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Laser 3D printing of CoCrFeMnNi high-entropy alloy
Accepted Manuscript Laser 3D printing of CoCrFeMnNi high-entropy alloy Xiaoyu Gao, Yunzhuo Lu PII: DOI: Reference:
S0167-577X(18)31653-7 https://doi.org/10.1016/j.matlet.2018.10.084 MLBLUE 25126
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
7 September 2018 9 October 2018 14 October 2018
Please cite this article as: X. Gao, Y. Lu, Laser 3D printing of CoCrFeMnNi high-entropy alloy, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet.2018.10.084
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.
Laser 3D printing of CoCrFeMnNi high-entropy alloy Xiaoyu Gao, Yunzhuo Lu* School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028, China *E-mail address: [email protected] (Yunzhuo Lu)
Abstract: Due to their superior properties, high-entropy alloys (HEAs) are considered as novel structural materials that can substitute conventional alloys. From the viewpoint of future applications, it is important to explore methods for producing complex shaped and homogeneous HEAs. In this study, laser 3D printing technology is employed to fabricate CoCrFeMnNi HEA. The microstructure and mechanical properties of laser 3D printed HEA are also evaluated. An equiaxed-to-columnar transition structure can be observed in the melt pool of the printed sample. The fine BCC phase is found to distribute at the grain boundaries of the FCC matrix, which is the major phase of the printed sample. The printed HEA exhibits an outstanding combination of high strength and excellent ductility. Keywords: laser 3D printing; high-entropy alloy; microstructure; laser processing
1. Introduction High-entropy alloys (HEAs) are a new class of materials that are composed of five or more principal alloying elements in equimolar or near equimolar ratios[1, 2]. This unique alloy design derives the properties of HEAs from multiple principal elements with the potential for combinations of mechanical and physical properties compared with traditional alloys[3, 4]. HEAs are therefore advantageous in many excellent properties [5, 6], which endow HEAs a wide potential applications [7, 8]. However, the main challenge that hinders the practical applications of HEAs is the limitations of fabrication methods[9]. Recently, HEAs are generally synthesized by the arc-melting and casting process. This fabrication route is unlikely to present an industrially suitable way for the production and use of HEAs, since it is difficult to produce HEA component
with complex shape. More importantly, the low cooling rates (10-20 K/s) during the conventional casting of HEAs in a crucible would result in strong phase separation[10]. With this in mind, it would appear that the laser 3D printing technology, which facilitates complex-part production and generates rapid solidification cooling rates, may be suitable for the fabrication of HEAs[11-13]. The cooling rates achieved by method can generally reach the values on the order of 103-104 K/s[14]. In addition, laser 3D printing is a near-net shape manufacturing process, potentially ensuring the fabrication of HEA component with complex geometry[15]. In this study, a CoCrFeMnNi alloy is selected as the model material to investigate the microstructure and mechanical properties of laser 3D printed HEA. An equiaxed-to-columnar transition structure can be observed in the melt pool of the printed sample. The fine BCC phase is found to distribute at the grain boundaries of the FCC matrix, which is the major phase of the printed sample. The printed HEA exhibits an outstanding combination of high strength and excellent ductility. 2. Experimental Laser 3D printing of CoCrFeMnNi HEA was performed with coaxial powder feeding laser 3D printing system equipped with a 6000 W fiber laser. A schematic of this equipment is shown in Fig.1(a). The diameter of laser beam was 2 mm. The laser power was 300 W, and the travel speed of the laser beam relative to the substrate surface was 600 mm/min. The CoCrFeNiMn HEA powders with a size distribution ranging from 45 to 100 μm were used in the laser 3D printing process, as shown in Fig.1(b). The layer spacing in z direction during multi-layer deposition was set to 0.6 mm. Cubic bulk HEA sample with a dimension of 50mm× 40mm× 10mm for microstructural analysis and tensile coupons were manufactured, as shown in Fig.1(c). Tensile tests were performed at a constant tensile rate of 0.1 mm/min at room temperatures. The detailed microstructures were characterized using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectrum(EDS), electron backscattered diffraction (EBSD). 3. Results and discussion The XRD pattern of the printed CoCrFeNiMn HEA is shown in Fig. 2(a). The XRD pattern of the powder is also presented in this figure for comparison. All patterns revealed a fcc single phase, except for subtle changes in the texture, indicating that no phase transformation occurs during the printing processes, in good agreement with previous studies[16].
