Atomic number 22. Atomic weight 47.90. Density 4.51 103 kg m−3.
Titanium is a light, nonmagnetic, tough and highly corrosion resistant biocompatible metal which exhibits good oxidation resistance, due to a titanium dioxide surface film which provides protection up to about 870 K. It has two allotropes: alpha, hexagonal close packed, below 1156 K and beta, body centered cubic, up to the melting point 1941 K.
"Unalloyed" titanium is strengthened by small amounts of interstitial alloying elements, primarily oxygen, the level of which is adjusted to provide a range of commercial grades. Other alloying elements are employed to alter the stability of the two allotropes and commercial alloys based on the alpha, beta, or mixtures of the two phases are available. Aluminum is the most important alpha stabilizer (together with oxygen) and vanadium is the most widely used beta stabilizer: the alpha plus beta alloy titanium 6 wt% aluminum 4 wt% vanadium is the oldest and most generally used alloy and, via thermomechanical treatment to modify microstructure, can provide strength in the range 900 to 1100 MPa. Special commercial alloys contain a range of other elements including, tin, zirconium, molybdenum, iron, chromium and silicon. Medium strength near alpha alloys, consisting predominantly of alpha phase, exhibit the best elevated temperature creep resistance, while beta alloys, which are readily cold workable and heat treatable to high (1200+ MPa) strength levels are employed in lower temperature structural applications.
Titanium and its alloys find applications in chemical engineering, power generation, medical prosthetics and aerospace engineering. The latter accounts for roughly 50% of titanium usage worldwide, excluding the CIS.
Titanium: A Technical Guide, (1988) M. J. Donachie, Jr. Ed., ASM International, Metals Park, Ohio.
Materials Properties Handbook: Titanium Alloys, (1994) R. Boyer, Ed., E. W. Ceilings and G. Welsch, ASM, Metals Park, Ohio.