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Processing and properties of porous titanium using space holder technique
Materials Science and Engineering A 506 (2009) 148–151
Contents lists available at ScienceDirect
Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea
Processing and properties of porous titanium using space holder technique Niu Wenjuan ∗ , Bai Chenguang, Qiu GuiBao, Wang Qiang College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China
a r t i c l e
i n f o
Article history: Received 19 August 2008 Received in revised form 17 November 2008 Accepted 17 November 2008 Keywords: Porous Ti Space-holder sintering process Biomaterials Pore morphology Mechanical properties
a b s t r a c t To satisfy the mechanical requirement of porous bone substitutes, the porous Ti with the porosity in the range of 55–75% was fabricated using the space-holder sintering process. The pore size is in the range of 200–500 m, and the mean value is 410 m. The mechanical properties were investigated by the compressive test. Results show that the plateau stress and Young’s modulus are in the range of 10–35 MPa and 3–6.4 GPa, respectively. The relationship between the mechanical properties and the relative density of porous Ti is found to obey a power law relation. The strength of the porous Ti is mainly affected by the density. The typical rupture section of compressed samples has the V-shape. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Although the great progress has been achieved in medical substitution materials, the fixation of implants remains a problem. Due to the effect of stress shield caused by different Young’s modulus [1], the mismatch between the biomaterials and the host bone has been identified as the major reason for implant loosening [2]. Fortunately, the strength and the Young’s modulus of the porous materials can be adjusted through the adjustments of the porosity to match the strength and the Young’s modulus of the nature bone. Moreover, the open-cellular structure of the porous materials permits the ingrowths of the new-bone tissue and the transport of the body fluids [3,4]. Investigations indicated that in porous bone substitutes, the optimal pore size for attachment and growth of osteoblasts and vasculature is approximately 300–400 m [5] or 200–500 m [4]. Presently, the successfully used implant porous materials are polymeric materials [6]. However, a major limitation of porous polymeric biomaterials is their relatively low module and strength properties making them unsuitable for load bearing bone substitute applications [7]. Metallic foams are novel materials with extremely low densities and unique combination of excellent mechanical, thermal, electrical and acoustic properties [8]. They offer opportunities for a wide range of applications, such as shock and impact energy absorbers, dust and fluid filters, engine exhaust mufflers, porous electrodes, high temperature gaskets, silencers, flame arresters, heaters, heat exchangers, catalyst supporters, con-
∗ Corresponding author. Tel.: +86 23 65111256. E-mail address: [email protected] (W. Niu). 0921-5093/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2008.11.022
struction materials [9–13]. It is well known that Ti and some Ti alloys are nowadays the most attractive metallic biomaterials due to their excellent mechanical properties, wonderful biocompatibility, and the good corrosion resistance [14,15]. Consequently, porous Ti and its alloys can be potentially used as the bone implants to control the porosity, pore size and shape as well as pore distribution. Several methods can produce porous Ti, such as loose powder sintering, slurry foaming [16], reactive sintering [17], hollow sphere sintering [18] and gas entrapped techniques [19]. However, most of the above-mentioned methods provide limited porosity. Recently, a new developed powder metallurgy technique using space holder materials comes into active with its advantages like adjustable porosity amount, pore shape, and pore size distribution [20–25]. In the present study, the porous Ti was fabricated by powder metallurgy technique using space holder materials. The final morphological features and mechanical properties were described. 2. Materials and methods Fig. 1 shows a schematic diagram of the powder metallurgy technique using space holder materials. In the present study, the pure Ti powder (purity grade, 4) of 44–74 m in size with irregular shape was used, and the morphology of it was shown in Fig. 2. Due to the ability to decompose completely at relatively low temperatures so as to avoid the reaction with the host powders, the spherical carbamide particles in the size range of 200–600 m were chosen as the space holder materials. The selection of the size of the spacer particles was determined according to empirical investigations [22].
W. Niu et al. / Materials Science and Engineering A 506 (2009) 148–151
149
3. Results and discussion 3.1. Structural features
Fig. 1. The processing stages in the powder metallurgy technique using space holder materials.
