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Ti–Zr–Fe–Si system amorphous alloys with excellent biocompatibility
Journal of Non-Crystalline Solids 354 (2008) 3935–3938
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Ti–Zr–Fe–Si system amorphous alloys with excellent biocompatibility Ling Bai, Chunxiang Cui *, Qingzhou Wang, Shaojing Bu, Yumin Qi School of Materials Science and Engineering, Hebei University of Technology, Dingzigu, Road No.1, Hongqiao District, Tianjin 300130, China
a r t i c l e
i n f o
Article history: Received 27 September 2007 Received in revised form 22 April 2008 Available online 19 June 2008 PACS: 81.05.Kf 61.43.Gt 89.90.+n
a b s t r a c t Ti-based amorphous alloys Ti70Zr6Fe7Si17 (at.%) and Ti64Zr5Fe6Si17Mo6Nb2 (at.%) are fabricated by a single roller spun-melt technique. The feature of the alloy composition satisfies Inoue’s three empirical rules. Amorphous structures of the both alloys were confirmed by the X-ray diffraction patterns. The both alloys were cultivated in the simulate body fluid (SBF) for 15 days and the experiment result shows that Ca phosphates depositions on alloys surfaces were gained. Moreover, n(Ca)/n(P) atom ratio of the deposition is about 1.6/1, which approach to that of human bone – 1.66/1, suggesting that the both alloys were with an excellent biocompatibility. Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Alloys Metal-matrix composites Biomaterials
1. Introduction
2. Experimental procedure
Ti-based alloys are widely used in biomaterials fields for many years because of their excellent mechanical property and biocompatibility. But with the development of science and technology, implant materials are faced more and more critical request. In the same time, some reports show that Ti-based amorphous alloys can exhibit higher tensile strength [1] above 2000 MPa, lower Young’s modulus no more than 150 GPa [2,3], and higher corrosion resistance which are merely obtained in the commercial crystalline alloys. Today, Ti-based amorphous alloys have been prepared in Ti–Cu–Al [4], Ti–Cu–Ni (Co) [5], Ti– Cu–Zr–Ni [6], Ti–Cu–Co–Al–Zr [7], Ti–Cu–Ni–Sn (Si) [8] and Ti– Zr–Ni–Fe [9] systems, Which all satisfies Inoue’s three empirical rules [10], i. e. (1) multi-component alloy systems consisting of more than three element, (2) significantly different atomic size ratios above about 12% among the main constituent elements, and (3) negative heats of mixing among the elements. But as one of compositions of biomaterials, some elements such as Cu, Ni and Al are not compatible with human body, which may lead to cytotoxicity and neurotoxicity. In this experiment, two new Ti-based amorphous alloys Ti70Zr6Fe7Si17 (at.%) and Ti64Zr5Fe6Si17Mo6Nb2 (at.%) were fabricated.
The Ti-based alloy ingots with nominal compositions of Ti64Zr5Fe6Si17Mo6Nb2 (at.%) and Ti70Zr6Fe7Si17 (at.%) were prepared by the method of arc-melting a mixture of pure Ti (P99.8, spongy), Zr, Fe, Si, Nb and Mo metals under a purified argon atmosphere. Alloy ribbons with a width of 3–5 mm and thickness of about 80 lm were obtained from bulk samples by an as-quenched technique under an argon atmosphere. The adoptive angular velocity of the-molybdenum wheel was 50 m/s. The phase composition and microstructure of the as-quenched alloy ribbons were examined by the X-ray diffraction (XRD) and transmission election microscopy (TEM), respectively. To test the biocompatibility, the alloys ribbons were cultivated in the simulate body fluid (SBF) for 15 days. Then, the alloy ribbons were taken out of SBF, washed with alcohol and acetone, respectively. The surface morphology and element analysis of the deposition were examined by scanning electron microscopy (SEM) and the energy dispersive spectroscopy (EDS), respectively.
