Ceramics-Silikáty 35, (3) 273 - 282 (1991)

A significant feature of plasma sprayed alumina coatings is the formation of a metastable spinel type crystal structure which can be explained in terms of the nucleation kinetics of alternative crystalline forms from the melt. The detailed structure of the metastable form observed in coatings, usually referred to as γ-Al₂O₃, differs from the γ- and η-forms of the usual nomenclature, and should, strictly, be given a new name. The mechanical, thermal, and probably other properties, of thermally sprayed alumina coatings are dominated by their lamellar microstructure, in particular, limited interlamellar contact. The microstructure also results in anisotropic behaviour. There is some evidence that the extent of interlamellar contact is improved by low pressure spraying and the use of higher particle velocities.