Advanced mechanical properties of powder metallurgy commercially pure titanium with a high oxygen concentration
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Oxygen is known to have a significant impact on the strength of Ti alloys, whereas it can also reduce the ductility substantially. Thus, the usage of oxygen to strengthen Ti is restricted in the industry. In this study, we rekindled the research of oxygen behavior in Ti with the purpose of developing Ti alloys with high strength and suitable ductility by using no expensive and poisonous element. To this end, experiments of producing high performance commercially pure Ti using only oxygen solid solution were carried out. The oxygen element was introduced into the Ti by two different powder metallurgy methods. The microstructural examination and mechanical test were performed for the samples, which indicated a strong hardening effect of oxygen in spite of the processing routes. Most importantly, the results suggested that a high elongation to failure of over 20% can still be obtained in the samples having yield stress over 800 MPa, up to an oxygen content of 0.8 wt%, which is far beyond the previously recognized limit.
I. INTRODUCTION
Owing to their high specific strength and exceptional creep and corrosion resistance, titanium alloys are widely used in aerospace, automotive, and petroleum industries.1 As well, due to the excellent compatibility and nontoxic property to human tissues, titanium is also attractive and used in dental implant and bone replacement.2 Today, there are a great number of Ti alloys from low strength and high corrosion resistance pure Ti to high mechanical performance alloys available in the market. A wise choice of these products depends on the purpose of their applications. For example, applications in automobile and aerospace structures require light weight and high strength and toughness, and sometimes also require high thermal resistance when used in turbine engine.3,4 On the other hand, safety and nontoxicity should be the priority for Ti applications in medical fields. It has been wellknown that commercially pure Ti (CP-Ti) and Ti–6Al–4V alloys have been widely used as implant materials. Yet, it has been reported that, in Ti-based biomaterials, the toxicity of alloying elements to living cells from the most to least can be listed as Cu, Al 5 Ni, Ag, V, Mn, Cr, Zr, Nb, Mo, Ta, Sn, and CP-Ti.5 In this regard, debates on using Ti alloys for medical implant have emerged with respect to the potential biological hazards of alloying elements used in the alloys. Thus, CP-Ti is considered as an excellent choice for medical use,6 and other Al and Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected], [email protected] b) These authors contributed equally to this work. DOI: 10.1557/jmr.2017.338
V-free alloys were also developed to substitute Ti–6Al–4V as implant materials.7 Nevertheless, most of the Ti alloys are consisting of expensive chemicals, such as Ta and Nb.2 It is the same case for Ti alloys available for structural applications, which usually contain chemical elements V, Co, Cr, Ni, and Mo.8–10 Those chemicals are very expensive an
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