Evaluation of a New Coating for Application to Ramjet Engine Combustion Chamber

In the present study, the adhesion and thermal characteristics of a new high temperature coating are evaluated. The new Korolon™ 1350A is applied by a conventional spray gun process at room temperature and does not require a bond coat when applied to Ni-based alloys. The coating thickness was varied from 127 to 254 μm. The coating/substrate adhesion was evaluated using a conventional bend test that subjects the coating to large elastic/plastic deformations. The coating showed no sign of delamination or fracture when subjected to 180° bend. Bend testing was also conducted following thermal cycling (95 to 815 °C) of the specimens in air. The coating showed no sign of oxidative degradation or delamination in bend testing. The thermal characteristics of the coating were evaluated under both convective and conductive heating conditions, including a guarded hot plate apparatus. After extensive testing and measurement of differential temperatures across the test specimens, it was estimated that the thermal conductivity of the coating is approximately 1 W/m K. The coating was then applied to aerothrottle panels and tested in a ramjet simulation test facility with flowing hot air at 1,200 °C. During this experiment the surface temperature on the coated panels reached 720 °C. Examination of the panels subsequent to testing showed no sign of degradation. Consistent with bench testing, a maximum temperature difference of 316 °C was measured between the heated surface and the back face with the coating applied to the heated surface. The results confirmed that the new coating is promising for elevated temperature use as a thermal barrier coating.