The National Titanium Designation System
National titanium standards, principally GB/T 3620.1 and GB/T 3621, divide titanium into TA and TC families. TA designates alpha and near-alpha alloys, including the commercially pure grades TA1, TA2, TA3 and TA4, while TC designates alpha-beta alloys strengthened by beta stabilisers. The number after the letters identifies the specific alloy, and the system is widely recognised internationally as an equivalent to ASTM and ISO designations.
TA2 corresponds to commercially pure titanium with a nominal purity of 99.2 percent, equivalent to ASTM Grade 2 and UNS R50400. TC4 is the domestic designation for Ti-6Al-4V, equivalent to ASTM Grade 5 and UNS R56400. TC11 is a domestically developed heat-resistant alpha-beta alloy containing about 6.5 percent aluminium, 3.5 percent molybdenum, 1.5 percent zirconium and 0.3 percent silicon, with no direct ASTM counterpart.
TA2: Commercially Pure Titanium for Corrosion Service
TA2 offers a minimum tensile strength of about 400 MPa with excellent formability and weldability, and its outstanding corrosion resistance in seawater, chlorides and oxidising acids makes it the default material for chemical vessels, heat exchangers, piping and marine equipment. Its UNS equivalent R50400 is recognised worldwide, and it is supplied as plate, sheet, bar, tube and forgings to GB/T 3621.
Processing of TA2 is straightforward: it is cold formable, weldable by gas tungsten arc welding with matching filler, and requires no heat treatment beyond annealing for most applications. Because of its low strength relative to alloys, TA2 parts are designed with thicker sections, but the material cost advantage and corrosion reliability keep it dominant in chemical and marine engineering.
TC4: The Structural Workhorse
TC4, equivalent to Ti-6Al-4V, combines minimum tensile strength of 895 MPa with good toughness and fatigue resistance, and it accounts for the majority of titanium used in aircraft structures, fasteners, pressure vessels and high-performance sporting goods. In domestic programmes it is specified for fuselage frames, wing skins, landing gear components and rocket motor casings, matching the global role of Ti-6Al-4V.
Processing of TC4 demands controlled hot working. Billets are forged in the alpha-beta field between about 900 and 980 degrees Celsius to develop a fine equiaxed microstructure, followed by annealing at 700 to 800 degrees Celsius. The alloy is machined with carbide tooling at conservative speeds, welded with matching filler under inert gas, and, for high-strength applications, solution treated and aged to raise tensile strength above 1100 MPa.
TC11: Heat-Resistant Alloy for Compressor Components
TC11 was developed for aero-engine compressor discs, blades and shafts operating at temperatures up to about 500 degrees Celsius. The molybdenum and silicon additions provide solid solution and precipitation strengthening that retain creep resistance and fatigue strength at service temperature, and the alloy's thermal stability is verified by long-duration exposure testing before engine qualification.
TC11 is processed by forging in the alpha-beta field followed by a complex two-stage heat treatment: solution treatment around 950 degrees Celsius, then ageing near 530 degrees Celsius, which produces a bimodal microstructure of equiaxed primary alpha in a transformed beta matrix. This microstructure balances high-temperature strength with low-cycle fatigue life, and the alloy is also used for high-pressure compressor discs in industrial gas turbines.
Selecting Among the Three Grades
The selection rule is simple. If the requirement is corrosion resistance, formability and weldability at moderate cost, choose TA2. If the part must carry structural load with minimum weight, choose TC4. If the part operates hot, in a compressor or turbine environment above 400 degrees Celsius, choose TC11. Each grade has an established processing route, and switching between them changes forging, heat treatment and machining parameters significantly.
Cross-reference tables in the national standards list the equivalents to ASTM, ISO and other systems, which helps international buyers specify the correct grade. For example, specifying TC4 with a note that it must meet ASTM B265 Grade 5 chemistry closes any ambiguity, and TC11 is ordered with its GB/T composition and mechanical property requirements stated on the drawing.
Frequently Asked Questions
Q: What is the difference between TA2 and TC4 titanium?
A: TA2 is commercially pure titanium for corrosion service with moderate strength, while TC4 is the Ti-6Al-4V structural alloy with roughly double the strength for load-bearing parts.
Q: What does TC4 titanium equal in ASTM terms?
A: TC4 is the domestic designation for Ti-6Al-4V, equivalent to ASTM Grade 5 and UNS R56400, and it is widely cross-referenced in international trade.
Q: Where is TC11 titanium used?
A: TC11 is used for aero-engine compressor discs, blades and shafts operating up to about 500 degrees Celsius, exploiting its creep and fatigue resistance.
Q: Is TA2 easy to weld?
A: Yes, TA2 welds readily with gas tungsten arc welding under inert gas shielding and matching filler, and no post-weld heat treatment is needed for most services.
Q: How is TC4 heat treated?
A: For structural service TC4 is annealed at 700 to 800 degrees Celsius; for maximum strength it is solution treated and aged, which raises tensile strength above 1100 MPa.