Figure 2(b) shows the side view OM image of the printed CoCrFeNiMn HEA at low magnification. The typical “fish scale” morphology of the melt pool is clearly visible in this figure. The melt pool marked by square shown in Fig. 2(b) at high magnification is presented in Fig. 2(c). Clearly, an equiaxed-to-columnar transition structure can be observed in the melt pool. The dendritic columnar structure grew perpendicular to the direction of the melt pool boundary, which is also the direction of the highest temperature gradient in the laser 3D printing process. This typical equiaxed-to-columnar transition microstructure can be confirmed by the EBSD IPF maps shown in Fig. 2(d). Here, [001] is designated as the reference direction for the inverse pole figure to code the color pattern, as indicated by the triangle (the inset in the upper-left corner). The different colors represent different grain growth orientations. The boundary of the melt pool shows equiaxed polygonal grains like the SEM observation, and the melt pool is composed of coarse directional solidified grains with the size of 30~150μm. The corresponding phase map of the region given in Fig. 2(d) is shown in Fig. 2(e). The second BCC solid phase, fine phase colored in blue, is found to precipitate separately between the grain boundaries (GBs) of the FCC matrix colored in red, i.e., the GBs of the FCC matrix in the printed high-entropy alloy are incompletely “wetted” by a second BCC solid phase. A variety of works, most notably by Straumal and coworkers, have revealed that the morphology of the second solid phase in the GB of the first solid phase is governed by the GB wetting phase transformations [17,18]. This incomplete GB wetting may originate from the low GB energy of grains in the FCC matrix, which is smaller than two times the GB energy of the interphase boundary between FCC and BCC [17-19]. Figure 3(a) shows the room-temperature tensile engineering stress-strain curve of the printed CoCrFeMnNi HEA. The printed HEA exhibits an excellent combination of strength and ductility, such as a high yield strength (σy) of 448 MPa and a high ultimate tensile strength (σUTS) of 620 MPa as well as a good uniform elongations to fracture (εf) of 57%. SEM image of the fracture surface shows ductile dimpled fracture (ductile transgranular), as shown in Fig.3 (b). Notably, the σUTS of the printed CoCrFeMnNi HEA is stronger than that of the as-cast alloy [20]. Moreover, the εf of the printed CoCrFeMnNi
HEA
is
comparative
to
that
of
the
as-cast
alloy.
The better comprehensive mechanical properties of the printed CoCrFeMnNi HEA is due to the synergistic effect of high cooling rate of laser processing and precipitation strengthening of BCC phase at grain boundary.
4. Conclusions In summary, a bulk CoCrFeMnNi HEA was successfully fabricated by laser 3D printing technology. An equiaxed-to-columnar transition structure can be observed in the melt pool of the printed sample. The dendritic columnar structure grew perpendicular to the direction of the melt pool boundary. The fine BCC phase distributed at the grain boundaries of the FCC matrix, which is the major phase of the printed CoCrFeMnNi HEA. The printed HEA exhibits an outstanding combination of high strength and excellent ductility. The σUTS of the printed CoCrFeMnNi HEA is stronger than that of the as-cast alloy. The εf of the printed CoCrFeMnNi HEA is comparative to that of the as-cast alloy.
