Bias voltage effect on the mechanical properties, adhesion and milling performance of PVD films on cemented carbide inserts

The potential of coated cutting inserts to withstand effectively cutting loads depends among others on the coating's mechanical properties and adhesion. These data are strongly affected by the applied PVD process parameters, even if the coatings comprise the same chemical composition. Hereupon, one significant parameter is the bias voltage during the film deposition. For detecting its effect on the occurring film mechanical properties, adhesion and wear behavior, PVD TiAlN coatings were deposited on cemented carbide inserts at diverse bias voltages. The properties of the manufactured coatings were determined via FEM-supported results evaluation of nanoindentations, perpendicular and inclined impact tests. Coatings produced at elevated bias voltage possess comparably increased mechanical properties and fatigue endurance. However, their adhesion deteriorates, thus reducing the coated inserts cutting performance especially when a good adhesion during a material removal process as in milling hardened steel is required. Relevant FEM calculations of this process were employed to explain the wear evolution on the flank and rake of the used coated tools considering their cutting edge geometry and their actual film's mechanical properties and adhesion dependent upon the applied bias voltage during the coating deposition.