Plasma-sprayed nanostructured Al sub 2 O sub 3 /TiO sub 2 powders and coatings

Air plasma spray has been used to produce metastable oxide-ceramic powders and coatings, starting with commercially available Al sub 2 O sub 3 /13TiO sub 2 powder feed. The feed material undergoes rapid melting and homogenization in the high-temperature zone of the plasma jet. A metastable x-Al sub 2 O sub 3 TiO sub 2 phase is formed when the molten droplets are quenched on a chilled substrate. The metastable phase has a defect spinel structure and a nanocrystalline grain size. When heated, it decomposes into an equilibrium two-phase structure, consisting of alpha -Al sub 2 O sub 3 and beta -Al sub 2 O sub 3 TiO sub 2 . Both types of ceramic materials have potential as hard, wear-resistant coatings.