Acknowledgments This work was supported by the National Natural Science Foundation of China under Grant Nos. 51671042, 51401041, 51671043 and the Liaoning Natural Science Foundation under Grant No. 201602126. References [1] J.W. Yeh, S.K. Chen, S.J. Lin, J.Y. Gan, T.S. Chin, T.T. Shun, C.H. Tsau, S.Y. Chang, Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes, Adv. Eng. Mater. 6(5) (2004) 299-303. [2] K.S. Lee, B. Bae, J. Kang, K.R. Lim, Y.S. Na, Multi-phase refining of an AlCoCrFeNi high entropy alloy by hot compression, Mater. Lett. (2017). [3] Y. Zhang, T.T. Zuo, Z. Tang, M.C. Gao, K.A. Dahmen, P.K. Liaw, Z.P. Lu, Microstructures and properties of high-entropy alloys, Prog. Mater Sci. 61(8) (2014) 1-93. [4] Y.J. Zhou, Y. Zhang, Y.L. Wang, G.L. Chen, Solid solution alloys of AlCoCrFeNiTix with excellent room-temperature mechanical properties, Appl. Phys. Lett. 90(18) (2007) 253. [5] X.F. Wang, Y. Zhang, Y. Qiao, G.L. Chen, Novel microstructure and properties of multicomponent CoCrCuFeNiTix alloys, Intermetallics 15(3) (2007) 357-362. [6] L. Zhang, D. Zhou, B. Li, Anomalous microstructure and excellent mechanical properties of Ni35Al21.67Cr21.67Fe21.67 high-entropy alloy with BCC and B2 structure, Mater. Lett. 216 (2018) 252-255. [7] J.W. Yeh, Recent progress in high-entropy alloys, European Journal of Control 31(6) (2006) 633-648. [8] D.B. Miracle, O.N. Senkov, A critical review of high entropy alloys and related concepts, Acta Mater. 122 (2017) 448-511. [9] H.Y. Diao, R. Feng, K.A. Dahmen, P.K. Liaw, Fundamental deformation behavior in high-entropy alloys: An overview, Curr. Opin. Solid State Mater. Sci. 21(5) (2017). [10] I. Kunce, M. Polanski, K. Karczewski, T. Plocinski, K.J. Kurzydlowski, Microstructural characterisation of high-entropy alloy AlCoCrFeNi fabricated by laser engineered net shaping, J. Alloys Compd. 648 (2015) 751-758.
[11] I. Kunce, M. Polanski, J. Bystrzycki, Structure and hydrogen storage properties of a high entropy ZrTiVCrFeNi alloy synthesized using Laser Engineered Net Shaping (LENS), Int. J. Hydrogen Energy 38(27) (2013) 12180-12189. [12] H. Shiratori, T. Fujieda, K. Yamanaka, Y. Koizumi, K. Kuwabara, T. Kato, A. Chiba, Relationship between the microstructure and mechanical properties of an equiatomic AlCoCrFeNi high-entropy alloy fabricated by selective electron beam melting, Mater. Sci. Eng., A 656 (2016) 39-46. [13] T. Fujieda, H. Shiratori, K. Kuwabara, M. Hirota, T. Kato, K. Yamanaka, Y. Koizumi, A. Chiba, S. Watanabe, CoCrFeNiTi-based high-entropy alloy with superior tensile strength and corrosion resistance achieved by a combination of additive manufacturing using selective electron beam melting and solution treatment, Mater. Lett. (2016). [14] J. Li, X. Cheng, D. Liu, S.Q. Zhang, Z. Li, B. He, H.M. Wang, Phase evolution of a heat-treatable aluminum alloy during laser additive manufacturing, Mater. Lett. 214 (2018) 56-59. [15] Z. Liu, W. Zhou, Y. Lu, H. Xu, Z. Qin, X. Lu, Laser 3D printing of W-Cu composite, Mater. Lett. (2018). [16] M. Laurent-Brocq, A. Akhatova, L. Perrière, S. Chebini, X. Sauvage, E. Leroy, Y. Champion, Insights into the phase diagram of the CrMnFeCoNi high entropy alloy, Acta Mater. 88 (2015) 355-365. [17] B.B. Straumal, A.S. Gornakova, Y.O. Kucheev, B. Baretzky, A.N. Nekrasov, Grain boundary wetting by a second solid phase in the Zr-Nb alloys, J. Mater. Eng. Perform. 21 (2012) 721-724. [18] B.B. Straumal, A.S. Gornakova, O.A. Kogtenkova, S.G. Protasova, V.G. Sursaeva, B. Baretzky, Continuous and discontinuous grain-boundary wetting in ZnxAl1−x, Phys. Rev. B 78 (2008) 054202. [19] G.A. López, E.J. Mittemeijer, B.B. Straumal, Grain boundary wetting by a solid phase; microstructural development in a Zn–5 wt% Al alloy, Acta Mater. 52 (2004) 4537-4545. [20] J.Y. He, W.H. Liu, H. Wang, Y. Wu, X.J. Liu, T.G. Nieh, Z.P. Lu, Effects of Al addition on structural evolution and tensile properties of the FeCoNiCrMn high-entropy alloy system, Acta Mater. 62 (2014) 105-113.
