A new look at CVD

Most cutting tools are coated via the physical vapor deposition process but chemical vapor deposition still has its place, depending on the application. A PVD coating is effective, for example, when endmilling, where a tool heats and cools as it enters and exits the cut, but a CVD coating better protects turning tools, which are in constant contact with the workpiece, said Martin Gardner, global product manager for ATI Stellram. “If we want to rough machine something, then we tend to use CVD because of the amount of heat being generated.”

Courtesy of ATI Stellram

The NL turning inserts from ATI Stellram have a thick CVD coating applied with a new process to control layer thickness.

Gardner added that conventional CVD coatings are from 9µm to 12µm thick, but the toolmaker developed an advanced CVD coating process that deposits multilayer coatings from 20µm to 25µm thick for its five new NL grade turning inserts: NL200, NL250, NL300, NL400 and NL920. The NL grades have a combination of four or five coating layers to suit specific applications, such as NL200 for cast iron.

The five layers are a TiN adhesion and finishing layer, a medium-temperature TiCN layer for wear resistance at high temperatures, a hard alpha-Al2O3 layer with a thermal barrier to resist wear at high surface speeds, a TiN/medium-temperature TiCN/TiN layer for adhesion and wear resistance and a high-temperature TiCN/TiN layer for adhesion and wear resistance at low to medium surface speeds.

To provide an overall thicker CVD coating, Gardner said the new deposition process properly mixes the coatings so they adhere to the substrate and other coatings without chipping or flaking.