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Microstructure and properties of high strength and high conductivity Cu-Cr alloy components fabricated by high power selective laser melting
Materials Letters 237 (2019) 306–309
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Microstructure and properties of high strength and high conductivity Cu-Cr alloy components fabricated by high power selective laser melting Shasha Zhang a, Haihong Zhu a,⇑, Luo Zhang a, Wenqi Zhang a, Huanqing Yang b, Xiaoyan Zeng a a b
Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China XI’AN Space Engine Company Limited, Xi’An 710100, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 17 October 2018 Received in revised form 11 November 2018 Accepted 20 November 2018 Available online 20 November 2018 Keywords: Cu-Cr alloy Laser processing Microstructure Mechanical properties Electronic conductivity
a b s t r a c t Although different kinds of metal materials have been built in the past years, it is difficult to fabricate the components of copper alloys with high strength and high conductivity due to their high reflectivity and thermal conductivity. In this paper, Cu-Cr alloy with high strength and high conductivity was successfully manufactured by high laser power selective laser melting. The microstructure, mechanical properties and conductivity were studied and compared before and after the heat treatment. The microstructure of the as-built sample was columnar grains with very fine cellular sub-structures and precipitates of Cr and Cr2O3. After heat treatment, the Cr particles precipitated from Cu matrix, resulting in simultaneous increase in strength and conductivity. The ultimate tensile strength of 468 MPa, yield strength of 377.33 MPa, and electrical conductivity of 98.31% IACS were achieved, which is even better than the samples fabricated by rolling with post heat treatment. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Copper and its alloys are widely used in the mechanical, power and petrochemical industries due to their excellent electrical and thermal conductivities, outstanding resistance to corrosion, ease of fabrication, good strength, and fatigue resistance [1]. Cu-Cr alloys are attractive candidates for aerospace and nuclear industry because they possess an excellent combination of mechanical strength and electrical or thermal conductivity [2]. At present, the Cu-Cr alloy parts are mainly manufactured by casting or forging. However, it is difficult to manufacture by welding, which makes it difficult to manufacture complex copper alloy parts, in particular with internal flow channels. Selective laser melting (SLM) can directly produce complexshaped metal parts with a near full density, high performance and accuracy, and has built different kinds of metallic components in the past years [3–5]. Copper alloys are difficult to process by SLM due to the high thermal conductivity and poor laser absorption. Researches on SLM copper alloy are mainly focused on Cu-Sn alloys [6], Cu-Al-Ni-Mn alloys [7] and Cu-Ni-Si alloys [8]. Usually, the thermal and electrical conductivities of the copper alloys decrease compared to pure copper due to the addition of other elements, which makes it easy to fabricate the copper alloy ⇑ Corresponding author. E-mail address: [email protected] (H. Zhu). https://doi.org/10.1016/j.matlet.2018.11.118 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
components. However, high strength and high conductivity Cu-Cr alloys contain very little Cr element, and hence have poor laser absorption and high thermal conductivity. Therefore, Cu-Cr alloy is very difficult to obtain high density and performance directly by using the conventional SLM equipment with the maximum laser power of 500 W or less. For instance, A. Popovich et al. [9] produced Cu-Cr-Zr-Ti alloy by SLM using the laser power of 400 W, but the relative density is only 97.9%, which can not meet the demands for industrial applications for most cases. In this paper, the Cu-Cr alloy QCr0.8 was firstly formed by SLM using the high laser power up to 2000 W. The microstructures and properties were studied before and after the heat treatment.
2. Experimetals Gas atomized Cu-Cr alloy QCr0.8 powders with a spherical shape were chosen as the starting material. The chemical composition of the powder is Cu-0.5Cr (wt%). A self-developed SLM equipment was used to manufacture QCr0.8 samples. It is mainly equipped with a continuous wave IPG YLR-2000 fiber laser (wavelength 1.07 lm; maximum output power of 2000 W). The samples with the relative density of 99.98% were produced by the optimized processing parameters (laser power 2000 W, scanning velocity 600 mm/s, hatching space 0.2 mm and layer thickness 0.05 mm).
S. Zhang et al. / Materials Letters 237 (2019) 306–309
The post heat treatment condition of the samples is annealing at 480 °C for 4 h followed by furnace cooling. The microstructure of the samples was characterized by an optical microscopy (Nikon EPIPHOT 300), a scanning electron microscope (SEM, FEI Nova NanoSEM 450) and a transmission electron microscope (TEM, FEI Tecnai-G2-F30). Phase structure was tested by the X-ray diffraction meter (PANalytical X’pert PRO). The grain size was analyzed by electron backscatter diffraction (EBSD). The microhardness was tested using a HVS-1000 microhardness tester. The tensile properties at room temperature were examined using the Zwick/Roell tester. Three specimens were measured for each experiment. The electrical resistances were taken using the CHT3540-1 DC resistance tester.
