 4c. Large crystal spacing and plastic deformation zone can be observed on other crystal planes of super-Ni where there is more resistance to cracks under shear load. Therefore, the shear strength of joint is mainly attributed to the plastic deformation and shifting of super-Ni crystals.
Phase
Ti
Ni
26.95 53.32 67.80
73.05 46.68 32.20
4. Conclusions Ni3Ti NiTi NiTi2
Super-Ni/NiCr laminated composite and Ti-6Al-4V were bonded by vacuum diffusion without interlayer at 950 C temperature for
Fig. 3. Effect of bonding time on shear strength of joints: (a) load-displace curve, (b) shear strength of joints.
198
K. Liu et al. / Vacuum 143 (2017) 195e198
Fig. 4. Fracture of joints: (a) fracture surface, (b) polylateral crystals, (c) EDS results.
various bonding time. The interface was composed of sequentially Ni3Ti, NiTi and NiTi2 layers. As the bonding time increased, the morphology of NiTi2 layer transformed from serrate to straight and eutectoid products (Ni3Ti þ NiTi2) were formed in NiTi layer whose width increased significantly. Shear strength of joints presented a trend from rising to drop and plastic deformation was improved by prolonging the bonding time. The maximum value of shear strength is 69.2 MPa obtained at bonding time of 60 min. Most joints fractured at the super-Ni/Ni3Ti interface. Acknowledgements This project was supported by National Natural Science Foundation of China (grant number 51575316) and the Natural Science Foundation of Shandong Province, China (grant number ZR2015EM040). References [1] J.H. Perepezko, The hotter the engine, the better, Science 326 (5956) (2009) 1068e1069. [2] L. Lan, W.D. Xuan, J. Wang, C.J. Li, Z.M. Ren, J.B. Yu, J.C. Peng, Interfacial microstructure of partial transient liquid phase bonding of Si3N4 to nickelbase superalloy using Ti/Au/Ni interlayers, Vacuum 130 (2016) 105e108.
[3] L. Jiang, S.Q. Guo, Y.Y. Bian, M. Zhang, W.Z. Ding, Interfacial behaviors of magnesia partially stabilized zirconia with nickel-based superalloy, Mat. Lett. 181 (2016) 313e316. [4] N. Wu, Y.J. Li, Q.S. Ma, Microstructure evolution and shear strength of vacuum brazed joint for super-Ni/NiCr laminated composite with Ni-Cr-Si-B amorphous interlayer, Mat. Des. 53 (2014) 816e821. [5] C.Z. Xia, Y.J. Li, U.A. Puchkov, J. Wang, Microstructural study of super Ni laminated composite/1Cr18Ni9Ti steel dissimilar welded joint, Mat. Sci. Tech. 26 (11) (2010) 1358e1362. [6] N. Wu, Y.J. Li, J. Wang, U.A. Puchkov, Vacuum brazing of super-Ni/NiCr laminated composite to Cr18-Ni8 steel with NiCrP filler metal, J. Mat. Process. Tech. 212 (4) (2012) 794e800. [7] S. Wang, Y.H. Ling, J.J. Wang, G.Y. Xu, Microstructure and mechanical properties of W/Cu vacuum diffusion bonding joints using amorphous FeeW alloy as interlayer, Vacuum 114 (2015) 58e65. [8] M.S. Kenevisi, S.M. Mousavi Khoie, A study on the effect of bonding time on the properties of Al7075 to Tie6Ale4V diffusion bonded joint, Mat. Lett. 76 (2012) 144e146. [9] S. Zakipour, M. Samavatian, A. Halvaee, A. Amadeh, A. Khodabandeh, The effect of interlayer thickness on liquid state diffusion bonding behavior of dissimilar stainless steel 316/Ti-6Al-4V system, Mat. Lett. 142 (2015) 168e171. [10] J.K. Liu, J. Cao, X.T. Lin, H.Y. Chen, J. Wang, J.C. Feng, Interfacial microstructure and joining properties of TiAl/Ti3AlC2 diffusion bonded joints using Zr and Ni foils as interlayer, Vacuum 102 (2014) 16e25. [11] X.J. Yuan, C.Y. Kang, Microstructural characteristics in vacuum TLP (Transient Liquid Phase) bonds using a novel iron-based interlayer based on duplex stainless steel base metal alloyed with a melting-point depressant, Vacuum 99 (2014) 12e16.