Improvement of high-speed turning performance of Ti–Al–N coatings by using a pretreatment of high-energy ion implantation

Abstract

Titanium–aluminium–nitride (Ti–Al–N) coatings were deposited by close-field unbalanced magnetron sputtering on WC-6 wt.%Co inserts at 450 °C. In the early stage of the experiment, ion implantation of titanium at high energies was performed with a metal vapor vacuum arc (MEVVA) source ion implanter in order to create a titanium composition gradient layer in the surface of tools for subsequent buffer layer and coating depositions. After the deposition, the coatings were analyzed by high-resolution transmission electron microscopy (TEM), cross-sectional scanning electron microscopy, Rockwell-C indentation tests, impact tests, and nanoindentation measurements. The turning performance was evaluated by a conventional turning machine at high cutting speeds without using coolants. It was found that by introducing the composition gradient layer, well-adherent Ti–Al–N coatings of about 4.0 μm total thickness with hardness of 32 GPa were obtained. In addition, improvement was found on the impact tests with less failure occurring. In the turning tests, the Ti–Al–N coatings prepared on the highly energetic Ti ion implantation showed the best turning performance, which endured over 50 min before the tool flank wear reached the maximum value of 0.3 mm, whereas only 28 min were endured for the tools without the pretreatment process. The greatly enhanced turning performance can be explained by the formation of the gradient layer, which can substantially reduce the stress gradient at the interface and the possibility of crack formation during cutting, and the enhanced hardness of the tooling materials, which can retard the plastic deformation when loading.