Figure 7. Initial Deposition Rate of TCP Vapor in Nitrogen at 700°C as a Function of Vapor Concentration deposit decrease significantly to a constant rate that continues for extended periods as previously shown in Figure 5.

The morphology of the TCP coatings on stainless steel wire have been examined using SEM. These coatings appear to be granular in nature, with the initial coating made up of small granules. The granules appear to increase in size as the coating becomes thicker. The initial granules are about 0.1p m in diameter, while the deposit after 30 minutes consists of particles of about 2pm in diameter. The size change appears to be related to the decreasing rate of deposit formation at 700 C. As the deposits become thick enough to have structural integrity, thermal expansion properties which are different from that of the stainless steel wire, cause the deposit layers to crack off when cooled. The edge of a cracked deposit shows the coating on the surface of the stainless steel to be find grained and porous. As the deposit thickens, it appears to increase in grain size and decrease in porosity.

FOUR-BALL WEAR TESTS - The TCP vapor delivery system has been applied to the four-ball wear tester at a temperature of 370°C in the ball pot. The 370 C temperature limitation in the wear tester is necessitated by the conventional bearings of the wear tester that are in close proximity to the test specimens and cannot be adequately insulated thermally from the test specimens. An extrapolation of deposit rate for TCP, based on the 500 to 800°C data

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