- Email: [email protected]
The decrease of Young's modulus in shear bands of amorphous Al87Ni8La5 alloy after deformation
Materials Letters 252 (2019) 114–116
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
The decrease of Young’s modulus in shear bands of amorphous Al87Ni8La5 alloy after deformation G. Abrosimova a,⇑, A. Aronin a,b, D. Fokin c, N. Orlova a, E. Postnova a a
Institute of Solid State Physics RAS, Chernogolovka, Russia The National University of Science and Technology MISiS, Moscow, Russia c OPTEC, Moscow, Russia b
a r t i c l e
i n f o
Article history: Received 13 May 2019 Accepted 23 May 2019 Available online 24 May 2019 Keywords: Shear band Diffusion Phase transformations Amorphous structure
a b s t r a c t Distribution of mechanical properties around the shear bands inAl87Ni8La5 amorphous alloy was studied by atomic force microscopy (Peak Force QNM). The amorphous alloy was subjected to cold rolling. The deformation value was 50%. Numerous shear bands were observed in the alloy samples after the rolling. It is shown that inhomogeneity of the distribution of local properties (inhomogeneity of the distribution of the effective Young‘s modulus) arises in the deformed sample. The inhomogeneities form a system of bands. The thickness of the bands is 50–250 nm. Location of the regions of the low Young’s modulus correlates with location of the shear bands. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction Amorphous metal and composite amorphous-nanocrystalline alloys are among the most widely investigated materials. An interest in them is caused by the peculiarities of their structure and high physical and chemical properties. Amorphous metal alloys in the form of both ribbons and rods and plates (the so-called bulk metallic glasses, BMG) have important fields of application. In general, their high magnetic and mechanical properties or their combination are used when applying the alloys. These materials have high yield strength, large elastic deformation [1–4], and high wear resistance [5]. The value of elastic deformation can reach 2% [6]. However, the plasticity of these alloys at room temperature is low. Plastic deformation at low temperatures is related to the formation and distribution of shear bands (deformation bands). Strain hardening upon plastic deformation similar to that in crystals does not occur; moreover, a material in shear bands softens due to a high concentration of free volume [7] and to a decrease in a short-range order degree. In shear bands, atoms have a high mobility, and a diffusion coefficient at room temperature exceeds that in a matrix by several orders of magnitude [8]. Shear bands are the areas of facilitated nanocrystals formation upon subsequent heating and even exposure at room temperature [9,10]. In view of foregoing, it is important to determine the characteristics of deformation bands and regions adjoining them to evaluate the ⇑ Corresponding author. E-mail address: [email protected] (G. Abrosimova). https://doi.org/10.1016/j.matlet.2019.05.099 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
mechanical properties of amorphous materials, as well as to find regularities in the formation of an amorphous-nanocrystalline structure. Shear bands have the thickness from several tens to hundreds of nanometers. During deformation they come to the sample surface, forming steps. The cross-sectional dimensions of the steps depend on the deformation extent and elastic properties of the material and are from several tens to hundreds of nanometers [7,11]. The mechanical properties of the shear bands are studied by nanoindentation [12–14]. In [13] the authors found that the size of a region around a shear band having low hardness is more than 100 mm. Thus, the size of this region is much greater than that of the shear band. In [14] it was determined that not only hardness but also the Young’s modulus decreases in a shear band and in a region around it. However, the spatial scale of changes is significantly less than that in [13].Today, the locality of a change in elastic and strength properties in a shear area and in a region along it is still unclear. The results described above are obtained by nanoindentation method which has spatial resolution insufficient for nanoobjects. Furthermore, it is unclear how the regions with modified mechanical properties will be located in case of numerous deformation bands, since all the results obtained earlier refer to the analysis of a single shear band. The aim of the present work is to investigate local distribution of the regions with different Young’s modulus in the samples which contain numerous deformation bands. The samples of Al87Ni8La5 amorphous alloy which is deformed at room temperature with the formation of shear bands are used as the objects [15].
