Eight part series on the relative effectiveness of laser cladding and HVOF spraying for corrosion resistance. Part 3 of 8
Index of Parts
- Open circuit potential measurement
- Potentiodynamic test
- Gravimetric Measurement
Potentiodynamic tests were conducted following OCP measurements under the same cell conditions to generate polarization curves (Tafel plots) and to determine the corrosion current density for each coating material. The applied potential range was from -1 V to +2 V. Data was collected at a scan rate of 0.166 mV/s.
The results of the potentiodynamic tests are presented in Table 3 in terms of corrosion potential Ecorr, corrosion current Icorr, and corrosion penetration rate (CPR). CPR is calculated as a direct function of Icorr
The corrosion potential (Ecorr) results indicate that laser clad coatings have higher corrosion potentials (i.e. less anodic) than thermal spray coatings. Among laser clad coatings, corrosion potential values are very similar. Among thermal sprayed coating, SS316 is most anodic, followed by Stellite 6 and IN-625.
Table 3: Potentiodynamic test results presented in terms of corrosion potential Ecorr, corrosion current Icorr, and corrosion penetration rate (CPR)
Figure 5 represents the corrosion rate data using a log scale on the Y axis. This representation confirms that among laser clad coatings, corrosion rate values are very similar and extremely low corrosion rates. On the other hand, thermal sprayed coatings exhibited significantly greater corrosion rates, with SS316 having by far the highest corrosion rate, followed by Stellite 6 and IN-625. However, the corrosion resistance of thermal sprayed coatings can be improved by sealing the coating with polymers .
Fig. 5: Corrosion penetration rate (CPR) data represented in log scale
 D. Chidambaram, C.R. Clayton, M.R. Dorfman, Surface Coatings & Tech 176 (2004) 307-317.