* Corresponding author. Tel./fax: +86 22 26564125. E-mail address: [email protected] (C. Cui). 0022-3093/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2008.05.015
3. Results Fig. 1 shows the XRD patterns of the both as-quenched Ti64Zr5Fe6Si17Mo6Nb2 and Ti70Zr6Fe7Si17 ribbons. An overlapped broad peak arising from an amorphous phase can be seen in the 2h range from 32° to 50° from the figure. Moreover, it is obvious that the alloy Ti64Zr5Fe6Si17Mo6Nb2 is superior to another alloy Ti70Zr6Fe7Si17 in amorphous forming ability. In addition, the most peaks of the latter can be identified as the phases of b-Ti and Ti5Si3.
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Fig. 1. X-ray diffraction patterns of the as-quenched both Ti64Zr5Fe6Si17Mo6Nb2 and Ti70Zr6Fe7Si17.
To further investigate the microstructure of the both alloys, the HREM observation of the Ti64Zr5Fe6Si17Mo6Nb2 and Ti70Zr6Fe7Si17 were also conducted, as shown in Fig. 2. And the selected area diffraction patterns (SADP) are indicated at the top right corner of Fig. 2, too. From Fig. 2, the microstructures of the both alloys mainly consist of continuous amorphous phase (white and bright) and nano-particles. And the nano-particles distribute uniformly on the surface of the amorphous phase and can be recognized as minor phases, i.e. b-Ti and Ti5Si3, associating with the X-ray thesis result. To test the biocompatibility of the both amorphous alloy ribbons, we dipped the materials into the simulated body fluid (SBF) to cultivate. After 15 days, the specimens were taken out of SBF, washed with alcohol and acetone, respectively. Fig. 3 shows the surface morphology of the both alloys obtained. It is found that a layer has been deposited on the surface of both alloys, which all consist of porous reticulation with irregular nanometer circles like honeycomb. 4. Disscusions It is important to investigate the features of alloy components in the glassy alloy systems. Most reported bulk glassy alloys except
Fig. 3. Surface morphology of Ti64Zr5Fe6Si17Mo6Nb2 (a and b) and Ti70Zr6Fe7Si17 (c and d) cultivated in SBF for 15 days; the corresponding element analysis of the deposition; (b) and (d) is the magnified version of (a) and (c), respectively.
Pd-based alloys have the empirical component rules. The reason why the alloys with these three-component rules can have high glass-forming ability (GFA) through the stabilization of supercooled liquid region has been attributed to the formation of a novel glassy structure which is characterized by highly dense packing, new local atomic configuration and long-range homogeneity with attractive interaction [11]. Both Ti64Zr5Fe6Si17Mo6Nb2 (at.%) and Ti70Zr6Fe7Si17 (at.%) satisfies the three empirical rules. Firstly, the both consist of more than three elements. Moreover, in Ti64Zr5Fe6Si17Mo6Nb2, the addition of Mo and Nb is effective for increase in the degree of the satisfaction of the three empirical rules, which may to some extent account for the reason why the alloy Ti64Zr5Fe6Si17Mo6Nb2 (at.%) is superior to another alloy in amorphous phase forming ability. Secondly, significantly different atomic size ratios are above about 12% among the main constituent elements. The rearrangement of the constituent elements with different atomic sizes may lead to a higher packing density. The atomic size of an element is quoted from a data book [12] as the atomic radius which is taken as half of the interatomic distance in a crystalline state. Table 1
Fig. 2. HREM image of Ti70Zr6Fe7Si17 (at.%) and Ti64Zr5Fe6Si17Mo6Nb2 (at.%) the corresponding SADP.
