Fatigue crack growth behaviour of two contrasting titanium alloys

Fatigue crack propagation rates have been measured for Ti-6Al-4V and Ti-5331S aeroengine disc materials using compact tension and corner-notched tensile testpieces. The loadings used simulate both the start-stop operations of aeroengines that lead to low-cycle fatigue and the in-flight vibrations that may cause high-cycle fatigue. It is suggested that the different fatigue crack growth behaviour of Ti-5331S, relative to that of Ti-6Al-4V, arises largely from the greater proportion of crack closure and short crack occurring in this alloy. Ti-5331S also exhibits a crack retardation effect due to the interaction between the processes of cyclic cleavage and striated crack growth which are associated with the high- and low-cycle fatigue components of the loading, whilst Ti-6Al-4V does not.