Wear progressions and tool life enhancement with AlCrN coated inserts in high-speed dry and wet steel lathing

In this paper, the tool life enhancement with a PVD-applied aluminum chromium nitride (AlCrN) coating (named Alcrona) for cemented carbide inserts is investigated. Microstructure wear progressions such as the abrasive wear mechanisms of AlCrN coated cemented carbide tool inserts under dry and wet machining at very high cutting speeds are fully analyzed based on experimental testings. The maximum cutting speed attained in the testing for the turning operations is 410 m/min. Various progressive stages of abrasive wear are observed through the experimental results. These wear results done on AlCrN coated carbide tool inserts are compared with other tool life data reported in the literature. It is found that at 260 m/min, Alcrona performs near 95% better in tool wear than TiAlN coated carbide tool under the same machining conditions. Comparing the performance of Alcrona coated tool inserts with that of TiN coated ones, the former can achieve approximately 33% more depth of cut and can attain higher cutting speed due to better thermal resistance of the coated inserts. This finding verifies the speculation that Alcrona coating enhances tool capability for metal cutting and improves tool life even under harsh cutting conditions. Types of microstructure wear phenomena captured during the course of the experimental study are micro-abrasion, micro-tensile fracture, micro-fatigue, micro-thermal cracks, micro-adhesion, built up edge and micro-attrition. The experimental cutting observations with the underlying tool inserts demonstrate that wear progresses with time and goes through various stages, namely running into wear, steady state wear, and tool failure wear. It is also evidenced that the use of coolant emulsion increases the tool life proportionally with respect to the cutting speeds and reduces the wear progress considerably. SEM and optical microscope images of the tool wear in progress have been taken at various stages to delve into the morphology of the tool inserts. These are interpreted with reasoning in the paper. (c) 2007 Elsevier B.V. All rights reserved.