3937
L. Bai et al. / Journal of Non-Crystalline Solids 354 (2008) 3935–3938 Table 1 Atomic radius of elements/nm Element
Ti
Zr
Fe
Si
Mo
Nb
Atomic radii
0.147
0.162
0.124
0.117
0.136
0.143
illustrates the atomic radius of elements. The atomic sizes of both alloys change more continuously in the order of Ti > Fe > Si, which may further increase the packing density. But the different atomic size ratio between Fe and Si is not above 12% yet, which to some extent may account for appearance of nanocrystal on the amorphous phase. And finally, the both alloys process negative heats of mixing among the elements. The generation of atomic pairs with various negative heats of mixing also increases the thermal stability of the supercooled liquid since a large amount of active energy is required for crystallization. Furthermore, the addition of Mo and Nb effectively increases the numbers of atomic pairs with negative heats of mixing, such as Ti–Mo as well as Si–Mo. The values of heat of mixing were quoted as enthalpy of mixing ðDHmix AB Þ [13] of the binary liquid in an A–B systems at an equi-atomic composition. Table 2 [10] shows the values of DHmix AB (kJ/mol) calculated by Miedema’s model for atomic pairs between elements in the both alloys. The mixing enthalpy of solid solution is comprised of chemical, elastic, and structural terms [14]. Since elastic, and structural contributions are absent in the liquid, the mixing enthalpy consists of only the chemical term, which can be determined based on
DHmix ¼
n X
Xij ci cj
Table 2 The values of DHmix AB /(kJ/mol) calculated by Miedema’s model for atomic pairs between elements
Ti Zr Fe Si Mo Nb
Ti
Zr
Fe
Si
Mo
Nb
0 0 17 66 4 2
0 0 25 84 6 4
17 25 0 35 2 16
66 84 35 0 35 56
4 6 2 35 0 6
2 4 16 56 6 0
cultivating in SBF for 15 days, which approach to that (about 1.66) for pure Hydroxyapatite (HA). Thus, the deposition is composed of HA. It can suggest that the amorphous Ti64Zr5Fe6Si17Mo6Nb2 (at.%) and Ti70Zr6Fe7Si17 (at.%) alloys possess favorable biocompatibility. HA has been widely used as a bulk implant in non-load bearing areas of the body and as coatings on implant metals. HA is a bioactive ceramic, which can bone of bone, because it is very similar to the mineral part of bone [18,19]. It has a fracture toughness of approximately 1 MPa/m [20]. So coating of HA has been produced to improve the poor mechanical properties [21,22]. Coating of HA has been used in orthopedic and dental implants. For the best bonding, the HA phase should be compact and thick to some extent [23,24]. The TEM image of the deposition is shown in Fig. 5. As show in Fig. 5, the deposition with compact nanometer circles is uniformly distributed on the surface of the alloys, which is very helpful to improve the mechanical properties and biocompatibility of the implant materials.
i¼1;i6¼j
the regular melt model [14,15] where Xij ð¼ 4DHmix AB Þ is the regular melt interaction parameter between ith and jth elements, ci is the atomic percentage of the ith component, and DHmix AB is the mixing enthalpy of binary liquid alloys. The calibration value of DHmix AB is mixðcaliÞ
used as DHAB
trans ¼ DHmix =2 for containing one nontransiAB DH mixðcaliÞ
¼ ðDHtrans þ DHtrans Þ=2 for containing two tion metal and DHAB i j trans nontransition metals. D H are 100, 30, 180, 310, 17, 34, and 25 kJ mol1 for containing H, B, C, N, Si, P, and Ge, respectively. According to the mentioned above, the enthalpys of mixing of the both alloys are 98.6887 kJ/mol and 66.9220 kJ/mol, respectively. It is noted the former is more negative in comparison with the latter, which also to some extent explains why the amorphous forming ability of Ti64Zr5Fe6Si17Mo6Nb2 (at.%) is superior to that of the other alloy. In conclusion, multi-component alloys system, different atomic size ratios above 12% and negative heats of mixing may lead to the formation of a highly dense random packed structure with low atomic diffusivity. It is generally believed that the higher the packing density, the higher the thermal stability and the higher the resistance of the supercooled liquid against transformation into crystalline phase [16]. From Fig. 3, it is showed that the aperture of the former is bigger than that of the latter. Porous structures help to reduce the density of metallic implants and stiffness mismatches between implant and host tissue. Moreover, the porous surface structure has significant influence on bone cell adhesion. The cells on the porous samples can attach to a greater surface area on the spherical deposited particles than can a smooth plate, and thus better adhesion is obtained with the rough surface of the porous samples. In addition, porous sample not only enhanced cell adhesion and proliferation, but also stimulated cell differentiation [17]. The element analysis result of the deposition tested by EDS is shown in Fig. 4. From Fig. 4 one can see the depositions are composed of Ca, P, O and C, etc., which are necessary for human bone. It is worth noted that the atomic ratio n(Ca)/n(P) for the deposition is about 1.6 after
Fig. 4. The corresponding element analysis of the deposition.
