Pure titanium undergoes an allotropic transformation from the hexagonal close-packed alpha phase to the body-centered cubic beta phase at a temperature of 882.5°C (1620.5°F). Alloying elements can act to stabilize either the alpha or beta phase. Through the use of alloying additions, the beta phase can be sufficiently stabilized to coexist with alpha at room temperature. This fact forms the basis for the creation of titanium alloys that can be strengthened by heat treating.

Titanium alloys are generally classified into three main categories: alpha alloys, which contain neutral alloying elements (such as Sn) and/or alpha stabilizers (such as Al, O) only and are not heat treatable; alpha + beta alloys, which generally contain a combination of alpha and beta stabilizers and are heat treatable to various degrees; and beta alloys, which are metastable and contain sufficient beta stabilizers (such as Mo , V) to completely retain the beta phase upon quenching, and can be solution treated and aged to achieve significant increases in strength.

Ti-3Al-8V-6Cr-4Mo-4Zr (Ti-3-8-6-4-4, commonly known as Beta-C TM ) is a metastable beta alloy developed in the 1960s. Like other beta alloys, it is used when particularly high strengths are needed along with the light weight and corrosion resistance offered by titanium. Ti-3-8-6-4-4 has gained in popularity among beta alloys because it is one of the easier beta alloys to melt, exhibiting low segregation, and to process, exhibiting good working and heat treating properties. Depending on the application, Ti-3-8-6-4-4 can be used in either the solution annealed (ST) or the solution treated plus aged (STA) conditions. Increases in strength on the order of 40% are obtained by solution treating and aging.

Applications:
Ti-3-8-6-4-4 is appropriate for applications where very high strength, light weight and corrosion resistance are important. It has become a standard material for a particular niche of specialized applications which have included aircraft springs and underground tubes and casing equipment for gas and oil well operations. It has also been used in fasteners and high-performance auto racing applications.