Microstructural and Tribological Characteristics of Air Plasma Sprayed Alumina-Titania Coatings

Abstract

Thermally sprayed coatings from nanostructured agglomerated ceramic powders have received considerable attention in recent past due to their improved performance over corresponding coatings from conventional powders. When complete melting of a fraction of agglomerated particles is prevented, unmelted and partially melted (PM) particles appear as inclusions within the fully melted matrix resulting in a bi-modal coating microstructure. In addition to uniform mixing of constituents, the enhanced performance of nanostructured coatings has also been attributed to above described bi-modal nature of the microstructure. Interestingly, even though nitrogen is cheaper and more widely available than argon, essentially all earlier works on plasma spraying of nanostructured coatings use argon as the primary plasma gas. In this chapter, the effect of critical plasma spray parameter (CPSP), which controls the specific power input to the plasma gas, on microstructural and wear characteristics of conventional and nanostructured alumina-titania (Al2O3-13wt%TiO2) coatings is studied systematically.