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Fe particle composites with excellent plasticity
Materials Letters 137 (2014) 139–142
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Ultrahigh strength MgZnCa eutectic alloy/Fe particle composites with excellent plasticity Jingfeng Wang a,n, Song Huang a, Yang Li a, Yiyun Wei b, Shengfeng Guo c, Fusheng Pan a a National Engineering Research Center for Magnesium Alloys, College of Materials Science and Engineering, Chongqing University, Chongqing 400044, PR China b China Academy of Engineering Physics, Mianyang 621900, PR China c School of Materials Science and Engineering, Southwest University, Chongqing 400715, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 21 July 2014 Accepted 1 September 2014 Available online 6 September 2014
The influence of Fe particle addition on MgZnCa eutectic-composition as-cast alloy was investigated. No difference was observed in the other main crystal phases, except for the Fe particles. Compared with the as-cast Mg69Zn27Ca4 ternary system, the alloy with Fe added exhibited higher strength and plasticity. The fracture stress of Mg69Zn27Ca4 with 4 vol% Fe reached nearly 700 MPa with 12% plasticity. The porous Fe particles increased the strength and toughness of the alloy. & 2014 Elsevier B.V. All rights reserved.
Keywords: Eutectic alloy Fe particle Microstructure Mechanical property
1. Introduction Ultrafine eutectic composites with microscale dendrites are novel materials used to improve the room-temperature plasticity of high-strength alloys [1–4]. Alloys with a eutectic composition show excellent casting performance and machinability [5]. Eutectic composites are usually converted into bulk metallic glass (BMG) composites to improve its elastic modulus and strength [6–8]. Among all eutectic composition alloys, magnesium alloys, as the lightest structural materials, have attracted the attention of researchers. The combination of Mg-based eutectic composites and BMGs is highly attractive because of their ultrahigh specific strength and good corrosion resistance [9,10]. However, these alloys usually have poor plasticity because plastic deformation is heterogeneous [11]. Most Mg-based eutectic composites catastrophically fail without a distinct plastic strain at room temperature, thereby limiting their potential applications. Various methods have been introduced to improve the plasticity of these materials, including adding ductile phase or particles, such as Fe or Mo, and introducing prefabricated defects [12–14]. However, most of these methods are performed in BMGs. Studies on the enhanced toughness in Mg-based eutectic composite alloys are seldom reported. BMGs are not widely used in engineering applications because of their high cost and difficulty in preparation. Recent studies have focused on MgZnCa eutectic composition
n
Corresponding author. Tel.: þ 86 23 65112153. E-mail address: [email protected] (J. Wang).
http://dx.doi.org/10.1016/j.matlet.2014.09.004 0167-577X/& 2014 Elsevier B.V. All rights reserved.
because of the low density of this alloy. However, the majority of research focused on MgZnCa BMGs [15,16]; studies on eutectic composites are lacking. Methods to improve the mechanical properties of the Mg-matrix eutectic composition alloy have yet to be developed. In this study, Fe particles were added into the MgZnCa eutectic composition as-cast alloy. E2 eutectic composition (Mg69Zn27Ca4 alloy) was selected based on the MgZnCa system schematic ternary diagram. The structure and mechanical properties of were investigated.
2. Experimental The raw materials used were as follows: industrially pure Mg (99.9 wt%), Zn (99.9 wt%), and Mg–30Ca alloy (30 wt% Ca). A master alloy with the composition of Mg69Zn27Ca4 was prepared by induction melting raw materials with induction furnace under the production of high-purity Ar atmosphere. During melting, high-purity, irregularly shaped Fe particles with the granularity of 300 were added into the matrix alloy under Ar atmosphere. Mechanical stirring was performed to enhance the homogeneous mixing of the particles with the melt. Fe particles (4 vol%) were added to the Mg69Zn27Ca4 alloy. Then, the melting alloy was injection into a quartz glass tube with 3 mm diameter and cooled in air. Finally, a cylindrical rod with 3 mm and 50 mm length was produced. The structure was characterized by X-ray diffraction (XRD, Rigaku D/MAX-2500PC) using Cu Kα radiation. The morphology
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J. Wang et al. / Materials Letters 137 (2014) 139–142
and elemental composition were determined by Vega II LMU SEM equipped with an EDS. The mechanical properties were tested by compressive experiments. Compressive specimens with 1.5 mm diameter and 3 mm length were used for the experiments on a SANS CMT5105 testing machine at a strain rate of 10 4 s 1 at room temperature. At least three samples were tested for each composition.
