The torsion or shear modulus of industrial pure titanium is 46GPa, and the shear modulus of titanium alloy is 43 ~ 51GPa. In order to improve the strength of titanium alloy, increasing the content of interstitial material will bring harmful effects on the impact resistance and fracture toughness of the alloy. According to the type and state of titanium alloy, the Charlton notch impact strength of denatured industrial pure titanium is 15 ~ 54J/㎡, and the casting state is about 4 ~ 10J/㎡. The impact strength of titanium alloy in the annealing state is 13 ~ 25.8J/㎡, and the aging state is slightly lower. The Charlton V-shaped notch impact strength of Ti-5Al-2.5Sn in the casting state is 10J/㎡, and that of Ti-6Al-4V is 20 ~ 23J/㎡. The lower the oxygen content of titanium alloys, the higher the value.
Many titanium alloys have high fracture toughness, or the ability of titanium alloys to resist crack growth is very good. Ti-6Al-4V in annealed state 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.
Titanium alloys can also maintain certain properties at high temperatures. General industrial titanium alloys can maintain their properties at 540 ° C, but can only be used for short time applications, and the temperature range for long enough is 450 ~ 480 ° C. At present, titanium alloys have been developed for use at 600℃. Titanium alloy as a missile material can be used for a long time at 540℃ temperature, but also can be used for a short time at 760℃ temperature. The high-temperature properties of several titanium alloys are shown.
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 alloys continues to increase, and the ductility gradually deteriorates. Many annealed titanium alloys also have sufficient ductility and fracture toughness at -195.5℃. Ti-5Al-2.5Sn with very low gap 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 properties of materials used to make low temperature gas containers and low temperature structural parts are 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 above 5%. Most titanium alloys have poor ductility at -252.7℃, while the elongation of Ti-6Al-4V reaches 12%.
