Elsevier

Materials Letters

Volume 269, 15 June 2020, 127661
Materials Letters

Bulk and surface design of MAO-treated Ti-15Zr-15Mo-Ag alloys for potential use as biofunctional implants

https://doi.org/10.1016/j.matlet.2020.127661Get rights and content

Highlights

  • Ti-15Zr-15Mo were modified by bulk alloying and surface treatment.

  • Samples exhibited β phase, adequate mechanical properties, and porous TiO2 layer.

  • Bulk and surface properties were suitable for use as biofunctional implants.

Abstract

This study investigated the effect of silver addition and micro-arc oxidation (MAO) treatment on the microstructure, selected mechanical properties, and surface characteristics of the Ti-15Zr-15Mo (wt%) alloy. The ingots were produced by argon arc-melting and subsequently subjected to thermomechanical treatments and surface modification. Phase composition and microstructure of the samples exhibited only the β phase. The samples possessed better mechanical biocompatibility (in terms of Vickers microhardness and Young’s modulus) than some commercial biomedical materials. MAO-treated surfaces exhibited a porous morphology and were mostly covered by TiO2 (anatase). Bioactive elements (Ca, P, and Mg) were incorporated into the oxide layer and inserted an apatite forming ability in the samples. These results indicated the great potential of the samples for use as biomedical implants.

Introduction

Titanium (Ti) and its alloys have extensively been employed as implantable materials due to their high specific strength, relative low Young’s modulus, excellent corrosion resistance, and recognized biocompatibility [1]. The addition of alloying elements turned possible the processing of high strength materials, which can properly support the biomechanical loads of the human body [2]. In our preliminary study, we investigated the potential of Ti-Zr-Mo alloys for use as biomedical implants, where it was found that Ti-15Zr-15Mo has the best combination of properties for these applications [3].

The bacterial infection has been indicated as one of the main factors in the failure of metallic implants. To overcome it, some studies have been designed novel implants with the addition of silver (Ag), once it can inhibit bacterial growth by blocking its enzymatic activity [4]. It was also shown that a small amount of Ag (1–5 wt%) in solid solution can provide adequate mechanical properties and biocompatibility [5].

As Ti is bioinert, it lacks a bioactive response, unaltering the regeneration and recovery time of damaged bone cells. This drawback has been overcome by surface treatments [6]. Micro-arc oxidation (MAO) is a low-cost technique based on the dielectric breakdown and plasma sparkling of the oxide layer when submitted to anodic potentials. The MAO-treated layer has high corrosion resistance, excellent biocompatibility and proven osseointegrative capability [6], [7]. By varying the electrolyte composition, some studies have also incorporated some bioactive ions into the surfaces, turning the outer layer friendly to the biological host [8], [9].

Aiming to introduce some biofunctional properties in the Ti-15Zr-15Mo alloy, this study investigated the effect of Ag addition in the bulk and bioactive elements (Ca, P, and Mg) incorporation on the surface, for potential use as biomedical implants.

Section snippets

Materials and methods

Ti-15Zr-15Mo-(1,3)Ag (wt%) samples were obtained in an argon arc-melting furnace and submitted to a homogenization heat-treatment (1273 K, 43.2 ks, slow cooling), hot-rolling (1273 K, air cooling), and solution treatment (1123 K, 21.6 ks, water quenching). MAO treatments were performed in a DC power source (Keysight, N5751A) at 300 V, 2.5 A, room temperature, for 60 s. The electrolyte was composed of 0.35 M calcium acetate monohydrate, 0.02 M β-glycerol phosphate, and 0.1 M magnesium acetate

Results and discussions

Table 1 presents the chemical composition from the bulk of the samples. The alloying elements possessed values closed to the nominal ones. The amount of oxygen and nitrogen remained lower than 1 wt%. The density values were almost identical to the theoretical ones. The chemical mapping (Fig. 1a) exhibited a good homogeneity of the solid solution. These results guarantee that the samples had excellent quality for the study.

The XRD patterns of the samples (Fig. 1b) exhibited only β phase peaks,

Conclusions

Ti-15Zr-15Mo samples were modified by Ag alloying and surface MAO treatment. Phase composition and microstructure were composed of the β phase as equiaxial grains. The Ag content unaltered the selected mechanical properties but enabled potential antibacterial effects. MAO treatment produced a porous oxide layer, formed mostly by TiO2 (anatase form). The surfaces were enriched with bioactive ions, having microscale roughness and adequate contact angle values, with a significant apatite forming

CRediT authorship contribution statement

J.E. Torrento: Investigation, Writing - original draft. C.R. Grandini: Investigation, Resources. T.S.P. Sousa: Investigation. L.A. Rocha: Investigation, Resources. T.M. Gonçalves: Investigation. L. Sottovia: Investigation. E.C. Rangel: Investigation. N.C. Cruz: Investigation, Resources. D.R.N. Correa: Conceptualization, Writing - review & editing, Project administration.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors are grateful for the School of Sciences at UNESP, Bauru (SP), and Brazilian Nanotechnology National Laboratory (LNNano) at Brazilian Center for Research in Energy and Materials (CNPEM), Campinas (SP), for the sample characterizations. This study was funded by FAPESP (grants #2015/00851-6 and #2016/25272-1) and CNPq (grants #481.313/2012-5 and #307.279/2013-8).

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