- Email: [email protected]
A cluster line approach to finding new Fe-B-Y-Nb-Zr bulk metallic glasses
Materials
Journal of University of Science and Technology Becing Volume 14, Supplement I , June 2007, Page 26
A cluster line approach to finding new Fe-B-Y-Nb-Zrbulk metallic glasses Nigel Pemberton-Pigottl), Qing Wang‘),Weirong Chen’v2),Qingyu Zhang”, Jiang Wu”, Yanhui Li’), Jianbing Qiang’), Chuang Dong’33) 1) State Key Laboratory of Materials Modification,Dalian University of Technology, Dalian 116024, China 2) Department of Mechanical Engineering, Dalian University, Dalian 116622, China 3) International Center for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, China (Received 2.006-06-05)
Abstract: The glass forming ability of the [(Fe,,,,,Y i,,3)ioo-J3x],,Nb2Zr2( ~ 9 - 2 6 )system was investigated using a series of cluster lines. Three types of clusters, an icosahedron (Fe,,Y), a capped Archimedes anti-prism (Fe,B,) and a capped trigonal prism (FqB), as well as a binary eutectic (Fe,,B,,) were considered. Bulk glassy alloy rods of 3 mm in diameter were synthesized using a copper mold suction-casting method. The glass transition temperature was observed for all samples in the boron range of 15.9at%-25.7at%, with the alloy at 15.9at% of boron having the best thermal properties. The ferrous-based bulk metallic glasses (BMG) obtained have high reduced glass transition temperatures with the maximum reaching 0.63 and large supercooled liquid regions with the maximum reaching I1 1 K. Magnetic testing revealed a large value of coercive force and remanent magnetization, being 11 kA/m and 0.1 T, respectively. Key words: bulk metallic glasses; Fe-B-Y-Nb-Zr alloys; composition design; cluster line
[Thisproject was financially supported by the National Natural Science Foundation of China (N0.50401020, 50671018, 50631010), and the Provincial Science and Technology Foundation of Liaoning, China.]
1. Introduction Recently, Fe-based and Co-based bulk metallic glasses (BMGs) have been drawing increasing attention due to their good mechanical and soft magnetic properties which can be exploited for structural and functional materials [ 1-31. Compared with Pd-, Zr-, and Cu-based BMGs, Fe- and Co-based BMGs have relatively weak glass forming abilities (GFA) and are formed only in multicomponent systems. Furthermore, it is more difficult to determine the BMG composition in multicomponent alloy systems due to their composition sensitivity. Therefore, composition design is a key step for investigating and developing a new multicomponent BMG. In this paper, we will introduce a cluster line approach into an Fe-based alloy system. The cluster line approach has been used successfully in the composition design of ternary quasicrystals and Zr- and Cu-based BMGs. In this method two opposing cluster lines are used and their intersection is assumed to indicate the best quasicrystal and BMG forming compositions [4-71. It has been shown that minor alloying by elements Corresponding author: Chuang Dong, E-mail: [email protected]
with significant atomic size differences from the main constitute elements can dramatically improve the GFAs of metallic glasses [lo]. It has also been shown [9-111 that an yttrium addition of about 2at% has a positive effect on the stabilizing of the amorphous phase. The Y has an oxygen scavenging effect through the formation of yttrium oxides in the melt, and also helps to adjust the alloy towards an eutectic, which both suppress the crystal nucleation. It has also been reported that boron contents in the range of 5at%27at% helps to produce a glassy behavior in Finemet type amorphous materials [12]. The addition of Zr and Nb has been reported to be beneficial for increasing the glass forming ability and for atomic dense packing [ 13-15]. Matsubara et al. have studied the geometric arrangements of Fe,oMloB20(M=Zr, Nb, and Cr) alloys and found that the structural unit in all three cases consists of a triangular prism with B at the center and six Fe and M atoms at the vertices, where the M elements randomly replace the Fe atoms. For the case of Zr and Nb the prisms are connected mainly by sharing their edges. This random replacement by the M elements causes a distortion of the triangular prisms
Nigel Pemberton-Pigott et al., A cluster line approach to finding new Fe-B-Y-I%-Zr bulk metallic glasses
making crystallization more difficult and thereby increasing the stability of the amorphous phase [16]. Based on the above considerations the ternary FeB-Y system was selected as a base, as it has already been shown to be stable when cast into rods with a diameter of 2 mm [17-181. The alloy compositions were designed by using the cluster line intersection method, and then adding minor elements Nb and Zr to the base compositions. Therefore, the Fe-B-Y-Nb-Zr system was investigated based on the cluster line method and minor alloying.
