Speaker and Affliation:
Prof. Tresa Pollock
Alcoa Distinguished Professor of Materials & Associate Dean of Engineering
Professor of Materials Science and Engineering
University of California
26th March, 2021 (Friday), 09:35 AM (India Standard Time)
Intermetallic precipitates are among the most effective strengthening agents for structural metallic alloys. Ordered intermetallic precipitates are generally resistant to shearing by dislocations, resulting in strengthening, but are also effective for damage tolerance since they will ultimately deform plastically in the presence of high local stresses. Ni-base superalloys are prototypical examples wherein L12 precipitates strengthen the solid solution nickel alloy matrix to high fractions of melting. The contribution of precipitate shearing to overall plasticity in Ni-base alloys has to date been assessed via post-deformed transmission electron microscopy studies of mechanically deformed samples. We report here on a novel in-situ approach to studying precipitate shearing and faulting in superalloys. This approach integrates MEMs straining stages with a STEM detector in the SEM, enabling dynamic observations of defects and their interactions with precipitates, faults and boundaries, studied with diffraction contrast. New insights on the frequency of shearing and the faulting mechanisms will be reported and the implications for alloy design will be discussed.