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(6) The depositions consist of porous structure with irregular nanometer circles like honeycomb. And the aperture of the former is bigger than that of the latter. Porous structures not only help to reduce the density of metallic implants and stiffness mismatches between implant and host tissue, but also has significant influence on bone cell adhesion.
Acknowledgements The project was aided financially by Key program of scientific and technical innovation of China (Project No. 02CJ-020218), Natural Science Foundation of Hebei Province (Project No. E2006000025). References [1] [2] [3] [4] Fig. 5. The TEM image of the deposition.
5. Conclusions
(1) Ti-based amorphous alloys Ti64Zr5Fe6Si17Mo6Nb2 (at.%) and Ti70Zr6Fe7Si17 (at.%) have been prepared for the first time, which all satisfies Inoue’s empirical rules. (2) The amorphous forming ability of Ti64Zr5Fe6Si17Mo6Nb2 (at.%) is superior to that of Ti70Zr6Fe7Si17 (at.%). (3) The phase of both alloys consist of continuous amorphous phase acting as the major phase and the nano-particles distributed on the amorphous surface acting as the minor phase, which mainly are composed of b-Ti and Ti5Si3. (4) The addition of Mo and Nb in the alloy Ti64Zr5Fe6Si17Mo6Nb2 (at.%) improve the amorphous forming ability. (5) The both Ti-based alloys process favorable biocompatibility. n(Ca)/n(P) ratio of the deposition on both alloys all closes to 1.6 after alloys were cultivated in SBF for 15 days, which approach that of Human bone of 1.66.
[5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]
A. Inoue, A. Takeuchi, Mater. Sci. Eng., A 375–377 (2004) 16. A. Inoue, Acta Mater. 48 (2000) 279. A. Inoue, A. Takeuchi, Mater. Trans. 43 (2002) 1892. A. Inoue, N. Nishiyama, K. Amiya, T. Zhang, T. Masumoto, Mater. Lett. 19 (1994) 131. T. Zhang, A. Inoue, T. Masumoto, Mater. Sci. Eng., A 181–182 (1994) 1423. X.D. Liu, M. Nagumo, U. Umemoto, Mater. Trans., JIM 39 (1998) 343. L. Battezzati, M. Baricco, P. Fortina, W.N. Myung, Mater. Sci. Eng., A 226–228 (1997) 503. T. Zhang, A. Inoue, Mater. Trans., JIM 39 (1998) 1001. R. Nicula, V. kuncser, A. Jianu, G. Filoti, E. Burkel, Mater. Sci. Eng., A 294 (2000) 539. A. Takeuchi, A. Inoue, Mater. Trans. 46 (2005) 2817. A. Inoue, A. Takeuchi, Mater. Trans. 43 (2002) 1892. Metal Databook, 4th Ed., Japan Institute of Metal, Maruzen, 2004, p. 8 (in Japanese). F.R. Boer, D.G. Perrifor, Cohesion in Metals, Elsevier Science Publishers B.V., Netherlands, 1988. M.X. Xia, S.G. Zhang, C.L. Ma, J.G. Li, Appl. Phys. Lett. 89 (2006) 091917. A. Takeuchi, A. Inoue, Mater. Sci. Eng., A 304–306 (2001) 446. T. Zhang, A. Inoue, Mater. Sci. Eng., A 304–306 (2001) 771. W.C. Xue, K.B. Vamsi, A. Bandyopadhyay, S. Bose, Acta Biomater. 3 (2007) 1007. R.B. Martins, M.W. Chapman, N.A. Sharkey, S.L. Zissimos, B. Bay, E.C. Shors, Biomaterials 14 (1993) 341. Z. Jianguo, Z. Xingdong, C. Muller-Mai, U. Gross, J. Mater. Sci., Mater. Med. 5 (1994) 243. M.B. Thomas, R.H. Doremus, Am. Ceram. Soc. Bull. 60 (1981) 258. J.M. Gomez-v, E. Saiz, A.P. Tomsia, T. Oku, K. Suganumam, G.W. Marshall, S.J. Marshall, Adv. Mater. 12 (2004) 894. C.Q. Ning, Y. Zhou, Biomaterials 23 (2002) 2909. K. Soballe, S. Overgaard, J. Bone Joint Surgeon 78-B (1996) 689. S.R. Sousa, M.A. Barbosa, Biomaterials 17 (1996) 397.
