In China, the industrial pure titanium is divided into four levels according to the number of impurities contained in it, namely TA1, TA2, TA3 and TA4. They correspond to grade 1 ~ 4 titanium in USA, namely Gr.1, Gr.2, Gr.3 and Gr.4.
With the decrease of purity, the strength and hardness of industrial pure titanium are improved, while the plasticity, impact toughness and fatigue resistance are reduced. TA3 and TA4 can be used when the strength, hardness and wear resistance are required. TA1 and TA2 can be used when the formability is required.
TA4 titanium alloy is a kind of α type titanium alloy. This kind of alloy exhibits α type single-phase state at room temperature and service temperature, and cannot be strengthened by heat treatment (annealing is the only form of heat treatment), mainly relying on solid solution strengthening.
The strength of TA4 at room temperature is generally lower than that of β'> and α+β titanium alloys (but higher than that of industrial pure titanium), while the strength and creep strength of TA4 at high temperature (500-600℃) are the highest among the three titanium alloys. And the structure is stable, oxidation resistance and welding performance is good, corrosion resistance and machinability is also good, but the plasticity is low (thermoplastic is still good), room temperature stamping performance is poor. The most widely used is TA7, it has moderate strength and enough plasticity in annealing state, good weldability, can be used below 500℃; When the content of interstitial elements (oxygen, hydrogen, nitrogen, etc.) is very low, it also has good toughness and comprehensive mechanical properties at ultra-low temperature, which makes it one of the excellent ultra-low temperature alloys.
TA4 tensile strength is slightly higher than industrial pure titanium, can be used as a medium strength range of structural materials. It is mainly used as welding wire in China, and is widely used in high-end electroplating industry abroad.
