- Email: [email protected]
Effect of Cu on microstructure evolution and mechanical properties of Fe-Nb dissimilar welds
Accepted Manuscript Effect of Cu on microstructure evolution and mechanical properties of Fe-Nb dissimilar welds Qiaoling Chu, Min Zhang, Jihong Li, Fuxue Yan, Cheng Yan PII: DOI: Reference:
S0167-577X(18)31465-4 https://doi.org/10.1016/j.matlet.2018.09.086 MLBLUE 24954
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
28 August 2018 8 September 2018 16 September 2018
Please cite this article as: Q. Chu, M. Zhang, J. Li, F. Yan, C. Yan, Effect of Cu on microstructure evolution and mechanical properties of Fe-Nb dissimilar welds, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet. 2018.09.086
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of Cu on microstructure evolution and mechanical properties of Fe-Nb dissimilar welds Qiaoling Chuab*, Min Zhanga*, Jihong Lia, Fuxue Yan a, Cheng Yanb a College of Materials Science and Engineering, Xi’an University of Technology, Xi’an, 710048, China. b School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), Brisbane, QLD 4001, Australia.
ABSTRACT In this paper, we report a thorough study of phase formation in Fe-Nb weld metals using a combination of microscopy and composition analysis. The correlation of microstructure and mechanical properties was established by nanoindentation. A simplified scenario of weld formation was proposed. Nb weld metal was dominated by the coarse Laves phase (Fe2Nb) with high hardness (~20.4GPa). With the addition of Cu, sound weld metal was obtained with alternative distribution of α-Fe, Cu phases and fine eutectic phases (α-Fe+Fe2Nb). These transformation products with lower hardness (α-Fe+Fe2Nb~11.6GPa) improved the overall mechanical properties of the weld metal. Keywords: Microstructure; Intermetallics; Phase transformation; Nanoindentation. 1. Introduction Welding of dissimilar materials is continuously attracting attention by the industry because of its potential benefits on increasing design flexibility and reducing cost [1]. Niobium (Nb) is a refractory metal which has many desirable properties that make them suitable for numerous engineering applications [2]. The Fe-Nb binary phase * Corresponding author: [email protected] (Dr. Qiaoling Chu), [email protected] (Prof. Min Zhang).
1
diagram denotes two intermetallic phases, namely the hexagonal C14-type Laves phase Fe2Nb and Fe7Nb6 [3-4]. Their significantly low ductility and brittle fracture characteristics limit the wide applications of Fe-Nb dissimilar joints [5]. Research studies demonstrate that such welds can be improved by addition of appropriate intermediate materials [6]. Bacher et al. [7] employed Cu as the braze filler to join Nb and AISI 316LN. Although some Fe-rich compounds formed at Nb/Cu interface, the resulted joints satisfied all the criteria for their application in ultra-high vacuum. The assumption of using Cu as intermediate is further supported by results that there are no intermetallics in Cu-Nb and Cu-Fe systems [8-9]. In this study, we attempt to improve the phase constitution in Fe-Nb weld metal via Cu intermediate. The relation between microstructure and mechanical properties was built by nanoindentation test. The phase formation mechanism in resultant weld metals was explained using a simplified model based on the phase diagrams. 2. Experimental procedures A commercial low alloy steel plate (0.2wt.% C, 0.35wt.% Si, 1.4%wt.% Mn) with the thickness of 2mm was butt welded with Nb filler (0.005wt.%C, 0.002wt.% Si, 0.001wt.% Cu, 0.0014wt.% Fe) using gas-tungsten arc welding. A composite filler (Cu20Nb, Nb~20wt.%) was developed to modify the final phase compositions in Nb weld metal. The microstructure and chemical compositions of the resultant welds were studied by SEM (JEOL-7001F) and TEM (JEOL-2100). Focused ion beam (FIB, FEI Quanta 200 3D dual beam) was used to prepare TEM samples. X-ray diffraction (XRD) patterns were collected using a Rigaku-binary diffractometer (Rigaku SmartLab) with a 2
