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

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

Venkateshwarlu Bolleddu (VIT University, India), Vikranth Racherla (Indian Institute of Technology Kharagpur, India) and Partha Pratim Bandyopadhyay (Indian Institute of Technology Kharagpur, India)
DOI: 10.4018/978-1-5225-4194-3.ch011


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.
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Plasma sprayed alumina coatings are used in many applications, e.g. valves, plungers, pump seals, shields for guided missiles, rocket nozzles, engine components, integrated circuits, vacuum tube envelops, railroad components, etc., (Ono et al., 1993), because of their high wear resistance, heat and thermal shock resistance, oxidation and hot corrosion resistance and electrical insulation (Gadow et al., 1998; Krishnan et al., 2006). They also bond well with metallic bond coats, resist wear and solid particle erosion and have high hardness and chemical stability even at elevated temperatures (Pantelis et al., 2000; Erickson et al., 2001). Alumina exists in nature in a number of hydrated states, e.g. Diaspore (α-AlO(OH)), Boehmite (γ-AlO(OH)), and gibbsite (γ-Al(OH)3) (Carim et al., 1997). Typically, the Bayer process is used to refine bauxite, the most important ore of aluminium, to obtain alumina.

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