Titanium Alloys
The high strength and low density of titanium and its alloys have from the first ensured a positive role for the metal in aero-engine and airframe applications. It is difficult to imagine how current levels of performance, engine power to weight ratios, airframe strength, aircraft speed and range and other critical factors could be achieved without titanium.
Titanium alloys capable of operating at temperatures from sub zero to 600°C are used in engines for discs, blades, shafts and casings from the front fan to the last stage of the high pressure compressor, and at the rear end of the engine for lightly loaded fabrications such as plug and nozzle assemblies.
Alloys with strength up to 1200MPa are used in a wide variety of airframe applications from small fasteners weighing a few grams to landing gear trucks and large wing beams weighing up to 1 ton. Currently titanium makes up to 10% of empty weight of aircraft such as the Boeing 777.
Some of the alloys available for aircraft applications are outlined in the following tables. The alloys are grouped by their ralative usages.
Table 1. More widely used titanium alloys in aircraft applications.
Alloy | Attributes/Applications |
Ti6Al4V | Workhorse, general purpose high strength alloy |
Ti6Al2Sn4Zr2Mo (6-2-4-2) | Creep and oxidation resistant engine alloy |
Ti6Al2Sn4Zr6Mo (6-2-4-6) | Creep and oxidation resistant engine alloy |
Ti3Al8V6Cr4Zr4Mo (Beta C) | Beta alloy with established spring applications |
Ti10V2Fe3Al (10-2-3) | Beta forging alloy used for 777 landing gear |
Ti15V3Cr3Sn3Al (15-3-3-3) | High strength heat treatable beta sheet alloy |
Ti3Al2.5V | Medium strength alloy used for hydraulic tubing |
Ti4Al4Mo2Sn (550) | Higher strength heat treatable airframe and engine alloy |
Ti5.5Al3.5Sn3Zr1Nb (829) | Advanced engine alloy, creep and oxidation resistant |
Ti5.8Al4Sn3.5Zr0.7Nb (834) | Advanced engine alloy, creep and oxidation resistant |
Ti5Al2Sn4Mo2Zr4Cr (Ti17) | Advanced engine alloy, creep and oxidation resistant |
Ti15Mo3Nb3Al0.2Si (21S) | Oxidation and corrosion resistant beta sheet alloy |
Table 2. Titanium alloys of increasing importance in aircraft applications.
Alloy | Attributes/Applications |
Ti6Al2Zr2Sn2Mo2Cr0.25Si (6.22.22) | Airframe alloy for F22 and JSF projects |
Ti4.5Al4Mo4Sn0.5Si (SP 700) | Competitor for Ti6Al4V for SPF and general use |
Table 3. Less widely used titanium alloys in aircraft applications, but alloys that may be critical in their application to specific fully validated components.
Alloy | Attributes/Applications |
Ti2Cu | Heat treatable sheet alloy |
Ti4Al4Mo4Sno.5Si (551) | High strength airframe alloy, very limited availability |
Ti8Al1Mo1V | Early alloy now mainly used for spares and replacements |
Ti-6-6-2 | High strength alloy with specific earlier applications |
Ti11Sn5Zr2.5Al1Mo0.2Si (679) | Earlier engine alloy rarely specified in new programmes |
Ti6Al5Zr0.5MoO.25Si (685) | Engine alloy now mainly for spares and replacements |