MSE Seminar: Timothy Smith, Orientation and Alloying Effects On Creep Strength in Ni-Based Superalloys

Abstract

Improved modeling of polycrystalline Ni-based superalloys requires a deeper understanding of the effects chemistry and orientation have on different creep deformation modes. Single crystal compression creep tests conducted under varying temperature and stress regimes were performed on two commercially available disk alloys, ME3 and ME501. Utilizing scanning transmission electron microscopy characterization techniques, twinning and superlattice extrinsic stacking faults were determined to be the active deformation mechanisms for the [001] oriented crystals. Ultra-high-resolution structure and composition analysis using energy dispersive spectroscopy, combined with density functional theory calculations, revealed differences in compositional variation along the extrinsic faults inside the g¢ precipitates between the two alloys. For ME501, this compositional variation corresponds with a shear induced solid-state phase transformation from g¢ to h phase. This nanoscale h phase creates a low-energy structure that inhibits thickening of stacking faults into twins, leading to significant improvement in creep properties and represents a newly discovered strengthening mechanism for Ni-base superalloys.

Bio

Tim Smith graduated from Bellefontaine City High School and attended Wright State University, obtaining a bachelor’s degree in Mechanical Engineering. During this time, he had the opportunity to work as a civilian research assistant at Wright-Patterson Air Force Base in the materials directorate. While there, he helped conduct research aimed at improving solid lubricant coatings and thermal interfaces in turbine engines. Afterwards, he decided to pursue his passion for materials science by working towards a PhD under Dr. Michael Mills at The Ohio State University. His thesis concentration is on how crystal orientation and alloying affects creep deformation in Ni-based superalloys through transmission electron microscopy analysis. Other projects that he has contributed to include, dislocation core analysis in high entropy alloys and improvements in characterization techniques using scanning transmission electron microscopy. He is currently a NASA Pathways Intern at the Glenn Research Center working on characterizing additively manufactured superalloys for the SLS engine and plans on working there full-time after graduation. When not working, his hobbies include; weight lifting, playing competitive sports and travelling abroad.