Anakkavur T. Santhanam

Performance of PVD TiN, TiCN, and TiAlN coated cemented carbide tools in turning

Abstract Ion-plated PVD TiN, TiCN, and high-ionization sputtered PVD TiAlN coatings were deposited on WC–6wt%Co hardmetal inserts. Microstructural and mechanical properties of the coatings and substrate were characterized. Coated tools were evaluated in turning of Inconel 718, medium carbon SAE 1045 steel, and ductile iron at low and high cutting speeds. TiAlN coated tools showed the best metalcutting performance, followed by the TiCN and TiN coated tools. The superior performance of the TiAlN coated tools, which was even greater at higher speeds, is related to the coatings higher resistance to abrasive and crater wear. These characteristics are a result of the higher hot hardness and oxidation resistance of TiAlN at the temperatures normally encountered at the tool tip during machining operations.

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.

Comparison of the steel-milling performance of carbide inserts with MTCVD and PVD TiCN coatings

This study is a comparison of the performance of PVD-TiN-, PVD-TiCN-, and MTCVD-TiCN-coated milling inserts. It is shown that metal-cutting conditions and insert geometry dictate the optimum performance for each type of coating. The importance of compressive residual stress in PVD coatings in delaying the initiation of damaging cracks at the edge is evident in these results. Conditions in which thermal shock is not severe, such as dry milling or lower-speed wet milling and the use of sharp cutting edges, are shown to maximize the performance of the PVD-TiCN-coated tool. On the other hand, the MTCVD coating necessitates a strong cutting edge geometry on a tough substrate to obtain good performance, in wet milling. Practical productivity implications, including environmental concerns, are considered.