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Interfacial reactions in Ti–Fe particles reinforced hydroxyapatite matrix composites
Materials Letters 128 (2014) 245–247
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Interfacial reactions in Ti–Fe particles reinforced hydroxyapatite matrix composites Q. Chang a,n, H.Q. Ru b,nn, D.L. Chen c, C.P. Zhang b, J.L. Yang a, S.L. Hu a a
School of Materials Science and Engineering, North University of China, Xueyuan Road 3, Taiyuan 030051, China Department of Materials Science and Engineering, School of Materials and Metallurgy, Northeastern University, Wenhua Road 3-11, Shenyang 110819, China c Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada b
art ic l e i nf o
a b s t r a c t
Article history: Received 31 January 2014 Accepted 22 April 2014 Available online 29 April 2014
A very important factor that influences the properties of a composite is related to the interfacial reaction. In present study, the hydroxyapatite (HA) materials reinforced by Ti–Fe particles were fabricated, and then the interfacial reactions between the HA and Ti–Fe were investigated. The results showed that the desirable Ti phase remained in the matrix after sintering since the introduction of Fe suppressed both the decomposition of HA and interaction between HA and Ti. Furthermore, it was found that a certain amount of small pores near/in interface was beneficial for obtaining an appropriate interfacial bonding between reinforcing Ti–Fe particles and HA matrix. & 2014 Elsevier B.V. All rights reserved.
Keywords: Ceramic composites Interfacial reactions Interfaces Hydroxyapatite Iron Titanium
1. Introduction Hydroxyapatite (HA), one of the most important bioceramics [1], plays a key role in the application of human hard tissue repair and reconstruction due to its excellent bioactivity and biocompatibility [2,3]. However, the low flexural strength and toughness of pure HA greatly limit its practical applications. In order to improve mechanical properties, HA-based composites have been widely investigated by various strategies. Among these additives, titanium (Ti) and its alloy have attracted special interest due to their superior mechanical properties as well as bioactivity [4]. The mechanical properties of HA matrix ceramic were greatly improved by adding Ti or its alloy powders [5,6]. However, a key problem—severe interfacial reaction between HA and Ti—exists [7]. While the interaction between HA and Ti produced a chemical bonding between HA and Ti, the severe interfacial reactions resulted in the degradation of Ti which led to the desirable Ti phase rarely remaining in the matrix after sintering. Furthermore, the interfacial reaction accelerated the decomposition of HA. The decomposition products would hinder densification [8], which resulted in a weak interface bonding between matrix and reinforcing particles. These issues led to only a limited improvement of mechanical properties of
n
Corresponding author. Tel.: þ 86 351 3559638; fax: þ 86 351 3557519. Corresponding author. Tel.: +86 24 83680248; fax: +86 24 83680248. E-mail addresses: [email protected] (Q. Chang), [email protected] (H.Q. Ru). nn
http://dx.doi.org/10.1016/j.matlet.2014.04.153 0167-577X/& 2014 Elsevier B.V. All rights reserved.
the composites. Therefore, it is highly crucial and great challenge to develop a way to control the interfacial reactions by optimizing the composition of the composites. Iron (Fe) is an indispensable element in the human body [9]. Itscontaining hydroxyapatite has attracted considerable attention in recent years [10]. One of the important findings of these studies was that the doping of Fe would be effective in improving the stability of HA. This implies that introducing Fe into HA/Ti composites would have a great potential to suppress the interfacial reaction between HA and Ti. Based on the expectation, in this study, we fabricated the HA composites reinforced by Ti–Fe particles, and investigated the interfacial reactions between the HA and Ti–Fe. The aim of this work was to illustrate the role of Fe on the interfacial reactions of the composites.
2. Materials and methods Nano-HA powder was synthesized using wet-chemical precipitation by reacting calcium hydroxide (Ca(OH)2) with orthophosphoric acid (H3PO4) [11]. Composite powders containing 5, 10, and 15 wt% of Ti-33 wt% Fe particles and HA were mixed by ball-milling for 12 h, and then dried at 80 1C. The mixed powders as well as pure HA powders were uniaxially pressed at 50 MPa, followed by cold-isostatic pressing at 200 MPa. The green compacts were subsequently pressureless sintered in vacuum at 950, 1000 and 1050 1C for 2 h using a heating rate of 3.33 1C/min and cooling rate of 5 1C/min.