27
Therefore, four cluster composition lines, Fe,B,-Y, Fes3B,,-Y, Fe9B-Y and Fe12Y-Bare constructed in the Fe-B-Y system, as shown in Fig. 1. Fe,B,-Y, Fe,,B,,Y and Fe,B-Y cluster lines intersect with the Fe,,Y-B cluster line at the points 1=(Fe68.6B25.7Y5,7), 2= (Fe77,6B,5,9Y6,5)and 3=(Fe83,7B9,3Y7), respectively. These intersection points can be expressed by the relation (Fe121,3Y1113)100-xBx (x=9-26 B). To these three base alloys of 2at% Nb and 2at% Zr were then added.
2. Composition design On the basis of past research on quasicrystals and BMGs, a new approach using a cluster line method was proposed for the composition design of ternary alloys [4-71. The cluster line method was used in a ternary system by marking a straight line linking a specific binary cluster to the remaining third element. The specific binary cluster is the nearest-neighbor coordination cluster centered by a small atom in the local structure of a crystalline phase. From topologically close-packing considerations, a limited number of binary clusters are available: CN12 icosahedrons, CNlO capped Archimedes anti-prisms, and CN6, CN9 and CNll capped trigonal prisms [4]. In the Fe-rich corner of the binary Fe-B system, two different types of clusters characterize the local structures of the Fe-B crystalline phases, both of which are centered by a B atom, the capped Archimedes anti-prism Fe,B,, and the capped trigonal prism Fe,B. Moreover, the Fe-B eutectic point Fe,,B,, can be regarded as an Fe,B cluster glued with a B atom (Fe,B+B=Fe,B2=Fe,2B18=Fe83B17) according to the cluster structure model [4]. The ternary crystalline phase Fe62B14Y3 is characterized by an Fe,,Y icosahedron cluster centered by an Fe atom. The closepacking degree of these clusters was calculated according to Miracle's topologically efficient clusterpacking structure model [19], as shown in Table 1. R' is the ideal critical radius ratio under the condition of efficient packing for a definite coordination number of the nearest-neighbor clusters, which is defined as rdrl, where ro is the radius of the center atom and Y, the average radius of the nearest-neighbor shell atoms. Roll is the actual ratio of the atoms in the cluster. The radii (ro)of Fe, B and Y used in our calculations are 1.27, 0.98, and 1.80 nm, respectively. A is defined as the difference between the Rol, value and the ideal R' value represented by d=(R,,-R*)IR*. It can be seen that the clusters satisfy the topological close-packing requirement.
Fig. 1. Composition chart of the Fe-B-Y ternary system. Relevant binary clusters Fe,,B,, Fe& and Fe,,Y are shown in detail (open circles=Fe, small solid circles=B, large solid circle=Y). The solid lines are cluster lines, and the compositions at intersection points 1,2 and 3 are listed.
3. Experimental procedure The ingots of [(Fe12/13Y1/13)100-xBx196Nb2~r2 (x=9-26) alloys were prepared by arc melting their pure elements under an argon atmosphere. The purity of the elements are 99.99wt% for Fe, 99.9wt% for Y and 99.5wt% for B. The alloy compositions represent the nominal atomic percentages. Each sample was cooled and melted at least 3 times to ensure compositional homogeneity. During this melting process the samples were weighed periodically to determine whether more B should be added to make up for any weight loss, as it is known that B is difficult to melt into an alloy from it's pure state without loss of material. The melted samples were then cast into rods of 3 mm in diameter, and about 40 mm in length, using a copper mold suction-casting technique. Structural identification of these alloys was carried out by means of X-ray diffraction (XRD) analysis near the bottom end of the rods using chromatic Cu K, radiation ( A O . 15406 nm). The thermal properties were measured using digital scanning calorimetry (DSC) on a TA QIOO, at a constant heating rate of 20 Wmin, and under the flow of pure argon gas. The glass transition temperature (T,) was assumed to be the first decrease of the exothermic heat flow to the left of the
J. Univ. Sci. Technol. Beijing, Vo1.14, Suppl. 1, Jun 2007
28
first exothermic peak on the DSC curve. The crystallization temperature (T,) was assumed to be the onset temperature of the first exothermic crystallization peak, while the melting temperature (T,) and the liquidus temperature (Tl) were assumed to be the first and second onset points on the endothermic melting peak, respectively. Magnetic properties of saturation magnetization ( B J , remanent magnetization (M,) and coercive force (H,)were measured with a vibrating sample magnetometer (VSM) under an applied field of 1600 W m .
index parameters that are considered to be important to the indication of the glass forming ability of an alloy, such as reduced glass transition temperature (T,=T,T,), supercooled liquid temperature region (AT=T,-T,), and gamma (T,=T,/[T,+T,]). In general, the GFA of an alloy is expected to increase with increasing the magnitude of these thermal index parameters. It is also considered that a T,,>0.6 and a T ~ 0 . 3 5are indicative of a good GFA [20]. As can be seen from Table 1, all three samples satisfy these requirements, except for (Fe,4.9B18,8Y6,3)962r2~2 whose Trgis 0.59.
