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Lecture

Strategy of multiple crack deflection at tailored interfaces for damage tolerant materials

Thursday (27.09.2018)
10:30 - 10:45 S1/01 - A1
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The lack of plasticity is a main drawback of utilization of hard ceramic materials in challenging applications where both hardness and toughness are required. Brittle fracture of hard yet brittle polycrystalline ceramics is preferred with respect to the formation of dislocations as it requires more energy than fracture at weak cleavage planes or at grain boundaries. Weak grain boundaries can, however, be used as an effective toughening element if they are specifically designed and orientated with respect to the expected crack path so that the crack becomes repeatedly deflected while dissipating energy during its extension. In that way, catastrophic brittle fracture turns in to a controllable deformation process resulting in enhanced damage tolerance of otherwise brittle materials [1]. Another approach for an effective fracture toughness enhancement is an implementation of additional interfaces into the material structure by incorporating layers well differing in their microstructure and mechanical properties. Such spatial structure and property heterogeneity typically results in suppression of crack propagation by the arrest or deflection of cracks at the interfaces of individual constituents [2]. In this work, we demonstrate a strategy for an effective fracture toughness enhancement by a combination of both these approaches. For that purpose, microstructurally and mechanically heterogeneous multilayer TiN/SiOx films, combining hard crystalline TiN layers with repeatedly tilted columnar grains with a zig-zag fashion and elastic amorphous SiOx layers, were designed with a specific architecture, which resulted in an enhancement of the fracture toughness of more than 150% with respect to the monolithic reference TiN films with a columnar microstructure. In order to reveal toughening mechanisms acting in this system, the microstructure of the films was characterized by position-resolved X-ray nanodiffraction in transmission geometry across their thicknesses and the mechanical response under loading by in-situ micromechanical testing of microcantilever beams inside a scanning and transmission electron microscope. The results document that a dedicated grain boundary and interface design is a powerful tool to control crack formation and propagation with a subsequent fracture toughness enhancement of hard polycrystalline ceramic materials.

Speaker:
Prof. Dr. Rostislav Daniel
Montanuniversität Leoben
Additional Authors:
  • Michael Meindlhumer
    Montanuniversität Leoben
  • Dr. Jakub Zalesak
    Montanuniversität Leoben
  • Bernhard Sartory
    Materials Center Leoben Forschung GmbH
  • Prof. Dr. Christian Mitterer
    Montanuniversität Leoben
  • Prof. Dr. Jozef Keckes
    Montanuniversität Leoben