Fatigue crack initiation in Ti–5Al–4Sn–2Zr–1Mo–0.7Nd–0.25Si high temperature titanium alloy

Ti–5Al–4Sn–2Zr–1Mo–0.7Nd–0.25Si alloy is a new high temperature titanium alloy for aeroengine use. In this paper, the fatigue crack initiation in this alloy was investigated. At applied maximum nominal stresses less than 500 MPa, most cracks initiate in the matrix away from the Nd-rich particles. Initiation of these cracks is related to the cracking of equiaxed α phase on the prior β grain boundaries. At high applied stresses, almost half of the cracks initiate in the matrix away form the Nd-rich particles and the other half initiate near Nd-rich particles. The probability that an Nd-rich particle initiates a fatigue crack decreases very rapidly as the particle size falls below 12 μm.