Wear and failure mechanisms of multilayered PVD TiN/TaN coated tools when milling austenitic stainless steel

As compared to todayʹs single layered coatings, multilayered PVD coatings offer improved mechanical and tribological properties. This work reports on milling austenitic stainless steel with cemented carbide tools coated with multilayered coatings. The purpose was to increase the understanding of wear and failure mechanisms during milling of austenitic stainless steel. Multilayered PVD TiN/TaN coatings deposited on cemented carbide substrates are presented and compared with single-layered TiN and TaN. It was found that the tool life was mainly limited by chipping of the cutting edge, caused by crack interaction. A mechanism for comb crack nucleation and growth is presented, which accounts for the beneficial effects of multilayered coatings on milling tools. Some additional mechanical and chemical wear mechanisms observed are also presented and discussed. Multilayered coatings made up of TiN and TaN proved to be suitable for milling austenitic stainless steel. TaN has shown to be too brittle to work well as a single-layer coating. However, by layering TaN with TiN, a tougher coating can be obtained. By doing so, a coating material with a small tendency to interact with the austenitic stainless steel is obtained. As a result of the smaller interaction, less comb cracks are formed.