Elsevier

Materials & Design

Volume 145, 5 May 2018, Pages 88-96
Materials & Design

Development of a novel TiNbTa material potentially suitable for bone replacement implants

https://doi.org/10.1016/j.matdes.2018.02.042Get rights and content

Highlights

  • An original submicrometric (β + γ)-TiNbTa material was successfully developed.

  • It was obtained via a combined Low Energy Mechanical Alloying and Pulsed Electric Current Sintering metallurgical process.

  • It was determined a novel fcc structure for Ti alloys (γ-TiNbTa alloy).

  • This material possesses a low Young's modulus and an outstanding yield strength.

  • This would allow obtaining (β + γ)-TiNbTa foams without mechanical strength damage.

Abstract

A novel (β + γ)-TiNbTa alloy has been developed by a combined low energy mechanical alloying (LEMA) and pulsed electric current sintering process (PECS). Microstructurally, this material presents interesting characteristics, such as a submicrometric range of particle size, a body-centered phase (β-TiNbTa) and, mainly, a novel face-centered cubic Ti-based alloy (γ-TiNbTa) not previously reported. Related to mechanical performance, the novel (β + γ)-TiNbTa shows a lower E (49 ± 3 GPa) and an outstanding yield strength (σy > 1860 MPa). This combination of original microstructure and properties makes to the (β + γ)-TiNbTa a novel material potentially suitable as biomaterial to fabricate bone replacement implants, avoiding the undesirable and detrimental stress-shielding problem and even the usual damage on the mechanical strength of Ti-based foams biomaterials.

Introduction

Commercially pure titanium (c.p. Ti grade 4) and the Ti6Al4V alloy (Ti grade 5), ASTM B265–10, are the most widely metallic materials used for bone replacements implants [1]. However, they present an important disadvantage, a high Young's modulus (between 100 and 105 GPa [2]) in comparison with the trabecular and cortical bone (10.4–14.8 GPa and 18.6–20.7 GPa, respectively [3]). This disparity of the stiffness between the implant material and the adjacent bone is detrimental to the stability of the bone–implant ensemble. The incorrect transference of the stress supported by the bone to the implant leads to bone resorption, osteopenia, i.e., the reduction in bone density, loosening of the implant and/or premature bone fracture [4,5]. Therefore, the key aspect to avoid stress shielding is matching the Young's modulus of the implant to that of the bone tissue [6]. For this purpose, research efforts have mainly followed by two different routes.

The first one is the development of cellular solids or foams (porous materials) from c.p.Ti or Ti6Al4V to decrease the density and, therefore, their Young's modulus based in the well-known inverse relationship between both properties [[7], [8], [9]]. Potential porous Ti-based biomaterials with homogeneous-, longitudinal-, and radial-graded interconnected porosity [10,11] replicating bone structure have been developed, with E value similar to that of the cortical bone (~20 GPa). However, the high porosity needed to reach this E value compromises other important characteristic of design, such as the yield strength (σy) under monotonic and/or fatigue loads [12,13]. Thus, the σy can be diminished from the 655 and 828 MPa for bulk Ti and Ti6Al4V [14], respectively, to 87 MPa for Ti foams with 67 vol% of porosity [15] and 167–69 MPa for Ti6Al4V foams with 50–70 vol% of porosity [13]. For comparison purpose, the yield strength for cortical bone determined by compression test is 135 ± 34 MPa [16].

The second path to obtain Ti-based biomaterials with low E is focused on the development of Ti-based alloys with different structure that of the c.p. Ti and the Ti6Al4V alloy. These phases present, at room temperature, α and (α + β) structures [17], respectively. The α phase is a hexagonal close-packed (hcp) structure, while the β phase is a body-centered cubic (bcc) structure. It is widely reported that metastable β-Ti alloys have lower E than α-Ti alloys, but still higher than the cortical and trabecular bones [18]. The β-Ti alloys possess a unique balance of low stiffness, formability, and weldability, making them suitable for a wide range of clinical applications [[19], [20], [21]].

