Watching the grain boundaries slide S. Wei, C. C. Tasan∗ Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA02139, U.S.A. ∗ tasan@mit.edu Keywords: intergranular fracture; thermal activation; in situ microscopy Unlike their strengthening contributions at ambient temperature, grain boundaries are the Achilles’ Heel of polycrystalline alloys at elevated temperatures. The enhanced atomic motion diversifies the plasticity micro-mechanisms, complicating the resultant damage and fracture mechanisms. Grain boundary sliding is one such example. Provided the extensive efforts using post-mortem characterizations, time-resolved studies of grain boundary sliding are scarce, and unambiguous understanding of its role in plastic strain accommodation and damage nucleation is still lacking. In this talk, we will present an in situ SEM-based high-temperature investigation of grain boundary sliding in a model Co-based alloy [1,2], emphasizing the mechanistic insights into plastic flow and damage inception. We will show that grain boundary sliding is not only correlated with a rare serrated-to-stable plastic flow transition, but also accommodates more than 20 % plastic strain at 750 ◦C under a strain rate of 10−4 s−1. With the aid of electron channeling contrast imaging, we also underpin the involvement of dislocation cross-slip in accommodating grain boundary sliding. Based on the testing conditions and the experimental observations, a series of deformation microevents are identified and their roles in intergranular damage nucleation will also be discussed. References [1] Wei, S.L., Tasan, C.C. (2023). On the plastic deformation of a CoCrFeNiW-C alloy at elevated temperatures: Part II. Grain boundary sliding and damage mechanisms. Acta Materialia, 252, 118898. [2] Wei, S.L., Moriarty, D.P., Xu, M., LeBeau, J.M., Tasan, C.C. (2023). On the plastic deformation of a CoCrFeNiW-C alloy at elevated temperatures: Part I. Serrated plastic flow and its latent dynamics. Acta Materialia, 242 118430. 31
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