THERMAL-CYCLING BEHAVIOR OF CoNiCrAlY BONDS COATED WITH THERMAL BARRIER COATINGS (TBCs) PRODUCED WITH ATMOSPHERIC PLASMA SPRAYING (APS)

Abstract

Thermal barrier coatings (TBCs) are commonly applied as a thermal insulation in order to protect against environmental influences in the components of high-temperature gas turbines and jet engines. Gas-turbine components are affected by aggressive conditions of the environment during the service, being subjected to failures such as corrosion, thermal shock and oxidation. Plasma-spray technology is used to produce metallic bonds and ceramic top coats as a cost-effective method to prolong the lifetime of TBCs. In the present research. CoNiCrAlY bond-coat and YSZ top-coat powders included in the TBCs were deposited onto Inconel 718 super alloy substrates using atmospheric plasma spraying (APS). The TBCs were exposed to a furnace cycling test at 1150 degrees C and one-hour cycles. The presence of porosity and cracks facilitating the diffusion of oxygen in the top-coating structure led to the formation of thermally grown oxides (TGOs) at the interface. In addition, the most effective factors of failures were the formation and growth of mixed oxides at the bond/top-coat interface and the presence of imperfections. According to the test results, an increasing number of thermal cycles resulted in a decrease in the lifetime of the TBCs related to the sintering of the top coating due to the effect of high temperature.