Initially, the carbamide particles with the size in the range of 0.71–1.19 mm were dissolved in the solution made by ethanol and water for about 5 min to decrease the size to the range of 200–600 m. To increase the green strength of powder compacts, Ti powders were mixed with the binder, polyethylene glycol. Then, the carbamide particles were added and sufficiently mixed in Vtype mixer for 1 h. The mixture was uniaxially pressed into the length of approximately 10 mm, using a cylindrical steel die with 12 mm in diameter. To avoid the oxidization, the heat treatment was conducted in a vacuum induction furnace. Based on the differential thermal analysis of the carbamide and the sintering process of Ti powders, the heat treatment includes three steps, i.e. at 200 ◦ C for 3 h, 350 ◦ C for 3 h and 1250 ◦ C for 3 h, followed by furnace cooling. Densities of the produced specimens were determined by Archimedes method. The details of pore morphology were observed by scanning electron microscopy (SEM). Structural features like pore size distribution was measured by quantitative image analysis software Image-Pro Plus. Mechanical properties of porous Ti were studied by the compression test performed on a CMT-5150 compression testing machine. Samples with height/diameter ratios of 0.65–1.1 were compressed at a strain rate of 10−3 s−1 .
Fig. 2. SEM image of Ti powders.
Porous Ti with porosities in the range of 55–75% was successfully fabricated by adding different volume ratio of carbamide. The structures of porous Ti are different with the change in the percentage of space holder, as shown in Fig. 3. It also can be clearly seen that there are two types of pores in the samples: the interconnected macropores obtained by the decomposition of carbamide particles; and the micropores obtained by partially sintering of Ti powders on the pore walls, the size of them is about several micrometers. Fig. 4 shows the pore size distribution in terms of mean diameter using image analysis method based on the SEM image. Several hundreds of pores were measured to estimate the pore size. The mean diameters were measured through pore’s centroid at 2◦ intervals. In the present study, 90% of the pores have the size in the range of 300–500 m and the mean value of pore size is 410 m. This kind of micropores is reported to the optimum pore size for the attachment and proliferation of the new-bone tissues and the transport of the body fluids [21]. 3.2. Mechanical properties The mechanical properties of porous Ti were studied by the compression test. Fig. 5 shows the nominal strain–stress curves of porous Ti with various porosities of 55–75%. It can be seen that these curves show the typical features of metallic foams [22,23], i.e. an elastic deformation stage at the beginning of deformation; a long plateau stage with a smooth flow stress while the strain increases, in this region the pores are compressed and distorted; and a densification stage where the flow stress increases rapidly, which indicates the compression behavior changes from cellular to bulk material. The plateau stress varies between 10 and 35 MPa, and it decreases with the increasing porosity. Simultaneously, the elastic modulus, which is determined from the slope of linear portion of each curve, also decreases with the increase of porosity. The maximum and minimum of elastic modules are 6.4 and 3 GPa, respectively. Various empirical relations have been proposed to describe the dependence of the mechanical properties of foams to their porosity content. These models are based primarily on the significance of either the load-bearing cross-sectional area or the stress concentration and the effective flaw size [26]. The former is used more frequently to describe the mechanical properties of porous materials. The Gibson and Ashby model [8] assumes the pore walls as solid metal and finds that the contribution of cell face stretching to the overall stiffness and strength of the foam is linearly dependent on the relative density term, /s , while the contribution of cell edge bending is non-linear. However, this model is valid to metal foams with a porosity of 70% or higher [23]. All the theoretical models are based on some idealized microstructures, e.g. uniform spherical, cylindrical or cubic pores arranged in a cubic array, and therefore the derived correlations between properties and porosity cannot usually be extended directly to real materials with pores of irregular shapes, non-uniform size and random distribution. In the present, the relationship between the plateau stress and the Young’s modulus on the relative density of porous Ti is found to obey a power law relation, as shown by the fitted line in Fig. 6. Eqs. (1) and (2) represent the relationships between the mechanical properties and the relative density, where is the plateau stress of porous Ti; s is the yield stress of the bulk material; /s is the relative density. In Eq. (2), E and Es is the Young’s modulus of porous Ti and bulk material, respectively. The density, yield stress and Young’s modulus of pure bulk Ti is 4.5 g/cm−3 , 480 MPa
150
W. Niu et al. / Materials Science and Engineering A 506 (2009) 148–151
Fig. 3. The structures of porous Ti: (a) 55% porosity; (b) 70% porosity; (c) 75% porosity; (d) a closer view of pore walls consisting of partially sintered powders.
and 110 GPa, respectively.
