Hahn, R., Tymoszuk, A. A., Wojcik, T., Ntemou, E., Hunold, O., Polcik, P., Kolozsvári, S., Primetzhofer, D., Mayrhofer, P. H., & Riedl-Tragenreif, H. (2023). Unraveling the superlattice effect for hexagonal transition metal diboride coatings. Scripta Materialia, 235, Article 115599. https://doi.org/10.1016/j.scriptamat.2023.115599
Superlattice structures enable the simultaneous enhancement in hardness (H) and fracture toughness (KIC) of ceramic-like coatings. While a deeper understanding of this effect has been gained for fcc-structured transition metal nitrides (TMN), hardly any knowledge is available for hexagonal diborides (TMB₂). Here we show that superlattices can—similarly to nitrides—increase the hardness and toughness of diboride films. For this purpose, we deposited TiB₂/WB₂ and TiB₂/ZrB₂ superlattices with different bilayer periods (Λ) by non-reactive sputtering. Nanoindentation and in-situ microcantilever bending tests yield a distinct H peak for the TiB₂/WB₂ system (45.5 ± 1.3 GPa for Λ = 6 nm) but no increase in KIC related to a difference in shear moduli (112 GPa). Contrary, the TiB₂/ZrB₂ system shows no peak in H, but for KIC with 3.70 ± 0.26 MPa∙m1/2 at Λ = 4 nm originating from differences in lattice spacing (0.14 Å), hence causing coherent stresses retarding crack growth.
en
Research facilities:
Röntgenzentrum Universitäre Service-Einrichtung für Transmissionselektronenmikroskopie
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Research Areas:
Surfaces and Interfaces: 50% Structure-Property Relationsship: 20% Non-metallic Materials: 30%
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