to Metals
to Titanium alloys
Dr. Dmitri Kopeliovich
Titanium α-β alloys are titanium alloys containing 4-6% of β-phase stabilizers: molybdenum (Mo), vanadium (V), tungsten (W), tantalum (Ta), silicon (Si).
Amount of β-phase is proportional to the content of β-phase stabilizers.
Titanium α-β alloys consist of a mixture of α and β phases.
Titanium α-β alloys are heat-treatable. They may be significantly strengthened by precipitation hardening. Solution treatment of α-β alloys causes increase of β-phase content in the alloy which is stable at temperatures above the Beta Transus. Quenching suppresses β-α transformation.
The metastable β-phase transforms to fine precipitation particles of α-phase during aging.
The precipitation treatment results in increase of mechanical strength and decrease of ductility.
Ti-6Al-4V is the most popular Titanium α-β Alloy - its total production is about half of all titanium alloys. Aluminum (Al) is added to the alloy as α-phase stabilizer and hardener due its solution strengthening effect. Vanadium (V) stabilizes ductile β-phase, providing hot workability of the alloy.
Titanium α-β Alloys have high tensile strength and fatigue strength, good hot formability and creep resistance up to 570ºF - 800ºF (300ºC - 425ºC).
Titanium α-β Alloys are used for manufacturing steam turbine blades, gas and chemical pumps, airframes and jet engine parts,pressure vessels, blades and discs of aircraft turbines, aircraft hydraulic tubing, rocket motor cases, cryogenic parts, marine components.
| Designation | O,% | Fe,% | Al,% | V,% | Mo,% | Sn,% | Others,% |
|---|---|---|---|---|---|---|---|
| Grade 5 (Ti-6Al-4V) | 0.08 max. | 0.25 max. | 5.5-6.75 | 3.5-4.5 | - | - | - |
| Ti-6Al-6V-2Sn | 0.08 max. | 0.35-1.0 | 5.0-6.0 | 5.0-6.0 | - | 1.5-2.5 | Cu=0.35-1.0 |
| Ti-6Al-2Sn-4Zr-6Mo | 0.5 max. | 0.15 max. | 5.5-6.5 | - | 5.5-6.5 | 1.75-2.25 | Zr=3.5-4.5 |
| Ti-4Al-4Mo-2Sn | 0.16-0.2 | 0.20 max. | 3.0-5.0 | - | 3.0-5.0 | 1.5-2.5 | Si=0.3-0.7 |
(Concentration of nickel - balance)