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

Cathodoluminescence (CL) properties were studied for metastable γ- and κ-Al 2O 3 coatings for cutting tool inserts. The alumina films demonstrate a strong CL, with peak energies depending on the Al 2O 3 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-Al 2O 3 are discussed.