= 0.375 s s E = 0.193 Es
Fig. 4. Spherical diameter distribution of Ti with a porosity of 70%.
Fig. 5. The compressive strain–stress curve of Ti with different porosities.
2.06
,
1.43 s
,
(R = 0.997)
(1)
(R = 0.979)
(2)
Fig. 7(a) shows the distribution of the pressure of the green compact during the uniaxially pressing process. Because of the pressure loss, the pressure distribution is un-uniform in the compact. The pressure at the top is larger than that at the bottom, and it decreases more quickly in the outer layer than that in the center. Thus in the longitudinal section center of the green compact, the iso-pressure curve has the V-shape. Investigations reported that the main factor influencing the density distribution of the compact is the pressure [27]. Hence, the iso-density line should have the uniform shape with
Fig. 6. The change of relative stress and relative Young’s modulus with relative density.
W. Niu et al. / Materials Science and Engineering A 506 (2009) 148–151
151
plateau stress and Young’s modulus are in the range of 10–35 MPa and 3–6.4 GPa, respectively. Hence, the Ti foams can satisfy the mechanical requirement of porous bone substitutes. The relationship between the mechanical properties and the relative density of porous Ti is found to obey a power law relation. The strength of the porous Ti is mainly affected by the density. The typical rupture section of compressed samples has the V-shape. Acknowledgements This research is financially supported by National Nature Science Foundation of China (grant 50504020) and Chongqing Natural Science Foundation (grant CSTC, 2008BB4051). References
Fig. 7. (a) The distribution of the pressing pressure in the green compact; (b) the typical rupture section of compressed sample with the inverse V-shape.
the iso-pressure line in the green compact. From Eqs. (1) and (2), it can be seen that the strength of the porous Ti is mainly affected by the density, and they should have the same change trend. So we can deduce that the iso-strength line of porous Ti also has the V-shape. In the present study, it was confirmed. Fig. 7(b) shows the typical rupture section of compressed samples with the inverse V-shape. When the applied stress exceeds a critical value, the rupture will happen along the iso-strength area. The reported strengths of the cancellous bones are in the range of 3–20 MPa [28] and the Young’s modulus of the nature bones are between 10 and 40 GPa [15]. The present porous Ti with porosities in the range of 55–75% still has the strength between 10 and 35 MPa and the elastic modules between 3 and 6.4 GPa. Consequently, the Ti foams can satisfy the mechanical requirement of porous bone substitutes. 4. Conclusion The powder metallurgy using the space holder technique can produce porous materials with the controllable porosity, pore size and pore morphology. In the present study, the porous Ti with the porosity in the range of 55–75% was fabricated. The pore size is in the range of 200–500 m, and the mean value is 410 m. The
[1] Q.T. Wang, Y.M. Zhang, N.S. Hu, Rare Met. Mater. Eng. 33 (2004) 442–444. [2] G. Ryan, A. Pandit, D.P. Apatsidis, Biomaterials 27 (2006) 2651. [3] L.D. Zardiackas, L.D. Dillon, D.W. Mitchell, L.A. Nunnery, R. Poggie, J. Biomed. Mater. Res. 58 (2001) 180. [4] J.T. Clemow, A.M. Weinstein, J.J. Klawitter, J. Koeneman, J. Anderson, J. Biomed. Mater. Res. 15 (1981) 73. [5] E. Tsuruga, H. Takita, H. Itoh, Y. Koboki, J. Biochem. 