Contents lists available at ScienceDirect
Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Ti–Zr–Fe–Si system amorphous alloys with excellent biocompatibility Ling Bai, Chunxiang Cui *, Qingzhou Wang, Shaojing Bu, Yumin Qi School of Materials Science and Engineering, Hebei University of Technology, Dingzigu, Road No.1, Hongqiao District, Tianjin 300130, China
a r t i c l e
i n f o
Article history: Received 27 September 2007 Received in revised form 22 April 2008 Available online 19 June 2008 PACS: 81.05.Kf 61.43.Gt 89.90.+n
a b s t r a c t Ti-based amorphous alloys Ti70Zr6Fe7Si17 (at.%) and Ti64Zr5Fe6Si17Mo6Nb2 (at.%) are fabricated by a single roller spun-melt technique. The feature of the alloy composition satisfies Inoue’s three empirical rules. Amorphous structures of the both alloys were confirmed by the X-ray diffraction patterns. The both alloys were cultivated in the simulate body fluid (SBF) for 15 days and the experiment result shows that Ca phosphates depositions on alloys surfaces were gained. Moreover, n(Ca)/n(P) atom ratio of the deposition is about 1.6/1, which approach to that of human bone – 1.66/1, suggesting that the both alloys were with an excellent biocompatibility. Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Alloys Metal-matrix composites Biomaterials
1. Introduction
2. Experimental procedure
Ti-based alloys are widely used in biomaterials fields for many years because of their excellent mechanical property and biocompatibility. But with the development of science and technology, implant materials are faced more and more critical request. In the same time, some reports show that Ti-based amorphous alloys can exhibit higher tensile strength [1] above 2000 MPa, lower Young’s modulus no more than 150 GPa [2,3], and higher corrosion resistance which are merely obtained in the commercial crystalline alloys. Today, Ti-based amorphous alloys have been prepared in Ti–Cu–Al [4], Ti–Cu–Ni (Co) [5], Ti– Cu–Zr–Ni [6], Ti–Cu–Co–Al–Zr [7], Ti–Cu–Ni–Sn (Si) [8] and Ti– Zr–Ni–Fe [9] systems, Which all satisfies Inoue’s three empirical rules [10], i. e. (1) multi-component alloy systems consisting of more than three element, (2) significantly different atomic size ratios above about 12% among the main constituent elements, and (3) negative heats of mixing among the elements. But as one of compositions of biomaterials, some elements such as Cu, Ni and Al are not compatible with human body, which may lead to cytotoxicity and neurotoxicity. In this experiment, two new Ti-based amorphous alloys Ti70Zr6Fe7Si17 (at.%) and Ti64Zr5Fe6Si17Mo6Nb2 (at.%) were fabricated.
