Texture Evolution During Laser Direct Metal Deposition of Ti-6Al-4V

Abstract

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.