G. Abrosimova et al. / Materials Letters 252 (2019) 114–116
2. Materials and methods The samples of Al87Ni8La5 alloy in the form of a ribbon with the width of about 1 cm and thickness of about 40 mm were prepared by rapid melt quenching onto a copper disk. The sample structure was controlled by X-ray diffraction. The peculiarities of the surface after the deformation were studied by scanning electron microscopy using a Supra 50VP electron microscope. The samples were deformed by cold rolling. The deformation value measured by a change in thickness was 50%. For the investigations by atomic force microscopy, the initial and deformed samples were polished. Polishing took several stages. At the first stage, the samples were subjected to mechanical polishing. At the second stage, the samples were subjected to ion polishing using argon ion beam with the energy of 2 keV. Such a scheme of sample preparation was necessary to remove a surface layer where an additional deformed surface layer is formed during polishing by using abrasive materials. Then, the local mechanical properties of the samples were investigated by atomic force microscopy. The local mechanical properties were studied by Peak Force QNM (Dimension Fast Scan TM Atomic Force Microscope (AFM), Bruker). Probes with single-crystal silicon tips were used. They are suitable for obtaining high-resolution maps of distribution of mechanical properties due to their high hardness. The resonance frequency of cantilevers with a nominal tip with the radius of 5 nm was 300 kHz. The oscillation frequency of Z-piezo crystal was 2 kHz. The maps of distribution of mechanical properties were plotted by the obtained force curves of the interaction between the probe and the sample surface. All measurements were carried out using standard Bruker probes. The load was changed in the range of 0.3–0.85 mN. The system recorded force curves and determined the maximum force of the interaction between the surface and the probe (PeakForce). The
115
feedback during scanning was maintained by the value of this quantity. At the same time, the data on surface topography were obtained by atomic force microscopy (AFM).
3. Results and discussion After the preparation and deformation, the samples were amorphous. The deformation did not lead to their crystallization. Fig. 1 shows the images of surface topography of the initial and deformed ribbon samples, respectively. The roughness of sample surface was about 20 nm. One could not observe the traces of shear bands coming to the surface after the polishing on the deformed sample. We did not observe the peculiarities of contrast change with an increase in load during the measurements in the initial nondeformed sample by PeakForce. In the deformed sample, it was found that nonuniformity of the distribution of local properties over the sample surface (nonuniformity of the distribution of the effective Young’s modulus) arises upon an increase in the load. Fig. 2 demonstrates the maps of distribution of mechanical properties obtained upon different loads. The inhomogeneities were most pronounced upon the load of 0.85 mN. The inhomogeneities were pronounced in the system of bands. These bands are marked with arrows in Fig. 2c. The thickness of the bands is 50–250 nm. The direction of rolling is indicated by the arrow in Fig. 2a. The values of band thickness, as well as the form of the bands and their distribution over the surface, correspond to the shear bands which are observed on the deformed samples surface by the scanning electron microscope (Fig. 3). In the images (Figs. 2 and 3) it is seen that the deformation bands are distributed uniformly.
Fig. 1. AFM images of the surface of Al87Ni8La5 samples (a is the initial sample, b is the deformed sample).
Fig. 2. Maps of distribution of mechanical properties (a – PeakForce = 0.3 mN, b – PeakForce = 0.6 mN, c – PeakForce = 0.85 mN).
116
G. Abrosimova et al. / Materials Letters 252 (2019) 114–116
Declaration of Competing Interest None. Acknowledgements The work was supported by State task of ISSP RAS and partially supported by RFBR (grant 19-03-00355). References
Fig. 3. SEM image of the Al87Ni8La5 sample surface after the rolling deformation.
Thus, there are numerous deformation bands in the subsurface region of the material deformed by rolling. The material in the deformation bands has a lower value of the Young’s modulus. The value of the regions of the low Young’s modulus is tenths of a micrometer. The regions of the low Young’s modulus are uniformly distributed over the sample. The cross-sectional dimensions of the regions of the low Young’s modulus (light bands in Fig. 2c) are tens and hundreds of nanometers (up to 0.5 mm). Note that the contrast between the bands and the matrix is sharp enough, which is the evidence of a dramatic change in the properties. At the same time, the properties of the amorphous alloy change insignificantly within several tenths of a micrometer (within the band). The obtained results refer to the samples where numerous deformation bands are observed, while in [13,14] the authors investigated the properties of samples with single shear bands. In our samples, the variations of mechanical properties were observed at the scale of tens and hundreds of nanometers which is considerably less than that in [12,13]. Thus, the following was determined with high locality by using PeakForce QNM - distribution of elastic properties (the Young’s modulus) in the deformed sample; - the scale of nonuniformity in the samples with numerous deformation bands was found; - it was shown that the size of the regions with the low Young’s modulus in Al87Ni8La5 amorphous alloy around the shear bands is tenths of a micrometer which is significantly less than that obtained earlier for Zr-based alloys.
