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Thermal stability and glass-forming ability of new Ti-based bulk metallic glasses
Journal of Non-Crystalline Solids 351 (2005) 3747–3751 www.elsevier.com/locate/jnoncrysol
Thermal stability and glass-forming ability of new Ti-based bulk metallic glasses Xia Ming-xu a, Zheng Hong-xing a, Liu Jian a, Ma Chao-li b, Li Jian-guo a
a,*
School of Materials Science and Engineering, Shanghai Jiao Tong University, 1954, Huashan Road, Shanghai 200030, China b School of Materials and Engineering, Bei Hang University, Beijing 100083, China Received 27 February 2005; received in revised form 3 September 2005
Abstract New Ti-based metallic glass (Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb)) alloys were prepared by melt spinning and copper mold casting. The effects of foreign atoms on the thermal stability and the glass-forming ability were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). The results show that the values of Trgs are 0.619, 0.609, 0.606, K and DTxs are 58, 54, 85, 78 K, respectively. The foreign atomÕs size factor (kRF RTij/RTi 0.12j) and mixP 0.597P ing heat factor ( xiHiF/ xiWi) are proposed to predict the glass-forming ability and thermal stability, respectively. 2005 Elsevier B.V. All rights reserved. PACS: 61.43.Dq; 64.70.Pf; 68.60.Dv
1. Introduction In the past, much attention has been devoted to the development of bulk metallic glassy alloys for their unique mechanical and physical properties. New multicomponent alloy systems with much lower critical cooling rates (6102 K/s) have been developed, some of which can be produced with a fully amorphous structure at thickness approaching 70 mm by using conventional casting processes [1–3]. At the same time, great efforts have also been made to understand the mechanism of amorphization for the prediction of alloy compositions with better glass-forming ability (GFA). In this regard, of which InoueÕs three empirical rules [3] suggests that the composition of a glass former generally should satisfy the following conditions: (a) three or more elements; (b) a difference of atomic size ratios higher than about 12% among the three main constituent elements; and (c) negative heats of mixing among the three main constituent elements. Points (a) and (b) indi-
*
Corresponding author. Tel.: +86 21 62932569; fax: +86 21 62933074. E-mail address: [email protected] (J.-g. Li).
0022-3093/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.09.033
cate the importance of topology in glass formation and (c) is supported by the experimental fact that the glass formation composition range generally coincides with the eutectic region. Egami et al. [4–6] proposed a correlation between the minimum solute concentrations required for glass formation and the extent of the atomic size mismatch in binary alloys: 3
C min ¼ 0:1=jðRB =RA Þ 1j; s
ð1Þ
where RA and RB are the atomic radii of the solvent A and the solute B, respectively. Miracle and Senkov [7] developed the above topological criterion for glass formation in binary and multicomponent alloy systems. This criterion indicated that fractions of a solute in interstitial and substitutional sites and the internal strain were functions of the radius ratio of solute and matrix elements, their elastic moduli, and absolute temperature. According to the criterion, the critical concentration initially decreases, reaches a minimum at R 0.8 and then increases as the radius ration decreases from 1 to 0.5. Additionally, there are also many thermodynamic [8] and electronic [9] models proposed.