3. Results and discussions Fig. 1a shows the XRD patterns of the as-cast Mg69Zn27Ca4 (alloy I) and that with 4 vol% Fe particles (alloy II). Many crystal peaks appeared in both alloys. The main sharp diffraction peaks were identified to be mixtures of hexagonal α-Mg, hexagonal MgZn2, and tetragonal Ca2Mg5Zn13 phases. Except for the three high-intensity crystalline peaks, no difference in the main peaks of the two alloys was observed. This result indicates that no obvious changes occurred in the crystalline peaks. The high-intensity crystalline peaks were indexed as Fe phases. Therefore, no intermetallic compound can be formed between the Fe and Mg69Zn27Ca4 matrix. The SEM backscattering electron micrographs of the MgZnCa and MgZnCa/Fe composites are shown in Fig. 1b and c respectively. Alloy Ι is composed of the primary α-Mg, the skeleton-like dendritic phase, and some bulk phases. However, the skeletonlike dendritic phase declined and a volume fraction of bulk phase was found as Fe content increased. Dendritic arm spacing and grain size in alloy Ι were obviously larger than those in alloy ΙΙ. EDS showed that only Mg and Zn were found in the fine dendrite, indicating that this dendrite corresponds to the MgZn phase. The bulk phase in alloy I mainly consisted of the Ca2Mg5Zn13 phase. In
alloy II, the dendrite was mainly composed of Mg and Zn. This result indicates that the dendrite also corresponds to the MgZn phase. The bulk phases in alloy II were rich in Fe, suggesting that the bulk phases in alloy II are Fe particles. Fig. 2 shows the surface scanning results of the area around the bulk phases and the element distribution of Mg, Zn, Ca, and Fe for alloy II. Only Fe was present in the bulk phases. This finding is similar to the EDS results, which means that the bulk phases are all Fe particles. The dendritic phase mainly consisted of Mg, Zn, and a few Ca. No defects or cracks were found between the Fe particles and the matrix. Fig. 3 shows the comparison of the mechanical properties of the alloys. The addition of Fe particles improved both the strength and plasticity of the alloy. The compressive strength and plasticity of the alloy with 4% Fe particles increased from 340 MPa to 700 MPa and from 0 to nearly 12%, respectively. The low mechanical properties of the MgZnCa alloy can be attributed to the mechanical failure exhibited before reaching the elastic limit. This failure does not occur when Fe particles are added. The Fe-added alloy had a TYS of 520 MPa. This finding confirms that the combination of Fe particles and MgZnCa matrix maintains the high strength of the Fe particles and the good plasticity of the ductile particles. Fig. 4 shows the fracture morphologies of the alloys. Alloy I showed a large amount of cracks (Fig. 4a). The surface of the sample was very rough because some of the alloy fragmented during the compressive experiment, indicating that the alloy is brittle. Cleavage-like features and some fragments were observed on the fracture surface of the dendrite/matrix composites (Fig. 4b). These results reveal the brittle nature of the alloy. MgZnCa with 4 vol% Fe was not thoroughly fractured. The heading state of the alloy is shown in Fig. 4c. The main crack
A
Fe MgZn Mg Ca2Mg5Zn13
Intensity
B Alloy II
Alloy I
C 30
40
50
60
70
80
90
2 (deg) Point A
wt. %
at. %
Point B
wt. %
at. %
Mg
21.61
40.09
Mg
38.41
62.27
Point C
wt. %
at. %
Zn
65.00
44.84
Zn
59.99
36.17
Mg
0.94
2.15
Ca
13.39
15.06
Ca
1.59
1.57
Zn
0.21
0.30
Ca
0.21
0.30
Fe
95.38
94.62
Fig. 1. Microstructures of the MgZnCa and MgZnCa/Fe alloys: (a) XRD patterns of the two alloys; (b) and (c) SEM image of the MgZnCa and MgZnCa/Fe alloys.
J. Wang et al. / Materials Letters 137 (2014) 139–142
141
Fig. 2. Surface scanning microstructure of the MgZnCa/Fe alloy and element distribution: (a) MgZnCa/Fe alloy, (b) Mg, (c) Ca, (d) Fe, (e) Zn.
