Journal of Materials Science & Technology

Journal of Materials Science & Technology 33 (2017) 682 689 Contents lists available at ScienceDirect Journal of Materials Science & Technology journal homepage: www.jmst.org Effects of Nb content in Ti Ni Nb brazing alloys on the microstructure and mechanical properties of Ti 22Al 25Nb alloy brazed joints Y. Wang, X.Q. Cai, Z.W. Yang, D.P. Wang, X.G. Liu, Y.C. Liu Tianjin Key Lab of Advanced Joining Technology, School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China article info abstract Article history: Received 30 December 2016 Received in revised form 2 February 2017 Accepted 3 March 2017 Available online 23 March 2017 Keywords: Ti 22Al 25Nb alloy Ti Ni Nb brazing alloy Nb content Microstructure Mechanical properties Vacuum brazing was successfully used to join Ti 22Al 25Nb alloy using Ti Ni Nb brazing alloys prepared by arc-melting. The influence of Nb content in the Ti Ni Nb brazing alloys on the interfacial microstructure and mechanical properties of the brazed joints was investigated. The results showed that the interfacial microstructure of brazed joint consisted of B2, O, 3, and Ti 2 Ni phase, while the width of brazing seams varied at different Nb contents. The room temperature shear strength reached 359 MPa when the joints were brazed with eutectic Ti 40 Ni 40 Nb 20 alloy at 1180 C for 20 min, and it was 321, 308 and 256 MPa at 500, 650 and 800 C, respectively. Cracks primarily initiated and propagated in 3 compounds, and partially traversed B2+O region. Moreover, the fracture surface displayed typical ductile dimples when cracks propagated through B2+O region, which was favorable for the mechanical properties of the brazed joint. 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology. 1. Introduction Ti 2 AlNb-based alloys were widely used in the aerospace industry because of their low density, high specific strength, nonmagnetic property and good oxidation resistance [1 4]. Nevertheless, the application of Ti 2 AlNb-based alloys was always limited because of high cost, complex manufacturing process and intrinsic brittleness [5]. A pivotal manufacturing technology for the application of Ti 2 AlNb-based alloys in aerospace applications will be joining. Therefore, the development of reliable technique to join Ti 2 AlNb-based alloys is indispensable to the engineering applications. At present, various joining techniques have been performed to obtain sound joints of Ti 2 AlNb-based alloys, such as fusion welding [6 8], diffusion bonding [9] and friction welding [10,11]. Brazing, as an economical and feasible joining method, has been gaining attentions in joining titanium alloys [12,13]. As far as brazing concerned, a key factor for the obtaining of satisfactory joints was the selection of applicable brazing alloys. Al-based and Ag-based brazing alloys were successfully applied to braze conventional titanium alloys [14 16]. However, the thermal resistance of joint was poor when using Al-based and Ag-based brazing alloy, and they failed to serve at temperatures higher than 450 C. In contrast, Ti-based brazing Corresponding author. E-mail addresses: tjuyangzhenwen@163.com, yangzw@tju.edu.cn (Z.W. Yang). alloy demonstrated excellent room and high temperature performance in brazing many titanium alloys. Ti Ni [17,18], Ti Ni V [19], Ti Ni Nb [20], Ti Cu Ni [21,22] and Ti Zr Ni Cu [23 25] brazing alloys were reported to join titanium alloys, and appropriating high temperature performance could be obtained. For example, Song et al. used Ti 40 Ni 40 Nb 20 (at.%) brazing alloy to braze (Ti 45Al 8.5Nb (W,B,Y) (at.%)), and the maximum shear strength at room temperature and high temperature (600 C) was of 308 and 172 MPa, respectively [20]. In addition, Ti Zr Ni Cu+Mo brazing alloy was previously applied to braze TiAl alloy (Ti 43Al 9V 0.3Y (at.