246
Q. Chang et al. / Materials Letters 128 (2014) 245–247
The bulk density of the samples was measured by the Archimedes method. The compositional analysis of the sintered products was analyzed using X-ray diffraction (XRD). The microstructure was examined using a scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM).
3. Results and discussion Fig. 1 shows the XRD patterns of synthetic HA and HA composites with different contents of Ti–Fe particles sintered at 1000 1C. It is seen that synthetic HA exhibited a typical XRD pattern of HA (JCPDS, 0090432) with no impurity phases (Fig. 1(b)), suggesting the HA structure obtained in this study was thermally stable enough while sintering at 1000 1C. For HA composite with 5% of Ti–Fe particles, it consisted mainly of HA, Ti and Fe, together with TiFe and traces of calcium titanate (CaTiO3) (Fig. 1(e)). With increasing content of Ti–Fe to 15%, peaks of β-tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP), the decomposition products of HA, were detected (Fig. 1(f)). These results indicated that both the decomposition of HA and interaction between HA and Ti took place. However, a significant result observed in our study was that the desirable Ti phase still remained in the composites regardless of the interaction between HA and Ti. This strongly suggested that the additive Fe played a key role in suppressing the extent of both the decomposition of HA and interaction between HA and Ti.
-HA -Ti CaTiO3
-Fe TCP
-TiFe -TTCP
(f)
(e)
Intensity,(a.u.)
(d)
(c)
(b)
(a) 20
30
40 2θ,degree
50
Fig. 2 shows the TEM images of sintered HA composites with 5% and 15% Ti–Fe particles. It was observed that the grain size of HA/15% (Ti–Fe) (Fig. 2(b)) was smaller than that of HA/5%(Ti–Fe) composite (Fig. 2(a)). The reduction in grain size could be associated with the incorporation of Fe into HA that led to a contraction of the lattice because Fe had a smaller atomic radius than Ca. The a- and c-axis values of pure HA, HA/5%(Ti–Fe) and HA/15%(Ti–Fe) are presented in Table 1. It is seen that the values of a- and c-axis decreased with increasing content of Ti–Fe particles. On the other hand, the contraction in the lattice dimensions could bring about less crystal growth, thus resulting in lower crystallization of HA after the introduction of iron, as revealed by XRD (Fig. 1). The selected-area diffraction patterns (SADPs) from HA observed in the microstructure are also shown and indexed in Fig. 2(c) and (d), which corroborated the hexagonal structure of HA unite cell. It should be mentioned here that the SADPs of other phases were not obtained since the crystals of them were too small. Besides, it was observed from Fig. 2 that the porosity of HA/15%(Ti– Fe) composite was higher than that of HA/5%(Ti–Fe) composite. This was related to two potential reasons. First, the amount of the secondary phases that could inhibit sintering increased with increasing amount of Ti–Fe particles, as discussed above (Fig. 1), giving rise to a decreasing density. Second, the incorporation of Fe into HA that led to a contraction of the lattice suppressed crystal growth so as to obstruct densification. As a consequence, in comparison with the composite with 5% Ti–Fe particles, the composite with 15% Ti–Fe particles exhibited a higher porosity. A good interfacial bonding would have a potential to enhance the mechanical properties of the composite [12]. Fig. 3 shows the interface microstructure of HA/15% (Ti–Fe) composite. It is seen that the reinforcing Ti–Fe particles had a good bonding with HA matrix while some pores appeared near/in the interface. The small amount of pores was derived from a little interaction between HA and Ti. Such interface would offer a potential to improve the mechanical properties of the composites. First, the small amount of pores could retard the crack propagation due to their certain radius of curvature in comparison with the sharp brittle crack [13]. Second, these pores could lead to partial debonding of the interface. The occurrence of partial debonding would increase the crack path and make the plastic stretching area bigger, giving rise to the absorption of more fracture energy. In this study, the fracture toughness was determined by measuring the crack length generated by Vickers indentation [14]. It was found that the fracture toughness of HA/15% (Ti–Fe) composite reached 1.3 MPa m1/2, an increase by 128% in comparison to pure HA obtained in our study. This indicated that there was an appropriate interfacial bonding for the obtained HA composites reinforced by Ti–Fe particles. It is interesting and important to consider how Fe can inhibit the decomposition of HA and interaction between HA and Ti. This could be understood as follows. As discussed above, some Fe particles in the neighborhood of HA incorporated into HA structure. The stability of such Fe-containing apatite was thus improved [10], leading to less decomposition of HA. In addition, the observation that Fe exhibited very fast diffusion in α-Ti and β-Ti at 836 1C [15] would provide a potential to impede the interaction between HA and Ti. As a result, both the decomposition of HA and interaction between HA and Ti were suppressed. At the same time, it should be mentioned here that the fast diffusion of Fe into Ti promoted the mobility of Ti which played a key role in enhancing the interface bonding between Ti–Fe particles and HA matrix.
