Titanium alloys divide into four metallurgical classes, and the class tells you far more about how an alloy will behave than the grade number does. Near-alpha alloys are weldable and creep resistant and run hottest, but cannot be hardened to high strength. Alpha-beta alloys — Ti-6Al-4V being the archetype — are heat treatable, strong and the general structural choice. Near-beta and metastable beta alloys are deeply hardenable and, crucially for fasteners, can be cold headed and thread rolled soft and then aged to full strength. Lean corrosion grades trade strength away entirely. The cards below are grouped by class, and the cross-reference table underneath maps every alloy designation to its page.
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1. Titanium threads gall. A titanium thread run against another titanium thread cold-welds and seizes, often badly enough that the fastener has to be cut off. Every joint needs an anti-seize or dry-film lubricant, a plated or coated thread, or a nut in a dissimilar material.
2. Titanium is galvanically noble. It will not corrode itself, but a titanium fastener in an aluminium, carbon steel, zinc or magnesium assembly drives accelerated corrosion of the structure around it.
3. Three absolute exclusions: no dry chlorine, no red fuming nitric acid, and rapid attack by hydrofluoric acid at any concentration. Fine swarf is a fire hazard.
4. The alloyed grades are not corrosion substitutes for commercially pure titanium. Aluminium and vanadium buy strength at the cost of resistance in reducing media. For corrosion duty use the commercially pure and lean grades; and note that alloys with aluminium above about 6% — Ti-8Al-1Mo-1V especially — are susceptible to stress corrosion cracking in methanol and hot salt under sustained tension.
There is a real engineering reason the beta alloys dominate titanium fastener work. An alpha-beta alloy at 1240 MPa has to be machined at that strength — slow, abrasive and hard on tooling, with a cut thread whose root interrupts the grain flow. A metastable beta alloy can be cold headed and thread rolled in the soft solution-treated condition and then aged to the same strength afterwards. The result is a cheaper part and a better thread, because a rolled thread carries continuous grain flow and a cold-worked surface, with the fatigue performance that follows. That is why Beta III and Ti-15-3 are cited specifically for aircraft fasteners, and why Beta C has a following in oilfield springs and bolting.
Several of these alloys are known by more than one name. Every designation in common use is listed here against its page.
| Alloy | Also Known As | UNS | Class | Specification | Datasheet |
|---|---|---|---|---|---|
| Grade 11 | Ti-0.15Pd | R52250 | Alpha, corrosion | ASTM B348 Gr 11 | Grade 11 → |
| Grade 12 | Ti-0.3Mo-0.8Ni | R53400 | Lean alloy, corrosion | ASTM B348 Gr 12 | Grade 12 → |
| Ti-8Al-1Mo-1V | 8Al-1Mo-1V, Ti-811, Grade 8 | R54810 | Near-alpha | AMS / MIL-T-9046, 9047 | Ti-811 → |
| Ti-6Al-2Sn-4Zr-2Mo | 6Al-2Sn-4Zr-2Mo, Ti-6242, Ti-6242S | R54620 | Near-alpha | AMS 4919 / 4975 / 4976 | Ti-6242 → |
| Grade 5 | Ti-6Al-4V, 6Al-4V | R56400 | Alpha-beta | ASTM B348 Gr 5 | Grade 5 → |
| Grade 9 | Ti-3Al-2.5V, “half 6-4” | R56320 | Lean alpha-beta | ASTM B348 Gr 9 | Grade 9 → |
| Grade 23 | Ti-6Al-4V ELI | R56401 | Alpha-beta, ELI | ASTM B348 Gr 23 / F136 | Grade 23 → |
| Ti-6Al-6V-2Sn | 6Al-6V-2Sn, Ti-662, Ti-6-6-2 | R56620 | Alpha-beta | AMS 4918 / 4971 / 4978 | Ti-662 → |
| Ti-6Al-2Sn-4Zr-6Mo | 6Al-2Sn-4Zr-6Mo, Ti-6246 | R56260 | Alpha-beta | AMS 4981 / MIL-T-9047 | Ti-6246 → |
| Ti-10V-2Fe-3Al | 10V-2Fe-3Al, Ti-10-2-3 | R56410 | Near-beta | AMS 4983 / 4984 / 4986 / 4987 | Ti-10-2-3 → |
| Grade 10 | Ti-11.5Mo-6Zr-4.5Sn, Beta III | R58030 | Metastable beta | AMS 4977 / 4980 | Beta III → |
| Grade 19 | Beta C, Ti-3Al-8V-6Cr-4Mo-4Zr | R58640 | Metastable beta | ASTM B348 Gr 19 | Beta C → |
| Ti-15Mo-3Nb-3Al-2Si | Beta 21S, Timetal 21S, Grade 21 | R58210 | Metastable beta | ASTM B348 Gr 21 | Beta 21S → |
| Ti-15V-3Cr-3Sn-3Al | 15V-3Cr-3Sn-3Al, Ti-15-3 | R58153 | Metastable beta | AMS 4914 / ASTM B265 | Ti-15-3 → |
Two things worth noting. Grades 8 and 10 are historical designations and do not appear in the current ASTM B265 or B348 grade lists, which run 1–7, 9, 11–21, 23 and upward — order those two against the UNS number and AMS specification, not the bare grade number. And the UNS for Ti-15V-3Cr-3Sn-3Al is reported inconsistently across sources, with R58153, R58010 and R58150 all in circulation; confirm it on the certificate. Commercially pure Grades 1, 2 and 7 are listed under Titanium.
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