Although these rules give useful directions for predicting glass-former compositions, they are rather limited. The development of new amorphous alloys is still very timeconsuming, involving for the selection and screening of different element combinations. Moreover, these rules are impractical on the selection of atoms added to an existing system for improving its properties. In the present paper, we explored the effect of alloying elements Sc, Hf, Ta and Nb on the glass-forming ability and thermal stability of the glass-former Ti53Cu15Ni18.5Al7Si3Zr3B0.5 and proposed two parameters to express the glass-forming ability and thermal stability, respectively. 2. Experimental procedure Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb) alloys were prepared by arc melting mixtures of high purity metals under a purified argon atmosphere. Boron was firstly alloyed with Ni in advance of arc melting with other raw materials to ensure compositional homogeneity. Ribbon samples were prepared by single-roller melt spinning with a cross-section of 0.02 · 1.0 mm2. Cast rods with diameters of 1.0, 1.5 and 2.0 mm were prepared by conventional copper mold casting method under a purified Ar atmosphere. The crystallization of the glass was assessed by an annealing treatment for 2 h. The structure of the bulk alloys was identified by X-ray diffraction. The thermal stability associated with glass transition temperature, Tg, crystallization temperature, Tx, first crystallization peak temperature, Tp, were examined at a heating rate of 0.67 K/s with a differential scanning calorimeter (DSC). Melting behavior (melting point, Tm, liquidus temperature, Tl) was determined by differential thermal analysis (DTA) at a heating rate of 0.17 K/s, respectively. The temperatures were calibrated with a pure In standard sample with temperature accuracy better than ±0.2 K. 3. Results Fig. 1 shows the XRD patterns of the cast rods with different foreign atoms. Only one broad peak was found in the patterns of Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf) 2 mm diameter rods. These broad peaks indicate that the rods are in a fully amorphous state. The results show that alloys containing Sc and Hf have a greater glass-forming ability than the alloys containing Ta and Nb. Sc and Hf suppressed the crystallization of the melts, but Ta and Nb do not play the same role. Fig. 2 shows the DSC curves of the alloysÕ ribbons. It is found that these alloys have a complex thermal response associated with multiple crystallization events during heating. The different curve shapes indicated different exothermic processes, i.e. different foreign atoms lead to the different crystallization processes. Moreover, clear glass transition behavior is observed in the temperature range before crystallization for the Ti53Cu15Ni18.5Al7Si3M3B0.5
Intensity (a.u.)
M.-x. Xia et al. / Journal of Non-Crystalline Solids 351 (2005) 3747–3751
M=Hafnium
Dmax=2mm
M=Scandium
Dmax=2mm Dmax=1.5mm
M=Niobium
Dmax=1.5mm
M=Tantalum
20
30
40 50 60 2Theta (Degree)
70
80
Fig. 1. X-ray diffraction patterns of the cast amorphous Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Sc, Hf, Ta, Nb) alloys.
Heating rate 0.67K/s
Exothermic
3748
M=Hafnium M=Scandium M=Niobium M=Tantalum
650
700
750
800
850
900
950
1000
Temperature, T/K Fig. 2. DSC patterns of the Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Sc, Hf, Ta, Nb) ribbons at 0.67 K/s.
glassy alloys. The liquidus temperatures (Tl) of the alloys were measured by DTA. The reduced glass transition temperature Trg (Trg = Tg/Tl), the supercooled liquid region DTx (DTx = Tx Tg), and the parameter c (c = Tx/(Tg + Tl)) [10] were calculated and listed in Table 1 with Tg, Tx and Tl. The radii of the foreign atoms and the maximum rod diameters of fully amorphous alloys (Dmax) are also listed in Table 1 to assess their interrelationship with glass-forming ability. The data in Table 1 indicate that Trg has a much closer relationship with glass-forming ability than DTx and c. The effect of the foreign atoms on thermal stability can be assessed by the Kissinger equation [12,13]. According to the peak shifts on the DSC curves obtained at different heating rates, the apparent activation energy of crystallization can be obtained by lnðB=T 2 Þ ¼ E=RT þ Constant;
ð2Þ
where B is the heating rate, E is the apparent activation energy for the process, R is the gas constant and T is a specific absolute temperature such as peak temperature Tp, which can be measured at selected heating rates B. By plotting
M.-x. Xia et al. / Journal of Non-Crystalline Solids 351 (2005) 3747–3751
3749
Table 1 Thermal stability and glass-forming ability of Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Sc, Hf, Ta, Nb) Elements
RF [11] (valence), nm
Tg, T/K
Tx, T/K
Tl, T/K
DTx, T/K
Trg
c
jRF RTijRTi
Dmax, mm
Sc Hf Ta Nb
0.1641(3) 0.1580(4) 0.1467(5) 0.1822(3)
709 695 675 669
767 749 760 747
1240 1230 1254 1252
58 54 85 78
0.619 0.609 0.606 0.597
0.394 0.389 0.394 0.389
0.122 0.081 0.003 0.246
2 2 <1.5 <1.5
R2 = 0.9436
-9.5
Ln(B/T 2 )
Intensity (a.u.)
M=Hafnium M=Scandium M=Niobium M=Tantalum
20
30
40
50
60
70
80
2 Theta (Degree) Fig. 4. XRD Patterns of the Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Hf, Nb, Ta, Sc) after 2 h annealed.
