Grain Boundaries, Interfaces, and Surfaces in Ceramics: Fundamental Structure—Property—Performance Relationships: Field Assisted Processes and Mechanics
Sponsored by: ACerS Basic Science Division, ACerS Electronics Division
Program Organizers: Rheinheimer Wolfgang, Forschungszentrum Jülich; Catherine Bishop, University of Canterbury; Shen Dillon, University of California, Irvine; Ming Tang, Rice University; John Blendell, Purdue University; Wayne Kaplan, Technion - Israel Institute of Technology; Melissa Santala, Oregon State University

Tuesday 2:00 PM
October 19, 2021
Room: B244/245
Location: Greater Columbus Convention Center

Session Chair: Xufei Fang, TU Darmstadt; Timofey Frolov, Lawrence Livermore National Laboratory

2:00 PM
Hall-petch Behavior in Stoichiometric and Al-rich Nanocrystalline ZnAl₂O₄: Luis Sotelo Martin¹; Ricardo Castro¹; ¹University of California, Davis
    Nanocrystalline ZnAl₂O₄ is a prime candidate for next-generation armored windows due to its enhanced mechanical properties and high thermal conductivity relative to other metal oxides (e.g. MgAl₂O₄, Al₂O₃, and ALON). Elevated hardness in nanocrystalline oxides has been widely attributed to Hall-Petch strengthening, but there exist conflicting reports on the low grain size limit to this relationship even within the same material system. This study provides a new perspective on the Hall-Petch inversion in nanocrystalline ceramics by showcasing the role of stoichiometry in grain size strengthening. Mechanical behavior was investigated in stoichiometric and Al-rich ZnAl_xO₄ (x = 2.01, 2.87) synthesized by reverse-strike co-precipitation and consolidated using spark plasma sintering. A Hall-Petch breakdown in Vickers hardness was observed only in stoichiometric ZnAl₂O₄ at grain sizes below 19 nm. These results demonstrate improved control of the Hall-Petch behavior in nanocrystalline ZnAl₂O₄ that can be applied in nanoceramic processing and tuning of mechanical properties.

2:20 PM
Surface and Fracture Energy in Layered Ceramics: Oriol Gavalda-Diaz¹; Katharina Marquardt¹; Eduardo Saiz¹; Finn Giuliani¹; ¹Imperial College London
    Layered materials such as graphite or MAX phases are present in many applications and environments such as geology, energy storage or nuclear energy. Their layered structure results in a material with stronger in-(basal)-plane than out-of-plane ({0001} basal plane) bonds. This results in a marked anisotropy in surface energy that can be employed, for instance, to engineer toughening in structural components but also as a way of storing ions in batteries. However, the quantification of interfacial and fracture energies in these materials have proven challenging. In this work we use small-scale fracture testing to evaluate the basal plane failure in two different layered materials: a Ti3SiC2 MAX phase and Highly Ordered Pyrolytic Graphite (HOPG). The goal is to measure basal plane delamination energies in order to understand how they are influenced by chemistry and how they affect fracture.