Microstructural control and mechanical properties of low-cost titanium alloys for next generation aircrafts

New titanium alloys have been developed for use in next-generation aircrafts by adding low-cost elements such as C, Fe, Al and Cr. Some of the newly developed alloys are Ti-4.5Al-2Mo-1.6V-0.5Fe-0.3Si-0.03C, referred to as KS Ti-9, and Ti-4.5Al-2.5Cr-1.2Fe-0.1C, referred to as KS Ti-531C. As opposed to the widely used Ti-6Al-4V (Ti64), KS Ti-9 can be rolled at much lower temperatures without employing pack-rolling, and the anisotropy in its mechanical strength is significant. Microstructural control process to reduce the anisotropy in the mechanical strength of KS Ti-9 has been investigated. Anisotropy controlling treatment (ACT) is found to be effective to reduce the anisotropy in the mechanical strength of KS Ti-9. KS Ti-531C, with good mechanical properties at room temperature, similar to those of Ti64, and high hot-workability with low flow stress during deformation at high temperatures, similar to that of commercially pure titanium (CPTi), has been developed for fabricating forged or extruded components. There still exists a possibility of the precipitation of titanium carbides depending on the kind of the microstructural control process used. The mechanical properties and the fatigue strength of KS Ti-531C with different microstructures have been investigated, (α + β)-annealed KS Ti-531C with an equiaxed α structure exhibits better ductility and fatigue strength than β-annealed KS Ti-531C with the Widmanstätten α structure because of the presence of titanium carbide precipitates in the β-annealed KS Ti-531C.