85 80 75 70 65 60 R2 = 0.99762
55 50 340
360
380
400
420
440
Active Energy (kJ/mol) Fig. 5. Activation energy versus DTx of the Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Hf, Nb, Ta, Sc). The curve shows the tendency of the data draw by Excel.
-9.3 M=Niobium M=Hafnium
-9.7
M=Scandium
-9.9
M=Tantalum
-10.1
Annealed at 793K for 2h
∆Tx (K)
ln(B/T2) versus 1/(RT), an approximately straight line will be obtained. The slope of the straight line is just the apparent activation energy (E) of the specified process. If Tp for different heating rates is chosen, the activation energy Ep can be calculated. In our experiments, the heating rates were chosen as 10, 20, 30 and 40 K/min, and the primary crystallization temperatures. Using these data, the activation energies of primary crystallization were calculated in Fig. 3. The results show that activation energies of the alloys with Sc, Hf, Ta, Nb are 356.31, 355.02, 437.27, 375.55 kJ/mol, respectively. It should be noticed that a lower activation energy is obtained in the crystallization of alloys with Sc and Hf, which confirms that glassy structures of Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf) are more easily transformed to crystalline phases at the same heating conditions. To further verify the Kissinger plots results, the glassy alloy ribbons were annealed at 793 K, the terminal temperature of the first crystallization, for 2 h in Ar atmosphere. Fig. 4 shows the XRD patterns of these annealing ribbon samples. Several sharp peaks formed in the annealed Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Hf, Sc) samples while only two peaks were found in the large humps characterizing the XRD of alloys containing Nb and Ta. That is to say, in the annealing process, the crystallizations of the alloys with Hf and Sc was more pronounced than the alloys with Nb and Ta for similar treatment times. Combining the DTx and activation energy of primary crystallization data for alloys, it is found that the higher the activation energy for crystallization, the more stable the alloys is, and the larger the value of DTx that is exhibited (Fig. 5). Conversely,
R2 = 0.9608
-10.3 -10.5
4. Discussion
-10.7 -10.9 -11.1 -11.3 0.155
the lower the activation energy for crystallization, the more unstable the alloy is, and the smaller the value of DTx is observed.
R2 = 0.9968 R2 = 0.9971 0.157
0.159
0.161
0.163
1/RT ×103
Fig. 3. Kissinger plots of the Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Sc, Hf, Ta, Nb). The activation energy can be calculated using the slope of the linear regression fit.
Bulk glassy alloys have more randomly denser packed atomic configurations than ordinary amorphous alloys [14]. The formation of liquid phase clusters with specific atomic configurations and multicomponent interactions on a short-range scale will increase the solid–liquid interfacial energy and decrease atomic diffusivity, thus suppressing the nucleation and growth of crystalline phases
M.-x. Xia et al. / Journal of Non-Crystalline Solids 351 (2005) 3747–3751
in melts [3]. The effects of atomic configurations and multicomponent interactions related to topological complexity and major atoms size effects have been discussed in Refs. [2–4]. The results suggest that a 12% difference in atomic radius is an important factor affecting the glassforming ability of alloys. This radius difference supports enough disorder in structural topology to enable the formation of amorphous structure during solidification. In our experiments, the atom size effect was also considered for glass-forming ability. The plots of size effect versus Trg are shown in Fig. 6. From the curve, we found that the large glass-forming ability would be obtained when kRF RTij/RTi 0.12j is small, where RF is radius of foreign atoms and RTi is radius of Ti, 1.462(4). The glassforming ability of glass former systems will be enhanced by increasing the density of the metallic glass matrix using foreign atoms with appropriate radius. According to this idea, we believed that Ti53Cu15Ni18.5Al7Si3Zr3B0.5 would have a larger glass-forming ability because Zr is chemically quite similar to Hf and the addition of Zr would increase the density of the topological structure in solidification. The results shown in Refs. [15,16] support this assumption. So, in general, a rule based on the Ôtopological principleÕ suggests that glass-forming ability can be improved by adding foreign atoms to improve the stability of the topological structures in the alloy. The mixing heats of the foreign atoms (Table 2) with all other elements [17] were another important factor in these experiments. The Inoue component rules indicate that
0.625 R2 = 0.83573
0.620
Trg
0.615 0.610 0.605 0.600 0.595 0.00
0.02
0.04
0.06
0.08
0.10
0.12
90 80
R2 = 0.7107 R2 = 0.78185
70 60 50 40 30
R2 = 0.99835
R2 = 0.95737
20 10 0 -10
Ti53Cu15Ni18.5Al7Si3B0.5M3(M=Ta,Nb,Hf,Sc,Zr) Zr65Ni5Cu15Al10M5(M=Fe,Co,Pd,Ag) Zr63.4Ni9.8Cu14.69Al9.75M2.5(M=V,Nb,Cr) Zr65Cu15Al10M10(M=Fe,Co,Pd,Ag)
-20 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1
0.0
Σx iHi/ Σ xiWi, KJ
Fig. 7. The relationship between mixing heats and thermal stability was showed by the dotted line draw by Excel.
