High temperature resistant titanium alloy fasteners

Currently, titanium alloy materials for fasteners are not used at high temperatures. In the field of aerospace, due to the new models of aircraft and aircraft flight speed continues to increase, the service temperature of the materials required to be increased. Therefore, high-temperature titanium alloy fasteners is also the future development trend, especially in the aerospace field, the new high-temperature titanium alloy materials are required to be able to 600 ~ 800 ℃ short-term service.

Usually use Ti2AlNb alloy to replace the heavier high temperature alloy, its deformation is more serious, and the use of Ti2AlNb alloy to replace the other titanium alloy materials or heavier, can not meet the requirements of the weight reduction; Ti-Al intermetallic compounds process plasticity is poor, the maturity is poor. Therefore, the future fasteners with high temperature titanium alloy materials are still nearly α-type and high aluminum equivalent two-phase titanium alloys.

At high temperatures, the strength and creep resistance of titanium alloys mainly depends on the solid solution strengthening of Al, Sn, Zr. However, the content of these elements cannot be increased indefinitely due to the limitation of aluminum equivalent. Therefore, titanium alloys are designed to be strengthened by multi-element composite alloying under proper control of the contents of Al, Sn and Zr. β-stabilizing element Mo has a solid solution strengthening effect on the high temperature strength and creep strength of high temperature titanium alloys, and the addition of small amounts of β-stabilizing elements can prevent the alloys from embrittlement. In addition, the content of Si in titanium alloys is crucial to the performance, after adding a mass fraction of about 0.2% Si, ellipsoidal silicides will be non-uniform, discontinuous precipitation in the α-sheet boundaries, which can effectively impede the movement of dislocations, resulting in a diffuse reinforcement, so that the creep performance of the alloys is greatly improved. However, the appearance of silicides at the same time on the thermal stability of the alloy organization also has a harmful effect, not only reduce the plasticity of the alloy, but also enhance the degree of ordering of the alloy, promote the generation of Ti3Al phase. Therefore, the Si content should be controlled at a low level, and the general mass fraction is not more than 0.5%. Therefore, multi-element composite strengthening is still the development direction of new high-temperature titanium alloy material design.