121 (1997) 317. [6] T.M. Freyman, I.V. Yannas, L.J. Gibson, Prog. Mater. Sci. 46 (2001) 273. [7] D.W. Hutmacher, Biomaterials 21 (2000) 2529. [8] L.J. Gibson, M.F. Ashby, Cellular Solids: Structure and Properties, second edition, Cambridge University Press, 1997. [9] Y. Yamada, K. Shimojima, Y. Sakaguchi, M. Mabuchi, M. Nakamura, T. Asahina, T. Mukai, H. Kanahashi, K. Higashi, Mater. Sci. Eng. A 280 (2000) 225. [10] G.J. Davies, S. Zhen, J. Mater. Sci. 18 (1983) 1899. [11] C.E. Wen, Y. Yamada, K. Shimojima, M. Mabuchi, M. Nakamura, T. Asahina, T. Aizawa, K. Higashi, Mater. Trans., JIM 41 (2000) 1192. [12] J. Banhart, J. Baumeister, M. Weber, Proceedings of the 1998 Powder Metallurgy World Conference and Exhibition, European Powder Metallurgy Association, UK, 1998, p. 201. [13] J. Banhart, C. Schmoll, U. Neumann, Proceedings of the Euromat’98 Conference on Materials in Oceanic Environment, vol. 1, 1998, p. 55. [14] Y. Okazaki, E. Nishimura, H. Nakada, K. Kobayashi, Biomaterials 22 (2001) 599. [15] M. Long, H.J. Rack, Biomaterials 19 (1998) 1621. [16] J.P. Li, S.H. Li, K. Groot, P. Layrolle, Key Eng. Mater. 218 (2002) 51. [17] M. Barrabés, P. Sevilla, J.A. Planell, F.J. Gil, Mater. Sci. Eng. C 28 (2008) 23. [18] D.C. Dunand, Adv. Eng. Mater. 6 (2004) 369. [19] N.G.D. Murray, D.C. Dunand, Acta Mater. 52 (2004) 2269. [20] A. Laptev, O. Vyal, M. Bram, H.P. Buchkremer, D. Stöver, Powder Metall. 48 (2005) 358. [21] G. Kotan, A.S. Bor, J. Eng. Environ. Sci. 31 (2007) 149. [22] C.E. Wen, M. Mabuchi, Y. Yamada, K. Shimojima, Y. Chino, T. Asahina, Scripta Mater. 45 (2001) 1147. [23] Z. Esen, S. Bor, Scripta Mater. 56 (2007) 341. [24] C.E. Wen, Y. Yamada, K. Shimojima, Y. Chino, T. Asahina, M. Mabuchi, J. Mater. Sci. Mater. Med. 13 (2002) 397. [25] M. Bram, C. Stiller, H.P. Buchkremer, D. Stover, H. Baur, Adv. Eng. Mater. 2 (2000) 196. [26] A. Hattiangadi, A. Bandyopadhyay, J. Am. Ceram. Soc. 11 (2000) 83. [27] H.F. Fischmeister, Powder Metall. 7 (1961) 82. [28] F. Tencer, K.D. Johnson, Biomechanics in Orthopaedic Applications: Bone Fracture and Fixation, Martin Dunitz, 1994.
Contents lists available at ScienceDirect
Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea
Processing and properties of porous titanium using space holder technique Niu Wenjuan ∗ , Bai Chenguang, Qiu GuiBao, Wang Qiang College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China
a r t i c l e
i n f o
Article history: Received 19 August 2008 Received in revised form 17 November 2008 Accepted 17 November 2008 Keywords: Porous Ti Space-holder sintering process Biomaterials Pore morphology Mechanical properties
a b s t r a c t To satisfy the mechanical requirement of porous bone substitutes, the porous Ti with the porosity in the range of 55–75% was fabricated using the space-holder sintering process. The pore size is in the range of 200–500 m, and the mean value is 410 m. The mechanical properties were investigated by the compressive test. Results show that the plateau stress and Young’s modulus are in the range of 10–35 MPa and 3–6.4 GPa, respectively. The relationship between the mechanical properties and the relative density of porous Ti is found to obey a power law relation. The strength of the porous Ti is mainly affected by the density. The typical rupture section of compressed samples has the V-shape. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Although the great progress has been achieved in medical substitution materials, the fixation of implants remains a problem. Due to the effect of stress shield caused by different Young’s modulus [1], the mismatch between the biomaterials and the host bone has been identified as the major reason for implant loosening [2]. Fortunately, the strength and the Young’s modulus of the porous materials can be adjusted through the adjustments of the porosity to match the strength and the Young’s modulus of the nature bone. Moreover, the open-cellular structure of the porous materials permits the ingrowths of the new-bone tissue and the transport of the body fluids [3,4]. Investigations indicated that in porous bone substitutes, the optimal pore size for attachment and growth of osteoblasts and vasculature is approximately 300–400 m [5] or 200–500 m [4]. Presently, the successfully used implant porous materials are polymeric materials [6]. However, a major limitation of porous polymeric biomaterials is their relatively low module and strength properties making them unsuitable for load bearing bone substitute applications [7]. Metallic foams are novel materials with extremely low densities and unique combination of excellent mechanical, thermal, electrical and acoustic properties [8]. They offer opportunities for a wide range of applications, such as shock and impact energy absorbers, dust and fluid filters, engine exhaust mufflers, porous electrodes, high temperature gaskets, silencers, flame arresters, heaters, heat exchangers, catalyst supporters, con-
