Texture Evolution During Laser Direct Metal Deposition of Ti-6Al-4V
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Titanium alloys are used in a wide variety of high-performance applications and hence the processing of titanium and the resulting microstructures after additive manufacturing has received significant attention. During additive manufacturing, the processing route involves the transition from a liquid to solid state. The addition of successive layers results in a complex microstructure due to solid-state transformations. The current study focuses on understanding the phase transformations and relate them to the transformation texture in Ti-6Al-4V to identify conditions leading to a strong alpha transformation texture. The as-deposited builds were characterized using optical microscopy and electron backscattered diffraction. The results showed columnar prior β grains with a martensitic structure after the deposition of a single layer. On subsequent depositions, the martensitic microstructure decomposed to a colony and basketweave microstructure with a stronger transformation texture. The alpha texture with a colony and basketweave microstructure showed a stronger transformation texture as a result of variant selection. Thus, by controlling the cooling rate of the build from the β transus, it is possible to control the alpha transformation texture.
The authors would like to thank the US Navy Small Business Innovation Research program for financial support. This Research was sponsored the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office, under contract DE-AC05-00OR22725 with UT-Battelle, LLC. This research at the Oak Ridge National Laboratory’s High Temperature Materials Laboratory was sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.
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