① The tensile strength of pure titanium is 265-353MPa, while that of titanium alloys is generally 686-11766MPa. Currently, the highest tensile strength can reach 1764MPa. Titanium alloys have the same strength as many steels, but the specific strength of steel is far inferior to that of titanium alloys.
② The compressive strength of titanium and titanium alloys shall not be lower than their tensile strength. The compressive yield strength and tensile yield strength of industrial pure titanium are roughly equal, while the compressive strength of Ti-6AI-4V and Ti-5AI-2.5Sn is slightly higher than the tensile strength.
③ The shear strength is generally 60%~70% of the tensile strength. The compressive yield strength of titanium and titanium alloy sheets is approximately 1.2-2.0 times the tensile strength.
④ Under normal atmospheric atmosphere, the endurance limit of processed and annealed titanium and titanium alloys is 0.5-0.65 tensile strength. When conducting 10 million fatigue tests in the notch state (Kt=3.9), the endurance limit of annealed Ti-6AI-4V is 0.2 times the tensile strength.
⑤ The hardness of processing industrial pure titanium with the highest purity level is usually less than 120HB (Brinell hardness hardness), and the hardness of other industrial pure processing titanium is 200~295HB. The hardness of pure titanium castings is 200-220HB. The hardness value of titanium alloy in the annealed state is 32-38HRC (Rockwell), equivalent to 298-349HB. The hardness of the cast Ti-5Al-2.5Sn and Ti-6AI-4V is 320HB, while the hardness of the low clearance impurity Ti-6Al-4V casting is 310HB.
⑥ The tensile elastic modulus of industrial pure titanium is 105-109GPa. Most titanium alloys have a tensile elastic modulus of 110-120GPa in the annealed state. Age hardened titanium alloys have slightly higher tensile modulus of elasticity than those in the annealed state, and the compressive modulus of elasticity is equal to or greater than the tensile modulus of elasticity. The specific elastic modulus of titanium alloy is equal to that of aluminum alloy, second only to beryllium, molybdenum, and some high-temperature alloys.
⑦ The torsional or shear modulus of industrial pure titanium is 46GPa, and the shear modulus of titanium alloys is 43-51GPa. In order to improve the strength of titanium alloy, increasing the content of interstitial materials will bring harmful effects on the impact resistance and fracture toughness of the alloy. According to the types and states of titanium alloys, the Charpy notch impact strength value of denatured industrial pure titanium is 15-54J/㎡, and it is about 4-10J/㎡ in the cast state. The impact strength of titanium alloy in the annealed state is 13-25.8J/m2, and it is slightly lower in the aged state. The Charpy V-notch impact strength of Ti-5AI-2.5Sn in the cast state is 10J/㎡, while that of Ti-6AI-4V is 20-23J/㎡. The lower the oxygen content of titanium alloys, the higher this value.
⑧ Many titanium alloys have high fracture toughness, or the ability to resist crack growth is very good. Annealed Ti-6AI-4V is a material with excellent toughness. When the notch concentration coefficient Kt=25.4mm, the ratio of notch tensile strength to non notch tensile strength is greater than 1.
⑨ Titanium alloys can maintain certain properties at high temperatures. Generally, industrial titanium alloys can maintain their performance at a temperature of 540 ℃, but they can only be used for short periods of time, with a temperature range of 450~480 ℃ for long periods of time. At present, titanium alloys have been developed for use at a temperature of 600 ℃. Titanium alloy as a missile material can be used for a long time at a temperature of 540 ℃, and can also be used for a short time at a temperature of 760 ℃.
⑩ Titanium and titanium alloys can still maintain their original mechanical properties at low and ultra-low temperatures. As the temperature decreases, the strength of titanium and titanium alloys continues to increase, while the ductility gradually deteriorates. Many annealed titanium alloys have sufficient ductility and fracture toughness at - 195.5 ℃. Ti-5AI-2.5Sn with extremely low interstitial elements can be used at a temperature of -252.7 ℃. The ratio of its notch tensile strength to non notch tensile strength is 0.95-1.15 at -25.7 ℃.
Liquid oxygen, liquid hydrogen, and liquid fluorine are important propellants in missiles and space devices. The low-temperature performance of materials used for making low-temperature gas containers and low-temperature structural components is very important. When the microstructure is equiaxed and the content of interstitial elements (oxygen, helium, hydrogen, etc.) is very low, the ductility of titanium alloys is still above 5%. Most titanium alloys exhibit poor ductility at temperatures of -252.7 ℃, while the elongation of Ti-6AI-4V reaches 12%.