4. Results and discussion Fig. 2 shows the XRD patterns of the [(Fe12/13Yl/l 3) 1~-xBx]96m2Zr2 alloys for x=9.3, 15.9, 18.8, and 25.7. No BMG is formed at the composition (Fe83,7B9,3Y7)96Zr2Nb2 obtained at the intersection of the Fe,B-Y and Fel2Y-B cluster lines, as the alloy structure consists mainly of Fe in solid solution. The alloys in Fig. 2 between the intersection points 1 (Fe68.6B25.7Y5.7)and (Fe77,6B15.9y6.5) that were minor alloyed with Nb and Zr show a slight amorphous halo in the 28 range of 40"-48". For these samples between intersection points 1 and 2 of Fig. 2 the smaller peaks are identified as minor a-Fe, Fe3B and an Fe2$6 phases.
.-3 2
W
+d
c
e.
1
I
15
25
35
45
55
65
75
85
28/ (")
Fig. 2. X-ray patters for [(Fe,,,,Y,,,),,,B,J,Nb,Zr, (x=9.3, 15.9, 18.8, and 25.7 B) rods of 3 mm in diameters. The smaller peaks for x=15.9,18.8 and 25.7 are identified as minor a-Fe, Fe,B and Fe,B, phases.
Fig. 3 shows the DSC traces of [(Fe,2/13Y1113)loo_xB,196Nb2Zr2 for the compositions with x=15.9, 18.8, and 25.7. An obvious glass transition before the exothermic crystallization peaks is manifest in all three traces. For x=15.9, 18.8, and 25.7 the values of Tg are 890, 837, and 875 K, respectively. The crystallization temperature for the case of x=25.7 had the highest T,=996 K, while for x=15.9 is slightly less at T,=986 K. For x=18.8 the DSC trace shows a relatively low value of T,=933 K followed by a small exothermic peak before stabilizing and then followed by another much larger crystallization peak. The T, and TI values for all three cases are around 1370 and 1415 K, respectively. The thermal parameters Tgr T,, T,, and TI for all three samples are listed in Table 2. From this data we are able to calculate several thermal
Suction cast 3 m m [(Fe,,,,,Y,,,,),,,B,1,Nb,Zr2 roc
4 L d
r
600
800
1000 1200 Temperature / K
1400
Fig. 3. DSC traces for suction cast [ ( F e l ~ 1 3 Y ~ l ~ ) l ~ ~ B ~ ] ~ Nb,Zrz (x=15.9, 18.8, and 25.7) rods with diameters of 3 mm.
Table 1. Atomic ratios for Fe-B and Fe-Y clusters. Cluster
Cluster type
Center atom
R*
r, / nm
r , / nm
Ro,l=rdy,
A/%
Fe,B, Fe,B
Archimedes anti-prism Capped trigonal prism
Fe,,Y
Icosahedron
Boron Boron Iron
0.799 0.710 0.902
0.98 0.98 1.27
1.212 1.27 1.314
0.809 0.772 0.967
1.2 8.7 7.2
Note: R' is the ideal atomic radius ratio, r , the average radius of the nearest-neighbor shell atoms, R , , the actual ratio of inner atom to surrounding atom, and A the percent difference between actual and ideal ratios.
For x=18.8 the supercooled liquid region had the smallest value of 96 K, while for x=15.9 and 25.7 the
AT values were 106 and 111 K, respectively. These are believed to be the largest values for the super-
29
Nigel Pemberton-Pigoft et al., A cluster line approach to finding new Fe-B-Y-Nb-Zrbulk metallic glasses
cooled liquid region of an iron based alloy reported to date [21-221. For the case of x=25.7 and 18.8 the samples appeared to be only partially amorphous as DSC and X-ray analysis near the center of the 3-mm rods showed a crystalline structure, whereas the x=l5.9 sample demonstrated amorphous behavior along the entire length of the 3-mm cast rod. From the calculated data in Table 2 it can be seen that the case of x=15.9 has higher thermal parameters and is thus .considered to be more thermally stable than the other two alloys. One can also see from Fig. 1 that this compo-
sition is located at the intersection of the cluster lines that originate at the Fe,,Y binary cluster and the Fes3B1, binary eutectic point. These two clusters are respectively an icosahedron (Fe,,Y) and a capped trigonal prism (Fe,B), and it is assumed that the formation of a bulk metallic glass is due to the favorable arrangement of these two close-packed clusters. These results indicate that BMGs can be found in the range of 15.9at%-25.7at% B when suction-cast into 3-mm diameter rods.
