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

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 similar to 5, similar to 15, similar to 30, similar to 45 and 66 (h-TiB2) 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 mu m 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 similar to 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 similar to 18 to similar to 41 GPa and an increasing fracture stress and toughness from similar to 7 to -13 GPa and similar to 4.6 to -5.5 MPam(1/2), respectively, by increasing the B content up to similar to 30 at.%. In contrast, a significant drop in hardness, fracture stress and fracture toughness was observed at similar to 45 at.% B. Thus it can be concluded, that both h-TiB2 and dual-phase fcc/h-Ti(B,N) coatings with maximized B content yield superior properties over TiN and consequently improved performance.

Automated summary

The study investigated the effect of B content on the microstructure, phase composition, and mechanical properties of CVD Ti(B,N) coatings. Experimental results showed that increasing B content led to changes in microstructure, with hardness and toughness increasing up to a certain B content before showing a significant drop.