A THERMAL AND MICROSTRUCTURE MODEL FOR LASER DEPOSITION OF TI-6AL-4V

Near-net shape processes, such as laser metal deposition (LMD), offer a unique combination of process flexibility, time savings, and reduced cost in producing titanium alloy components. The current challenge in processing titanium alloys using LMD methods is understanding the complex microstructural evolution as a part is fabricated layer by layer. The microstructure is affected by the repeated thermal cycling that occurs during the deposition process. The current work focuses on the thermal and microstructural modeling of multilayered Ti-6Al-4V deposits. Prior work with LMD-Ti-6Al-4V has shown that a complex microstructure evolves consisting of a two-phase alpha+beta structure. Depending on the location within the part, the Widmanstätten alpha may exhibit a colony (layer band) or basketweave morphology. A thermal model has been developed using finite difference techniques to predict the thermal history of LMD processes. The characteristics of a thermal cycle are used to qualitatively map the evolution of equilibrium and nonequilibrium phases in the deposit. The results of the thermal and microstructure models will be discussed in relation to the as-deposited microstructure