higher glass-forming ability can be obtained when the main components have negative heats of mixing. However, the heats of mixing foreign atomsÕ for other components is often omitted. When the effect of the heat of mixing on the thermal stability was considered, we found that there exists a non-monotonic relationship between heat of mixing and P P thermal stability. The mixing heat factor, xi H iF = xi W i versus DTx is plotted in Fig. 7, where xi is the concentration of the ith constituent, HiF is mixing heat among the foreign atom and the ith constituent, and Wi is atom weight of the ith constituent. plot reveals P The P a para-curve relationship between xi H iF = xi W i and DTx, which suggests that the crystallization of the systems is a process controlled by interactions between the atoms. According to this rule, introducing specific foreign atoms would enhance the stability of bulk metallic glass former systems. The same relationships were also found in the other systems [18,19], and the data of these systems were also plotted in Fig. 7 with Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb). The P resultsPshow that the para-curve relationships between xi H iF = xi W i and DTx exists in other systems, and that it can be used to predict the stability of glass formers with foreign atoms.
0.14
5. Conclusion
||RTi-Ri|/RTi-0.12| Fig. 6. The dependence of glass-forming ability on the radius difference between the foreign atoms and Ti. The tendency curves draw by Excel.
Table 2 Hmix (kJ/mol) [17] of the foreign atoms with other components
Ti Cu Ni Al Si B
100
∆Tx, K
3750
Hf
Nb
Ta
Sc
0 17 42 39 60 51
2 3 30 16 39 39
1 2 29 19 39 39
8 24 39 38 57 40
Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb) glassy rods with diameters 2 mm were obtained by copper mold casting. The thermal analysis results show that the value of Trgs and DTxs of Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb) are 0.619, 0.609, 0.606, 0.597 and 58, 54, 85, 78 K, respectively. Maximum diameters of alloys, the activation energies of primary crystallization and XRD patterns of alloys annealed for 2 h suggest that Trg and DTx have intimate relationship with glass-forming ability and thermal stability of the alloys, respectively. The foreign atomÕs P size factor P(kRFRTij/RTi 0.12j) and mixing heat factor ( xiHiF/ xiWi) were proposed to predict the glassforming ability and thermal stability, respectively.
M.-x. Xia et al. / Journal of Non-Crystalline Solids 351 (2005) 3747–3751
Acknowledgements The authors express their appreciation for the financial support of the National Natural Science Foundation of China under Grant No. 50274051 and the National Science Fund for Distinguished Young Scholars of China under Grant No. 50125101.
[7] [8] [9] [10] [11] [12] [13] [14]
References [15] [1] A. Inoue, Prog. Mater. Sci. 43 (1998) 365. [2] W.L. Johnson, in: W.L. Johnson, A. Inoue, C.T. Liu (Eds.), Bulk Metallic Glasses, MRS Symposium Proceedings, Materials Research Society, Warrendale, PA, 1999, p. 311. [3] A. Inoue, Acta Mater. 48 (2000) 279. [4] T. Egami, Y. Waseda, J. Non-Cryst. Solids 64 (1984) 113. [5] T. Egami, J. Non-Cryst. Solids 205–207 (1996) 575. [6] T. Egami, Mater. Sci. Eng. A 226–228 (1997) 261.