307
3. Results and discussion Fig. 1a, b present the optical micrographs of the as-built sample. The relative density of the sample is 99.98%. The molten pools can be seen on vertical section with the columnar grains growing along the building direction. The cellular sub-structures with a size smaller than 1 lm can be observed in Fig. 1d. The cells grow towards the center of the molten pool. The microstructure of the annealed sample has almost no change at all compared to the as-built sample (Fig. 1e). However, the precipitates of Cr particles can be observed in the high magnification image (Fig. 1f), which indicates that the Cr particles precipitated from Cu matrix during annealing treatment.
Fig. 1. Optical micrographs of the as-built sample on (a) vertical section and (b) horizontal section, SEM images of the (c) (d) as-built sample on vertical section and (e) (f) annealed sample on vertical section.
308
S. Zhang et al. / Materials Letters 237 (2019) 306–309
The results of the phase analysis of the powder, as-built and annealed samples are shown in Fig. 2. The main phase observed in these samples is a-Cu. No clear phase of Cr can be found in all the samples. The main reason may be that the total content of Cr in the materials is only 0.5 wt%, which is beyond the precipitated phase detection limit of XRD instrument restriction. Besides, the diffraction peaks of the as-built samples shift to low diffraction angles compared with the powder, indicating that the lattice constant of the SLMed samples increases. It can be asserted that Cr was dissolved in the a-Cu matrix of the as-built samples attributing to the high cooling rate during SLM. Compared with the as-built samples, the diffraction peaks of the annealed sample shift to high diffraction angles, implying that the lattice constant decreases, which further indicates that the Cr particles precipitated from Cu matrix during annealing treatment.
TEM was used to further confirm the microstructure and phase composition of the as-built sample. Fig. 3 depicts TEM micrographs of the as-built sample. Many precipitates with the average size of 30 nm and dislocations are observed in the bright field image (Fig. 3a, b). The precipitates consist of spherical and diamond particles. Fig. 3c and d show the typical precipitates in the matrix, which is confirmed by the fast Fourier transformation (FFT) image. The spherical precipitate is consistent with the Cr phase. This result agrees with the previous work, in which the spherical precipitates can be observed in the Cu–Cr samples prepared by severe plastic deformation [10]. The diamond particles is consistent with the Cr2O3 phase, which is caused by the oxidation of the powder during SLM. Cr atoms are more oxygenated than Cu atoms in the solidification process, resulting in formation of Cr2O3 phase.
Fig. 2. XRD patterns of the powder, as-built and annealed samples.
Fig. 3. TEM micrographs of the as-built sample. (a) and (b) bright field images; (c) and (d) HRTEM images of the precipitates and the inset shows the FFT image.
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S. Zhang et al. / Materials Letters 237 (2019) 306–309 Table 1 Properties of as-built samples, annealed samples and heat treated samples after rolling.
