INFLUENCE OF CREEP-FATIGUE INTERACTION ON HIGH-TEMPERATURE FATIGUE-CRACK GROWTH-BEHAVIOR OF TI-1100

A series of crack growth experiments has been preformed on the near al pha titanium alloy, Ti-1100, to determine the mechanism of the creep-f atigue interaction. Based on pure creep crack growth results, the incr ease in the creep-fatigue crack growth rate is not amenable to separat e contributions of creep crack growth and fatigue crack growth. A mech anism has been proposed to account for the increase in creep-fatigue c rack growth rate that is based on the planar slip of titanium alloys w hich results in the formation of dislocation pileups at the prior beta grain boundaries and leads to intergranular fracture. This mechanism has been validated through crack growth experiments preformed on a Ti- 1100 that has been microstructurally modified through the precipitatio n of internal slip barriers. These show that the intergranular fractur e and increase in crack growth rate are absent.