Abstract
The fatigue crack growth (FCG) behaviors of fully-lamellar and bi-lamellar Ti-6Al-3Nb-2Zr-1Mo alloy were investigated comparably. The FCG rate of bi-lamellar structure is lower than that of fully-lamellar structure, especially at the low stress intensity factor range (ΔK < 40 MPa m1/2). The fatigue crack growth path, deformed sub-structure and surface damage morphology were observed by SEM and TEM. For the fully-lamellar structure, because the same orientation of α lamellae and Burgers relationship between α and β lamellas in the α colony, the fatigue cracks often grow along a straight line in the α colony by cutting the β lamellas. For the bi-lamellar structure, because the resistance of secondary α (αs) precipitations in the β lamellas to dislocation slips, the frequency of crack propagation along the α/β interface increases. The fatigue cracks often grow along a zigzag in the α colony, which results in the fatigue crack growth path is more circuitous than that of the fully-lamellar structure in α colonies, and this is the main reason that the FCG rate of bi-lamellar structure is lower than that of fully-lamellar structure. This research has an important engineering significance to improve the low cycle fatigue (LCF) performance of the coarse lamellar structured Ti alloys.
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