As-built Annealed Rolled + heat treated [12]
Microhardness/HV
UTS/MPa
r0.2/MPa
EL/%
Conductivity/%I ACS
84.19 138.77 110.2
234.67 ± 3.70 468.00 ± 2.96 451
173.94 ± 1.18 377.33 ± 1.59 383
26.02 ± 0.46 19.20 ± 0.58 22.1
37.78 98.31 78.6
Table 1 shows the properties of as-built and annealed samples. After heat treatment, the microhardness of 138.77 HV, ultimate tensile strength (UTS) of 468 MPa, yield strength (r0.2) of 377.33 MPa, elongation (EL) of 19.20% and electrical conductivity of 98.31%IACS are achieved. The higher strength and electrical conductivity are achieved compared with that of the as-built samples. Especially, the annealed samples have higher strength and electrical conductivity compared with heat treated samples after rolling. The strength improvement after heat treatment attributes generally to the grain size of Cu matrix and second phase precipitations. The average grain size of as-built sample is 21.85 lm, and that of annealed sample is 21.49 lm. It indicated that the change of grain size has little effect on the strength improvement. The precipitates is coherent with Cu matrix as shown in Fig. 3. The estimated maximum increment of the shear stress by coherent precipitation is written as [2]:
Dscsmax ¼ 1:84Gef
1=2
ð1Þ
where G is the shear modulus, e is the function of the degree of misfit, and f is the volume fraction of the precipitate. The increment of maximum yield strength contributed is obtained as
Drcsmax ¼ M Dscsmax
ð2Þ
where M is the Taylor factor. By inserting the related parameters (M ¼ 3:06, G ¼ 42:1GPa, e ¼ 0:015) into Equation (1) and (2), the increment of maximum strength contributed by coherent precipitates is obtained as:
Drcsmax ¼ 3556f
1=2
ð3Þ
The increment of r0.2 after heat treatment is calculated by the following equations:
Dr0:2 ¼ Drcsmax;annealed Drcsmax;SLM
ð4Þ
where Drcsmax;annealed is the increment of maximum strength after heat treatment, Drcsmax;SLM is that of as-built sample. The volume fraction of the precipitates of as-built sample is 0.05%, while that of the annealed sample is 0.58%, which were measured by image-pro plus soft. The increment of r0.2 after heat treatment is 191.30 MPa by calculating. It is very close to the increment of r0.2 203.39 MPa obtained in this work. The strength improvement after heat treatment attributes mainly to the Cr precipitation from Cu matrix. The electrical conductivity of as-built sample is only 37.78% IACS due to the supersaturated solid solution of Cr in Cu matrix. The solute Cr atoms in the copper matrix act as impurity centers
for the scattering of electron motions and thus deteriorate the electrical conductivity significantly [11]. After heat treatment, the electrical conductivity rapidly increases to 98.31% IACS because the supersaturated Cu-Cr alloy decomposed and the Cr particles were precipitated from Cu matrix. 4. Conclusions The high mechanical properties and high conductivity QCr0.8 copper alloy components were successfully fabricated by high power SLM. The microstructure and properties have been analyzed. The microstructure of the as-built sample consists of columnar grains with very fine cellular sub-structures and precipitates. After heat treatment, the Cr particles precipitated from Cu matrix. UTS of 468 MPa, yield strength of 377.33 MPa, elongation of 19.20% and electrical conductivity of 98.31% IACS are achieved. The properties of annealed samples improve significantly compared with the as-built samples, which are even better than the samples fabricated by rolling with post heat treatment. Acknowledgement This work is supported by the Direct Fund of WNLO, the Fundamental Research Funds for the Central Universities through program (HUST: 2016XYZD005), and human spaceflight program of China (D050302). The authors would also like to thank the Analytical and Testing Center of HUST for the XRD, SEM and FTEM analysis. References [1] G.H.A. Bagheri, J. Alloy Compd. 676 (2016) 120–126. [2] J.B. Correia, H.A. Davies, C.M. Sellars, Acta Mater. 45 (1997) 177–190. [3] L. Zhang, S. Zhang, H. Zhu, Z. Hu, G. Wang, X. Zeng, Mater. Des. 160 (2018) 9– 20. [4] T. Qi, H. Zhu, H. Zhang, J. Yin, L. Ke, X. Zeng, Mater. Des. 135 (2017) 257–266. [5] T. Trosch, J. Strößner, R. Völkl, U. Glatzel, Mater. Lett. 164 (2016) 428–431. [6] S. Scudino, C. Unterd Rfer, K.G. Prashanth, H. Attar, N. Ellendt, V. Uhlenwinkel, J. Eckert, Mater. Lett. 156 (2015) 202–204. [7] T. Gustmann, A. Neves, U. Kühn, P. Gargarella, C.S. Kiminami, C. Bolfarini, J. Eckert, S. Pauly, Addit. Manuf. 11 (2016) 23–31. [8] Y. Zhou, X. Zeng, Z. Yang, H. Wu, J. Alloy Compd. 743 (2018) 258–261. [9] A. Popovich, V. Sufiiarov, I. Polozov, E. Borisov, D. Masaylo, A. Orlov, Mater. Lett. 179 (2016) 38–41. [10] S.V. Dobatkin, J. Gubicza, D.V. Shangina, N.R. Bochvar, N.Y. Tabachkova, Mater. Lett. 153 (2015) 5–9. [11] S. Zhang, R. Li, H. Kang, Z. Chen, W. Wang, C. Zou, T. Li, T. Wang, Mater. Sci. Eng. A 680 (2017) 108–114. [12] C.Z. Xu, Q.J. Wang, M.S. Zheng, J.W. Zhu, J.D. Li, M.Q. Huang, Q.M. Jia, Z.Z. Du, Mater. Sci. Eng. A 459 (2007) 303–308.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Microstructure and properties of high strength and high conductivity Cu-Cr alloy components fabricated by high power selective laser melting Shasha Zhang a, Haihong Zhu a,⇑, Luo Zhang a, Wenqi Zhang a, Huanqing Yang b, Xiaoyan Zeng a a b
Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China XI’AN Space Engine Company Limited, Xi’An 710100, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 17 October 2018 Received in revised form 11 November 2018 Accepted 20 November 2018 Available online 20 November 2018 Keywords: Cu-Cr alloy Laser processing Microstructure Mechanical properties Electronic conductivity
a b s t r a c t Although different kinds of metal materials have been built in the past years, it is difficult to fabricate the components of copper alloys with high strength and high conductivity due to their high reflectivity and thermal conductivity. In this paper, Cu-Cr alloy with high strength and high conductivity was successfully manufactured by high laser power selective laser melting. The microstructure, mechanical properties and conductivity were studied and compared before and after the heat treatment. The microstructure of the as-built sample was columnar grains with very fine cellular sub-structures and precipitates of Cr and Cr2O3. After heat treatment, the Cr particles precipitated from Cu matrix, resulting in simultaneous increase in strength and conductivity. The ultimate tensile strength of 468 MPa, yield strength of 377.33 MPa, and electrical conductivity of 98.31% IACS were achieved, which is even better than the samples fabricated by rolling with post heat treatment. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Copper and its alloys are widely used in the mechanical, power and petrochemical industries due to their excellent electrical and thermal conductivities, outstanding resistance to corrosion, ease of fabrication, good strength, and fatigue resistance [1]. Cu-Cr alloys are attractive candidates for aerospace and nuclear industry because they possess an excellent combination of mechanical strength and electrical or thermal conductivity [2]. At present, the Cu-Cr alloy parts are mainly manufactured by casting or forging. However, it is difficult to manufacture by welding, which makes it difficult to manufacture complex copper alloy parts, in particular with internal flow channels. Selective laser melting (SLM) can directly produce complexshaped metal parts with a near full density, high performance and accuracy, and has built different kinds of metallic components in the past years [3–5]. Copper alloys are difficult to process by SLM due to the high thermal conductivity and poor laser absorption. Researches on SLM copper alloy are mainly focused on Cu-Sn alloys [6], Cu-Al-Ni-Mn alloys [7] and Cu-Ni-Si alloys [8]. Usually, the thermal and electrical conductivities of the copper alloys decrease compared to pure copper due to the addition of other elements, which makes it easy to fabricate the copper alloy ⇑ Corresponding author. E-mail address: [email protected] (H. Zhu). https://doi.org/10.1016/j.matlet.2018.11.118 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
components. However, high strength and high conductivity Cu-Cr alloys contain very little Cr element, and hence have poor laser absorption and high thermal conductivity. Therefore, Cu-Cr alloy is very difficult to obtain high density and performance directly by using the conventional SLM equipment with the maximum laser power of 500 W or less. For instance, A. Popovich et al. [9] produced Cu-Cr-Zr-Ti alloy by SLM using the laser power of 400 W, but the relative density is only 97.9%, which can not meet the demands for industrial applications for most cases. In this paper, the Cu-Cr alloy QCr0.8 was firstly formed by SLM using the high laser power up to 2000 W. The microstructures and properties were studied before and after the heat treatment.
2. Experimetals Gas atomized Cu-Cr alloy QCr0.8 powders with a spherical shape were chosen as the starting material. The chemical composition of the powder is Cu-0.5Cr (wt%). A self-developed SLM equipment was used to manufacture QCr0.8 samples. It is mainly equipped with a continuous wave IPG YLR-2000 fiber laser (wavelength 1.07 lm; maximum output power of 2000 W). The samples with the relative density of 99.98% were produced by the optimized processing parameters (laser power 2000 W, scanning velocity 600 mm/s, hatching space 0.2 mm and layer thickness 0.05 mm).
S. Zhang et al. / Materials Letters 237 (2019) 306–309
The post heat treatment condition of the samples is annealing at 480 °C for 4 h followed by furnace cooling. The microstructure of the samples was characterized by an optical microscopy (Nikon EPIPHOT 300), a scanning electron microscope (SEM, FEI Nova NanoSEM 450) and a transmission electron microscope (TEM, FEI Tecnai-G2-F30). Phase structure was tested by the X-ray diffraction meter (PANalytical X’pert PRO). The grain size was analyzed by electron backscatter diffraction (EBSD). The microhardness was tested using a HVS-1000 microhardness tester. The tensile properties at room temperature were examined using the Zwick/Roell tester. Three specimens were measured for each experiment. The electrical resistances were taken using the CHT3540-1 DC resistance tester.
