061

*For more detail on aluminum, yttrium, and oxygen peak locations see Table 2.

both standards was referenced to the Is carbon peak of 284.6eV and all other peaks were corrected accordingly. These locations are shown in Table 2. The peaks were acquired by averaging multiple (5) small range (20eV wide) scans around each location of interest. As mentioned before, in the case of partially overlapping peaks, a peak synthesis routine was used to separate and identify these peaks.

Depth Profiling

To measure the changes in composition of the coating elements as they vary through the protective oxide film on the coatings, the original surface was sputtered off in successive layers while the specimen was in the UHV chamber of the analyzer. This was done with the ion gun attached to the analyzer chamber. The ion gun allows an accelerated ionized beam of argon atoms to impinge on the specimen surface. By a collision process this strips off the surface layers. Typical ion gun parameters used were:

• Emission 25 milliamps

• Pressure 20x10"^ pascals

• Beam rastered to cover the entire surface

By using a tantalum oxide standard, ^a2®5» these parameters were found to represent a sputter rate of 30x10"® cm/ min for that standard. The standard preparation procedures used are given in the Appendix. After the desired thickness is removed an XPS spectrum is acquired and quantified. This' process is continued to the total depth desired. This allows a plot of composition versus depth. Accumulated sputter times at which analyses were made were 0, 1, 3, 15, 47, 79, 159, 191, 231, 247, 263, 287, 303, 319, 343, 351, 367, 391, 407, 455, and 480 minutes.

Material

The specimen configuration used is as shown in Figure 4. This specimen was made of cast Rene 80. This nickel-base alloy is the one used for the first stage hot-section turbine blades of the LM-2500 engine. Prior to machining, the alloy was given a solution heat treatment of:

2225°F (1220°C)-2 hr in air - air cooled 2000°F (1095°C)-4 hr in air - air cooled

The machining process removed any oxides formed during the heat treatment. The specimens were then coated by Temescal. This company coats the actual turbine blades for the Navy's LM-2500 engines. Actual production coating procedures were used. The coating was applied by physical vapor deposition to a thickness of 0.126 mm (5 mils). Coatings with the compositions shown in Table 3 were produced. These compositions were selected to allow for the investigation of the effect of varying the chromium content in the bulk coating on the oxide film composition. After the application of the coating, the specimens were given the following heat treatment:

torr) - vacuum cooled, 1550°F (845°C) - 16 hr in argon -argon cooled.

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