[1] A. Inoue, A. Takeuchi, Recent development and application products of bulk glassy alloys, Acta Mater. 59 (2011) 2243–2267, https://doi.org/10.1016/j. actamat.2010.11.027. [2] D.V. Louzguine-Luzgin, A. Inoue, Bulk metallic glasses. Formation, structure, properties, and applications, in: K.H.J. Buschow (Ed.), Handbook of Magnetic Materials V 21, 2013, pp. 131–171, https://doi.org/10.1016/B978-0-44459593-5.00003-9. [3] G. Abrosimova, A. Aronin, Amorphous and nanocrystalline metallic alloy, Prog. Metallic Alloys (2016) 45–83, https://doi.org/10.5772/64499. [4] M.F. Ashby, A.L. Greer, Metallic glasses as structural materials, Scr. Mater. 54 (2006) 321–326, https://doi.org/10.1016/j.scriptamat.2005.09.051. [5] D.V. Louzguine-Luzgin, H.K. Nguyen, K. Nakajima, S.V. Ketov, A.S. Trifonov, A study of the nanoscale and atomic-scale wear resistance of metallic glasses, Mater. Lett. 185 (2016) 54–58, https://doi.org/10.1016/j.matlet.2016.08.035. [6] M.M. Trexler, N.N. Thadhani, Mechanical properties of bulk metallic glasses, Prog. Mater Sci. 55 (2010) 759–839, https://doi.org/10.1016/j. pmatsci.2010.04.002. [7] A.L. Greer, Y.Q. Cheng, E. Ma, Shear bands in metallic glasses, Mater. Sci. Eng. R 74 (2013) 71–132, https://doi.org/10.1016/j.mser.2013.04.001. [8] A.S. Aronin, D.V. Louzguine-Luzgin, Onnanovoids formation in shear bands of an amorphous Al-based alloy, Mech. Mater. 113 (2017) 19–23, https://doi.org/ 10.1016/j.mechmat.2017.07.007. [9] G. Abrosimova, A. Aronin, O. Barkalov, D. Matveev, O. Rybchenko, V. Maslov, V. Tkach, Structural transformations in the Al85Ni6.1Co2Gd6Si0.9 amorphous alloy during multiple rolling, Phys. Solid State 53 (2011) 229–233, https://doi.org/ 10.1134/S1063783411020028. [10] N. Boucharat, R. Hebert, H. Rosner, R. Valiev, G. Wilde, Nanocrystallization of amorphous Al88Y7Fe5 alloy induced by plastic deformation, Scr. Mater. 53 (2005) 823–828, https://doi.org/10.1016/j.scriptamat.2005.06.004. [11] G. Abrosimova, A. Aronin, Nanocrystal formation in Al- and Ti-based amorphous alloys at Deformation, J. Alloys Compd. 747 (2018) 26–30, https://doi.org/10.1016/j.jallcom.2018.03.014. [12] Byung-Gil Yoo, Yong-Jae Kim, Oh. Jun-Hak, U. Ramamurty, J. Jang, On the hardness of shear bands in amorphous alloys, Scr. Mater. 61 (2009) 951–954, https://doi.org/10.1016/j.scriptamat.2009.07.037. [13] J. Pan, Q. Chen, L. Liu, Y. Li, Softening and dilatation in a single shear band, Acta Mater. 59 (2011) 5146–5158, https://doi.org/10.1016/j.actamat.2011.04.047. [14] R. Maaß, K. Samwer, W. Arnold, C.A. Volkert, A single shear band in a metallic glass: local core and wide soft zone, Appl. Phys. Lett. 105 (2014) 17190, https://doi.org/10.1063/1.4900791. [15] G. Abrosimova, A. Aronin, A. Budchenko, Amorphous phase decomposition in Al–Ni–RE system alloys, Mater. Lett. 139 (2015) 194–196, https://doi.org/ 10.1016/j.matlet.2014.10.076.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
The decrease of Young’s modulus in shear bands of amorphous Al87Ni8La5 alloy after deformation G. Abrosimova a,⇑, A. Aronin a,b, D. Fokin c, N. Orlova a, E. Postnova a a
Institute of Solid State Physics RAS, Chernogolovka, Russia The National University of Science and Technology MISiS, Moscow, Russia c OPTEC, Moscow, Russia b
a r t i c l e
i n f o
Article history: Received 13 May 2019 Accepted 23 May 2019 Available online 24 May 2019 Keywords: Shear band Diffusion Phase transformations Amorphous structure