Table 2. Thermal properties from the DSC traces of [(Fe,,,,Y,,,,),,B,],Nb,Zr, diameter T,IK 996 933 986
T,/K 890 837 875
Alloy (Fe68.6B25.7Y5,7)96Zr2Nb2
(Fe74.9Bi8,8Y6,3)96Zr2Nb2
(Fe77.6Bi5.9Y6.5)96zr2Nb2
T,IK 1374 1370 1371
Fig. 4 shows the typical B-H magnetization loop of the (Fe74.9B18,8Y6,3)96Nb2Zr2 BMG. The saturation magnetization ( B J , remanent magnetization ( M J , and coercive force (H,) are 0.88 T, 0.1 T, and 10.9 W m , respectively. In order to be a good soft magnetic material the coercive force should be Hc<10N m , whereas a hard magnetic material will have a coercive force of more than several thousand amp-turns per meter. Thus, the above BMGs are considered to be hard magnetic materials.
I
I
-600
I
I
I
I
I
,
-200 200 400 600 800 -0 2 H I (kA m I) -0.4
Fig. 4. Magnetization(B) versus applied magnetic field (H) curve of the [(Fe,,,3Y,,,3),,B,],,Nb2Zr2 (x=18.8) rod with a diameter of 3 mm. The values of saturation magnetization (BJ, remanent magnetization ( M J , and coercive force (H,) are shown.
5. Conclusion Using a cluster line approach and a copper mold suction-casting technique a portion of the Fe-B-Y-ZrNb quinary system was successfully investigated. Bulk metallic glasses were found in the range falling between the intersections of three separate cluster lines originating at Fe8&, Fe8B3 and Fel,Y representing a range of 15.9at%-25.7at% B. Alloys in this range showed a large value of coercive force Hc=10.9
T,/K 1415 1411 1416
T,, 0.63 0.59 0.62
(x=15.9, 18.8, and 25.7) rods of 3 mm in
AT 106 96 111
T, 0.43 0.41 0.43
kA/m, a saturation magnetization of B,=0.88 T, and remanent magnetization of M,=O. 1 T, demonstrating hard magnetic properties. It was also found that the (Fe,,,6B 15.9Y6.5)96Zr2Nb2 alloy located at the intersection of the Fes3B,,-Y and Fe,,Y-B cluster lines exhibited the best thermal stability in terms of the gamma parameter (T,=0.43), reduced glass transition temperature (T,=0.62), and supercooled liquid region (AT=lll K), enabling the fabrication of rods with a diameter of 3 mm. This is believed to be the largest supercooled liquid region reported to date for any Febased BMG. The glass-forming tendency of these alloys further validates the cluster-based approach to finding BMGs.
References A. Inoue, B. L. Shen, and A. Takeuchi, Developments and applications of bulk glassy alloys in late transition metal base system, Matel: Trans. JIM, 47(2006), No.5, p.1275. B.L. Shen, M. Akiba, and A. Inoue, Excellent softferromagnetic bulk glassy alloys with high saturation magnetization, Appl. Phys. Lett., 88(2006), No. 13, p. 131907. B.L. Shen, A. Inoue, and C.T. Chang, Super high strength and good soft-magnetic properties of (Fe,Co)-B-Si-Nb bulk glassy alloys with high glass-forming ability, Appl. Phys. Lett., 85(2004), No.21, p.4911. C. Dong, J.B. Qiang, Y.M. Wang, et al., Cluster-based composition rule for stable ternary quasicrystals in AI-(Cu, Pd, Ni)-TM systems, Philo. Mug., 86(2006), No.3-5, p.263. J.H. Xia, J.B. Qiang, Y.M. Wang, et al., Ternary bulk metallic glasses formed by minor alloying of Cu8Zrs icosahedron. Appl. Phys. Lett., 88(2006), No.10, p.101907. Q. Wang, J.B. Qiang, Y.M. Wang, et ul., Formation and optimization of Cu-based Cu-Zr-A1 bulk metallic glasses, Matel: Sci. Forum, 475-479(2005), No. 1, p.338 1.
