Reactivity of PVD cathodic arc coated hardmetal tools with Inconel 718: Correlation between diffusion couples and tool wear in drilling tests

Abstract

The reactivity of Al0.66Ti0.33N, Al0.31Ti0.62Si0.07N, Al0.60Cr0.40N, and Al0.38Cr0.54Si0.07N cathodic arc-coated hardmetal tools with Inconel 718 has been evaluated by using diffusion couple experiments at 900 degrees C and 1100 degrees C. As expected, a strong reaction occurs at these temperatures between Inconel 718 and uncoated hard-metal samples leading to the formation of & eta; phases; mainly M12C and M6C carbides. PVD coatings act as diffusion barriers limiting the presence of such reactions as long as they maintain their structure in contact with Inconel 718 at high temperatures. Diffusion couple experiments confirm that Cr-containing coatings are significantly more unstable than Al0.66Ti0.33N or Al0.31Ti0.62Si0.07N materials, thus leading to notable differences in cutting performance. The relation between diffusion couple results and drill wear mechanisms in drilling Inconel 718 with different coating materials are also analysed. The best results are obtained either with Al0.66Ti0.33N or Al0.31Ti0.62Si0.07N coated drills, where the coating remains longer time at the cutting edge leading to more efficient protection, especially at the drill corner.