G. Sivakumar

Hybrid Plasma-Sprayed Thermal Barrier Coatings Using Powder and Solution Precursor Feedstock

A novel approach of hybridizing the conventional atmospheric plasma spraying (APS) technique with the solution precursor plasma spray (SPPS) route to achieve thermal barrier coatings (TBCs) with tailored configurations is presented. Such a hybrid process can be conveniently adopted for forming composite, multi-layered and graded coatings employing simultaneous and/or sequential feeding of solution precursor as well as powder feedstock, yielding distinct TBC microstructures that bear promise to further extend coating durability. TBC specimens generated using conventional APS technique, the SPPS method and through APS-SPPS hybrid processing have been comprehensively characterized for microstructure, phase constitution, hardness and thermal cycling life, and the results were compared to demonstrate the advantages that can ensue from hybrid processing.

Hybrid Processing with Powders and Solutions : A Novel Approach to Deposit Composite Coatings

Thermal spraying employing either solution precursor or suspension feedstock offers an exciting opportunity to obtain coatings with microstructures and characteristics that differ vastly compared to those conventionally produced using spray-grade powders. Both solution precursor plasma spray and suspension plasma spray techniques have been explored extensively in recent years for depositing wide ranging ceramic coatings for various functional applications. Encouraged by the properties achieved using the above solution-based feedstocks, a hybrid approach involving dual injection of solutions and powders, either simultaneously or sequentially, has been proposed and demonstrated to yield novel coating architectures. Although prior work on such hybrid processing is very limited, this overview seeks to present the concept, outline associated challenges, and demonstrate its efficacy to realize coatings with exciting and unusual properties using some illustrative examples.

Effect of SPPS Process Parameters on In-Flight Particle Generation and Splat Formation to Achieve Pure α-Al2O3 Coatings

Abstract The present paper describes the role of process conditions in developing phase-pure α-Al2O3 coatings using solution precursor plasma spraying. Different precursor combinations were employed and two key parameters, namely plasma power and substrate pre-heat temperature, were varied. Detailed studies of in-flight formed particles and splat characteristics were found to correlate well with the Al2O3 coating characteristics. The Al2O3-forming precursor formulation was also found to be crucial in determining the phase constitution of the deposited coatings.

Thermal Spray Coatings for Blast Furnace Tuyere Application

The components in an integrated steel plant are invariably exposed to harsh working environments involving exposure to high temperatures, corrosive gases, and erosion/wear conditions. One such critical component in the blast furnace is the tuyere, which is prone to thermal damage by splashing of molten metal/slag, erosive damage by falling burden material, and corrosion from the ensuing gases. All the above, collectively or independently, accelerate tuyere failure, which presents a potential explosion hazard in a blast furnace. Recently, thermal spray coatings have emerged as an effective solution to mitigate such severe operational challenges. In the present work, five different coatings deposited using detonation spray and air plasma spray techniques were comprehensively characterized. Performance evaluation involving thermal cycling, hot corrosion, and erosion tests was also carried out. Based on the studies, a coating system was suggested for possible tuyere applications and found to yield substantial improvement in service life during actual field trials.