In Situ Characterization of Effect of Rapid Thermal Cycling During Additive Manufacturing on Deformation-Induced Transformations and Micro-Mechanical Properties

This award supports fundamental research on additive manufacturing of metallic materials, in which the primary goal is to uncover the relationships between thermal processing cycles, microstructure, and mechanical properties in parts made through additive manufacturing. In the laser-based additive manufacturing techniques studied here, a powder feedstock material is delivered to a desired location, and a laser locally melts the powder to fuse it to the material below, building up a component one layer at a time. The thermal cycles generated by the subsequent laser passes affect the microstructure of the underlying material, and therefore the mechanical properties (e.g., strength and ductility) of the component. Here, two materials systems will be examined: a titanium alloy that undergoes diffusion-based phase transformation upon cooling, and a stainless steel alloy that undergoes diffusionless deformation-induced phase transformation upon mechanical loading. This research aims to: elucidate the effect of thermal history on the local microstructure and mechanical properties in additive manufactured materials, and develop physically based plasticity models that take into account the effect of thermal history, resulting microstructure, and microstructural evolution on the local plasticity properties.

Additive manufacturing has great potential to transform U.S. manufacturing, allowing for the production of custom-designed structural components for countless applications where the cost to develop tools for forging, casting, or forming of metal components is not warranted for the small number required (e.g., replacement parts for aging Department of Defense airplanes, ships, and submarines) in an economical procedure with less waste material than traditional subtractive manufacturing. Fundamental research will lead to the development of fully integrated computational models in which the processing parameters (e.g., laser power, path, and speed) are determined to produce an end net shape component with specified mechanical properties, providing the infrastructure for a design space with practically no limitations on geometries that can be fabricated.