∗ Corresponding author. Tel.: +86 23 65111256. E-mail address: [email protected] (W. Niu). 0921-5093/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2008.11.022
struction materials [9–13]. It is well known that Ti and some Ti alloys are nowadays the most attractive metallic biomaterials due to their excellent mechanical properties, wonderful biocompatibility, and the good corrosion resistance [14,15]. Consequently, porous Ti and its alloys can be potentially used as the bone implants to control the porosity, pore size and shape as well as pore distribution. Several methods can produce porous Ti, such as loose powder sintering, slurry foaming [16], reactive sintering [17], hollow sphere sintering [18] and gas entrapped techniques [19]. However, most of the above-mentioned methods provide limited porosity. Recently, a new developed powder metallurgy technique using space holder materials comes into active with its advantages like adjustable porosity amount, pore shape, and pore size distribution [20–25]. In the present study, the porous Ti was fabricated by powder metallurgy technique using space holder materials. The final morphological features and mechanical properties were described. 2. Materials and methods Fig. 1 shows a schematic diagram of the powder metallurgy technique using space holder materials. In the present study, the pure Ti powder (purity grade, 4) of 44–74 m in size with irregular shape was used, and the morphology of it was shown in Fig. 2. Due to the ability to decompose completely at relatively low temperatures so as to avoid the reaction with the host powders, the spherical carbamide particles in the size range of 200–600 m were chosen as the space holder materials. The selection of the size of the spacer particles was determined according to empirical investigations [22].
W. Niu et al. / Materials Science and Engineering A 506 (2009) 148–151
149
3. Results and discussion 3.1. Structural features
Fig. 1. The processing stages in the powder metallurgy technique using space holder materials.
Initially, the carbamide particles with the size in the range of 0.71–1.19 mm were dissolved in the solution made by ethanol and water for about 5 min to decrease the size to the range of 200–600 m. To increase the green strength of powder compacts, Ti powders were mixed with the binder, polyethylene glycol. Then, the carbamide particles were added and sufficiently mixed in Vtype mixer for 1 h. The mixture was uniaxially pressed into the length of approximately 10 mm, using a cylindrical steel die with 12 mm in diameter. To avoid the oxidization, the heat treatment was conducted in a vacuum induction furnace. Based on the differential thermal analysis of the carbamide and the sintering process of Ti powders, the heat treatment includes three steps, i.e. at 200 ◦ C for 3 h, 350 ◦ C for 3 h and 1250 ◦ C for 3 h, followed by furnace cooling. Densities of the produced specimens were determined by Archimedes method. The details of pore morphology were observed by scanning electron microscopy (SEM). Structural features like pore size distribution was measured by quantitative image analysis software Image-Pro Plus. Mechanical properties of porous Ti were studied by the compression test performed on a CMT-5150 compression testing machine. Samples with height/diameter ratios of 0.65–1.1 were compressed at a strain rate of 10−3 s−1 .
Fig. 2. SEM image of Ti powders.
