Influence of Carbon Additions On the Properties of Ti-5Al-5Mo-5V-3Cr-0.5Fe

Microstructural features in metastable β-Ti alloys, such as continuous layers of grain boundary alpha (GBA) in Ti-5Al-5Mo-5V-3Cr-0.5Fe (Timetal 555), are known to affect mechanical properties. Several methods to control the amount of GBA are available, including carbon additions as shown recently by Wu and Loretto. Other methods of managing GBA include using metastable transition precipitates to nucleate α more rapidly, and hot working the material to recrystallize both alpha and beta phases. Each of these methods to reduce GBA affects properties such as fracture behavior and fatigue life differently. In carbon-free Timetal 555, high strength conditions commonly exhibit ductile intergranular fracture in four-point bending fatigue, as well as short lifetimes when tested with the maximum cyclic stress near the yield stress. This talk focuses on the differences in four-point bending fatigue lifetime and fracture behavior between two of methods of controlling GBA: Timetal 555 containing carbon provided by Wu and Loretto, and carbon-free material provided by Boeing.