A New High Strength Titanium Fastener Alloy

Developing titanium alloy with a higher strength to density ratio has attracted great attention, especially in the aerospace industry where weight reduction is important for energy efficiency and product performance. However, the processing difficulty, and resulting inhomogeneous and coarse microstructure constantly cast a limit on the properties that the titanium alloy can be further improved, and generally, the increment in strength means the compromise of other engineering properties such as the inverse relationship in tensile strength and ductility. In this project, a new titanium alloy has been designed with simple alloying element control and conventional thermo-mechanical processing, which is ready to be scaled up. A resulting microstructure with uniform and fine grains and strengthening phases, and the removal of boundary segregation problem lead to a material with both improvements in tensile strength and tensile elongation. The ultimate tensile strength is higher than 1500MPa while ductility is still higher than 12%. This material can go through the essential thread forming process with the final product capable to have tensile strength higher than 1500MPa, shear strength higher than 830MPa and threaded fatigue strength higher than 600MPa, which are tested based on the standard requirement for aerospace threaded fasteners. This will be more than 30% strength improvement and potentially more than 20% weight saving when replacing the current Ti-6Al-4V fasteners by this material.