Processing and properties of highly porous Ti6Al4V mimicking human bones
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idier Bouvard University Grenoble Alpes, CNRS, SIMAP, Grenoble 38000, France
José Lemus-Ruiz IIMM, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Michoacán C.P. 58060, México
Omar Jiménez Departamento de Ingeniería de Proyectos, Universidad de Guadalajara, Zapopan 45100, Jalisco, México (Received 15 October 2017; accepted 2 February 2018)
Ti6Al4V alloy samples with large pores suitable for bone implants are fabricated by pressing and sintering. Ti6Al4V powder is mixed with different volume fractions of salt particles. The sintering behavior up to 1260 °C is studied by dilatometry and pore features are observed by scanning electron microscopy and X-ray microtomography. Sintered materials with a relative density between 0.26 and 0.97 are obtained. 3D image analysis proves that large pores form a connected network when the amount of salt is 20% and above. The Young’s modulus and the yield stress of sintered materials deduced from compression tests span over wide ranges of values, which are consistent with real bone data. A simple analytical model is proposed to estimate the relative density as a function of the fraction of salt. This model combined with classical Gibson and Ashby’s power equations for mechanical properties can predict the fraction of salt required to obtain prescribed properties.
I. INTRODUCTION
In the past decades, miscellaneous metals and alloys have been used to fabricate bone implants. Among them, it can be mentioned some classes of stainless steels, cobalt-based alloys, and the most widely used titanium and its alloys.1–6 Titanium alloys have been considered due to their good combination of mechanical, corrosive, and biological properties.7,8 Nowadays, most metallic bone implants are still fabricated by traditional manufacturing techniques such as casting, forging, and machining. However, their high elastic modulus compared to that of natural bones usually produces a mismatch between the bone and the implant due to stress shielding, which is one of the three major causes of aseptic loosening.9,10 Most of bone implantation failures are linked to bone cracking developed near the join with the implant. As the bone is a complex and dynamic tissue, in which structure and density are regulated by the applied load, it is desirable that the elastic modulus and yield stress of the implant are close to those of the natural bones to avoid bone resorption.11 The optimal elastic modulus and yield stress depend on the kind of bone to Contributing Editor: Amit Bandyopadhyay a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.35
be replaced, e.g., cortical or trabecular. A wide set of mechanical properties of bones are listed by Wang et al. in their review.12 According to them, the elastic modulus of bones ranges between 0.06 and 20 GPa and their yield stress ranges between 5 and 200 MPa. The properties of implants can be adjusted by introducing pores in the bulk material as it was proposed by Gibson and Ashby.13 Porous implants are especially promising
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