307
3. Results and discussion Fig. 1a, b present the optical micrographs of the as-built sample. The relative density of the sample is 99.98%. The molten pools can be seen on vertical section with the columnar grains growing along the building direction. The cellular sub-structures with a size smaller than 1 lm can be observed in Fig. 1d. The cells grow towards the center of the molten pool. The microstructure of the annealed sample has almost no change at all compared to the as-built sample (Fig. 1e). However, the precipitates of Cr particles can be observed in the high magnification image (Fig. 1f), which indicates that the Cr particles precipitated from Cu matrix during annealing treatment.
Fig. 1. Optical micrographs of the as-built sample on (a) vertical section and (b) horizontal section, SEM images of the (c) (d) as-built sample on vertical section and (e) (f) annealed sample on vertical section.
308
S. Zhang et al. / Materials Letters 237 (2019) 306–309
The results of the phase analysis of the powder, as-built and annealed samples are shown in Fig. 2. The main phase observed in these samples is a-Cu. No clear phase of Cr can be found in all the samples. The main reason may be that the total content of Cr in the materials is only 0.5 wt%, which is beyond the precipitated phase detection limit of XRD instrument restriction. Besides, the diffraction peaks of the as-built samples shift to low diffraction angles compared with the powder, indicating that the lattice constant of the SLMed samples increases. It can be asserted that Cr was dissolved in the a-Cu matrix of the as-built samples attributing to the high cooling rate during SLM. Compared with the as-built samples, the diffraction peaks of the annealed sample shift to high diffraction angles, implying that the lattice constant decreases, which further indicates that the Cr particles precipitated from Cu matrix during annealing treatment.
TEM was used to further confirm the microstructure and phase composition of the as-built sample. Fig. 3 depicts TEM micrographs of the as-built sample. Many precipitates with the average size of 30 nm and dislocations are observed in the bright field image (Fig. 3a, b). The precipitates consist of spherical and diamond particles. Fig. 3c and d show the typical precipitates in the matrix, which is confirmed by the fast Fourier transformation (FFT) image. The spherical precipitate is consistent with the Cr phase. This result agrees with the previous work, in which the spherical precipitates can be observed in the Cu–Cr samples prepared by severe plastic deformation [10]. The diamond particles is consistent with the Cr2O3 phase, which is caused by the oxidation of the powder during SLM. Cr atoms are more oxygenated than Cu atoms in the solidification process, resulting in formation of Cr2O3 phase.
Fig. 2. XRD patterns of the powder, as-built and annealed samples.
Fig. 3. TEM micrographs of the as-built sample. (a) and (b) bright field images; (c) and (d) HRTEM images of the precipitates and the inset shows the FFT image.
309
S. Zhang et al. / Materials Letters 237 (2019) 306–309 Table 1 Properties of as-built samples, annealed samples and heat treated samples after rolling.