J. Univ. Sci. Technol. Beijing, Vo1.14, Suppl. 1, Jun 2007 Y.M. Wang, C.H. Shek, J.B. Qiang, et al., The e/a criterion for the largest glass-forming abilities of the Zr-Al-Ni(Co) alloys, Mater: Trans. JIM, 45(2004), No.4, p.1180. Z.P. Lu and C.T. Liu, Role of minor alloying additions in formation of bulk metallic glasses: A review, J. Mater: Sci., 39(2004), No.12, p.3965. Z. Yong, M.X. Pan, D.Q. Zhao, et al., Formation of ZrBased bulk metallic glass from low purity of materials by yttrium addition, Mater: Trans. JIM, 41(2000), No.11, p.1410. [lo] Z.P. Lu, C.T. Liu, J.R. Thompson, and W.D. Porter, Structural amorphous steels, Phys. Rev. Lett., 92(2004), No.24, p.245503. [ 111 C.T. Liu and Z.P. Lu, Effect of minor alloying additions on glass formation in bulk metallic glasses, Intermetallics, 13(2005), p.415 [12] I. Mat’ko, E. Illekovh, P. Svec, P. Duhaj, and K. Czomoravh, Local ordering model in Fe-Si-B amorphous alloys, Mater. Sci. Eng., A226-228( 1997), p.280. [13] T. Zhang, A. Inoue, and T. Masumoto, Amorphous Zr-AlTM (TM=Co, Ni, Cu) alloys with significant supercooled liquid region of over 100 K, Mater: Trans. JIM, 32( 1991), No.11, p.1005. [I41 L.Q. Ma and A. Inoue, On glass-forming ability of Fe-
based amorphous alloys, Mater: Lett., 38(1999) p.58. [15] M. Shapaan, J. Libfir, J. Lendvai, and L.K. Varga, Crystallization behavior of Fe,,Nb,-JrJJ,, bulk amorphous alloy, Mate,: Sci. Eng. A, 375-377(2004), p.789. [16] E. Matsubara, S . Sato, M. Imafuku, et ul., Structural study of amorphous Fe,,,M,,B,, (M=Zr, Nb, and Cr) alloys by Xray diffraction, Mater: Sci. Eng. A, 312(2001), p.136. [17] C.Y. Lin, H.Y. Tien, and T.S. Chin, Soft magnetic ternary iron-boron-based bulk metallic glasses, Appl. Phys. Lett., 86(2005), No.16, p.162501. [ 181 J. Zhang, H. Tan, Y.P. Feng, et al., The effect of Y on glass forming ability, Scripta Muter., 53(2005), No.2, p.183. [19] D.B. Miracle and W.S. Sanders, The influence of efficient atomic packing on the constitution of metallic glasses, Philos. Mag., 83(2003), No.20, p.2409. [20] B. Zhang, D.Q. Zhao, M.X. Pan, et al., Amorphous metallic plastic, Phys. Rev. Lett., 94(2005), p.205502. [21] M. Xu, M.X. Quan, Z.Q. Hu, et al., Formation of amorphous Fe6,Co6Zr6Nb,Cr,B,, with a remarkable supercooled liquid region before crystallization, Phys. B , 315(2002), p.96. [22] S.J. Poon, G.J. Shiflet, F.Q. Guo, et al., Glass formability of ferrous- and aluminum-based structural metallic alloys, J. Non Cryst. Solids, 3 17(2003), p. 1.
Journal of University of Science and Technology Becing Volume 14, Supplement I , June 2007, Page 26
A cluster line approach to finding new Fe-B-Y-Nb-Zrbulk metallic glasses Nigel Pemberton-Pigottl), Qing Wang‘),Weirong Chen’v2),Qingyu Zhang”, Jiang Wu”, Yanhui Li’), Jianbing Qiang’), Chuang Dong’33) 1) State Key Laboratory of Materials Modification,Dalian University of Technology, Dalian 116024, China 2) Department of Mechanical Engineering, Dalian University, Dalian 116622, China 3) International Center for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, China (Received 2.006-06-05)
Abstract: The glass forming ability of the [(Fe,,,,,Y i,,3)ioo-J3x],,Nb2Zr2( ~ 9 - 2 6 )system was investigated using a series of cluster lines. Three types of clusters, an icosahedron (Fe,,Y), a capped Archimedes anti-prism (Fe,B,) and a capped trigonal prism (FqB), as well as a binary eutectic (Fe,,B,,) were considered. Bulk glassy alloy rods of 3 mm in diameter were synthesized using a copper mold suction-casting method. The glass transition temperature was observed for all samples in the boron range of 15.9at%-25.7at%, with the alloy at 15.9at% of boron having the best thermal properties. The ferrous-based bulk metallic glasses (BMG) obtained have high reduced glass transition temperatures with the maximum reaching 0.63 and large supercooled liquid regions with the maximum reaching I1 1 K. Magnetic testing revealed a large value of coercive force and remanent magnetization, being 11 kA/m and 0.1 T, respectively. Key words: bulk metallic glasses; Fe-B-Y-Nb-Zr alloys; composition design; cluster line
[Thisproject was financially supported by the National Natural Science Foundation of China (N0.50401020, 50671018, 50631010), and the Provincial Science and Technology Foundation of Liaoning, China.]