60
Fig. 1. XRD patterns of the sintered samples: (a) HA (JCPDS, 009-0432), (b) synthetic HA, (c) Fe (JCPDS, 006-0696), (d) Ti (JCPDS, 005-0682), (e) HA/5% (Ti–Fe), and (f) HA/15% (Ti–Fe).
4. Conclusions The interfacial reactions between HA and Ti–Fe reinforcing particles were investigated in this study. By detailed analysis using
Q. Chang et al. / Materials Letters 128 (2014) 245–247
0110
247
1010
0111
0000
2110
0000
Fig. 2. TEM images and electron diffraction analysis of HA/Ti–Fe composites sintered in vacuum at 1000 1C: (a) image of HA/5% (Ti–Fe), (b) image of HA/15% (Ti–Fe), (c) and (d) electron diffraction patterns of HA.
Table 1 a- and c-axis values of HA structure before and after adding Ti–Fe reinforcing particles. Sample
a (Å)
c (Å)
Pure HA HA/5% (Ti–Fe) HA/15% (Ti–Fe)
9.459 9.384 9.356
6.901 6.882 6.880
between HA and Ti that existed near/in the interface had a positive effect in obtaining an appropriate interfacial bonding, which was favorable for improving the mechanical properties of the composites.
Acknowledgments The authors would like to thank the financial support of National Natural Science Foundation of China (NSFC Grant no. 51272039) and the Natural Sciences and Engineering Research Council of Canada (NSERC) in the form of International Research Collaboration. Q. Chang is also grateful for the financial support by China Scholarship Council, and the Natural Science Foundation of North University of China. References
Fig. 3. TEM image of the interface between Ti–Fe particles and HA matrix in the HA/15% (Ti–Fe) composite.
XRD and TEM, it was found that both the decomposition of HA and interaction between HA and Ti were inhibited due to the introduction of Fe, giving rise to the desirable Ti phase maintained in the matrix. A small amount of pores due to a little interaction
[1] Best SM, Porter AE, Thian ES, Huang J. J Eur Ceram Soc 2008;28:1319–27. [2] Zakaria SM, Sharif SH, Othman MR, Yang F, Jansen JA. Tissue Eng Part B Rev 2013;19:431–41. [3] Lin KL, Zhang ML, Zhai WY, Qu HY, Chang J. J Am Ceram Soc 2011;94:206–12. [4] Long M, Rack HJ. Biomaterials 1998;19:1621–39. [5] Thian ES, Loh NH, Khor KA, Tor SB. Biomaterials 2002;23:2927–38. [6] Kumar A, Dhara S, Biswas K. J Biomed Mater Res B 2013;101B:223–36. [7] Yang YZ, Kim KH, Mauli AC, Ong JL. Biomaterials 2004;25:2927–32. [8] Wang PE, Chaki TK. J Mater Sci Mater Med 1993;4:150–8. [9] Bogard RW, Oliver JD. Appl Environ Microbiol 2007;73:7501–5. [10] Kramer ER, Morey AM, Staruch M, Suib SL, Jain M, Budnick JI, et al. J Mater Sci 2013;48:665–73. [11] Kweh SWK, Khor KA, Cheang P. J Mater Process Tech 1999;89–90:373–7. [12] Bartolomé JF, Beltrán JI, Gutiérrez-González CF, Pecharromán C, Muñoz MC, Moya JS. Acta Mater 2008;56:3358–66. [13] Kumar R, Prakash KH, Cheang P, Khor KA. Acta Mater 2005;53:2327–35. [14] Kruzic JJ, Ritchie RO. J Am Ceram Soc 2003;86:1433–6. [15] Wei W, Liu Y, Zhou K, Huang B. Powder Metall 2003;46:246–50.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Interfacial reactions in Ti–Fe particles reinforced hydroxyapatite matrix composites Q. Chang a,n, H.Q. Ru b,nn, D.L. Chen c, C.P. Zhang b, J.L. Yang a, S.L. Hu a a
School of Materials Science and Engineering, North University of China, Xueyuan Road 3, Taiyuan 030051, China Department of Materials Science and Engineering, School of Materials and Metallurgy, Northeastern University, Wenhua Road 3-11, Shenyang 110819, China c Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada b
art ic l e i nf o
a b s t r a c t
Article history: Received 31 January 2014 Accepted 22 April 2014 Available online 29 April 2014
