In-situ beta phase rolling in direct laser fabricated Ti-6Al-4V

One of the biggest challenge of expanding the market of using direct laser fabricating (DLD) to manufacturing big Ti-6Al-4V components is the large columnar prior-beta grain along the building direction due to intrinsic directional cooling. This type of long prior-beta grain with elongated morphology across several deposition layers can cause anisotropy tensile properties, limiting the applications for aerospace area especially titanium and nickel alloy. A novel in-situ beta phase rolling technique is realised to alter the size of the prior-beta grain by deforming the beta phase simultaneously while depositing with relatively small amount of force. Equaixed and uniform prior-beta grains are achieved along the whole sample with similar grain size. Isotropic tensile properties is achieved and there is about 100MPa increase in yield and ultimate tensile strength are realised as well. It is suspected that the improved mechanical properties are due to the synergistic effect of the parent beta grain size and equiaxed morphology. This research shows that by changing the initial prior-beta grain, the subsequent alpha colony, alpha lath length can be tuned. Moreover, the high cycle fatigue properties of horizontal and vertical samples after in-situ beta phase rolling are investigated. In a word, the new in-situ beta phase rolling method offers an efficient way to improve the overall performance of DLDed Ti-6Al-4V.