Nanocomposite coatings within the system Ti–B–N deposited by plasma assisted chemical vapor deposition

Ti–B–N coatings have been deposited by plasma assisted chemical vapor deposition (PACVD) onto tool steels and were evaluated with respect to their structure, mechanical and tribological properties. The boron content of the coatings investigated was varied from 7 to 52 at. %. All coatings were compared to single-phase TiN and TiB2 films. For increasing boron content, a nanoscaled dual-phase structure consisting of different amounts of TiN and TiB2 phases was found. Likewise, the hardness increased from 20 to a maximum of 36 GPa. VDI indentation as well as surface fatigue testing, where cyclic loads up to 80 kN are applied to the tool surface by cylindrical cemented carbide indenters, indicated excellent coating adhesion. Biaxial stresses were evaluated using a cantilever beam method. In ball-on-disk testing, the lowest friction coefficient of about 0.17–0.22 against a 100Cr6 ball was yielded for TiN coatings and for coatings with boron contents below 9 at. % B. Boron additions exceeding this limit resulted in increasing friction coefficients of up to 0.8. Abrasive wear rates determined using a microscale abrasion tester decreased continuously from 6.9×10−13 to 8.2×10−14 m2/N with increasing boron content from 7 to 52 at. %, respectively. The results obtained indicate that PACVD Ti–B–N coatings are an excellent choice for tribological applications under severe conditions like deep drawing or cold forming.

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