PVD-Al2O3-coated cemented carbide cutting tools

With the introduction of the bipolar pulsed dual magnetron sputtering (BP-DMS) technique, a wide range of opportunities has opened up for the deposition of insulating layers such as Al2O3 as well as of conductive compound layers such as TixAl-xN. In BP-DMS, two magnetrons in a pair alternately act as a cathode and an anode; during the cathode phase, the target is sputter-cleaned, hence ensuring a metallic surface during the anode phase and a stable long-term operation. At high-enough frequencies (25-50 kHz), possible electron charging of insulating layers will be suppressed and the otherwise troublesome phenomenon of arcing will be limited. The BP-DMS method has made it possible to deposit hard ( > 2000 HV) nanocrystalline gamma-Al2O3 textured in the [440] direction at substrate temperatures as low as 700 DGC, which is a much lower temperature than the conventional chemical vapor deposition (CVD) temperatures (1000-1050 DGC) for the deposition of the Al2O3 polymorphs a and K. In this paper, a study of the process, in terms of recording the process characteristic data and evaluating the influence of magnetic field has been done. For a set of parameters, cemented carbide cutting inserts have been coated and tested. Inserts with a double layer of gamma-Al2O3 and TiAlN or TiN have been evaluated in cutting operations such as turning, threading, and end-milling, often with machining conditions (cutting data) more suitable for physical vapor deposition (PVD)- than CVD-coated tools. Some results are presented in this paper. It has been shown that the addition of a 2- mum-thick gamma-Al2O3 layer decreases the wear rate. The gamma-Al2O3/TiAlN (TiN)-coated inserts exhibit tool lives longer than the single-coated inserts especially at higher cutting speeds.