Cu target. Nanoindentation was conducted using Berkovich indenter (Hysitron Triboindenter TL-950). An array of total 120 indents (60×2) was set for each weld metal. The measured hardness of each phase was averaged from at least ten indents. 3. Results and discussion Fig. 1a-c show the backscattered electron (BSE) images of microstructure in Nb weld metal. The compositions of typical phases determined from EDS analysis are listed in Table 1. Severe cracks are observed in Nb weld metal. Fig. 1a shows the microstructure at Fe-Nb interface, where coarse cellular structures (Fe2Nb) grow perpendicular to the interface and present dominant distribution in Nb weld metal. Fe-rich regions which incorporate eutectic phase (α-Fe+Fe2Nb) form between Fe2Nb cellular and Fe base metal, as shown in Fig. 1a and b. EBSD phase mapping in Fig. 1c confirms this characterized phase distribution. The coarse cellular structure has an average hardness of 20.4GPa, whereas eutectic compounds show lower hardness value (~6.7GPa). The low magnification image of Fe-Cu20Nb interface is shown in Fig. 1d. The resultant weld is free from cracks. Unlike Nb weld metal, homogeneous microstructure form in Cu20Nb weld metal. For Cu-Fe-Nb phase diagram, Fe2Nb phase has significant homogeneity ranges [9]. Together with the EDS results, Cu20Nb weld metal is primary composed of Fe solid solution, eutectic compounds (α-Fe+Fe2Nb) and Cu solid solution phase. The eutectic compounds with fine lamellar structures are distributed among the Fe solid solution, as displayed in Fig. 1e. Up to 8.33 at. % Cu is dissolved in Fe solid solution, as listed in Table 1. The EBSD phase mapping in Fig. 1f shows that Cu solid 3
solution (yellow) presents bulk and fine particle morphology in Cu20Nb weld metal. This characteristic distribution is similar to that presented in [10] where Zn individual particles precipitate along Al/Al grain boundaries (GBs). It is regarded as incompletely wetting of Al/Al GBs by Zn solid solution. Fe solid solution in Cu20Nb weld metal exhibits an average hardness of 9.1GPa. The eutectic compounds show higher hardness (~11.6GPa) than that in Nb weld metal (Fig. 1b), which is probably attributed to some Cu particles dispersed in. Cu solid solution presents an average hardness of 1.8GPa.
Fig. 1. (a)-(c) Microstructure in Nb weld metal; (d)-(f) Microstructure in Cu20Nb weld metal. BM: base metal; WM: weld metal. Table 1 Chemical compositions and hardness of various phases (at. %). Fe
Cu
Nb
Phases
Hardness /GPa
90.36
-
9.64
α-Fe+Fe2Nb
6.7
71.50
-
28.50
Fe2Nb
20.4
89.62
8.33
2.05
α-Fe
9.1
77.93
11.68
10.39
α-Fe+Fe2Nb
11.6
10.01
89.99
-
Cu
1.8
Fig. 2a shows TEM bright field image of Cu20Nb weld metal, associated with selected area diffraction (SAD) patterns. Cellular structures which are identified as Fe2Nb are randomly distributed in Fe-rich matrix (indexed as α-Fe). It should be noted 4
that these Fe2Nb structures formed by eutectic reaction present fine lamellar morphology under SEM observation (Fig. 1e). In addition, Cu solid solution (indicated by yellow arrow) is also identified with a dimeter of ~100nm. XRD phase identification is performed and the results are shown in Fig. 2b. Nb and Cu20Nb weld metals are mainly consisted of Fe2Nb+α-Fe and α-Fe+Fe2Nb+Cu compounds, respectively.
