The aim of the study presented in this paper was to develop the next generation of production ready air plasma sprayed thermal barrier coating with a low conductivity and long lifetime. In order to achieve these goals; a number of coating architectures were produced using commercially available plasma spray guns. Modifications were made to powder chemistry including; high purity powders for sintering resistance, Dysprosia stabilised Zirconia powders and powders containing porosity formers. Agglomerated & Sintered (A&S) and Hollow Oven Spherical Powder (HOSP) morphologies were used to attain beneficial microstructures. Finally, dual layer coatings were produced using the different powder morphologies. Evaluation of the thermal conductivity of the coating systems from room temperature to 1200°C was conducted using laser flash technique. Tests were done on as-sprayed samples and samples heat treated for 100 hours at 1150°C in order to evaluate the first stage sintering resistance of the coating systems. Thermal conductivity results were correlated to coating microstructure using image analysis of porosity and crack content. The results show the influence of beneficial porosity on reducing the thermal conductivity of the produced coatings.

Widely studied in the 1980s, the insulation of pistons in engines aimed at reducing the heat losses and thus increasing the indicated efficiency. However, those studies stopped in the beginning of the 1990s due to NOx emission legislation, and also due to acceptable oil prices. Nowadays, with the improvement of exhaust after treatment systems (Diesel Particulate Filter, Selective Catalytic Reduction, and Diesel Oxidation Catalyst) and engine technologies (Exhaust Gas Recirculation), there are more trade-offs for NOx reduction. Besides, the fast rise of the oil prices tends to come back to insulation technologies in order to save fuel. This paper deals with the realization of a 1 mm thick plasma sprayed thermal barrier coating with a graded transition between the topcoat and the bondcoat on top of a serial piston for heavy-duty truck engines (11L displacement – Exhaust Gas recirculation – Single Stage Turbocharger with Variable Geometry Turbine and intercooler). The effects of the insulated pistons on the engine performance are also discussed.

The aim of this work, devoted to yttria stabilised zirconia (YSZ) thermal barrier coatings, is to produce by DC plasma spraying a single thick pass macro cracked orthogonally to the substrate. YSZ was plasma sprayed in air atmosphere on Hastelloy X substrates, with a NiCrAlY bond coat. A three-zone microstructure is observed, where lamellae and columns are present. The measurements of deposition stresses during spraying allow explaining the macrocrack formation.

The objective of this study is to increase the deposition rate in the plasma-spray manufacturing of thermal barrier coatings without altering the quality of the coatings. The experimental part involves the measurement of in-flight particle characteristics and analysis of coatings properties when varying the hydrogen content of the plasma-forming gas, the torch nozzle diameter and the powder feed rate. The experimental results of particle measurements are discussed in the light of the gas flow fields projected by a 3-D model of the plasma spray process.