Figure captions Figure 1 (a) A schematic of coaxial powder feeding laser 3D printing system equipped with a 6000 W fiber laser. (b) SEM morphologies of CoCrFeMnNi HEA powders. (c) The outer appearance image of the printed bulk CoCrFeMnNi HEA sample with a dimension of 50mm× 40mm× 10mm. Figure 2 (a) XRD patterns of the printed CoCrFeNiMn HEA and powders. (b) The side view OM image of the printed CoCrFeNiMn HEA at low magnification. (c) Highly magnified SEM image of the melt pool marked by square shown in (b). (d) Typical EBSD IPF maps of the printed CoCrFeNiMn HEA. (e) The corresponding phase map of the region given in (d). Figure 3 (a) Room-temperature tensile engineering stress-strain curve of the printed CoCrFeMnNi HEA. (b) SEM image of the fracture surface shows ductile dimpled fracture (ductile transgranular).
Fig.1
Fig.2
Fig.3
Highlights 1. Laser 3D printing technology is employed to fabricate CoCrFeMnNi HEA. 2. Fine BCC phase is found to distribute at the grain boundaries of the FCC matrix. 3. Printed HEA exhibits an outstanding combination of high strength and ductility.
S0167-577X(18)31653-7 https://doi.org/10.1016/j.matlet.2018.10.084 MLBLUE 25126
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
7 September 2018 9 October 2018 14 October 2018
Please cite this article as: X. Gao, Y. Lu, Laser 3D printing of CoCrFeMnNi high-entropy alloy, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet.2018.10.084
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.
Laser 3D printing of CoCrFeMnNi high-entropy alloy Xiaoyu Gao, Yunzhuo Lu* School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028, China *E-mail address: [email protected] (Yunzhuo Lu)
Abstract: Due to their superior properties, high-entropy alloys (HEAs) are considered as novel structural materials that can substitute conventional alloys. From the viewpoint of future applications, it is important to explore methods for producing complex shaped and homogeneous HEAs. In this study, laser 3D printing technology is employed to fabricate CoCrFeMnNi HEA. The microstructure and mechanical properties of laser 3D printed HEA are also evaluated. An equiaxed-to-columnar transition structure can be observed in the melt pool of the printed sample. The fine BCC phase is found to distribute at the grain boundaries of the FCC matrix, which is the major phase of the printed sample. The printed HEA exhibits an outstanding combination of high strength and excellent ductility. Keywords: laser 3D printing; high-entropy alloy; microstructure; laser processing
1. Introduction High-entropy alloys (HEAs) are a new class of materials that are composed of five or more principal alloying elements in equimolar or near equimolar ratios[1, 2]. This unique alloy design derives the properties of HEAs from multiple principal elements with the potential for combinations of mechanical and physical properties compared with traditional alloys[3, 4]. HEAs are therefore advantageous in many excellent properties [5, 6], which endow HEAs a wide potential applications [7, 8]. However, the main challenge that hinders the practical applications of HEAs is the limitations of fabrication methods[9]. Recently, HEAs are generally synthesized by the arc-melting and casting process. This fabrication route is unlikely to present an industrially suitable way for the production and use of HEAs, since it is difficult to produce HEA component
with complex shape. More importantly, the low cooling rates (10-20 K/s) during the conventional casting of HEAs in a crucible would result in strong phase separation[10]. With this in mind, it would appear that the laser 3D printing technology, which facilitates complex-part production and generates rapid solidification cooling rates, may be suitable for the fabrication of HEAs[11-13]. The cooling rates achieved by method can generally reach the values on the order of 103-104 K/s[14]. In addition, laser 3D printing is a near-net shape manufacturing process, potentially ensuring the fabrication of HEA component with complex geometry[15]. In this study, a CoCrFeMnNi alloy is selected as the model material to investigate the microstructure and mechanical properties of laser 3D printed HEA. An equiaxed-to-columnar transition structure can be observed in the melt pool of the printed sample. The fine BCC phase is found to distribute at the grain boundaries of the FCC matrix, which is the major phase of the printed sample. The printed HEA exhibits an outstanding combination of high strength and excellent ductility. 