Fig. 2. (a) TEM bright field image of Cu20Nb weld metal; (b) XRD patterns. Due to the severe cracks in Nb weld, zero ultimate tensile strength (UTS) is revealed. Cu20Nb weld shows a high strength value (UTS~357MPa). It is most probably due to the phase improvement in Cu20Nb weld. In order to analyze the effect of Cu on microstructure and mechanical properties in the resulted weld metals, we break down the whole transformations into a number of stages, shown in Fig. 3. As presented in Fig. 1a-c, Nb weld metal exhibits heterogeneous distribution. The resultant weld metal could then be classified as Fe-rich and Nb-rich regions. At temperature between 2459℃ and 1373℃, cellular dendrites Fe2Nb form in the Nb-rich liquid (L↔LE+Fe2Nb), while dendrites δ-Fe form near Fe base metal (L↔LE+ δ-Fe) [3-4]. The GBs of Fe2Nb and δ-Fe phases are completely wetted by LE. With the temperature decreasing, the transition from complete to incomplete GB wetting occurs and contact angle (θ) increases gradually [10-11]. The property of GBs in solid+liquid
5
region determines the strength at Fe BM/Nb WM interface [12-13]. Below 1373℃, fine lamellar structures (α-Fe+Fe2Nb) form by eutectic reaction (LE↔δ-Fe+Fe2Nb). The residual liquid is then gradually depleted and hereafter some solid-state transformations form, i.e., δ-Fe↔γ-Fe+Fe2Nb at 1183℃ and γ-Fe+Fe2Nb↔α-Fe at 943℃ [3-4].
Fig. 3. Schematic diagrams showing the progression of phase transformations in Nb and Cu20Nb weld metals during the solidification. Compared with Nb weld metal, the composition and microstructure distribution in Cu20Nb present fairly uniform (Fig. 1d-f). The global concentration of Nb in weld metal falls into the hypoeutectic region [14]. During the molten cooling, pro-eutectic δ-Fe forms. The weld metal is then composed of dendrite δ-Fe phase and interdendritic liquid (LE+LCu) at 1538℃~1373℃ [3-4]. Similarly, eutectic reaction occurs at ~1337℃ and form fine lamellar structures. Seen from the lower right image, in the δ-Fe+LCu two phase region, the grain boundary transformation for the δ-Fe GBs wetting by LCu occurs. The GB wetting phase transition in δ-Fe+LCu two phase region is discontinuous, while that in δ-Fe+LE+Cu two phase region is continuous [10-11]. The residual LCu solidifies at ~1084℃ and forms Cu-rich islands. As the temperature drops, solid-state transformations form, which is similar to that in Nb weld metal.
6
It has been widely acknowledged that the mechanical integrity of the joint can be highly affected by the type, amount and distribution of the intermetallic phases [15]. Nanoindentation confirms the brittleness of Fe2Nb phase at ambient temperature. The cracking susceptibility of such phase is high enough when it forms in large scale [16-17]. With the addition of Cu, the main reaction in the weld metal is the hypoeutectic reaction which forms the fine lamellar structures (α-Fe+Fe2Nb). Such characteristic phase distribution could offer excellent mechanical properties [18]. 4. Conclusions This paper presented a study of the microstructure evolution and mechanical properties in Fe-Nb weld metals. Several points about the phase selection and solidification sequence in the weld metals have been suggested. The coarse cellular Fe2Nb phase with high hardness value (~20.4GPa) was dominant in Nb weld metal. The final phase constitution was modified when used the composite filler (Cu20Nb). The resulted weld metal was consisted of Fe, Cu solid solution phases and fine eutectic products (α-Fe~9.1GPa, Cu~1.8GPa, α-Fe+Fe2Nb~11.6GPa). Tensile test showed high strength value (~357MPa) in Cu20Nb weld metal. Acknowledgements This work was supported by Star-tup Found for Doctors of Xi’an University of Technology (101-451118006) and Australian Research Council Discovery Project (DP180102003). The data reported in this paper were obtained at the Central Analytical Research Facility (CARF) at the Institute for Future Environments (QUT).
