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 10 1 ¯ 2 10 1 ¯ 1 deformation twins (DTs) spanning multiple α/β 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 (α 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. • Compared with equiaxed and bimodal structure, the lamellar structure exhibits the highest resistance to FCG rate. • The high resistance to FCG of lamellar structure is due to the coupling effect of crack deflection and twin boundary barrier. • Deformation twins spanning multiple α/β layers were observed in lamellar structure near the fatigue crack propagation path. [ABSTRACT FROM AUTHOR]