800
Mg-Zn-Ca+Fe 4%
700 600
Stress/MPa
500 400 300 200
As-cast Mg-Zn-Ca
100 0
0
2
4
6
8
10
12
14
16
18
Strain/% Fig. 3. Mechanical properties of the MgZnCa and MgZnCa/Fe alloys.
was the obvious shear band with the nearly 451 angle of the compressive loading axis. This observation implies that numerous dislocations accumulated and slipped around the alloy, thereby improving plasticity. The surface of the sample after compressive testing was smooth, and no other cracks appeared. The fracture surface was observed at high magnification after the sample was carefully separated from the 451 crack of the compressive loading axis. Cleavage-like features were observed in the alloy without Fe, but not in the alloy with Fe. The sample was also more ductile as evidenced by the presence of fractural steps with river-like patterns.
Brittle materials usually fracture under the shear-banding mechanism [17]. The shear bands are usually initiated at the sites of local stress concentration. Many skeleton-like dendritic phases with some bulk phases were observed in the MgZnCa alloy. The phases with a large size were very brittle and were the source of stress concentration during deformation. The interface between the dendrite and the matrix was not secure; fragments appeared on the fracture surface. Cracks formed and thus made the surface rough. After Fe addition, the dendrite was difficult to distinguish from the matrix of the fracture surface. The large difference between the elastic modulus of the Fe particles and the MgZnCa matrix caused the stress concentration in the particle–matrix interface to trigger the initiation of shear bands. The Fe particles acted in a way similar to the ductile reinforcements. Similar results were observed in the amorphous brittle matrix [12,14]. The Fe particles generated interfaces between the reinforcements and the matrix, causing multiple shear bands to form within or around the Fe particles. The dendritic phases were small, and the deformation was uniform. Moreover, the Fe particles could bear higher loads transferred during plastic deformation because of the high Young’s modulus. The strength and ductility considerably increased.
4. Conclusions The influence of Fe particle addition on the microstructure, mechanical properties, and corrosion behavior of MgZnCa alloys was investigated. No difference in the other main crystal phases was observed in the two alloys, except for the Fe particles. Compared with as-cast Mg69Zn27Ca4 ternary system, the alloy with Fe added demonstrated higher strength and plasticity. The
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J. Wang et al. / Materials Letters 137 (2014) 139–142
Fig. 4. SEM images of the fracture surfaces of Mg69Zn27Ca4 (a) and (b) and Mg69Zn27Ca4/Fe (c) and (d) samples.
fracture stress of Mg69Zn27Ca4 with 4 vol% Fe reached nearly 700 MPa with 12% plasticity. The porous Fe particles provided increased the strength and toughness of the alloy. Acknowledgement The authors are grateful for the National Natural Science Foundation Commission of China (Grant no. 51271206), the National Basic Research Program of China (Grant no. 2013 CB632201), and the financial support from the Program for New Century Excellent Talents in University (Grant no. NCET-11-0554). References [1] Gleiter H. Acta Mater 2000;48:1–29. [2] Inoue A. Nat Mater 2003;2:661–3.
[3] Park JM, Kim YC, Kim WT, Kim DH. Mater Trans 2004;44:595–8. [4] Song GA, Han JH, Park JM, Yi S, Kim DH, Kim KB. J Alloys Compd 2011;509S: S353–S356. [5] Koves G, Mondolfo LF. J Iron Steel Inst 1964;202:424. [6] Ren YL, Zuo JH, Qiu KQ, Zhang HF, Hu ZQ. Intermetallics 2004;12:1205–9. [7] Yang BJ, Yao JH, Zhang J, Yang HW, Wang JQ, Ma E. Scr Mater 2009;61:423–6. [8] Conner RD, Dandliker RB, Johnson WL. Acta Mater 1998;46:6089–102. [9] Song GA, Lee JS, Park JS, Lee NS, Lee WH, Kim KB. J Alloys Compd 2009;481:135–9. [10] Wu XF, Si Y, Suo ZY, Kang Y, Qiu KQ. Mater Sci 2009;44:6035–9. [11] Song GA, Kim DH, Lee MH, Lee JK, Park JM, Eckert J, et al. Mater Lett 2010;64:534–6. [12] Ma H, Xu J, Ma E. Appl Phys Lett 2003;83:2793–5. [13] Pan DG, Zhang HF, Wang AM, Hu ZQ. Appl Phys Lett 2006;89:261904. [14] Jang JS, Ciou JY, Hung TH, Huang JC, Du XH. Appl Phys Lett 2008;92:011930. [15] Zhao YY, Ma E, Xu J. Scr Mater 2008;58:496–9. [16] Li QF, Weng HR, Suo ZY, Ren YL, Yuan XG, Qiu KQ. Mater Sci Eng A 2008;487:301–8. [17] Argon AS. Acta mater 1979;27:47–58.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Ultrahigh strength MgZnCa eutectic alloy/Fe particle composites with excellent plasticity Jingfeng Wang a,n, Song Huang a, Yang Li a, Yiyun Wei b, Shengfeng Guo c, Fusheng Pan a a National Engineering Research Center for Magnesium Alloys, College of Materials Science and Engineering, Chongqing University, Chongqing 400044, PR China b China Academy of Engineering Physics, Mianyang 621900, PR China c School of Materials Science and Engineering, Southwest University, Chongqing 400715, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 21 July 2014 Accepted 1 September 2014 Available online 6 September 2014
The influence of Fe particle addition on MgZnCa eutectic-composition as-cast alloy was investigated. No difference was observed in the other main crystal phases, except for the Fe particles. Compared with the as-cast Mg69Zn27Ca4 ternary system, the alloy with Fe added exhibited higher strength and plasticity. The fracture stress of Mg69Zn27Ca4 with 4 vol% Fe reached nearly 700 MPa with 12% plasticity. The porous Fe particles increased the strength and toughness of the alloy. & 2014 Elsevier B.V. All rights reserved.
