Microstructure and thermal stability of corundum-type (Al0.5Cr0.5)2O3 solid solution coatings grown by cathodic arc evaporation

Abstract Corundum-type (Al x Cr 1 − x ) 2 O 3 coatings were grown by reactive cathodic arc evaporation in an oxygen atmosphere using AlCr targets with an Al/Cr atomic ratio of 1. Since the (Al x Cr 1 − x ) 2 O 3 solid solution shows a miscibility gap below 1300 °C, where spinodal decomposition is predicted, the microstructural changes upon annealing were investigated by a combination of transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and differential scanning calorimetry. The as-deposited coating consists primarily of the corundum-type (Al x Cr 1 − x ) 2 O 3 solid solution, with smaller fractions of cubic (Al x Cr 1 − x ) 2 O 3 . An additional Al-rich amorphous phase and a Cr-rich crystalline phase stem from the droplets incorporated. The corundum-type (Al x Cr 1 − x ) 2 O 3 solid solution is still present after vacuum annealing at 1050 °C for 2 h, whereas the cubic (Al x Cr 1 − x ) 2 O 3 phase has transformed to corundum-type (Al x Cr 1 − x ) 2 O 3 . Cr and Cr 2 O 3 have been detected in the annealed coating, the latter most probably originating from the partial oxidation of Cr-rich droplets. Upon crystallization of the amorphous phase fractions present, γ-Al 2 O 3 is formed, which then transforms into α-Al 2 O 3 . No evidence for decomposition of the corundum-type (Al x Cr 1 − x ) 2 O 3 solid solution could be found within the temperature range up to 1400 °C.