[16] [17] [18] [19]
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D.B. Miracle, O.N. Senkov, Mater. Sci. Eng. A 347 (2003) 50. S.H. Whang, Mater. Sci. Eng. A 57 (1983) 87. S.R. Nagel, J. Tauc, Phys. Rev. Lett. 35 (1975) 380. Z.P. Lu, C.T. Liu, Acta Mater. 50 (2002) 3501. T. Hahn, International Tables for Crystallography, Kluwer Academic Publishers, Boston, MA, 1995, 681. H.E. Kissinger, Analyt. Chem. 29 (1957) 1702. Y.Q. Gao, W. Wang, J. Non-Cryst. Solids 81 (1986) 129. A.R. Yavari, A. Inoue, in: W.L. Johnson, A. Inoue, C.T. Liu (Eds.), Bulk Metallic Glasses, Material Research Society Symposium Proceedings, MRS, Warrendal, PA, 1999, p. 21. C.L. Ma, S. Ishihara, H. Soejima, N. Nishiyama, A. Inoue, Mater. Trans. 45 (2004) 1802. C.L. Ma, H. Soejima, S. Ishihara, K. Amiya, N. Nishiyama, A. Inoue, Mater. Trans. 45 (2004) 3223. F.R. de Boer, R. Boom, W.C.M. Mattens, A.R. Miedema, A.K. Niessen, Cohesion in Metals, North-Holland, 1989, p. 291. A. Inoue, T. Shibata, T. Zhang, Mater. Trans. JIM 12 (1995) 1420. Z.P. Lu, C.T. Liu, Y.D. Dong, J. Non-Cryst. Solids 341 (2004) 93.
Thermal stability and glass-forming ability of new Ti-based bulk metallic glasses Xia Ming-xu a, Zheng Hong-xing a, Liu Jian a, Ma Chao-li b, Li Jian-guo a
a,*
School of Materials Science and Engineering, Shanghai Jiao Tong University, 1954, Huashan Road, Shanghai 200030, China b School of Materials and Engineering, Bei Hang University, Beijing 100083, China Received 27 February 2005; received in revised form 3 September 2005
Abstract New Ti-based metallic glass (Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb)) alloys were prepared by melt spinning and copper mold casting. The effects of foreign atoms on the thermal stability and the glass-forming ability were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). The results show that the values of Trgs are 0.619, 0.609, 0.606, K and DTxs are 58, 54, 85, 78 K, respectively. The foreign atomÕs size factor (kRF RTij/RTi 0.12j) and mixP 0.597P ing heat factor ( xiHiF/ xiWi) are proposed to predict the glass-forming ability and thermal stability, respectively. 2005 Elsevier B.V. All rights reserved. PACS: 61.43.Dq; 64.70.Pf; 68.60.Dv
1. Introduction In the past, much attention has been devoted to the development of bulk metallic glassy alloys for their unique mechanical and physical properties. New multicomponent alloy systems with much lower critical cooling rates (6102 K/s) have been developed, some of which can be produced with a fully amorphous structure at thickness approaching 70 mm by using conventional casting processes [1–3]. At the same time, great efforts have also been made to understand the mechanism of amorphization for the prediction of alloy compositions with better glass-forming ability (GFA). In this regard, of which InoueÕs three empirical rules [3] suggests that the composition of a glass former generally should satisfy the following conditions: (a) three or more elements; (b) a difference of atomic size ratios higher than about 12% among the three main constituent elements; and (c) negative heats of mixing among the three main constituent elements. Points (a) and (b) indi-
*
Corresponding author. Tel.: +86 21 62932569; fax: +86 21 62933074. E-mail address: [email protected] (J.-g. Li).
0022-3093/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.09.033
cate the importance of topology in glass formation and (c) is supported by the experimental fact that the glass formation composition range generally coincides with the eutectic region. Egami et al. [4–6] proposed a correlation between the minimum solute concentrations required for glass formation and the extent of the atomic size mismatch in binary alloys: 3
C min ¼ 0:1=jðRB =RA Þ 1j; s
ð1Þ
where RA and RB are the atomic radii of the solvent A and the solute B, respectively. Miracle and Senkov [7] developed the above topological criterion for glass formation in binary and multicomponent alloy systems. This criterion indicated that fractions of a solute in interstitial and substitutional sites and the internal strain were functions of the radius ratio of solute and matrix elements, their elastic moduli, and absolute temperature. According to the criterion, the critical concentration initially decreases, reaches a minimum at R 0.8 and then increases as the radius ration decreases from 1 to 0.5. Additionally, there are also many thermodynamic [8] and electronic [9] models proposed.