1. Introduction Recently, Fe-based and Co-based bulk metallic glasses (BMGs) have been drawing increasing attention due to their good mechanical and soft magnetic properties which can be exploited for structural and functional materials [ 1-31. Compared with Pd-, Zr-, and Cu-based BMGs, Fe- and Co-based BMGs have relatively weak glass forming abilities (GFA) and are formed only in multicomponent systems. Furthermore, it is more difficult to determine the BMG composition in multicomponent alloy systems due to their composition sensitivity. Therefore, composition design is a key step for investigating and developing a new multicomponent BMG. In this paper, we will introduce a cluster line approach into an Fe-based alloy system. The cluster line approach has been used successfully in the composition design of ternary quasicrystals and Zr- and Cu-based BMGs. In this method two opposing cluster lines are used and their intersection is assumed to indicate the best quasicrystal and BMG forming compositions [4-71. It has been shown that minor alloying by elements Corresponding author: Chuang Dong, E-mail: [email protected]
with significant atomic size differences from the main constitute elements can dramatically improve the GFAs of metallic glasses [lo]. It has also been shown [9-111 that an yttrium addition of about 2at% has a positive effect on the stabilizing of the amorphous phase. The Y has an oxygen scavenging effect through the formation of yttrium oxides in the melt, and also helps to adjust the alloy towards an eutectic, which both suppress the crystal nucleation. It has also been reported that boron contents in the range of 5at%27at% helps to produce a glassy behavior in Finemet type amorphous materials [12]. The addition of Zr and Nb has been reported to be beneficial for increasing the glass forming ability and for atomic dense packing [ 13-15]. Matsubara et al. have studied the geometric arrangements of Fe,oMloB20(M=Zr, Nb, and Cr) alloys and found that the structural unit in all three cases consists of a triangular prism with B at the center and six Fe and M atoms at the vertices, where the M elements randomly replace the Fe atoms. For the case of Zr and Nb the prisms are connected mainly by sharing their edges. This random replacement by the M elements causes a distortion of the triangular prisms
Nigel Pemberton-Pigott et al., A cluster line approach to finding new Fe-B-Y-I%-Zr bulk metallic glasses
making crystallization more difficult and thereby increasing the stability of the amorphous phase [16]. Based on the above considerations the ternary FeB-Y system was selected as a base, as it has already been shown to be stable when cast into rods with a diameter of 2 mm [17-181. The alloy compositions were designed by using the cluster line intersection method, and then adding minor elements Nb and Zr to the base compositions. Therefore, the Fe-B-Y-Nb-Zr system was investigated based on the cluster line method and minor alloying.
27
Therefore, four cluster composition lines, Fe,B,-Y, Fes3B,,-Y, Fe9B-Y and Fe12Y-Bare constructed in the Fe-B-Y system, as shown in Fig. 1. Fe,B,-Y, Fe,,B,,Y and Fe,B-Y cluster lines intersect with the Fe,,Y-B cluster line at the points 1=(Fe68.6B25.7Y5,7), 2= (Fe77,6B,5,9Y6,5)and 3=(Fe83,7B9,3Y7), respectively. These intersection points can be expressed by the relation (Fe121,3Y1113)100-xBx (x=9-26 B). To these three base alloys of 2at% Nb and 2at% Zr were then added.
2. Composition design On the basis of past research on quasicrystals and BMGs, a new approach using a cluster line method was proposed for the composition design of ternary alloys [4-71. The cluster line method was used in a ternary system by marking a straight line linking a specific binary cluster to the remaining third element. The specific binary cluster is the nearest-neighbor coordination cluster centered by a small atom in the local structure of a crystalline phase. From topologically close-packing considerations, a limited number of binary clusters are available: CN12 icosahedrons, CNlO capped Archimedes anti-prisms, and CN6, CN9 and CNll capped trigonal prisms [4]. In the Fe-rich corner of the binary Fe-B system, two different types of clusters characterize the local structures of the Fe-B crystalline phases, both of which are centered by a B atom, the capped Archimedes anti-prism Fe,B,, and the capped trigonal prism Fe,B. Moreover, the Fe-B eutectic point Fe,,B,, can be regarded as an Fe,B cluster glued with a B atom (Fe,B+B=Fe,B2=Fe,2B18=Fe83B17) according to the cluster structure model [4]. The ternary crystalline phase Fe62B14Y3 is characterized by an Fe,,Y icosahedron cluster centered by an Fe atom. The closepacking degree of these clusters was calculated according to Miracle's topologically efficient clusterpacking structure model [19], as shown in Table 1. R' is the ideal critical radius ratio under the condition of efficient packing for a definite coordination number of the nearest-neighbor clusters, which is defined as rdrl, where ro is the radius of the center atom and Y, the average radius of the nearest-neighbor shell atoms. Roll is the actual ratio of the atoms in the cluster. The radii (ro)of Fe, B and Y used in our calculations are 1.27, 0.98, and 1.80 nm, respectively. A is defined as the difference between the Rol, value and the ideal R' value represented by d=(R,,-R*)IR*. It can be seen that the clusters satisfy the topological close-packing requirement.
Fig. 1. Composition chart of the Fe-B-Y ternary system. Relevant binary clusters Fe,,B,, Fe& and Fe,,Y are shown in detail (open circles=Fe, small solid circles=B, large solid circle=Y). The solid lines are cluster lines, and the compositions at intersection points 1,2 and 3 are listed.
