Deposition of Ti–B–N (single and multilayer) and Zr–B–N coatings by chemical vapor deposition techniques on cutting tools

Coatings in the systems Ti–B–N and Zr–B–N were investigated because of their high potential in metal cutting. Therefore TiN, TiB2, TiBN, multilayers like [TiN–TiB2]x or [TiN–TiBN]x (x=3–100), ZrN and ZrBN coatings were deposited on cemented carbides using chemical vapor deposition (CVD). When keeping the boron content larger than 5 wt.% TiBN, coatings resulted in mixtures of TiN and TiB2. The TiN/TiB2 ratio, microstructure, hardness and wear resistance of the coatings were controlled by varying deposition temperatures and gas flows in the CVD process. Compared to TiN and TiB2 coatings, deposition rates in TiBN coatings became noticeably higher. TiBN coatings exhibited high hardness (HV 3500–5000) at moderate deposition temperatures (700–900 °C). Deposition temperatures below 900 °C successfully suppressed boron diffusion and formation of a CoWB phase on the surface of the cemented carbide tool. Due to the moderate deposition temperatures, TiBN coatings showed very good adhesion. Boron diffusion was responsible for poor adhesion in TiB2 coatings. For milling tests TiN, TiB2, TiBN, multilayer coatings like [TiN–TiB2]x or [TiN–TiBN]x with a TiB2 content of 10–95%, ZrN and ZrBN were investigated. All TiBN coatings showed good wear resistance against abrasion. At a certain level of the TiN/TiB2 ratio, the TiBN coatings suppressed thermal cracks. Although the Zr–B–N and Ti–B–N systems seemed to be very similar, results showed differences in deposition chemistry and properties.