Keywords: Eutectic alloy Fe particle Microstructure Mechanical property
1. Introduction Ultrafine eutectic composites with microscale dendrites are novel materials used to improve the room-temperature plasticity of high-strength alloys [1–4]. Alloys with a eutectic composition show excellent casting performance and machinability [5]. Eutectic composites are usually converted into bulk metallic glass (BMG) composites to improve its elastic modulus and strength [6–8]. Among all eutectic composition alloys, magnesium alloys, as the lightest structural materials, have attracted the attention of researchers. The combination of Mg-based eutectic composites and BMGs is highly attractive because of their ultrahigh specific strength and good corrosion resistance [9,10]. However, these alloys usually have poor plasticity because plastic deformation is heterogeneous [11]. Most Mg-based eutectic composites catastrophically fail without a distinct plastic strain at room temperature, thereby limiting their potential applications. Various methods have been introduced to improve the plasticity of these materials, including adding ductile phase or particles, such as Fe or Mo, and introducing prefabricated defects [12–14]. However, most of these methods are performed in BMGs. Studies on the enhanced toughness in Mg-based eutectic composite alloys are seldom reported. BMGs are not widely used in engineering applications because of their high cost and difficulty in preparation. Recent studies have focused on MgZnCa eutectic composition
n
Corresponding author. Tel.: þ 86 23 65112153. E-mail address: [email protected] (J. Wang).
http://dx.doi.org/10.1016/j.matlet.2014.09.004 0167-577X/& 2014 Elsevier B.V. All rights reserved.
because of the low density of this alloy. However, the majority of research focused on MgZnCa BMGs [15,16]; studies on eutectic composites are lacking. Methods to improve the mechanical properties of the Mg-matrix eutectic composition alloy have yet to be developed. In this study, Fe particles were added into the MgZnCa eutectic composition as-cast alloy. E2 eutectic composition (Mg69Zn27Ca4 alloy) was selected based on the MgZnCa system schematic ternary diagram. The structure and mechanical properties of were investigated.
2. Experimental The raw materials used were as follows: industrially pure Mg (99.9 wt%), Zn (99.9 wt%), and Mg–30Ca alloy (30 wt% Ca). A master alloy with the composition of Mg69Zn27Ca4 was prepared by induction melting raw materials with induction furnace under the production of high-purity Ar atmosphere. During melting, high-purity, irregularly shaped Fe particles with the granularity of 300 were added into the matrix alloy under Ar atmosphere. Mechanical stirring was performed to enhance the homogeneous mixing of the particles with the melt. Fe particles (4 vol%) were added to the Mg69Zn27Ca4 alloy. Then, the melting alloy was injection into a quartz glass tube with 3 mm diameter and cooled in air. Finally, a cylindrical rod with 3 mm and 50 mm length was produced. The structure was characterized by X-ray diffraction (XRD, Rigaku D/MAX-2500PC) using Cu Kα radiation. The morphology
140
J. Wang et al. / Materials Letters 137 (2014) 139–142
and elemental composition were determined by Vega II LMU SEM equipped with an EDS. The mechanical properties were tested by compressive experiments. Compressive specimens with 1.5 mm diameter and 3 mm length were used for the experiments on a SANS CMT5105 testing machine at a strain rate of 10 4 s 1 at room temperature. At least three samples were tested for each composition.