The Ti-based alloy ingots with nominal compositions of Ti64Zr5Fe6Si17Mo6Nb2 (at.%) and Ti70Zr6Fe7Si17 (at.%) were prepared by the method of arc-melting a mixture of pure Ti (P99.8, spongy), Zr, Fe, Si, Nb and Mo metals under a purified argon atmosphere. Alloy ribbons with a width of 3–5 mm and thickness of about 80 lm were obtained from bulk samples by an as-quenched technique under an argon atmosphere. The adoptive angular velocity of the-molybdenum wheel was 50 m/s. The phase composition and microstructure of the as-quenched alloy ribbons were examined by the X-ray diffraction (XRD) and transmission election microscopy (TEM), respectively. To test the biocompatibility, the alloys ribbons were cultivated in the simulate body fluid (SBF) for 15 days. Then, the alloy ribbons were taken out of SBF, washed with alcohol and acetone, respectively. The surface morphology and element analysis of the deposition were examined by scanning electron microscopy (SEM) and the energy dispersive spectroscopy (EDS), respectively.
* Corresponding author. Tel./fax: +86 22 26564125. E-mail address: [email protected] (C. Cui). 0022-3093/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2008.05.015
3. Results Fig. 1 shows the XRD patterns of the both as-quenched Ti64Zr5Fe6Si17Mo6Nb2 and Ti70Zr6Fe7Si17 ribbons. An overlapped broad peak arising from an amorphous phase can be seen in the 2h range from 32° to 50° from the figure. Moreover, it is obvious that the alloy Ti64Zr5Fe6Si17Mo6Nb2 is superior to another alloy Ti70Zr6Fe7Si17 in amorphous forming ability. In addition, the most peaks of the latter can be identified as the phases of b-Ti and Ti5Si3.
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L. Bai et al. / Journal of Non-Crystalline Solids 354 (2008) 3935–3938
Fig. 1. X-ray diffraction patterns of the as-quenched both Ti64Zr5Fe6Si17Mo6Nb2 and Ti70Zr6Fe7Si17.
To further investigate the microstructure of the both alloys, the HREM observation of the Ti64Zr5Fe6Si17Mo6Nb2 and Ti70Zr6Fe7Si17 were also conducted, as shown in Fig. 2. And the selected area diffraction patterns (SADP) are indicated at the top right corner of Fig. 2, too. From Fig. 2, the microstructures of the both alloys mainly consist of continuous amorphous phase (white and bright) and nano-particles. And the nano-particles distribute uniformly on the surface of the amorphous phase and can be recognized as minor phases, i.e. b-Ti and Ti5Si3, associating with the X-ray thesis result. To test the biocompatibility of the both amorphous alloy ribbons, we dipped the materials into the simulated body fluid (SBF) to cultivate. After 15 days, the specimens were taken out of SBF, washed with alcohol and acetone, respectively. Fig. 3 shows the surface morphology of the both alloys obtained. It is found that a layer has been deposited on the surface of both alloys, which all consist of porous reticulation with irregular nanometer circles like honeycomb. 4. Disscusions It is important to investigate the features of alloy components in the glassy alloy systems. Most reported bulk glassy alloys except
Fig. 3. Surface morphology of Ti64Zr5Fe6Si17Mo6Nb2 (a and b) and Ti70Zr6Fe7Si17 (c and d) cultivated in SBF for 15 days; the corresponding element analysis of the deposition; (b) and (d) is the magnified version of (a) and (c), respectively.
