The Titanium Grade System
In the ASTM system, titanium grades are numbered from 1 upward, with the commercially pure grades at the low end and the alloy grades following. The Chinese system uses TA designations for alpha-type alloys, TC for alpha-beta alloys and TB for beta alloys, and the two systems are often cross-referenced in trade.
The grade number or designation defines both the chemical composition and the minimum mechanical properties, and it is the basis of every order and material certificate.
Commercially Pure Grades
Commercially pure titanium Grades 1 to 4 differ mainly in oxygen content, which controls strength and ductility. Grade 1 is the softest and most formable, Grade 2 is the general-purpose industrial grade, Grade 3 offers higher strength, and Grade 4 is the strongest pure grade and the standard for dental implants.
The pure grades offer the best corrosion resistance in oxidising and chloride media, excellent weldability and moderate strength, and they dominate chemical and marine applications.
Alpha and Near-Alpha Alloys
Alpha alloys such as Ti-5Al-2.5Sn and near-alpha alloys such as Ti-6.5Al-2Zr-1Mo-1V are strengthened by aluminium and other alpha-stabilising elements. They offer the best creep resistance and high-temperature stability, and they are used for components that serve at 400 to 500 degrees Celsius.
These alloys weld well and retain toughness at cryogenic temperature, which suits both hot aero-engine structure and liquefied gas equipment.
Alpha-Beta Alloys
Alpha-beta alloys, led by Ti-6Al-4V, are the workhorses of the titanium family. They combine high strength, good ductility, heat-treatability and excellent fatigue performance, and they can be forged, rolled and welded.
Ti-6Al-4V is specified for airframe structure, engine parts, medical implants, marine hardware and high-performance industrial components, and it accounts for the largest share of titanium alloy consumption.
Beta Alloys
Beta alloys contain high levels of beta stabilisers such as vanadium, molybdenum and chromium, and they develop very high strength after ageing, in some cases above 1300 MPa. They also have the best cold formability in the solution-treated condition.
Beta alloys are used for springs, fasteners, landing gear components and other parts demanding maximum strength-to-weight ratio, at the cost of higher density and lower ductility than alpha-beta alloys.
Selecting the Right Grade
Selection starts with the service environment: corrosion determines whether a pure grade suffices, temperature determines whether an alpha alloy is needed, and strength determines the alloy family. Cost, formability and weldability are then balanced against the property requirement.
In practice, Grade 2 serves general corrosion duty, Ti-6Al-4V serves structural and fatigue-critical duty, and the specialist grades are reserved for temperature, strength or corrosion extremes.
Frequently Asked Questions
Q: How are titanium grades classified?
A: Titanium grades are classified as commercially pure, alpha, alpha-beta and beta, by chemical composition and mechanical properties.
Q: What is the most common titanium alloy?
A: Ti-6Al-4V, ASTM Grade 5, is the most widely used titanium alloy.
Q: What is the difference between Grades 1 and 4?
A: Grades 1 to 4 differ in oxygen content and strength, with Grade 4 the strongest commercially pure grade.
Q: Which titanium grade serves at 500 degrees Celsius?
A: Alpha and near-alpha alloys such as Ti-5Al-2.5Sn and Ti-6.5Al-2Zr-1Mo-1V serve in the 400 to 500 degrees Celsius range.
Q: Which grade offers the highest strength?
A: Beta alloys develop the highest strength after ageing, in some cases above 1300 MPa.
