The relationship between microstructures and mechanical properties such as tensile and fatigue properties were systematically investigated by conducting several heat treatments on Ti–4.5Al–4Cr–0.5Fe–0.2C (KS EL-F) and Ti–4.5Al–2Cr–1Fe–0.1C (KS EL-Fmod) for next-generation aircraft applications. TiC and TiCr2 are formed in KS EL-F and KS EL-Fmod annealed at temperatures higher than β-transus and aged at 773 K, respectively. However, the precipitation trends of TiC and TiCr2 are considerably higher in the case of KS EL-F because the amounts of both these precipitates are drastically suppressed in KS EL-Fmod even when the heat treatments are identical. As-received KS EL-F and KS EL-Fmod exhibit excellent fatigue strength as compared with annealed Ti–6Al–4V. Although the presence of TiCr2 tends to decrease the fatigue strength, the aged KS EL-Fmod exhibits higher fatigue strength than the as-received KS EL-Fmod with very low TiCr2 amounts. Therefore, the aging treatment for KS EL-Fmod can be effective in improving the fatigue strength.
