Influence of microstructure on the fatigue crack growth behavior of a near-alpha TWIP Ti alloy

The fatigue crack growth (FCG) behaviors of a twin inducing plasticity (TWIP) Ti-5Al-1 V-Sn-1Zr-0.8Mo (Ti5111) alloy with three typical microstructures were investigated. Compared with the equiaxed and bimodal structures, the lamellar structure exhibited a higher resistance to the FCG rate, but it displayed a lower strength and { }( ) elongation to failure. Many 1012 1011 deformation twins (DTs) spanning multiple alpha/beta layers were observed in the lamellar structure near the FCG path. The same type of DT was also observed in the equiaxed structure, although its density was significantly lower than that of the lamellar structure, and no DTs were found in the bimodal structure. The higher resistance to FCG of the lamellar structure results from its large effective microstructural unit size (alpha colony), which is most favorable to deflecting cracks and increasing crack path tortuosity, and is associated with the blocking effect of deformation twin boundaries on crack propagation.