3. Results and discussions Fig. 1a shows the XRD patterns of the as-cast Mg69Zn27Ca4 (alloy I) and that with 4 vol% Fe particles (alloy II). Many crystal peaks appeared in both alloys. The main sharp diffraction peaks were identified to be mixtures of hexagonal α-Mg, hexagonal MgZn2, and tetragonal Ca2Mg5Zn13 phases. Except for the three high-intensity crystalline peaks, no difference in the main peaks of the two alloys was observed. This result indicates that no obvious changes occurred in the crystalline peaks. The high-intensity crystalline peaks were indexed as Fe phases. Therefore, no intermetallic compound can be formed between the Fe and Mg69Zn27Ca4 matrix. The SEM backscattering electron micrographs of the MgZnCa and MgZnCa/Fe composites are shown in Fig. 1b and c respectively. Alloy Ι is composed of the primary α-Mg, the skeleton-like dendritic phase, and some bulk phases. However, the skeletonlike dendritic phase declined and a volume fraction of bulk phase was found as Fe content increased. Dendritic arm spacing and grain size in alloy Ι were obviously larger than those in alloy ΙΙ. EDS showed that only Mg and Zn were found in the fine dendrite, indicating that this dendrite corresponds to the MgZn phase. The bulk phase in alloy I mainly consisted of the Ca2Mg5Zn13 phase. In
alloy II, the dendrite was mainly composed of Mg and Zn. This result indicates that the dendrite also corresponds to the MgZn phase. The bulk phases in alloy II were rich in Fe, suggesting that the bulk phases in alloy II are Fe particles. Fig. 2 shows the surface scanning results of the area around the bulk phases and the element distribution of Mg, Zn, Ca, and Fe for alloy II. Only Fe was present in the bulk phases. This finding is similar to the EDS results, which means that the bulk phases are all Fe particles. The dendritic phase mainly consisted of Mg, Zn, and a few Ca. No defects or cracks were found between the Fe particles and the matrix. Fig. 3 shows the comparison of the mechanical properties of the alloys. The addition of Fe particles improved both the strength and plasticity of the alloy. The compressive strength and plasticity of the alloy with 4% Fe particles increased from 340 MPa to 700 MPa and from 0 to nearly 12%, respectively. The low mechanical properties of the MgZnCa alloy can be attributed to the mechanical failure exhibited before reaching the elastic limit. This failure does not occur when Fe particles are added. The Fe-added alloy had a TYS of 520 MPa. This finding confirms that the combination of Fe particles and MgZnCa matrix maintains the high strength of the Fe particles and the good plasticity of the ductile particles. Fig. 4 shows the fracture morphologies of the alloys. Alloy I showed a large amount of cracks (Fig. 4a). The surface of the sample was very rough because some of the alloy fragmented during the compressive experiment, indicating that the alloy is brittle. Cleavage-like features and some fragments were observed on the fracture surface of the dendrite/matrix composites (Fig. 4b). These results reveal the brittle nature of the alloy. MgZnCa with 4 vol% Fe was not thoroughly fractured. The heading state of the alloy is shown in Fig. 4c. The main crack
A
Fe MgZn Mg Ca2Mg5Zn13
Intensity
B Alloy II
Alloy I
C 30
40
50
60
70
80
90
2 (deg) Point A
wt. %
at. %
Point B
wt. %
at. %
Mg
21.61
40.09
Mg
38.41
62.27
Point C
wt. %
at. %
Zn
65.00
44.84
Zn
59.99
36.17
Mg
0.94
2.15
Ca
13.39
15.06
Ca
1.59
1.57
Zn
0.21
0.30
Ca
0.21
0.30
Fe
95.38
94.62
Fig. 1. Microstructures of the MgZnCa and MgZnCa/Fe alloys: (a) XRD patterns of the two alloys; (b) and (c) SEM image of the MgZnCa and MgZnCa/Fe alloys.
J. Wang et al. / Materials Letters 137 (2014) 139–142
141
Fig. 2. Surface scanning microstructure of the MgZnCa/Fe alloy and element distribution: (a) MgZnCa/Fe alloy, (b) Mg, (c) Ca, (d) Fe, (e) Zn.
