Alpha and Near-Alpha Titanium Alloys
Alpha and near-alpha titanium alloys are strengthened by aluminum, tin and zirconium — elements that dissolve in the hexagonal alpha phase — with at most a trace of beta stabilizer such as molybdenum or vanadium. The result is a microstructure that barely changes on heating, so these alloys hold creep strength to 500–600 °C where Grade 5 has softened, stay tough at cryogenic temperatures and weld as cleanly as CP titanium. Grade 6 (Ti-5Al-2.5Sn) yields about 800 MPa, Ti-6242 about 900 MPa, and none of them responds to age hardening: strength is set by chemistry and the anneal, not by a quench.
Popular alpha and near-alpha titanium grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| Ti-6242 | 930 | 1,000 | 4.54 | Poor | Good | Compressor discs and blades to 540 °C |
| Grade 6 | 810 | 860 | 4.48 | Poor | Very good | Weldable alpha alloy; cryogenic tanks and pumps |
| Grade 12 | 420 | 550 | 4.51 | Poor | Excellent | Hot brine and crevice corrosion without palladium |
| Ti-8Al-1Mo-1V | 950 | 1,000 | 4.37 | Poor | Good | Stiffest titanium; compressor blades |
| IMI 834 | 910 | 1,030 | 4.55 | Poor | Fair | Hottest compressor stages, to 600 °C |
| TA15 | 900 | 990 | 4.46 | Poor | Very good | Welded airframe structure to 500 °C |
| Ti Grade 18 | 570 | 690 | 4.48 | Poor | Very good | Ti-3Al-2.5V with palladium for sour tubing |
All 34 alpha and near-alpha titanium grades
Choose alpha and near-alpha titanium for
Compressor discs, blades and casings running at 450–600 °C, hot exhaust and nacelle structure, cryogenic tanks, valves and impellers, welded airframe frames that cannot be re-heat-treated, and chemical-plant hardware in hot brine that Grade 2 would pit in — anywhere weldability and stability at temperature outrank peak room-temperature strength.
Look elsewhere when
The part is sized by room-temperature strength or fatigue (Grade 5 annealed or STA, Ti-6Al-6V-2Sn), it needs more than about 1,000 MPa yield in a thick forging (Ti-10-2-3 or Ti-5553), it is cold-formed sheet or tube (Grade 9 or Ti-15-3), the service is plain corrosion below 300 °C where Grade 2 is enough, or the temperature exceeds about 600 °C — that is nickel-alloy territory (Inconel 718).
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Alpha and near-alpha titanium by application
- Hot engine and exhaust parts
- Ti-6242 for discs, blades, spacers and casings to about 540 °C; IMI 834 or IMI 829 for the last compressor stages at 600 °C; Ti-8Al-1Mo-1V where blade stiffness governs. All three are forged and machined in the duplex-annealed condition.
- Cryogenic hardware
- Grade 6 in the extra-low-interstitial grade for liquid-hydrogen and liquid-oxygen tanks, valve bodies and pump impellers — it stays ductile at 20 K where standard-oxygen alloys turn brittle. Grade 23 is the alpha-beta alternative.
- Welded structure at temperature
- TA15 and Grade 6 for frames, brackets and ducting that are welded and used without a post-weld solution treatment; joint strength stays close to base metal because there is no aging response to lose.
- Hot brine and sour service
- Grade 12 for heat exchangers and evaporators in chloride brine above 80 °C where Grade 2 crevice-corrodes; Ti Grade 18 (Ti-3Al-2.5V-0.05Pd) and Ti Grade 28 for downhole and sour-gas tubing that also needs Grade 9 strength.
Working with alpha and near-alpha titanium
- Machining
- Slower than Grade 5: Ti-6242 and IMI 834 are high-aluminum alloys that work-harden and hold heat at the cutting edge, so run 20–30 % lower surface speed than Ti-6Al-4V with sharp carbide, high feed and flood coolant. Grade 12 machines like Grade 2. Rough, stress-relieve at 480–650 °C, then finish — forgings move when a heavy skin comes off.
- Welding
- The most weldable titanium alloys after the CP grades: TIG, plasma and electron-beam under complete argon shielding, matching filler (ERTi-9 for Grade 9, ERTi-12 for Grade 12) or CP filler where a softer joint is acceptable. Ti-6242 and Ti-8Al-1Mo-1V need a post-weld stress relief; Ti-8Al-1Mo-1V welds must be kept away from salt to avoid stress corrosion.
