Design of Ni-Base Superalloys for Additive Manufacturing

Illinois Institute Of Technology, Chicago IL

Investigators

Abstract

Additive manufacturing techniques can provide immense design flexibility for the fabrication of geometrically complex metallic structures. For production of nickel-based superalloy components such as those used in advanced gas turbine engines, these manufacturing techniques may enable transformational design concepts and contribute to the development of ultra-efficient power systems for aerospace propulsion, space exploration and power generation. One of the major challenges associated with additively manufactured Ni-based superalloy components is that the extreme temperature gradients encountered during processing negatively impact the underlying structure and mechanical properties of the material. This award supports fundamental research aimed at understanding how to make Ni-based superalloys amenable for processing via additive manufacturing. By introducing benign additives, Ni-based superalloys that are tolerant to extreme thermal cycles can be developed. This multidisciplinary research program will assist in the training and education of engineering students, and will bring exposure to scientific research to high school students and teachers through outreach programs. Additive manufacturing processes that utilize a laser power source tend to produce parts with a highly textured grain structure due to the directional nature of the governing heat transfer conditions during the build. The characteristic columnar grain structure induces a high degree of mechanical and physical anisotropy which may lead to cracking or "hot tearing" when a continuous, interdendritic eutectic phase forms along the grain boundaries. The aim of this research is to establish a fundamental understanding of inoculant-induced heterogeneous nucleation in additively manufactured Inconel 718. Varying levels of metal, intermetallic and reactive oxide particles comprised of elements common to Inconel 718 will be systematically blended with the powder feedstock and used to additively build structures in a directed metal deposition (DMD) and powder bed selective laser melting (SLM) system. The effectiveness of these inoculants on modifying the resulting grain structure of the fabricated structures will be evaluated using advanced characterization techniques. Systematic assessment of the interfacial reaction products along the inoculant interfaces will enable quantification of the mechanisms governing solidification and free growth of the solid during additive manufacturing. Nano-scale 3D local electrode atom probe (LEAP) characterization will be performed on the interface to assess the composition and structure. This will enable the development of an optimized post-fabrication thermal treatment that will enable dissolution and homogenization of the residual inoculant particles. The experimental results and observations will be applied to develop phenomenological and physics-based models that are expected to suggest new directions for the development materials amenable for additive manufacture.