As-built Annealed Rolled + heat treated [12]
Microhardness/HV
UTS/MPa
r0.2/MPa
EL/%
Conductivity/%I ACS
84.19 138.77 110.2
234.67 ± 3.70 468.00 ± 2.96 451
173.94 ± 1.18 377.33 ± 1.59 383
26.02 ± 0.46 19.20 ± 0.58 22.1
37.78 98.31 78.6
Table 1 shows the properties of as-built and annealed samples. After heat treatment, the microhardness of 138.77 HV, ultimate tensile strength (UTS) of 468 MPa, yield strength (r0.2) of 377.33 MPa, elongation (EL) of 19.20% and electrical conductivity of 98.31%IACS are achieved. The higher strength and electrical conductivity are achieved compared with that of the as-built samples. Especially, the annealed samples have higher strength and electrical conductivity compared with heat treated samples after rolling. The strength improvement after heat treatment attributes generally to the grain size of Cu matrix and second phase precipitations. The average grain size of as-built sample is 21.85 lm, and that of annealed sample is 21.49 lm. It indicated that the change of grain size has little effect on the strength improvement. The precipitates is coherent with Cu matrix as shown in Fig. 3. The estimated maximum increment of the shear stress by coherent precipitation is written as [2]:
Dscsmax ¼ 1:84Gef
1=2
ð1Þ
where G is the shear modulus, e is the function of the degree of misfit, and f is the volume fraction of the precipitate. The increment of maximum yield strength contributed is obtained as
Drcsmax ¼ M Dscsmax
ð2Þ
where M is the Taylor factor. By inserting the related parameters (M ¼ 3:06, G ¼ 42:1GPa, e ¼ 0:015) into Equation (1) and (2), the increment of maximum strength contributed by coherent precipitates is obtained as:
Drcsmax ¼ 3556f
1=2
ð3Þ
The increment of r0.2 after heat treatment is calculated by the following equations:
Dr0:2 ¼ Drcsmax;annealed Drcsmax;SLM
ð4Þ
where Drcsmax;annealed is the increment of maximum strength after heat treatment, Drcsmax;SLM is that of as-built sample. The volume fraction of the precipitates of as-built sample is 0.05%, while that of the annealed sample is 0.58%, which were measured by image-pro plus soft. The increment of r0.2 after heat treatment is 191.30 MPa by calculating. It is very close to the increment of r0.2 203.39 MPa obtained in this work. The strength improvement after heat treatment attributes mainly to the Cr precipitation from Cu matrix. The electrical conductivity of as-built sample is only 37.78% IACS due to the supersaturated solid solution of Cr in Cu matrix. The solute Cr atoms in the copper matrix act as impurity centers
for the scattering of electron motions and thus deteriorate the electrical conductivity significantly [11]. After heat treatment, the electrical conductivity rapidly increases to 98.31% IACS because the supersaturated Cu-Cr alloy decomposed and the Cr particles were precipitated from Cu matrix. 4. Conclusions The high mechanical properties and high conductivity QCr0.8 copper alloy components were successfully fabricated by high power SLM. The microstructure and properties have been analyzed. The microstructure of the as-built sample consists of columnar grains with very fine cellular sub-structures and precipitates. After heat treatment, the Cr particles precipitated from Cu matrix. UTS of 468 MPa, yield strength of 377.33 MPa, elongation of 19.20% and electrical conductivity of 98.31% IACS are achieved. The properties of annealed samples improve significantly compared with the as-built samples, which are even better than the samples fabricated by rolling with post heat treatment. Acknowledgement This work is supported by the Direct Fund of WNLO, the Fundamental Research Funds for the Central Universities through program (HUST: 2016XYZD005), and human spaceflight program of China (D050302). The authors would also like to thank the Analytical and Testing Center of HUST for the XRD, SEM and FTEM analysis. References [1] G.H.A. Bagheri, J. Alloy Compd. 676 (2016) 120–126. [2] J.B. Correia, H.A. Davies, C.M. Sellars, Acta Mater. 45 (1997) 177–190. [3] L. Zhang, S. Zhang, H. Zhu, Z. Hu, G. Wang, X. Zeng, Mater. Des. 160 (2018) 9– 20. [4] T. Qi, H. Zhu, H. Zhang, J. Yin, L. Ke, X. Zeng, Mater. Des. 135 (2017) 257–266. [5] T. Trosch, J. Strößner, R. Völkl, U. Glatzel, Mater. Lett. 164 (2016) 428–431. [6] S. Scudino, C. Unterd Rfer, K.G. Prashanth, H. Attar, N. Ellendt, V. Uhlenwinkel, J. Eckert, Mater. Lett. 156 (2015) 202–204. [7] T. Gustmann, A. Neves, U. Kühn, P. Gargarella, C.S. Kiminami, C. Bolfarini, J. Eckert, S. Pauly, Addit. Manuf. 11 (2016) 23–31. [8] Y. Zhou, X. Zeng, Z. Yang, H. Wu, J. Alloy Compd. 743 (2018) 258–261. [9] A. Popovich, V. Sufiiarov, I. Polozov, E. Borisov, D. Masaylo, A. Orlov, Mater. Lett. 179 (2016) 38–41. [10] S.V. Dobatkin, J. Gubicza, D.V. Shangina, N.R. Bochvar, N.Y. Tabachkova, Mater. Lett. 153 (2015) 5–9. [11] S. Zhang, R. Li, H. Kang, Z. Chen, W. Wang, C. Zou, T. Li, T. Wang, Mater. Sci. Eng. A 680 (2017) 108–114. [12] C.Z. Xu, Q.J. Wang, M.S. Zheng, J.W. Zhu, J.D. Li, M.Q. Huang, Q.M. Jia, Z.Z. Du, Mater. Sci. Eng. A 459 (2007) 303–308.