Nickel-base superalloys are extensively used in the fabrication of gas turbine hot-section components as this class of alloys offers higher yield strength with increase in operating temperature due to the presence of secondary phase precipitates. Traditionally, hot-section components are manufactured using conventional manufacturing methods such as investment casting. However, a realization of complex designs with functionally graded materials, microstructures or properties are not feasible with the conventional manufacturing methods. Additionally, if the parts suffer material loss due to prolonged service or manufacturing defects, it is impossible to repair the superalloy components using conventional methods as these alloys are extremely difficult to weld. Additive manufacturing (AM)-based processes offer an alternative as, when properly controlled, they have shown encouraging results in depositing as-desired microstructures through optimization of processing conditions for a range of metallic material systems. However, fundamental research to advance the scientific understanding of the AM-based processing of high-performance structural materials such as nickel-base superalloys is lacking. Furthermore, lack of knowledge on how the material microstructures and properties are affected by the processing parameters significantly hinders the capabilities of the AM-based processes in producing high quality parts in nickel-base superalloys. The goal of this dissertation research is to advance the scientific understanding of the underlying physics of melting and re-solidification, microstructure, and properties of various nickel-base superalloys deposited using a powder bed fusion (PBF)-based AM process, scanning laser epitaxy (SLE). Multiphysics-based simulation, experimental validation, and advanced materials characterization techniques are combined to advance the AM-based processing of nickel-base superalloys enabling repair of hot-section components with as-desired microstructure and properties.
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MATIN Development Team