Methods: Two groups of specimens (n=2x8) cast from a Co-Cr base alloy (Octa-C) and cpTi (Biotan) were prepared. Four specimens of each group were subjected to spark-erosion (SE) and the rest were conventionally ground and polished (CP). Two spark- eroded and two conventionally finished specimens of each group were used to obtain cyclic current potential curves with a MCS. A saturated calomel electrode was used as a reference electrode (E0=241 mV vs.SHE). Acquisition parameters were –1V up to +1.5V (versus SHE) potential range,10mV/s scan rate and 0.008cm2 sampling area. Each measurement was replicated three time on each specimen. The remaining two specimens per group were subjected to electrochemical impedance spectroscopy (EIS) at open circuit potential, employing a 106 to 0.01Hz frequency range by applying a 15 mV sinusoidal potential. The data were collected and analyzed employing Corrware and Corrview software respectively, whereas they were statistically analyzed with independent t-test (a<0,05).
Results: Conventionally polished specimens showed passivation in a wider potential compared to the spark-eroded. Moreover, the corrosion resistance of the alloys tested showed statistically significant difference between the conventionally polished and the spark eroded, with the latter demonstrating lower values (Rp Co-Cr for CP:4,4E3±1,5E3, Rp Co-Cr for SE:2,7E3±1,6E2, Rp cpTi for CP:19,2E3±6E3, Rp cpTi for SE:4E3±0,9E3). Spark-eroded alloys demonstrated a peak at potential values between 0,5-1V, which is attributed to Cu corrosion.
Conclusion: Spark-erosion decreases corrosion resistance of the Co-Cr and cpTi alloys tested, a finding which might be attributed to Cu leaching during electrochemical testing.
This study was supported by the Greek State Scholarships Foundation (IKY) and the German Academic Exchange Service (DAAD).