7
References [1] W. Guo, G.Q. You, G.Y. Yuan, et al. J. Alloys Compd. 695 (2017) 3267-3277. [2] B. O'Brien, J. Stinson. J. Mech. Behav. Biomed. Mater. 1 (2008) 303-312. [3] H. Okamoto. J. Phase Equilib. 23 (2002) 112. [4] S. Voß, M. Palm, F. Stein, et al. J. Phase Equilib. 32 (2011) 97-104. [5] C.T. Liu, J.H. Zhu, M.P. Brady, et al. Intermetallics 8 (2000) 1119-1129. [6] I. Tomashchuk, D. Grevey, P. Sallamand. Mater. Sci. Eng. A 622 (2015) 37-45. [7] J.P. Bacher, E. Chiaveri, B. Trincat. CERN/EF/RF 7 (1987) 1-6. [8] I. Magnabosco, P. Ferro, F. Bonollo, et al. Mater. Sci. Eng. A 424 (2006) 163-173. [9] V. Raghavan. J. Phase Equilib. 23 (2002) 263-266. [10] S.G. Protasova, O.A. Kogtenkova, B.B. Straumal, et al. J. Mater. Sci. 46 (2011) 4349-4353. [11] A.A. Mazilkin, G.E. Abrosimova, et al. J. Mater. Sci. 46 (2011) 4336-4342. [12] B.B. Straumal, P. Zięba, W. Gust. Int. J. Inorg. Mater. 3 (2001) 1113-1115. [13] B.B. Straumal, A.S. Gornakova, O.A. Kogtenkova, et al. Phys. Rev. B 78, 054202 (2008). [14] S. Kou. Acta Mater. 88 (2015) 366-374. [15] T. Wang, B.G. Zhang, J.C. Feng, et al. Mater. Charac. 73 (2012) 104-113. [16] M.P. Sello, W.E. Stumpf. Mater. Sci. Eng. A 527 (2010) 5194-5202. [17] S. Kou. John Wiley and Sons, Hoboken, NJ, 2003. [18] Y. Yamamoto, M. Takeyama, Z.P. Lu, et al. Intermetallics 16 (2008) 453-462.
8
Highlights
Fe2Nb phase dominant in Nb weld had an average hardness of 20.4GPa. Final phase constitution was modified with the composite filler (Cu20Nb). Microstructure-mechanical properties relationship was developed by nanoindentation.
9
S0167-577X(18)31465-4 https://doi.org/10.1016/j.matlet.2018.09.086 MLBLUE 24954
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
28 August 2018 8 September 2018 16 September 2018
Please cite this article as: Q. Chu, M. Zhang, J. Li, F. Yan, C. Yan, Effect of Cu on microstructure evolution and mechanical properties of Fe-Nb dissimilar welds, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet. 2018.09.086
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of Cu on microstructure evolution and mechanical properties of Fe-Nb dissimilar welds Qiaoling Chuab*, Min Zhanga*, Jihong Lia, Fuxue Yan a, Cheng Yanb a College of Materials Science and Engineering, Xi’an University of Technology, Xi’an, 710048, China. b School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT), Brisbane, QLD 4001, Australia.
ABSTRACT In this paper, we report a thorough study of phase formation in Fe-Nb weld metals using a combination of microscopy and composition analysis. The correlation of microstructure and mechanical properties was established by nanoindentation. A simplified scenario of weld formation was proposed. Nb weld metal was dominated by the coarse Laves phase (Fe2Nb) with high hardness (~20.4GPa). With the addition of Cu, sound weld metal was obtained with alternative distribution of α-Fe, Cu phases and fine eutectic phases (α-Fe+Fe2Nb). These transformation products with lower hardness (α-Fe+Fe2Nb~11.6GPa) improved the overall mechanical properties of the weld metal. Keywords: Microstructure; Intermetallics; Phase transformation; Nanoindentation. 1. Introduction Welding of dissimilar materials is continuously attracting attention by the industry because of its potential benefits on increasing design flexibility and reducing cost [1]. Niobium (Nb) is a refractory metal which has many desirable properties that make them suitable for numerous engineering applications [2]. The Fe-Nb binary phase * Corresponding author: [email protected] (Dr. Qiaoling Chu), [email protected] (Prof. Min Zhang).