%)) in our group [24], and the maximum shear strength was of 233 MPa. However, limited investigations have been reported on using Ti-based brazing alloy to braze Ti 2 AlNb-based alloy. On account of the good compatibility between Ti 22Al 25Nb alloys and brazing alloy, in this study, high temperature Ti 50 x/2 Ni 50 x/2 Nb x alloys were applied to braze Ti 22Al 25Nb alloys. The effects of Nb content on the interfacial microstructure and the mechanical properties of the Ti 22Al 25Nb joints were investigated. In addition, the effects of testing temperature on the joining properties of the brazed joints were also studied. 2. Materials and experimental procedures The Ti 2 AlNb-based alloys in this study was received in the form of a cast rod with a nominal composition of Ti 22Al 25Nb (at.%). Specimens with two different sizes of 15 mm 10 mm 3 mm and 5 mm 5 mm 5 mm were cut from Ti 22Al 25Nb rod by http://dx.doi.org/10.1016/j.jmst.2017.03.021 1005-0302/ 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Y. Wang et al. / Journal of Materials Science & Technology 33 (2017) 682 689 683 Fig. 1. Backscattered electron image (BEI) of (a) hypo-eutectic Ti 45Ni 45Nb 10 alloy, (b) eutectic Ti 40Ni 40Nb 20 alloy, and (c) hyper-eutectic Ti 37Ni 37Nb 26 alloy. spark cutting. The Ti 50-x/2 Ni 50-x/2 Nb x (x = 10, 20, 26) (at.%) brazing alloys were performed by arc-melting high purity (>99.6% wt%) of Ti, Ni, and Nb, and the thickness of brazing alloy foils was of 180 m. The contacting surface of each specimen was ground on SiC paper and cleaned ultrasonically in an acetone solution for 10 min. The Ti 50-x/2 Ni 50-x/2 Nb x foils were sandwiched between the Ti 22Al 25Nb alloys. The assembled specimens were heated to 1180 C for 20 min in a vacuum furnace with a pressure about 1 10 3 Pa. The joints were then cooled down to 500 Cat 15 C/min, and finally cooled to ambient temperature. After the brazing process, the cross sections of brazed joints were prepared with standard metallographic techniques and etched in a solution of 0.8HF-1.2HNO 3-5HCl-93H 2 O (ml). The interfacial microstructures were investigated by scanning electron microscopy (SEM, FEI Nano SEM 430). Chemical analysis was performed as qualitative mappings with an energy dispersive spectrometer (EDS). Transmission electron microscopy (TEM, Tecnai G2 F20) was performed to observe the morphology of the reaction phases in the joint. The lattice structure of the joint production was determined by selected area electron diffraction (SAED). Focused ion beam (FIB, Helios 600i) was used to obtain the TEM sample from brazed joint. The test for shear strength of brazed specimen was carried out at a displacement rate of 0.5 mm/min by INSTRON 1186 at room temperature (RT) and at elevated temperature of 500, 650 and 800 C, respectively. Four brazed specimens were analyzed at each test temperature. X-ray diffraction (XRD) of the fracture surfaces was performed using a BRUKER D8 Advance XRD with monochromated Cu K radiation. SEM was used to observe the fracture location and morphology, and then the relationship of experiment parameter, microstructure and mechanical properties were analyzed. 3. Results and discussion 3.1. Characterization of Ti 50-x/2 Ni 50-x/2 Nb x brazing alloys Fig. 1 illustrates the typical microstructure of Ti 50 x/2 Ni 50 x/2 Nb x (x = 10, 20, 26) (at.