*Self-Healing in Titanium Alloys: A Materials Science Perspective DOI: http://dx.doi.org/10.5772/intechopen.92348*

retractable for multi-role and all-weather purposes (**Figure 1**) [20]. Each of these building projects uses large quantities of CP titanium leading to the increased usage in the civil engineering area in Japan. Another "new area" in which titanium use is growing is the area of consumer products, such as spectacle frames, cameras, watches, jewelry, and various kinds of sporting goods. The largest application in the area of sporting goods is golf club heads. Other examples are tennis rackets, bicycle


**Table 1.**

*Advanced Functional Materials*

allowing self-healing of ionomers.

has to be pre-embedded.

future research.

**2. Titanium: A special engineering material**

of a composite material with some other smart material like NiTi [10, 11] are been utilized in metals and other inanimate materials. For example, damage to oxide films, which normally protect the surfaces of metals such as aluminum (Al) and titanium (Ti) from corrosion, can be repaired by reoxidation in air, which can be seen as a form of self-repair. Also identified are the self-healing properties obtained by encapsulating a solder material into a metallic matrix [11–13]. Self-healing behavior was also observed in a commercial Al alloy after suitable heat treatment [14] and some other precipitation-forming systems [15, 16]. Healing can be initiated by means of an external source of energy as was shown in the case of a bullet penetration [17] where the ballistic impact caused local heating of the material by

There are several different strategies to impart self-healing functionality that have been developed and the number of publications dealing with various aspects of self-healing materials has increased markedly in recent years. On the whole, the vast majority of the articles deal with polymer composites and cementous materials. Research in the field of metallic systems is still in its infancy. However, the emergence of self-healing in metallic materials, such as titanium adjured to be biocompatible and explored here presents an exciting paradigm for an ideal combination of metallic and biological properties in application traditionally dominated by metallic materials. Depending on the method of healing, self-healing in metallic system can be classified into two categories: (i) intrinsic ones that are able to heal cracks or repair damage by the metals themselves and (ii) extrinsic in which healing agent

This chapter begins with an overview on the importance of titanium as an engineering of self-healing materials. Since all processes of self-repair, including healing in living bodies depends on rapid transportation of repair substance to the injured part and reconstruction of the tissues, Therefore, the knowledge of basic principle of solid state diffusion is essential for understanding the self-repair processes, such as phase transformation, precipitation and shape memory effects taking place titanium and other alloys, were briefly discussed. The chapter concludes by considering

Titanium has been an important development in the history of non-ferrous industry. Titanium is an attractive material with excellent corrosion resistance and high strength-to-weight ratio. It combines the strength of iron and steel with the light weight of aluminum, which accounts for its widespread use. Industrial applications of titanium materials have recently expanded widely in many areas such as the aerospace, chemical plants, automobiles, and aviation industries, and even in high performance sports equipment, and in the medical field for bone. Their biological compatibility is particularly of interest to the medical industry implants and replacement devices [17]. Currently, the chemical industry is the largest user of titanium due to its excellent corrosion resistance, particularly in the presence of oxidizing acids. The ballistic properties of titanium are also excellent on a densitynormalized basis. Some physical properties as compared with other engineering materials by Hanson are presented in **Table 1** [18]. Detailed discussions on other

applications of titanium in other areas can be found elsewhere [18, 19].

Besides the areas mentioned above, building applications such as exterior walls and roofing material have emerged as a new market for titanium. Using CP titanium as building material has become especially popular in Japan [20]. One example is the Fukuoka Dome, built in 1993, which is covered with titanium roofing,

**124**

*Physical properties of titanium compared with other metals [18].*

**Figure 1.**

*(a) Arial approach view of the Fukuoka dome, built in 1993, which is covered with (b) titanium roofing, retractable for multi-role and all-weather purposes.*


#### **Table 2.**

*Physical properties of titanium and some of its alloys [18].*

#### *Advanced Functional Materials*

frames, spikes in sprinters. Their low coefficient of thermal expansion is also an important factor. The ballistic properties of titanium are also excellent on a densitynormalized basis. Future applications are likely to be in the areas of steam turbine blading, flue gas desulphurization plant consumer products and many marine applications. Some of the basic characteristics of titanium and its alloys are listed in **Table 2** in [18] and compared to those of other structural metallic materials based on Fe, Ni, and Al. Detailed discussions on other applications of titanium in other areas can be found elsewhere [4].
