2001 Volume 42 Issue 4 Pages 707-711
This study was performed to investigate the influence of the oxygen flow rate in HVOF spraying on the oxidation behavior of Cr3C2 (7 mass%NiCr) coatings. The oxide was formed on the coatings during HVOF spraying regardless of the oxygen flow rate. The oxide observed at the coatings was Cr2O3, but chromium oxides of other forms were not observed. Cr3C2 (7 mass%NiCr) coatings were stable in a temperature range up to 1073 K for 50 h. However, the oxidation behavior of the coatings at 1273 K showed great difference from that at temperature up to 1073 K and the oxygen flow rate had a significant influence on the oxidation behavior of the coatings. The surface of the coatings sprayed with 229 and 243 l/min-oxygen flow rate became porous by the aggressive evaporation of CO, CO2 gases and the oxide clusters were partially formed after isothermal oxidation at 1273 K for 50 h. The oxide clusters were complex oxides consisted of Ni and Cr, whereas the porous surface was composed of only Cr2O3. TG analysis revealed that the mass loss by intensive evaporation of gaseous oxide, in the case of the coatings sprayed with 229 l/min-oxygen flow rate, began after the oxidation time of approximately 42 h at 1273 K . The apparent activation energy (Q) for oxidation varied from 89.04 to 99.96 kJ mol−1 with increasing oxygen flow rate.