March_2022_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A R C H 2 0 2 2 1 6 A dditive manufacturing (AM) pro- vides a tremendous opportunity to synergistically couple materi- als, design, and manufacturing strate- gies. One can strive toward fabricating parts with targeted properties by en- abling site-specific metal-metal or met- al-ceramic compositional transitions. Parts with site-specific composition and hybrid microstructures are relevant in an application space where certain sections of the component encounter considerably higher temperatures than others. For example, one may design composite parts with Nb-base refracto- ry alloys for hotter sections (requiring increased high temperature strength and creep resistance) while opting for relatively low cost and low gamma prime containing IN718 at zones operat- ing below 1400°F [1-4] . Note that conven- tional welding and joining approaches are adopted to deal with parts operat- ing at widely varying temperatures. For example, Fig. 1 illustrates a commercial, bimetallic joined struc- ture for an engine part where the per- formance requirements of the airfoils (SX material) and disk section are quite different. Even within a turbine disk, the performance requirement for the out- er rim of the disk needs material with a larger-grained microstructure that is creep resistant as opposed to the low cycle fatigue (LCF)-limited, fine-grained core of the disk [5] . Although conventional joining processes are limited in their ability to create components comprised of multi- ple dissimilar materials, AM processing provides an approach to circumvent these restrictions through composition- ally grading materials. Considerations include: Feasibility: The approach allows the transition from one terminal alloy composition to another, even when they are nonweldable [4] . In this case, a gradual compositional gradation via an additive route makes such a transition feasible. In some cases, an intermediate EXPLORING GRADIENT PATHWAYS IN HIGH TEMPERATURE, FUNCTIONALLY GRADED ALLOYS A new approach aims to fabricate parts with targeted, site-specific properties for a wide range of applications in extreme environments within the aviation, space, and energy sectors. Soumya Nag, Brian Jordan, Ke An, and Jaimie Tiley, FASM* Oak Ridge National Laboratory, Tennessee Chuan Zhang and Fan Zhang CompuTherm LLC, Middleton, Wisconsin *Member of ASM International Fig. 1 — Illustration of site-specific property requirements in an aircraft engine part. The airfoil sees much higher temperature than the blade, hence the former is SX as opposed to PX disks. Within the disks there is a need for zone-based microstructures – LCF-limited core with finer grain size and creep-limited rimwith coarser grains [5] .