A very important factor that influences the properties of a composite is related to the interfacial reaction. In present study, the hydroxyapatite (HA) materials reinforced by Ti–Fe particles were fabricated, and then the interfacial reactions between the HA and Ti–Fe were investigated. The results showed that the desirable Ti phase remained in the matrix after sintering since the introduction of Fe suppressed both the decomposition of HA and interaction between HA and Ti. Furthermore, it was found that a certain amount of small pores near/in interface was beneficial for obtaining an appropriate interfacial bonding between reinforcing Ti–Fe particles and HA matrix. & 2014 Elsevier B.V. All rights reserved.
Keywords: Ceramic composites Interfacial reactions Interfaces Hydroxyapatite Iron Titanium
1. Introduction Hydroxyapatite (HA), one of the most important bioceramics [1], plays a key role in the application of human hard tissue repair and reconstruction due to its excellent bioactivity and biocompatibility [2,3]. However, the low flexural strength and toughness of pure HA greatly limit its practical applications. In order to improve mechanical properties, HA-based composites have been widely investigated by various strategies. Among these additives, titanium (Ti) and its alloy have attracted special interest due to their superior mechanical properties as well as bioactivity [4]. The mechanical properties of HA matrix ceramic were greatly improved by adding Ti or its alloy powders [5,6]. However, a key problem—severe interfacial reaction between HA and Ti—exists [7]. While the interaction between HA and Ti produced a chemical bonding between HA and Ti, the severe interfacial reactions resulted in the degradation of Ti which led to the desirable Ti phase rarely remaining in the matrix after sintering. Furthermore, the interfacial reaction accelerated the decomposition of HA. The decomposition products would hinder densification [8], which resulted in a weak interface bonding between matrix and reinforcing particles. These issues led to only a limited improvement of mechanical properties of
n
Corresponding author. Tel.: þ 86 351 3559638; fax: þ 86 351 3557519. Corresponding author. Tel.: +86 24 83680248; fax: +86 24 83680248. E-mail addresses: [email protected] (Q. Chang), [email protected] (H.Q. Ru). nn
http://dx.doi.org/10.1016/j.matlet.2014.04.153 0167-577X/& 2014 Elsevier B.V. All rights reserved.
the composites. Therefore, it is highly crucial and great challenge to develop a way to control the interfacial reactions by optimizing the composition of the composites. Iron (Fe) is an indispensable element in the human body [9]. Itscontaining hydroxyapatite has attracted considerable attention in recent years [10]. One of the important findings of these studies was that the doping of Fe would be effective in improving the stability of HA. This implies that introducing Fe into HA/Ti composites would have a great potential to suppress the interfacial reaction between HA and Ti. Based on the expectation, in this study, we fabricated the HA composites reinforced by Ti–Fe particles, and investigated the interfacial reactions between the HA and Ti–Fe. The aim of this work was to illustrate the role of Fe on the interfacial reactions of the composites.
2. Materials and methods Nano-HA powder was synthesized using wet-chemical precipitation by reacting calcium hydroxide (Ca(OH)2) with orthophosphoric acid (H3PO4) [11]. Composite powders containing 5, 10, and 15 wt% of Ti-33 wt% Fe particles and HA were mixed by ball-milling for 12 h, and then dried at 80 1C. The mixed powders as well as pure HA powders were uniaxially pressed at 50 MPa, followed by cold-isostatic pressing at 200 MPa. The green compacts were subsequently pressureless sintered in vacuum at 950, 1000 and 1050 1C for 2 h using a heating rate of 3.33 1C/min and cooling rate of 5 1C/min.