3. Experimental procedure The ingots of [(Fe12/13Y1/13)100-xBx196Nb2~r2 (x=9-26) alloys were prepared by arc melting their pure elements under an argon atmosphere. The purity of the elements are 99.99wt% for Fe, 99.9wt% for Y and 99.5wt% for B. The alloy compositions represent the nominal atomic percentages. Each sample was cooled and melted at least 3 times to ensure compositional homogeneity. During this melting process the samples were weighed periodically to determine whether more B should be added to make up for any weight loss, as it is known that B is difficult to melt into an alloy from it's pure state without loss of material. The melted samples were then cast into rods of 3 mm in diameter, and about 40 mm in length, using a copper mold suction-casting technique. Structural identification of these alloys was carried out by means of X-ray diffraction (XRD) analysis near the bottom end of the rods using chromatic Cu K, radiation ( A O . 15406 nm). The thermal properties were measured using digital scanning calorimetry (DSC) on a TA QIOO, at a constant heating rate of 20 Wmin, and under the flow of pure argon gas. The glass transition temperature (T,) was assumed to be the first decrease of the exothermic heat flow to the left of the
J. Univ. Sci. Technol. Beijing, Vo1.14, Suppl. 1, Jun 2007
28
first exothermic peak on the DSC curve. The crystallization temperature (T,) was assumed to be the onset temperature of the first exothermic crystallization peak, while the melting temperature (T,) and the liquidus temperature (Tl) were assumed to be the first and second onset points on the endothermic melting peak, respectively. Magnetic properties of saturation magnetization ( B J , remanent magnetization (M,) and coercive force (H,)were measured with a vibrating sample magnetometer (VSM) under an applied field of 1600 W m .
index parameters that are considered to be important to the indication of the glass forming ability of an alloy, such as reduced glass transition temperature (T,=T,T,), supercooled liquid temperature region (AT=T,-T,), and gamma (T,=T,/[T,+T,]). In general, the GFA of an alloy is expected to increase with increasing the magnitude of these thermal index parameters. It is also considered that a T,,>0.6 and a T ~ 0 . 3 5are indicative of a good GFA [20]. As can be seen from Table 1, all three samples satisfy these requirements, except for (Fe,4.9B18,8Y6,3)962r2~2 whose Trgis 0.59.
4. Results and discussion Fig. 2 shows the XRD patterns of the [(Fe12/13Yl/l 3) 1~-xBx]96m2Zr2 alloys for x=9.3, 15.9, 18.8, and 25.7. No BMG is formed at the composition (Fe83,7B9,3Y7)96Zr2Nb2 obtained at the intersection of the Fe,B-Y and Fel2Y-B cluster lines, as the alloy structure consists mainly of Fe in solid solution. The alloys in Fig. 2 between the intersection points 1 (Fe68.6B25.7Y5.7)and (Fe77,6B15.9y6.5) that were minor alloyed with Nb and Zr show a slight amorphous halo in the 28 range of 40"-48". For these samples between intersection points 1 and 2 of Fig. 2 the smaller peaks are identified as minor a-Fe, Fe3B and an Fe2$6 phases.
.-3 2
W
+d
c
e.
1
I
15
25
35
45
55
65
75
85
28/ (")
Fig. 2. X-ray patters for [(Fe,,,,Y,,,),,,B,J,Nb,Zr, (x=9.3, 15.9, 18.8, and 25.7 B) rods of 3 mm in diameters. The smaller peaks for x=15.9,18.8 and 25.7 are identified as minor a-Fe, Fe,B and Fe,B, phases.
Fig. 3 shows the DSC traces of [(Fe,2/13Y1113)loo_xB,196Nb2Zr2 for the compositions with x=15.9, 18.8, and 25.7. An obvious glass transition before the exothermic crystallization peaks is manifest in all three traces. For x=15.9, 18.8, and 25.7 the values of Tg are 890, 837, and 875 K, respectively. The crystallization temperature for the case of x=25.7 had the highest T,=996 K, while for x=15.9 is slightly less at T,=986 K. For x=18.8 the DSC trace shows a relatively low value of T,=933 K followed by a small exothermic peak before stabilizing and then followed by another much larger crystallization peak. The T, and TI values for all three cases are around 1370 and 1415 K, respectively. The thermal parameters Tgr T,, T,, and TI for all three samples are listed in Table 2. From this data we are able to calculate several thermal
Suction cast 3 m m [(Fe,,,,,Y,,,,),,,B,1,Nb,Zr2 roc
4 L d
r
600
800
1000 1200 Temperature / K
1400
Fig. 3. DSC traces for suction cast [ ( F e l ~ 1 3 Y ~ l ~ ) l ~ ~ B ~ ] ~ Nb,Zrz (x=15.9, 18.8, and 25.7) rods with diameters of 3 mm.
