Phase transformation in κ- and γ-Al2O3 coatings on cutting tool inserts

✍ Scribed by D.H. Trinh; K. Back; G. Pozina; H. Blomqvist; T. Selinder; M. Collin; I. Reineck; L. Hultman; H. Högberg

• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 723 KB
• Volume: 203
• Category: Article
• ISSN: 0257-8972
• DOI: 10.1016/j.surfcoat.2008.12.028

✦ Synopsis

The phase transformation in as-deposited, metastable κand γ-alumina coatings on cutting inserts has been studied by a combination of X-ray diffraction, scanning electron microscopy and cathodoluminescence. In the case of κ-alumina, mechanical forces during metal cutting lower the transformation temperature of the metastable phases to the thermodynamically stable α-alumina phase from 1050 °C to 930 °C. This is the reason why that coating has a similar performance during metal cutting when compared to the stable α-alumina phase. The transformation temperature in γ-alumina coated cutting tools is found to be as low as 950-975 °C. Cathodoluminescence (CL) has been demonstrated as a possible method for differentiation between the various alumina phases. Specifically, both κand γ-alumina films have revealed a strong room temperature CL with different peak energies depending on the phase. CL of the metastable alumina coatings annealed at the transformation temperatures corresponds to the stable α-alumina phase.