Suspension Plasma Spraying is a relatively new thermal spaying technique to produce advanced thermal barrier coatings. This technique enables the production of a variety of structures from highly dense, highly porous, segmented or columnar coatings. In this work a comparative study is performed on six different suspension plasma sprayed thermal barrier coatings which were produced using axial injection and different process parameters. The influence of coating morphology and porosity on thermal properties was of specific interest. Tests carried out include microstructural analysis with SEM, phase analysis using XRD, porosity calculation using Archimedes experimental setup, pore distribution analysis using mercury infiltration technique and thermal diffusivity/conductivity measurements using laser flash analysis. The results showed that columnar and cauliflower type coatings were produced by axial suspension plasma spraying process. Better performance coatings were produced with relatively higher overall energy input given during spraying. Coatings with higher energy input, lower thickness and wider range of submicron and nanometer sized pores distribution showed lower thermal diffusivity and hence lower thermal conductivity. Also, in-situ heat treatment did not show dramatic increase in thermal properties.

The flame spraying process has been analysed using three-dimensional Computational Fluid Dynamics (CFD) simulations. The process employed at the Volvo Aero Corporation for the coating of fan and compressor housings has been modelled. The gas combustion was simulated as a multi-component chemically reacting flow. The standard, two equations, k-ε turbulence model was employed. A statistical analysis of the computer simulation experiments revealed that particle velocity and particle temperature were dependent on four process parameters, namely the acetylene flow rate, the carrier gas flow, the powder feed rate and the spray distance. The most important factors influencing particle velocity and temperature were the acetylene flow rate and the carrier gas flow. The carrier gas flow rate was shown to have an unexpectedly large influence on particle in-flight properties. Simulations were repeated with particles of different median diameters. The study revealed that a very high correlation existed between particle temperature and particle velocity for particles of the same median diameter. Furthermore, the particle median diameter, when compared with the investigated process parameters, was found to have a more pronounced influence on both particle temperature and velocity. It would appear that the use of powder lots comprised of sufficiently fine-grained powders is the most promising single contribution towards increasing deposition efficiency that can be applied to the current process.