Pd-based alloys have the empirical component rules. The reason why the alloys with these three-component rules can have high glass-forming ability (GFA) through the stabilization of supercooled liquid region has been attributed to the formation of a novel glassy structure which is characterized by highly dense packing, new local atomic configuration and long-range homogeneity with attractive interaction [11]. Both Ti64Zr5Fe6Si17Mo6Nb2 (at.%) and Ti70Zr6Fe7Si17 (at.%) satisfies the three empirical rules. Firstly, the both consist of more than three elements. Moreover, in Ti64Zr5Fe6Si17Mo6Nb2, the addition of Mo and Nb is effective for increase in the degree of the satisfaction of the three empirical rules, which may to some extent account for the reason why the alloy Ti64Zr5Fe6Si17Mo6Nb2 (at.%) is superior to another alloy in amorphous phase forming ability. Secondly, significantly different atomic size ratios are above about 12% among the main constituent elements. The rearrangement of the constituent elements with different atomic sizes may lead to a higher packing density. The atomic size of an element is quoted from a data book [12] as the atomic radius which is taken as half of the interatomic distance in a crystalline state. Table 1
Fig. 2. HREM image of Ti70Zr6Fe7Si17 (at.%) and Ti64Zr5Fe6Si17Mo6Nb2 (at.%) the corresponding SADP.
3937
L. Bai et al. / Journal of Non-Crystalline Solids 354 (2008) 3935–3938 Table 1 Atomic radius of elements/nm Element
Ti
Zr
Fe
Si
Mo
Nb
Atomic radii
0.147
0.162
0.124
0.117
0.136
0.143
illustrates the atomic radius of elements. The atomic sizes of both alloys change more continuously in the order of Ti > Fe > Si, which may further increase the packing density. But the different atomic size ratio between Fe and Si is not above 12% yet, which to some extent may account for appearance of nanocrystal on the amorphous phase. And finally, the both alloys process negative heats of mixing among the elements. The generation of atomic pairs with various negative heats of mixing also increases the thermal stability of the supercooled liquid since a large amount of active energy is required for crystallization. Furthermore, the addition of Mo and Nb effectively increases the numbers of atomic pairs with negative heats of mixing, such as Ti–Mo as well as Si–Mo. The values of heat of mixing were quoted as enthalpy of mixing ðDHmix AB Þ [13] of the binary liquid in an A–B systems at an equi-atomic composition. Table 2 [10] shows the values of DHmix AB (kJ/mol) calculated by Miedema’s model for atomic pairs between elements in the both alloys. The mixing enthalpy of solid solution is comprised of chemical, elastic, and structural terms [14]. Since elastic, and structural contributions are absent in the liquid, the mixing enthalpy consists of only the chemical term, which can be determined based on
DHmix ¼
n X
Xij ci cj
Table 2 The values of DHmix AB /(kJ/mol) calculated by Miedema’s model for atomic pairs between elements
Ti Zr Fe Si Mo Nb
Ti
Zr
Fe
Si
Mo
Nb
0 0 17 66 4 2
0 0 25 84 6 4
17 25 0 35 2 16
66 84 35 0 35 56
4 6 2 35 0 6
2 4 16 56 6 0
cultivating in SBF for 15 days, which approach to that (about 1.66) for pure Hydroxyapatite (HA). Thus, the deposition is composed of HA. It can suggest that the amorphous Ti64Zr5Fe6Si17Mo6Nb2 (at.%) and Ti70Zr6Fe7Si17 (at.%) alloys possess favorable biocompatibility. HA has been widely used as a bulk implant in non-load bearing areas of the body and as coatings on implant metals. HA is a bioactive ceramic, which can bone of bone, because it is very similar to the mineral part of bone [18,19]. It has a fracture toughness of approximately 1 MPa/m [20]. So coating of HA has been produced to improve the poor mechanical properties [21,22]. Coating of HA has been used in orthopedic and dental implants. For the best bonding, the HA phase should be compact and thick to some extent [23,24]. The TEM image of the deposition is shown in Fig. 5. As show in Fig. 5, the deposition with compact nanometer circles is uniformly distributed on the surface of the alloys, which is very helpful to improve the mechanical properties and biocompatibility of the implant materials.
