TiAlN is a hard coating and since the 1980s it is extensively used in the cutting tool industry. Detailed wear behaviour of TiAlN coated inserts during turning has to our knowledge only been addressed in a few studies. None of these studies addressed the effect of the Al-content in TiAlN or the influence of microstructural changes of the coatings, e.g. how spinodal decomposition affects the active wear mechanisms.

In the present work, detailed investigations of the wear mechanisms of cathodic arc deposited Ti1-xAlxN (x = 0, 0.25, 0.55, and 0.66) cutting tool inserts during longitudinal turning of austenitic stainless-steel 316L were conducted at high cutting speed of 220 m/min. TiAlN coatings with 2.5-2.7 µm thickness were deposited onto WC-Co tools (TPUN 160308E30-K) by an industrial scale arc deposition system. Hardness measurements, XRD, SEM, (S)TEM and EDS were used to study the relationship between wear mechanisms and the Al-content. TEM samples were prepared by FIB in the crater region.

The crater wear is dominated by abrasive wear for all coatings [1]. Ti1-xAlxN coatings with x ≤ 0.53 presented the best wear resistance and least abrasive wear. For these coatings, a thick adhered layer composed of oxides and metallic species from the steel formed in the crater region. However, there was no diffusion of workpiece material into the coating. The high Al-content Ti0.38Al0.62N coating showed the worst crater wear resistance. This was assigned to interdiffusion of workpiece elements and oxygen into the coating. The interdiffusion is a consequence of spinodal decomposition of the cubic TiAlN-phase and results in more severe abrasive wear.

[1] Moreno, M., Andersson, J. M., Boyd, R., Johansson-Jöesaar, M. P., Johnson, L. J. S., Odén, M., & Rogström, L. (2021). Crater wear mechanism of TiAlN coatings during high-speed metal turning. Wear, 484-485, 204016.

Keywords

TiAlN, turning operation, electron microscopy, wear mechanisms