Table 1. Atomic ratios for Fe-B and Fe-Y clusters. Cluster
Cluster type
Center atom
R*
r, / nm
r , / nm
Ro,l=rdy,
A/%
Fe,B, Fe,B
Archimedes anti-prism Capped trigonal prism
Fe,,Y
Icosahedron
Boron Boron Iron
0.799 0.710 0.902
0.98 0.98 1.27
1.212 1.27 1.314
0.809 0.772 0.967
1.2 8.7 7.2
Note: R' is the ideal atomic radius ratio, r , the average radius of the nearest-neighbor shell atoms, R , , the actual ratio of inner atom to surrounding atom, and A the percent difference between actual and ideal ratios.
For x=18.8 the supercooled liquid region had the smallest value of 96 K, while for x=15.9 and 25.7 the
AT values were 106 and 111 K, respectively. These are believed to be the largest values for the super-
29
Nigel Pemberton-Pigoft et al., A cluster line approach to finding new Fe-B-Y-Nb-Zrbulk metallic glasses
cooled liquid region of an iron based alloy reported to date [21-221. For the case of x=25.7 and 18.8 the samples appeared to be only partially amorphous as DSC and X-ray analysis near the center of the 3-mm rods showed a crystalline structure, whereas the x=l5.9 sample demonstrated amorphous behavior along the entire length of the 3-mm cast rod. From the calculated data in Table 2 it can be seen that the case of x=15.9 has higher thermal parameters and is thus .considered to be more thermally stable than the other two alloys. One can also see from Fig. 1 that this compo-
sition is located at the intersection of the cluster lines that originate at the Fe,,Y binary cluster and the Fes3B1, binary eutectic point. These two clusters are respectively an icosahedron (Fe,,Y) and a capped trigonal prism (Fe,B), and it is assumed that the formation of a bulk metallic glass is due to the favorable arrangement of these two close-packed clusters. These results indicate that BMGs can be found in the range of 15.9at%-25.7at% B when suction-cast into 3-mm diameter rods.
Table 2. Thermal properties from the DSC traces of [(Fe,,,,Y,,,,),,B,],Nb,Zr, diameter T,IK 996 933 986
T,/K 890 837 875
Alloy (Fe68.6B25.7Y5,7)96Zr2Nb2
(Fe74.9Bi8,8Y6,3)96Zr2Nb2
(Fe77.6Bi5.9Y6.5)96zr2Nb2
T,IK 1374 1370 1371
Fig. 4 shows the typical B-H magnetization loop of the (Fe74.9B18,8Y6,3)96Nb2Zr2 BMG. The saturation magnetization ( B J , remanent magnetization ( M J , and coercive force (H,) are 0.88 T, 0.1 T, and 10.9 W m , respectively. In order to be a good soft magnetic material the coercive force should be Hc<10N m , whereas a hard magnetic material will have a coercive force of more than several thousand amp-turns per meter. Thus, the above BMGs are considered to be hard magnetic materials.
I
I
-600
I
I
I
I
I
,
-200 200 400 600 800 -0 2 H I (kA m I) -0.4
Fig. 4. Magnetization(B) versus applied magnetic field (H) curve of the [(Fe,,,3Y,,,3),,B,],,Nb2Zr2 (x=18.8) rod with a diameter of 3 mm. The values of saturation magnetization (BJ, remanent magnetization ( M J , and coercive force (H,) are shown.
5. Conclusion Using a cluster line approach and a copper mold suction-casting technique a portion of the Fe-B-Y-ZrNb quinary system was successfully investigated. Bulk metallic glasses were found in the range falling between the intersections of three separate cluster lines originating at Fe8&, Fe8B3 and Fel,Y representing a range of 15.9at%-25.7at% B. Alloys in this range showed a large value of coercive force Hc=10.9
T,/K 1415 1411 1416
T,, 0.63 0.59 0.62
(x=15.9, 18.8, and 25.7) rods of 3 mm in
AT 106 96 111
T, 0.43 0.41 0.43
kA/m, a saturation magnetization of B,=0.88 T, and remanent magnetization of M,=O. 1 T, demonstrating hard magnetic properties. It was also found that the (Fe,,,6B 15.9Y6.5)96Zr2Nb2 alloy located at the intersection of the Fes3B,,-Y and Fe,,Y-B cluster lines exhibited the best thermal stability in terms of the gamma parameter (T,=0.43), reduced glass transition temperature (T,=0.62), and supercooled liquid region (AT=lll K), enabling the fabrication of rods with a diameter of 3 mm. This is believed to be the largest supercooled liquid region reported to date for any Febased BMG. The glass-forming tendency of these alloys further validates the cluster-based approach to finding BMGs.
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