Direct Digital Manufacturing (DDM) of Metallic Components: Controlled Thermal Processing

The objective of this Phase I proposal is to demonstrate microstructure modeling and thermal control in order to achieve fatigue properties comparable to wrought material in the Ti-6Al-4V produced by direct digital manufacturing (DDM). The Phase I will begin with selection of a demonstration deposit. A process design will be developed for the deposit by emulating the existing procedure for closed-loop control within the thermo-mechanical process simulation of laser-based DDM. This will provide a measure of non-uniformity of thermal cycling in the deposit. A Ti-6Al-4V microstructure model will be utilized to tailor a thermal cycling path that will result in improved microstructure homogeneity and mechanical properties. The emulation of the closed-loop control will be enhanced to include the thermal cycle induced by the additive material on the previously deposited material. An improved DDM Process Design will be developed in order to match the mean thermal cycling path in the deposit with the path designed using the microstructure model. A fine control of the thermal cycling will be obtained by designing auxiliary devices that act as heat sources or sinks and equalize the thermal cycling. A demonstration deposit will be produced and fatigue testing will be performed on samples located along the direction of deposit and along its two normal directions. During the Phase I Option, the microstructure homogeneity of the deposit will be characterized. In addition, the DDM Process Design procedure will be shown for an electron-beam based DDM process.