%) in backscattered electron Fig. 2. XRD pattern of hypo-eutectic Ti 45Ni 45Nb 10 alloy, eutectic Ti 40Ni 40Nb 20 alloy, and hyper-eutectic Ti 37Ni 37Nb 26 alloy. (BSE) mode. In addition, XRD analyses of Ti 50-x/2 Ni 50-x/2 Nb x alloys were performed, as shown in Fig. 2. The results showed that the eutectic Ti 40 Ni 40 Nb 20 alloy mainly comprised the eutectic microstructure of -Nb + TiNi, and the white -Nb solid solution was embedded in the gray TiNi matrix. Hypo-eutectic Ti 45 Ni 45 Nb 10 alloy consisted of dark grey pro-eutectic TiNi and light gray eutectic structure -Nb + TiNi. Besides the typical eutectic structure of -Nb + TiNi, the white blocky -Nb pro-eutectic phase was found in the hyper-eutectic Ti 37 Ni 37 Nb 26 alloy. The microstructures of Ti Ni Nb brazing alloys with three kinds of different Nb contents were consistent with the TiNi Nb phase diagram analysis [26,27]. According to TiNi Nb phase diagram [26], it can be seen that the TiNi Nb eutectic temperature is approximately 1150.7 C. Thus, the brazing temperature of 1180 C was selected in this study, which is slightly higher than the eutectic temperature of the TiNi Nb alloys. 3.2. Typical microstructure of Ti 22Al 25Nb/Ti 40 Ni 40 Nb 20 /Ti 22Al 25Nb brazed joint Fig. 3 illustrates a typical microstructure and the corresponding EDS mappings of different elements of the Ti 22Al 25Nb alloy

684 Y. Wang et al. / Journal of Materials Science & Technology 33 (2017) 682 689 Fig. 3. Microstructure and corresponding elemental distribution of Ti 22Al 25Nb alloy joint brazed with eutectic Ti 40Ni 40Nb 20 brazing alloy at 1180 C for 20 min: (a) microstructure and (b e) elements area distribution images. joint brazed with a eutectic Ti 40 Ni 40 Nb 20 (at.%) brazing alloy at 1180 C for 20 min. The interface was fully bonded and no defects such as cracks and pores were found. In addition, the brazing seam can be divided into two zones, including zone I adjacent to the Ti 22Al 25Nb substrate and a central zone II. According to the elemental distribution across the Ti 22Al 25Nb alloy joint showing in Fig. 3(b), it is noted that the content of Al in the brazing seam was high, while there was no Al in the Ti 40 Ni 40 Nb 20 brazing alloy. It demonstrated that intensive dissolution and diffusion of element Al occurred during brazing. Fig. 3(c) shows the element Ti was uniformly distributed in the brazing seam and Ti 22Al 25Nb alloy. Fig. 3(d) reveals that Nb concentration in dark grey phase was lower than that in grayish phase. In contract, the content of element Ni in dark grey phase was higher than that in grayish phase, as shown in Fig. 3(e). Fig. 4 shows more details of the microstructure of brazed joint. It can be seen that zone I (see Fig. 3(a)) primarily comprised a continuous grayish area (marked A) and zone II (see Fig. 3(a)) consisted of three characteristic area (marked by B, C, and D, respectively). The compositions of each phase marked in Fig. 4 were measured by EDS, and the results are listed in Table 1. According to EDS results, area A and area C were mainly made up of Ti, Al, and Nb with a similar composition of Ti 2 AlNb. EDS results of the dark grey area (B) in zone II (see Fig. 3(a)) showed a composition of 42.46Ti, 19.38Al, 13.50Nb, Table 1 EDS results of chemical compositions at each location in Fig. 4 (at.%). Locations Al Nb Ti Ni Possible phases A 16.73 32.19 46.83 4.25 B2+O B 19.38 13.50 42.46 24.66 3 C 16.40 33.07 46.92 3.61 B2+O D 8.50 3.33 58.68 29.49 Ti 2Ni and 24.66Ni (at.%), which accords with the Al 3 NiTi 2 ( 3 ) phase, according to the Ti Ni Al ternary phase diagram [28]. In addition, the atomic ratio of Ti and Ni in area D was equal to 2:1, indicating the formation of Ti 2 Ni phase in central zone II (see Fig. 3(a)). TEM analysis was performed to further identify the reaction phases and characterize the morphology of brazed joint, as shown in Fig. 5. The selected area electron diffraction (SAED) patterns of phases marked by solid circle and dotted circle in Fig. 5(a) are shown in Fig. 5(b) and (c), respectively. From Fig. 5(b), the SAED pattern demonstrated that two phases of B2 and O were formed in brazed joint. The orientation relations of the two phases were [ 111]B2//[1 10]O and (110)B2//(001)O, which was in agreement with the orientation relations reported in Ref. [29]. So, the grayish areas in Fig. 4 were identified as that of O and B2 phases. The hexagonal crystal structure of 3 phase formed in brazed joint, as shown

