531.1 531.85 Minor Major

73.85 74.6 Minor Major

*A11 peaks are calibrated to 284.6eV; all values * 0.25eV tValues obtained from reference 3.

#A11 CoCrAlY coatings are in the heat treated condition followed by 1 minute of argon sputter cleaning.

RESULTS AND DISCUSSION Quantitative Analysis

The results of the quantitative analysis are shown in Figures. 5, 6, and 7 and are listed on Tables 4, 5, and 6. The data plots show the quantitative analysis in weight percent on the coordinate axis with the corresponding sputtering time shown on the ordinate axis. For reference purposes the approximate depth of sputtering related to a given sputtering time.is also shown. This approximation represents the depth of sputtering as derived from a Ta205 standard and should .serve as an adequate guide to the depth of sputtering on the coatings. These sputter/quantitative runs were made for the 20, 29, and 35 wt% chromium containing coatings. They show that the initial oxide scales in all cases are essentially rich in aluminum, yttrium, and oxygen with only minor amounts of chromium or cobalt. The significant yttrium in the outer layers of the coatings is interesting in that only 0.2 wt% is added to the bulk coating but approximately 5 to 6 wt% is found in the outer protective oxide scale. Preferential segregation of element to the surface of an alloy has been found to occur in other alloy systems, such as Cu-Ni^. With time of sputtering the composition of coatings, particularly for the 35 wt% chromium containing coating, begin to approach the bulk coating composition. Accordingly, the oxygen levels drop from that of the initial layer, but they are not yet zero after the total sputtering time of 480 minutes or approximately 1.3 jtm in depth. This oxygen probably represents coating defects (called leaders) which are common in PVD CoCrAlY coatings. These leaders are typically alumina.


Coating Composition* (wt %)





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