a b s t r a c t Distribution of mechanical properties around the shear bands inAl87Ni8La5 amorphous alloy was studied by atomic force microscopy (Peak Force QNM). The amorphous alloy was subjected to cold rolling. The deformation value was 50%. Numerous shear bands were observed in the alloy samples after the rolling. It is shown that inhomogeneity of the distribution of local properties (inhomogeneity of the distribution of the effective Young‘s modulus) arises in the deformed sample. The inhomogeneities form a system of bands. The thickness of the bands is 50–250 nm. Location of the regions of the low Young’s modulus correlates with location of the shear bands. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction Amorphous metal and composite amorphous-nanocrystalline alloys are among the most widely investigated materials. An interest in them is caused by the peculiarities of their structure and high physical and chemical properties. Amorphous metal alloys in the form of both ribbons and rods and plates (the so-called bulk metallic glasses, BMG) have important fields of application. In general, their high magnetic and mechanical properties or their combination are used when applying the alloys. These materials have high yield strength, large elastic deformation [1–4], and high wear resistance [5]. The value of elastic deformation can reach 2% [6]. However, the plasticity of these alloys at room temperature is low. Plastic deformation at low temperatures is related to the formation and distribution of shear bands (deformation bands). Strain hardening upon plastic deformation similar to that in crystals does not occur; moreover, a material in shear bands softens due to a high concentration of free volume [7] and to a decrease in a short-range order degree. In shear bands, atoms have a high mobility, and a diffusion coefficient at room temperature exceeds that in a matrix by several orders of magnitude [8]. Shear bands are the areas of facilitated nanocrystals formation upon subsequent heating and even exposure at room temperature [9,10]. In view of foregoing, it is important to determine the characteristics of deformation bands and regions adjoining them to evaluate the ⇑ Corresponding author. E-mail address: [email protected] (G. Abrosimova). https://doi.org/10.1016/j.matlet.2019.05.099 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
mechanical properties of amorphous materials, as well as to find regularities in the formation of an amorphous-nanocrystalline structure. Shear bands have the thickness from several tens to hundreds of nanometers. During deformation they come to the sample surface, forming steps. The cross-sectional dimensions of the steps depend on the deformation extent and elastic properties of the material and are from several tens to hundreds of nanometers [7,11]. The mechanical properties of the shear bands are studied by nanoindentation [12–14]. In [13] the authors found that the size of a region around a shear band having low hardness is more than 100 mm. Thus, the size of this region is much greater than that of the shear band. In [14] it was determined that not only hardness but also the Young’s modulus decreases in a shear band and in a region around it. However, the spatial scale of changes is significantly less than that in [13].Today, the locality of a change in elastic and strength properties in a shear area and in a region along it is still unclear. The results described above are obtained by nanoindentation method which has spatial resolution insufficient for nanoobjects. Furthermore, it is unclear how the regions with modified mechanical properties will be located in case of numerous deformation bands, since all the results obtained earlier refer to the analysis of a single shear band. The aim of the present work is to investigate local distribution of the regions with different Young’s modulus in the samples which contain numerous deformation bands. The samples of Al87Ni8La5 amorphous alloy which is deformed at room temperature with the formation of shear bands are used as the objects [15].