1
diagram denotes two intermetallic phases, namely the hexagonal C14-type Laves phase Fe2Nb and Fe7Nb6 [3-4]. Their significantly low ductility and brittle fracture characteristics limit the wide applications of Fe-Nb dissimilar joints [5]. Research studies demonstrate that such welds can be improved by addition of appropriate intermediate materials [6]. Bacher et al. [7] employed Cu as the braze filler to join Nb and AISI 316LN. Although some Fe-rich compounds formed at Nb/Cu interface, the resulted joints satisfied all the criteria for their application in ultra-high vacuum. The assumption of using Cu as intermediate is further supported by results that there are no intermetallics in Cu-Nb and Cu-Fe systems [8-9]. In this study, we attempt to improve the phase constitution in Fe-Nb weld metal via Cu intermediate. The relation between microstructure and mechanical properties was built by nanoindentation test. The phase formation mechanism in resultant weld metals was explained using a simplified model based on the phase diagrams. 2. Experimental procedures A commercial low alloy steel plate (0.2wt.% C, 0.35wt.% Si, 1.4%wt.% Mn) with the thickness of 2mm was butt welded with Nb filler (0.005wt.%C, 0.002wt.% Si, 0.001wt.% Cu, 0.0014wt.% Fe) using gas-tungsten arc welding. A composite filler (Cu20Nb, Nb~20wt.%) was developed to modify the final phase compositions in Nb weld metal. The microstructure and chemical compositions of the resultant welds were studied by SEM (JEOL-7001F) and TEM (JEOL-2100). Focused ion beam (FIB, FEI Quanta 200 3D dual beam) was used to prepare TEM samples. X-ray diffraction (XRD) patterns were collected using a Rigaku-binary diffractometer (Rigaku SmartLab) with a 2
Cu target. Nanoindentation was conducted using Berkovich indenter (Hysitron Triboindenter TL-950). An array of total 120 indents (60×2) was set for each weld metal. The measured hardness of each phase was averaged from at least ten indents. 3. Results and discussion Fig. 1a-c show the backscattered electron (BSE) images of microstructure in Nb weld metal. The compositions of typical phases determined from EDS analysis are listed in Table 1. Severe cracks are observed in Nb weld metal. Fig. 1a shows the microstructure at Fe-Nb interface, where coarse cellular structures (Fe2Nb) grow perpendicular to the interface and present dominant distribution in Nb weld metal. Fe-rich regions which incorporate eutectic phase (α-Fe+Fe2Nb) form between Fe2Nb cellular and Fe base metal, as shown in Fig. 1a and b. EBSD phase mapping in Fig. 1c confirms this characterized phase distribution. The coarse cellular structure has an average hardness of 20.4GPa, whereas eutectic compounds show lower hardness value (~6.7GPa). The low magnification image of Fe-Cu20Nb interface is shown in Fig. 1d. The resultant weld is free from cracks. Unlike Nb weld metal, homogeneous microstructure form in Cu20Nb weld metal. For Cu-Fe-Nb phase diagram, Fe2Nb phase has significant homogeneity ranges [9]. Together with the EDS results, Cu20Nb weld metal is primary composed of Fe solid solution, eutectic compounds (α-Fe+Fe2Nb) and Cu solid solution phase. The eutectic compounds with fine lamellar structures are distributed among the Fe solid solution, as displayed in Fig. 1e. Up to 8.33 at. % Cu is dissolved in Fe solid solution, as listed in Table 1. The EBSD phase mapping in Fig. 1f shows that Cu solid 3
solution (yellow) presents bulk and fine particle morphology in Cu20Nb weld metal. This characteristic distribution is similar to that presented in [10] where Zn individual particles precipitate along Al/Al grain boundaries (GBs). It is regarded as incompletely wetting of Al/Al GBs by Zn solid solution. Fe solid solution in Cu20Nb weld metal exhibits an average hardness of 9.1GPa. The eutectic compounds show higher hardness (~11.6GPa) than that in Nb weld metal (Fig. 1b), which is probably attributed to some Cu particles dispersed in. Cu solid solution presents an average hardness of 1.8GPa.
