In result of the spray process normally a phase change from α-alumina (corundum) in the feedstock powder to predominantly α-alumina in the coating takes place. This is a well known but often neglected fact in the preparation and use of alumina coatings. This is of special interest since the high usage properties of thermally sprayed alumina coatings are generally derived from sintered alumina ceramics which consist of corundum. It is expected that the prevention of this phase transformation will significantly change the mechanical, electrical and other properties of thermally sprayed alumina coatings. There is controversial information about the possibility of stabilization of α-alumina by additions of chromia in the literature. In this work the stabilization using different spray processes (water stabilized plasma WSP, gas stabilized plasma APS and HVOF) was studied. Mechanical mixtures of alumina and chromia were used, as well as pre-alloyed powders consisting of solid solutions. The coatings were studied by X-ray diffraction and metallographic cross-sections. It was shown that in the case of the mechanically mixed powders the stabilization predominantly depends on the applied spray process. The stabilization by use of the WSP process was confirmed.

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