1. The two have different compositions, with TA18 being a nearly alpha type titanium alloy and TC4 being a (alpha+beta) type titanium alloy.

2. The welding performance and cold forming performance of TA18 titanium alloy tube are superior to TC4, and TC4 has better comprehensive mechanical properties.

3. Different uses: TA18 titanium alloy pipes are suitable for making high-pressure lightweight conduits on aircraft, while TC4 titanium pipes are more widely used and can be used for landing gear wheels and structural components, fasteners, brackets, aircraft accessories, frames, beam structures, pipelines, etc.

Titanium alloy TA18 is a nearly alpha type titanium alloy with a composition of Ti-3Al-2.5V. It has better welding and cold forming properties than TC4, a density of 4.47g/cubic centimeter, a room temperature elastic modulus of 118-123GPa, a phase transition point of 925 ℃, and a hardness of 15-17 HRC.

TC4 is composed of Ti-6Al-4V, a titanium alloy strengthened by heat treatment, which has good weldability, thin plate formability, and forging performance. Used for manufacturing jet engine compressor blades, impellers, and other components such as landing gear wheels and structural parts, fasteners, brackets, aircraft accessories, frames, beam structures, pipelines, with a wide range of applications.

Overall, TA18 alloy is a low-alloy near alpha titanium alloy with good cold formability and welding performance. Its room temperature strength is 20% to 50% higher than that of industrial pure titanium, and it has good corrosion resistance in many media. Therefore, TA18 alloy has become an ideal material for making high-pressure resistant lightweight conduits on aircraft due to its excellent comprehensive performance. TC4 titanium alloy belongs to the (α+β) type titanium alloy, which has a series of advantages such as excellent corrosion resistance, low density, high specific strength, good toughness and weldability. It has been successfully applied in aerospace, petrochemical, shipbuilding, automotive, pharmaceutical and other sectors.