| AVS 58th Annual International Symposium and Exhibition | |
| Advanced Surface Engineering Division | Thursday Sessions |
| Session SE-ThM |
| Session: | Nanostructured Thin Films and Coatings |
| Presenter: | Paul Mayrhofer, Montanuniversität Leoben, Austria |
| Authors: | P.H. Mayrhofer, Montanuniversität Leoben, Austria L. Chen, Montanuniversität Leoben, Austria J. Paulitsch, Montanuniversität Leoben, Austria Y. Du, Central South University, China |
| Correspondent: | Click to Email |
The excellent hardness, good abrasive and sliding wear resistance and high thermal stability and oxidation resistance favor Ti1-xAlxN to be used as hard protective coating in a variety of industrial applications such as advanced machining and forming tools, automobile and aerospace industry or for semiconductor electronics. Although, thin films based on this material system are investigated in detail, only little is known on the sequential relations between deposition conditions, chemistry, structure and physical and mechanical properties.
Here we show that Ti1-xAlxN coatings can be synthesized by magnetron-sputtering in single-phase cubic (NaCl, c) structure for x = Al/(Ti+Al) ratios up to 0.62 and single-phase hexagonal (ZnS-wurtzite, w) structure for x ≥ 0.75. These critical values for the individual favored structures strongly depend on the deposition conditions used such as N2-partial pressure and resulting growth rate. Generally, a low N2-partial pressure and a high growth rate favor the cubic structure. Increasing Al content of the single-phase cubic coatings results in increased hardness (to ~35 GPa for c-Ti0.38Al0.62N), earlier onset of the decomposition towards the stable phases c-TiN and w-AlN (across the formation of Ti-rich and Al-rich cubic nm-sized domains) and increased oxidation resistance. The single-phase wurtzite-structure coatings exhibit a high thermal stability and better oxidation resistance as compared to the single-phase cubic structure coatings. Even after 40h at 800 °C in ambient atmosphere the w-Ti0.25Al0.75N coating exhibits only an ~1 µm thin dense oxide layer on top of the ~2 µm remaining nitride, whereas the other coatings are already fully oxidized.
The coatings with a dual-phase or mixed-phase structure in the as deposited state show a reduced thermal stability and oxidation resistance as compared to the single-phase cubic or wurtzite structure coatings.
Furthermore, we show that a post-deposition annealing treatment of c-Ti0.48Al0.52N to 900 °C results in a hardness increase from 29 to 32 GPa (due to the formation of cubic nm-sized domains) as well as an increased oxidation resistance. Hence, our results provide insight in designing-strategies for coatings with increased mechanical, thermal stability and oxidation resistance.