Fig. 1. (a)-(c) Microstructure in Nb weld metal; (d)-(f) Microstructure in Cu20Nb weld metal. BM: base metal; WM: weld metal. Table 1 Chemical compositions and hardness of various phases (at. %). Fe
Cu
Nb
Phases
Hardness /GPa
90.36
-
9.64
α-Fe+Fe2Nb
6.7
71.50
-
28.50
Fe2Nb
20.4
89.62
8.33
2.05
α-Fe
9.1
77.93
11.68
10.39
α-Fe+Fe2Nb
11.6
10.01
89.99
-
Cu
1.8
Fig. 2a shows TEM bright field image of Cu20Nb weld metal, associated with selected area diffraction (SAD) patterns. Cellular structures which are identified as Fe2Nb are randomly distributed in Fe-rich matrix (indexed as α-Fe). It should be noted 4
that these Fe2Nb structures formed by eutectic reaction present fine lamellar morphology under SEM observation (Fig. 1e). In addition, Cu solid solution (indicated by yellow arrow) is also identified with a dimeter of ~100nm. XRD phase identification is performed and the results are shown in Fig. 2b. Nb and Cu20Nb weld metals are mainly consisted of Fe2Nb+α-Fe and α-Fe+Fe2Nb+Cu compounds, respectively.
Fig. 2. (a) TEM bright field image of Cu20Nb weld metal; (b) XRD patterns. Due to the severe cracks in Nb weld, zero ultimate tensile strength (UTS) is revealed. Cu20Nb weld shows a high strength value (UTS~357MPa). It is most probably due to the phase improvement in Cu20Nb weld. In order to analyze the effect of Cu on microstructure and mechanical properties in the resulted weld metals, we break down the whole transformations into a number of stages, shown in Fig. 3. As presented in Fig. 1a-c, Nb weld metal exhibits heterogeneous distribution. The resultant weld metal could then be classified as Fe-rich and Nb-rich regions. At temperature between 2459℃ and 1373℃, cellular dendrites Fe2Nb form in the Nb-rich liquid (L↔LE+Fe2Nb), while dendrites δ-Fe form near Fe base metal (L↔LE+ δ-Fe) [3-4]. The GBs of Fe2Nb and δ-Fe phases are completely wetted by LE. With the temperature decreasing, the transition from complete to incomplete GB wetting occurs and contact angle (θ) increases gradually [10-11]. The property of GBs in solid+liquid
5
region determines the strength at Fe BM/Nb WM interface [12-13]. Below 1373℃, fine lamellar structures (α-Fe+Fe2Nb) form by eutectic reaction (LE↔δ-Fe+Fe2Nb). The residual liquid is then gradually depleted and hereafter some solid-state transformations form, i.e., δ-Fe↔γ-Fe+Fe2Nb at 1183℃ and γ-Fe+Fe2Nb↔α-Fe at 943℃ [3-4].
Fig. 3. Schematic diagrams showing the progression of phase transformations in Nb and Cu20Nb weld metals during the solidification. Compared with Nb weld metal, the composition and microstructure distribution in Cu20Nb present fairly uniform (Fig. 1d-f). The global concentration of Nb in weld metal falls into the hypoeutectic region [14]. During the molten cooling, pro-eutectic δ-Fe forms. The weld metal is then composed of dendrite δ-Fe phase and interdendritic liquid (LE+LCu) at 1538℃~1373℃ [3-4]. Similarly, eutectic reaction occurs at ~1337℃ and form fine lamellar structures. Seen from the lower right image, in the δ-Fe+LCu two phase region, the grain boundary transformation for the δ-Fe GBs wetting by LCu occurs. The GB wetting phase transition in δ-Fe+LCu two phase region is discontinuous, while that in δ-Fe+LE+Cu two phase region is continuous [10-11]. The residual LCu solidifies at ~1084℃ and forms Cu-rich islands. As the temperature drops, solid-state transformations form, which is similar to that in Nb weld metal.
