Design and Fabrication of Additively Manufactured Functionally Graded Materials

Metallic functionally graded materials (FGMs), in which elemental composition, and therefore physicals and mechanical properties, change with position within a single component have a wide range of potential applications. A technological approach that enables grading, in three dimensions, between disparate alloys or metals would transform the engineering design paradigm, opening up an entirely new design space in which properties could be spatially tailored within components. It would no longer be necessary for an engineer to select a single alloy for a component, or rely solely on fixturing or abrupt dissimilar welding or cladding to transition from one alloy to the next; rather, the engineer could specify the spatial properties needed for an application, and design an appropriate FGM to satisfy these requirements simultaneously. The primary aim of this project is to integrate experimental processing, characterization, andcomputational calculations to enable the design of metallic functionally graded materialsfabricated via directed enertrate or layer below, creating a melt pool, and powder feedstock is flowed through nozzles into the melt pool. As the laser scans the horizontal layer, the melt pool solidifies and fuses to the layer below. The process is repeated until the component is complete. DED is a powerful technology that can enable the fabrication of compositionally graded FGMs through the use of two or more powder containers feeding into the nozzles. By changing the relative volume fractions of the powders flowing through the nozzles, the composition of the component can be varied with position, allowing for the spatial tailoring of roperies, such as density, strength, magnetism, and thermal conductivity. The hypothesis of the proposed research is that thermodynamic phase stability and solidification calltifunctional performance of 3D components. Todevelop and demonstrate the approach for designing and fabricating tailored FGMs, we will study a model FGM system of AISI 316 stainless steel (SS316) graded to Ni-base superalloy Inconel 625 (IN625) via DED AM. Both terminal alloys are relevant in todays Naval applications. The technical approach includes: (1) constructing a new multi-component thermodynamic database, to include key elements within SS316 and IN625, using high throughput methods for firs principles calculations based on density functional theory (DFT) and thermodynamic modeling based on the CALPHAD (CALculation of PHAse Diagram) approach; (2) performing thermodynamic equilibrium calculations, Scheil simulations of solidification, and kinetic simulations of phase transformations to design compositional pathways, from SS316 to IN625, along which the formation of detrimental topologically close packed (TCP) phases is minimized;(3) fabricating the designed FGMs via DED AM; (4) experimentally characterizing location dependent chemistry, phases, and mechanical properties in the FGMs; (5) comparing experimentally observed and computationally predicted phases, and if discrepancies exist, using the new data to further improve the thermodynamic database using high throughput methods, finally comparing computational predictions using the refined database with experimental findings. If ll include further kinetic simulations and additional high throughput DFT-based calculations and CALPHAD modeling to refine thermodynamic and atomic mobility databases in projects beyond this proposed 3-year project. This research will provide a foundation of fundamental understanding of phase transformation in AM needed for the design of FGMs and new alloys for AM, including high entropy alloys.