The anisotropy of high cycle fatigue property and fatigue crack growth behavior of Ti-6Al-4V alloy fabricated by high-power laser metal deposition

In the present work, several large Ti-6Al-4V blocks were successfully fabricated by high-power laser metal deposition (HP-LMD). The high cycle fatigue (HCF) property and fatigue crack growth (FCG) behavior of the asbuild Ti-6Al-4V alloy were investigated from two sampling directions (horizontal and vertical). The results showed that the fatigue limit of horizontal and vertical specimens was 357.5 MPa and 358.57 MPa, respectively. However, the HCF performance of vertical specimens was superior to horizontal specimen under a high-stress level. In addition, the HCF performance of both horizontal and vertical specimens was inferior to the wrought Ti-6Al-4V. Meanwhile, the FCG rate of vertical specimen was lower than that of horizontal specimen in both near-threshold region and Paris region. The anisotropic microstructure (prior beta columnar grains with preferential orientation and alpha colonies) was found to be the main reason that contributed to an anisotropic HCF property and FCG behavior. For horizontal specimen, the fatigue crack interacted with only one or two columnar grains, thus leading to a lower FCG resistance. For vertical specimen, the fatigue crack interacted with multiple columnar grains, which led to a better plasticity and enhanced FCG resistance.