Abstract
This work studied the effect of building orientations and post-process heat treatments on the fatigue crack growth behavior of Ti-6Al-4V manufactured by laser metal deposition. The fatigue crack growth rate experiments were carried out in three sampling directions (YZ, ZY, XY) in order to evaluate the anisotropy. In addition, the heat-treated samples (YZ, ZY, XY) were used for comparison, which were heat-treated under the vacuum at 900 ℃ for 2 h followed by air cooling and 550 ℃ for 4 h followed by air cooling. The results showed that the ∆KT values before and after heat treatment were 13.6 and 15 MPa∙m1/2, respectively. In the hypo-transitional region, the effect of columnar grains orientation and uniaxial residual stress led to anisotropy in fatigue crack growth rate for as-built specimens. This effect is significantly attenuated after the post-process heat treatment. The coarsened α laths effectively changed the crack propagation behavior and improve the fatigue crack growth resistance of the material. In the hyper-transitional region, the fatigue crack growth was controlled by the inherent fatigue crack growth resistance rather than the microstructure, resulting in negligible differences in all fatigue crack growth rate curves.
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