Although the metastable β-Ti is a high-temperature phase, with an α  β dimorphic allotropic transformation at transition temperature of 882 °C [22], it is possible to maintain the β-Ti thanks to the existence of some transition metals that act as β stabilizers at room temperature. The β stabilizer elements mainly include Mo, V, Nb, Ta, and Zr as β-isomorphous [23,24] and Cr, Co, Cu, Fe, and Ni as β-eutectoid elements [22,25]. The advantage of the β-isomorphous elements is the high amount of substitutional solid solution and their inability to form Ti intermetallic compounds, with high E [[26], [27], [28]], according to their binary phase diagrams.

Thus, based on this assertion, β-Ti alloys have been developed with Young's modulus relatively low (minimum E value of 35 GPa) [29,30] and close to that of the cortical bone (~21 GPa). However, their E still remains far from that of trabecular bone (~14 GPa). Nb, Ta, and Zr are the main alloyed elements due to their higher biocompatibility [31] and their β-isomorphous character. Also, these new β-Ti alloys present, as general trend, yield strength lower than c.p. Ti, Ti6Al4V and other first generation alloys with alfa structure. As example, the β-Ti-Nb-Ta-Zr alloys showed σy values between 530 and 804 MPa and the β-Ti-Nb-Sn-Mo-Zr between 668 and 825 MPa [19,32,33]. Therefore, it would not be possible to develop β-Ti alloys (bulk or foams) with an optimal combination of both low E and optimal yield strength similar to the cortical and trabecular bones.

Therefore, an alternative approach to meet the aforementioned E and σy requirements would be the development of amorphous and nanocrystalline alloys, or even, Ti alloys with novel structures [34]. These efforts should be directed at decreasing the E value to a level close to that of the trabecular bone and minimizing the loss of mechanical strength for porous Ti alloys. These requirements could be met by amorphous [35,36] and nanocrystalline materials, which have higher strength values as compared to other microstructured polycrystalline materials [37]. Additionally, the development of other structures for Ti alloys, such as tetragonal structure for the intermetallic γ-TiAl [38], could be another interesting approach to address stress shielding due to expected discrepancy in mechanical behavior.

Therefore, the aim of this work is to develop an amorphous and/or nanostructured Ti alloy bulk material with structure different of the traditional hcp α-Ti and bcc β-Ti alloys. This is expected in order to obtain an optimal product, decreasing Young's modulus (E) while increasing yield strength (σy), for use as raw material to fabricate bulk or foam bone replacement implants, without the detrimental stress-shielding behavior.

For this purpose, we employed the combined low-energy mechanical alloying (LEMA) and the pulsed electric current sintering (PECS) powder metallurgy processes. LEMA was selected for its ability to produce homogeneous materials and induce amorphization and phase transformation [39]. PECS is a sintering method that simultaneously uses high current density and pressure to consolidate materials in a short period of time, commonly seconds or minutes, due to the possibility to apply higher heating rates than conventional sintering techniques. This PECS sintering technique was selected for its ability to maintain the nanostructure and partially amorphous characteristic on the consolidated powders [40].

Two elements, Nb and Ta, were introduced to obtain a Ti-based alloy with 57Ti-30Nb-13Ta (atomic percent [at.%]) nominal composition. Both elements were selected due to their β stabilizing behavior, to ensure the absence of the α phase (due to its higher E value), biocompatibility [41,42], and ability to prevent particle increase [43]. In addition, Nb was introduced in high amounts since mechanical alloying causes it to undergo an allotropic transformation from β (bcc) phase to γ (fcc) phase [44]. We expect that this Nb transformation can induce the same transformation for the 57Ti-30Nb-13Ta (at.%) material.

Section snippets

Materials and method

Elemental powders of titanium (CAS number 7440-32-6, 99.6% purity, <325 mesh, NOAH tech, San Antonio, TX, USA), niobium (CAS number 7440-03-1, 99.9% purity, <325 mesh, NOAH tech.), and tantalum (CAS number 7440-25-7, 99.9% purity, <325 mesh, NOAH tech.), with nominal composition of 57Ti-30Nb-13Ta (at.%), were used to develop a TiNbTa potential biomaterial. The mechanical alloying process was carried out under low-energy (LEMA) conditions to prevent the grain growth that can occur in the case of

Microstructural characterization

The TiNbTa potential biomaterial for bone tissue replacement implants developed in this study showed in the XRD patterns two and three phases for the as-milled and as-sintered specimens, respectively (Fig. 1a). In both specimens, two structures were assigned, a body-centred cubic (bcc, Im3m) and a face-centred cubic (fcc, Fm3m) structure, designed as β and γ phases, respectively. Both structures were corroborated by comparison with the references files existing in the PDF4+ database for the bcc

Conclusions

  • By applying a combination of LEMA and PECS powder metallurgy processes, it was successfully developed a novel TiNbTa material with interesting microstructural and mechanical characteristics that make it suitable for bone replacements implants.