2. Experimental Laser 3D printing of CoCrFeMnNi HEA was performed with coaxial powder feeding laser 3D printing system equipped with a 6000 W fiber laser. A schematic of this equipment is shown in Fig.1(a). The diameter of laser beam was 2 mm. The laser power was 300 W, and the travel speed of the laser beam relative to the substrate surface was 600 mm/min. The CoCrFeNiMn HEA powders with a size distribution ranging from 45 to 100 μm were used in the laser 3D printing process, as shown in Fig.1(b). The layer spacing in z direction during multi-layer deposition was set to 0.6 mm. Cubic bulk HEA sample with a dimension of 50mm× 40mm× 10mm for microstructural analysis and tensile coupons were manufactured, as shown in Fig.1(c). Tensile tests were performed at a constant tensile rate of 0.1 mm/min at room temperatures. The detailed microstructures were characterized using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectrum(EDS), electron backscattered diffraction (EBSD). 3. Results and discussion The XRD pattern of the printed CoCrFeNiMn HEA is shown in Fig. 2(a). The XRD pattern of the powder is also presented in this figure for comparison. All patterns revealed a fcc single phase, except for subtle changes in the texture, indicating that no phase transformation occurs during the printing processes, in good agreement with previous studies[16].
Figure 2(b) shows the side view OM image of the printed CoCrFeNiMn HEA at low magnification. The typical “fish scale” morphology of the melt pool is clearly visible in this figure. The melt pool marked by square shown in Fig. 2(b) at high magnification is presented in Fig. 2(c). Clearly, an equiaxed-to-columnar transition structure can be observed in the melt pool. The dendritic columnar structure grew perpendicular to the direction of the melt pool boundary, which is also the direction of the highest temperature gradient in the laser 3D printing process. This typical equiaxed-to-columnar transition microstructure can be confirmed by the EBSD IPF maps shown in Fig. 2(d). Here, [001] is designated as the reference direction for the inverse pole figure to code the color pattern, as indicated by the triangle (the inset in the upper-left corner). The different colors represent different grain growth orientations. The boundary of the melt pool shows equiaxed polygonal grains like the SEM observation, and the melt pool is composed of coarse directional solidified grains with the size of 30~150μm. The corresponding phase map of the region given in Fig. 2(d) is shown in Fig. 2(e). The second BCC solid phase, fine phase colored in blue, is found to precipitate separately between the grain boundaries (GBs) of the FCC matrix colored in red, i.e., the GBs of the FCC matrix in the printed high-entropy alloy are incompletely “wetted” by a second BCC solid phase. A variety of works, most notably by Straumal and coworkers, have revealed that the morphology of the second solid phase in the GB of the first solid phase is governed by the GB wetting phase transformations [17,18]. This incomplete GB wetting may originate from the low GB energy of grains in the FCC matrix, which is smaller than two times the GB energy of the interphase boundary between FCC and BCC [17-19]. Figure 3(a) shows the room-temperature tensile engineering stress-strain curve of the printed CoCrFeMnNi HEA. The printed HEA exhibits an excellent combination of strength and ductility, such as a high yield strength (σy) of 448 MPa and a high ultimate tensile strength (σUTS) of 620 MPa as well as a good uniform elongations to fracture (εf) of 57%. SEM image of the fracture surface shows ductile dimpled fracture (ductile transgranular), as shown in Fig.3 (b). Notably, the σUTS of the printed CoCrFeMnNi HEA is stronger than that of the as-cast alloy [20]. Moreover, the εf of the printed CoCrFeMnNi
HEA
is
comparative
to
that
of
the
as-cast
alloy.