Y. Wang et al. / Journal of Materials Science & Technology 33 (2017) 682 689 685 Fig. 4. Magnified microstructures of Ti 22Al 25Nb alloy brazed joint: (a) zone I and (b) zone II. Fig. 5. TEM results of the reaction phases in the joint: (a) morphology of reaction phases, (b) the SAED pattern was obtained from the solid circle in (a), and (c) was obtained from the dotted circle in (a). in Fig. 5(c). Therefore, dark grey phase (marked by B) in Fig. 4(b) was 3 phase. Based on the analysis above, the formation of brazed joint can be described as follows: the eutectic Ti 40 Ni 40 Nb 20 brazing alloy melted and converted into liquid when the brazing temperature was up to 1150.7 C. During the temperature up to 1180 C, the Ti 22Al 25Nb alloy was partially dissolved, and the Al and Nb diffused into the molten Ti 40 Ni 40 Nb 20 brazing alloy. The concentrations of Al and Nb in the liquid brazing alloy increased. phase in the central zone II began to precipitate when the constituents of Ti, Al, and Nb were similar to Ti 2 AlNb, which translated into ordered bcc phase B2 during cooling. It is noted that the Ni content in B2 was no more than 5 at.%, and most of the Ni was detected in the 3 phase. The same phenomenon was also reported in Ref. [20]. With the growth of the /B2 phase, the surplus Ni atom would remain in the residual liquid phase. Therefore, elemental Ni was enriched in the remnant liquid phase and finally reacted with Ti and Al to form the 3 phase during the brazing process. 3 was found to melt congruently at 1289 C, as reported in Ref. [28]. This is consistent with the above experimental results. According to Ti Ni phase diagram [30],Ti 2 Ni phase precipitated when the temperature reached 984 C, so it can be inferred that the Ti 2 Ni phase precipitated from the residual liquid phase at last. It is noted that the B2 phases in joint were surrounded by the 3 phases, and the black Ti 2 Ni phases were mainly distributed in the boundaries between B2 and the 3 phase, which were contributed to deducing the formation mechanisms. Furthermore, the /B2 phase transformed across the four phase regions during the process of cooling, involving /B2, 2 + /B2, 2 + /B2+O, and /B2+O, according to the Ti 22Al xnb phase diagram [31]. Thus, the O phase precipitated from /B2 during the cooling. In conclusion, the Ti 22Al 25Nb alloy joint brazed with a eutectic Ti 40 Ni 40 Nb 20 (at.%) brazing alloy at 1180 C for 20 min mainly consisted of 3, B2, O, and Ti 2 Ni phase. 3.3. Effect of Nb content on the microstructure of brazed joints Fig. 6 shows the effect of Nb content on the microstructure of Ti 22Al 25Nb alloy joints brazed at 1180 C for 20 min. According to Fig. 6(a)-(c), it is noted that the width of brazing seams at different Nb contents were distinct. The width of the brazing seam was about 167, 240 and 215 m for joint brazed using hypoeutectic Ti 45 Ni 45 Nb 10, eutectic Ti 40 Ni 40 Nb 20, and hyper-eutectic Ti 37 Ni 37 Nb 26 brazing alloy, respectively. It manifested that the dissolution of Ti 22Al 25Nb substrate into the liquid phase was the highest when the brazing alloy was Ti 40 Ni 40 Nb 20. According to microstructure in Fig. 1 (b) and the TiNi Nb phase diagram