i¼1;i6¼j
the regular melt model [14,15] where Xij ð¼ 4DHmix AB Þ is the regular melt interaction parameter between ith and jth elements, ci is the atomic percentage of the ith component, and DHmix AB is the mixing enthalpy of binary liquid alloys. The calibration value of DHmix AB is mixðcaliÞ
used as DHAB
trans ¼ DHmix =2 for containing one nontransiAB DH mixðcaliÞ
¼ ðDHtrans þ DHtrans Þ=2 for containing two tion metal and DHAB i j trans nontransition metals. D H are 100, 30, 180, 310, 17, 34, and 25 kJ mol1 for containing H, B, C, N, Si, P, and Ge, respectively. According to the mentioned above, the enthalpys of mixing of the both alloys are 98.6887 kJ/mol and 66.9220 kJ/mol, respectively. It is noted the former is more negative in comparison with the latter, which also to some extent explains why the amorphous forming ability of Ti64Zr5Fe6Si17Mo6Nb2 (at.%) is superior to that of the other alloy. In conclusion, multi-component alloys system, different atomic size ratios above 12% and negative heats of mixing may lead to the formation of a highly dense random packed structure with low atomic diffusivity. It is generally believed that the higher the packing density, the higher the thermal stability and the higher the resistance of the supercooled liquid against transformation into crystalline phase [16]. From Fig. 3, it is showed that the aperture of the former is bigger than that of the latter. Porous structures help to reduce the density of metallic implants and stiffness mismatches between implant and host tissue. Moreover, the porous surface structure has significant influence on bone cell adhesion. The cells on the porous samples can attach to a greater surface area on the spherical deposited particles than can a smooth plate, and thus better adhesion is obtained with the rough surface of the porous samples. In addition, porous sample not only enhanced cell adhesion and proliferation, but also stimulated cell differentiation [17]. The element analysis result of the deposition tested by EDS is shown in Fig. 4. From Fig. 4 one can see the depositions are composed of Ca, P, O and C, etc., which are necessary for human bone. It is worth noted that the atomic ratio n(Ca)/n(P) for the deposition is about 1.6 after
Fig. 4. The corresponding element analysis of the deposition.
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L. Bai et al. / Journal of Non-Crystalline Solids 354 (2008) 3935–3938
(6) The depositions consist of porous structure with irregular nanometer circles like honeycomb. And the aperture of the former is bigger than that of the latter. Porous structures not only help to reduce the density of metallic implants and stiffness mismatches between implant and host tissue, but also has significant influence on bone cell adhesion.
Acknowledgements The project was aided financially by Key program of scientific and technical innovation of China (Project No. 02CJ-020218), Natural Science Foundation of Hebei Province (Project No. E2006000025). References [1] [2] [3] [4] Fig. 5. The TEM image of the deposition.
5. Conclusions
(1) Ti-based amorphous alloys Ti64Zr5Fe6Si17Mo6Nb2 (at.%) and Ti70Zr6Fe7Si17 (at.%) have been prepared for the first time, which all satisfies Inoue’s empirical rules. (2) The amorphous forming ability of Ti64Zr5Fe6Si17Mo6Nb2 (at.%) is superior to that of Ti70Zr6Fe7Si17 (at.%). (3) The phase of both alloys consist of continuous amorphous phase acting as the major phase and the nano-particles distributed on the amorphous surface acting as the minor phase, which mainly are composed of b-Ti and Ti5Si3. (4) The addition of Mo and Nb in the alloy Ti64Zr5Fe6Si17Mo6Nb2 (at.%) improve the amorphous forming ability. (5) The both Ti-based alloys process favorable biocompatibility. n(Ca)/n(P) ratio of the deposition on both alloys all closes to 1.6 after alloys were cultivated in SBF for 15 days, which approach that of Human bone of 1.66.
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