Oliver Preuß* | Enrico Bruder | Fangping Zhuo | Sebastian Bruns | Kuan Ding | Karsten Durst | Jürgen Rödel | Xufei Fang

Department of Materials and Earth Sciences, Alarich-Weiss-Str. 2, 64287 Darmstadt, Technical University of Darmstadt

*Email: preuss@ceramics.tu-darmstadt.de

Dislocation-tuned functionality in ceramic oxides is gaining serious research attention, with promising proofs-of-concept realized most recently including increased electrical conductivity [1], ferroelectric properties [2] and superconductivity [3]. Yet introducing dislocations into brittle ceramics remains a grand challenge, especially at room temperature. Here, we demonstrate a simple method [4] using a large spherical tip (2.5 mm in diameter) to cyclically indent the sample surface to mechanically tune the dislocation densities over 3-4 orders of magnitude (from 1010 m-2 up to 1014 m-2) in single-crystal KNbO3. A crack-free plastic zone size of ~200 μm is achieved on the sample surface at room temperature. More interestingly, both damage tolerance (threshold for crack initiation) and fracture toughness (threshold for crack propagation) have been improved. To be specific, under a critical load with Vickers indentation inside the plastic zone, the crack initiation is fully suppressed. Beyond the critical load, the crack length is decreased by over 60%. The interactions of crack tip and dislocations as well as other microstructure are examined in detail by optical microscopy, electron channelling contrast imaging, and piezoresponse force microscopy methods to shed light on the microstructure evaluation and its impact on the mechanical properties. Our findings open new questions that may raise interests for the tribology studies in ductile ceramics, including but not limited to the dislocation density increase, domain wall fragmentation, and further crack formation induced by cyclic ball indentation.

References

[1] Muhammad, Q. K. et al., Nano Energy, 2021, 85, 105944

[2] Höfling, M. et al., Science, 2021, 372, 961-964

[3] Hameed, S. et al., Nat. Mater., 2022, 21, 54-61

[4] Okafor, C. et al., J. Am. Ceram. Soc. 2022, 105, 2399–2402

Personal information (presenter):

My name is Oliver Preuß and I am currently a PhD student in the Department of Materials and Earth Sciences at Technical University of Darmstadt. I have been working on damage tolerance and toughening of diamond coatings and ceramic oxides during my Bachelor and Master theses.