Effects of Porosity on Mechanical Properties and Corrosion Resistances of PM-Fabricated Porous Ti-10Mo Alloy

Wei Xu,Shidi Yang,Xin Lu,Xuanhui Qu,Chengcheng Liu,Shaomin Lv,Bing Zhang

doi:10.3390/met8030188

Abstract

Porous binary Ti-10Mo alloys were prepared using non-spherical titanium, molybdenum powders by the powder metallurgy (PM) space holder technique. Based on the three-dimensional analysis of porosity characteristics, a detailed assessment of the effects of porosity on mechanical properties and corrosion resistances in phosphate-buffered saline (PBS) was carried out. For comparison, PM-fabricated CP-Ti with 50.5% porosity sintered at 1200 °C for 2 h and dense Ti-10Mo alloy sintered at 1450 °C for 2 h (relative density is 97.2% and porosity is 2.8%) were studied simultaneously. The results show that with the space-holder volume contents rising from 63 to 79%, the open porosity and average pore size (d50) increase remarkably, while the pore size distribution (d10–d90) tends to be stable at about 100 μm. The average pore sizes (d50) of porous Ti-10Mo alloy can be controlled in the range of 70–380 μm. The PM-fabricated porous Ti-10Mo alloy can achieve a wide range of mechanical properties, with yield compression strength of 248.2–76.9 MPa, and elastic modulus of 6.4–1.7 GPa. In addition, the yield compression strength and the elastic modulus meet the linear regression and exponential formula, respectively. With the porosity of Ti-10Mo alloy increasing from 2.8 to 66.9%, the corrosion rate rises exponentially from 1.6 g/m2·day to 17.1 g/m2·day. In comparison to CP Ti with nearly the same porosity, Ti-10Mo alloy shows significantly higher corrosion resistance. As a result, the relationships between porosity and mechanical properties, corrosion resistances of Ti-10Mo alloys were established, which can be used as a design reference in material selection for orthopedic applications.

Highlights

Titanium and its alloys have been widely used in biomedical applications and have a great potential in making orthopedic implants due to their high specific strength, low elastic modulus, excellent biocompatibility and corrosion resistance in the human body environment [1]
Porous Ti-10Mo alloys can be fabricated by powder metallurgy (PM) of adding NH4 HCO3 with low-cost non-spherical elemental powders
The PM-fabricated porous Ti-10Mo alloy is characterized by typical Widmanstaten structure

Summary

Introduction

Titanium and its alloys have been widely used in biomedical applications and have a great potential in making orthopedic implants due to their high specific strength, low elastic modulus, excellent biocompatibility and corrosion resistance in the human body environment [1]. Current major biomedical titanium alloys in used, including the most conventional extra-low interstitial (ELI) Ti-6Al-4V Elastic modulus (~110 GPa) of these alloys is still much higher than that of cortical bone, which may bring severe ‘stress shielding’ [2]. Metals 2018, 8, 188 and Drug Administration (FDA)-approved proprietary alloys Ti-13Nb-13Zr and Ti-12Mo-6Zr-2Fe and the non-proprietary alloy Ti-15Mo. In particular, binary Ti-Mo alloys containing 4–20% Mo have attracted significant attention due to their simplicity and reasonable cost [3,4,5,6,7], as well as the capability of offering a very low amount of artifacts in magnetic resonance imaging (MRI) compared to other β-titanium alloys

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