Porous Ti with porosities in the range of 55–75% was successfully fabricated by adding different volume ratio of carbamide. The structures of porous Ti are different with the change in the percentage of space holder, as shown in Fig. 3. It also can be clearly seen that there are two types of pores in the samples: the interconnected macropores obtained by the decomposition of carbamide particles; and the micropores obtained by partially sintering of Ti powders on the pore walls, the size of them is about several micrometers. Fig. 4 shows the pore size distribution in terms of mean diameter using image analysis method based on the SEM image. Several hundreds of pores were measured to estimate the pore size. The mean diameters were measured through pore’s centroid at 2◦ intervals. In the present study, 90% of the pores have the size in the range of 300–500 m and the mean value of pore size is 410 m. This kind of micropores is reported to the optimum pore size for the attachment and proliferation of the new-bone tissues and the transport of the body fluids [21]. 3.2. Mechanical properties The mechanical properties of porous Ti were studied by the compression test. Fig. 5 shows the nominal strain–stress curves of porous Ti with various porosities of 55–75%. It can be seen that these curves show the typical features of metallic foams [22,23], i.e. an elastic deformation stage at the beginning of deformation; a long plateau stage with a smooth flow stress while the strain increases, in this region the pores are compressed and distorted; and a densification stage where the flow stress increases rapidly, which indicates the compression behavior changes from cellular to bulk material. The plateau stress varies between 10 and 35 MPa, and it decreases with the increasing porosity. Simultaneously, the elastic modulus, which is determined from the slope of linear portion of each curve, also decreases with the increase of porosity. The maximum and minimum of elastic modules are 6.4 and 3 GPa, respectively. Various empirical relations have been proposed to describe the dependence of the mechanical properties of foams to their porosity content. These models are based primarily on the significance of either the load-bearing cross-sectional area or the stress concentration and the effective flaw size [26]. The former is used more frequently to describe the mechanical properties of porous materials. The Gibson and Ashby model [8] assumes the pore walls as solid metal and finds that the contribution of cell face stretching to the overall stiffness and strength of the foam is linearly dependent on the relative density term, /s , while the contribution of cell edge bending is non-linear. However, this model is valid to metal foams with a porosity of 70% or higher [23]. All the theoretical models are based on some idealized microstructures, e.g. uniform spherical, cylindrical or cubic pores arranged in a cubic array, and therefore the derived correlations between properties and porosity cannot usually be extended directly to real materials with pores of irregular shapes, non-uniform size and random distribution. In the present, the relationship between the plateau stress and the Young’s modulus on the relative density of porous Ti is found to obey a power law relation, as shown by the fitted line in Fig. 6. Eqs. (1) and (2) represent the relationships between the mechanical properties and the relative density, where is the plateau stress of porous Ti; s is the yield stress of the bulk material; /s is the relative density. In Eq. (2), E and Es is the Young’s modulus of porous Ti and bulk material, respectively. The density, yield stress and Young’s modulus of pure bulk Ti is 4.5 g/cm−3 , 480 MPa
150
W. Niu et al. / Materials Science and Engineering A 506 (2009) 148–151
Fig. 3. The structures of porous Ti: (a) 55% porosity; (b) 70% porosity; (c) 75% porosity; (d) a closer view of pore walls consisting of partially sintered powders.
and 110 GPa, respectively.
= 0.375 s s E = 0.193 Es
Fig. 4. Spherical diameter distribution of Ti with a porosity of 70%.
Fig. 5. The compressive strain–stress curve of Ti with different porosities.
2.06
,
1.43 s
,
(R = 0.997)
(1)
(R = 0.979)
(2)
Fig. 7(a) shows the distribution of the pressure of the green compact during the uniaxially pressing process. Because of the pressure loss, the pressure distribution is un-uniform in the compact. The pressure at the top is larger than that at the bottom, and it decreases more quickly in the outer layer than that in the center. Thus in the longitudinal section center of the green compact, the iso-pressure curve has the V-shape. Investigations reported that the main factor influencing the density distribution of the compact is the pressure [27]. Hence, the iso-density line should have the uniform shape with
Fig. 6. The change of relative stress and relative Young’s modulus with relative density.
W. Niu et al. / Materials Science and Engineering A 506 (2009) 148–151
151
plateau stress and Young’s modulus are in the range of 10–35 MPa and 3–6.4 GPa, respectively. Hence, the Ti foams can satisfy the mechanical requirement of porous bone substitutes. The relationship between the mechanical properties and the relative density of porous Ti is found to obey a power law relation. The strength of the porous Ti is mainly affected by the density. The typical rupture section of compressed samples has the V-shape. Acknowledgements This research is financially supported by National Nature Science Foundation of China (grant 50504020) and Chongqing Natural Science Foundation (grant CSTC, 2008BB4051). References
Fig. 7. (a) The distribution of the pressing pressure in the green compact; (b) the typical rupture section of compressed sample with the inverse V-shape.
