Phase identification in γ- and κ-alumina coatings by cathodoluminescence

Cathodoluminescence (CL) properties were studied for metastable γ- and κ-Al2O3 coatings for cutting tool inserts. The alumina films demonstrate a strong CL, with peak energies depending on the Al2O3 polymorphs. The phase transformation caused by heat treatment is shown to correlate with strong CL modification in the annealed coatings. Spatially resolved CL is found to be a powerful nondestructive technique for identification of different alumina phases on the microscopic level. The corresponding optical properties of γ- and κ-Al2O3 are discussed.