246
Q. Chang et al. / Materials Letters 128 (2014) 245–247
The bulk density of the samples was measured by the Archimedes method. The compositional analysis of the sintered products was analyzed using X-ray diffraction (XRD). The microstructure was examined using a scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM).
3. Results and discussion Fig. 1 shows the XRD patterns of synthetic HA and HA composites with different contents of Ti–Fe particles sintered at 1000 1C. It is seen that synthetic HA exhibited a typical XRD pattern of HA (JCPDS, 0090432) with no impurity phases (Fig. 1(b)), suggesting the HA structure obtained in this study was thermally stable enough while sintering at 1000 1C. For HA composite with 5% of Ti–Fe particles, it consisted mainly of HA, Ti and Fe, together with TiFe and traces of calcium titanate (CaTiO3) (Fig. 1(e)). With increasing content of Ti–Fe to 15%, peaks of β-tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP), the decomposition products of HA, were detected (Fig. 1(f)). These results indicated that both the decomposition of HA and interaction between HA and Ti took place. However, a significant result observed in our study was that the desirable Ti phase still remained in the composites regardless of the interaction between HA and Ti. This strongly suggested that the additive Fe played a key role in suppressing the extent of both the decomposition of HA and interaction between HA and Ti.
-HA -Ti CaTiO3
-Fe TCP
-TiFe -TTCP
(f)
(e)
Intensity,(a.u.)
(d)
(c)
(b)
(a) 20
30
40 2θ,degree
50
Fig. 2 shows the TEM images of sintered HA composites with 5% and 15% Ti–Fe particles. It was observed that the grain size of HA/15% (Ti–Fe) (Fig. 2(b)) was smaller than that of HA/5%(Ti–Fe) composite (Fig. 2(a)). The reduction in grain size could be associated with the incorporation of Fe into HA that led to a contraction of the lattice because Fe had a smaller atomic radius than Ca. The a- and c-axis values of pure HA, HA/5%(Ti–Fe) and HA/15%(Ti–Fe) are presented in Table 1. It is seen that the values of a- and c-axis decreased with increasing content of Ti–Fe particles. On the other hand, the contraction in the lattice dimensions could bring about less crystal growth, thus resulting in lower crystallization of HA after the introduction of iron, as revealed by XRD (Fig. 1). The selected-area diffraction patterns (SADPs) from HA observed in the microstructure are also shown and indexed in Fig. 2(c) and (d), which corroborated the hexagonal structure of HA unite cell. It should be mentioned here that the SADPs of other phases were not obtained since the crystals of them were too small. Besides, it was observed from Fig. 2 that the porosity of HA/15%(Ti– Fe) composite was higher than that of HA/5%(Ti–Fe) composite. This was related to two potential reasons. First, the amount of the secondary phases that could inhibit sintering increased with increasing amount of Ti–Fe particles, as discussed above (Fig. 1), giving rise to a decreasing density. Second, the incorporation of Fe into HA that led to a contraction of the lattice suppressed crystal growth so as to obstruct densification. As a consequence, in comparison with the composite with 5% Ti–Fe particles, the composite with 15% Ti–Fe particles exhibited a higher porosity. A good interfacial bonding would have a potential to enhance the mechanical properties of the composite [12]. Fig. 3 shows the interface microstructure of HA/15% (Ti–Fe) composite. It is seen that the reinforcing Ti–Fe particles had a good bonding with HA matrix while some pores appeared near/in the interface. The small amount of pores was derived from a little interaction between HA and Ti. Such interface would offer a potential to improve the mechanical properties of the composites. First, the small amount of pores could retard the crack propagation due to their certain radius of curvature in comparison with the sharp brittle crack [13]. Second, these pores could lead to partial debonding of the interface. The occurrence of partial debonding would increase the crack path and make the plastic stretching area bigger, giving rise to the absorption of more fracture energy. In this study, the fracture toughness was determined by measuring the crack length generated by Vickers indentation [14]. It was found that the fracture toughness of HA/15% (Ti–Fe) composite reached 1.3 MPa m1/2, an increase by 128% in comparison to pure HA obtained in our study. This indicated that there was an appropriate interfacial bonding for the obtained HA composites reinforced by Ti–Fe particles. It is interesting and important to consider how Fe can inhibit the decomposition of HA and interaction between HA and Ti. This could be understood as follows. As discussed above, some Fe particles in the neighborhood of HA incorporated into HA structure. The stability of such Fe-containing apatite was thus improved [10], leading to less decomposition of HA. In addition, the observation that Fe exhibited very fast diffusion in α-Ti and β-Ti at 836 1C [15] would provide a potential to impede the interaction between HA and Ti. As a result, both the decomposition of HA and interaction between HA and Ti were suppressed. At the same time, it should be mentioned here that the fast diffusion of Fe into Ti promoted the mobility of Ti which played a key role in enhancing the interface bonding between Ti–Fe particles and HA matrix.