Although these rules give useful directions for predicting glass-former compositions, they are rather limited. The development of new amorphous alloys is still very timeconsuming, involving for the selection and screening of different element combinations. Moreover, these rules are impractical on the selection of atoms added to an existing system for improving its properties. In the present paper, we explored the effect of alloying elements Sc, Hf, Ta and Nb on the glass-forming ability and thermal stability of the glass-former Ti53Cu15Ni18.5Al7Si3Zr3B0.5 and proposed two parameters to express the glass-forming ability and thermal stability, respectively. 2. Experimental procedure Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb) alloys were prepared by arc melting mixtures of high purity metals under a purified argon atmosphere. Boron was firstly alloyed with Ni in advance of arc melting with other raw materials to ensure compositional homogeneity. Ribbon samples were prepared by single-roller melt spinning with a cross-section of 0.02 · 1.0 mm2. Cast rods with diameters of 1.0, 1.5 and 2.0 mm were prepared by conventional copper mold casting method under a purified Ar atmosphere. The crystallization of the glass was assessed by an annealing treatment for 2 h. The structure of the bulk alloys was identified by X-ray diffraction. The thermal stability associated with glass transition temperature, Tg, crystallization temperature, Tx, first crystallization peak temperature, Tp, were examined at a heating rate of 0.67 K/s with a differential scanning calorimeter (DSC). Melting behavior (melting point, Tm, liquidus temperature, Tl) was determined by differential thermal analysis (DTA) at a heating rate of 0.17 K/s, respectively. The temperatures were calibrated with a pure In standard sample with temperature accuracy better than ±0.2 K. 3. Results Fig. 1 shows the XRD patterns of the cast rods with different foreign atoms. Only one broad peak was found in the patterns of Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf) 2 mm diameter rods. These broad peaks indicate that the rods are in a fully amorphous state. The results show that alloys containing Sc and Hf have a greater glass-forming ability than the alloys containing Ta and Nb. Sc and Hf suppressed the crystallization of the melts, but Ta and Nb do not play the same role. Fig. 2 shows the DSC curves of the alloysÕ ribbons. It is found that these alloys have a complex thermal response associated with multiple crystallization events during heating. The different curve shapes indicated different exothermic processes, i.e. different foreign atoms lead to the different crystallization processes. Moreover, clear glass transition behavior is observed in the temperature range before crystallization for the Ti53Cu15Ni18.5Al7Si3M3B0.5
Intensity (a.u.)
M.-x. Xia et al. / Journal of Non-Crystalline Solids 351 (2005) 3747–3751
M=Hafnium
Dmax=2mm
M=Scandium
Dmax=2mm Dmax=1.5mm
M=Niobium
Dmax=1.5mm
M=Tantalum
20
30
40 50 60 2Theta (Degree)
70
80
Fig. 1. X-ray diffraction patterns of the cast amorphous Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Sc, Hf, Ta, Nb) alloys.
Heating rate 0.67K/s
Exothermic
3748
M=Hafnium M=Scandium M=Niobium M=Tantalum
650
700
750
800
850
900
950
1000
Temperature, T/K Fig. 2. DSC patterns of the Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Sc, Hf, Ta, Nb) ribbons at 0.67 K/s.
glassy alloys. The liquidus temperatures (Tl) of the alloys were measured by DTA. The reduced glass transition temperature Trg (Trg = Tg/Tl), the supercooled liquid region DTx (DTx = Tx Tg), and the parameter c (c = Tx/(Tg + Tl)) [10] were calculated and listed in Table 1 with Tg, Tx and Tl. The radii of the foreign atoms and the maximum rod diameters of fully amorphous alloys (Dmax) are also listed in Table 1 to assess their interrelationship with glass-forming ability. The data in Table 1 indicate that Trg has a much closer relationship with glass-forming ability than DTx and c. The effect of the foreign atoms on thermal stability can be assessed by the Kissinger equation [12,13]. According to the peak shifts on the DSC curves obtained at different heating rates, the apparent activation energy of crystallization can be obtained by lnðB=T 2 Þ ¼ E=RT þ Constant;
ð2Þ
where B is the heating rate, E is the apparent activation energy for the process, R is the gas constant and T is a specific absolute temperature such as peak temperature Tp, which can be measured at selected heating rates B. By plotting
M.-x. Xia et al. / Journal of Non-Crystalline Solids 351 (2005) 3747–3751
3749
Table 1 Thermal stability and glass-forming ability of Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Sc, Hf, Ta, Nb) Elements
RF [11] (valence), nm
Tg, T/K
Tx, T/K
Tl, T/K
DTx, T/K
Trg
c
jRF RTijRTi
Dmax, mm
Sc Hf Ta Nb
0.1641(3) 0.1580(4) 0.1467(5) 0.1822(3)
709 695 675 669
767 749 760 747
1240 1230 1254 1252
58 54 85 78
0.619 0.609 0.606 0.597
0.394 0.389 0.394 0.389
0.122 0.081 0.003 0.246
2 2 <1.5 <1.5
R2 = 0.9436
-9.5
Ln(B/T 2 )
Intensity (a.u.)
