Titanium alloys are classified along a continuum of alpha, near-alpha, alpha-beta, and beta alloys. These classifications describe the microstructure of titanium.
Titanium has two dominant allotropic (ability for a chemical element to exist in two or more different forms) phases—α+β (alpha and beta). These alpha and beta phases determine the different properties among titanium alloys. The alpha phase is close-packed hexagonal, and the beta phase is body-centered cubic. Alloying elements cause titanium atoms to arrange themselves into either of these phases. The elements that induce the alpha phase include aluminum, oxygen, nitrogen, and carbon, while the beta phase is induced by elements such as vanadium, molybdenum, iron, chromium, and manganese.
- Alpha alloys are not heat treatable, have low to medium strength, reasonably good ductility and weldability, and possess excellent properties in cryogenic environments.
- Near-alpha alloys are alloyed with 1–2% of beta phase stabilizers such as molybdenum, silicon, or vanadium.
- Alpha-beta alloys are heat treatable and offer medium to high strength. They are weldable, though there’s some risk of ductility reduction in the welded area, and have good hot forming qualities. However, cold forming can be difficult.
- Beta alloys are readily heat treatable, generally weldable, and maintain high strength at intermediate temperature levels. They are suitable for hot and cold forming applications.
Unlike the relatively simple commercially pure titanium grades 1, 2, 3, and 4, titanium alloys are classified by grade, alloying elements, and sometimes both. You’ll find more than 30 grades of titanium and several more titanium alloys more popularly known by their titanium and alloying elements. Two of the most frequently used titanium alloys in the local manufacturing process are Titanium 6Al-4V (Grade 5) and Titanium 10V-2Fe-3Al.