Pélisson, Aude. Al-Si-N transparent hard nanostructured coatings. 2009, PhD Thesis, University of Basel, Faculty of Science.
Official URL: http://edoc.unibas.ch/diss/DissB_8830
The hardness and biaxial residual stress of the ﬁlms were studied by nanoindentation and mechanical proﬁlometry, respectively. While hardness is about 20–25 GPa in pure AlN and SiNy , it reaches 32 GPa in Al-Si-N thin ﬁlms at 8–12 at.% of Si, concentration at which a negligible residual compressive stress (< 0.5 GPa) is measured. This hardness enhancement over a broad composition range is explained by the interplay of several hardening mechanisms: on the one hand, the formation of an Al-Si-N solid solution and the grain reﬁnement cause a reduction of dislocation activity within the crystalline phase; on the other hand, as the two-phase nanocomposite structure is formed, the presence of SiNy at the GBs hinders deformation by GB sliding. The optical properties of the ﬁlms are moreover only little inﬂuenced by variations of the ﬁlm composition: a refractive index in the range 2.00–2.12 at 633 nm wavelength, corresponding to 80 % light transmission, is measured. The structural, mechanical and optical properties of the ﬁlms are stable upon annealing for 2h at 1000◦ C in argon. Al(-Si-)N/SiNy multilayer coatings were deposited as a model system to study interfacial properties which are diﬃcult to access in 3D nanocomposite structures. XRD and high-resolution TEM reveal that up to 0.7–1.0 nm (∼ 2.5–3.5 monolayers) of crystalline silicon nitride can be epitaxially stabilized on an AlN (001) surface. This ﬁnding reinforces the assumption of an ordering of the SiNy GB layer and the formation of coherent interfaces in Al-Si-N nanocomposite coatings. It provides an explanation for the moderate hardness enhancement obtained in Al-Si-N coatings that probably results of a gradual structural transition at the interfaces. Moreover ﬁnite solubility in the Al-Si-N system is associated to a moderate thermodynamic driving force for phase separation. This probably calls for a composition gradient at the interfaces, all the more as a non-equilibrium deposition process is used. Interfaces in the Al-Si-N system are therefore expected to be penetrable obstacles e.g for dislocations upon plastic deformation. If incorporated at the grain boundaries, oxygen impurities may also lower the interface cohesion energy and facilitate GB sliding. The present work shows that optically transparent coatings can be produced of Al-SiN with a hardness exceeding 30 GPa at low deposition temperatures. The investigations presented in this thesis provide a thorough understanding of the material and of the evolution of its properties with the silicon content in the ﬁlms.
|Advisors:||Hug, Hans J.|
|Committee Members:||Oelhafen, Peter C. and Patscheider, Joerg and Schneider, Jochen M.|
|Faculties and Departments:||05 Faculty of Science > Departement Physik > Physik > Experimentalphysik (Hug)|
|Bibsysno:||Link to catalogue|
|Number of Pages:||234|
|Last Modified:||30 Jun 2016 10:41|
|Deposited On:||16 Oct 2009 07:24|
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