Influence of B content on microstructure, phase composition and mechanical properties of CVD Ti(B,N) coatings

Michael Tkadletz, Nina Schalk, Alexandra Lechner, Lukas Hatzenbichler, David Holec, Christina Hofer, Marco Deluca, Bernhard Sartory, Andrey Lyapin, Jaakko Julin, Christoph Czettl

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Abstract

Within this work the effect of the B content on the microstructure, phase composition and mechanical properties of CVD Ti(B,N) coatings is investigated. Ti(B,N) coatings with B contents from 0 (fcc-TiN) to ∼5, ∼15, ∼30, ∼45 and 66 (h-TiB 2) at.% have been deposited by CVD. The elemental composition of the coatings was confirmed by ERDA and their microstructure was investigated using XRD and SEM. With increasing B content, a transition from a fcc to a h-dominated structure via dual-phase fcc/h-Ti(B,N) was observed, which was accompanied by a decreasing grain size from the µm to nm range. Combinatorial use of Raman spectroscopy, XPS and APT measurements indicated B-rich grain boundary segregations and the formation of increasing amounts of h-Ti(B,N) 2 clusters embedded within an fcc-Ti(B,N) matrix up to B contents of ∼30 at.%, while for ∼45 at.% B the matrix was predominantly composed of h-Ti(B,N) 2. Complementary ab initio calculations predicting the phase formation confirmed the interpretation of the experimental results. In terms of the mechanical properties, nanoindentation measurements and micromechanical testing revealed a rise in hardness from ∼18 to ∼41 GPa and an increasing fracture stress and toughness from ∼7 to ∼13 GPa and ∼4.6 to ∼5.5 MPam 1/2, respectively, by increasing the B content up to ∼30 at.%. In contrast, a significant drop in hardness, fracture stress and fracture toughness was observed at ∼45 at.% B. Thus it can be concluded, that both h-TiB 2 and dual-phase fcc/h-Ti(B,N) coatings with maximized B content yield superior properties over TiN and consequently improved performance.

Original languageEnglish
Article number101323
Number of pages9
JournalMaterialia
Volume21.2022
Issue numberMarch
DOIs
Publication statusPublished - 10 Jan 2022

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