  • The microstructure developed showed different zones with different particle sizes, but always in the submicrometric range.

  • In all zones detected for the novel TiNbTa material, two Ti-based alloys were observed. The first one was the typical β-TiNbTa alloy

Acknowledgments

This work was supported under postdoctoral grant No. 3150060, which is financed by the FONDECYT fund (Government of Chile). Authors want to thanks to the University of Seville for the use of its general research service (CITIUS) under the grant no. 2017/833 and to the Nanomaterials and Nanotechnology Research Center (CINN-CSIC-UNIOVI) for the availability of the PECS device.

References (71)

  • M. Niinomi et al.

    Development of new metallic alloys for biomedical applications

    Acta Biomater.

    (2012)
  • M. Geetha et al.

    Ti based biomaterials, the ultimate choice for orthopaedic implants – a review

    Prog. Mater. Sci.

    (2009)
  • S. Bahl et al.

    Engineering the next-generation tin containing beta titanium alloys with high strength and low modulus for orthopedic applications

    J. Mech. Behav. Biomed. Mater.

    (2018)
  • I. Kopova et al.

    Newly developed Ti-Nb-Zr-Ta-Si-Fe biomedical beta titanium alloys with increased strength and enhanced biocompatibility

    Mater. Sci. Eng. C

    (2016)
  • S. Ehtemam-Haghighi et al.

    Evaluation of mechanical and wear properties of TixNb7Fe alloys designed for biomedical applications

    Mater. Des.

    (2016)
  • I.V. Okulov et al.

    Composition optimization of low modulus and high-strength TiNb-based alloys for biomedical applications

    J. Mech. Behav. Biomed. Mater.

    (2017)
  • M. Kikuchi et al.

    Elastic moduli of cast Ti–Au, Ti–Ag, and Ti–Cu alloys

    Dent. Mater.

    (2006)
  • J. She et al.

    High volume intermetallics reinforced Ti-based composites in situ synthesized from Ti-Si-Sn ternary system

    Mater. Sci. Eng. A

    (2011)
  • M. Tane et al.

    Peculiar elastic behavior of Ti-Nb-Ta-Zr single crystals

    Acta Mater.

    (2008)
  • D. Raabe et al.

    Theory-guided bottom-up design of β-titanium alloys as biomaterials based on first principles calculations: theory and experiments

    Acta Mater.

    (2007)
  • S.-j. Dai et al.

    Design of new biomedical titanium alloy based on d-electron alloy design theory and JMatPro software

    Trans. Nonferrous Metals Soc. China

    (2013)
  • D. Kuroda et al.

    Design and mechanical properties of new beta type titanium alloys for implant materials

    Mater. Sci. Eng. A

    (1998)
  • E. Chicardi et al.

    Development of a novel fcc structure for an amorphous-nanocrystalline Ti-33Nb-4Mn (at.%) ternary alloy

    Mater. Charact.

    (2018)
  • A. Inoue et al.

    High-strength Cu-based bulk glassy alloys in Cu–Zr–Ti and Cu–Hf–Ti ternary systems

    Acta Mater.

    (2001)
  • A. Inoue et al.

    High-strength Zr-based bulk amorphous alloys containing nanocrystalline and nanoquasicrystalline particles

    Sci. Technol. Adv. Mater.

    (2000)
  • T.G. Nieh et al.

    Hall-Petch relation in nanocrystalline solids

    Scr. Met. Mater.

    (1991)
  • Z.P. Wan et al.

    Experimental study and numerical simulation of dynamic recrystallization behavior of TiAl-based alloy

    Mater. Des.

    (2017)
  • C. Suryanarayana

    Mechanical alloying and milling

    Prog. Mater. Sci.

