**Abstract**

The stability, elastic and electronic properties of titanium aluminide compounds have been systematically studied by the first-principles calculation. The calculated lattice parameters are consistent with the results found in the literature. The three Ti-Al binary compounds are thermodynamically stable intermetallics depending on their negative formation enthalpy. It has been found that the Ti-Al binary compounds are composed of both metallic and covalent bonds. Elastic properties revealed that these alloys are more resistant to deformation along *the a-* and *c-axis*. Besides, the (001)[100] deformation would be easier than (010)[100] deformation for these alloys. The results found in this chapter give a reliable reference for the design of novel Ti-Al binary alloys.

**Keywords:** Titanium aluminide, elastic properties, stability, first-principles calculation

### **1. Introduction**

Titanium aluminide-based alloys (TiAl) have attracted more attention as a potential coating material for high-temperature structural applications. They have many applications in engineering due to their high melting points, high tensile strength, good stiffness, low density, high corrosion, and oxidation resistance at elevated temperature [1–3]. TiAl has an ordered tetragonal face-centered γ-TiAl phase and a hexagonal α2 (Ti3Al) phase DO19. Experimental works highlighted that the deformation mechanism (α2 + γ) binary phase is mainly made by ordinary dislocation, super-dislocations, and twinning following the compact plane (111) [4–6]. However, TiAl intermetallic compounds suffer from low ductility and toughness at room temperature, which seriously limits their broad range of applications [7].

To understand the bonding and materials characteristics of this type of system, many experimental and theoretical studies have been investigated. A study of fundamental properties such as the nature of interatomic bonding, the stability of crystal structures, elastic properties, dislocations, grain boundaries, interfaces, as well as point defects and diffusion are therefore warranted to gain more insight into the behavior of these intermetallic alloys under high temperatures [8]. Sun et al. [9] have synthesized a new multilayer TiAl intermetallic by spark plasma sintering, which provides a novel possibility to improve fracture toughness. It is believed that TiAl intermetallic compounds with different Al contents play important roles in controlling the microstructure and mechanical properties.

Several ab-initio studies of the structural stability, elastic properties, and the nature of bonding have been reported for γ-TiAl, α2-Ti3Al, and B2-TiAl [10–13]. To optimize ion beam treatment of TiAl based intermetallic alloys for better performance. It is essential to gain a deeper insight into radiation effects in these materials. From the fundamental perspective, TiAl intermetallic compounds represent a good model system for studying radiation effects in ordered metallic alloys for future engineering applications. To understand some of the physical properties of these compounds, knowledge of the phase stability and elastic properties of TiAl binary compounds is required. In this chapter, we summarized the calculated results of TiAl intermetallic compounds using density functional density (DFT).
