Mechanical properties of titanium:
① The tensile strength of pure titanium is 265 ~ 353mpa, and that of general titanium alloy is 686 ~ 1176mpa. At present, the maximum is 1764mpa. Titanium alloy has the same strength as many steels, but the specific strength of steel is far lower than that of titanium alloy.
② The compressive strength of titanium and titanium alloy shall not be lower than its tensile strength. The compressive yield strength and tensile yield strength of industrial pure titanium are roughly the same, 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 bearing yield strength of titanium and titanium alloy sheet is about 1.2 ~ 2.0 times of tensile strength.
④ Under normal atmospheric atmosphere, the endurance limit of processed and annealed titanium and titanium alloy is 0.5 ~ 0.65 tensile strength. When 10 million fatigue tests are carried out 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 the highest purity processed industrial pure titanium is usually less than 120hb (Brinell hardness), and the hardness of other industrial pure processed titanium is 200 ~ 295hb. The hardness of pure titanium castings is 200 ~ 220HB. The hardness value of titanium alloy in annealed state is 32 ~ 38hrc (Rockwell), equivalent to 298 ~ 349hb. The hardness of as cast ti-5al-2.5sn and Ti-6AI-4V is 320hb, and the hardness of low gap impurity Ti-6Al-4V casting is 310hb.
⑥ The tensile elastic modulus of industrial pure titanium is 105 ~ 109GPa, and the tensile elastic modulus of most titanium alloys in annealed state is 110 ~ 120gpa. The age hardened titanium alloy has a slightly higher tensile elastic modulus than that in the annealed state, and the compressive elastic modulus is equal to or greater than the tensile elastic modulus. The specific elastic modulus of titanium alloy is equal to that of aluminum alloy, second only to beryllium, molybdenum and some superalloys.
⑦ The torsional or shear modulus of industrial pure titanium is 46 GPA, and the shear modulus of titanium alloy is 43 ~ 51 GPa. In order to improve the strength of titanium alloy, increasing the content of interstitial matter will have a harmful impact on the impact resistance and fracture toughness of the alloy. According to the type and state of titanium alloy, the Charpy Notch Impact Strength of modified industrial pure titanium is 15 ~ 54j / ㎡ and about 4 ~ 10J / ㎡ in casting state. The impact strength of titanium alloy in annealing state is 13 ~ 25.8j / ㎡, which is slightly lower in aging state. The Charpy V-notch impact strength of cast ti-5ai-2.5sn is 10J / ㎡, and that of Ti-6AI-4V is 20 ~ 23j / ㎡. The lower the oxygen content of titanium alloy, the higher the value.
⑧ Many titanium alloys have high fracture toughness, or the ability of titanium alloys to resist crack propagation is very good. Ti-6AI-4V in annealed state is a material with excellent toughness. When the notch concentration factor KT = 25.4mm, the ratio of notch tensile strength to non notch tensile strength is greater than 1.
⑨ Titanium alloy can maintain certain properties at high temperature. General industrial titanium alloys can maintain their properties at 540 ℃, but they can only be used for a short time, and the temperature range for a long time is 450 ~ 480 ℃. At present, titanium alloy has been developed for use at 600 ℃. As a missile material, titanium alloy can be used for a long time at 540 ℃ and for a short time at 760 ℃.
⑩ Titanium and titanium alloys can still maintain their original mechanical properties at low and ultra-low temperatures. With the decrease of temperature, the strength of titanium and titanium alloy increases, while the ductility decreases gradually. Many annealed titanium alloys also have sufficient ductility and fracture toughness at - 195.5 ℃. Ti-5ai-2.5sn containing very low interstitial elements can be used at - 252.7 ℃. The ratio of 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 to make low-temperature gas containers and low-temperature structural parts 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 alloy is still more than 5%. Most titanium alloys have poor ductility at - 252.7 ℃, while the elongation of Ti-6AI-4V reaches 12%.
