An aerospace application of commercially pure titanium is in fuel storage tanks containing liquid hydrogen for space vehicles. However, one important engineering property of titanium is the ability to retain strength and ductility at very low temperatures, and therefore is useful for cryogenic applications. Pure titanium is rarely, if ever, used in aircraft. However, it is not advantageous to strengthen titanium using impurity elements because there is a large loss in ductility, thermal stability and creep resistance. In comparison, the ultimate strength of titanium with a small amount of oxygen (0.2–0.4%) is 300–450 MPa. For example, ultra-high purity titanium (with an oxygen content of under 0.01%) has an ultimate tensile strength of about 250 MPa. Titanium contains trace amounts of impurities such as iron and atomic oxygen, and they have the beneficial effect of increasing strength and hardness by solid solution hardening. Commercially pure titanium contains a low concentration of impurities which remain in the metal after refining and processing from the rutile ore. However, the specific strength of pure titanium is not as high as the aluminium alloys because of its higher density.
Table 9.2 shows that some grades of pure titanium have a tensile strength of more than 450 MPa, which is similar to the 2000 aluminium alloys used in aircraft structures. Because of this, the titanium implant acts more like the natural joint, and as a result, the risk of some complications like bone resorption and atrophy are reduced. Additionally, the elastic nature of titanium and titanium alloys is lower than that of the other metals used in knee implants. Titanium and its alloys have a lower density compared to other metals used in knee implants. Titanium and titanium alloys have great corrosion resistance, making them an inert biomaterial (will not change after being implanted in the body). The most used titanium alloy in knee implants is Ti6Al4V. They commonly contain amounts of vanadium and aluminum in addition to titanium. Titanium alloys are biocompatible in nature. For example, pure titanium is sometimes used to create fiber metal, a layer of metal fibers bonded to the surface of an implant that allows bone to grow into the implant or allows cement to better bond to the implant for stronger fixation. Pure titanium is generally used in implants where high strength is not necessary. Paulo Davim, in Mechanical Behaviour of Biomaterials, 2019 Titanium and titanium alloys
Attention is also paid to the commercially viable processing routes for manufacturing of nanostructured CP Ti, its superior mechanical properties and functional performance, and the future prospective uses of this unique material in biomedical engineering. For these medical applications, > 9000 nanostructured items have been placed with no reported cases of failure. This chapter gives an overview on the application of nanostructured CP Ti in two types of implants: small-diameter dental implants and maxillofacial mini-implants. Improved biocompatibility and bioactivity of nanostructured CP Ti allow the minimization of the postsurgery rehabilitation period of patients. The superior strength of nanostructured CP Ti provides an opportunity to reduce the size of biomedical implants so miniaturized implants can bear the same mechanical load as their conventional counterparts. Nanostructured commercially pure titanium (CP Ti) has become technologically and commercially interesting because of its enhanced mechanical and functional properties. Lowe, in Titanium in Medical and Dental Applications, 2018 Abstract
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