M=Hafnium M=Scandium M=Niobium M=Tantalum
20
30
40
50
60
70
80
2 Theta (Degree) Fig. 4. XRD Patterns of the Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Hf, Nb, Ta, Sc) after 2 h annealed.
85 80 75 70 65 60 R2 = 0.99762
55 50 340
360
380
400
420
440
Active Energy (kJ/mol) Fig. 5. Activation energy versus DTx of the Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Hf, Nb, Ta, Sc). The curve shows the tendency of the data draw by Excel.
-9.3 M=Niobium M=Hafnium
-9.7
M=Scandium
-9.9
M=Tantalum
-10.1
Annealed at 793K for 2h
∆Tx (K)
ln(B/T2) versus 1/(RT), an approximately straight line will be obtained. The slope of the straight line is just the apparent activation energy (E) of the specified process. If Tp for different heating rates is chosen, the activation energy Ep can be calculated. In our experiments, the heating rates were chosen as 10, 20, 30 and 40 K/min, and the primary crystallization temperatures. Using these data, the activation energies of primary crystallization were calculated in Fig. 3. The results show that activation energies of the alloys with Sc, Hf, Ta, Nb are 356.31, 355.02, 437.27, 375.55 kJ/mol, respectively. It should be noticed that a lower activation energy is obtained in the crystallization of alloys with Sc and Hf, which confirms that glassy structures of Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf) are more easily transformed to crystalline phases at the same heating conditions. To further verify the Kissinger plots results, the glassy alloy ribbons were annealed at 793 K, the terminal temperature of the first crystallization, for 2 h in Ar atmosphere. Fig. 4 shows the XRD patterns of these annealing ribbon samples. Several sharp peaks formed in the annealed Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Hf, Sc) samples while only two peaks were found in the large humps characterizing the XRD of alloys containing Nb and Ta. That is to say, in the annealing process, the crystallizations of the alloys with Hf and Sc was more pronounced than the alloys with Nb and Ta for similar treatment times. Combining the DTx and activation energy of primary crystallization data for alloys, it is found that the higher the activation energy for crystallization, the more stable the alloys is, and the larger the value of DTx that is exhibited (Fig. 5). Conversely,
R2 = 0.9608
-10.3 -10.5
4. Discussion
-10.7 -10.9 -11.1 -11.3 0.155
the lower the activation energy for crystallization, the more unstable the alloy is, and the smaller the value of DTx is observed.
R2 = 0.9968 R2 = 0.9971 0.157
0.159
0.161
0.163
1/RT ×103
Fig. 3. Kissinger plots of the Ti53Cu15Ni18.5Al7M3Si3B0.5 (M = Sc, Hf, Ta, Nb). The activation energy can be calculated using the slope of the linear regression fit.