60
Fig. 1. XRD patterns of the sintered samples: (a) HA (JCPDS, 009-0432), (b) synthetic HA, (c) Fe (JCPDS, 006-0696), (d) Ti (JCPDS, 005-0682), (e) HA/5% (Ti–Fe), and (f) HA/15% (Ti–Fe).
4. Conclusions The interfacial reactions between HA and Ti–Fe reinforcing particles were investigated in this study. By detailed analysis using
Q. Chang et al. / Materials Letters 128 (2014) 245–247
0110
247
1010
0111
0000
2110
0000
Fig. 2. TEM images and electron diffraction analysis of HA/Ti–Fe composites sintered in vacuum at 1000 1C: (a) image of HA/5% (Ti–Fe), (b) image of HA/15% (Ti–Fe), (c) and (d) electron diffraction patterns of HA.
Table 1 a- and c-axis values of HA structure before and after adding Ti–Fe reinforcing particles. Sample
a (Å)
c (Å)
Pure HA HA/5% (Ti–Fe) HA/15% (Ti–Fe)
9.459 9.384 9.356
6.901 6.882 6.880
between HA and Ti that existed near/in the interface had a positive effect in obtaining an appropriate interfacial bonding, which was favorable for improving the mechanical properties of the composites.
Acknowledgments The authors would like to thank the financial support of National Natural Science Foundation of China (NSFC Grant no. 51272039) and the Natural Sciences and Engineering Research Council of Canada (NSERC) in the form of International Research Collaboration. Q. Chang is also grateful for the financial support by China Scholarship Council, and the Natural Science Foundation of North University of China. References
Fig. 3. TEM image of the interface between Ti–Fe particles and HA matrix in the HA/15% (Ti–Fe) composite.
XRD and TEM, it was found that both the decomposition of HA and interaction between HA and Ti were inhibited due to the introduction of Fe, giving rise to the desirable Ti phase maintained in the matrix. A small amount of pores due to a little interaction
[1] Best SM, Porter AE, Thian ES, Huang J. J Eur Ceram Soc 2008;28:1319–27. [2] Zakaria SM, Sharif SH, Othman MR, Yang F, Jansen JA. Tissue Eng Part B Rev 2013;19:431–41. [3] Lin KL, Zhang ML, Zhai WY, Qu HY, Chang J. J Am Ceram Soc 2011;94:206–12. [4] Long M, Rack HJ. Biomaterials 1998;19:1621–39. [5] Thian ES, Loh NH, Khor KA, Tor SB. Biomaterials 2002;23:2927–38. [6] Kumar A, Dhara S, Biswas K. J Biomed Mater Res B 2013;101B:223–36. [7] Yang YZ, Kim KH, Mauli AC, Ong JL. Biomaterials 2004;25:2927–32. [8] Wang PE, Chaki TK. J Mater Sci Mater Med 1993;4:150–8. [9] Bogard RW, Oliver JD. Appl Environ Microbiol 2007;73:7501–5. [10] Kramer ER, Morey AM, Staruch M, Suib SL, Jain M, Budnick JI, et al. J Mater Sci 2013;48:665–73. [11] Kweh SWK, Khor KA, Cheang P. J Mater Process Tech 1999;89–90:373–7. [12] Bartolomé JF, Beltrán JI, Gutiérrez-González CF, Pecharromán C, Muñoz MC, Moya JS. Acta Mater 2008;56:3358–66. [13] Kumar R, Prakash KH, Cheang P, Khor KA. Acta Mater 2005;53:2327–35. [14] Kruzic JJ, Ritchie RO. J Am Ceram Soc 2003;86:1433–6. [15] Wei W, Liu Y, Zhou K, Huang B. Powder Metall 2003;46:246–50.