J. G. Legoux, C. Moreau, National Research Council Canada (CNRC-NRC), Boucherville,, QC, Canada; E. Irissou, Industrial Materials Institute / -National Research Council Canada, Boucherville, QC, Canada
When describing the cold spray process, one of the most widely used concepts is the critical velocity. Current models predicting critical velocities takes explicitly into account the temperature of the sprayed particles but not that of the surface (substrate or already deposited layers) on which the particle impact. This surface temperature is expected to play an important role since the deformation process leading to particle bonding and coating formation takes place both on the particle and the substrate side. The aim of this work is to investigate the effect of the substrate temperature on the coating formation process. Experiments were performed using both aluminum and tin powders as coating materials. These materials have a rather large difference in critical velocities that gives the possibility to cover a broad range of deposition velocity to critical velocity ratio using typical low pressure process parameters. The sample surface temperature was varied from room temperature to a high fraction of the melting point of the coating material for both tin and aluminum. The coating formation was also investigated as a function of the powder feed rate, the gun transverse speed and the particle velocity. Both single particle impact samples and thick coatings were produced and characterized. Both the particle-substrate and interparticle bondings were evaluated by SEM, adhesion tests as well as gas permeability. Experimental results are discussed in terms of the calculated critical velocity, bonding mechanisms and deposition efficiency.
Summary: When describing the cold spray process, one of the most widely used concepts is the critical velocity. Current models predicting critical velocities takes explicitly into account the temperature of the sprayed particles but not that of the surface (substrate or already deposited layers) on which the particle impact. This surface temperature is expected to play an important role since the deformation process leading to particle bonding and coating formation takes place both on the particle and the substrate side. The aim of this work is to investigate the effect of the substrate temperature on the coating formation process. Experiments were performed using both aluminum and tin powders as coating materials. These materials have a rather large difference in critical velocities that gives the possibility to cover a broad range of deposition velocity to critical velocity ratio using typical low pressure process parameters. The sample surface temperature was varied from room temperature to a high fraction of the melting point of the coating material for both tin and aluminum. The coating formation was also investigated as a function of the powder feed rate, the gun transverse speed and the particle velocity. Both single particle impact samples and thick coatings were produced and characterized. Both the particle-substrate and interparticle bondings were evaluated by SEM, adhesion tests as well as gas permeability. Experimental results are discussed in terms of the calculated critical velocity, bonding mechanisms and deposition efficiency.