6
It has been widely acknowledged that the mechanical integrity of the joint can be highly affected by the type, amount and distribution of the intermetallic phases [15]. Nanoindentation confirms the brittleness of Fe2Nb phase at ambient temperature. The cracking susceptibility of such phase is high enough when it forms in large scale [16-17]. With the addition of Cu, the main reaction in the weld metal is the hypoeutectic reaction which forms the fine lamellar structures (α-Fe+Fe2Nb). Such characteristic phase distribution could offer excellent mechanical properties [18]. 4. Conclusions This paper presented a study of the microstructure evolution and mechanical properties in Fe-Nb weld metals. Several points about the phase selection and solidification sequence in the weld metals have been suggested. The coarse cellular Fe2Nb phase with high hardness value (~20.4GPa) was dominant in Nb weld metal. The final phase constitution was modified when used the composite filler (Cu20Nb). The resulted weld metal was consisted of Fe, Cu solid solution phases and fine eutectic products (α-Fe~9.1GPa, Cu~1.8GPa, α-Fe+Fe2Nb~11.6GPa). Tensile test showed high strength value (~357MPa) in Cu20Nb weld metal. Acknowledgements This work was supported by Star-tup Found for Doctors of Xi’an University of Technology (101-451118006) and Australian Research Council Discovery Project (DP180102003). The data reported in this paper were obtained at the Central Analytical Research Facility (CARF) at the Institute for Future Environments (QUT).
7
References [1] W. Guo, G.Q. You, G.Y. Yuan, et al. J. Alloys Compd. 695 (2017) 3267-3277. [2] B. O'Brien, J. Stinson. J. Mech. Behav. Biomed. Mater. 1 (2008) 303-312. [3] H. Okamoto. J. Phase Equilib. 23 (2002) 112. [4] S. Voß, M. Palm, F. Stein, et al. J. Phase Equilib. 32 (2011) 97-104. [5] C.T. Liu, J.H. Zhu, M.P. Brady, et al. Intermetallics 8 (2000) 1119-1129. [6] I. Tomashchuk, D. Grevey, P. Sallamand. Mater. Sci. Eng. A 622 (2015) 37-45. [7] J.P. Bacher, E. Chiaveri, B. Trincat. CERN/EF/RF 7 (1987) 1-6. [8] I. Magnabosco, P. Ferro, F. Bonollo, et al. Mater. Sci. Eng. A 424 (2006) 163-173. [9] V. Raghavan. J. Phase Equilib. 23 (2002) 263-266. [10] S.G. Protasova, O.A. Kogtenkova, B.B. Straumal, et al. J. Mater. Sci. 46 (2011) 4349-4353. [11] A.A. Mazilkin, G.E. Abrosimova, et al. J. Mater. Sci. 46 (2011) 4336-4342. [12] B.B. Straumal, P. Zięba, W. Gust. Int. J. Inorg. Mater. 3 (2001) 1113-1115. [13] B.B. Straumal, A.S. Gornakova, O.A. Kogtenkova, et al. Phys. Rev. B 78, 054202 (2008). [14] S. Kou. Acta Mater. 88 (2015) 366-374. [15] T. Wang, B.G. Zhang, J.C. Feng, et al. Mater. Charac. 73 (2012) 104-113. [16] M.P. Sello, W.E. Stumpf. Mater. Sci. Eng. A 527 (2010) 5194-5202. [17] S. Kou. John Wiley and Sons, Hoboken, NJ, 2003. [18] Y. Yamamoto, M. Takeyama, Z.P. Lu, et al. Intermetallics 16 (2008) 453-462.
8
Highlights
Fe2Nb phase dominant in Nb weld had an average hardness of 20.4GPa. Final phase constitution was modified with the composite filler (Cu20Nb). Microstructure-mechanical properties relationship was developed by nanoindentation.
9