Pure titanium undergoes an allotropic transformation from the hexagonal close-packed alpha phase to the body-centered cubic beta phase at a temperature of 882.5ºC (1620.5ºF). 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 6Al-4V ELI is a higher-purity (“extra-low interstitial”) version of Ti 6Al-4V, with lower specified limits on iron and the interstitial elements C and O. It is an alpha+beta alloy.
Ti 6Al-4V ELI has been the material of choice for many medical and dental applications due to its excellent biocompatibility. The ELI grade has superior damage tolerance (fracture toughness, fatigue crack growth rate) and better mechanical properties at cryogenic temperatures compared to standard grade Ti 6Al-4V.
Ti 6Al-4V ELI may be considered in any biomedical application, particularly for implantable components, because of its biocompatibility, good fatigue strength, and low modulus. It could also be considered for any application where a combination of high strength, light weight, good corrosion resistance, and high toughness are required, especially at cryogenic temperatures. Some typical applications where this alloy has been used successfully include joint replacements, bone fixation devices, surgical clips, and cryogenic vessels.