800
Mg-Zn-Ca+Fe 4%
700 600
Stress/MPa
500 400 300 200
As-cast Mg-Zn-Ca
100 0
0
2
4
6
8
10
12
14
16
18
Strain/% Fig. 3. Mechanical properties of the MgZnCa and MgZnCa/Fe alloys.
was the obvious shear band with the nearly 451 angle of the compressive loading axis. This observation implies that numerous dislocations accumulated and slipped around the alloy, thereby improving plasticity. The surface of the sample after compressive testing was smooth, and no other cracks appeared. The fracture surface was observed at high magnification after the sample was carefully separated from the 451 crack of the compressive loading axis. Cleavage-like features were observed in the alloy without Fe, but not in the alloy with Fe. The sample was also more ductile as evidenced by the presence of fractural steps with river-like patterns.
Brittle materials usually fracture under the shear-banding mechanism [17]. The shear bands are usually initiated at the sites of local stress concentration. Many skeleton-like dendritic phases with some bulk phases were observed in the MgZnCa alloy. The phases with a large size were very brittle and were the source of stress concentration during deformation. The interface between the dendrite and the matrix was not secure; fragments appeared on the fracture surface. Cracks formed and thus made the surface rough. After Fe addition, the dendrite was difficult to distinguish from the matrix of the fracture surface. The large difference between the elastic modulus of the Fe particles and the MgZnCa matrix caused the stress concentration in the particle–matrix interface to trigger the initiation of shear bands. The Fe particles acted in a way similar to the ductile reinforcements. Similar results were observed in the amorphous brittle matrix [12,14]. The Fe particles generated interfaces between the reinforcements and the matrix, causing multiple shear bands to form within or around the Fe particles. The dendritic phases were small, and the deformation was uniform. Moreover, the Fe particles could bear higher loads transferred during plastic deformation because of the high Young’s modulus. The strength and ductility considerably increased.
4. Conclusions The influence of Fe particle addition on the microstructure, mechanical properties, and corrosion behavior of MgZnCa alloys was investigated. No difference in the other main crystal phases was observed in the two alloys, except for the Fe particles. Compared with as-cast Mg69Zn27Ca4 ternary system, the alloy with Fe added demonstrated higher strength and plasticity. The
142
J. Wang et al. / Materials Letters 137 (2014) 139–142
Fig. 4. SEM images of the fracture surfaces of Mg69Zn27Ca4 (a) and (b) and Mg69Zn27Ca4/Fe (c) and (d) samples.
fracture stress of Mg69Zn27Ca4 with 4 vol% Fe reached nearly 700 MPa with 12% plasticity. The porous Fe particles provided increased the strength and toughness of the alloy. Acknowledgement The authors are grateful for the National Natural Science Foundation Commission of China (Grant no. 51271206), the National Basic Research Program of China (Grant no. 2013 CB632201), and the financial support from the Program for New Century Excellent Talents in University (Grant no. NCET-11-0554). References [1] Gleiter H. Acta Mater 2000;48:1–29. [2] Inoue A. Nat Mater 2003;2:661–3.
[3] Park JM, Kim YC, Kim WT, Kim DH. Mater Trans 2004;44:595–8. [4] Song GA, Han JH, Park JM, Yi S, Kim DH, Kim KB. J Alloys Compd 2011;509S: S353–S356. [5] Koves G, Mondolfo LF. J Iron Steel Inst 1964;202:424. [6] Ren YL, Zuo JH, Qiu KQ, Zhang HF, Hu ZQ. Intermetallics 2004;12:1205–9. [7] Yang BJ, Yao JH, Zhang J, Yang HW, Wang JQ, Ma E. Scr Mater 2009;61:423–6. [8] Conner RD, Dandliker RB, Johnson WL. Acta Mater 1998;46:6089–102. [9] Song GA, Lee JS, Park JS, Lee NS, Lee WH, Kim KB. J Alloys Compd 2009;481:135–9. [10] Wu XF, Si Y, Suo ZY, Kang Y, Qiu KQ. Mater Sci 2009;44:6035–9. [11] Song GA, Kim DH, Lee MH, Lee JK, Park JM, Eckert J, et al. Mater Lett 2010;64:534–6. [12] Ma H, Xu J, Ma E. Appl Phys Lett 2003;83:2793–5. [13] Pan DG, Zhang HF, Wang AM, Hu ZQ. Appl Phys Lett 2006;89:261904. [14] Jang JS, Ciou JY, Hung TH, Huang JC, Du XH. Appl Phys Lett 2008;92:011930. [15] Zhao YY, Ma E, Xu J. Scr Mater 2008;58:496–9. [16] Li QF, Weng HR, Suo ZY, Ren YL, Yuan XG, Qiu KQ. Mater Sci Eng A 2008;487:301–8. [17] Argon AS. Acta mater 1979;27:47–58.