The solubility of boron in graphite was determined in the temperature interval of 1800° to 2500°C. The maximum solubility was 2.35 at. % at 2350°C; the solution was shown to be substitutional.
The failure of a Zr02-8 percent Y203/Ni-14 percent Cr-14 percent Al-0.1 percent Zr coating system on Rene'41 in Mach 0.3 burner rig tests has been characterized. High flame and metal temperatures were employed in order to accelerate coating failure. Failure by delamination was shown to precede surface cracking or spalling. This type of failure could be duplicated by cooling down the specimen after a single long duration isothermal high temperature cycle in a burner rig or a furnace, but only if the atmosphere was oxidizing. Stresses due to thermal expansion mismatch on cooling coupled with the effects of plastic deformation of the bond coat and oxidation of the irregular bond coat are the probable life limiting factors. Heat up stresses alone could not fail the coating in the burner rig tests. Spalling eventually occurs on heat up but only after the coating has already failed through delamination.
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