Thermal Stability of Alumina-based Hard Coatings
Research output: Thesis › Doctoral Thesis
Within the present thesis, the thermal stability of sputtered and arc evaporated alumina-based coating materials was investigated in terms of changes of their morphology during thermal load. Since alumina exists, besides the thermodynamically stable corundum structured α-Al2O3, in a variety of metastable modifications, for their application as protective coatings on cutting tools, the knowledge of their thermal stability is of vital importance. Therefore, different metastable Al2O3 coatings were produced by magnetron sputtering. In all cases, transformation into the α-Al2O3 phase occurred at temperatures of about 1100 °C. In order to meet the demand of low deposition temperatures and thus to synthesize a protective coating on thermally sensitive cutting tools, in a second attempt the α-Al2O3 phase was stabilized by the isostructural Cr2O3 phase, forming a corundum-based (AlxCr1-x)2O3 solid solution. The solid solutions synthesized by arc evaporation were investigated and the thermal stability against decomposition was also determined. To conclude, the demand for protective coatings, which can be synthesized at low deposition temperatures and exhibit a sufficient thermal stability, is fulfilled by the metastable corundum-based (AlxCr1-x)2O3 solid solutions. These coatings might be interesting candidates for high-temperature and cutting applications, where high performance materials are needed.