686 Y. Wang et al. / Journal of Materials Science & Technology 33 (2017) 682 689 Fig. 6. Effect of Nb content on the microstructure of Ti 22Al 25Nb brazed joints: (a) hypo-eutectic Ti 45Ni 45Nb 10 alloy, (b) eutectic Ti 40Ni 40Nb 20 alloy, and (c) hyper-eutectic Ti 37Ni 37Nb 26 alloy. [26], Ti 40 Ni 40 Nb 20 alloy mainly consists of eutectic structure of { -Nb + TiNi}. Therefore, the eutectic Ti 40 Ni 40 Nb 20 brazing alloy liquefied completely when the brazing temperature exceeded eutectic temperature of 1150.7 C, and then Ti 22Al 25Nb alloy was continually dissolved into the molten Ti 40 Ni 40 Nb 20 brazing alloy. For Ti 37 Ni 37 Nb 26 brazing alloy, it mainly consists of a large proportion of eutectic structure { -Nb + TiNi} and partially proeutectic -Nb phase. When the brazing temperature exceeded 1150.7 C, eutectic structure of { -Nb + TiNi} began melting, and then pro-eutectic -Nb and Ti 22Al 25Nb substrate was dissolved into the molten liquid. However, Ti 45 Ni 45 Nb 10 alloy primarily comprised pro-eutectic TiNi and a small amount of eutectic structure { -Nb + TiNi}. Only a small proportion of eutectic structure { - Nb + TiNi} began to melting when the temperature was up to 1150.7 C, and then a good deal of primary phase pro-eutectic TiNi was required to be dissolved into the molten eutectic structure. Therefore, the dissolution of Ti 22Al 25Nb substrate into the molten Ti 45 Ni 45 Nb 10 brazing alloy was lower than Ti 40 Ni 40 Nb 20 brazing alloy when the brazing temperature at 1180 C. The thickness of brazing seams was the largest when the joint was brazed with Ti 40 Ni 40 Nb 20 brazing alloy. Moreover, the original Ni element in Ti 40 Ni 40 Nb 20 was less than Ti 45 Ni 45 Nb 10 brazing alloy, and the 3 phase formed in the joint brazed with Ti 40 Ni 40 Nb 20 brazing alloy was less than the joint brazed with Ti 45 Ni 45 Nb 10 brazing alloy. 3.4. Mechanical properties and fracture analysis of the Ti 22Al 25Nb brazed joints Fig. 7 presents the shear strength of the joints brazed at different Nb content, and tested at different testing temperatures. The average room temperature (RT) joint strength of Ti 22Al 25Nb alloy brazed with Ti Ni Nb brazing alloys was very high, and all of them were higher than 300 MPa. The maximum RT joint strength of 359 MPa was obtained when Ti 22Al 25Nb alloy was brazed with the eutectic Ti 40 Ni 40 Nb 20 brazing alloy, as shown in Fig. 7(a). Ti 22Al 25Nb alloy is often applied to high temperature environments. Therefore, the high temperature behavior of brazed joint is necessary to be investigated, and the high temperature Fig. 7. Effect of (a) Nb content and (b) test temperature on the shear strength of Ti 22Al 25Nb brazed joints.

Y. Wang et al. / Journal of Materials Science & Technology 33 (2017) 682 689 687 (500, 650 and 800 C) shear tests were performed. Fig. 7(b) shows the shear strength of Ti 22Al 25Nb alloy brazed using eutectic Ti 40 Ni 40 Nb 20 alloy at 1180 C for 20 min under different testing temperatures. According to the results, the joint strength decreased gradually with the increase of testing temperature. Even so, the shear strength still remained 256 MPa when the test temperature was up to 800 C. The shear strength retention of the Ti 22Al 25Nb joints brazed at 500, 650 and 800 C was 89.7%, 86.0% and 71.5%, respectively. The results suggested that the excellent high temperature properties of Ti 22Al 25Nb brazed joints can be obtained using Ti 50-x/2 Ni 50-x/2 Nb x. Fig. 8 illustrates the cross-section of the Ti 22Al 25Nb alloy joint brazed with eutectic Ti 40 Ni 40 Nb 20 brazing alloy at 1180 C for 20 min after RT shear test. It can be found that fracture took place along zone II (dee Fig. 6). From Fig. 8(b), it can be seen that the initiation and propagation of cracks primarily occurred in the 3 compound. According to Ref. [32,33], the Young s modulus (E) and hardness (H) of the 3 phase were the highest. The plastic deformation of the brittle 3 compound was uncoordinated with that of B2+O region and Ti 22Al 25Nb substrate under shear forces. Thus, the initiation and propagation of cracks primarily occurred in this phase. The hard and brittle 3 compounds formed in the brazing seam were the weakest region in the joint. Moreover, the distribution and morphology