Microstructural and porosity variations in the plasma-sprayed Ni-alloy coatings prepared at different spraying powers

The aim of this paper was to investigate the effect of spraying power on the microstructure and porosity plasma-spraying coating. A series of Ni-based coatings were prepared. The coating porosity was evaluated by using a proposed image analysis method. For each coating sample, 20 readings of porosity were randomly taken and then adjusted by subtracting the two largest and two smallest readings. For both data sets, statistical analyses of porosity variations were made to assess whether the porosity data sets followed the Weibull or Gaussian distributions. The studies employed in the present study implied that a statistically based evaluation of the porosity may account for the variations in microstructures of the coatings that were practically observed. Some important results can be obtained. From the statistical trend, the porosity of the coating increased with decreasing the spraying power. However, when the spraying power was sufficiently high (57 kW in this paper), almost all of the powder particles were fully melted. In such a case, with further increasing the spraying power, the porosity of the coating was almost not sensitive to the spraying power. The adjustment of porosity data set by subtracting the two largest data and two smallest data could lead to the change in the distribution shape since it led to the decrement of the data scattering.