- Heat treatment
- There is no hardening step: mill anneal at 700–800 °C, or for Ti-6242 a duplex anneal (solution treat just below the beta transus at about 955 °C, then stabilize 8 h at 595 °C) that sets creep resistance rather than strength. Stress-relieve machined parts at 480–650 °C, always in vacuum or argon above 500 °C — the alpha alloys pick up oxygen fastest.
- Forming
- Grade 12 bends cold about like Grade 2 (2–2.5 t); the aluminum-bearing alloys are hot-formed at 600–800 °C with springback under 5 °, and Ti-6242 sheet is superplastically formed for ducts and nacelle skins. Cold forming of Grade 6 and Ti-6242 is limited to gentle radii.
Other titanium series
Alpha and Near-Alpha Titanium Alloys — frequently asked
What is alpha and near-alpha titanium?
Alpha and near-alpha titanium alloys are strengthened by aluminum, tin and zirconium — elements that dissolve in the hexagonal alpha phase — with at most a trace of beta stabilizer such as molybdenum or vanadium. The result is a microstructure that barely changes on heating, so these alloys hold creep strength to 500–600 °C where Grade 5 has softened, stay tough at cryogenic temperatures and weld as cleanly as CP titanium. Grade 6 (Ti-5Al-2.5Sn) yields about 800 MPa, Ti-6242 about 900 MPa, and none of them responds to age hardening: strength is set by chemistry and the anneal, not by a quench.
Which grade of alpha and near-alpha titanium should I use?
Ti-6242 (Ti-6Al-2Sn-4Zr-2Mo) is the engine alloy: compressor discs, blades, spacers and casings that run at 450–540 °C, where its creep resistance beats every alpha-beta grade; the silicon-bearing variant Ti-6Al-2Sn-4Zr-2Mo-0.1Si extends that a little further. Grade 6 is the older all-alpha alloy — weldable, about 800 MPa yield, and in its extra-low-interstitial form the standard for liquid-hydrogen and liquid-oxygen tankage and cryogenic pump parts. Ti-8Al-1Mo-1V has the highest stiffness of any titanium (about 120 GPa) for compressor blades that must not flutter, at the price of salt stress-corrosion sensitivity. IMI 834 and IMI 829 are the 600 °C near-alpha alloys for the hottest compressor stages, and TA15 is the Chinese near-alpha structural grade for welded airframe frames to 500 °C. Grade 12 (Ti-0.3Mo-0.8Ni) belongs here too but is a corrosion grade, not an aerospace one: Grade 2 formability with better crevice-corrosion resistance in hot brine and about 345 MPa yield.
Which grade of alpha and near-alpha titanium is the strongest?
Ti-6Al-2Sn-4Zr-6Mo has the highest yield strength in the series at 1,100 MPa; Ti-4Al-4Mo-2Sn follows at 1,030 MPa. Values are for each grade's default condition.
Which grade of alpha and near-alpha titanium is easiest to machine?
PT-7M (machinability fair, 38/100), then Ti Grade 15 (35/100).
Is alpha and near-alpha titanium heat-treatable?
No. These grades are strengthened by cold work and softened by annealing, not by heat treatment; the conditions are listed on each grade page.
Ti-6242 or Grade 5 for a hot part?
Below about 300–350 °C Grade 5 wins: it is stronger at room temperature (880 versus about 900 MPa yield is a wash, but Grade 5 STA reaches 1,100), cheaper and in every stock form. Above that Ti-6242 pulls ahead — its creep rate at 500 °C is an order of magnitude lower, and it keeps about 70 % of its room-temperature strength at 540 °C where Grade 5 is limited to roughly 400 °C continuous. Ti-6242 also welds with less loss of properties. Pick by the sustained metal temperature and the creep allowance, not by the tensile table.
Why does Grade 12 replace Grade 7 in brine service?
Both resist crevice corrosion in hot chlorides far better than Grade 2, but Grade 7 does it with 0.12–0.25 % palladium and Grade 12 with 0.3 % molybdenum and 0.8 % nickel — much cheaper alloying. Grade 12 is also stronger (about 345 MPa yield against 275) so tube walls can be thinner, and it forms and welds about like Grade 2. Grade 7 is still the answer for reducing acids — hydrochloric and sulphuric — where the nickel-molybdenum grade does not hold up.