of the reaction products in the brazed joint also influenced the joint strength. The blocky B2+O regions were randomly distributed in 3 compound when the joint was brazed with eutectic Ti 40 Ni 40 Nb 20 brazing alloy. The cracks propagated from the continuous 3 compound to blocky B2+O regions, and the presence of blocky B2+O regions impeded the crack propagation, as observed in Fig. 8(c). Under this circumstance, the transformation of crack required a large shear force. However, the more 3 compound was concentrated in the joint brazed with Ti 45 Ni 45 Nb 10 Table 2 EDS results of chemical compositions at each location in Fig. 9 (at.%). Locations Al Nb Ti Ni Possible phases A 18.88 14.48 42.31 24.33 3 B 17.12 33.00 45.56 04.32 B2+O C 17.58 12.61 44.41 25.40 3 D 14.28 23.55 50.90 11.27 B2+O E 20.50 14.50 42.04 22.96 3 F 15.22 27.51 48.49 08.78 B2+O G 15.38 11.16 45.84 27.62 3 H 17.63 23.77 53.25 05.35 B2+O brazing alloy, cracks initiated and propagated in the 3 compound easily. So, the shear strength of joint was lower. The fracture surface of Ti 22Al 25Nb joint brazed with a eutectic Ti 40 Ni 40 Nb 20 brazing alloy at 1180 C for 20 min after shear test were examined. Fig. 9 shows the typical fracture surfaces of the joint after shear testing at different temperatures. The EDS analysis results of the different zones in Fig. 9 are listed in Table 2. The XRD analysis of the fracture surface is shown in Fig. 10. The results demonstrated that the 3, B2 and O phases were detected in the fracture surface. Combined with the microstructural observation and phase analysis, it was clear to see that the fracture occurred mainly through 3 phase, which were of typical cleavage fracture features. In addition, when the fracture propagated through the B2+O region, the fracture exhibited typical characteristics of ductile dimples, which was favorable for the strength of the joint. Therefore, it can be concluded that a mixed brittle and ductile failure mode was observed for the Ti 22Al 25Nb brazed joint tested at RT, as shown in Fig. 9(a, b). However, the dimples were vanished when the brazed joints suffered shear testing at a high temperature. The fractographs in Fig. 9(c h) displayed cleavage dominated fracture Fig. 8. Typical fracture paths of Ti 22Al 25Nb joints brazed with eutectic Ti 40Ni 40Nb 20 brazing alloy: (a) low magnification SEM image, (b) and (c) high magnification SEM image.

688 Y. Wang et al. / Journal of Materials Science & Technology 33 (2017) 682 689 Fig. 9. Fractographs of Ti 22Al 25Nb joints brazed with eutectic Ti40 Ni40 Nb20 brazing alloy after shear test at (a, b) RT, (c, d) 500 C, (e, f) 650 C and (g, h) 800 C. when the testing temperature was higher than 500 C. According to the fracture analysis, the brittle 3 compound was the weakest part in the whole joint. The crack preferred to initiated and propagated in the 3 compound. In addition, the random distribution of blocky B2 and O phase in 3 compound contributed to improve the joint strength. 4. Conclusions (1) The interfacial microstructure of Ti 22Al 25Nb alloy brazed joints was primarily comprised of B2, O, 3, and Ti2 Ni. The orientation relations of B2 and O were [ 111]B2//[1 10]O and (110)B2//(001)O. (2) The width of brazing seams varied at different Nb contents. The maximum RT shear strength reached 358 MPa when the joint was brazed with eutectic Ti40 Ni40 Nb20 brazing alloy, while it was 321, 308 and 256 MPa at 500, 650 and 800 C, respectively. (3) Cracks primarily initiated and propagated in the brittle 3 compound, and partially traversed the B2+O regions. Moreover, ductile dimples were observed when the fracture propagated through the B2+O region, which is favorable for the mechanical properties of the joint. However, the dimples were vanished when the joint suffered shear testing at high temperatures.