    (2001)
  • H. Matsuno et al.

    Biocompatibility and osteogenesis of refractory metal implants, titanium, hafnium, niobium, tantalum and rhenium

    Biomaterials

    (2001)
  • A.H. Hussein et al.

    Biocompatibility of new Ti-Nb-Ta base alloys

    Mater. Sci. Eng. C

    (2016)
  • E. Chicardi et al.

    Hot-pressing of (Ti,Mt)(C,N)-Co-Mo2C (Mt = Ta,Nb) powdered cermets synthesized by a mechanically induced self-sustaining reaction

    Chem. Eng. J.

    (2016)
  • P.P. Chattopadhyay et al.

    A metastable allotropic transformation in Nb induced by planetary ball milling

    Mater. Sci. Eng. A

    (2001)
  • C. Salvo et al.

    Study on the microstructural evolution of Ti-Nb based alloy obtained by high-energy ball milling

    J. Alloys Compd.

    (2017)
  • R.A. Gittens et al.

    Implant osseointegration and the role of microroughness and nanostructures: lessons for spine implants

    Acta Biomater.

    (2014)
  • L. Salou et al.

    Enhanced osseointegration of titanium implants with nanostructured surfaces: an experimental study in rabbits

    Acta Biomater.

    (2015)
  • Cited by (19)

    • Surface functionalization of gallium nitride for biomedical implant applications

      2023, Applied Surface Science
      Citation Excerpt :

      Though, the most widely used medical-grade titanium implants (i.e., Ti-6Al-4V) are not the ideal candidates for implanting purposes as Ti-6Al-4V pursues higher elastic modulus to the human bone, which causes a detrimental stress-shielding effect [6–8]. Despite the cytotoxicity of aluminum and vanadium [9–11], titanium alloy-based implants often fail due to infection/inflammation [12], metal corrosion [13], bone loss [14], and soft tissue integration-related issues [15]. Therefore, significant challenges have driven a need for novel biocompatible material alternatives with high functionalities for research related to biomedical implants [8,18–20], in addition to the surface functionalization of titanium alloys to reduce implant failures [2,16–18].

    • Degradation of Mg-Zn-Y-Nd alloy intestinal stent and its effect on the growth of intestinal endothelial tissue in rabbit model

      2022, Journal of Magnesium and Alloys
      Citation Excerpt :

      Biomaterials have been widely employed in clinical medicine, including orthopedic implants or cardiovascular stents [1–6], including intestinal stents to treat intestinal stenosis [7–11].

    • Systematic Study of (MoTa)<inf>x</inf>NbTiZr Medium- and High-Entropy Alloys for Biomedical Implants- In Vivo Biocompatibility Examination

      2021, Journal of Materials Science and Technology
      Citation Excerpt :

      The induction of porosity in alloys can help to reduce the bulk modulus of the alloys, but it occurs at the expense of other important parameters and mechanical properties [2]. Moreover, Al and V are considered to be cytotoxic [3–6] and should be replaced with biocompatible elements such as Nb, Zr, or Ta [7–9]. The strength or hardness of an alloy can be roughly related to its wear resistance.

    • In vitro evaluation of electrochemically bioactivated Ti6Al4V 3D porous scaffolds

      2021, Materials Science and Engineering C
      Citation Excerpt :

      One of most popular materials used for titanium implant production is Ti6Al4V alloy. Its Young's modulus is 100–105 GPa, which is superior to the cortical (18.6–20.7 GPa) and trabecular (10.4–14.8 GPa) bones [5–7]. Young modulus mismatches cause stress-shielding syndrome followed by implant-associated complications and implant failure [5,8–11].

    • Compressive performance of an arbitrary stiffness matched anatomical Ti64 implant manufactured using Direct Metal Laser Sintering

      2018, Materials and Design
      Citation Excerpt :

      Historically orthopaedic implants have been manufactured using cast or forged solid pieces of metal, that are 4–8 times stiffer than natural bone. These traditional manufacturing processes were a barrier to generating complex geometrical cellular features that can vary the strength of Ti64 implants to make the implant perform like bone [4]. Previous studies have shown that cellular structure architecture can affect both mechanical and bio-compatibility properties [5].

    View all citing articles on Scopus
    View full text