Pure Titanium vs Titanium Alloy Screws: What Is the Difference?
Feb 04, 2024
Pure Titanium and Titanium Alloy Screws: The Basics
Titanium screws fall into two families: commercially pure (CP) titanium, which is essentially unalloyed metal, and titanium alloys, which combine titanium with elements such as aluminum, vanadium, molybdenum, and niobium. The choice affects strength, corrosion resistance, fatigue life, cost, and the standards the fastener must meet. This article compares the two families so buyers can specify the right screw for the job.
Chemical Composition
| Material | Key Composition (wt %) |
|---|---|
| CP Titanium Grade 2 | Ti ≥ 99.2, Fe ≤ 0.30, O ≤ 0.25, C ≤ 0.08 |
| CP Titanium Grade 4 | Ti ≥ 98.9, Fe ≤ 0.50, O ≤ 0.40, C ≤ 0.08 |
| Ti-6Al-4V (Grade 5) | Al 5.5-6.5, V 3.5-4.5, Fe ≤ 0.40, O ≤ 0.20 |
| Ti-6Al-4V ELI (Grade 23) | Al 5.5-6.5, V 3.5-4.5, Fe ≤ 0.25, O ≤ 0.13 |
Mechanical Properties Compared
| Material | Tensile Strength (MPa) | 0.2% Yield (MPa) | Elongation (%) |
|---|---|---|---|
| Grade 2 (annealed) | ≥ 345 | ≥ 275 | ≥ 20 |
| Grade 4 (annealed) | ≥ 550 | ≥ 483 | ≥ 15 |
| Grade 5 (annealed) | ≥ 895 | ≥ 828 | ≥ 10 |
| Grade 23 (annealed) | ≥ 860 | ≥ 795 | ≥ 10 |
Values follow ASTM B348 for bar and rod. High-strength titanium alloys can exceed the tensile strength of many alloy structural steels while weighing only about 60% as much, which is why titanium fasteners are standard in aerospace.
Practical Differences in Service
Strength - alloy screws carry higher clamp loads at the same diameter, or allow smaller diameters for the same load.
Corrosion resistance - CP titanium resists most chemical and marine environments; alloys such as Ti-6Al-4V are similar in most media but slightly less resistant in some reducing acids.
Galling - both families gall under sliding contact; molybdenum-disulfide or silver plating, and anti-seize compounds, are recommended for threaded assembly.
Fatigue - alloy fasteners offer higher fatigue strength, important in vibration and cyclic loading.
Biocompatibility - ELI grades (Grade 23) are specified for bone screws and implant fixation per ASTM F136 and ISO 5832-3.
Formability and cost - pure titanium is easier to cold head and costs less; alloy screws often require warm heading or machining.
How to Choose
For chemical, marine, and general industrial fasteners where corrosion resistance is the priority and loads are moderate, CP titanium Grade 2 or Grade 4 is usually sufficient and economical. For aerospace structural fasteners, high-strength joints, and applications subject to fatigue, choose an alpha-beta alloy such as Ti-6Al-4V, supplied to ASTM F468 or AMS 4967. For surgical implants, use Grade 23 (Ti-6Al-4V ELI) to ASTM F136 or ISO 5832-3.
Frequently Asked Questions
Are pure titanium screws weaker than titanium alloy screws?
Yes, in most cases. Grade 2 CP titanium has a minimum tensile strength of about 345 MPa, while annealed Ti-6Al-4V exceeds 895 MPa, so alloy screws are used where higher clamp loads are required.
Can pure titanium screws be used in seawater?
Yes. CP titanium resists pitting and crevice corrosion in seawater and is widely used in marine fasteners, often without coating.
Why are titanium alloy screws preferred in aerospace?
Because they combine high strength, low density, and excellent fatigue resistance, reducing structural weight in airframes and engines.
Do titanium screws require special installation?
They gall easily, so anti-seize compounds, controlled torque, and stainless steel or titanium tooling are recommended to prevent seizing during assembly.
Which standard covers titanium fasteners?
ASTM F468 covers bolts, screws, and studs in nonferrous metals including titanium; bar stock is supplied to ASTM B348, and implant screws to ASTM F136 or ISO 5832-3.
Are alloy screws available in medical grades?
Yes. Ti-6Al-4V ELI (Grade 23) is the standard implant grade, providing high strength with superior fracture toughness and biocompatibility.