G. Abrosimova et al. / Materials Letters 252 (2019) 114–116
2. Materials and methods The samples of Al87Ni8La5 alloy in the form of a ribbon with the width of about 1 cm and thickness of about 40 mm were prepared by rapid melt quenching onto a copper disk. The sample structure was controlled by X-ray diffraction. The peculiarities of the surface after the deformation were studied by scanning electron microscopy using a Supra 50VP electron microscope. The samples were deformed by cold rolling. The deformation value measured by a change in thickness was 50%. For the investigations by atomic force microscopy, the initial and deformed samples were polished. Polishing took several stages. At the first stage, the samples were subjected to mechanical polishing. At the second stage, the samples were subjected to ion polishing using argon ion beam with the energy of 2 keV. Such a scheme of sample preparation was necessary to remove a surface layer where an additional deformed surface layer is formed during polishing by using abrasive materials. Then, the local mechanical properties of the samples were investigated by atomic force microscopy. The local mechanical properties were studied by Peak Force QNM (Dimension Fast Scan TM Atomic Force Microscope (AFM), Bruker). Probes with single-crystal silicon tips were used. They are suitable for obtaining high-resolution maps of distribution of mechanical properties due to their high hardness. The resonance frequency of cantilevers with a nominal tip with the radius of 5 nm was 300 kHz. The oscillation frequency of Z-piezo crystal was 2 kHz. The maps of distribution of mechanical properties were plotted by the obtained force curves of the interaction between the probe and the sample surface. All measurements were carried out using standard Bruker probes. The load was changed in the range of 0.3–0.85 mN. The system recorded force curves and determined the maximum force of the interaction between the surface and the probe (PeakForce). The
115
feedback during scanning was maintained by the value of this quantity. At the same time, the data on surface topography were obtained by atomic force microscopy (AFM).
3. Results and discussion After the preparation and deformation, the samples were amorphous. The deformation did not lead to their crystallization. Fig. 1 shows the images of surface topography of the initial and deformed ribbon samples, respectively. The roughness of sample surface was about 20 nm. One could not observe the traces of shear bands coming to the surface after the polishing on the deformed sample. We did not observe the peculiarities of contrast change with an increase in load during the measurements in the initial nondeformed sample by PeakForce. In the deformed sample, it was found that nonuniformity of the distribution of local properties over the sample surface (nonuniformity of the distribution of the effective Young’s modulus) arises upon an increase in the load. Fig. 2 demonstrates the maps of distribution of mechanical properties obtained upon different loads. The inhomogeneities were most pronounced upon the load of 0.85 mN. The inhomogeneities were pronounced in the system of bands. These bands are marked with arrows in Fig. 2c. The thickness of the bands is 50–250 nm. The direction of rolling is indicated by the arrow in Fig. 2a. The values of band thickness, as well as the form of the bands and their distribution over the surface, correspond to the shear bands which are observed on the deformed samples surface by the scanning electron microscope (Fig. 3). In the images (Figs. 2 and 3) it is seen that the deformation bands are distributed uniformly.
Fig. 1. AFM images of the surface of Al87Ni8La5 samples (a is the initial sample, b is the deformed sample).
Fig. 2. Maps of distribution of mechanical properties (a – PeakForce = 0.3 mN, b – PeakForce = 0.6 mN, c – PeakForce = 0.85 mN).
116
G. Abrosimova et al. / Materials Letters 252 (2019) 114–116
Declaration of Competing Interest None. Acknowledgements The work was supported by State task of ISSP RAS and partially supported by RFBR (grant 19-03-00355). References
Fig. 3. SEM image of the Al87Ni8La5 sample surface after the rolling deformation.
Thus, there are numerous deformation bands in the subsurface region of the material deformed by rolling. The material in the deformation bands has a lower value of the Young’s modulus. The value of the regions of the low Young’s modulus is tenths of a micrometer. The regions of the low Young’s modulus are uniformly distributed over the sample. The cross-sectional dimensions of the regions of the low Young’s modulus (light bands in Fig. 2c) are tens and hundreds of nanometers (up to 0.5 mm). Note that the contrast between the bands and the matrix is sharp enough, which is the evidence of a dramatic change in the properties. At the same time, the properties of the amorphous alloy change insignificantly within several tenths of a micrometer (within the band). The obtained results refer to the samples where numerous deformation bands are observed, while in [13,14] the authors investigated the properties of samples with single shear bands. In our samples, the variations of mechanical properties were observed at the scale of tens and hundreds of nanometers which is considerably less than that in [12,13]. Thus, the following was determined with high locality by using PeakForce QNM - distribution of elastic properties (the Young’s modulus) in the deformed sample; - the scale of nonuniformity in the samples with numerous deformation bands was found; - it was shown that the size of the regions with the low Young’s modulus in Al87Ni8La5 amorphous alloy around the shear bands is tenths of a micrometer which is significantly less than that obtained earlier for Zr-based alloys.
