Amorphous zones in flame sprayed alumina–titania–zirconia compounds

The formation of amorphous phases in thermally sprayed coatings is a common phenomenon. This work examines the distribution of the amorphous content in flame sprayed Al2O3–TiO2–ZrO2-compounds. An amorphous percentage appears even in pure alumina and the percentage increases with increasing amount of TiO2- and ZrO2-addition. Amorphous sub-lamellae appear in all examined compositions. If a system with a miscibility gap in the liquid state, such as Al2O3–ZrO2, is applied, the formation of secondary amorphous regions is observed. The amorphous sub-lamellae or primary amorphous region is induced only by rapid cooling, the secondary amorphous regions are induced by rapid cooling plus a spinodal demixing effect.