Influence of environment on low cycle fatigue damage in Ti6Al4V and Ti 6246 titanium alloys

An experimental study of the initiation and propagation of short cracks naturally obtained on low cycle fatigue (LCF) smooth specimens has been carried out on β and αβ forged titanium alloys. Tests were done at room temperature in ambient air and in vacuum. Three different microstructures have been used. Regularly interrupted tests showed that crack initiation is delayed when tests are performed in vacuum. Surface crack densities were lower in vacuum than in air. Crack growth rates can be either strongly slowed down or unaffected by inert media, depending on the microstructure. Crack initiation sites were modified by air environment for the β forged alloy only. For one αβ forged alloy, an internal failure origin occurred in vacuum. The influence of environment on both crack initiation and short crack propagation is discussed in terms of effective slip length and stress-assisted hydrogen embrittlement.