Material System Design Tool to Enable Functionally Graded Materials

The Phase I research objective is to demonstrate feasibility of a material system design tool for multi-material Functionally Graded Materials (FGMs) to improve the mechanical performance and environmental protection of structural and subsystem components. The FGM designs will be created using an ICME-based tool that combines thermodynamic modeling with AM process modeling for the Directed Energy Deposition (DED) process. The FGMs will include material combinations with poor thermodynamic compatibility, which requires the use of buffer materials and the prediction of a material composition gradient pathway.  The composition gradient pathway will consist of transitions between the base material, one or more buffer layers, and the target material. Starting with the base and target materials, and choices for the buffer layers, the ICME-based system will include algorithms to avoid deleterious phases, mitigate cracking, and predict the effect of DED process parameters on critical parameters such as dilution profile and layer thickness, as follows: Thermodynamic modeling will be used to design the composition gradient pathway to: (i) avoid the formation of deleterious phases, (ii) tailor the thermal expansion coefficient, and (iii) minimize susceptibility for hot cracking. DED process modeling will be used to achieve the composition gradient, either continuous or discrete, by predicting DED processing parameters (e.g., scan path, powder feed rate, standoff distance, power, scan velocity, and hatch spacing) to manage dilution, thickness of the FGM transition zone, thermal stress, and the evolution of thermal history during DED as a function of the FGM sample geometry. The Phase I will demonstrate this methodology to design two FGM systems and buffer elements, namely between (i) Ti-6Al-4V and IN718, and (ii) 316L and Cu. The Phase I Option will demonstrate design of a third FGM system and buffer elements between 316L and Ti-6Al-4V. Each FGM design will be validated by producing FGM samples with buffer materials, and characterizing their microstructure and mechanical properties. Phase II will demonstrate the tool by designing five or more FGM systems that are useful to Navy applications.