Tensile and fatigue crack growth behavior of commercially pure titanium produced by laser powder bed fusion additive manufacturing

The effects of build orientation and post heat treatments on the tensile and fatigue crack growth (FCG) behavior of commercially pure titanium (CP-Ti) manufactured by laser powder bed fusion (LPBF) using grade 2 powder were examined. Two orthogonal build orientations were used in conjunction with hot isostatic pressing (HIP) both above (950 degrees C) and below (730 degrees C) the beta-transus temperature and property comparisons were also made to commercially available wrought material. The HIP treatments coarsened the a grain structure, reduced the tensile strength, and increased the fatigue crack growth threshold. The LPBF materials were generally stronger and more fatigue resistant than the wrought material due higher interstitial oxygen and nitrogen content. Additionally, higher tensile strength values were found for one build orientation with higher nitrogen content that was attributed to the different thermal histories during LPBF. However, the build orientation effect was not observed for the FCG behavior of the LPBF material and the FCG resistance at low growth rates were mainly controlled by the grain size. This was in sharp contrast to the wrought material which showed strong anisotropy in the microstructure sensitive fatigue crack growth regime due to strong crystallographic texture. At higher growth rates, FCG became microstructure insensitive when the cyclic plastic zone size became of similar order of magnitude to the grain size.