PVD-Al 2O 3-coated cemented carbide cutting tools

Abstract

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 Al 2O 3 as well as of conductive compound layers such as Ti x Al 1− x N. 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 γ-Al 2O 3 textured in the [440] direction at substrate temperatures as low as 700 °C, which is a much lower temperature than the conventional chemical vapor deposition (CVD) temperatures (1000–1050 °C) for the deposition of the Al 2O 3 polymorphs α and κ. 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 γ-Al 2O 3 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-μm-thick γ-Al 2O 3 layer decreases the wear rate. The γ-Al 2O 3/TiAlN (TiN)-coated inserts exhibit tool lives longer than the single-coated inserts especially at higher cutting speeds.