Y. Wang et al. / Journal of Materials Science & Technology 33 (2017) 682 689 689 Fig. 10. XRD analysis of the fracture surface of Ti 22Al 25Nb joints brazed with eutectic Ti 40Ni 40Nb 20 brazing alloy after shear test at: (a) RT, (b) 500 C, (c) 650 C and (d) 800 C. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Grant No. 51574177), the China Natural Founds for Distinguished Young Scientists (Grant No. 51325401), and the National High Technology Research and Development Program of China ( 863 Program, Granted No. 2015AA042504). References [1] D. Banerjee, A.K. Gogia, T.K. Nandy, V.A. Joshi, Acta Metall. 36 (1988) 871 882. [2] J. Wu, L. Xu, Z.G. Lu, B. Lu, Y.Y. Cui, R. Yang, J. Mater. Sci. Technol. 31 (2015) 1251 1257. [3] C.J. Cowen, C.J. Boehlert, Intermetallics 14 (2006) 412 422. [4] C. Leyens, H. Gedanitz, Scr. Mater. 41 (1999) 901 906. [5] A. Lasalmonie, Intermetallics 14 (2006) 1123 1129. [6] Z.L. Lei, Z.J. Dong, Y.B. Chen, J. Zhang, R.C. Zhu, Mater. Des. 46 (2013) 151 156. [7] B.B. Kong, G. Liu, D.J. Wang, K.H. Wang, S.J. Yuan, Mater. Des. 90 (2016) 723 732. [8] D.T. Cai, J.H. Chen, X.F. Mao, C.Y. Hao, Intermetallics 38 (2013) 63 69. [9] C.W. Wang, T. Zhao, G.F. Wang, J. Gao, H. Fang, J. Mater, Process. Technol. 222 (2015) 122 127. [10] X. Chen, F.Q. Xie, T.J. Ma, W.Y. Li, X.Q. Wu, J. Alloys Compd. 646 (2015) 490 496. [11] X. Chen, F.Q. Xie, T.J. Ma, W.Y. Li, X.Q. Wu, Mater. Des. 94 (2016) 45 53. [12] Z.Y. Wu, R.K. Shiue, C.S. Chang, J. Mater. Sci. Technol. 26 (4) (2010) 311 316. [13] H.S. Ren, H.P. Xiong, B. Chen, S.J. Pang, B.Q. Chen, L. Ye, J. Mater. Sci. Technol. 32 (2016) 372 380. [14] T. Tetsui, Intermetallics 9 (2001) 253 260. [15] R.K. Shiue, S.K. Wu, S.Y. Chen, Acta Mater. 51 (2003) 1991 2004. [16] R.K. Shiue, S.K. Wu, S.Y. Chen, Intermetallics 11 (2003) 661 671. [17] X.Q. Si, H.Y. Zhao, J. Cao, X.G. Song, D.Y. Tang, J.C. Feng, Mater. Sci. Eng. A 636 (2015) 522 528. [18] P. He, D. Liu, E. Shang, M. Wang, Mater. Charact. 60 (2009) 30 35. [19] X.G. Song, J. Cao, H.Y. Chen, Y.F. Wang, J.C. Feng, Mater. Sci. Eng. A 551 (2012) 133 139. [20] X.G. Song, J. Cao, Y.Z. Liu, J.C. Feng, Intermetallics 22 (2012) 136 141. [21] I.C. Wallis, H.S. Ubhi, M.-P. Bacos, P. Josso, J. Lindqvist, D. Lundstrom, Intermetallics 12 (2004) 303 316. [22] C.T. Chang, Y.C. Du, R.K. Shiue, C.S. Chang, Mater. Sci. Eng. A 420 (2006) 155 164. [23] P. He, J.C. Feng, H. Zhou, Mater. Sci. Eng. A 392 (2005) 81 86. [24] Q.W. Qiu, Y. Wang, Z.W. Yang, X. Hu, D.P. Wang, Mater. Des. 90 (2016) 650 659. [25] X.Q. Li, L. Li, K. Hu, S.G. Qu, Intermetallics 57 (2015) 7 16. [26] M. Piao, S. Miyazaki, K. Otsuka, N. Nishida, Mater. Trans. JIM 33 (1992) 337 345. [27] C. Bewerse, L.C. Brinson, D.C. Dunand, Mater. Sci. Eng. A 627 (2015) 360 368. [28] J.C. Schuster, Z. Pan, S.H. Liu, F. Weitzer, Y. Du, Intermetallics 15 (2007) 1257 1267. [29] C.J. Boehlert, B.S. Majumdar, V. Seetharaman, D.B. Miracle, Metall. Mater. Trans. A 30 (1999) 2305 2323. [30] K. Otsuka, X. Ren, Prog. Mater. Sci. 50 (2005) 511 678. [31] V. Raghavan, J. Phase Equilib. Diffus. 26 (2005) 360 368. [32] X.Q. Cai, Y. Wang, Z.W. Yang, D.P. Wang, Y.C. Liu, J. Alloys Compd. 679 (2016) 9 17. [33] J. Cao, J.K. Liu, X.G. Song, X.T. Lin, J.C. Feng, Mater. Des. 56 (2014) 115 121.