E. Turunen, T. Varis, VTT Technical Research Centre of Finland, Espoo, Finland; J. Knuuttila, J. Leivo, J. Silvonen, Millidyne Oy, Tampere, Finland; U. Kanerva, VTT Technical research centre of Finland, VTT, Espoo, Finland
The potential of the high velocity oxy-fuel (HVOF) thermal spray process for reduced porosity in coatings compared to those produced by other ambient thermal spray processes is well known. The ability to produce high density ceramic coatings offers potential in high performance applications in the field of wear, corrosion resistance and dielectric coatings. However, due to extreme operational limits of the HVOF process, the process-structure-relationship must be well optimized. It has been also demonstrated fact that benefits from HVOF ceramic coatings can be obtained only, if particles are melted enough and good lamella adhesion is produced. One strategy to improve melting of ceramic particles in relative low flame temperatures of HVOF process is to modify particle crystal structure and composition.
In this paper the effect on the powder microstructure and the composition on deposition efficiency of spray process as well as on the mechanical and protective properties of the HVOF sprayed are studied. Effect of fuel gas, hydrogen vs. propane, was also demonstrated. Studied materials were alumina, chromia and titania based pure and composite agglomerated powders. Coating properties such as microstructure, hardness, abrasive wear resistance, relative fracture toughness and elastic modulus was compared to the coating manufactured by using conventional fused and crushed powders.
Summary: The potential of the high velocity oxy-fuel (HVOF) thermal spray process for reduced porosity in coatings compared to those produced by other ambient thermal spray processes is well known. Benefits from dense HVOF ceramic coatings can be obtained only, if particles are melted enough and good lamella adhesion is produced. One strategy to improve melting of ceramic particles in relative low flame temperatures of HVOF process is to modify particle crystal structure and composition. In this paper the effect on the powder microstructure and the composition on deposition efficiency of spray process as well as on the mechanical and protective properties of the HVOF sprayed are studied.
