The effect of oxygen flow rate in HVOF spraying on oxidation behavior of Cr3C2 (7 mass %NiCr) coatings

This study was performed to investigate the influence of the oxygen how rat e in HVOF spraying on the oxidation behavior of Cr3C2 (7 mass%NiCr) coating s. 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 chr omium oxides of other forms were not observed. Cr3C2 (7 mass%NiCr) coatings were s table in a temperature range up to 1073 K for 50h. However, the oxi dation 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 inf luence on the oxidation behavior of the coatings. The surface of the coatin gs sprayed with 229 and 243 l/min-oxygen flow rate became porous by the agg ressive evaporation of CO, CO2 eases and the oxide clusters were partially formed after isothermal oxidation at 1273 K for 50 h. The oxide clusters we re complex oxides consisted of Ni and Cr, whereas the porous surface was co mposed of only Cr2O3 TG analysis revealed that the mass loss by intensive e vaporation 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 (e) for oxidation varied from 89 .04 to 99.96kJ mol(-1) with increasing oxygen flow rate.