Linking thermal history to mechanical behavior in directed energy deposited materials

Additive manufacturing is a promising process that has the capability for process optimization and materials development of novel, multi-material and functional components of complex geometries due to the rapid and localized directional solidification of molten metallic alloys. Directed energy deposition, an additive manufacturing process that uses a high powered laser to melt blown metallic powder, introduces large gradients and sensitivity in thermal histories within a built component that lead to unique phase transformations, microstructures, residual stress and anisotropic mechanical behavior. Control of the overall mechanical behavior of DED-built components relies on control of thermal history at localized areas. Research at Northwestern University, in collaboration with Argonne National Laboratory, uses in-situ monitoring techniques such as infrared (IR) cameras, an IR two-wave pyrometer to monitor the melt pool, and a high-powered synchrotron to capture the phase change during build. Relationships between temperature, solidification rate and thermal gradient are made with the resulting microstructural characteristic and mechanical behavior at localized areas of each build. Linking thermal history to mechanical behavior of additively-built parts will lead to increased thermal control for optimal properties and open the door to alloy development.