Thermally-induced phase transformation sequence of arc evaporated Ta-Al-N coatings

Differential scanning calorimetty and thermogravimetric analyses combined with XRD and TEM investigations demonstrate that single-phase face-centred cubic Ta0.89Al0.11N1.2 coatings decompose into wurtzite AlN and hexagonal Ta2N phases upon vacuum annealing to 1500 degrees C. The Ta2N phase transformation proceeds via hexagonal Ta5N6 at similar to 1000 degrees C and hexagonal epsilon-TaN at similar to 1100 degrees C. A significant N-2-loss between 1300 degrees C and 1500 degrees C, without a structural change of the Ta2N phase, suggests the formation of TaN0.3 at the Ta-rich Ta2N phase field. (C) 2015 Elsevier Ltd. All rights reserved.