Bulk glassy alloys have more randomly denser packed atomic configurations than ordinary amorphous alloys [14]. The formation of liquid phase clusters with specific atomic configurations and multicomponent interactions on a short-range scale will increase the solid–liquid interfacial energy and decrease atomic diffusivity, thus suppressing the nucleation and growth of crystalline phases
M.-x. Xia et al. / Journal of Non-Crystalline Solids 351 (2005) 3747–3751
in melts [3]. The effects of atomic configurations and multicomponent interactions related to topological complexity and major atoms size effects have been discussed in Refs. [2–4]. The results suggest that a 12% difference in atomic radius is an important factor affecting the glassforming ability of alloys. This radius difference supports enough disorder in structural topology to enable the formation of amorphous structure during solidification. In our experiments, the atom size effect was also considered for glass-forming ability. The plots of size effect versus Trg are shown in Fig. 6. From the curve, we found that the large glass-forming ability would be obtained when kRF RTij/RTi 0.12j is small, where RF is radius of foreign atoms and RTi is radius of Ti, 1.462(4). The glassforming ability of glass former systems will be enhanced by increasing the density of the metallic glass matrix using foreign atoms with appropriate radius. According to this idea, we believed that Ti53Cu15Ni18.5Al7Si3Zr3B0.5 would have a larger glass-forming ability because Zr is chemically quite similar to Hf and the addition of Zr would increase the density of the topological structure in solidification. The results shown in Refs. [15,16] support this assumption. So, in general, a rule based on the Ôtopological principleÕ suggests that glass-forming ability can be improved by adding foreign atoms to improve the stability of the topological structures in the alloy. The mixing heats of the foreign atoms (Table 2) with all other elements [17] were another important factor in these experiments. The Inoue component rules indicate that
0.625 R2 = 0.83573
0.620
Trg
0.615 0.610 0.605 0.600 0.595 0.00
0.02
0.04
0.06
0.08
0.10
0.12
90 80
R2 = 0.7107 R2 = 0.78185
70 60 50 40 30
R2 = 0.99835
R2 = 0.95737
20 10 0 -10
Ti53Cu15Ni18.5Al7Si3B0.5M3(M=Ta,Nb,Hf,Sc,Zr) Zr65Ni5Cu15Al10M5(M=Fe,Co,Pd,Ag) Zr63.4Ni9.8Cu14.69Al9.75M2.5(M=V,Nb,Cr) Zr65Cu15Al10M10(M=Fe,Co,Pd,Ag)
-20 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1
0.0
Σx iHi/ Σ xiWi, KJ
Fig. 7. The relationship between mixing heats and thermal stability was showed by the dotted line draw by Excel.
higher glass-forming ability can be obtained when the main components have negative heats of mixing. However, the heats of mixing foreign atomsÕ for other components is often omitted. When the effect of the heat of mixing on the thermal stability was considered, we found that there exists a non-monotonic relationship between heat of mixing and P P thermal stability. The mixing heat factor, xi H iF = xi W i versus DTx is plotted in Fig. 7, where xi is the concentration of the ith constituent, HiF is mixing heat among the foreign atom and the ith constituent, and Wi is atom weight of the ith constituent. plot reveals P The P a para-curve relationship between xi H iF = xi W i and DTx, which suggests that the crystallization of the systems is a process controlled by interactions between the atoms. According to this rule, introducing specific foreign atoms would enhance the stability of bulk metallic glass former systems. The same relationships were also found in the other systems [18,19], and the data of these systems were also plotted in Fig. 7 with Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb). The P resultsPshow that the para-curve relationships between xi H iF = xi W i and DTx exists in other systems, and that it can be used to predict the stability of glass formers with foreign atoms.
0.14
5. Conclusion
||RTi-Ri|/RTi-0.12| Fig. 6. The dependence of glass-forming ability on the radius difference between the foreign atoms and Ti. The tendency curves draw by Excel.
Table 2 Hmix (kJ/mol) [17] of the foreign atoms with other components
Ti Cu Ni Al Si B
100
∆Tx, K
3750
Hf
Nb
Ta
Sc
0 17 42 39 60 51
2 3 30 16 39 39
1 2 29 19 39 39
8 24 39 38 57 40
Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb) glassy rods with diameters 2 mm were obtained by copper mold casting. The thermal analysis results show that the value of Trgs and DTxs of Ti53Cu15Ni18.5Al7Si3M3B0.5 (M = Sc, Hf, Ta, Nb) are 0.619, 0.609, 0.606, 0.597 and 58, 54, 85, 78 K, respectively. Maximum diameters of alloys, the activation energies of primary crystallization and XRD patterns of alloys annealed for 2 h suggest that Trg and DTx have intimate relationship with glass-forming ability and thermal stability of the alloys, respectively. The foreign atomÕs P size factor P(kRFRTij/RTi 0.12j) and mixing heat factor ( xiHiF/ xiWi) were proposed to predict the glassforming ability and thermal stability, respectively.
M.-x. Xia et al. / Journal of Non-Crystalline Solids 351 (2005) 3747–3751
Acknowledgements The authors express their appreciation for the financial support of the National Natural Science Foundation of China under Grant No. 50274051 and the National Science Fund for Distinguished Young Scholars of China under Grant No. 50125101.
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