Mechanical properties, structure and performance of chemically vapor-deposited and physically vapor-deposited coated carbide tools

Abstract

The relative merits of TiN coatings produced by physical vapor deposition (PVD) and chemical vapor deposition (CVD) on cemented carbide tools are examined by a comparison of microstructure, mechanical properties and metal-cutting performance of two hard metal alloys in the uncoated condition and after coating with either type. Intrinsic microstructural differences between PVD and CVD coatings are attributed to the differences in deposition process conditions. It was found that the transverse rupture strength (TRS) of the ground substrates decreased after CVD coating or high temperature treatment but remained relatively unchanged after PVD coating. The TRS values are correlated with the residual stress states of the TiN coating and the WC phase of the underlying substrate. The optimum condition for high TRS and minimum edge chipping sensitivity was obtained in the ground and PVD coated hard metal where the TiN coating and the WC phase were under relatively high residual compression. The best metal-cutting performance in both turning and milling tests was obtained with the substrate exhibiting high deformation resistance and the PVD TiN coating which had a higher microhardness and beneficial compressive residual stress.