J. Oberste Berghaus, J. G. Legoux, Industrial Materials Institute / -National Research Council Canada, Boucherville, QC, Canada; C. Moreau, National Research Council Canada (CNRC-NRC), Boucherville,, QC, Canada; T. Chraska, Institute of Plasma Physics ASCR, Praha 8, Czech Republic; F. Tarasi, Concordia University, Montreal, QC, Canada
Micro-laminates and nanocomposites of Al2O3 and ZrO2 can potentially exhibit higher fracture toughness, slower crack growth and lower thermal conductivity than alumina or zirconia alone. The potential of these improvements for abrasion protection and thermal barrier coatings is generating considerable interest in developing techniques for producing these functional coatings with optimized microstructures. In the present study, Al2O3 -43% ZrO2 composite coatings were deposited by suspension plasma spraying of submicron feedstock powders, using an internal injection plasma torch. The liquid carrier employed in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to dense coatings of thin and finely alternating ceramic layers, with a limited degree of alloying and amorphous phase formation. In-flight particle states were measured for a number of plasma operating conditions of varying torch current, gas flow rates and composition, and related to the resulting microstructure and phase composition (EDS, SEM, XRD). Thermal conductivity, as well as mechanical properties, such as hardness (Vickers Hv0.3), abrasion (ASTM G65) and erosion resistance (ASTM G75) were evaluated. The thermal conductivity was found to be lower in the composite coating as compared to suspension plasma sprayed YSZ. Furthermore, it was observed that the mechanical properties improve with a refinement in the layer structure and low amorphous phase content. Results indicate that small in-flight particles foster segregation of the ceramic constituents within a molten droplet, forming the unique microstructures. The role of feedstock particle size on amorphous and nano-composite phase formation is discussed.
Summary: Micro-laminates and nanocomposites of Al2O3 and ZrO2 coatings, composed of thin and finely alternating ceramic layers, with a limited degree of alloying and amorphous phase formation, were produced by suspension plasma spraying. Thermal conductivity, as well as mechanical properties, such as hardness (Vickers Hv0.3), abrasion (ASTM G65) and erosion resistance (ASTM G75) were evaluated. It was observed that the mechanical properties improve with a refinement in the layer structure and low amorphous phase content
