| Popis: |
A chromia-dispersed Co Cr coating has been deposited by means of reactive sputtering. Low temperature hot corrosion tests at 700°C, in an O 2 -SO 2 -SO 3 gaseous environment, with the specimen coated with Na 2 SO 4 , and cyclic oxidation at 1000°C, were conducted for both the dispersed and dispersion-free Co Cr coatings with equal Cr content. Compared with the dispersion-free coating, the chromia dispersed coating showed a markedly increased resistance to corrosion, and a slightly decreased resistance to oxide spallation. The corrosion products and morphology studies proved that the improved corrosion resistance on the dispersed coating is due to the effect of chromia dispersoids in promoting protective Cr 2 O 3 scale formation. After a 2 h anneal in vacuum at 1100°C, the chromia-dispersed coating became less resistant to corrosion than the as-sputtered, but remarkedly more resistant to spallation than the dispersion-free. The former was due to loss of part of the dispersed Cr 2 O 3 during the annealing, and the latter may be attributed to the following fact: the Cr 2 O 3 scale growth mode of the Co Cr coating was observed to be modified by the chromia dispersion, and the scale convolutions which developed on the dispersion-free coating were absent from the dispersed coating. |
