Structure and phase evolution of Cr-Al-N coatings during annealing

Cr-Al-N coatings are favored for wear protection of tools, dies, molds, as well as for components used in the automotive and aerospace industry due to their excellent mechanical and thermal properties. Cr-AI-N coatings crystallize in the cubic modification for AIN mole fractions below -0.7, whereas higher Al contents favor the hexagonal modification. Here, we use a combination of differential scanning calorimetry and X-ray diffraction to study the structure and phase evolution of Cr-Al-N coatings during annealing up to 1450 degrees C. The results indicate that cubic Cr-Al-N decomposes during thermal annealing to form AIN precipitates. Hence, the remaining matrix becomes Cr-rich and N-loss at elevated temperatures is promoted. Annealing of hexagonal Cr-Al-N coatings results in the precipitation of CrN. The remaining matrix becomes Al-rich and transforms into AlN. Consequently, CrN is encapsulated in AIN and hence, the N-loss occurs at higher temperatures as compared to cubic Cr-Al-N. The obtained results serve as a basis for further developments of Cr-Al-N films to effectively retard the decomposition process and the N-loss. @ 2008 Elsevier B.V. All rights reserved.