the iso-pressure line in the green compact. From Eqs. (1) and (2), it can be seen that the strength of the porous Ti is mainly affected by the density, and they should have the same change trend. So we can deduce that the iso-strength line of porous Ti also has the V-shape. In the present study, it was confirmed. Fig. 7(b) shows the typical rupture section of compressed samples with the inverse V-shape. When the applied stress exceeds a critical value, the rupture will happen along the iso-strength area. The reported strengths of the cancellous bones are in the range of 3–20 MPa [28] and the Young’s modulus of the nature bones are between 10 and 40 GPa [15]. The present porous Ti with porosities in the range of 55–75% still has the strength between 10 and 35 MPa and the elastic modules between 3 and 6.4 GPa. Consequently, the Ti foams can satisfy the mechanical requirement of porous bone substitutes. 4. Conclusion The powder metallurgy using the space holder technique can produce porous materials with the controllable porosity, pore size and pore morphology. In the present study, the porous Ti with the porosity in the range of 55–75% was fabricated. The pore size is in the range of 200–500 m, and the mean value is 410 m. The
[1] Q.T. Wang, Y.M. Zhang, N.S. Hu, Rare Met. Mater. Eng. 33 (2004) 442–444. [2] G. Ryan, A. Pandit, D.P. Apatsidis, Biomaterials 27 (2006) 2651. [3] L.D. Zardiackas, L.D. Dillon, D.W. Mitchell, L.A. Nunnery, R. Poggie, J. Biomed. Mater. Res. 58 (2001) 180. [4] J.T. Clemow, A.M. Weinstein, J.J. Klawitter, J. Koeneman, J. Anderson, J. Biomed. Mater. Res. 15 (1981) 73. [5] E. Tsuruga, H. Takita, H. Itoh, Y. Koboki, J. Biochem. 121 (1997) 317. [6] T.M. Freyman, I.V. Yannas, L.J. Gibson, Prog. Mater. Sci. 46 (2001) 273. [7] D.W. Hutmacher, Biomaterials 21 (2000) 2529. [8] L.J. Gibson, M.F. Ashby, Cellular Solids: Structure and Properties, second edition, Cambridge University Press, 1997. [9] Y. Yamada, K. Shimojima, Y. Sakaguchi, M. Mabuchi, M. Nakamura, T. Asahina, T. Mukai, H. Kanahashi, K. Higashi, Mater. Sci. Eng. A 280 (2000) 225. [10] G.J. Davies, S. Zhen, J. Mater. Sci. 18 (1983) 1899. [11] C.E. Wen, Y. Yamada, K. Shimojima, M. Mabuchi, M. Nakamura, T. Asahina, T. Aizawa, K. Higashi, Mater. Trans., JIM 41 (2000) 1192. [12] J. Banhart, J. Baumeister, M. Weber, Proceedings of the 1998 Powder Metallurgy World Conference and Exhibition, European Powder Metallurgy Association, UK, 1998, p. 201. [13] J. Banhart, C. Schmoll, U. Neumann, Proceedings of the Euromat’98 Conference on Materials in Oceanic Environment, vol. 1, 1998, p. 55. [14] Y. Okazaki, E. Nishimura, H. Nakada, K. Kobayashi, Biomaterials 22 (2001) 599. [15] M. Long, H.J. Rack, Biomaterials 19 (1998) 1621. [16] J.P. Li, S.H. Li, K. Groot, P. Layrolle, Key Eng. Mater. 218 (2002) 51. [17] M. Barrabés, P. Sevilla, J.A. Planell, F.J. Gil, Mater. Sci. Eng. C 28 (2008) 23. [18] D.C. Dunand, Adv. Eng. Mater. 6 (2004) 369. [19] N.G.D. Murray, D.C. Dunand, Acta Mater. 52 (2004) 2269. [20] A. Laptev, O. Vyal, M. Bram, H.P. Buchkremer, D. Stöver, Powder Metall. 48 (2005) 358. [21] G. Kotan, A.S. Bor, J. Eng. Environ. Sci. 31 (2007) 149. [22] C.E. Wen, M. Mabuchi, Y. Yamada, K. Shimojima, Y. Chino, T. Asahina, Scripta Mater. 45 (2001) 1147. [23] Z. Esen, S. Bor, Scripta Mater. 56 (2007) 341. [24] C.E. Wen, Y. Yamada, K. Shimojima, Y. Chino, T. Asahina, M. Mabuchi, J. Mater. Sci. Mater. Med. 13 (2002) 397. [25] M. Bram, C. Stiller, H.P. Buchkremer, D. Stover, H. Baur, Adv. Eng. Mater. 2 (2000) 196. [26] A. Hattiangadi, A. Bandyopadhyay, J. Am. Ceram. Soc. 11 (2000) 83. [27] H.F. Fischmeister, Powder Metall. 7 (1961) 82. [28] F. Tencer, K.D. Johnson, Biomechanics in Orthopaedic Applications: Bone Fracture and Fixation, Martin Dunitz, 1994.