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FOCUS ISSUE

PLASTICITY AND FRACTURE AT THE NANOSCALES

Revealing the ductility of nanoceramic MgAl2O4 Bin Chen1,a), Yuanjie Huang1, Jianing Xu1, Xiaoling Zhou1, Zhiqiang Chen1, Hengzhong Zhang1, Jie Zhang2, Jianqi Qi2, Tiecheng Lu2, Jillian F. Banfield3, Jinyuan Yan4, Selva Vennila Raju4, Arianna E. Gleason4,b), Simon Clark4, Alastair A. MacDowell4 1

Center for High Pressure Science & Technology Advanced Research, Pudong, Shanghai 201203, China Department of Physics, Sichuan University, Chengdu, Sichuan 610064, China 3 Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA 4 Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, California 94720, USA a) Address all correspondence to this author. e-mail: [email protected] b) Present address: SLAC National Accelerator Laboratory, Menlo Park, CA 94,305, USA. 2

Received: 1 October 2018; accepted: 11 March 2019

Ceramics are strong but brittle. According to the classical theories, ceramics are brittle mainly because dislocations are suppressed by cracks. Here, the authors report the combined elastic and plastic deformation measurements of nanoceramics, in which dislocation-mediated stiff and ductile behaviors were detected at room temperature. In the synchrotron-based deformation experiments, a marked slope change is observed in the stress–strain relationship of MgAl2O4 nanoceramics at high pressures, indicating that a deformation mechanism shift occurs in the compression and that the nanoceramics sample is elastically stiffer than its bulk counterpart. The bulk-sized MgAl2O4 shows no texturing at pressures up to 37 GPa, which is compatible with the brittle behaviors of ceramics. Surprisingly, substantial texturing is seen in nanoceramic MgAl2O4 at pressures above 4 GPa. The observed stiffening and texturing indicate that dislocation-mediated mechanisms, usually suppressed in bulk-sized ceramics at low temperature, become operative in nanoceramics. This makes nanoceramics stiff and ductile.

Introduction Ceramics are typically resistant to heat, wear, and corrosion, and thus have been widely used in a range of applications that include kitchen wares, dental implants, lasing materials, missile domes, and the protective tiles of space shuttles. However, ceramics are brittle. Ductility, a valued characteristic of many metals, is rarely seen in ceramics at room temperature. Ceramics break easily and therefore are limited in their use for high-stress applications. If their brittleness can be overcome, their applications could be much expanded. To achieve ductility in ceramics, making ceramics with nanocrystals has attracted a lot of interest in the last several decades [1, 2, 3, 4]. Since the late 1980s, many researchers have proposed that brittle ceramics, which lack sufficient dislocation activity, may exhibit improved ductility in the nanometer range because of greatly increased diffusivities [2, 5, 6]. The deformation of nanocrystalline materials remains controversial [7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17]. I