Statistical analyses of porosity variations in plasma-sprayed Ni-based coatings

A series of Ni–Cr–B–Si–C coatings were prepared at different hydrogen gas flow rates by using a novel supersonic plasma spraying system. Porosity measurements of the coatings were made by using the 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. Both data sets were statistically analysed to assess whether they followed the Weibull distribution or Gaussian distribution. Results showed that the porosity value of the coating was related to the microstructure of the coating. From the statistical trend, the porosity of the coating increased with decreasing the hydrogen gas flow rate. When the hydrogen gas flow rate was low, the porosity data of the coating were highly scattered. The present study has established that the homogeneity of the plasma-sprayed coating, at least as characterized by the porosity, was related to the spraying parameters.