The better comprehensive mechanical properties of the printed CoCrFeMnNi HEA is due to the synergistic effect of high cooling rate of laser processing and precipitation strengthening of BCC phase at grain boundary.
4. Conclusions In summary, a bulk CoCrFeMnNi HEA was successfully fabricated by laser 3D printing technology. An equiaxed-to-columnar transition structure can be observed in the melt pool of the printed sample. The dendritic columnar structure grew perpendicular to the direction of the melt pool boundary. The fine BCC phase distributed at the grain boundaries of the FCC matrix, which is the major phase of the printed CoCrFeMnNi HEA. The printed HEA exhibits an outstanding combination of high strength and excellent ductility. The σUTS of the printed CoCrFeMnNi HEA is stronger than that of the as-cast alloy. The εf of the printed CoCrFeMnNi HEA is comparative to that of the as-cast alloy.
Acknowledgments This work was supported by the National Natural Science Foundation of China under Grant Nos. 51671042, 51401041, 51671043 and the Liaoning Natural Science Foundation under Grant No. 201602126. References [1] J.W. Yeh, S.K. Chen, S.J. Lin, J.Y. Gan, T.S. Chin, T.T. Shun, C.H. Tsau, S.Y. Chang, Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes, Adv. Eng. Mater. 6(5) (2004) 299-303. [2] K.S. Lee, B. Bae, J. Kang, K.R. Lim, Y.S. Na, Multi-phase refining of an AlCoCrFeNi high entropy alloy by hot compression, Mater. Lett. (2017). [3] Y. Zhang, T.T. Zuo, Z. Tang, M.C. Gao, K.A. Dahmen, P.K. Liaw, Z.P. Lu, Microstructures and properties of high-entropy alloys, Prog. Mater Sci. 61(8) (2014) 1-93. [4] Y.J. Zhou, Y. Zhang, Y.L. Wang, G.L. Chen, Solid solution alloys of AlCoCrFeNiTix with excellent room-temperature mechanical properties, Appl. Phys. Lett. 90(18) (2007) 253. [5] X.F. Wang, Y. Zhang, Y. Qiao, G.L. Chen, Novel microstructure and properties of multicomponent CoCrCuFeNiTix alloys, Intermetallics 15(3) (2007) 357-362. [6] L. Zhang, D. Zhou, B. Li, Anomalous microstructure and excellent mechanical properties of Ni35Al21.67Cr21.67Fe21.67 high-entropy alloy with BCC and B2 structure, Mater. Lett. 216 (2018) 252-255. [7] J.W. Yeh, Recent progress in high-entropy alloys, European Journal of Control 31(6) (2006) 633-648. [8] D.B. Miracle, O.N. Senkov, A critical review of high entropy alloys and related concepts, Acta Mater. 122 (2017) 448-511. [9] H.Y. Diao, R. Feng, K.A. Dahmen, P.K. Liaw, Fundamental deformation behavior in high-entropy alloys: An overview, Curr. Opin. Solid State Mater. Sci. 21(5) (2017). [10] I. Kunce, M. Polanski, K. Karczewski, T. Plocinski, K.J. Kurzydlowski, Microstructural characterisation of high-entropy alloy AlCoCrFeNi fabricated by laser engineered net shaping, J. Alloys Compd. 648 (2015) 751-758.