[1] A. Inoue, A. Takeuchi, Recent development and application products of bulk glassy alloys, Acta Mater. 59 (2011) 2243–2267, https://doi.org/10.1016/j. actamat.2010.11.027. [2] D.V. Louzguine-Luzgin, A. Inoue, Bulk metallic glasses. Formation, structure, properties, and applications, in: K.H.J. Buschow (Ed.), Handbook of Magnetic Materials V 21, 2013, pp. 131–171, https://doi.org/10.1016/B978-0-44459593-5.00003-9. [3] G. Abrosimova, A. Aronin, Amorphous and nanocrystalline metallic alloy, Prog. Metallic Alloys (2016) 45–83, https://doi.org/10.5772/64499. [4] M.F. Ashby, A.L. Greer, Metallic glasses as structural materials, Scr. Mater. 54 (2006) 321–326, https://doi.org/10.1016/j.scriptamat.2005.09.051. [5] D.V. Louzguine-Luzgin, H.K. Nguyen, K. Nakajima, S.V. Ketov, A.S. Trifonov, A study of the nanoscale and atomic-scale wear resistance of metallic glasses, Mater. Lett. 185 (2016) 54–58, https://doi.org/10.1016/j.matlet.2016.08.035. [6] M.M. Trexler, N.N. Thadhani, Mechanical properties of bulk metallic glasses, Prog. Mater Sci. 55 (2010) 759–839, https://doi.org/10.1016/j. pmatsci.2010.04.002. [7] A.L. Greer, Y.Q. Cheng, E. Ma, Shear bands in metallic glasses, Mater. Sci. Eng. R 74 (2013) 71–132, https://doi.org/10.1016/j.mser.2013.04.001. [8] A.S. Aronin, D.V. Louzguine-Luzgin, Onnanovoids formation in shear bands of an amorphous Al-based alloy, Mech. Mater. 113 (2017) 19–23, https://doi.org/ 10.1016/j.mechmat.2017.07.007. [9] G. Abrosimova, A. Aronin, O. Barkalov, D. Matveev, O. Rybchenko, V. Maslov, V. Tkach, Structural transformations in the Al85Ni6.1Co2Gd6Si0.9 amorphous alloy during multiple rolling, Phys. Solid State 53 (2011) 229–233, https://doi.org/ 10.1134/S1063783411020028. [10] N. Boucharat, R. Hebert, H. Rosner, R. Valiev, G. Wilde, Nanocrystallization of amorphous Al88Y7Fe5 alloy induced by plastic deformation, Scr. Mater. 53 (2005) 823–828, https://doi.org/10.1016/j.scriptamat.2005.06.004. [11] G. Abrosimova, A. Aronin, Nanocrystal formation in Al- and Ti-based amorphous alloys at Deformation, J. Alloys Compd. 747 (2018) 26–30, https://doi.org/10.1016/j.jallcom.2018.03.014. [12] Byung-Gil Yoo, Yong-Jae Kim, Oh. Jun-Hak, U. Ramamurty, J. Jang, On the hardness of shear bands in amorphous alloys, Scr. Mater. 61 (2009) 951–954, https://doi.org/10.1016/j.scriptamat.2009.07.037. [13] J. Pan, Q. Chen, L. Liu, Y. Li, Softening and dilatation in a single shear band, Acta Mater. 59 (2011) 5146–5158, https://doi.org/10.1016/j.actamat.2011.04.047. [14] R. Maaß, K. Samwer, W. Arnold, C.A. Volkert, A single shear band in a metallic glass: local core and wide soft zone, Appl. Phys. Lett. 105 (2014) 17190, https://doi.org/10.1063/1.4900791. [15] G. Abrosimova, A. Aronin, A. Budchenko, Amorphous phase decomposition in Al–Ni–RE system alloys, Mater. Lett. 139 (2015) 194–196, https://doi.org/ 10.1016/j.matlet.2014.10.076.