MSE Seminar: Jacob Jensen, Characterization of a High Strength, Refractory High Entropy Alloy, AlMo0.5NbTa0.5TiZr

PhD Candidate advised by Dr. Hamish Fraser

All dates for this event occur in the past.

264 MacQuigg Labs
105 W. Woodruff Ave
Columbus, OH 43210
United States

Abstract

High entropy alloys (HEAs) are a new class of materials that have garnered significant interest over the last decade due to their intriguing balance of properties including high strength, toughness, and corrosion resistance. HEAs appear to offer new pathways to lightweighting in aerospace structural applications but more thorough characterization studies are needed to assess the viability of the recently developed multicomponent materials. One such HEA, AlMo0.5NbTa0.5TiZr, was selected to be the basis for this characterization study due to its strength at elevated temperatures and low density compared to Ni-based superalloys. The HEA microstructure was characterized at multiple length scales using XRD, SEM, TEM and STEM, and EDS. The microstructure was found to consist of a periodic, coherent two phase mixture, where a disordered bcc phase is aligned orthogonally in an ordered B2 phase. In order to gain a comprehensive understanding of the morphology of these phases and obtain a novel perspective of 3D elemental segregation in the alloy, STEM-HAADF micrographs and EDS spectral images were utilized in the tomographic reconstruction of the microstructure, which was inherently difficult to observe through conventional characterization techniques. Through microstructural evolution heat treatment studies, the nanoscale interpenetrating microstructure was discovered to form via a conditional spinodal reaction pathway involving a congruent ordering transformation preceding spinodal decomposition. The microstructure of the alloy was ultimately refined by incremental variations to the base alloy composition in an effort to remove deleterious intermetallic phases adversely affecting ductility. The excellent compressive strength across a range of operating temperatures and ability to tailor the microstructure by compositional modifications indicate that the AlMo0.5NbTa0.5TiZr alloy may be a suitable aerospace structural material.

Bio

Jake received his B.S. degree in ceramics and materials engineering from Clemson University (Go Tigaaaaas!) in 2012 before starting at THE Ohio State the following fall. Jake’s research at tOSU has focused primarily on the characterization of high entropy alloys in collaboration with the Air Force Research Lab in Dayton, OH as part of the AFRL/DAGSI research fellowship program. Following his PhD, Jake will be continuing to work with (and hopefully not break) electron microscopes at FEI, now Thermo Fisher Scientific, as an applications engineer.

Jake has had many notable accomplishments in graduate school including winning every research poster contest he has entered (…by taping an iPad with videos of colorful spinning microstructural features to the poster), but his proudest moments occurred on the pitch/field/court/bench. In addition to being an integral part of an all-MSE intramural dodgeball team that competed in back-to-back championships, Jake humbly led an MSE/WE softball team to the elite 8 of tOSU’s ultracompetitive slow pitch tournament as the one of the best player/managers to ever lace them up on the hallowed grounds of Freddy Beekman Park Wheel Field 4. His fondest memories include arguing with apathetic referees about strike zones and declining a walk after being hit by a pitch, calling his shot, and then striking out swinging on the next pitch. Jake is excited to start the next chapter of his life in sunny Portland, OR but hopes to see all his colleagues and friends at Little Bar for one more round before the big move.