[11] I. Kunce, M. Polanski, J. Bystrzycki, Structure and hydrogen storage properties of a high entropy ZrTiVCrFeNi alloy synthesized using Laser Engineered Net Shaping (LENS), Int. J. Hydrogen Energy 38(27) (2013) 12180-12189. [12] H. Shiratori, T. Fujieda, K. Yamanaka, Y. Koizumi, K. Kuwabara, T. Kato, A. Chiba, Relationship between the microstructure and mechanical properties of an equiatomic AlCoCrFeNi high-entropy alloy fabricated by selective electron beam melting, Mater. Sci. Eng., A 656 (2016) 39-46. [13] T. Fujieda, H. Shiratori, K. Kuwabara, M. Hirota, T. Kato, K. Yamanaka, Y. Koizumi, A. Chiba, S. Watanabe, CoCrFeNiTi-based high-entropy alloy with superior tensile strength and corrosion resistance achieved by a combination of additive manufacturing using selective electron beam melting and solution treatment, Mater. Lett. (2016). [14] J. Li, X. Cheng, D. Liu, S.Q. Zhang, Z. Li, B. He, H.M. Wang, Phase evolution of a heat-treatable aluminum alloy during laser additive manufacturing, Mater. Lett. 214 (2018) 56-59. [15] Z. Liu, W. Zhou, Y. Lu, H. Xu, Z. Qin, X. Lu, Laser 3D printing of W-Cu composite, Mater. Lett. (2018). [16] M. Laurent-Brocq, A. Akhatova, L. Perrière, S. Chebini, X. Sauvage, E. Leroy, Y. Champion, Insights into the phase diagram of the CrMnFeCoNi high entropy alloy, Acta Mater. 88 (2015) 355-365. [17] B.B. Straumal, A.S. Gornakova, Y.O. Kucheev, B. Baretzky, A.N. Nekrasov, Grain boundary wetting by a second solid phase in the Zr-Nb alloys, J. Mater. Eng. Perform. 21 (2012) 721-724. [18] B.B. Straumal, A.S. Gornakova, O.A. Kogtenkova, S.G. Protasova, V.G. Sursaeva, B. Baretzky, Continuous and discontinuous grain-boundary wetting in ZnxAl1−x, Phys. Rev. B 78 (2008) 054202. [19] G.A. López, E.J. Mittemeijer, B.B. Straumal, Grain boundary wetting by a solid phase; microstructural development in a Zn–5 wt% Al alloy, Acta Mater. 52 (2004) 4537-4545. [20] J.Y. He, W.H. Liu, H. Wang, Y. Wu, X.J. Liu, T.G. Nieh, Z.P. Lu, Effects of Al addition on structural evolution and tensile properties of the FeCoNiCrMn high-entropy alloy system, Acta Mater. 62 (2014) 105-113.
Figure captions Figure 1 (a) A schematic of coaxial powder feeding laser 3D printing system equipped with a 6000 W fiber laser. (b) SEM morphologies of CoCrFeMnNi HEA powders. (c) The outer appearance image of the printed bulk CoCrFeMnNi HEA sample with a dimension of 50mm× 40mm× 10mm. Figure 2 (a) XRD patterns of the printed CoCrFeNiMn HEA and powders. (b) The side view OM image of the printed CoCrFeNiMn HEA at low magnification. (c) Highly magnified SEM image of the melt pool marked by square shown in (b). (d) Typical EBSD IPF maps of the printed CoCrFeNiMn HEA. (e) The corresponding phase map of the region given in (d). Figure 3 (a) Room-temperature tensile engineering stress-strain curve of the printed CoCrFeMnNi HEA. (b) SEM image of the fracture surface shows ductile dimpled fracture (ductile transgranular).
Fig.1
Fig.2
Fig.3
Highlights 1. Laser 3D printing technology is employed to fabricate CoCrFeMnNi HEA. 2. Fine BCC phase is found to distribute at the grain boundaries of the FCC matrix. 3. Printed HEA exhibits an outstanding combination of high strength and ductility.